Envisat Radar Altimetry Products For Cryospheric Studies
Abstract
Ice sheets and sea ice play a key role in the global climate system due to their albedo and as a huge store of freshwater. Sea-ice is also a barrier between the ocean and the atmosphere and drives the thermohaline circulation of the oceans. These critical components of the climate system are not well modelled but are clearly important if accurate predictions of the consequences of global warming are to be made. The vast, remote and inhospitable polar regions experience frequent cloud cover and long periods of darkness. They are best observed by satellite-borne active radars.
The Altimetry mission on-board ENVISAT, ESA's largest environmental remote sens- ing satellite to be launched on 1st March 2002, is designed to guarantee the continu- ity of observations started by ERS-1 and ERS-2. It includes an advanced dual fre- quency new generation Radar Altimeter (RA-2), the Microwave Radiometer (MWR), the positioning instrument DORIS and the laser retro reflector (LRR). RA-2 has a new tracker philosophy: robust collection of accurately quantified radar echo data, particularly robust at handling non-ocean like echoes and conversion to meaningful geophysical quantities (re-tracking) done solely on ground. Moreover, RA-2 switches autonomously between 3 different range window width to adapt to different surfaces and avoid losing track. RA-2 has also the new capability of providing limited bursts of individual, i.e. un-averaged, Ku-band echoes at 1800 Hz, for theoretical research on backscattering and precise monitoring of bright targets. The data products are greatly improved. All data -over all surfaces- are processed si- multaneously by 4 different retrackers (Ocean, Ice1, Ice2 and Sea-Ice) to let the users choose the most suitable for their particular application. The Ice1 retracking is the range estimation technique for ice-sheet echoes used on ERS data. Ice 2 retracking is aimed at ocean-like echoes returned from ice-sheets. The Sea-Ice retracking is for specular echoes from areas of sea ice: parameters are supplied to discriminate echoes originating from ice and water surfaces. Combining these measurements provide esti- mates of ice freeboard from which sea ice thickness can be determined. Users wishing to develop specialised retracking algorithms will access the echo waveforms delivered alongside the Geophysical Data Records, including the brightness temperatures from MWR.- Publication:
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EGS General Assembly Conference Abstracts
- Pub Date:
- 2002
- Bibcode:
- 2002EGSGA..27.6093B