Technology With Beidou Reflected Signal

As a novel technology of altimetry,Global Navigation Satellite System-reflected(GNSS-R)signals which were proposed by Martín-Neira in 1993,has been received more and more researchers from many countries because of their lower manufacturing cost,multi-free signal,all-weather and wide coverage and et al.At present,the main application of GNSS-R technology includes ocean altimetry,snow and sea ice detection,wind speed inversion,oil slicks detection and et al.Global sea level rise and tsunami disaster monitoring,ocean circulation determination,ocean tidal model establishment and mesoscale climate model research are inseparable from ocean altimetry.There are three main methods of GNSS-R altimetry,namely code altimetry,phase altimetry and signal to noise ratio(SNR)altimetry.Among them,code altimetry is the basic method of GNSS-R measurement,which has the advantages of high stability,less processing data and inversion speed,but its inversion is low.Both the inversion models of phase altimetry and signal-to-noise ratio(SNR)altimetry are more complicated than that of code altimetry,but their inversions are more accurate.However,most of the studies on these models are based on GPS signals or Galileo signals.BeiDou Navigation Satellite System(BDS),developed by China independently,is a hybrid constellation,which includes three kinds of satellites,Medium Earth Orbit(MEO)satellites,Inclined Geo synchronous Orbit(IGSO)satellites and Geostationary Earth Orbit(GEO)satellites,and is apparently different from other navigation systems,such as GPS's constellation.BDS has been in full service to provide open services to the most part of the Asia-Pacific region,since December 27,2012.With the development of BDS,BDS will provide a stable signal source for the GNSS-R altimetry field and further enhance the temporal and spatial resolution of GNSS-R ocean altimetry.Meanwhile,BDS can provide a new research direction and enriches the diversity of altimetry experiment situations because of its unique hybrid constellation.Since there were less reaches about ocean altimetry using BDS's reflection signals at last,this paper will focus on analysis of the feasibilities of phase altimetry and SNR altimetry using BDS's reflection signals.Over the past three years,our team has successfully took many experiments about code or phase altimetry using GPS reflection signals and some experiments about code altimetry using BDS's reflection signals,and try our best to improve the process speed of our software receiver.Based on these successful experimental experiences and solid knowledge,we took several experiments about phase altimetry and SNR altimetry using BDS's reflection signals.In this paper,we introduced two representative ocean altimetry experiments which base on phase altimetry and SNR altimetry in Dayangshan ocean area.In the phase altimetry experiment,we combined with the characteristic of BDS's hybrid constellation to analyze the IGSO / MEO and GEO phase altimetry models,respectively,and successfully inversed sea surface height.In SNR altimetry experiment,we also successfully inversed sea surface height by using SNR altimetry model.The main contents of this paper are as follows:1.The structures of BDS's hybrid constellation and signals were briefly introduced.Three main altimetry models,which include code altimetry,phase altimetry and SNR altimetry,were introduced,respectively.Some error models of ocean altimetry,which include the ocean roughness,the ionosphere error,the tropospheric error and the curvature of the earth,were introduced,respectively,and we analyzed the influence and the scope of application of these error models for altimetry methods in some level.2.In the Dayangshan ocean area,we took an experiment of phase altimetry using BDS's IGSO or GEO satellite reflected signals by using two antennas,which include a D-RHCP(left-handed circularly polarized direct signal)antenna and an R-LHCP(left-handed circularly polarized reflection signal)antenna,and a GNSS-R software receiver to receive and process the satellite signals.In the experiment,the sea surface height was retrieved by the data processing of IGSO or GEO phase altimetry models.Comparing with the actual tide data,all the altimetry results based on the IGSO / MEO phase altimetry model generally reach the sub-meter accuracy,and the altimetry results based on the GEO phase altimetry model reach centimeter accuracy in some period.3.In the Dayangshan ocean area,we carried out an experiment of SNR altimetry using BDS's IGSO or MEO satellite reflected signals by using a single measurement antenna and a receiver which were used to receive and process the satellite signals,respectively.According to the data processing of the SNR altimetry model,we used BDS's reflected on BDS's three frequencies(B1,B2,B3)to inversed the sea surface height in about a month.Comparison with the actual tide data,the correlation coefficients of altimetry results on the three frequencies signals were higher than 96%,and their inversion accuracies were generally reach sub-meter.Meanwhile,some influence factors of altimetry,such as the complex environment(mountainous,multi-vegetation,etc.)and the extreme weather(storm,wind),were analyzed in some level.