Sea Ice Thickness Detection Using Bei Dou-r Signal And Analysis Of Sea Surface Roughness

BeiDou Satellite Navigation System(BeiDou System)is a self-built independent satellite navigation system in China.It is an important part of the Global Navigation Satellite System(GNSS)and the most important space infrastructure in China.When the BeiDou satellite signal propagates to the earth's surface,the navigation signal interacts with the Earth's surface to produce random scattering that carries the physical information of the reflective surface.According to the signal-to-noise ratio,pseudo-random code delay,carrier phase and Doppler frequency of the BeiDou satellite reflected signal,the physical parameters of the Earth's surface can be inverted.This technique is called BeiDou reflection(BeiDou-R)signal remote sensing technology.Sea ice is an important part of the Earth's cryosphere,sea ice research has received widespread attention as the global warming effect has intensified.Many methods are used for sea ice detection research,including GNSS-R remote sensing technology.The hotspots of GNSS-R sea ice detection technology are mainly concentrated in the two major directions of sea ice thickness detection and sea ice density detection.The method of combining BeiDou-R sea surface altimetry technology with sea ice static balance model to invert sea ice thickness has not seen similar research at home and abroad.The error source of shore-based BeiDou-R sea surface height measurement mainly comes from sea surface roughness.Few scholars at home and abroad have qualitatively analyzed the influence of surface roughness of sea ice on sea surface height measurement error.In this paper,the sea ice thickness inversion model is established.The BeiDou-R signal is used to carry out the sea surface carrier phase altimetry.The sea surface roughness error correction model is established.The shore-based experiment is carried out to verify the correctness of the inversion sea ice thickness.The accuracy of the error correction model is analyzed.The main research contents of this paper are as follows:1.The principle of spread spectrum communication technology of BeiDou satellite navigation system is introduced.The process of capturing and tracking satellite signals is briefly summarized in combination with BeiDou satellite signal system.2.The sea surface height geometric model under the shore-based experimental scene is introduced.According to the GNSS-R sea surface altimetry technology and the sea ice static balance model,the sea ice thickness inversion model based on the BeiDou-R technology is established.Comparing the current four methods of sea surface height measurement of BeiDou-R,including code height measurement,carrier phase height measurement,interference signal height measurement and signal-noise ratio(SNR)height measurement,the carrier phase height measurement is emphasized according to the needs of sea ice thickness inversion research.The phase altimetry technical principle and the corresponding data processing flow are introduced.3.The influence of sea surface roughness error on the BeiDou-R sea surface altimetry is analyzed.The characteristics of electromagnetic wave reflection are introduced.The mathematical analysis of the surface roughness of sea ice is analyzed.Combined with the analysis of the phase winding phenomenon produced by the BeiDouR signal on the reflective surface,the research focus of this paper is put forward:The carrier phase altimetry technique generates the phenomenon of false winding points when the residual interference phase(phase difference)is unwrapped in the data processing process.The disentanglement strategy of the residual interference phase of the winding is proposed according to the distribution characteristics of the false winding points under different conditions.The sea surface roughness error correction model is established,and the results of the carrier phase altimetry are corrected to obtain the correct sea ice thickness inversion results.4.The BeiDou-R data collected from the Bohai Bay experiment was used to invert the sea ice thickness,and the roughness correction model was used to correct the sea surface altimetry results.After analyzing the experimental results,it is found that the accuracy of the sea surface altimetry error RMSE value is improved by more than 50% in a short time(one day),and the corrected sea surface height result is between 3.105 m and 3.135 m,and the average sea surface height is 3.11 m,and the calculated sea ice thickness is 11.12 cm,which is consistent with the thickness of the collected sea ice samples.In the long time(two weeks),the accuracy of the sea surface altimetry error RMSE value is improved by 70%.Above,the corrected sea surface height inversion result is 2.9m~ 3.15 m,the average sea level height inversion result is 3.10 m,the calculated sea ice thickness data is 4cm~22cm,and the calculated average sea ice thickness is 14.62 cm.,consistent with the thickness of the collected sea ice samples.