Diurnal SAR variability due to ice and snow air interface wetness overnight changes.

For a water content over 8%, the transmitted component of a SAR beam becomes negligible. The electromagnetic wave interaction with the interface discontinuity is then determined by the scattering efficiency of surface roughness rms and correlation height. It is illustrated by the difference of contrast observed on images acquired from a same scene one late in the afternoon after a warm day and the development of a wet interface, and the other, early in the morning after a cool night and growth of frost flower in place of the wet interface. The increased the rms height of newly formed crystals reduce the angle dependence of the backscattered signal and therefore the contrast on the scene, however, the increased volume scattering in snow covered areas seems to be the main factor causing a resolution difference on the ridge network between images recorded on morning and at the end of the afternoon. A detailed survey of the air-snow or air-ice interface of the snow cover and ice blocks surfaces. Surface wetness, snow wetness content and surface roughness are documented. Radar data measured on a variety of snow and ice interfaces are presented and analyzed. We show that the presence of a wet film on snow and ice surfaces produces an increased forward scattering whereas interfaces covered with newly crystallized ice display an enhanced backscattering.