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  • 1.
    Archer, Jenny
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Dahlgren, Hanna
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lanchester, Betty
    School of Physics and Astronomy, University of Southampton, UK.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Dynamics and characteristics of black aurora as observed by high resolution ground-based imagers and radar2011In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 32, no 11, p. 2973-2985Article in journal (Refereed)
    Abstract [en]

    High-resolution, multi-spectral data from the ground-based low-light auroral imager ASK (Auroral Structure and Kinetics) are used to characterize the fine structure of black aurora. Sixteen events comprising sheared and unsheared black arcs, as well as black patches and rings, constitute the analysed dataset. Simultaneous measurements of emissions caused by high- and low-energy precipitation make it possible to relate the characteristics of different black structures to the energy of the precipitating electrons. The reductions of high-energy particles versus low-energy particles in the black regions compared to the diffuse background are investigated for the different forms of black aurora. Two separate mechanisms have been suggested to cause black aurora. The larger reduction of high-energy precipitation within the fine-scale black structures discussed here favours a magnetospheric mechanism that blocks high-energy electrons from being scattered into the loss cone. European Incoherent SCATter radar (EISCAT) electron density profiles are available for one of the nights, and are compared to the optical measurements.

  • 2. ASKNE, J
    et al.
    LEPPARANTA, M
    Thompson, Thomas
    SMHI.
    THE BOTHNIAN EXPERIMENT IN PREPARATION FOR ERS-1, 1988 (BEPERS-88) - AN OVERVIEW1992In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 13, no 13, p. 2377-2398Article in journal (Refereed)
    Abstract [en]

    BEPERS-88 was an extensive field campaign on the use of Synthetic Aperture Radar (SAR) in sea ice remote sensing in the Baltic Sea. This experiment was performed in order to study the possibilities of using the ERS-1 satellite SAR (and radar altimeter) in connection with the brackish ice in the Baltic Sea. The Canada Centre for Remote Sensing CV-580 C/X-band SAR was flown and an extensive validation programme was carried out. The data have been used for SAR image analysis, backscatter investigations, geophysical validation of SAR over sea ice, and evaluation of the potentials of SAR in operational ice information services. The results indicate that SAR can be used to discriminate between ice and open water, classify ice types into three categories, quantify ice ridging intensity, and determine the ice drift. As an operational tool SAR is expected to be an excellent complement to NOAA imagery and ground truth.

  • 3.
    Ban, Yifang
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics.
    Howarth, P. J.
    Orbital effects on ERS-1 SAR temporal backscatter profiles of agricultural crops1998In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 19, no 17, p. 3465-3470Article in journal (Refereed)
    Abstract [en]

    Multi-temporal radar backscatter characteristics of crops and their underlying soils were analysed for an agricultural area in south-western Ontario, Canada using nine dates of ERS-1 SAR imagery acquired during the 1993 growing season. From the calibrated data, SAR temporal backscatter profiles were generated for each crop type. The results indicate that small changes in incidence-angle can have strong impacts on radar backscatter. Thus, attention must be given to local incidence-angle effects when using ERS-1 SAR data,especially when comparing backscatter coefficients of the same area from different scenes or different areas within the same scene.

  • 4.
    Ban, Yifang
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics (closed 20110301).
    Hu, Hongtao
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics (closed 20110301).
    Rangel, Irene M.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics (closed 20110301).
    Fusion of Quickbird MS and RADARSAT SAR data for urban land-cover mapping: object-based and knowledge-based approach2010In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 31, no 6, p. 1391-1410Article in journal (Refereed)
    Abstract [en]

    The objective of this research is to evaluate Quickbird multi-spectral (MS) data, multi-temporal RADARSAT Fine-Beam C-HH synthetic aperture radar (SAR) data and fusion of Quickbird MS and RADARSAT SAR for urban land-use/land-cover mapping. One scene of Quickbird multi-spectral imagery was acquired on 18 July 2002 and five-date RADARSAT fine-beam SAR images were acquired during May to August 2002. Quickbird MS images and RADARSAT SAR data were classified using an object-based and rule-based approach. The results demonstrated that the object-based and knowledge-based approach was effective in extracting urban land-cover classes. For identifying 16 land-cover classes, object-based and rule-based classification of Quickbird MS data yielded an overall classification accuracy of 87.9% (kappa: 0.868). For identifying 11 land-cover classes, object-based and rule-based classification of RADARSAT SAR data yielded an overall accuracy: 86.6% (kappa: 0.852). Decision level fusion of Quickbird classification and RADARSAT SAR classification was able to take advantage of the best classifications of both optical and SAR data, thus significantly improving the classification accuracies of several land-cover classes (25% for pasture, 19% for soybeans, 17% for rapeseeds) even though the overall classification accuracy of 16 land-cover classes increased only slightly to 89.5% (kappa: 0.885).

  • 5.
    Ban, Yifang
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics.
    Marullo, Salvatore
    Eklundh, Lars
    European Remote Sensing: progress, challenges, and opportunities2017In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 38, no 7, p. 1759-1764Article in journal (Refereed)
  • 6.
    Beltrán-Abaunza, José M.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Kratzer, Susanne
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hoglander, Helena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Using MERIS data to assess the spatial and temporal variability of phytoplankton in coastal areas2017In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 38, no 7, p. 2004-2028Article in journal (Refereed)
    Abstract [en]

    This study aims to highlight how satellite data can be used for an improved understanding of ecological processes in a narrow coastal bay. The usefulness of the Medium Resolution Imaging Spectrometer (MERIS) data (2003-2011) as a complement to the in situ monitoring in Himmerferdenn (HF) bay is used as an example that can also be applied to other coastal areas. HF bay is one of the most frequently monitored coastal areas in the world, allowing for a rigorous comparison between satellites and ship-based monitoring data. MERIS data was used for the integration of chlorophyll-a (chl-a) over each waterbody in the HF area, following the national waterbody classification by the Swedish Meteorological and Hydrological Institute (SMHI). Chl-a anomaly maps were produced for the bay and its adjacent areas. The maps could be used to show events with high chl-a, both with natural causes (e.g. a Prymnesium polylepis bloom observed in summer 2008) and of anthropogenic causes (e.g. failure in the local sewage treatment plant resulting in a strong spring bloom in 2006). Anomaly maps thereby allow to scan larger coastal stretches to discriminate areas that may require additional sampling by ship, or to identify areas that do not differ much from the median value of the MERIS time series.

  • 7. Bennartz, R
    et al.
    Michelson, Daniel
    SMHI, Core Services.
    Correlation of precipitation estimates from spaceborne passive microwave sensors and weather radar imagery for BALTEX PIDCAP2003In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 24, no 4, p. 723-739Article in journal (Refereed)
    Abstract [en]

    This paper describes the evaluation of a-combined radar and passive microwave dataset obtained during the PIDCAP study of the Baltic Sea Experiment (BALTEX), where three-dimensional volumes of data from the Gotland radar were obtained timed according to the overpasses of the DMSP-satellites F10 and F13. Both satellites are 'equipped with a Special Sensor Microwave/Imager (SSM/I), suitable for precipitation retrievals. We compare radar precipitation estimates, convolved to the native resolution of the SSM/I, at different altitudes with polarization and scattering indices (S-85) derived from the SSM/I. For all 22 overpasses investigated here radar precipitation estimates at 3-4 km altitude correlate well with the SSM/I-derived S-85 (average correlation coefficient = 0.70). Although more directly linked to surface precipitation, polarization indices have been found to be less correlated with radar data, due to limitations inherent in the remote sensing of precipitation at higher latitudes. A stratification of the dataset into frontal and convective events revealed significant variations in these relationships for different types of precipitation events, thus reflecting different cloud microphysical processes associated with precipitation initialization. The relationship between S85 and radar rain estimates at higher altitudes varies considerably for different convective and frontal events. The sensitivity of S-85 to radar-derived rain rate ranges from 3.1 K mm(-1) h(-1) for a strong convective event to about 25 K mm(-1) h(-1) for the frontal and about 70 mm(-1) h(-1) for the small-scale convective events. For extrapolated surface precipitation estimates, sensitivities decrease to 14 mm(-1) h(-1) and 25 mm(-1) h(-1) for frontal and small-scale convective precipitation, respectively.

