Jason-1/Jason-2 metocean comparisons and monitoring

Abstract

The initial tandem phase of the Jason-2 mission is important for the calibration of the entire altimetric system, not just the records of sea surface height. However, as well as allowing a bulk comparison of metocean parameters such as wave height and backscatter strength (used to infer wind speed), it affords a more detailed opportunity to understand the artefacts within each instrument. The wave height comparison shows no bias between the instruments, with the mismatch error of consecutive points independent of one another. The backscatter difference is not a simple offset, but has a trend with weak non-linear variations. The technique for backscatter monitoring using Ku-/C-band differences is validated during the tandem phase, and extended to show ~59-day oscillations throughout the Jason-1 mission. This effect, which is predominantly in the C-band, is related to changing solar exposure, due to the fraction of orbit in eclipse varying as the orbit precesses. Such anomalies were partially present in TOPEX-B data, but are not noticeable for Jason-2. It is recommended that all TOPEX, Jason-1 and Jason-2 data be transformed to a consistent scale, allowing for the bias and trend terms in the offsets between instruments, and correcting for any long-period drifts in individual calibration; this will enable a single wind speed algorithm to be applied to the combined satellite data