Abstract

      The world's sea level has increased by 2mm/year over the past century, it is predicted to rise between 50 and 70 cm within the next hundred years. The threat of flooding from the thermal expansion of the ocean and melting of mountain glaciers can be devastating. With the premise that the main contributing factors of the sea level rise come from Greenland and Antarctica, a program to monitor the mass balance of the Greenland ice sheet was initiated by NASA in 1993 known as the PARCA (Program for Arctic Regional Climate Assessment) initiative.

The Radar Systems and Remote Sensing Laboratory (RSL) at the University of Kansas has played a significant role in PARCA by collecting and monitoring the mass and overall ice dynamicsof the ice sheets in Greenland with the use of an ice penetrating radar. The University of Kansas developed the Coherent Antarctic Radar Depth Sounder (CARDS) in the 1980s for the use of data collecting in Antarctica. However, there were several shortcomings with this system which resulted in less than optimum performance. As a result, this system was redesigned and rebuilt in 1996. Although the Improved Coherent Antarctic Radar Depth Sounder (ICARDS) eliminated previous problems faced by CARDS, it was oversized. This led to the development of the Next-Generation Coherent Radar Depth Sounder (NG-CORDS) system, which is an airborne radar that uses complementary Surface-Acoustic-Wave (SAW) devices for both signal generation and matched filtering of a linear chirp wave form. NG-CORDS uses Radio Frequency Integrated Circuits (RFICs) and Microwave Monolithic Integrated Circuits (MMICs) with 12-bit A/D converters instead of the two 8-bit A/D converters previously used by CARDS. Recent field experiments have used the ACORDS (Advanced COherent Radar Depth Sounder which is a more compact design. ACORDS is an enhanced version of the NG-CORDS that incorporated the latest digital technology in the radar system. It is unique because of its ability to generate the transmit waveform digitally and uses band pass sampling and digital pulse compression techniques. By having the improved Radar Depth Sounder, data has and continues to be collected from Greenland’s ice sheet. These data acquisitions have to be obtained periodically to provide solid measurement of the ice and its behavior. Even though there are some challenges remaining with the ACORDS system, such as surface clutter due to heavy crevassing masking the bedrock return and signal loss due to increased melting in some outlet glaciers, over 90% of the collected data were of good quality.