  • 8.
    Brown, Ian A.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Assessing eco-scarcity as a cause of the outbreak of conflict in Darfur: a remote sensing approach2010In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 31, no 10, p. 2513-2520Article in journal (Refereed)
    Abstract [en]

    The conflict in Darfur, Western Sudan, is frequently represented in the media as a dispute over access to resources by competing communities. Environmental degradation is often cited as either a causal or a contributory factor to the outbreak of the conflict and its prolongation. In this paper, Normalized Difference Vegetation Index (NDVI) data are used as a measure of 'eco-scarcity' to assess the notion that the outbreak of conflict was the result of competition for resources between communities. It is shown that there is no evidence in the vegetation mapping for a worsening of the ecological situation in Western and Northern Darfur states around the outbreak of the conflict. On the contrary, the years prior to the outbreak of the conflict experienced better than average vegetation growth in the context of the past 25 years.

  • 9.
    Carlund, Thomas
    et al.
    SMHI, Core Services.
    Håkansson, Bertil
    SMHI, Research Department, Oceanography.
    Land, P
    Aerosol optical depth over the Baltic Sea derived from AERONET and SeaWiFS measurements2005In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 26, no 2, p. 233-245Article in journal (Refereed)
    Abstract [en]

    Three years of data on aerosol optical depth (tau(a)) from the Aerosol Robotic Network (AERONET) station on the island of Gotland in the Baltic Sea have been analysed and compared with Sea-viewing Wide Field of view Sensor (SeaWiFS) data. Normally, the atmosphere over Gotland could be considered as clear, with a daily median value Of tau(a) at 500 nm of about 0.08. The median value of Angstrom's wavelength exponent (alpha) for wavelengths between 440 nm and 870 nm was 1.37, indicating that the dominant aerosol is more of a continental than of a pure maritime type. SeaWiFS GAC level 2 data on tau(a) and alpha were compared to data from the ground-based AERONET station. For the 37 cases of simultaneous satellite and ground-based measurements under cloud-free skies it was found that, on average, the value of tau(a)(865 nm) from SeaWiFS was about 0.02 higher than tau(a)(870 nm) from the AERONET station. At the same time approximate tau(a)(440 nm) from SeaWiFS was about 0.03 lower than tau(a)(440 nm) of AERONET. alpha(510, 865) from SeaWiFS was, on average, 1.2 lower than alpha(500, 870) from the AERONET measurements. These results cannot explain the very frequent occurences of negative values of normalized water-leaving radiance at 412 nm and 443 nm in the SeaWiFS reprocessing #3 data.

  • 10.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Grassl, H.
    Comparison of low brightness temperatures derived from the AVHRR thermal channels with in situ measurements in Antarctica2009In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 30, no 2, p. 525-532Article in journal (Refereed)
    Abstract [en]

    Data from the National Oceanic and Atmospheric Administration (NOAA) satellites' Advanced Very High Resolution Radiometers (AVHRRs) represent the longest record (more than 25 years) of continuously available satellite-based thermal measurements, and have well-chosen spatial and spectral resolutions. As a consequence, these data are used extensively to develop cloud climatologies. However, for such applications, accurate calibration and intercalibration of both solar and thermal channels of the AVHRRs is necessary so as to homogenize the data obtained from the different AVHRR sensors. AVHRR thermal channels 4 and 5 are routinely used in threshold-based hierarchical decision-tree cloud detection and classification algorithms, and therefore an evaluation of the stability of these channels at low temperatures is important. In this letter, the AVHRR channel 4 and 5 brightness temperatures (BTs) are compared at five stations in Antarctica. The data for the period of June, July and August (the coldest months of every year and with minimal atmospheric influence) from 1982 to 2006 were used for the evaluations. The calibration and intercalibration of the thermal channels are found to be very robust. The root mean square errors (RMSEs) range from 2.2 to 3.4K and the correlation coefficients from 0.84 to 0.95. No apparent artefacts or artificial jumps in the BTs are visible in the data series after changes of sensors. The BTs from the thermal channels of the AVHRRs can be used for preparing cloud climatologies, as their intercalibration is found to be consistent across different afternoon satellites.

  • 11.
    Eriksson, Patrick
    et al.
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Ekström, Mattias
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Melsheimer, Christian
    Universität Bremen, Institute of Environmental Physics.
    Buehler, Stefan
    Efficient forward modelling by matrix representation of sensor responses2006In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 27, no 9-10, p. 1793-1808Article in journal (Refereed)
    Abstract [en]

    The polarization, frequency and spatial responses of the sensor can be considered by calculating the Stokes vector of monochromatic pencil beam radiances for a set of frequencies and viewing directions, and weight these radiances with the instrument responses. This paper presents a highly efficient solution for this calculation procedure. The basic idea is to pre-calculate a matrix that represents the mapping from polarisation, frequency and spatial values to measured data. Sensor impacts can then be included by a simple matrix multiplication. The full sensor matrix can be obtained by determining the response matrix for the sensor parts individually. Data reduction methods can also be incorporated. A simple method for optimizing the calculation grids is further presented. The described approach for sensor modeling has been implemented in two public available softwares for atmospheric radiative transfer simulations.

  • 12.
    Evgenieva, Tsvetina
    et al.
    Institute of Electronics, Bulgarian Academy of Sciences.
    Wiman, Bo L. B.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Kolev, Nikolay
    Institute of Electronics, Bulgarian Academy of Sciences.
    Savov, P.
    Department of Physics, Ivan Rilski University.
    Donev, E.
    Department of Meteorology & Geophyiscs, St. Kliment Ohridski University.
    Ivanov, D.
    Department of Meteorology & Geophyiscs, St. Kliment Ohridski University.
    Danchovski, V.
    Department of Meteorology & Geophyiscs, St. Kliment Ohridski University.
    Kaprielov, B.
    Institute of Electronics, Bulgarian Academy of Sciences.
    Grigorieva, V.
    Institute of Electronics, Bulgarian Academy of Sciences.
    Iliev, Ts.
    Central Laboratory of Solar-Terrestrial Influences, Bulgarian Academy of Sciences.
    Kolev, I.
    Institute of Electronics, Bulgarian Academy of Sciences.
    Three-point observation in the troposphere over Sofia-Plana Mountain,Bulgaria2011In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 32, no 24, p. 9343-9363Article in journal (Refereed)
    Abstract [en]

    Based on a novel combination of approaches and instruments, this article presents campaign-based results from atmospheric boundary layer (ABL) height and aerosol optical depth (AOD) measurements carried out at two different experimental sites in Sofia, as well as from three-point measurements of aerosol number concentrations. Several instruments (lidar (developed by the IE), ceilometer, aerosol particle counter, sun photometer and meteorological sensors) were used in this study. Based on joint interpretation of the instruments' data we assess the influence of the atmospheric aerosol in the planetary boundary layer and the significant influence of aerosol layers and high clouds on AOD values. Measurements of AOD in the city basin gave values in the range 0.22-0.41 for cloud-free skies, and up to around 0.8 under partly cloudy conditions. The information obtained during the two campaigns indicates that aerosol particle concentrations were lower in park areas than along heavy-traffic thoroughfares in the city, but higher than in the mountain area. In conclusion, our study demonstrates the potential of employing a broad array of instruments for the study of boundary layer and aerosol over large, valley-situated and heavily urbanized city areas.

  • 13.
    Flygare, Ann-Marie
    Department of Forest Resource Management and Geomatics, Swedish University of Agricultural Sciences, Umeå, Sweden.
    A comparison of contextual classification methods using Landsat TM1997In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 18, no 18, p. 3835-3842Article in journal (Refereed)
    Abstract [en]

    The performance of contextual classification methods is evaluated using Landsat TM data. Classes of pixels adjacent to the pixel to be classified are assumed to be conditionally independent given the class of the pixel to be classified. An assumption of autocorrelated spectral reflectance is made in three of the methods. Methods that utilize information from one image and images from two different occasions are compared. Our results indicate that an autocorrelation method utilizing images from two different occasions performs optimally.

