NASA - National Aeronautics and Space Administration

The Center for Remote Sensing of Ice Sheets has developed an ultra-wideband radar that operates over the frequency from 2 to 8 GHz to map near-surface internal layers in polar firn with fine vertical resolution. The radar has also been used to measure thickness of snow over sea ice. Information about snow thickness is essential to estimate sea ice thickness from ice freeboard measurements performed with satellite radar and laser altimeters. This radar has been successfully flown on NASA P-3 and DC-8 aircraft.

In July 2005, the Johns Hopkins University, Applied Physics Laboratory began “Pathfinder Airborne Radar Ice Sounder (PARIS)” funded under the NASA Instrument Incubator Program (IIP). The primary objective of this project was the first feasibility demonstration of successful radar sounding of ice sheet layering and bottom topography from a high-altitude platform. Major contributing factors included a high-fidelity 150-MHz radar, supported by along-track partially- coherent processing. “High-fidelity” implies very wide dynamic range, extreme linearity, and very low sidelobes generated by the transmitted pulse. “Partially- coherent processing” implies the delay-Doppler technique, previously proven in airborne radar altimeter and low-altitude radar ice sounding embodiments. The radar was mounted on the NASA P-3, and deployed on a mission over the Greenland ice sheet in the spring of 2007. Data were recorded on board as well as displayed in flight on a quick-look processor. The data subsequently were processed in the laboratory to quantify performance characteristics, including dynamic range, sidelobe level control, and contrast improvement from the delay-Doppler algorithm.

The transmit waveform is a 5-MHz bandwidth chirp at a 150-MHz operating frequency with a trapezoidal envelope. Such severe weighting is essential to reduce the ringing commonly associated with the initial on-off transition of weakly-weighted waveforms. The 180-W (peak) linear-FM pulse has ~6 MHz bandwidth. The amplifier is class AB to help ensure the high linearity needed to suppress the internal clutter (sidelobes) generated by the chirp waveform. Laboratory measurements of the driver and power amplifier show excellent linearity with a two-tone third-order inter-modulation of at least -26 dBc at peak power.

There is no down conversion or IF signal within the receiver, greatly simplifying the design, and eliminating most potential sources of distortion and intermodulation. Upon reception, the radar A/D operates on the RF signal directly out of the LNA. The sample rate is well below Nyquist, but it is chosen so that the resulting spectra shift an alias of the main signal to offset baseband in a clear channel. The receiver includes variable attenuators to adjust the voltage range of the signal input to the analog-to- digital converter as well as sensitivity time control (STC) to increase the effective dynamic range of the response as a function of depth of penetration. The overall noise figure of the receiver is less than 5.5 dB with a gain of over 60 dB and a 45 dBm third-order intercept point.

The digital components consist of a field programmable gate array (FPGA) radar synchronizer, a direct digital synthesizer (DDS), and an under-sampling analog-to-digital converter (ADC). All components of the digital subsection are clocked by a stable 66.6 MHz reference oscillator. The radar data are time-tagged by reference to GPS. The flights included passes over the summit ridge, from which results show internal layering, and the bottom profile at several km depth.

The Center for Remote Sensing of Ice Sheets (CReSIS) has developed radars (MCoRDS) that operate over the frequency range from 140 to 230 MHz with multiple receivers developed for airborne sounding and imaging of ice sheets. MCoRDS radars have an adjustable radar bandwidth of 20 MHz to 60 MHz. Multiple receivers permit digital beamsteering for suppressing cross-track surface clutter that can mask weak ice-bed echoes and strip-map synthetic aperture radar (SAR) images of the ice-bed interface. With 200 W of peak transmit power, a loop sensitivity > 190 dB is achieved. These radars are flown on twin engine and long-range aircraft including NASA P-3 and DC-8.

The Digital Mapping System (DMS) is an airborne digital camera system that acquires high resolution natural color and panchromatic imagery from low and medium altitude research aircraft. The DMS includes an Applanix Position and Orientation system to allow precision image geo-rectification. Data acquired by DMS are used by a variety of scientific programs to monitor variation in environmental conditions, assess global change, and respond to natural disasters.

Mission data are processed and archived by the Airborne Sensor Facility (ASF) located at the NASA Ames Research Center in Mountain View, CA. DMS imagery from Operation IceBridge are archived at the National Snow and Ice Data Center in Boulder, CO.

Instrument Type: Canon/Zeiss Camera with IMU/GPS
Measurements: 21-Mpixel natural color Imagery

The Airborne Topographic Mapper (ATM) was a scanning LIDAR developed and used by NASA for observing the Earth's topography for several scientific applications, foremost of which is the measurement of changing arctic and antarctic icecaps and glaciers. It typically flies on aircraft at an altitude between 400 and 800 meters above ground level, and measures topography to an accuracy of ten to twenty centimeters by incorporating measurements from GPS (global positioning system) receivers and inertial navigation system (INS) attitude sensors.

The ATM instruments was based at NASA's Wallops Flight Facility (WFF) in Virginia. They commonly fly aboard the NASA P3-B based at WFF and have flown aboard other P-3 aircraft, the NASA DC-8, several twin-otters (DHC-6), and a C-130; they can fly on most Twin Otter/King Air-class aircraft. The ATM has flown surveys in Greenland nearly every year since 1993. Other uses have included measurement of sea ice, verification of satellite radar and laser altimeters, and measurement of sea-surface elevation and ocean wave characteristics. The altimeter often flies in conjunction with a variety of other instruments. The ATM has been participating in NASA's Operation IceBridge since 2009.

The ATM program was terminated in 2022.

Fine depth resolution profiling of the top 100 m of the ice column is achieved with this radar designed to map variations in the snow accumulation rate. When operated from aircraft, it operates from 600 to 900 MHz providing 28-cm depth resolution in ice and when operated on the ground (500 MHz to 2 GHz) a 5.6-cm depth resolution in ice is achieved. This fine depth resolution enables area extensive spatial mapping of the annual accumulation layers.