The Underwater Topographic Survey Supported By GNSS High Precision Dynamic Altimetry

In small and medium water depth measurement project, the measurement results need a series of correction and calculation, and water level and dynamic draft correction are two aspects that cannot be neglected. The correction of water level is generally used to correct some region according to the tidal station data with mathematical model calculation or used single tidal station. The empirical formula is used to realize the correction of dynamic draft in using the dynamic draft of the ship to replace the one at the replacement. They has a positive effect on the hydrographic and ship navigation safety. But they still have the following problems: the water level and the dynamic draft are not synchronized with the sounding points; the latter has the advantages of low precision, complicated operation and high cost, and the former has similar problems in complex terrain, far away from the land, high velocity and big drop.This paper proposes a correction method for dynamic draft and water level based on the GNSS ellipsoidal height. First, the GNSS ellipsoidal height is converted to a transducer-center, and the changes in the ellipsoidal height of the transducer-center, which are caused by waves, are then filtered out by a wavelet analysis. The height of the water level is obtained after Fourier fitting and the translation calculation. Finally, the dynamic draft can be obtained from the ellipsoidal height following the separation of the water level influence and the waves.Then, the water level of ellipsoidal height and the one at the tide gauge are fitted by the least square method, and the water level of the measured area is obtained from a datum (National Vertical Datum 1985, mean level of the sea or depth datum). The method for the bathymetric survey is basically similar to the traditional survey. The former needs only a few drifting measurements in a short time. The results of the experiment show that the precision of the dynamic draft of the transducer-center and water level can reach the centimeter level by using this method to meet the requirements of the IHO specifications, and the dynamic draft and water level correspond to the bathymetric values. This method significantly extends the control distance of the water level in a single tide station, and realizes the transfer of the tidal datum level in the small area.