Abstract:
The Oceans and Ice Branch of NASA's Goddard Space Flight Center has processed satellite radar altimetry and aircraft laser altimetry over the continental ice sheets of Greenland and Antarctica and surrounding sea ice to calculate surface elevations. The radar processing is currently being funded by the NASA Mission to Planet Earth Pathfinder Program.
The data ... have been obtained from the Seasat, Geosat, ERS-1, ERS-2 and GFO satellites radar altimeter missions and from the Arctic Ice Mapping (AIM) mission which utilizes NASA's Airborne Topographic Mapper (ATM) laser altimeter. Radar Altimetry data from Seasat, Geosat, ERS-1, ERS-2 and GFO satellites is available for distribution upon request. Data from ENVISAT will be available in the near future.
The following data products are available:
Level 1: Waveform Data Records
Orbital format waveform data records at the full data rate which contain the time, location altimeter return waveform, and retracking parameters.
The altimeter waveform return gives a measure of the surface roughness on scales of sub-meter to tens of kilometers and indicates if surface penetration and/or volume scattering is present. These results are used to investigate regional, interdecadal and interannual changes in the ice sheet and sea ice surface characteristics. The returns are also used to identify sea ice boundaries and extent.
Level 2: Ice Data Records
Orbital format ice data records at the full data rate which contain the time, precise location, altimeter height measurement, corrected precise surface elevation, atmospheric corrections, tidal values, retracking corrections, and AGC. These data are updated on-line as more precise orbits, corrections, and tide values become available.
These data are mainly used by scientists who are trying to improve the algorithms to calculate the corrections or who require knowledge of what effect the corrections have on the data. Most researchers do not require this much detail and would be better served by the georeference data bases which contain the precise surface height after all corrections have been applied at the full data rate.
Level 3: Geo-referenced Database
Contain surface height measurements derived from altimetry data, ordered by geographic areas or "bins". Each data record contains the geodetic position, revolution number, surface elevation relative to a reference ellipsoid, and slope correction. This database contains detailed elevation information for the full-rate along track data.
Level 4: Elevation Grids
Gridded elevations are calculated from the data by a weighted fitting of a bi-quadratic function (bi-linear where data distribution is poor) on a polar stereographic projection with a nominal spacing of 5 km (ERS-1) 10 km (GEOSAT) and 20 km (Seasat).
The dense topographic coverage is crucial for a variety of glaciological studies, from numerical modeling of the ice dynamics to monitoring of key glaciological features: ice drainage basins, ice-shelf grounding lines, ice divides, subglacial lakes, ice shelf fronts, and ice rises.
Crossover Data
The crossover data give interpolated elevations for different tracks at the same location including the corrections also interpolated to the crossover location. These data are best used for ice sheet change studies.
[This summary was adapted from the GSFC Ice Altimetry WWW pages.]
Laboratory for Hydrospheric Processes
NASA/Goddard Space Flight Center
Code 614
City:
Greenbelt
Province or State:
MD
Postal Code:
20771
Country:
USA
Publications/References
Davis, C.H. and H.J. Zwally,"Geographic and Seasonal Variations in the Surface Properties of the Ice Sheets by Satellite Radar Altimetry", Journal of Glaciology, Vol. 39, 1993
Lingle, C.S., L.-h. Lee, H.J. Zwally and T.C. Seiss, "Recent Elevation Increase on Lambert Glacier, Antarctica, From Orbit Crossover Analysis of Satellite Radar Altimetry", Annals of ... Glaciology, 20, 1994
Martin, T.V.,H.J. Zwally,A.C. Brenner, and R.A. Bindschadler "Analysis and Retracking of Continental Ice Sheet Radar Altimeter Waveforms", J. Geophys. Res.,88, C3, 1983.
Zwally, H.J, A.C. Brenner, J.A. Major, and R.A. Bindschadler, and J.G. Marsh, "Growth of Greenland Ice Sheet: Measurement", Science Vol 246, 1989a
