Absolute Calibration in Bass Strait, Australia: TOPEX, Jason-1 and OSTM/Jason-2

Updated absolute bias estimates are presented from the Bass Strait calibration site (Australia) for the TOPEX/Poseidon (T/P), Jason-1 and the Ocean Surface Topography Mission (OSTM/Jason-2) altimeter missions. Results from the TOPEX side A and side B data show biases insignificantly different from zero when assessed against our error budget (-15 \textpm 20 mm, and -6 \textpm 18 mm, respectively). Jason-1 shows a considerably higher absolute bias of +93 \textpm 15 mm, indicating that the observed sea surface is higher (or the range shorter), than truth. For OSTM/Jason-2, the absolute bias is further increased to +172 \textpm 18 mm (determined from T/GDR data, cycles 001\textendash079). Enhancements made to the Jason-1 and OSTM/Jason-2 microwave radiometer derived products for correcting path delays induced by the wet troposphere are shown to benefit the bias estimate at the Bass Strait site through the reduction of land contamination. We note small shifts to bias estimates when using the enhanced products, changing the biases by +11 and +3 mm for Jason-1 and OSTM/Jason-2, respectively. The significant, and as yet poorly understood, absolute biases observed for both Jason series altimeters reinforces the continued need for further investigation of the measurement systems and ongoing monitoring via in situ calibration sites.