Bruce Haines (Caltech/JPL, USA); Rashmi Shah (Caltech/JPL, USA)

We present results from a global comparison of the Jason-2 (J2) and Jason-3 (J3) measurement systems during their formation-flying phase. Our analysis leverages the identical oceanographic and environmental conditions that are effectively being observed by the two systems during this phase, since they are flying along the same ground track but only 82 seconds apart. We characterize both geographically correlated and systematic differences between the two measurement systems, with the goal of facilitating a seamless transition of the reference altimeter mission from J2 to J3.

Our study emphasizes the evaluation of orbit solutions for each mission and associated geographically-correlated errors, relative Ku- and C-band altimeter range biases, potential relative altimeter tracker bias, and relative calibration bias in the radiometer measurements of wet troposphere delay. We also inter-compare overall data noise from each measurement system using the typical metrics of sea surface height (SSH) differences, as well as SSH cross-over differences.

Early results from IGDR-D data reveal a J3-J2 inter-satellite SSH bias of approximately -3 cm (J3 measuring lower than J2). This bias is primarily due to a relative Ku-band range bias of +2.1 cm (J3 measuring longer than J2), and Ku-band ionosphere correction bias of +0.5 cm. The latter arises from the confluence of the relative Ku-band range bias and an observed relative C-band range bias of -0.9 cm. The remaining contributor to the observed relative SSH bias is a relative drift in the radiometer wet troposphere correction that is expected to be mitigated with an improved calibration to the J3 radiometer. We also observe a systematic +/- 2 cm east/west pattern in the J3-J2 IGDR-D SSH differences that is eliminated when using orbit solutions based upon GPS tracking data.