Design and development of a coherent radar depth sounder for measurement of Greenland ice sheet thickness.

摘要

The mass balance of the Greenland ice sheet plays an important role in the rise of the Earth's sea level. The continuous rise over the last century has led to the initiation of a program by NASA to measure the surface elevation and thickness of the Greenland ice sheet. Remote sensing methods, using airborne altimeters and radio echo sounders, are the least expensive, safest, and most effective methods of obtaining these ice parameters.; The University of Kansas operated the radio echo sounder in this program. A thorough evaluation of the Coherent Antarctic Radar Depth Sounder (CARDS) system, built in the 1980s, was performed in the first field experiment while collecting useful data. The CARDS loop sensitivity was about 20 dB less than its theoretical specifications. All the problems were identified during the field experiment and it was decided to redesign and rebuild the CARDS system.; The analog section of CARDS was redesigned and rebuilt. The digital system was upgraded to work with a higher-speed computer and the antenna mounts were reconstructed by NASA engineers. This new system, Improved Coherent Arctic and Antarctic Radar Depth Sounder (ICARDS), performed to its theoretical specifications in the fourth field experiment. During the field experiment, a large volume of data were collected. These data were processed and supplied to users in the level 0 form; they have been and are being used by scientists all over the world.; ICARDS was constructed using the conventional technology which the remote sensing community has been using since the mid 1970s. We decided to build a next-generation system, Next-Generation Coherent Radar Depth Sounder (NG-CORDS), using today's technology. A prototype analog section was first developed and then a final field-useable unit was constructed. Radio frequency integrated circuits (RFICs) and microwave monolithic integrated circuits (MMICs) were used, and the entire RF module was contained within a {dollar}8sp{lcub}primeprime{rcub}times 10.17sp{lcub}primeprime{rcub}times 4sp{lcub}primeprime{rcub}{dollar} enclosure. The performance was laboratory tested and proved to be better than the ICARDS.; Finally, the progress of this project was summarized, and a market analysis for the NG-CORDS was done. The science and engineering requirements of the project are met, and the project spending is within budget. The market analysis said that the demand for the NG-CORDS in the science community alone is insufficient to take NG-CORDS commercial.