GNSS-R陆面遥感散射特性研究
摘要
导航卫星的反射信号携带地表信息可以被专门的接收机接收利用,形成一种新兴的遥感手段GNSS-R遥感。在海洋领域,GNSS-R可以用来反演海面风场、有效波高、潮位和海水盐度等信息。在陆面领域,低成本、小功耗和高时空分辨率等诸多优点,使其可以成为土壤水分、植被等地物参数监测反演的有效手段。本文旨在对GNSS-R陆面遥感的散射特性进行研究,以期实现GNSS-R的实用化陆面参数遥感研究。
导航卫星群作为发射源,专门的GNSS-R接收机可以接收直射信号经地表反射的信号,这样形成一种收发分置的双基地雷达(bistatic radar)工作模式。因此对于GNSS-R散射特性研究需要采用双站散射模型。根据现有双站散射模型的文献：针对裸土,本文将原有的PO、GO和SPM模型以及AIEM模型修改为双站散射形式：根据现有Bi-mimics文献,在森林后向散射Mimics模型的基础上,加入散射的天顶角和方位角,在代码中实现了双站散射模型Bi-mimics模型。修改时涉及到相位矩阵和消光矩阵等的变化,同时地表反射率矩阵和散射矩阵也要修改为相应的双站形式。与海面相比,陆面粗糙度较小,一般认为接收机接收到的能量主要是来自于第一菲尼尔区的镜像散射能量,其余漫散射的能量较微弱,可以忽略不计。因此需要将上述双站散射模型中的角度设置为镜像角度,得到镜像散射模型Spec-mimcis模型,以此为研究工具,对农作物和森林的生物量特性进行分析,理论研究表明GNSS-R可以成为植被生物量监测的有效工具。
为克服电离层的影响,导航卫星发射的直射信号为右旋圆极化信号,该信号经地表反射后,极性会发生改变,而反射信号本身相对较弱,因此需要相应极性天线对信号进行接收,以降低极化损耗,充分利用反射信号。本文针对陆面遥感反射信号的极化特性进行研究,将裸土散射模型和上述Bi-mimics模型、Spec-mimics模型中的Stokes矢量进行修改,使其可以计算任意极化的散射系数。以Mimics手册中的Aspen为模型输入参数,模拟分析了RHCP发射,线极化(H、V极化)和圆极化(RHCP、LHCP)接收时散射系数随入射角的变化。理论研究表明RHCP极化信号经地表反射后,LHCP极性的反射信号无论是裸土还是植被都是只有在大的入射角(小仰角)时存在镜像散射值。但是对于RHCP,H、V极性的反射信号,在各个角度都有响应,RV极化时候,动态响应最大。当接收机可以追踪一颗或多颗卫星在不同仰角下的能量时(如SMIGOL)采用动态响应大的V极化天线较为有效；当接收机只能接收最高仰角的信号(如SMEX02中的DMR)时,LHCP极化的天线只会在某些角度范围内存在响应。实际的GNSS-R接收机可以在同一时刻接收到多颗卫星在不同仰角下的能量,适宜的角度(天顶角和方位角)以及极化组合来进行地物参数的监测和反演有待进一步研究,而地表实测数据对理论的验证也需同步展开。
因此,基础理论推动下的实用化GNSS-R陆面遥感监测网络的形成是未来工作研究的重心和难点。
GNSS-R is a new promising remote sensing technique, in which the special designed receivers collect the reflected signals of GNSS. As for ocean scenarios, GNSS-R can be used to retrieve ocean surface wind, sea wind height, tide, sea salinity, among others. For land scenarios, low cost, small power, high spatial and time resolutions are the advantages, so this technique is considered to be a promising tool to retrieve land surface geophysical parameters, such as soil moisture and vegetation height or biomass. GNSS-R land surface scattering characteristics are studied in this dissertation in order to make GNSS-R land surface parameters retrievals practical.
Constellation of GNSS is transmitters, the special designed GNSS-R receivers collect the land or ocean surface reflected signals. Therefore, it is a kind of bistatic radar, for which bistatic scattering models are needed. For bare surface, the original used scattering model PO, GO and SPM models are modified to bistatic scattering. Bi-mimics model is developed based on the original backscattering Mimics. By adding scattering zenith angles and azimuth angles in Mimics, the corresponding angles in phase matrixes and extinction matrixes are needed to be modified. Meanwhile the angles in ground reflectivtity matrix and scattering matrix are modified. Compared to ocean surface, roughness scales of land surface are small, so it is commonly recognized that the reflected signal is largely coming from the specular reflection point of first Fresnel zone. The diffuse scattering power is too weak to be received. The angles in the above bisatic scattering models are set to specular ones to do research. As for vegetation study, Spec-mimics is developed and utilized as a study tool to analyze vegetation (crop and forest) biomass. Theoretical studies indicate that GNSS-R has the potential to monitor biomass.
