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Comparison of Retracking Algorithms Using Airborne Radar and Laser Altimeter Measurements of the Greenland Ice SheetThis paper compares four continental ice sheet radar altimeter retracking algorithms using airborne radar and laser altimeter data taken over the Greenland ice sheet in 1991. The refurbished Advanced Application Flight Experiment (AAFE) airborne radar altimeter has a large range window and stores the entire return waveform during flight. Once the return waveforms are retracked, or post-processed to obtain the most accurate altitude measurement possible, they are compared with the high-precision Airborne Oceanographic Lidar (AOL) altimeter measurements. The AAFE waveforms show evidence of varying degrees of both surface and volume scattering from different regions of the Greenland ice sheet. The AOL laser altimeter, however, obtains a return only from the surface of the ice sheet. Retracking altimeter waveforms with a surface scattering model results in a good correlation with the laser measurements in the wet and dry-snow zones, but in the percolation region of the ice sheet, the deviation between the two data sets is large due to the effects of subsurface and volume scattering. The Martin et al model results in a lower bias than the surface scattering model, but still shows an increase in the noise level in the percolation zone. Using an Offset Center of Gravity algorithm to retrack altimeter waveforms results in measurements that are only slightly affected by subsurface and volume scattering and, despite a higher bias, this algorithm works well in all regions of the ice sheet. A cubic spline provides retracked altitudes that agree with AOL measurements over all regions of Greenland. This method is not sensitive to changes in the scattering mechanisms of the ice sheet and it has the lowest noise level and bias of all the retracking methods presented.
Document ID
19980017788
Acquisition Source
Headquarters
Document Type
Contractor Report (CR)
External Source(s)
doi:10.1109/36.387585
Authors
Ferraro, Ellen J. (Raytheon Co. Wayland, MA United States)
Swift, Calvin T. (Massachusetts Univ. Amherst, MA United States)
Date Acquired
September 6, 2013
Publication Date
May 1, 1995
Publication Information
Publication: IEEE Transactions on Geoscience and Remote Sensing
Publisher: Institute of Electrical and Electronics Engineers
Volume: 33
Issue: 3
ISSN: 0196-2892
Subject Category
Earth Resources And Remote Sensing
Report/Patent Number
NAS 1.26:207160
NASA/CR-95-207160
Funding Number(s)
CONTRACT_GRANT: NAGw-3685
Distribution Limits
Public
Copyright
Public Use Permitted.

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