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Ocean Surface Topography from Space
CaVaMuMi: Calibration and Validation of altimeter observations and models by means of global multi-mission crossover analysis


Denise Dettmering - (Deutsches Geodätisches Forschungsinstitut der Technischen Universität München (DGFI-TUM))

Co-Principle Investigator(s):
  Marcello Passaro
Christian Schwatke

CaVaMuMi: Calibration and Validation of altimeter observations and models by means of global multi-mission crossover analysis
Geographically correlated mean SSH errors computed for Jason-3 and Jason-2.
The satellite altimeter scenario of the past two decades provides continuous and precise monitoring of the ocean surface with a beneficial spatio-temporal sampling. Since 1992 two or more contemporaneous missions are continuously available. For climate studies a consistent long-term data record is a fundamental requirement. However, combining missions with different sampling capabilities requires a careful pre-processing and calibration of all altimeter systems. The latter can be done by a global cross-calibration of all missions. In addition, a cross-calibration is able to provide information on the quality of single missions and to reveal e.g. instrument drifts or differences in the center-of-origin realization of satellite’s orbits.

The project will conduct inter-calibrations of contemporaneous altimeter systems based on extended crossover analyses on a global scale. For the period from 1992 up to the present, the study performs calibration and validation of all available altimeter missions. The focus is set to Jason-3 and Jason-2. However, all other missions will also be included: past missions (TOPEX, Jason-1), as well as external missions (ERS-1/2, Envisat, Saral, GFO, IceSat, HY-2A, Cryosat-2, Sentinel-3) and future missions (i.e., Jason-CS, as soon as they are available).

The study will use an extended multi-mission crossover analysis approach in order to assess the performance of each mission. The cross-calibration is realized globally by adjusting an extremely large set of single- and dual-satellite sea surface height (SSH) crossover differences performed between all contemporaneous altimeter systems. The total set of crossover differences creates a highly redundant network and enables a robust estimate of radial errors with a dense and rather complete sampling for all altimeter systems analyzed. Iterative variance component estimation is applied to obtain an objective relative weighting between altimeter systems with different performance.

The analysis yields time series of radial errors of each mission and can be used to derive inter-mission biases, to identify potential altimeter drifts, as well as to extract information on the quality of precise orbit determination (POD) and geophysical corrections (e.g., wet tropospheric errors). In addition, a long-term data record will be constructed allowing for precise sea level monitoring on different temporal and spatial scales.

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