In order to reduce ionospheric effects, the GNSS transmitted signals are right handed circular polarization, whose polarization characteristics are changed after reflecting from the earth surface. Therefore the corresponding polarized attenna of receiver should be carefully considered to decrease signals loss. This dissertation focuses on the land surface reflected signals polarization charateristics study. Modified stokes vectors are modified in bare surface scattering model and the above Bi-mimics model, Spec-mimics model to calculate bistatic or specular scattering cross sections for any combination of transmitter and receiver polarizations. Aspen in Mimics handbook is used as model input, relationship between scattering coefficients of RHCP transmitted, linear(H,V) and circular(RHCP, LHCP) polarized received versus scattering angles are analyzed. Theoretical study indicates that as for RHCP transmitted signals, the LHCP reflected signals (bare surface or vegetation) exist only in larger incident angles (smaller elevation angles). But the reflected signals exist in any incident angles as for linear polarized (H, V) reflectivity, where V polarization has larger dynamic range. In conclusion, when the receiver can track signals at any elevation angles for one or several satellites(such as SMIGOL), the V polarized receiver antenna is favored; LHCP attenna respond only at some angles when only the highest elevation angle can be tracked(such as DMR used in SMEX02airborne GPS-R experiment).
However, further in-situ experiments are needed to calibrate the above theoretical results. And practical constructions of GNSS-R land surface retrieval and monitoring network are the focuses and difficulties of future study.
导航卫星群作为发射源,专门的GNSS-R接收机可以接收直射信号经地表反射的信号,这样形成一种收发分置的双基地雷达(bistatic radar)工作模式。因此对于GNSS-R散射特性研究需要采用双站散射模型。根据现有双站散射模型的文献：针对裸土,本文将原有的PO、GO和SPM模型以及AIEM模型修改为双站散射形式：根据现有Bi-mimics文献,在森林后向散射Mimics模型的基础上,加入散射的天顶角和方位角,在代码中实现了双站散射模型Bi-mimics模型。修改时涉及到相位矩阵和消光矩阵等的变化,同时地表反射率矩阵和散射矩阵也要修改为相应的双站形式。与海面相比,陆面粗糙度较小,一般认为接收机接收到的能量主要是来自于第一菲尼尔区的镜像散射能量,其余漫散射的能量较微弱,可以忽略不计。因此需要将上述双站散射模型中的角度设置为镜像角度,得到镜像散射模型Spec-mimcis模型,以此为研究工具,对农作物和森林的生物量特性进行分析,理论研究表明GNSS-R可以成为植被生物量监测的有效工具。
为克服电离层的影响,导航卫星发射的直射信号为右旋圆极化信号,该信号经地表反射后,极性会发生改变,而反射信号本身相对较弱,因此需要相应极性天线对信号进行接收,以降低极化损耗,充分利用反射信号。本文针对陆面遥感反射信号的极化特性进行研究,将裸土散射模型和上述Bi-mimics模型、Spec-mimics模型中的Stokes矢量进行修改,使其可以计算任意极化的散射系数。以Mimics手册中的Aspen为模型输入参数,模拟分析了RHCP发射,线极化(H、V极化)和圆极化(RHCP、LHCP)接收时散射系数随入射角的变化。理论研究表明RHCP极化信号经地表反射后,LHCP极性的反射信号无论是裸土还是植被都是只有在大的入射角(小仰角)时存在镜像散射值。但是对于RHCP,H、V极性的反射信号,在各个角度都有响应,RV极化时候,动态响应最大。当接收机可以追踪一颗或多颗卫星在不同仰角下的能量时(如SMIGOL)采用动态响应大的V极化天线较为有效；当接收机只能接收最高仰角的信号(如SMEX02中的DMR)时,LHCP极化的天线只会在某些角度范围内存在响应。实际的GNSS-R接收机可以在同一时刻接收到多颗卫星在不同仰角下的能量,适宜的角度(天顶角和方位角)以及极化组合来进行地物参数的监测和反演有待进一步研究,而地表实测数据对理论的验证也需同步展开。
因此,基础理论推动下的实用化GNSS-R陆面遥感监测网络的形成是未来工作研究的重心和难点。
GNSS-R is a new promising remote sensing technique, in which the special designed receivers collect the reflected signals of GNSS. As for ocean scenarios, GNSS-R can be used to retrieve ocean surface wind, sea wind height, tide, sea salinity, among others. For land scenarios, low cost, small power, high spatial and time resolutions are the advantages, so this technique is considered to be a promising tool to retrieve land surface geophysical parameters, such as soil moisture and vegetation height or biomass. GNSS-R land surface scattering characteristics are studied in this dissertation in order to make GNSS-R land surface parameters retrievals practical.
