FIELD OBSERVATIONS OF THE ELECTROMAGNETIC PROPERTIES OF FIRST-YEAR SEA-ICE

An interdisciplinary held experiment was conducted during April and Ma y of 1994 at Point Barrow, AK, to investigate the relationship between the electromagnetic and physical-biological properties of first-year sea ice. Electromagnetic signatures of bare and snow-covered first-yea r ice were measured over a broad spectral range, including ultraviolet through near-infrared albedo, microwave emissivity, and radar backsca tter. Observations indicated that the scattering of visible light vari ed significantly with depth in response to changes in the size and ori entation of the ice crystals and in the number of brine and air inclus ions. The scattering of visible light was greatest in the surface laye r where there were numerous inclusions, and crystals tended to be smal l and randomly oriented. Changes in albedo over small horizontal dista nces were found to be related to surface layer conditions, including t he number of air bubbles and particulate levels. Even for bare ice, tr ansmittances were small with peaks in the blue-green. Scattering excee ds absorption throughout the snow and ice except in the skeletal layer colonized by bottom ice algae. Passive microwave emissivities showed a substantial difference between snow-covered and snow-free sites due to the effects of impedance matching at lower frequencies and volume s cattering at higher frequencies produced by the snow. Spatial variabil ity in the emissivity was quite small except at 90 GHz, where the emis sivity was most sensitive to the amount of depth hoar. Radar backscatt er coefficients were 5-6 dB larger for oblique viewing angles over sno w-covered ice.