<title>Enhanced-resolution ERS-1 scatterometer imaging with irregular samples</title>

Abstract

Scatterometers are low resolution radars originally designed o measure winds over the ocean from space. They measure the normalized radar backscatter coefficient from which the wind is estimated. Over land and ice (sigma) <SUP>0</SUP> is very sensitive to surface conditions and is useful for various scientific studies. Unfortunately, the low resolution of the measurements limits the application of the data. The scatterometer image reconstruction (SIR) algorithm can produce significantly enhanced resolution radar images by taking advantage of measurement overlap from multiple passes of the radar over the target site. The resulting measurements are on an irregular grid and may have different response functions making the analysis of the non-linear SIR algorithm very complicated. Analysis of SIR is further complicated by the fact that it is bivariate: two separate but related images (A and B) are determined from the (sigma) <SUP>0</SUP> measurements where (sigma) <SUP>0</SUP> is related to A and B by the expression (sigma) <SUP>0</SUP> equals A + B ((theta) - 40 degrees) where (theta) is the incidence angle of the measurement which varies from measurement to measurement. In this paper we provide a theoretical framework for scatterometer image reconstruction and resolution enhancement on irregular grids and provide examples of the resolution enhancement possible for the ERS-1 AMI scatterometer. The paper should be of interest to other researchers dealing with resolution enhancement on irregular grids.