Constellation of GNSS is transmitters, the special designed GNSS-R receivers collect the land or ocean surface reflected signals. Therefore, it is a kind of bistatic radar, for which bistatic scattering models are needed. For bare surface, the original used scattering model PO, GO and SPM models are modified to bistatic scattering. Bi-mimics model is developed based on the original backscattering Mimics. By adding scattering zenith angles and azimuth angles in Mimics, the corresponding angles in phase matrixes and extinction matrixes are needed to be modified. Meanwhile the angles in ground reflectivtity matrix and scattering matrix are modified. Compared to ocean surface, roughness scales of land surface are small, so it is commonly recognized that the reflected signal is largely coming from the specular reflection point of first Fresnel zone. The diffuse scattering power is too weak to be received. The angles in the above bisatic scattering models are set to specular ones to do research. As for vegetation study, Spec-mimics is developed and utilized as a study tool to analyze vegetation (crop and forest) biomass. Theoretical studies indicate that GNSS-R has the potential to monitor biomass.
In order to reduce ionospheric effects, the GNSS transmitted signals are right handed circular polarization, whose polarization characteristics are changed after reflecting from the earth surface. Therefore the corresponding polarized attenna of receiver should be carefully considered to decrease signals loss. This dissertation focuses on the land surface reflected signals polarization charateristics study. Modified stokes vectors are modified in bare surface scattering model and the above Bi-mimics model, Spec-mimics model to calculate bistatic or specular scattering cross sections for any combination of transmitter and receiver polarizations. Aspen in Mimics handbook is used as model input, relationship between scattering coefficients of RHCP transmitted, linear(H,V) and circular(RHCP, LHCP) polarized received versus scattering angles are analyzed. Theoretical study indicates that as for RHCP transmitted signals, the LHCP reflected signals (bare surface or vegetation) exist only in larger incident angles (smaller elevation angles). But the reflected signals exist in any incident angles as for linear polarized (H, V) reflectivity, where V polarization has larger dynamic range. In conclusion, when the receiver can track signals at any elevation angles for one or several satellites(such as SMIGOL), the V polarized receiver antenna is favored; LHCP attenna respond only at some angles when only the highest elevation angle can be tracked(such as DMR used in SMEX02airborne GPS-R experiment).
However, further in-situ experiments are needed to calibrate the above theoretical results. And practical constructions of GNSS-R land surface retrieval and monitoring network are the focuses and difficulties of future study.
引文
[1]Wood E F. Global scale hydrology-Advances in land surface modeling. Reviews of Geophysics and Space Physics. United States).1991,29(CONF-910878--).
[2]Njoku E G, Entekhabi D. Passive microwave remote sensing of soil moisture. Journal of Hydrology.1996,184(1-2):101-129.
[3]Kerr Y H, Waldteufel P, Wigneron J P, et al. Soil moisture retrieval from space:The Soil Moisture and Ocean Salinity (SMOS) mission. Geoscience and Remote Sensing, IEEE Transactions on.2001,39(8):1729-1735.
[4]Entekhabi D, Njoku E G, O'Neill P E, et al. The soil moisture active passive (SMAP) mission. Proceedings of the IEEE.2010,98(5):704-716.
[5]Zreda M, Desilets D, Tpa F, et al. Measuring soil moisture content non-invasively at intermediate spatial scale using cosmic-ray neutrons. Geophysical Research Letters.2008,35:L21402.
[6]Larson K M, Small E E, Gutmann E D, et al. Use of GPS receivers as a soil moisture network for water cycle studies. Geophysical Research Letters.2008,35:L24405, doi:10.1029/2008GL036013
[7]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.地球物理学报.2011,54(11)：2735-2744.
[8]Njoku E G, Entekhabi D. Passive microwave remote sensing of soil moisture. Journal of Hydrology.1996,184(1-2):101-129.
[9]白伟华GNSS-R海洋遥感技术研究：(博士论文).北京：中国科学院空间科学与应用研究中心,2008
[10]Jin S, Komjathy A. GNSS reflectometry and remote sensing:New objectives and results. Advances in Space Research.2010,46(2):111-117.
[11]刘经南,邵连军,张训械,等GNSS-R研究进展及其关键技术.武汉大学学报(信息科学版)2007,32(11)：955-960.
[12]Martin-Neira M. A Passive Reflectometry and Interferometry System(PARIS)-Application to ocean altimetry. ESA journal.1993,17(4):331-355.
[13]Auber J C, Bibaut A, Rigal J M. Characterization of Multipath on Land and Sea at GPS Frequencies. Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994), Salt Lake City, UT, September 1994,1155-1171.
[14]Katzberg S J, Garrison J L, Center L R. Utilizing GPS to determine ionospheric delay over the ocean. Citeseer,1996.
[15]Garrison J L, Katzberg S J. Detection of ocean reflected GPS signals:theory and experiment. Southeastcon'97.'Engineering new New Century'., Proceedings. IEEE, Blacksburg, VA,1997,290- 294.
[16]Garrison J L, Katzberg S J. The application of reflected GPS signals to ocean remote sensing. Remote Sensing of Environment.2000,73(2):175-187.
[17]Zavorotny V U, Voronovich A G. Scattering of GPS signals from the ocean with wind remote sensing application. Geoscience and Remote Sensing, IEEE Transactions on.2000,38(2):951-964.
