Sea Surface Altimetry Using GNSS Signal And Analysis Of Deviation

The Global Navigation Satellite System(GNSS)is a satellite system that using GPS,Beidou,GLONASS,and other navigation satellite systems which can provide the continuous and stable signal to positioning and navigation around the world.When the continuous GNSS signal reflects through the earth's surface,it will have some effect on the earth's surface.Random scattering from a roughness surface could cause a mixture of reflected components.The signal amplitude,code phase,carrier phase and other information have being changed.Therefore,the signal delay and Doppler shift of the GNSS reflection signal to invert the various physical parameters of the Earth's surface.Which is GNSS reflection signal technology.GNSS technology mainly relies on the free satellite signals of global navigation satellites.It is a passive remote sensing technology.It has the advantages of abundant signal sources,low cost,wide coverage,and the ability to achieve all-weather monitoring without being affected by the weather.In recent years,it has become a research hotspot in the field of aerospace,remote sensing,marine science and other fields at home and abroad.At present,the GNSS technology has been widely used in many fields such as sea surface height measurement,sea surface wind field inversion,sea surface effective wave height measurement,sea ice thickness and sea ice concentration monitoring,and soil moisture detection.Sea surface level is one of the important physical parameters of the ocean and it has an important impact on the lives and production along the coast.Sea surface altimetry is one of the important applications of GNSS technology.Sea surface altimetry has an important significance to tsunami and storm surge warning.At present,there are two main methods for GNSS sea surface altimetry: pseudo code altimetry and phase altimetry.Pseudo-code altimetry uses the C/A code of satellite signals.Its model is simple,easy to implement and widely used.But limited by the chip length of the C/A code(a chip length is approximately 291.3 m),the accuracy of the code altimetry is low.The accuracy of the phase altimetry is high,but it requires the phase of the reflected signal to be continuous,which is difficult to achieve in the case of a rough reflection surface.The error sources affecting the sea surface altimetry mainly include ionosphere delay,atmospheric delay,receiving antenna error and sea surface roughness.At present,no scholars have qualitatively analysis effect of the surface roughness on the altimetry.The emphasis of this paper is to propose a method to characterize the surface roughness by phase difference of reflection signal,according to this method,a roughness error correction model is established.The feasibility of the method and the performance of the model are verified by experiments,we can increase the accuracy of the code measurement by more than 10% using the error correction model we established.The main research contents of this paper are as follows:1.This paper introduces the principle of GNSS spread spectrum communication technology in detail,the acquisition and tracking of satellite signals are briefly introduced in combination with the module structure of software receiver.2.To assume that the earth's surface for horizontal and considering the earth curvature effect on the altimetry accuracy of two kinds of altimetry geometric model,and analyses the two models of usage scenarios,and mainly introduced two methods of GNSS altimetry: code altimetry and phase altimetry.3.Analysis the common error sources in GNSS sea surface height altimetry,and emphatically expounds the importance of reflective surface roughness in sea surface height altimetry,the electromagnetic wave propagation,polarization,reflection is introduced in detail.The statistical description of surface roughness is analyzed emphatically.Mainly studies how to utilize the wave spectrum,significant wave height ICF are described in the surface roughness measuring method,based on this,advances the core part of this article:We put forward a new method for representing the surface roughness of reflector and the roughness error correction model is established based on this method.4.Conducted two experiments,the experiment on the DiShui Lake in Shanghai,and the Zhujiajian sea surface experiment in Zhoushan City.After analysis of the experimental results,the altimetry accuracy of Beidou 10 satellite has increased 0.02 m after using the roughness correction model,which was increased by 14%.For the GPS7 satellite,The RMS value of altimetry error was decreased from 0.45 m to 0.33 m,the altimetry accuracy was increased by about 26% after using the roughness correction model.In the IGSO and MEO satellite altimetry,the improvement of the altimetry accuracy was more than 10%.The proposed roughness error correction model is feasible.Then,we corrected the sea surface altimetry data.When the original altimetry accuracy was not high,we decreased the error RMS of inversion height from 3.66 m to 2.3 m,improved the accuracy by about 37%.The DMT was decreased from 2.5 m to 1.9 m,the accuracy was increased by 24%.