  • 14. Gilichinsky, Michael
    et al.
    Sandström, Per
    Reese, Heather
    Kivinen, Sonja
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Moen, Jon
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Mats
    Mapping ground lichens using forest inventory and optical satellite data2011In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 32, no 2, p. 455-472Article in journal (Refereed)
    Abstract [en]

    Lichen is a major forage resource for reindeer and may constitute up to 80% of areindeer’s winter diet. The reindeer grazing area in Sweden covers almost half of thecountry, with reindeer using mountainous areas in the summer and forested areas inthe winter. Knowledge about the spatial distribution of ground lichens is importantfor both practical and decision-making purposes. Since the early 1980s, remotesensing research of lichen cover in northern environments has focused on reindeergrazing issues. The objective of this study was to use lichen information collected inthe Swedish National Forest Inventory (NFI) as training data to classify opticalsatellite images into ground lichen cover classes. The study site was located within thereindeer husbandry area in northern Sweden and consisted of the common areabetween two contiguous Satellite Pour l’Observation de la Terre (SPOT)-5 scenesand one Landsat-7 Enhanced Thematic Mapper Plus (ETMþ) scene. Three classificationmethods were tested: Mahalanobis distance, maximum likelihood andspectral mixture analysis. Post-classification calibration was applied using a membershipprobability threshold in order to match the NFI-measured proportions oflichen coverage classes. The classification results were assessed using an independentlycollected field dataset (229 validation areas). The results demonstrated highclassification accuracy of SPOT imagery for the classification of lichen-abundantand lichen-poor areas when using theMahalanobis distance classifier (overall accuracy84.3%, kappa ¼ 0.68). The highest classification accuracy for Landsat wasachieved using a maximum likelihood classification (overall accuracy 76.8%, kappa¼ 0.53). These results provided an initial indication of the utility of NFI data astraining data in the process of mapping lichen classes over large areas.

  • 15.
    Hannerz, Fredrik
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Lotsch, Alexander
    Assessment of remotely sensed and statistical inventories of African agricultural fields2008In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, International Journal of Remote Sensing, Vol. 29, no 13, p. 3787-3804Article in journal (Refereed)
    Abstract [en]

    This paper critically examines different sources of remotely sensed and statistical inventories of African agricultural fields. Substantial discrepancies are found across alternative sources of information in both the extent and location of agricultural fields. In one-third of the countries, the difference between lowest and highest field extent estimate exceeds 25% of the total country area, and the maximum difference at the continental level is 2.6 million km2. Much of the disagreement between land-cover maps arises from areas of low cropping density. These inconsistencies have important implications when using these data directly, e.g. for the assessment of land cover changes, or indirectly in economic or physical models, and indicate a need to explicitly quantify uncertainties arising from the limitations in land-cover data. They also highlight the need for development of regional land information systems for baseline development and informed policy decisions.

  • 16.
    Håkansson, Bertil
    et al.
    SMHI, Research Department, Oceanography.
    Moberg, Mats
    SMHI.
    THE ALGAL BLOOM IN THE BALTIC DURING JULY AND AUGUST 1991, AS OBSERVED FROM THE NOAA WEATHER-SATELLITES1994In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 15, no 5, p. 963-965Article in journal (Refereed)
  • 17.
    Håkansson, Bertil
    et al.
    SMHI, Research Department, Oceanography.
    Moberg, Mats
    SMHI.
    Thompson, Thomas
    SMHI.
    REAL-TIME USE OF ERS-1 SAR IMAGERY FOR ICE SERVICE AND ICEBREAKING OPERATIONS IN THE BALTIC SEA1995In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 16, no 17, p. 3441-3458Article in journal (Refereed)
    Abstract [en]

    Sea ice forms every winter in the Baltic Sea and several icebreakers in Sweden and Finland keep the major ports in the area open for sea-trade all the year around. Information and forecasts of the sea ice formation, drift and deformation are vital for safe and efficient winter navigation. In this respect, Synthetic Aperture Radar (SAR) imagery is of great interest, since this technique is almost cloud independent and has potential for real-time ice mapping. The usefulness of SAR imagery for sea ice operations has been evaluated in the Baltic Sea. The imagery was used both for ice mapping, for icebreaker operations and ship routeing. Images presented onboard the icebreakers were highly appreciated and easily interpreted by the crew. The data were frequently used for ship routeing (33 per cent) of merchant vessels and for direct icebreaker assistance (53 per cent). It was concluded by several icebreaker masters that an image resolution of about 100 m was indeed enough to distinguish ridged areas and in the same time obtain a large enough geographical coverage per image.

  • 18.
    Kari, Elina
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Kratzer, Susanne
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Beltrán-Abaunza, José M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Harvey, E. Therese
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Vaiciute, Diana
    Retrieval of suspended particulate matter from turbidity - model development, validation, and application to MERIS data over the Baltic Sea2017In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 38, no 7, p. 1983-2003Article in journal (Refereed)
    Abstract [en]

    Suspended particulate matter (SPM) causes most of the scattering in natural waters and thus has a strong influence on the underwater light field, and consequently on the whole ecosystem. Turbidity is related to the concentration of SPM which usually is measured gravimetrically, a rather time-consuming method. Measuring turbidity is quick and easy, and therefore also more cost-effective. When derived from remote sensing data the method becomes even more cost-effective because of the good spatial resolution of satellite data and the synoptic capability of the method. Turbidity is also listed in the European Union's Marine Strategy Framework Directive as a supporting monitoring parameter, especially in the coastal zone. In this study, we aim to provide a new Baltic Sea algorithm to retrieve SPM concentration from in situ turbidity and investigate how this can be applied to satellite data. An in situ dataset was collected in Swedish coastal waters to develop a new SPM model. The model was then tested against independent datasets from both Swedish and Lithuanian coastal waters. Despite the optical variability in the datasets, SPM and turbidity were strongly correlated (r = 0.97). The developed model predicts SPM reliably from in situ turbidity (R-2 = 0.93) with a mean normalized bias (MNB) of 2.4% for the Swedish and 14.0% for the Lithuanian datasets, and a relative error (RMS) of 25.3% and 37.3%, respectively. In the validation dataset, turbidity ranged from 0.3 to 49.8 FNU (Formazin Nephelometric Unit) and correspondingly, SPM concentration ranged from 0.3 to 34.0 g m(-3) which covers the ranges typical for Baltic Sea waters. Next, the medium-resolution imaging spectrometer (MERIS) standard SPM product MERIS Ground Segment (MEGS) was tested on all available match-up data (n = 67). The correlation between SPM retrieved from MERIS and in situ SPM was strong for the Swedish dataset with r = 0.74 (RMS = 47.4 and MNB = 11.3%; n = 32) and very strong for the Lithuanian dataset with r = 0.94 (RMS = 29.5% and MNB = -1.5%; n = 35). Then, the turbidity was derived from the MERIS standard SPM product using the new in situ SPM model, but retrieving turbidity from SPM instead. The derived image was then compared to existing in situ data and showed to be in the right range of values for each sub-area. The new SPM model provides a robust and cost-efficient method to determine SPM from in situ turbidity measurements (or vice versa). The developed SPM model predicts SPM concentration with high quality despite the high coloured dissolved organic matter (CDOM) range in the Baltic Sea. By applying the developed SPM model to already existing remote sensing data (MERIS/Envisat) and most importantly to a new generation of satellite sensors (in particular OLCI on board the Sentinel-3), it is possible to derive turbidity for the Baltic Sea.

