Oceanic tides from Geosat altimetry

Abstract

Direct tidal analysis of the altimetry from the Geosat Exact Repeat Mission's first year is used to derive estimates of the diurnal and semidiurnal oceanic tides. The geoid is removed by collinear differences at 34.1-day separation, and the orbit error is reduced by subtracting a slowly modulated 1 cycle/revolution term. A sequence of independent analyses at grid areas of 1 ø latitude x 1.5 ø longitude using "orthotide" functions ensures complete definition of the diurnal and semidiurnal species. Global admittance maps for M2 and S2 within the latitudes 58øN and 59øS compare well with ground truth at 66 open-ocean sites. Maps of differences between Geosat and the Naval Surface Weapons Center model show important areas of the order of 10-15 cm. The integral for the global power input from the moon gives 2.5! TW (M2), 0.44 TW (S2), lower than many previous estimates, but in agreement with figures deduced from a recent analysis of satellite orbits. Schwiderski, 1990], but we shall be ,concerned with the simpler situation provided by an orbit whose Earth track repeats itself almost exactly every T days, where in the present case of the ERM, T = 17.0505.With a repeating orbit, (1) may be applied to every point along the Earth track with a time lead r = nT, n being any small integer. Such a scheme is particularly suitable to tidal variations because a harmonic element a cos wt in g(0, it, t) is merely transformed in A•'(0, it, t) to 3069

Eddy activities of the surface layer in the western North Pacific detected by satellite altimeter and radiometer

“…Finally, it should be mentioned that the tidal correction error can cause aliasing at 317 days oscillation in case of M 2 constituent (Cartwright and Ray, 1990;Jacobs et al, 1992;Schlax and Chelton, 1994a, b). We estimate the potential tidal correction error component which has the same period (317 days), wavelength (7.97° in longitude) and westward phase propagation feature as the aliased tide correction error for M 2 (Schlax and Chelton, 1994b) using the least square fit.…”

An investigation of ocean tides derived from along‐track altimetry

“…The first method is the response method of Munk and Cartwright [1966] with the modifications of Groves and Reynolds [1975]. This method, first used by Cartwright and Ray [1990] on Geosat data, is useful for the analysis of altimeter data because it relates the response at different tidal frequencies smoothly over each tidal band. Also, tidal constituents that are not separated sufficiently by the Rayleigh criterion because of limited data can be well represented if the two tidal constituents are in different tidal bands.…”

“…Use of collinear differences could improve the signal to noise ratio and thus improve the quality of the estimates. Cartwright and Ray [1990] did this to Geosat data to amplify the signal. Using a collinear difference of three cycles would help improve the AT estimates, including Kx, which has the most problems from aliasing.…”

Sea surface height variations in the Yellow and East China Seas: 1. Linear response to local wind stress

“…For the case of wind-driven SSH, knowledge of the time of the measurements and the simultaneous forcing function allows the analysis to be made through a statistical approach. Another example is diurnal and semidiurnal tides which are aliased by the altimeter sampling scheme [Schlax and Chelton, 1994;Jacobs et al, 1992;Cartwright and Ray, 1990]. In spite of the undersampling, much work has been done to use altimeter data to estimate tides both globally in deep water [Egbert et al, 1994] and locally in shallow water [Yanagi et al, 1996].…”