[18]Komjathy A, Zavorotny V U, Axelrad P, et al. GPS Signal Scattering from Sea Surface::Wind Speed Retrieval Using Experimental Data and Theoretical Model. Remote Sensing of Environment. 2000,73(2):162-174.
[19]Soulat F, Caparrini M, Germain O, et al. Sea state monitoring using coastal GNSS-R. Arxiv preprint physics/0406029V1.2004.
[20]Lofgren J S, Haas R, Johansson J M. Monitoring coastal sea level using reflected GNSS signals. Advances in Space Research.2011,47(2):213-220.
[21]Sabia R, Caparrini M, Camps A, et al. Potential synergetic use of GNSS-R signals to improve the sea-state correction in the sea surface salinity estimation:Application to the SMOS mission. Geoscience and Remote Sensing, IEEE Transactions on.2007,45(7 Part 1):2088-2097.
[22]Nunziata F, Migliaccio M. GNSS sea surfactant monitoring.
[23]Valencia E, Camps A, Park H, et al. Oil slicks detection using GNSS-R. Geoscience and Remote Sensing Symposium, IEEE International.2011:4383-4386.
[24]Rodriguez-Alvarez N, Bosch-Lluis X, Camps A, et al. Water level monitoring using the interference pattern GNSS-R technique.Geoscience and Remote Sensing Symposium, IEEE International.2011. IEEE,2011:2334-2337.
[25]Zavorotny V U, Voronovich A G. Scattering of GPS signals from the ocean with wind remote sensing application. IEEE Transactions on Geoscience and Remote Sensing.2000,38(2):951-964.
[26]Komjathy A, Zavorotny V U, Axelrad P, et al. GPS Signal Scattering from Sea Surface:Wind Speed Retrieval Using Experimental Data and Theoretical Model. Remote Sensing of Environment. 2000,73(2):162-174.
[27]Masters D S. Surface remote sensing applications of GNSS bistatic radar:Soil moisture and aircraft altimetry:[dissertation]. Boulder:Univ. of Colorado,2004.
[28]Rodriguez-Alvarez N, Bosch-Lluis X, Camps A, et al. Review of crop growth and soil moisture monitoring from a ground-based instrument implementing the Interference Pattern GNSS-R Technique. Radio Science.2011,46:RS0C03, doi:10.1029/2011RS004680.
[29]http://www-lisic.univ-littoral.fr/spacereflecto2011/_Workshop/_presentation/S4/01_Alberto_Alonso/SpaceReflecto_SMIGOL.pdf.
[30]Valencia E, Camps A, Vall-Llossera M, et al. GNSS-R Delay-Doppler Maps over land: Preliminary results of the GRAJO field experiment. Geoscience and Remote Sensing Symposium (IGARSS),2010 IEEE International,2010:3805-3808.
[31]Rodriguez-Alvarez N, Bosch-Lluis X, Camps A, et al. Soil Moisture Retrieval Using GNSS-R Techniques:Experimental Results Over a Bare Soil Field. IEEE Transactions on Geoscience and Remote Sensing.2009,47(11):3616-3624
[32]Rodriguez-Alvarez N, Marchan-Hernandez J F, Camps A, et al. Topographic profile retrieval using the Interference Pattern GNSS-R technique. Geoscience and Remote Sensing Symposium, IEEE International.2009,3:420-423.
[33]Rodriguez-Alvarez N, Monerris A, Bosch-Lluis X, et al. Soil moisture and vegetation height retrieval using GNSS-R techniques. Geoscience and Remote Sensing Symposium,2009 IEEE International.2009,3:869-872.
[34]Rodriguez-Alvarez N, Camps A, Vall-Llossera M, et al. Land Geophysical Parameters Retrieval Using the Interference Pattern GNSS-R Technique. Geoscience and Remote Sensing, IEEE Transactions on.2010,99:1-14.
[35]Jacobson M D. Snow-covered lake ice in GPS multipath reception-Theory and measurement. Advances in Space Research.2010,46(2):221-227.
[36]Larson K M, Small E E, Gutmann E, et al. Using GPS multipath to measure soil moisture fluctuations:initial results. GPS Solutions.2008,12(3):173-177.
[37]Zavorotny V, Larson K M, Braun J, et al. A physical model for GPS multipath caused by land reflections:Toward bare soil moisture retrievals. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing.2010,3(1):100-110
[38]Small E E, Larson K M, Braun J J. Sensing vegetation growth with reflected GPS signals. Geophysical Research Letters.2010,37:L12401.
[39]Kavak A, Xu G, Vogel W J. GPS multipath fade measurements to determine L-band ground reflectivity properties. Proc. NAPEX XX.1996:257-263.
[40]Kavak A, Vogel W J, Guanghan X. Using GPS to measure ground complex permittivity. Electronics Letters.1998,34(3):254-255.
[41]Masters D, Katzberg S, Axelrad P. Airborne GPS bistatic radar soil moisture measurements during SMEX02. Geoscience and Remote Sensing Symposium, IEEE International,2003, (2):896-898.