  • 19.
    Karlsson, Karl-Göran
    SMHI, Research Department, Atmospheric remote sensing.
    DEVELOPMENT OF AN OPERATIONAL CLOUD CLASSIFICATION MODEL1989In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 10, no 4-5, p. 687-693Article in journal (Refereed)
  • 20. Knudby, Anders
    et al.
    Nordlund, Lina
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Remote sensing of seagrasses in a patchy multi-species environment2011In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 32, no 8, p. 2227-2244Article in journal (Refereed)
    Abstract [en]

    We tested the utility of IKONOS satellite imagery to map seagrass distribution and biomass in a 4.1 km2 area around Chumbe Island, Zanzibar, Tanzania. Considered to be a challenging environment to map, this area is characterized by a diverse mix of inter- and subtidal habitat types. Our mapped distribution of seagrasses corresponded well to field data, although the total seagrass area was underestimated due to spectral confusion and misclassification of areas with sparse seagrass patches as sparse coral and algae-covered limestone rock. Seagrass biomass was also accurately estimated (r2 = 0.83), except in areas with Thalassodendron ciliatum (r2 = 0.57), as the stems of T. ciliatum change the relationship between light interception and biomass from that of other species in the area. We recommend the use of remote sensing over field-based methods for seagrass mapping because of the comprehensive coverage, high accuracy and ability to estimate biomass. The results obtained with IKONOS imagery in our complex study area are encouraging, and support the use of this data source for seagrass mapping in similar areas.

  • 21.
    Kolios, Stavros
    et al.
    Knowledge and Intelligent Computing Laboratory, Informatics and Telecommunication Technology, TEI of Epirus.
    Georgoulas, George G
    Knowledge and Intelligent Computing Laboratory, Informatics and Telecommunication Technology, TEI of Epirus.
    Stylios, Chrysostomos D.
    Knowledge and Intelligent Computing Laboratory, Informatics and Telecommunication Technology, TEI of Epirus.
    Achieving downscaling of Meteosat thermal infrared imagery using artificial neural networks2013In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 34, no 21, p. 7706-7722Article in journal (Refereed)
    Abstract [en]

    This study presents the successful application of artificial neural networks (ANNs) for downscaling Meteosat Second Generation thermal infrared satellite imagery. The scope is to examine, propose, and develop an integrated methodology to improve the spatial resolution of Meteosat satellite images. The proposed approach may contribute to the development of a general methodology for monitoring and downscaling Earth's surface characteristics and cloud systems, where there is a clear need for contiguous, accurate, and high-spatial resolution data sets (e.g. improvement of climate model input data sets, early warning systems about extreme weather phenomena, monitoring of parameters such as solar radiation fluxes, land-surface temperature, etc.). Moderate Resolution Imaging Spectroradiometer (MODIS) images are used to validate the downscaled Meteosat images. In terms of the ANNs, a multilayer perceptron (MLP) is used and the results are shown to compare favourably against a linear regression approach.

  • 22. Kumar, Madathiparambil Ranganathapai Ramesh
    et al.
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    Levy, Gad
    Sankar, Syam
    Bakan, Stephan
    Grassl, Hartmut
    A multi-sensor climatological view of double ITCZs over the Indian Ocean2012In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 33, no 9, p. 2925-2936Article in journal (Refereed)
    Abstract [en]

    We characterize the climatological features of the double inter-tropical convergence zones (DITCZs) over the western Indian Ocean during November-December by a synergistic analysis of the Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite (HOAPS III) data (1988-2005) and the National Aeronautics and Space Administration's (NASA's) A-Train data (2002-2009). We investigate rainfall, freshwater flux and cloud liquid water, cloud fraction and relative humidity over the DITCZs. In addition, the daily rainfall data from the Global Precipitation Climatology Project (GPCP) are used to document the DITCZs during the El Nino southern oscillation (ENSO) events. An analysis of the GPCP data shows that the DITCZs are clearly discernible during strong ENSO events (1997, 2002 and 2006), in sharp contrast to the DITCZs in the eastern Pacific Ocean, where they are absent during ENSOs. Further, these convergence zones on either side of the equator are of short duration, approximately 3-6 pentads during November and December. All satellite sensor data sets consistently capture the major features of DITCZs. As an accurate simulation of DITCZs in coupled global climate models remains a challenge, the results from the present study would provide a platform for evaluating these models.

  • 23.
    Larsson, Richard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    A note on modelling of the oxygen spectral cross-section in the Atmospheric Radiative Transfer Simulator – Zeeman effect combined with line mixing in the Earth’s atmosphere2014In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 35, no 15, p. 5845-5853Article in journal (Refereed)
    Abstract [en]

    A new module to the Atmospheric Radiative Transfer Simulator is presented that models the strong oxygen spectral band at 60 GHz. The module handles the line mixing effect and works with or without additionally calculating the Zeeman effect. It is shown how the module may be internally reduced to calculations of the Zeeman effect at higher altitudes, and to calculations of the line mixing effect at lower altitudes. The article ends with a short discussion on what is being done to validate the module, and what may be done to refine the theoretical description of line mixing in the simulator.

  • 24.
    Margold, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jansson, Krister
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Evaluation of data sources for mapping glacial meltwater features2012In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 33, no 8, p. 2355-2377Article in journal (Refereed)
    Abstract [en]

    The meltwater system of disintegrating ice sheets provides an important source of information for the reconstruction of ice-retreat patterns during deglaciation. Recent method development in glacial geomorphology, using satellite imagery and digital elevation models (DEMs) for glacial landform mapping, has predominantly been focused on the identification of lineation and other large-scale accumulation features. Landforms created by meltwater have often been neglected in these efforts. Meltwater features such as channels, deltas and fossil shorelines were traditionally mapped using stereo interpretation of aerial photographs. However, during the transition into the digital era, driven by a wish to cover large areas more economically, meltwater features were lost in most mapping surveys. We have evaluated different sets of satellite images and DEMs for their suitability to map glacial meltwater features (lateral meltwater channels, eskers, deltas, ice-dammed lake drainage channels and fossil shorelines) in comparison with the traditional mapping from aerial photographs. Several sets of satellite images and DEMs were employed to map the landform record of three reference areas, located in northwestern Scotland, northeastern Finland and western Sweden. The employed satellite imagery consisted of Landsat 7 Enhanced Thematic Mapper Plus (ETM+), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Satellite Pour l’Observation de la Terre (SPOT) 5 and Indian Remote Sensing (IRS)1C, and the DEMs used were from NEXTMap Britain, Panorama, National elevation data set of Sweden and National Land Survey of Finland. ASTER images yielded better results than the panchromatic band of Landsat 7 ETM+ in all three regions, despite the same spatial resolution of the data. In agreement with previous studies, this study shows that DEMs display accumulation features such as eskers suitably well. Satellite images are shown to be insufficiently detailed for the interpretation of smaller features such as meltwater channels. Hence, satellite imagery and DEMs of intermediate resolution contain meltwater system information only at a general level that allows for the identification of landforms of medium to large sizes. It is therefore pertinent that data with an appropriate spatial and spectral resolution are accessed to fulfil the need of a particular mapping effort. Stereointerpretation of aerial photographs continues to be an advisable method for local meltwater system reconstructions; alternatively, it can be replaced by mapping fromhigh-resolution DEMs such as NEXTMap Britain. For regional to sub-continental reconstructions, the use of ASTER satellite imagery is recommended, because it provides both spectral and spatial resolutions suitable for the identification of meltwater features on a medium to large scale.

  • 25.
    McCarthy, Jenny
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Management and Assessment.
    Gumbricht, Thomas
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    McCarthy, T S
    Ecoregion classification in the Okavango Delta, Botswana from multitemporal remote sensing2005In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 26, no 19, p. 4339-4357Article in journal (Refereed)
    Abstract [en]

    The Okavango inland Delta in Botswana is characterized by a high spatial and temporal variation in vegetation patches and flooding. Predicting the effects of escalating development projects in this pristine wildlife area is hampered by a lack of accurate maps. Efforts using traditional statistical methods have been futile. The processes forming this highly dynamic environment, however, give rise to a well-documented consistency in the land cover pattern at scales ranging from single island architecture to an overall gradient in wetland, flood plain and island occurrence. We conducted a classification in a two-step process starting with statistical methods, and then refining using indices and flooding data. The indices and flooding data were created and selected to make possible the inferring of knowledge about the patterns at different scales through declarative IF ... THEN ... statements. The initial statistical classification achieved a best result of 46% accuracy for 10 classes, whereas the rule-based classification achieved an accuracy of 63%. Application of the derived classification for mapping islands and topography shows a surprisingly high accuracy.

