This paper will present a methodology to optimize the design of a mismatch filter using the least squares solution. This approach utilizes two parameters referred to as the designed mainlobe width and the diagonal loading value. The metrics under consideration for this filter design are mainlobe width, peak sidelobe level (PSL), mean sidelobe level (MSL), and mismatch loss. Using this technique significant improvements of over 40 dB PSL and nearly 25 dB MSL are gained for less than 1 dB degradation in mismatch loss and slight increase in mainlobe width. This design is based on waveforms that are physically realizable and are often found in weather radar and other remote sensing applications.

Prediction of the polar ice sheets' contribution to sea-level change has prompted an intensive glacial characterization with fine spatial and temporal resolution. To provide key metrics required by predictive mass balance models including surface topography, ice thickness, and basal conditions (topography, roughness, frozen or wet boundary conditions, grounding-line position), an expanding series ...

Three-dimensional topographic maps of the bed 2.5 km beneath the Greenland ice sheet in a 10-km × 10-km region centered on the NEEM drill site (77.45°N 51.06°W) are produced using different processes - interpolation, interferometry, and tomography. Descriptions of the data collection and processing are followed by the terrain maps which are compared. Effects of basal slope and roughness on basal backscattering were modeled in an attempt to highlight the contribution of bed wetness variations in basal SAR intensity maps.

The Center for Remote Sensing of Ice Sheets (CReSIS) was formed to investigate and generate a greater understanding of ice sheets and their relationship to the global climate, specifically sea-level rise. To provide the detailed ice thickness data required for more accurate ice sheet models, CReSIS determined a new airborne radar system was required. A few requirements for the radar sensor include the ability to be installed on a number of airborne platforms, capable of collecting simultaneous data from up to 16 independent receive channels, and providing real-time display of processed data for quality analysis.

The Multichannel Coherent Radar Depth Sounder (MCoRDS) system was developed by the Center for Remote Sensing of Ice Sheets (CReSIS) to map the thickness of ice sheets. This radar system was used in Antarctica as one of the primary sensors for NASA's Operation Ice Bridge (OIB) during the fall of 2009. Compared to its predecessors, MCoRDS features several new capabilities which enabled it to successfully capture ice thickness measurements over multiple glaciers on an aerial platform. This paper will focus on the capabilities of MCoRDS and also provide a sample of the processed radar results.

During NASA's Operation Ice Bridge a gridded survey was flown over Pine Island Glacier (PIG). This survey was a finer grid than previously flown over this area. The data collected confirm that the majority of the ice at the bottom of PIG is below sea level which could be a major cause in the speed-up of the ice flow in that area. These data can be used in flow rate calculations and to the mass balance in that area.

The Multi-Channel Coherent Radar D e p t h S o u n d e r (MCoRDS) system was developed by the Center for Remote Sensing of Ice Sheets (CReSIS) at the University of Kansas to map the thickness and underlying bed elevation for glaciers in Antarctica on the NASA Operation Ice Bridge (OIB) mission. Scientists believe that the lubricating effect of liquid water at the bed-ice interface will significantly increase the glacial flow resulting in more ice being discharged into the ocean. Bed elevation that is below sea level is particularly susceptible to this effect. Therefore, to better predict the future movement of ice sheets in Antarctica, scientists and modellers need to know the current elevations and topography of the bed beneath several outlet glaciers in Antarctica. The MCoRDS system, flown on the NASA DC-8, was designed to sound these glaciers capturing the surface and bed echoes from both low and high altitude flights. The ice thickness can be obtained from these measurements and, in conjunction with altimeter data, the bed elevation can be determined allowing modellers and scientists to better understand the current status of these glaciers, as well as, identifying those at risk of increasing in velocity.

We have developed improved versions of three different radar systems and integrated them as an airborne instrumentation suite for sounding and imaging Polar ice sheets. The first instrument consists of a multi-channel, coherent, pulsed radar operating at VHF with up to 20 MHz bandwidth. This instrument is capable of sounding a few-kilometer thick ice while flying at altitudes up to 10 km above mean sea level. The second instrument is designed to operate at UHF using a burst of narrow-bandwidth signals to digitally synthesize a bandwidth of in excess of 300 MHz. This apparatus is used to measure internal layers of the ice sheet to a depth close to 100 m. The third component to the instrumentation package is based on a frequency-modulated continuous wave (FMCW) radar, which operates at microwave (Ku band) frequencies with up to 1 GHz of instantaneous bandwidth. This radar set is used to measure the ice sheet surface elevation profile with centimeter accuracy. We are presenting a description of each system, with emphasis on the VHF depth sounder. We also present sample field test results obtained during the 2009 austral summer season in Antarctica, as a validation of the performance of the instrument package.

We discuss results from a high-sensitivity, multichannel, very high frequency, and surface-based radar depth sounder/imager. The instrument was used to map deep internal layers and characterize basal conditions over a 240-km(2) grid in the vicinity of the West Antarctic Ice Sheet Divide ice core site. The ice thickness at the core site was found to be about 3470 m, and we detected internal layers to within 350 m of the ice/bed interface. Radar-detected layer stratigraphy does not show evidence of flow-induced disturbances that might complicate the depth-age relationship and the interpretation of climate history preserved in the ice. We also found that bed reflectivity over the region varies by more than 30 dB. Approximately 15 dB of this variability appears to be the result of transitions from a frozen to a thawed bed in a number of places. The remainder probably results from changes in bed roughness. Our data are important for planning drilling to the bed, as well as providing constraints and boundary conditions for regional ice-flow models.

In August of 2008 a radar survey was conducted at the NEEM site in Greenland. An example echogram showing internal layers all the way to the bed, a digital elevation map around the drill site, and a side looking synthetic aperture radar image will be presented. The echogram appears to show a fairly continuous Eemian layer where predicted by modeling. Additionally the area around the drill site is very flat although some slope variation is observed. Finally side looking SAR images show reflected power variations that need more analysis to determine their source.

A VHF-band radar is being developed to characterize polar ice sheets and their basal conditions from a UAV developed specifically for low-altitude polar operation. The radar's 195-MHz center frequency, 30-MHz bandwidth, and 200-W transmit power will map internal layers and ice thickness with a depth resolution of less than 3 m in ice, and image the ice-bed interface. To satisfy the mass and volume constraints of the UAV, a distributed architecture was developed employing transmit/receive modules mounted on each of the eight wing-mounted wide-bandwidth Vivaldi antennas. An eight-channel digital waveform generator will be used to create transmit waveforms to simultaneously measure ice thickness and map internal layers along the nadir track, and image ice-bed interface on the left and right sides of the platform in strip-map mode.

An avionics system for an autonomous UAV platform supporting VHF depth sounding and SAR is under development. The system is divided into navigation, communication, and data processing or logging. This design provides accurate position, velocity, acceleration, and attitude data. It supports over-the- horizon communication via an Iridium satellite link. The data collected by this system will allow for motion effects of the UAV to be compensated for, to enable SAR image formation.