[42]Zavorotny V, Masters D, Gasiewski A, et al. Seasonal polarimetric measurements of soil moisture using tower-based gps bistatic radar. Geoscience and Remote Sensing Symposium, IEEE International,2003,2,781-783.
[43]Zavorotny V U, Voronovich A G. Bistatic GPS signal reflections at various polarizations from roughland surface with moisture content. Geoscience and Remote Sensing Symposium, IEEE International,2000,7:2852-2854
[44]Kato R, Saito H, Fukuda S. Experimental study for GNSS-R polarimetry. Geoscience and Remote Sensing Symposium, IEEE International,2011:2853-2856.
[45]Mickler D, Axelrad P, Born G. Using GPS reflections for satellite remote sensing. Acta Astronautica.2004,55(1):39-49.
[46]Emery W J, Axelrad P, Nerem R S, et al. Student reflected GPS experiment (SuRGE). Geoscience and Remote Sensing Symposium, IEEE International.2001,3:1518-1520.
[47]Gleason S, Adjrad M, Unwin M. Sensing Ocean, Ice and Land Reflected Signals from Space: Results from the UK-DMC GPS Reflectometry Experiment. ION GNSS 18th International Technical Meeting of the Satellite Division.2005.1679-1685
[48]Camps A, Park H, Valencia E, et al. Preliminary error budget of a GNSS-R spaceborne mission. Geoscience and Remote Sensing Symposium, IEEE International.2011:3444-3447.
[49]关止,赵凯,宋冬生.利用反射GPS信号遥感土壤湿度.地球科学进展.2006,21(007)：747-750.
[50]王迎强,严卫,符养,等.机载GPS反射信号土壤湿度测量技术.遥感学报.2009,13(4)：670-685
[51]邵连军,张训械,孙强,等.GPS信号海面散射特性和初步实验结果.电波科学学报.2008,23(4).699-703
[52]王波,王红光,赵振维,等.GPS海面反射信号特性仿真分析.全球定位系统.2008,33(6)：13-16
[53]http://baike.baidu.com/view/628443.htm
[54]王惠南.GPS导航原理与应用.北京：科学出版社,2003.
[55]http://baike.baidu.com/view/152877.htm.
[56]http://baike.baidu.com/view/45519.htm.
[57]http://baike.baidu.com/view/590829.htm.
[58]Auber J C, Bibaut A, Riga] J M. Characterization of multipath on land and sea at GPS frequencies Alexandria, VA:Institute of Navigation,1994:1155-1171.
[59]Katzberg S J, Garrison J L. Utilizing GPS to determine ionospheric delay over the ocean. NASA Tech. Memo,1996.
[60]Masters D. GPS signal scattering from land for moisture content determination. Geoscience and Remote Sensing Symposium, IEEE International.2000.7:3090-3092
[61]Larson K M, Braun J J, Small E E, et al. GPS multipath and its relation to near-surface soil moisture content. Selected Topics in Applied Earth Observations and Remote Sensing, IEEE Journal of.2010,3(1):91-99
[62]李紫薇,于暘GNSS-R海洋微波遥感前沿技术进展.遥感学报.2009：13,250-254.
[63]Garcia-Fernandez M, Egido A, Caparrini M. StarGym, a GNSS-R end-to-end simulator.
[64]Larson K M, Gutmann E D, Zavorotny V U, et al. Can we measure snow depth with GPS receivers?. Geophys. Res. Lett.2009,36:17.
[65]Jacobson M D. Inferring Snow Water Equivalent for a Snow-Covered Ground Reflector Using GPS Multipath Signals. Remote Sensing.2010,2(10):2426-2441.
[66]Jacobson M D. Snow-covered lake ice in GPS multipath reception-Theory and measurement. Advances in Space Research.2010,46(2):221-227.
[67]Komjathy A, Maslanik J, Zavorotny V U, et al. Sea Ice Remote Sensing Using Surface Reflected GPS Signals. Geoscience and Remote Sensing Symposium, IEEE International 2000, 7:2855-2857.
[68]Komjathy A, Maslanik J A, Zavorotny V U, et al. Towards GPS surface reflection remote sensing of sea ice conditions.6th International Conference on Remote Sensing for Marine and Coastal Environments, Charleston, SC, United States,2000.
[69]Wiehl M, Legresy B, Dietrich R. Potential of reflected GNSS signals for ice sheet remote sensing. Progress In Electromagnetics Research.2003,40:177-205.
[70]Gleason S, Adjrad M, Unwin M. Sensing Ocean, Ice and Land Reflected Signals from Space: Results from the UK-DMC GPS Reflectometry Experiment. ION GNSS 18th,2005.
[71]Nunziata F, Migliaccio M. An Electromagnetic Bistatic Scattering Model for GNSS Sea Surfactant Monitoring. Proceedings of the European Navigation Conference-Global Navigation Satellite Systems, Napoli,Italy,2009
[72]Treuhaft R N, Lowe S T, Zuffada C, et al.2-cm GPS altimetry over Crater Lake. Geophys. Res. Lett.2001,28(23):4343-4346.
