A Low Frequency Radar for Direct Measurement of Sea Ice Thickness: Implications of Ice Surface Roughness

Sea ice thickness is thought to be a primary indicator of global greenhouse warming, yet it has proven to be one of the most difficult variables to measure particularly on meaningful synoptic and climatic scales, including from satellites. An instrument concept study and associated field experiment system development are underway to measure the sea ice thickness directly with VHF radar. This system precludes the use of very wide bandwidth as in radar sounder, but instead uses new instrument technology as a combined spatial- and frequency-domain interferometer. Thickness is derived from phase obtained from a combination of slightly different narrow-band frequencies and incidence angles. The use of VHF is required to overcome the lossy nature of sea ice and penetrate to many meters of thickness to detect the sea-ice ocean interface. The approach relies heavily on the larger contrast in dielectric constant between the sea-ice/ocean than the sea-ice/snow as well as the sea ice bottom roughness, that results in a stronger backscatter return from the sea-ice ocean interface than sea-ice snow interface. The detailed formulations of the theoretical basis of this concept are presented in accompanying paper. Key information on surface roughness characteristics at relatively fine-scales, particularly of ice undersides for which comparatively little is known, and sea ice medium composition (for example, brine inclusions and air bubbles) are needed to develop the scientific basis of these technologies, as well as to develop the measurement strategy of a spaceborne sensor. In this presentation, we present an overview of the radar concept, fine-scale bottom roughness measurements from different upward looking sonar data sets, and an approach for a meaningful spatial and temporal measurement strategy for a future spaceborne instrument.