ERS-1 Synthetic Aperture Radar Research Articles

Greenland Ice Sheet Surface Properties and Ice Dynamics from ERS-1 SAR Imagery

C-band synthetic aperture radar (SAR) imagery from the European Space Agency's ERS-1 satellite reveals the basic zonation of the surface of the Greenland Ice Sheet. The zones have backscatter signatures related to the structure of the snowpack, which varies with the balance of accumulation and melt at various elevations. The boundaries of zones can be accurately located with the use of this high-resolution imagery. The images also reveal a large flow feature in northeast Greenland that is similar to ice streams in Antarctica and may play a major role in the discharge of ice from the ice sheet.

Description of a program for SAR investigation of the Greenland ice sheet and an example of margin change detection using SAR

In order to interpret changes in the Greenland ice sheet as indications of climatic variation, it is necessary to place observations of local changes in a regional context. This requires a comprehensive monitoring effort which addresses both the inland ice and changes in the ice margin. This paper describes the design of a program for regional investigation of the Greenland ice sheet using synthetic aperture radar (SAR), and discusses the utility of SAR data for detection of change in the ice sheet margin. Comprehensive coverage of the Greenland ice sheet by ERS-1 SAR will allow us to map the boundaries of snow facies on the ice sheet and investigate recent changes in the ice margin. We will use geo-referenced images to map the current boundaries of snow facies, providing a baseline which can be used to detect future change. We demonstrate the utility of SAR for detecting recent changes in the ice margin. SAR images clearly show the ice edge, moraines, and ice marginal lakes. These features can be compared with published maps and earlier images in order to document changes in the margin of the ice sheet. We show evidence for recession of a section of the western margin of the ice sheet. The recession, which occurred between 1938 and 1978, ranges from a few hundred meters at high elevations to several kilometers at calving faces in both ice marginal lakes and fjords. ERS-1 SAR will provide the first opportunity to pursue a comprehensive investigation of the state of the Greenland ice sheet. The ability to address conditions on the ice and to look at margin changes in a systematic way will allow us to develop a stronger framework for interpreting changes in the ice sheet in terms of climatic variation.

Description of a program for SAR investigation of the Greenland ice sheet and an example of margin change detection using SAR

In order to interpret changes in the Greenland ice sheet as indications of climatic variation, it is necessary to place observations of local changes in a regional context. This requires a comprehensive monitoring effort which addresses both the inland ice and changes in the ice margin. This paper describes the design of a program for regional investigation of the Greenland ice sheet using synthetic aperture radar (SAR), and discusses the utility of SAR data for detection of change in the ice sheet margin.Comprehensive coverage of the Greenland ice sheet by ERS-1 SAR will allow us to map the boundaries of snow facies on the ice sheet and investigate recent changes in the ice margin. We will use geo-referenced images to map the current boundaries of snow facies, providing a baseline which can be used to detect future change.We demonstrate the utility of SAR for detecting recent changes in the ice margin. SAR images clearly show the ice edge, moraines, and ice marginal lakes. These features can be compared with published maps and earlier images in order to document changes in the margin of the ice sheet. We show evidence for recession of a section of the western margin of the ice sheet. The recession, which occurred between 1938 and 1978, ranges from a few hundred meters at high elevations to several kilometers at calving faces in both ice marginal lakes and fjords.ERS-1 SAR will provide the first opportunity to pursue a comprehensive investigation of the state of the Greenland ice sheet. The ability to address conditions on the ice and to look at margin changes in a systematic way will allow us to develop a stronger framework for interpreting changes in the ice sheet in terms of climatic variation.

The relation between SAR imagery and regional sea ice ridging characteristics from BEPERS-88

Abstract In the Bothnian Experiment in Preparation for ERS-1 (BEPERS-88) airborne laser profiles and Synthetic Aperture Radar (SAR) images were obtained simultaneously over the pack ice in the Bay of Bothnia, Baltic Sea. The possibility of mapping ice ridging characteristics using SAR has been analysed. SAR intensity histograms and ridging statistics have been compared in regions with length scales from 3 to 23 km. The measures for the intensity of ridging were taken from the profilometer data as functions of the number of ridges and mean ridge height. The results show that, from SAR intensity distribution, an average of 10 per cent upper tail divided by the overall average is a good predictor for the ridging intensity. This predictor explains 80-90 per cent of the variance.

BEPERS pilot study: an experiment with X-band synthetic aperture radar over Baltic Sea ice

AbstractRemote-sensing methods are the primary ones used for ice mapping in the Baltic Sea. A major methodological improvement is now being introduced by satellite radars due to their weather independency and high resolution. To learn how to use ERS-1 synthetic aperture radar (SAR) data, an extensive field programme BEPERS (Bothnian Experiment in Preparation for ERS-1) with airborne SARs has been arranged. The BEPERS pilot study was undertaken in 1987 using the French VARAN-S X-band SAR. The SAR was flown on 1 day over four study areas of size approximately 10 km x 50 km, and intensive validation observations were made. The data were most useful for the education they provided on how to work with SAR in sea-ice mapping. They have been used for developing SAR image-analysis methods, back-scatter modelling investigations and geophysical validation of SAR imagery. Cleaning-up of images consisted of speckle reduction and segmentation. Back-scatter characteristics of undeformed ice and ridges were examined. Ice-type classification was based on the box-classification method. Eight ice types were defined but basically only two types, undeformed ice/open water and deformed ice, could be discriminated. Two basic problems of high practical importance remained: how to discriminate between (1) open water and undeformed ice, and (2) ridged ice and brash ice. The data further showed illustrative examples of SAR imagery over sea ice.