[73]Ulaby F T, Moore R K. Fung A K. Microwave remote sensing:Active and passive. Volume 1-Microwave remote sensing fundamentals and radiometry. Artech House, Dedham, MA.1981.
[74]Ulaby F T, Moore R K, Fung A K. Microwave Remote Sensing:Active and Passive. Artech House, Dedham, MA,1982.
[75]Ulaby F T, Moore R K, Fung A K. Microwave Remote Sensing:Active and Passive, vol.Ⅲ, Volume Scattering and Emission Theory, Advanced Systems and Applications. Inc., Dedham, Massachusetts.1986:1797-1848.
[76]Chen K S, Wu T D, Tsang L, et al. Emission of rough surfaces calculated by the integral equation method with comparison to three-dimensional moment method simulations. Geoscience and Remote Sensing, IEEE Transactions on.2003,41(1):90-101.
[77]Fung A K, Chen K S. Microwave scattering and emission models and their applications. Norwood, MA:Artech House,1994.
[78]Ulaby F T, El-Rayes M A. Microwave dielectric spectrum of vegetation-Part II: Dual-dispersion model. Geoscience and Remote Sensing, IEEE Transactions on.1987(5):550-557.
[79]Matzler C, Sume A. Microwave radiometry of leaves. Microwave Radiometry and Remote Sensing Applications.1989:133-148.
[80]Karam M A, Fung A K, Antar Y. Electromagnetic wave scattering from some vegetation samples. Geoscience and Remote Sensing, IEEE Transactions on.2002,26(6):799-808.
[81]Fung A K. Microwave scattering and emission model and their applications. Norwood, MA: Artech House,1994..
[82]Stiles J M. A coherent polarimetric microwave scattering model for grassland structures and canopies[Dissertation], Univ. of Michigan,1996.
[83]Stiles J M, Sarabandi K. Electromagnetic scattering from grassland. Ⅰ. A fully phase-coherent scattering model. Geoscience and Remote Sensing, IEEE Transactions on.2000,38(1):339-348.
[84]Stiles J M, Sarabandi K, Ulaby F T. Electromagnetic scattering from grassland. Ⅱ. Measurement and modeling results. Geoscience and Remote Sensing, IEEE Transactions on.2000, 38(1):349-356.
[85]王芳.微波农作物相干和非相干理论散射模型及其应用研究：(博士学位论文).北京：北京师范大学,2006.
[86]Ulaby F T, Sarabandi K, Mcdonald K, et al. Michigan microwave canopy scattering model. International Journal of Remote Sensing.1990,11(7):1223-1253.
[87]Liang P, Pierce L E, Moghaddam M. Radiative transfer model for microwave bistatic scattering from forest canopies. Geoscience and Remote Sensing, IEEE Transactions on.2005,43(11): 2470-2483.
[88]庄钊文,肖顺平,王雪松.雷达极化信息处理及其应用.北京：国防工业出版社,1999.
[89]Ruck G T, Barrick D E, Stuart W D, et al. Radar Cross Section Handbook, vol.1 and 2. Plenum Press,1970.
[90]Elachi C, Kuga Y, Mcdonald K, et al. Radar polarimetry for geoscience applications.1990.
[91]Masters D, Axelrad P, Katzberg S. Initial results of land-reflected GPS bistatic radar measurements in SMEX02. Geoscience and Remote Sensing, IEEE Transactions on.2004,92(4): 507-520.
[92]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. Geoscience and Remote Sensing, IEEE Transactions on.2006,100(1):17-28.
[93]Caparrini M. Using reflected GNSS signals to estimate surface features over wide ocean areas. ESTEC Working Paper,1998.
[94]Ferrazzoli P, Guerriero L, Pierdicca N, et al. Forest biomass monitoring with GNSS-R: theoretical simulations. Advances in Space Research.2010,47(10):1823-1832.
[95]Anderson M. SMEX02 Watershed Vegetation Sampling Data, Walnut Creek, Iowa. Boulder, CO:Nat. Snow Ice Data Center. Digital media,2003.
[96]Anderson M. SMEX02 Watershed Vegetation Sampling Data, Walnut Creek, Iowa. Boulder, CO:Nat. Snow Ice Data Center. Digital media,2003.
[97]Jackson T J, Mckee L. SMEX02 land surface information:geolocation, surface roughness, and photographs. Boulder, CO:National Snow and Ice Data Center. Digital media.2004.
[98]Jackson T J, Cosh M H, Dulaney. W. SMEX02 land surface information:geolocation, surface roughness, and photographs. Boulder, CO:National Snow and Ice Data Center. Digital media.2004.
[99]Bracaglia M, Ferrazzoli P, Guerriero L. A fully polarimetric multiple scattering model for crops. Remote sensing of environment.1995,54(3):170-179.
[100]Laaperi A. Experimental results from oil thickness measurements with the microprocessor controlled microwave radiometer.1983 International Geoscience and Remote Sensing Symposium San Francisco, CA,United States.1983
[101]Dobson M C, Ulaby F T, Letoan T, et al. Dependence of radar backscatter on coniferous forest biomass. Geoscience and Remote Sensing, IEEE Transactions on.1992,30(2):412-415.
