Integration of HF/VHF antennas on a compact UAS equipped with a radar depth sounder for ice sounding

Ice-sheet models are necessary to understand changes being observed in Greenland and Antarctica, and predict ice sheets' response in a warming climate. Information on ice thickness, bed topography and basal conditions is required to accurately model ice dynamics. Most of the rapid changes are taking place around ice-sheets' margins with fast-flowing outlet glaciers. These areas are very rough and contain warm ice with debris and other inclusions, and thus low frequency radars are required to minimize volume scatter. Also these radars must have a 2-D aperture synthesis capability to reduce surface scatter from extremely rough surface because the surface and volume scatter can mask weak echoes from the ice-bed interface. Therefore, a UAS that can fly on a closed-spaced lines in the cross-track direction for synthesizing a 2-D aperture is needed. In view of this, we have developed a compact UAS, G1X with 5.3 m wingspan, equipped with a 2-kg radar. The onboard radar operates at 14 MHz and 35 MHz with bandwidths of about 1 MHz and 4 MHz, respectively. The G1X carries two separate antennas integrated conformally onto its wings. Because of the small platform, it was extremely challenging to integrate the long-wavelength antennas as well as the onboard metallic mechanical structures, electronics boxes and wirings. Managing electromagnetic interference between avionics and radar systems also requires close collaboration in aircraft system and payload system design in a small UAS. In our presentation, we will first describe our radar system and platform and then we will focus on the design and implementation of the HF/VHF antennas for UAS integration. During the UAS operation in the field, we have characterized the radar antennas inflight and data collected were used to optimize the antenna bandwidths and thus the radar data quality. Radar echograms collected before and after the antenna optimization will be presented for comparison. Finally, we will show ice-sheet thickness data collected during remote-controlled and autonomous flights as part of the science mission near the Whillans ice stream in West Antarctica during the Winter 2013 field season.