Shallow water tidal determination from altimetry - the M4 constituent

With the long duration of accurate satellite altimetric measurements from the TOPEX/POSEIDON and the ERS satellites (ERS-1 and ERS-2) it is interesting to investigate if satellite altimetry can provide more  accurate tidal models on continental shelves. The call for increasing accuracy in shelf regions, calls for inclusion of more than just semi-diurnal and diurnal constituents in future global ocean tide models. This is because a considerable part of the tidal variability on the shelves is caused by sha1low water constituents. One example is the M₄ constituent, which exceeds 50 centimetres at several locations on the northwest European shelf. So far satellite altimetry has not been considered for resolving these constituents, due to its accuracy and coarse ground-track resolution. Reliable empirical estimates of the major shallow water tide constituent called M₄, can be obtained from TOPEX/POSEIDON, by combining along-track and crossover observations. Estimates are presented in this study and compared with tide gauges and existing hydrodynamic models.