[102]Willis N J. Bistatic radar. Artech House,1991.
[103]Martinez-Vazquez A, Camps A, Duffo N, et al. Full polarimetric emissivity of vegetation-cov ered soils:Vegetation structure effects. Geoscience and Remote Sensing Symposium, IEEE International.2002,6:3542-3544.
[104]Egido A, Ruffini G, Caparrini M, et al. Soil Moisture Monitorization Using GNSS Reflected Signals.1ST Colloquium Scientific and Fundamental Aspects of the Galileo Programme.2008.
[105]Zuffada C, Zavorotny V. GPS reflections for Oceanography, ice and surface hydrology.2004: 29.
[106]Monerris,A, Rodriguez-Alvarez,N, Vall-llossera,M.,et al. The GPS and Radiometric Joint Observations experiment at the REMEDHUS site (Zamora-Salamanca Region, Spain). Proceedings of the IEEE international Geosciences and Remote Sensing Symposium. Cape Town, South Africa, 2009.
[2]Njoku E G, Entekhabi D. Passive microwave remote sensing of soil moisture. Journal of Hydrology.1996,184(1-2):101-129.
[3]Kerr Y H, Waldteufel P, Wigneron J P, et al. Soil moisture retrieval from space:The Soil Moisture and Ocean Salinity (SMOS) mission. Geoscience and Remote Sensing, IEEE Transactions on.2001,39(8):1729-1735.
[4]Entekhabi D, Njoku E G, O'Neill P E, et al. The soil moisture active passive (SMAP) mission. Proceedings of the IEEE.2010,98(5):704-716.
[5]Zreda M, Desilets D, Tpa F, et al. Measuring soil moisture content non-invasively at intermediate spatial scale using cosmic-ray neutrons. Geophysical Research Letters.2008,35:L21402.
[6]Larson K M, Small E E, Gutmann E D, et al. Use of GPS receivers as a soil moisture network for water cycle studies. Geophysical Research Letters.2008,35:L24405, doi:10.1029/2008GL036013
[7]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.地球物理学报.2011,54(11)：2735-2744.
[8]Njoku E G, Entekhabi D. Passive microwave remote sensing of soil moisture. Journal of Hydrology.1996,184(1-2):101-129.
[9]白伟华GNSS-R海洋遥感技术研究：(博士论文).北京：中国科学院空间科学与应用研究中心,2008
[10]Jin S, Komjathy A. GNSS reflectometry and remote sensing:New objectives and results. Advances in Space Research.2010,46(2):111-117.
[11]刘经南,邵连军,张训械,等GNSS-R研究进展及其关键技术.武汉大学学报(信息科学版)2007,32(11)：955-960.
[12]Martin-Neira M. A Passive Reflectometry and Interferometry System(PARIS)-Application to ocean altimetry. ESA journal.1993,17(4):331-355.
[13]Auber J C, Bibaut A, Rigal J M. Characterization of Multipath on Land and Sea at GPS Frequencies. Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994), Salt Lake City, UT, September 1994,1155-1171.
[14]Katzberg S J, Garrison J L, Center L R. Utilizing GPS to determine ionospheric delay over the ocean. Citeseer,1996.
[15]Garrison J L, Katzberg S J. Detection of ocean reflected GPS signals:theory and experiment. Southeastcon'97.'Engineering new New Century'., Proceedings. IEEE, Blacksburg, VA,1997,290- 294.
[16]Garrison J L, Katzberg S J. The application of reflected GPS signals to ocean remote sensing. Remote Sensing of Environment.2000,73(2):175-187.
[17]Zavorotny V U, Voronovich A G. Scattering of GPS signals from the ocean with wind remote sensing application. Geoscience and Remote Sensing, IEEE Transactions on.2000,38(2):951-964.
[18]Komjathy A, Zavorotny V U, Axelrad P, et al. GPS Signal Scattering from Sea Surface::Wind Speed Retrieval Using Experimental Data and Theoretical Model. Remote Sensing of Environment. 2000,73(2):162-174.
[19]Soulat F, Caparrini M, Germain O, et al. Sea state monitoring using coastal GNSS-R. Arxiv preprint physics/0406029V1.2004.
[20]Lofgren J S, Haas R, Johansson J M. Monitoring coastal sea level using reflected GNSS signals. Advances in Space Research.2011,47(2):213-220.
[21]Sabia R, Caparrini M, Camps A, et al. Potential synergetic use of GNSS-R signals to improve the sea-state correction in the sea surface salinity estimation:Application to the SMOS mission. Geoscience and Remote Sensing, IEEE Transactions on.2007,45(7 Part 1):2088-2097.
[22]Nunziata F, Migliaccio M. GNSS sea surfactant monitoring.
[23]Valencia E, Camps A, Park H, et al. Oil slicks detection using GNSS-R. Geoscience and Remote Sensing Symposium, IEEE International.2011:4383-4386.
