Enhanced-Resolution Reconstruction of ASCAT Backscatter Measurements

A wind scatterometer measures the normalized radar cross section σ° of the Earth's surface in order to estimate the ocean near-surface wind. Each measurement is the weighted integral of σ° over an area, so samples of σ° are filtered by a measurement spatial response function (SRF). Enhanced-resolution σ° data may be produced from σ° measurements and their associated SRF using image reconstruction algorithms. These enhancedresolution data products are useful for land and ice studies in addition to high-resolution ocean wind retrieval. The spatial resolution and noise may be improved by combining data for multiple passes, trading off temporal resolution for spatial resolution. In this paper, we consider the production of enhanced-resolution σ° image reconstruction from the Advanced Scatterometer (ASCAT) on the MetOp satellites for land and ice regions. Two previously introduced image reconstruction algorithms, the weighted AVErage (AVE) and Scatterometer Image Reconstruction (SIR), are applied to ASCAT data, as well as a conventional gridding method. We select optimum values of the reconstruction parameters for ASCAT. The imaging algorithms are compared and evaluated, as quantified by the spatial resolution, pixel mean and variance, and pixel correlation of the produced images. The effective spatial resolution of the AVE and SIR reconstructed images is on the order of 15 to 20 km, an improvement over the nominal spatial resolution of 25 and 50 km for the spatially averaged swath-oriented ASCAT L1B products.