Constraints on the Repetitivity of the Orbit of an Altimetric Satellite: Estimation of the Cross-Track Slope

Abstract The effect of a poorly constrained repetitivity of the orbit of an altimetric satellite is analyzed. From existing data, 35% of the marine geoid slopes are found to excess 1.5 cm km−1. This may be due either to short-distance-scale features (seamounts, fracture, and subduction zones) or to the large-scale geoid (in the Indian and North Atlantic oceans). A geoid cross-track slope (CTS) can be calculated locally from the tracks inside the repetitivity band. Assuming that the various measurement errors and ocean variability signals are decorrelated, it has a precision of 0.2–2 cm km−1, depending on the orbit cycle (which constrains the number of repeal passes per year) and on the width of the band (from 1 to 10 km in thew calculations). This can be used as a correction but increases the noise level by at least 50%. Alternatively, the CTS can be derived from a mean sea surface. This adequately corrects for the large-wale signals but, with present mean sea surfaces, it is inadequate for the short-dist...