Vol. 4, No. 1, 130-138, 2005

Abstract
During the early melt period, the air-ice and air-snow temperature conditions may vary from melting to freezing within 12 hours. When solar irradiance and air temperature are at their maximum, the increased wetness of the snow layer coupled with the development of a liquid film on exposed ice faces increases the contrast between ridges and flat ice areas. We present two images recorded at 4 am and 4 pm that show this natural enhancement process of ridges when a liquid phase is present on ice blocks (4 pm). Besides, it also shows that, on the contrary, the development of new ice crystals during the night create conditions that highly reduce the contrast between ridges and flat ice areas (4 am image).

For smooth wet surfaces the backscattering at normal incidence is dominated by the coherent component. In addition, the non-coherent component is maximum at normal incidence. The variability in surface slope orientations being a characteristic of ridge areas, we computed probability densities that pixels from ridge regions would be identified as ridge pixels. Both coherent and non-coherent models show a dependence on block size and the applied threshold value. As anticipated, the coherent model gives the highest probability levels with a maximum for cubic blocks of 0.4 m. The maximum value with non-coherent backscattering is reached for 1 m blocks.

ISSN 1729-3782