  • 26.
    Morozov, Evgeny
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Nansen International Environmental and Remote Sensing Centre, Russia.
    Kondrik, D.
    Fedorova, A.
    Pozdnyakov, D.
    Tang, D. L.
    Pettersson, L.
    A spaceborne assessment of cyclone impacts on Barents Sea surface temperature and chlorophyll2015In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 36, no 7, p. 1921-1941Article in journal (Refereed)
    Abstract [en]

    A pilot satellite-based investigation of modulations exerted upon mixed-layer phytoplankton fields by cyclones was performed for the first time across a selected part of the Arctic Ocean, the Barents Sea (BS). Resorting to a synergistic approach, cyclones were first identified from NCEP/NC.R data for the summer period during 2003-2013, and their propagation throughout the BS was further surveyed. The above-water wind force was retrieved from QuikSCAT data. These data were further accompanied by ocean colour data from SeaWiFS and MODIS to examine the spatial and temporal distributions of surficial phytoplankton chlorophyll concentration (chl) dynamics along the trajectory of the cyclone's footprint across the sea. Sea surface temperature was retrieved from MODIS data. The specific trajectory of cyclone passage across the BS area, depression depth, and wind speed proved to be conjointly the main factors determining the sign, amplitude, and duration of modulations of phytoplankton chl. The spaceborne data obtained over more than a decade indicate that, on balance, the cyclone passage led to increase in chl within the cyclone footprint area. On average, this increase did not exceed 1-2 mu g l(-1), which is nevertheless appreciable given that the mean chl within the cyclone footprint rarely exceeded 1 mu g l(-1). However, chl enhancement within the footprint area lasted only within the range of a few days to a fortnight, with the footprint area generally accounting for about 14% of the BS area. During the vegetation season (April-August, rarely till mid-September), the number of cyclones prone to optical and infrared remote sensing was about 2-3. In light of the above, arguably the cyclones studied are hardly capable of boosting annual primary productivity in the BS. Moreover, it can be conjectured that the same conclusion can be drawn with respect to the pelagic Arctic tracts that are generally less productive and more extensively cloud-covered than the BS. However, this supposition requires further studies in order to advance our understanding of the actual role of cyclones in modulation of Arctic Ocean productivity and ecosystem functioning.

  • 27.
    Mård Karlsson, Johanna
    et al.
    Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK).
    Arnberg, Wolter
    Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK).
    Quality analysis of SRTM and HYDRO1K: a case study of flood inundation in Mozambique2011In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 32, no 1, p. 267-285Article in journal (Refereed)
    Abstract [en]

    Many countries still lack national digital elevation models (DEMs) and have to rely on global datasets, which can negatively influence the reliability of flood model results. Mozambique is considered the most risk prone country for floods in Southern Africa. In this study a quality and accuracy assessment of two global DEMs (Shuttle Radar Topography Mission (SRTM) and HYDRO1K) is presented for a simple static flood inundation model of lower Limpopo Basin. This is accomplished with a local fit and vertical accuracy assessment of global datasets on a local scale as well as simulations of flood extent in the floodplain carried out by filling the DEMs with water according to the 2000 flood event. The results from the vertical accuracy assessment show that global DEMs can be used on a local scale. However, flood simulations performed on original DEMs contain inadequacies and are misleading with both under-and overestimation of the flooded area, while simulation performed on locally fitted DEMs shows a better agreement with the actual event. This study clearly shows that DEMs with questionable accuracy and resolution should be used with great caution in flood inundation modelling because they could result in deceptive model predictions, and lead to devastating after-effects in risk prone areas.

  • 28.
    Mård Karlsson, Johanna
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Arnberg, Wolter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Quality analysis of SRTM and HYDRO1K: a case study of flood inundation in Mozambique2011In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 32, no 1, p. 267-285Article in journal (Refereed)
    Abstract [en]

    Many countries still lack national digital elevation models (DEMs) and have to rely on global datasets, which can negatively influence the reliability of flood model results. Mozambique is considered the most risk prone country for floods in Southern Africa. In this study a quality and accuracy assessment of two global DEMs (Shuttle Radar Topography Mission (SRTM) and HYDRO1K) is presented for a simple static flood inundation model of lower Limpopo Basin. This is accomplished with a local fit and vertical accuracy assessment of global datasets on a local scale as well as simulations of flood extent in the floodplain carried out by filling the DEMs with water according to the 2000 flood event. The results from the vertical accuracy assessment show that global DEMs can be used on a local scale. However, flood simulations performed on original DEMs contain inadequacies and are misleading with both under-and overestimation of the flooded area, while simulation performed on locally fitted DEMs shows a better agreement with the actual event. This study clearly shows that DEMs with questionable accuracy and resolution should be used with great caution in flood inundation modelling because they could result in deceptive model predictions, and lead to devastating after-effects in risk prone areas.

  • 29.
    Niu, Xin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Ban, Yifang
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Multi-temporal RADARSAT-2 polarimetric SAR data for urban land-cover classification using an object-based support vector machine and a rule-based approach2013In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 34, no 1, p. 1-26Article in journal (Refereed)
    Abstract [en]

    We have investigated multi-temporal polarimetric synthetic aperture radar (SAR) data for urban land-cover classification using an object-based support vector machine (SVM) in combinations of rules. Six-date RADARSAT-2 high-resolution polarimetric SAR data in both ascending and descending passes were acquired in the rural-urban fringe of the Greater Toronto Area during the summer of 2008. The major land-use/land-cover classes include high-density residential areas, low-density residential areas, industrial and commercial areas, construction sites, parks, golf courses, forests, pasture, water, and two types of agricultural crops. Various polarimetric SAR parameters were evaluated for urban land-cover mapping and they include the parameters from Pauli, Freeman and Cloude-Pottier decompositions, the coherency matrix, intensities of each polarization, and their logarithm forms. The multi-temporal SAR polarimetric features were classified first using an SVM classifier. Then specific rules were developed to improve the SVM classification results by extracting major roads and streets using shape features and contextual information. For the comparison of the polarimetric SAR parameters, the best classification performance was achieved using the compressed logarithmic filtered Pauli parameters. For the evaluation of the multi-temporal SAR data set, the best classification result was achieved using all six-date data (kappa = 0.91), while very good classification results (kappa = 0.86) were achieved using only three-date polarimetric SAR data. The results indicate that the combination of both the ascending and the descending polarimetric SAR data with an appropriate temporal span is suitable for urban land-cover mapping.

  • 30.
    Niu, Xin
    et al.
    Natl Univ Def Technol, Peoples R China.
    Ban, Yifang
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics.
    Dou, Yong
    RADARSAT-2 fine-beam polarimetric and ultra-fine-beam SAR data for urban mapping: comparison and synergy2016In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 37, no 12, p. 2810-2830Article in journal (Refereed)
    Abstract [en]

    The aim of this article is to investigate the capabilities of multitemporal RADARSAT-2 fine-beam polarimetric synthetic aperture radar (SAR) data and RADARSAT-2 ultra-fine-beam C-band single-polarization HH SAR (C-HH SAR) data for detailed urban land-cover mapping using a contextual approach. With an adaptive Markov random field and a spatially variant finite mixture model, contextual information was effectively explored to improve the mapping accuracy. A texture enhancement in FMM was further proposed to improve the classification accuracy. Moreover, a rule-based approach exploring object features and spatial relationships was employed to extract road, street, and park. Three-date RADARSAT-2 fine-beam polarimetric SAR (PolSAR) and three-date RADARSAT-2 ultra-fine-beam C-HH SAR data over the Greater Toronto area were used for the evaluation. For 10 major classes, the overall accuracy (OA) is 51% for C-HH SAR data and 79% for PolSAR data. Compared with C-HH SAR, PolSAR data produced better results for identifying various urban patterns. Although with multi-date, the C-HH SAR data showed low capability to distinguish high-density residential area and industry commercial area (Ind.). Considerable low-density residential area (LD) was misclassified as forest. Identification of the construction site (Cons.) and golf course were poor. Nevertheless, the efficiency of the multitemporal C-HH SAR textures for distinguishing the built-up areas was observed. By texture enhancement with the synergy of the PolSAR and C-HH SAR data, the mapping results could be significantly improved, especially for LD, forest, and crops. The OA is improved by 2.7% for PolSAR data, and 11.1% for C-HH SAR data. Road, street, and park could be extracted by the rule-based approach with OA about 77% for 13 classes.

