Research On Shallow Water Depth Inversion By X-band Radar

The depth information of the shallow water near the shore is closely related to human production activities.Timely and accurate water depth information not only provides basic data for offshore platform production activities,but also ensures the application of offshore equipment and facilitates the passage of ships in narrow channels.Therefore,obtaining water depth data has become one of the main research directions of researchers.Traditional water depth measurement methods,such as shipboard echo equipment and bathymeter,have the disadvantages of high cost and low efficiency.In view of these shortcomings,remote sensing measurement technology has been greatly developed,such as spaceborne radar,shore-based high-frequency ground wave radar,etc.Compared with the other remote sensing equipment,X-band radar has the characteristics of low cost,all-weather and wide range.The complex seabed topography and surface currents in the shallow coastal waters of the coast affect the propagation of waves.Based on this propagation,the depth and surface currents can be retrieved from the abundant wave information.Although researchers at home and abroad have made some progress in the study of this subject,the error of the research results is large,and the inversion effect in the coastal waters is not ideal.In recent years,there is no new breakthrough in water depth inversion.In the view of above' existing problems,this paper proposes two new algorithms to offset the effect of surface flow on water depth,by analyzing the dispersion formula based on the least square method.The first algorithm is to eliminate the Doppler frequency shift term,but this algorithm requires the vectors of sea surface flow field and the wave number,which are perpendicular to each other.This situation is not common in the actual sea area,so it is limited to certain restrictions.On this basis,the second algorithm has been proposed,which slices the three-dimensional image spectrum,finds the best surface flow vector in each direction and performs cosine function fitting to obtain the surface flow vector of the entire inversion sea area,and finally inverts to get accurate water depth.In the shallow seas with a water depth of less than 20m,the prediction accuracy of tide table is greater than that of the actual measurement by contact measurement equipment,and in complex sea environments,it is impossible to use the contact measurement equipment to obtain water depth data.In this situation,the water depth inversion algorithm cannot be obtained by data comparison,so a new comparison method is proposed to verify the accuracy of the algorithm,which makes a difference between the water depth data after inversion and that of the electronic chart,then compares the obtained tide height data and the forecast tide height data of the sea area to be measured.This method can greatly reduce the comparison cost,and the comparison result is more accurate.By analyzing the comparison results of water depth data and electronic chart,it is illustrated that the inversion algorithm is reasonable and feasible,and the accuracy can reach decimeter level,within the allowable error range.In addition,there is always a relatively fixed error between the two sets of data.The possible cause of the inference is the gradual change of the seabed has an influence on the inversion algorithm.