Evolution of the TOPEX products from MGDR-B to GDR-F over 1992-2002
Event: 2020 Ocean Surface Topography Science Team Meeting (virtual)
Session: Regional and Global CAL/VAL for Assembling a Climate Data Record
Presentation type: Type Forum
In this presentation, we show results from the calibration and validation of the reprocessed TOPEX products. The reprocessed TOPEX products result from ground retracking of the altimeter waveforms [Desjonquères et al., 2019], updated sea state bias model [Putnam et al., 2020], ITRF14-based precise orbit determination solutions (courtesy of GSFC and CNES), and GDR-F standards for geophysical models from CNES. In particular, we isolate the impact of updates in each of the components of the sea level anomaly (SLA) curve since the latest release (MGDR-B) until the most recent standard (GDR-F). The reprocessed altimeter ranges and their calibrations differ with respect to MGDR-B by about 1 cm over TOPEX side-A. The effect of the waveform retracking is also seen in the differences of ionosphere and sea state bias corrections. Furthermore, the recently reprocessed radiometer wet path delay differs from the MGDR-B version by a drift of 0.9 mm/yr over side-A. We also examine SLA crossover differences between GDR-F and MGDR-B over TOPEX side-A and side-B and highlight the three largest contributors. Most notably, the implementation of the GDR-F geophysical models reduces crossover variance by nearly 440 mm^2 as compared to MGDR-B geophysical models. The application of new orbits from GSFC and CNES decrease the variance by 275 mm^2 and provide the most visible reduction in geographically-correlated errors. Lastly, the reprocessed ranges attenuate the hemispheric bias that had previously plagued the MGDR-B products.