  • 31. Patil, S. D.
    et al.
    Thompson, B.
    Stockholm University.
    Revadekar, J. V.
    On the variation of the tropospheric ozone over Indian region in relation to the meteorological parameters2009In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 30, no 11, p. 2813-2826Article in journal (Refereed)
    Abstract [en]

    Using monthly mean satellite measurements of TOMS/SBUV tropospheric ozone residual (TOR) data and meteorological parameters (tropopause height (TPH), 200hPa geopotential height (GPH) and outgoing longwave radiation (OLR)) during 1979-2001, seasonal variability of TOR data and their association with meteorological parameters are outlined over the Indian region. Prominent higher values of TOR (44-48DU, which is higher than the globally averaged 31.5DU) are observed over the northern parts of the country during the summer monsoon season (June-September). Similar to the TOR variation, meteorological parameters (tropopause height, 200hPa geopotential height and outgoing longwave radiation) also show higher values during the summer monsoon season, suggesting an in phase relationship and strong association between them because of deep convection present during summer monsoon time. The monthly trends in TOR values are found to be positive over the region. TOR has significant positive correlations (5% level) with GPH, and negative correlations with OLR and TPH for the month of September. The oxidation chains initiated by CH4 and CO show the enhanced photochemical production of ozone that would certainly become hazardous to the ecological system. Interestingly, greenhouse gases (GHG) emissions were found to have continuously increased over the Indian region during the period 1990-2000, indicating more anthropogenic production of ozone precursor gases causing higher level of tropospheric ozone during this period.

  • 32. Philipson, Petra
    et al.
    Kratzer, Susanne
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ben Mustapha, Selima
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Strömbeck, Niklas
    Stelzer, Kerstin
    Satellite-based water quality monitoring in Lake Vänern, Sweden2016In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 37, no 16, p. 3938-3960Article in journal (Refereed)
    Abstract [en]

    Lake Vänern, Sweden, is one of Europe’s largest lakes and has a historical, cultural, ecological as well as economic importance. Lake water quality monitoring is required by national and international legislations and directives, but present programmes are insufficient to meet the requirements. To complement in situ based monitoring, the possibility to obtain reliable information about spatial and temporal water quality trends in Lake Vänern from the ENVISAT mission’s MERIS instrument was evaluated. The complete archive (2002–2012) of MERIS (Medium Resolution Imaging Spectrometer) full resolution data was processed using the water processor developed by Free University Berlin (FUB) to derive aerosol optical thickness (AOT), remote-sensing reflectance (Rrs) and water quality parameters: chlorophyll-a (chl-a) concentration, coloured dissolved organic matter absorption at 443 nm (CDOM), and total suspended matter (TSM) concentration. The objective was to investigate if, either, FUB reflectance products in combination with potential lake-specific band ratio algorithms for water quality estimation, or directly, FUB water quality products, could complement the existing monitoring programme.

    Application of lake-specific band ratio algorithms requires high-quality reflectance products based on correctly estimated AOT. The FUB reflectance and AOT products were evaluated using Aerosol Robotic Network – Ocean Color (AERONET-OC) match-up data measured at station Pålgrunden in Lake Vänern. The mean absolute percentage differences (MAPDs) of the final reflectance retrievals at 413, 443, 490, 555, and 665 nm were 510%, 48%, 33%, 34%, and 33%, respectively, corresponding to a large positive bias in 413 nm, positive bias in 443–555 nm, and a negative bias in 665 nm. AOT was strongly overestimated in all bands.

    The FUB water quality products were evaluated using match-up in situ data of chl-a, filtered absorbance (AbsF(420)) and turbidity as AbsF(420) is related to CDOM and turbidity is strongly related to TSM. The in situ data was collected within the Swedish national and regional monitoring programmes. In order to widen the range of water constituents and add more data to the analysis, data from four large Swedish lakes (Vänern, Vättern, Mälaren, and Hjälmaren) was included in the analysis. High correlation (≥ 0.85) between in situ data and MERIS FUB derived water quality estimates were obtained, but the absolute levels were over- (chl-a) or under- (CDOM) estimated. TSM was retrieved without bias.

    Calibration algorithms were established for chl-a and CDOM based on the match-up data from all four lakes. After calibration of the MERIS FUB data, realistic time series could be derived that were well in line with in situ measurements. The MAPDs of the final retrievals of chl-a, AbsF(420) and Turbidity in Lake Vänern were 37%, 15%, and 35%, respectively, corresponding to mean absolute differences (MADs) of 0.9 µg l−1, 0.17 m−1, and 0.32 mg l−1 in absolute values.

    The partly inaccurate reflectance estimations in combination with both positive and negative bias imply that successful application of band ratio algorithms is unlikely. The high correlation between MERIS FUB water quality products and in situ data, on the other hand, shows a potential to complement present water quality monitoring programmes and improve the understanding and representability of the temporally and spatially sparse in situ observations. The monitoring potential shown in this study is applicable to the Sentinel-3 mission’s OLCI (Ocean Land Colour Instrument), which was launched by the European Space Agency (ESA) in February 2016 as a part of the EC Copernicus programme.

  • 33.
    Qin, Yuchu
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Niu, Z.
    Chen, F.
    Li, B.
    Ban, Yifang
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Object-based land cover change detection for cross-sensor images2013In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 34, no 19, p. 6723-6737Article in journal (Refereed)
    Abstract [en]

    Accurate and timely land cover change detection at regional and global scales is necessary for both natural resource management and global environmental change studies. Satellite remote sensing has been widely used in land cover change detection over the past three decades. The variety of satellites which have been launched for Earth Observation (EO) and the large volume of remotely sensed data archives acquired by different sensors provide a unique opportunity for land cover change detection. This article introduces an object-based land cover change detection approach for cross-sensor images. First, two images acquired by different sensors were stacked together and principal component analysis (PCA) was applied to the stacked data. Second, based on the Eigen values of the PCA transformation, six principal bands were selected for further image segmentation. Finally, a land cover change detection classification scheme was designed based on the land cover change patterns in the study area. An image-object classification was implemented to generate a land cover change map. The experiment was carried out using images acquired by Landsat 5 TM and IRS-P6 LISS3 over Daqing, China. The overall accuracy and kappa coefficient of the change map were 83.42% and 0.82, respectively. The results indicate that this is a promising approach to produce land cover change maps using cross-sensor images.

  • 34.
    Schafer, Martina L.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Population and Conservation Biology.
    Lundstrom, Jan O.
    Detection of temporary flooded areas with potential floodwater mosquito production using imaging radar2012In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 33, no 6, p. 1943-1953Article in journal (Refereed)
    Abstract [en]

    Temporarily flooded areas can produce enormous numbers of floodwater mosquitoes, causing tremendous nuisance to people living in the vicinity. The aim of this study is to develop a remote-sensing method for detecting temporary flooded areas that can produce floodwater mosquitoes. For this objective, synthetic aperture radar (SAR) imagery from the European Remote Sensing satellite (ERS-2) and the Environmental Satellite (Envisat) are chosen. The images cover both flooded and dry periods around Lake Farnebofjarden, located in the lowlands of the River Dalalven, central Sweden, during the vegetation season between 2000 and 2006. Unsupervised classification and principal component analysis (PCA) are tested as methods for detecting floodwater mosquito production sites. In the unsupervised classification experiment, four types of images are tested. The classification of a synthetic colour image gives the best result with an overall accuracy of 85.7% and a kappa value of 0.7, as well as a 46% detection rate of field-mapped flooded areas. PCA is performed on a data set of 16 time series radar images. The resulting principal component (PC) bands provide information about flooding probability as well as vegetation structures. Regular flooding increases the probability for an area to provide breeding sites for floodwater mosquitoes. Thus, this approach will be very useful in estimating the risk of floodwater mosquito establishment.

