P.I.'s Richard Ray and Brian Beckley of the MEaSUREs project "Integrated Multi-Mission Ocean Altimeter Data for Climate Research" announce that a new 20-year plus SSH ESDR (TPJAOS v1.0) based on TOPEX/Poseidon, Jason1&2 merged altimeter records is available from the JPL PO.DAAC.The objective of the new ESDR is to provide a coherent and consistent time series of SSH from multi-mission altimeter data that meets the most stringent accuracy requirements demanded to provide credible mean sea level estimates for climate research. The development is a collaborative effort under the auspices of the NASA MEaSURE’s program from NASA/GSFC, JPL, University of South Florida, University of Colorado, and the NOAA Laboratory for Satellite Altimetry.
The measurement of mean sea-level (MSL) change from satellite altimetry requires extreme stability of the altimeter measurement since the signal being measured is at the level of a few mm/yr. To a great extent, determining sea-level rise and assessing error bounds are geodetic problems. Reference frame accuracy and stability directly affect MSL estimates. This means that the orbit and reference frame within which the altimeter measurements are situated, and the associated altimeter corrections, must be stable and accurate enough to permit a robust MSL estimate. Foremost, orbit quality and consistency are critical to satellite altimeter measurement accuracy. The orbit defines the altimeter reference frame, and orbit error directly affects the altimeter measurement. Orbit error remains a major component in the error budget of all past and present altimeter missions. For example, inconsistencies in the ITRF (International Terrestrial Reference Frame) used to produce the precision orbits at different times cause systematic inconsistencies to appear in the multi-mission time-frame between TOPEX and Jason-1, and can affect the intermission calibration of these data. In an effort to adhere to cross-mission consistency we have generated the full time series of orbits for TOPEX/Poseidon (TP), Jason-1, and Jason-2 (Ocean Surface Topography Mission) based on recent improvements in the satellite force models, reference systems, and modeling strategies.
The figure shows global mean sea level variations from TOPEX, Jason-1, and Jason-2 with respect to 1993-2002 mean, plotted every 10 days (color-coded dots). The solid black line is a 60-day Hanning filter of the altimetric time series. The red line is a linear fit (estimated simultaneously with seasonal terms) of the smoothed variations from 1993-2012 showing a global mean sea level rise estimate of 3.1 mm/yr (after application of 0.3 mm/yr GIA). The inset image shows Jason-2 MSL variations.
Further information and the new ESDR is available from the PO.DAAC at http://podaac.jpl.nasa.gov/Integrated_Multi-Mission_Ocean_AltimeterData .
Reference: Beckley, B.D., N.P. Zelensky, S.A. Holmes, F.G. Lemoine, R.D. Ray, G.T. Mitchum, S. Desai, S.T. Brown. (2010) Assessment of the Jason-2 extension to the TOPEX/Poseidon, Jason-1 sea-surface height time series for global mean sea level monitoring, Marine Geodesy, 33(S1): 447-471, Supplemental Issue on OSTM/Jason-2 calibration/validation, Vol. 1, DOI: 10.1080/01490419.2010.491029.