Abstract's details

Assessment of the last TOPEX SideB reprocessing

Hélène Roinard (CLS, France)


Laure MICHAUD (CLS, France); François BIGNALET-CAZALET (CNES, France); Nicolas PICOT (CNES, France)

Event: 2019 Ocean Surface Topography Science Team Meeting

Session: Regional and Global CAL/VAL for Assembling a Climate Data Record

Presentation type: Type Poster

Contribution: PDF file


The reference Mean Sea Level (MSL) record strongly relies on four missions: TOPEX/Poseidon and its successors Jason-1, Jason-2 and Jason-3 on the same historical orbit. The global trend uncertainty has been estimated close to 0.5 mm/yr (Ablain et al., 2015) over the whole altimetry period (1993-2013). However, this uncertainty rises (0.8 mm/yr) only considering the TOPEX period (1993-2002) (Ablain et al., 2013). In order to better understand TOPEX errors, JPL and CNES have been working together for several years in order to provide a reprocessed TOPEX altimeter dataset for users.

The TOPEX/Poseidon mission was the first precise altimeter mission specially designed for studying the circulation of the world’s oceans. The TOPEX/Poseidon mission furnished altimetry data for 13 years (1992 – 2005). Equipped with a redundant main altimeter (TOPEX) and an experimental altimeter (Poseidon-1, which was operated roughly one cycle in ten), altimeter data were first furnished by the TOPEX-sideA instrument. Nevertheless changes in the sideA Point Target Response (PTR) degraded (from mid-1996 onwards) progressively the altimeter measurements [Hayne and Hancock, 1998]. The main impacts were an increase of Significant Wave Height (SWH), an increase of range rms, and an error on range estimate. Sea State Bias (SSB) was also impacted at it is based on SWH. In February 1999, TOPEX side-A was turned off and TOPEX side-B was turned on.

In order to correct for this PTR drift of TOPEX-A a retracking of the data is necessary. Several retracking releases have been computed over the last years, those analysis have been presented in previous OSTST sessions.  For the last two years, CNES and NASA have worked on the reprocessing of the new TOPEX release of Geophysical Data Records. The latest retracking release include results from MLE4, MLE3 and gaussian methods. In addition, this new version of reprocessed dataset will include the best geophysical corrections available during this period (provided by CNES in 2018).

In this study, we propose to analyze the impact of this new TOPEX retracking over sideB at a first step. Therefore parameters from the retracking (range, SWH) or based on retracked parameters (SSB) are compared with previous data version. The reference parameters are non retracked data used in CMEMS2018 products (which are based on MGDR products concerning altimeter parameters) and updated geophysical and orbit standards. The new solutions are also compared with Jason-1 data. Furthermore mesoscale performances (SSH differences at crossovers) and global mean sea level are also computed and compared to CMEMS2018 standards.

Poster show times:

Room Start Date End Date
The Gallery Tue, Oct 22 2019,16:15 Tue, Oct 22 2019,18:00
The Gallery Thu, Oct 24 2019,14:00 Thu, Oct 24 2019,15:45
Hélène Roinard