  • 35. Varpe, Sandeep R.
    et al.
    Kolhe, Amol R.
    Kutal, Ganesh C.
    Pawar, Ganesh V.
    Payra, Swagata
    Budhavant, Krishnakant B.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Maldives Climate Observatory at Hanimaadhoo, Republic of the Maldives; Indian Institute of Science, India.
    Aher, Gajanan R.
    Devara, Panuganti C. S.
    Heterogeneity in aerosol characteristics at the semi-arid and island AERONET observing sites in India and Maldives2018In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 39, no 19, p. 6137-6169Article in journal (Refereed)
    Abstract [en]

    Multi-year Aerosol Robotic Network (AERONET) direct Sun retrieved and inversion algorithm derived aerosol products at a semi-arid, urban site, Jaipur (26.90 degrees N, 75.80 degrees E) and island observing site, Maldives Climate Observatory-Hanimaadhoo (MCO-Hanimaadhoo, 6.74 degrees N, 73.17 degrees E) are analysed to investigate heterogeneity in aerosol optical and microphysical properties. Results reveal the existence of a large seasonal diversity in the frequency distributions of aerosol optical depth (AOD(500) (nm), AOD(1020) (nm)) and angstrom ngstrom exponent (AE(440-870) (nm)) during different seasons at Jaipur and MCO-Hanimaadhoo. These are indicative of the advection of different aerosol types (viz., black carbon (BC) aerosol, organic aerosol, sulfate particle, dust, sea salt, nitrate particle, and mixtures thereof) from a variety of production mechanisms influenced by strong seasonal changes of anthropogenic activities as well as modulations induced by the climatic condition. The cumulative frequency analysis of the single scattering albedo (SSA) difference (i.e. Delta SSA = SSA(440) (nm) - SSA(1020) (nm)) shows that at Jaipur Delta SSA is predominantly negative (around 88% days) while at MCO-Hanimaadhoo it is positive (around 74% days). The positive and negative values of Delta SSA are respectively linked to a stronger absorption by BC mixed anthropogenic pollution aerosols at 1020 nm and to a stronger absorption by mineral dust containing iron oxide at 440 nm. The spectral behaviour of SSA, thus, facilitates investigation of the existence of iron oxide or BC in aerosols. The 'Bivariate Kernel density' plots of SSA versus fine-mode fraction (FMF) of AOD(440) (nm)/AE(440-870) (nm) reveal that at Jaipur the aerosol ensemble consists of coarse-mode particles (AE and FMF cluster in the range 0.2-0.4), a dominant category along with significant fine-mode and much less mixed category. At MCO-Hanimaadhoo fine-mode particle category (with FMF and AE cluster in the range 0.90-0.95 and 1.2-1.6 respectively) is the only dominant category. The persisting log-normal bimodal feature in aerosol volume size distribution (AVSD) is observed both at Jaipur and MCO-Hanimaadhoo. The modal volume concentration of coarse-mode aerosol decreases from FMF of AOD(675) (nm) = 0.25 (inherently belonging to the coarse-mode regime) to FMF of AOD(675) (nm) = 0.95 (inherently belonging to the fine-mode regime). This transformation in coarse-to fine-mode volume concentration is associated with a steady rise in AE(440-874) (nm) supporting this changeover.

  • 36.
    Vu, Tuong Thuy
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics (closed 20110301).
    Ban, Yifang
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics (closed 20110301).
    Context-based mapping of damaged buildings from high-resolution optical satellite images2010In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 31, no 13, p. 3411-3425Article in journal (Refereed)
    Abstract [en]

    In the early stages of post-disaster response, a quick and reliable damage assessment map is essential.As time is a critical factor, automated damage mapping from remotely sensed images is the expected solution to drastically reduce data acquisition and computation time. Recently, high-resolution satellite images, such as QuickBird data, have been in high demand by damage assessment analysts and disaster management practitioners. However, the existing automated mapping approaches hardly accommodate such high-resolution data. This research aims at developing a new context-based automated approach for earthquake damage mapping from high-resolution satellite images. Relevant contextual information (including structure, shape, size, edge texture, spatial relations) describing the damage situation is formulated and up-scaled on a morphological scale-space. Speed optimization is achieved by parallel processing implementation. The developed approach was tested with two QuickBird images acquired on 26 June 2005 and 3 June 2008 over YingXiu town, Sichuan, China, which suffered the devastating 12 May 2008 earthquake. In comparison to the reference, the developed mapping approach could achieve over 80% accuracy for computation of the damage ratio. Future research is planned to test the approach on various disaster cases for both optical and radar images using a grid-computing platform towards a cost-effective damage mapping solution.

  • 37.
    Wang, Wei
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics.
    Xiang, Deliang
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics.
    Ban, Yifang
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics.
    Zhang, Jun
    Natl Univ Def Technol, Coll Elect Sci & Engn, Changsha, Hunan, Peoples R China..
    Wan, Jianwei
    Natl Univ Def Technol, Coll Elect Sci & Engn, Changsha, Hunan, Peoples R China..
    Enhanced edge detection for polarimetric SAR images using a directional span-driven adaptive window2018In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 39, no 19, p. 6340-6357Article in journal (Refereed)
    Abstract [en]

    Automatic edge detection for polarimetric synthetic aperture radar (PolSAR) images plays a fundamental role in various PolSAR applications. The classic methods apply the fixed-shape windows to detect the edges, whereas their performance is limited in heterogeneous areas. This article presents an enhanced edge detection method for PolSAR data based on the directional span-driven adaptive (DSDA) window. The DSDA window has variable sizes and flexible shapes, and is constructed by adaptively selecting samples that follow the same statistical distribution. Therefore, it can overcome the limitation of classic fixed-shape windows. To obtain refined and reliable edge detection results in heterogeneous urban areas, we adopt the spherically invariant random vector (SIRV) product model since the complex Wishart distribution is often not met. In addition, a span ratio is combined with the SIRV distance to highlight the dissimilarity measure and to improve the robustness of the proposed method. The simulated PolSAR data and three real data sets from experimental synthetic aperture radar, electromagnetics institute synthetic aperture radar, and Radarsat-2 systems are used to validate the performance of the enhanced edge detector. Both quantitative evaluation and visual presentation of the results demonstrate the effectiveness of the proposed method and its superiority over the classic edge detectors.

  • 38.
    Wickramanayake, Anura
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Hanshel, Michael
    MDA.
    Hobbs, Stephen
    Cranfield University.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Ekman, Jonas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Lehrbass, Brad
    MDA Geospatial Services.
    Seasonal Variation of Coherence in SAR Interferograms in Kiruna, Northern Sweden2016In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 37, no 2, p. 370-387Article in journal (Refereed)
    Abstract [en]

    This article presents the results of a study conducted to quantify the seasonal variation of coherence in synthetic aperture radar (SAR) interferograms in Kiruna, Northern Sweden. In SAR interferometry (InSAR), coherence is an important concept that provides a good indication of the phase stability of the scatterers. Therefore, in this study, the degree of coherence is used as a parameter to identify the seasonal variation interferograms. For this study, 34 Radarsat-2 ultra-fine beam mode (U6D) images of the Kiruna area (67°51ʹN, 20°14ʹE) and the improved digital elevation model (DEM) created by merging the Radarsat-2 DEM and ASTER DEM were used to produce 561 differential interferograms. The interferograms were arranged in three different ways for the analysis, with the first including common master interferograms (with the summer master image), the second including the sequential interferograms that have the shortest temporal baseline, and the third accounting for all possible combinations of the interferograms (full network of interferograms). Following this step, the variation of coherence for forest areas, urban areas, and flat waste rock areas was studied. This study shows that interferograms generated for the Kiruna region exhibit seasonal variations in coherence due to the ground snow layer in winter. Furthermore, when there is water on the ground due to the melting of the snow layer (in the spring) or due to rains in autumn, the coherence is reduced considerably. Another significant feature is that there is a significant change in summer-to-summer coherence for some regions even over the course of a few years. Based on this study, it is clear that the winter Radarsat-2 U6D beam mode images are not suitable for differential interferometric SAR (DInSAR) deformation measurements in flat waste rock regions in Kiruna. It is expected that even with winter images, PSInSAR or CTM techniques will be able to provide better deformation measurements, but, in this study, those techniques were not assessed. The next step will be to study the seasonal variations in coherence in natural or man-made targets/persistent scatterers using persistent scatter InSAR (PSInSAR) or coherence target monitoring (CTM) techniques

