A First Assessment of the ASAR Wave Mode Properties and Its Complex Imagette Product Characteristics

Abstract

With its ASAR wave mode, the ENVISAT mission provides a continuity of the ERS-1/2 wave mode, but with more flexible measurement capabilities and an enhanced product variety offered to the user community. Wave vignettes can be taken at 100 km spacing in flight direction either in VV or HH polarization using any of the seven ASAR standard beams. Furthermore, two beams can be used alternatively providing a set of two imaging parameter constellations during one over-flight. Single-look phase-preserving complex imagettes and cross spectra as well as SAR ocean wave spectra are offered as standard products. The complex imagettes WVI product will be radiometrically calibrated using mainly the same methods and calibration sites as for complex image mode products (ESA transponders, rain forest). Through the wave mode, high resolution ASAR data snapshots are globally available for a complete orbit and thus are an appropriate means for around-orbit calibration activities and a routine monitoring of orbit position dependent parameters, e.g. the Doppler frequency. In this paper, we present the first quantitative ASAR wave mode characteristics mainly derived from complex level 1 WVI products. Parameters addressed are image quality and radiometric results, Doppler behavior, inhomogeneity, echo data statistics, etc. Two experiments for a quantitative assessment of the azimuth focusing quality are described. Differences between the ERS and ASAR wave mode and their impact on the processing into complex imagettes are outlined as well. All investigations are performed as part of the ENVISAT / ASAR calibration and validation activities.