北斗GEO卫星微动条件下的GNSS-R土壤湿度反演
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摘要
全球定位系统GPS发射的L波段导航信号源已被用于估测地球表面的土壤湿度,但由于卫星具有一定的重返周期,所以对固定区域土壤湿度反演的性能受到不断变化的星下点轨迹的限制。北斗GEO(geostationary earth orbit)卫星是地球静止轨道卫星,同时又存在着周期性的微动,利用它的反射信号来反演土壤湿度受到其微动特性的影响。针对这个问题,作者研究了利用GEO卫星反射信号功率进行固定区域内土壤湿度反演的可行性。首先分析了GEO卫星的微动特征和反射区域的变化;然后采用包络提取和三次多项式插值的方法来恢复SNR的趋势变化规律,以消除因为GEO卫星轻微运动带来的周期性波动和噪声,并且根据现场收集的部分实验数据确定的校准参数对反射系数进行校正;最后,使用测试数据进行土壤湿度反演,得到每半小时固定区域的连续土壤湿度反演值。结果表明,土壤湿度反演值与原位土壤湿度值的变化趋势基本一致,反演的平均绝对误差小于4.63%。可见,BDS GEO卫星信号可以作为GNSS反射计的重要数据来源。
The L-band navigation signal source emitted by the global positioning system( GPS) has been used to retrieve the soil moisture in the surface of the Earth,but their retrieval performance is limited by their continuously varying footprints due to the repeat cycle of satellites. The Bei Dou GEO satellites are geostationary orbit satellites but with slight periodic fluctuations,so the soil moisture retrieval using its reflected signal is affected by its slight movement characteristics. In response to this problem,the feasibility of using Bei Dou system( BDS) geostationary earth orbit( GEO) satellites reflected signal power was studied to perform soil moisture retrieval in a fixed area. The micro-motion characteristics of the GEO satellites reflection area was first analyzed and the changed of;Then the trend of SNR by envelope extraction and cubic polynomial interpolation to eliminate the periodic fluctuations was restored and noise caused by the slight movement of GEO,and the calibrated parameter values were also determined by employing part of the experimental dataset collected in the field; Finally the continuous soil moisture was retrievedin the fixed area per half hour using the test data. The results show that the estimated soil moisture changes are largely consistent with the in situ soil moisture data; And the mean absolute error of the estimation is less than 4. 63%. It is concluded that the BDS GEO satellites represent an important source of data for GNSS reflectometry.
The L-band navigation signal source emitted by the global positioning system( GPS) has been used to retrieve the soil moisture in the surface of the Earth,but their retrieval performance is limited by their continuously varying footprints due to the repeat cycle of satellites. The Bei Dou GEO satellites are geostationary orbit satellites but with slight periodic fluctuations,so the soil moisture retrieval using its reflected signal is affected by its slight movement characteristics. In response to this problem,the feasibility of using Bei Dou system( BDS) geostationary earth orbit( GEO) satellites reflected signal power was studied to perform soil moisture retrieval in a fixed area. The micro-motion characteristics of the GEO satellites reflection area was first analyzed and the changed of;Then the trend of SNR by envelope extraction and cubic polynomial interpolation to eliminate the periodic fluctuations was restored and noise caused by the slight movement of GEO,and the calibrated parameter values were also determined by employing part of the experimental dataset collected in the field; Finally the continuous soil moisture was retrievedin the fixed area per half hour using the test data. The results show that the estimated soil moisture changes are largely consistent with the in situ soil moisture data; And the mean absolute error of the estimation is less than 4. 63%. It is concluded that the BDS GEO satellites represent an important source of data for GNSS reflectometry.
引文
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2 Vey S,Güntner A,Wickert J,et al.Long-term soil moisture dynamics derived from GNSS interferometric reflectometry:A case study for Sutherland,South Africa[J].GPS Solutions,2016,20(4):641-654
3 Yan S,Li Z,Yu K,et al.GPS-R L1 interference signal processing for soil moisture estimation:An experimental study[J].EURASIP Journal on Advances in Signal Processing,2014(1):107
4 Chew C,Small E E,Larson K M.An algorithm for soil moisture estimation using GPS-interferometric reflectometry for bare and vegetated soil[J].GPS Solutions,2016,20(3):525-537
5 严颂华,龚健雅,张训械,等.GNSS-R测量地表土壤湿度的地基实验[J].地球物理学报,2011,54(11):2735-2744Yan Songhua,Gong Jianya,Zhang Xunxie,et al.Ground based GNSS-R observations for soil moisture[J].Chinese Journal of Geophysics[J],2011,54(11):2735-2744
6 Zavorotny V,Masters D,Gasiewski A,et al.Seasonal polarimetric measurements of soil moisture using tower-based GPS bistatic radar[C]//The proceeding of Geoscience and Remote Sensing Symposium,2003.New York:IEEE,2003
7 Katzberg S J,Torres O,Grant M S,et al.Utilizing calibrated GPS reflected signals to estimate soil reflectivity and dielectric constant:Results from SMEX02[J].Remote Sensing of Environment,2006,100(1):17-28
8 Chew C,Shah R,Zuffada C,et al.Demonstrating soil moisture remote sensing with observations from the UK Tech Demo Sat-1 satellite mission[J].Geophysical Research Letters,2016,43(7):3317-3324
9 Clarizia M P,Ruf C S.Wind speed retrieval algorithm for the cyclone global navigation satellite system(CYGNSS)mission[J].IEEE Transactions on Geoscience and Remote Sensing,2016,54(8):4419-4432
10 Kong J A,Tsang L,Ding K H.Scattering of electromagnetic waves,theories and applications[M].New York:Wiley,2000
11 Zavorotny V U,Voronovich A G.Scattering of GPS signals from the ocean with wind remote sensing application[J].IEEE Transactions on Geoscience and Remote Sensing,2000,38(2):951-964
12 Dobson M C,Ulaby F T,Hallikainen M T,et al.Microwave dielectric behavior of wet soil-Part II:Dielectric mixing models[J].IEEE Transactions on Geoscience and Remote Sensing,1985(1):35-46
13 Larson K M,Nievinski F G.GPS snow sensing:results from the Earth Scope Plate Boundary Observatory[J].GPS Solutions,2013,17(1):41-52
14 Scholkmann F,Boss J,Wolf M.An efficient algorithm for automatic peak detection in noisy periodic and quasi-periodic signals[J].Algorithms,2012,5(4):588-603