  • 39.
    Witt, Georg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Size and shape of ice grains in the mesopause region2011In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 32, no 11, p. 3029-3041Article in journal (Refereed)
    Abstract [en]

    The paper is devoted to optical remote-sensing techniques successfully applied to investigations of the mesospheric aerosol layer, starting with a short history of the development of optical sounding experiments. In the following part, a theoretical basis of scattering measurements is discussed. A brief description of the theoretical principles of optical analysis of aerosol properties, ending with a survey of current activity and, as yet, unresolved problems is presented. It can be concluded that there is a consensus regarding the size range of mesospheric aerosol particles. The contribution of the smallest particles cannot be assessed by current optical methods. The combination of the scattering measurement with an electromechanical impact detector is a promising technique. The true size distribution, more correctly a statistical average of many possible distributions, must rely on numerical modelling. Regarding the shape of the particles, the noctilucent-cloud particles are not perfect spheres. New insight into this problem can be expected from the ongoing observational program of the Atmospheric Chemistry Experiment (ACE) and Aeronomy of Ice in the Mesosphere (AIM).

  • 40.
    Wästfelt, Anders
    Stockholm University, Faculty of Social Sciences, Department of Human Geography.
    Land use qualities identified in remotely-sensed images2009In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 30, no 9, p. 2411-2427Article in journal (Refereed)
    Abstract [en]

    Land use can be defined as the intentional use of a specific piece of land resulting in patterns of ecological responses that are visible in land cover and landscape. The responses to land use often result in a heterogeneous combination of classes of land cover. Existing methods used in the classification of satellite imagery are limited in their capacity to handle categories consisting of heterogeneous or multiple land cover classes. Accordingly, a spatial relational post-classification (SRPC) method has been developed which uses a spatial relational post-classification of land cover classes based on the incorporation of information about identified land use qualities. This paper explains how this method works, and presents the results from a case study of the surroundings of Sotasa village located in southern Sweden. Different land cover classes were aggregated semantically into two land use quality classes. In conclusion, it is argued that it is possible to make the semantic shift from reflectance to land use qualities using the developed method on satellite data, and that this provides considerable scope for the future analysis of land use.

  • 41.
    Xiang, Deliang
    KTH, School of Architecture and the Built Environment (ABE). National University of Defense Technology, China.
    The cross-scattering component of polarimetric SAR in urban areasand its application to model-based scattering decompositionIn: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901Article in journal (Refereed)
    Abstract [en]

    After the work of Freeman, Durden, Pottier, and Yamaguchi, manydecomposition techniques have been proposed for urban areas, mainly to resolvethe overestimation problem of volume scattering. Since it has been validated thatthe cross-polarised (HV) scattering is caused not only by forests but also byrotated dihedrals, in this paper, we propose a cross scattering coherency matrix tomodel the HV component from orientated and complex buildings and thendemonstrate its performance on model-based scattering decomposition. Thebuilding orientation angle is considered in this coherency matrix, making itflexible and adaptive in the decomposition. Therefore, the HV components fromforests and orientated urban areas can be modelled respectively. Twodecomposition procedures are applied in this paper. The first one is to validatethe effectiveness of this scattering model. We regard the HV component fromurban areas as cross scattering, which is an independent scattering componentadded to the Yamaguchi four-component decomposition. Another one is theurban area decomposition application using this scattering model. Decompositionis implemented for urban and natural areas respectively and the HV componentfrom urban areas is regarded as their volume scattering. This procedure is similarto many other state-of-the-art methods for urban areas and needs to discriminatethe urban and natural areas before decomposition. Spaceborne Radarsat-2 C band,the Airborne Synthetic Aperture Radar (AIRSAR) L band and UninhabitedAerial Vehicle Synthetic Aperture Radar (UAVSAR) L band full polarimetricSAR data are used to validate the performance of this cross scattering coherencymatrix. The HV component of orientated buildings is generated, leading to abetter decomposition result for urban areas.

  • 42.
    Xiang, Deliang
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics. National University of Defense Technology, China.
    Ban, Yifang
    Su, Yi
    The cross-scattering component of polarimetric SAR in urban areas and its application to model-based scattering decomposition2016In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 37, no 16Article in journal (Refereed)
    Abstract [en]

    After the work of Freeman, Durden, Pottier, and Yamaguchi, manydecomposition techniques have been proposed for urban areas, mainly to resolvethe overestimation problem of volume scattering. Since it has been validated thatthe cross-polarised (HV) scattering is caused not only by forests but also byrotated dihedrals, in this paper, we propose a cross scattering coherency matrix tomodel the HV component from orientated and complex buildings and thendemonstrate its performance on model-based scattering decomposition. Thebuilding orientation angle is considered in this coherency matrix, making itflexible and adaptive in the decomposition. Therefore, the HV components fromforests and orientated urban areas can be modelled respectively. Twodecomposition procedures are applied in this paper. The first one is to validatethe effectiveness of this scattering model. We regard the HV component fromurban areas as cross scattering, which is an independent scattering componentadded to the Yamaguchi four-component decomposition. Another one is theurban area decomposition application using this scattering model. Decompositionis implemented for urban and natural areas respectively and the HV componentfrom urban areas is regarded as their volume scattering. This procedure is similarto many other state-of-the-art methods for urban areas and needs to discriminatethe urban and natural areas before decomposition. Spaceborne Radarsat-2 C band,the Airborne Synthetic Aperture Radar (AIRSAR) L band and UninhabitedAerial Vehicle Synthetic Aperture Radar (UAVSAR) L band full polarimetricSAR data are used to validate the performance of this cross scattering coherencymatrix. The HV component of orientated buildings is generated, leading to abetter decomposition result for urban areas.

  • 43.
    Yousif, Osama
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics.
    Ban, Yifang
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics.
    A novel approach for object-based change image generation using multitemporal high-resolution SAR images2017In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 38, no 7, p. 1765-1787Article in journal (Refereed)
    Abstract [en]

    Object-based change detection offers a unique approach for high-resolution images to capture meaningful detailed change information while suppressing noise in change detection results. In this approach, mean intensities of objects are commonly used as a feature and images comparison is carried out based on simple mathematical operations such as ratioing. The strong intensity variations within an object - a consequence of high spatial resolution - combined with synthetic aperture radar (SAR) image speckle degrade the accuracy of object mean intensity estimate, and consequently, affect the quality of the estimated object-based change image. A change quantification approach that takes into account the characteristics of high-resolution SAR images, that is, SAR speckle and the strong intensity variation, is proposed. By descending to the pixel level, a new representation of change data (i.e. the change signal) is proposed. With this representation, change quantification boils down to measuring the roughness of the change signal. Two techniques to assess the intensity of change at the object-level, based on Fourier and wavelet transforms (WT) of the change signal, are proposed. Their main advantages lie in their ability to capture the dominant change behaviour of the object, while being insusceptible to irrelevant disturbances. The proposed approach is evaluated using two multitemporal data sets of TerraSAR-X images acquired over Beijing and Shanghai. The qualitative and quantitative analyses of the results demonstrate the superior discrimination power of the proposed change variables compared with the object-based modified ratio (MR) and the absolute log ratio (LR) images.

1 - 43 of 43
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