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Value of the Jason-1 Geodetic Phase to Study Rapid Oceanic Changes and Importance for Defining a Jason-2 Geodetic Orbit

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  • 1 CLS, Ramonville-Saint-Agne, France
  • 2 LEGOS/CTOH, Toulouse, France
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Abstract

Because of the drifting nature of the ground track of Jason-1 during its geodetic mission (GM), there are 1200 overlap events where the Jason-1 GM and Jason-2 tracks align perfectly (less than their altimeter footprint radius) over thousands of kilometers. These overlap events sample homogeneously all longitudes and all time differences (dt) ranging from a few minutes to 10 days or more.

When dt is almost zero, the difference is characterized by altimeter noise and its modulation by waves. As dt increases, the rapid ocean variability is revealed. The first statistical analysis of the 1200 events yields variance maps, spectra, autocorrelation, and space–time scales that are consistent with past observations (e.g., the 3-day phase of ERS-1). This paper highlights the value of this Jason-1 GM overlap dataset for more sophisticated studies of the rapid ocean variability. There are two major limitations: 1) the noise level of Jason-class altimeters prevents analyzing scales smaller than 80 km and 2) short time differences also absorb a fraction of the derivative of slower signals.

These findings are important if a geodetic mission is considered for Jason-2 in the coming years (e.g., when the satellite starts to exhibit aging problems): a well-chosen geodetic orbit for Jason-2 has the potential to collect a better distribution of overlap events with Jason-3. To that extent, thousands of orbits were screened to find the options that would provide good geodetic and mesoscale sampling and also maximize the overlap sampling of a tentative Jason-2 GM phase.

Supplemental information related to this paper is available at the Journals Online website: http://dx.doi.org/10.1175/JTECH-D-16-0015.s1.

Corresponding author address: Gerald Dibarboure, CLS, 8-10 Rue Hermes, 31520 Ramonville St-Agne, France. E-mail: gerald.dibarboure@cls.fr

Abstract

Because of the drifting nature of the ground track of Jason-1 during its geodetic mission (GM), there are 1200 overlap events where the Jason-1 GM and Jason-2 tracks align perfectly (less than their altimeter footprint radius) over thousands of kilometers. These overlap events sample homogeneously all longitudes and all time differences (dt) ranging from a few minutes to 10 days or more.

When dt is almost zero, the difference is characterized by altimeter noise and its modulation by waves. As dt increases, the rapid ocean variability is revealed. The first statistical analysis of the 1200 events yields variance maps, spectra, autocorrelation, and space–time scales that are consistent with past observations (e.g., the 3-day phase of ERS-1). This paper highlights the value of this Jason-1 GM overlap dataset for more sophisticated studies of the rapid ocean variability. There are two major limitations: 1) the noise level of Jason-class altimeters prevents analyzing scales smaller than 80 km and 2) short time differences also absorb a fraction of the derivative of slower signals.

These findings are important if a geodetic mission is considered for Jason-2 in the coming years (e.g., when the satellite starts to exhibit aging problems): a well-chosen geodetic orbit for Jason-2 has the potential to collect a better distribution of overlap events with Jason-3. To that extent, thousands of orbits were screened to find the options that would provide good geodetic and mesoscale sampling and also maximize the overlap sampling of a tentative Jason-2 GM phase.

Supplemental information related to this paper is available at the Journals Online website: http://dx.doi.org/10.1175/JTECH-D-16-0015.s1.

Corresponding author address: Gerald Dibarboure, CLS, 8-10 Rue Hermes, 31520 Ramonville St-Agne, France. E-mail: gerald.dibarboure@cls.fr
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