BEPERS pilot study: an experiment with X-band synthetic aperture radar over Baltic Sea ice

Abstract Remote-sensing methods are the primary ones used for ice mapping in the Baltic Sea. A major methodological improvement is now being introduced by satellite radars due to their weather independency and high resolution. To learn how to use ERS-1 synthetic aperture radar (SAR) data, an extensive field programme BEPERS (Bothnian Experiment in Preparation for ERS-1) with airborne SARs has been arranged. The BEPERS pilot study was undertaken in 1987 using the French VARAN-S X-band SAR. The SAR was flown on 1 day over four study areas of size approximately 10 km x 50 km, and intensive validation observations were made. The data were most useful for the education they provided on how to work with SAR in sea-ice mapping. They have been used for developing SAR image-analysis methods, back-scatter modelling investigations and geophysical validation of SAR imagery. Cleaning-up of images consisted of speckle reduction and segmentation. Back-scatter characteristics of undeformed ice and ridges were examined. Ice-type classification was based on the box-classification method. Eight ice types were defined but basically only two types, undeformed ice/open water and deformed ice, could be discriminated. Two basic problems of high practical importance remained: how to discriminate between (1) open water and undeformed ice, and (2) ridged ice and brash ice. The data further showed illustrative examples of SAR imagery over sea ice.

Knowledge-Based SAR Processing and Geocoding: The Elementary Components of the German Processing and Archiving Facility for High Throughput and High-Precision Processing of ERS-1 SAR Data

Future microwave sensors such as the active microwave instrument (AMI) of the first European remote sensing satellite (ERS-1) to be launched in 1990 will be increasingly conducted in an operational mode. This fact implies an increased amount of synthetic aperture radar (SAR) data to be processed systematically, and, furthermore, combines with the growing needs of the user community in terms of various product levels, adequate production, and organization schemes. Among these needs are the requirements regarding much improved radiometric and absolute geometric accuracy of the generated SAR images. Therefore, an end-to-end SAR processing system has been designed that is significantly different from existing ones. The challenging requirements for high precision combined with high throughput of the generated products will be met by two systems: the knowledge-based intelligent SAR processor (ISAR) and the geocoding system. They represent the backbone of a distributed computer network engaged in SAR processing and image restitution within the German Processing and Archiving Facility (D-PAF) for ERS-1, which shall be built up and operated by the German Aerospace Research Establishment (DFVLR). This paper describes the requirements for the system as well as the specific hardware and software concepts.

The Influence of Surface Oil on C-and Ku-Band Ocean Backscatter

A comparative study of ocean backscatter depression due to surface oil has been carried out using Ku-and C-band scatterometers supported by some X-and C-band synthetic aperture radar (SAR) imagery. The depression of radar backscatter for both C-and Ku-band HH-polarized radiation has been measured for the incidence angle range from 20° to 50° on two days, September 16 and 17, 1983 on which the average wind and wave height conditions were 3-6 m/s, 0.3 m and ~10-14 m/s, 1.2 m, respectively. Results show that the depression in Ku-band backscatter increases from approximately 3-5 dB at 20° to ~10 dB or more at 30°-40° and then decreases at the larger incidence angles. Generally, the angular dependence of C-band backscatter depression was similar to that at Ku-band, but the peak depression was shifted to slightly larger angles and usually exceeded Ku peak 1-2 dB. The Ku-band results are in good agreement with previous work [9] that tentatively explained the angular results of backscatter depression on the basis of a selective damping of the first-order Bragg resonant waves by the oil film. This explanation, however, is inconsistent with the results of the present work when both C-and Ku-band are considered. The significance of the data is discussed in the context of present and future radar systems (e. g., the ESA ERS-1 SAR and the Radarsat SAR).

Ready-to-use GIS Information From RemotelySensed SAR Data

SAR data are not suitable for direct use by the GIS community. A wide variety of users, ranging from urban planners to Earth resource managers or insurance brokers, have been managing territorial information in Geographical Information Systems. They want to get relevant and updated information, ready to be inserted into their systems. In order to fulfil these requirements, the relevant information must be first extracted from the radiometric data gathered by the satellite sensors. Information must then be made available in a suitable format. A study has been performed to address the aspect of the realisation of GIS products, generated from remotely sensed data, and tailored to be closer to the end users needs. In a study performed for the European Space Agency, Planetek investigated whether new, GIS-oriented products, derived from ERS-1 and ERS-2 Synthetic Aperture Radar (SAR) data, could be provided to these user communities. The study has been focused on two key issues: an identification of the kind of product required by end users, and a specification of an appropriate format for product distribution. In order to validate the concept proposed in this study, it has been decided to perform a detailed study of one product. As sample product we selected the flood map. The result is a vector map of the flooded zones, which is of immediate usage for final users. Transactions on Information and Communications Technologies vol 18, © 1998 WIT Press, www.witpress.com, ISSN 1743-3517