摘要:

Global estimates of directional ocean wave spectra from space can help to spur improvements in the accuracy of existing ocean wave forecasts. The results of three ocean wave experiments conducted since 1978 indicate that a low altitude (∼300km) free-flying SAR could accurately monitor the performance of global wave models, and thus could help to assess the impact of both scatterometer-aided wind fields and improved wave model physics. The first opportunity to demonstrate such a potential should occur around the mid-1990s, when the European ERS scatterometer and the US Shuttle Space Radar Laboratory should be operating simultaneously.

ISSN:0143-1161    

DOI:10.1080/01431169108955203

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Seasat demonstrated the potential of spaceborne synthetic aperture radar (SAR) for the study and routine monitoring of ocean waves on global scales, but it also raised questions about how these waves were imaged. Here we describe comparisons of wave spectra extracted from Seasat SAR data with simultaneous buoy measurements as tests of wave-imaging theory. Because of the large range-to-velocity ratio (128 seconds) of the Seasat SAR, its images are expected to be particularly sensitive to motions of the sea surface. These motions give rise to the imaging mechanism known as velocity bunching and a smearing of the image in azimuth. However, we do not obtain good agreement between the buoy and SAR-derived spectra when these effects are expected to be important. Similar results are obtained with data from the second Shuttle Imaging Radar SI R-B. The Seasat and SIR-B results combined allow us to assess both our overall understanding of how ocean waves are imaged by spaceborne SAR and the deficiencies in procedures to recover wave spectra from such data. The implications of these results for the plans to observe ocean waves with the SAR on the European Remote Sensing Satellite ERS-1 are discussed.

ISSN:0143-1161    

DOI:10.1080/01431169108955204

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

This paper reviews the evolution of satellite microwave radiometry in Europe in the 10 years since 1978, when Scanning Multichannel Microwave Radiometer (SMMR) instruments were put into orbit on Seasat-A and Nimbus-7. In Europe there has been significant progress since early concept studies, and this is summarized in terms of system studies, technology development, and instrument development. Looking to the future, it is suggested that to achieve a cost effective instrument the design should be optimized for a fairly narrow range of applications. As an example of this approach, a possible instrument aimed at mapping of polar sea ice is described.

ISSN:0143-1161    

DOI:10.1080/01431169108955205

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The suite of sensors flown onboard Seasat during 1978 has provided glaciologists with valuable tools for the study of ice masses, particularly in the polar regions. Of the sensor package, the most useful instruments for glaciology have been the radar altimeter and the synthetic aperture radar. The former has demonstrated the ability to map the surface of ice sheets in considerable detail (possibly to better than 50 mm over ice shelves) and over a very short period of time. Such maps provide the first step towards evaluating the long term mass balance of these ice masses. Such studies are of central importance to global climate modelling, investigation of the ‘greenhouse effect’ and prediction of world sea levels. Radar altimeter mapping has also provided unparalleled detail on surface topography relevant to ice dynamics investigations. The small dataset of Seasat Synthetic Aperture Radar (SAR) imagery gathered over ice masses, principally in Iceland and Greenland (there was no coverage of Antarctica), has begun to reveal useful detail of surface and near-surface phenomena such as flowlines, meltwater percolation, and snow and ice facies invaluable for glaciolog-ical reconnaissance. In particular recent studies have shown the value of a multi-sensor approach with the combination of SAR and multi-spectral imagery. It is likely that X- and C-band SARs will prove better for snow and ice discrimination than the L-band system on Seasat. The Scatterometer and Scanning multi-channel microwave radiometer instruments on Seasat have yielded data over ice masses which are still in the early stages of evaluation. Nevertheless there are strong indications of the value of these data for investigation of surface melt phenomena and temperature-accumulation patterns.

ISSN:0143-1161    

DOI:10.1080/01431169108955206

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The most basic glaciological requirement for investigations of ice sheets and ice shelves is a measurement of surface elevation. Prior to 1978, no technique operated from the surface, aircraft or satellites had provided elevation data with sufficient accuracy and spatial temporal coverage to address continent-wide problems such as whether the Antarctic ice sheet is growing or shrinking. Although on an oceanographic mission, Seasat gave the first extensive evidence that a satellite radar altimeter can achieve high precision mapping for widespread glaciological application. In the decade since its launch, analysis of data from its brief mission has showed the capability of measuring elevations to an accuracy of up to 25 cm, mapping the outer margins of ice shelves, identifying grounding lines, profiling icebergs and providing information on surface features. Although problems such as coverage, mission continuity and special data processing still need to be addressed, Seasat demonstrated the very real contributions which future altimeters such as that to be flown ERS-1 will make to studies of the polar regions.

ISSN:0143-1161    

DOI:10.1080/01431169108955207

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor