The seasonal cycle of ERS scatterometer signatures over perennial Antartic sea ice and associated surface ice properties and processes

Abstract

Time series of satellite radar backscatter coefficients of the European Remote-sensing Satellite (ERS-1/-2) scattcrometer are presented for perennial sea-ice regions in the Antarctic from June 1991 to June 1999. There is a pronounced seasonal cycle, with higher backscatter in summer than in winter. On average, backscatter increases from spring values of -16.3 dB to summer values of -10.7 dB within 96 days. This rapid rise and the summer maximum are occasionally interrupted by sudden strong signal drops. After late summer/early autumn, backscatter decreases again and slowly approaches winter values. The seasonal cycle is interpreted in terms of processes at the ice surface. The spring backscatter rise is associated with internal snowmelt and the formation of superimposed ice. This process commences once the surface energy balance becomes positive. Sudden backscatter drops are caused by temporary meltwater saturation of the snow during episodic events of warm-air advection. In the autumn, when superimposed-ice formation ceases due to surface cooling, gradual surface flooding with sea water becomes the dominant process, causing the observed decreasing backscatter. The reoccurrence of the seasonal backscatter cycle in most regions points to the widespread formation of superimposed ice on perennial Antarctic sea ice.