ON THE RESPONSE OF POLARIMETRIC SYNTHETIC-APERTURE RADAR SIGNATURES AT 24-CM WAVELENGTH TO SEA-ICE THICKNESS IN ARCTIC LEADS

We investigate observationally and theoretically the response of polar imetric backscattering at 24-cm wavelength to the thickness of Arctic sea ice in leads and first-year ice features. We employ backscattering data acquired by the Jet Propulsion Laboratory airborne synthetic ape rture radar (SAR) during March 1988 in the Beaufort Sea, together with nearly simultaneous passive microwave imagery acquired by the U.S. Na vy K(a) band radiometric mapping system. We find that 24-cm copolar ra tios and copolar phases vary strongly with apparent ice thickness. We observe copolar phase shifts between -10-degrees and -50-degrees (rela tive to multiyear ice phases) for new ice features in the imagery, as well as positive copolar phases in a first-year ice feature. Copolar r atios also vary with apparent thickness, from values larger than those expected theoretically for seawater to values slightly lower than tho se expected for thick ice. We derive a signature model based on scatte ring from a rough air/sea ice interface with realistic vertical profil es of brine volume and relative permittivity beneath. Model prediction s for copolar ratios and phases show ice thickness-dependent variation s consistent with those observed. We present simulation results showin g that plausible ice thickness variations between pixels in a multiloo k average diminish, but do not eliminate, the signature response to th ickness. This suggests that direct thickness estimation of sea ice in leads may be possible using polarimetric SAR at wavelengths of 24 cm o r longer.