[24]Rodriguez-Alvarez N, Bosch-Lluis X, Camps A, et al. Water level monitoring using the interference pattern GNSS-R technique.Geoscience and Remote Sensing Symposium, IEEE International.2011. IEEE,2011:2334-2337.
[25]Zavorotny V U, Voronovich A G. Scattering of GPS signals from the ocean with wind remote sensing application. IEEE Transactions on Geoscience and Remote Sensing.2000,38(2):951-964.
[26]Komjathy A, Zavorotny V U, Axelrad P, et al. GPS Signal Scattering from Sea Surface:Wind Speed Retrieval Using Experimental Data and Theoretical Model. Remote Sensing of Environment. 2000,73(2):162-174.
[27]Masters D S. Surface remote sensing applications of GNSS bistatic radar:Soil moisture and aircraft altimetry:[dissertation]. Boulder:Univ. of Colorado,2004.
[28]Rodriguez-Alvarez N, Bosch-Lluis X, Camps A, et al. Review of crop growth and soil moisture monitoring from a ground-based instrument implementing the Interference Pattern GNSS-R Technique. Radio Science.2011,46:RS0C03, doi:10.1029/2011RS004680.
[29]http://www-lisic.univ-littoral.fr/spacereflecto2011/_Workshop/_presentation/S4/01_Alberto_Alonso/SpaceReflecto_SMIGOL.pdf.
[30]Valencia E, Camps A, Vall-Llossera M, et al. GNSS-R Delay-Doppler Maps over land: Preliminary results of the GRAJO field experiment. Geoscience and Remote Sensing Symposium (IGARSS),2010 IEEE International,2010:3805-3808.
[31]Rodriguez-Alvarez N, Bosch-Lluis X, Camps A, et al. Soil Moisture Retrieval Using GNSS-R Techniques:Experimental Results Over a Bare Soil Field. IEEE Transactions on Geoscience and Remote Sensing.2009,47(11):3616-3624
[32]Rodriguez-Alvarez N, Marchan-Hernandez J F, Camps A, et al. Topographic profile retrieval using the Interference Pattern GNSS-R technique. Geoscience and Remote Sensing Symposium, IEEE International.2009,3:420-423.
[33]Rodriguez-Alvarez N, Monerris A, Bosch-Lluis X, et al. Soil moisture and vegetation height retrieval using GNSS-R techniques. Geoscience and Remote Sensing Symposium,2009 IEEE International.2009,3:869-872.
[34]Rodriguez-Alvarez N, Camps A, Vall-Llossera M, et al. Land Geophysical Parameters Retrieval Using the Interference Pattern GNSS-R Technique. Geoscience and Remote Sensing, IEEE Transactions on.2010,99:1-14.
[35]Jacobson M D. Snow-covered lake ice in GPS multipath reception-Theory and measurement. Advances in Space Research.2010,46(2):221-227.
[36]Larson K M, Small E E, Gutmann E, et al. Using GPS multipath to measure soil moisture fluctuations:initial results. GPS Solutions.2008,12(3):173-177.
[37]Zavorotny V, Larson K M, Braun J, et al. A physical model for GPS multipath caused by land reflections:Toward bare soil moisture retrievals. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing.2010,3(1):100-110
[38]Small E E, Larson K M, Braun J J. Sensing vegetation growth with reflected GPS signals. Geophysical Research Letters.2010,37:L12401.
[39]Kavak A, Xu G, Vogel W J. GPS multipath fade measurements to determine L-band ground reflectivity properties. Proc. NAPEX XX.1996:257-263.
[40]Kavak A, Vogel W J, Guanghan X. Using GPS to measure ground complex permittivity. Electronics Letters.1998,34(3):254-255.
[41]Masters D, Katzberg S, Axelrad P. Airborne GPS bistatic radar soil moisture measurements during SMEX02. Geoscience and Remote Sensing Symposium, IEEE International,2003, (2):896-898.
[42]Zavorotny V, Masters D, Gasiewski A, et al. Seasonal polarimetric measurements of soil moisture using tower-based gps bistatic radar. Geoscience and Remote Sensing Symposium, IEEE International,2003,2,781-783.
[43]Zavorotny V U, Voronovich A G. Bistatic GPS signal reflections at various polarizations from roughland surface with moisture content. Geoscience and Remote Sensing Symposium, IEEE International,2000,7:2852-2854
[44]Kato R, Saito H, Fukuda S. Experimental study for GNSS-R polarimetry. Geoscience and Remote Sensing Symposium, IEEE International,2011:2853-2856.
[45]Mickler D, Axelrad P, Born G. Using GPS reflections for satellite remote sensing. Acta Astronautica.2004,55(1):39-49.
[46]Emery W J, Axelrad P, Nerem R S, et al. Student reflected GPS experiment (SuRGE). Geoscience and Remote Sensing Symposium, IEEE International.2001,3:1518-1520.
[47]Gleason S, Adjrad M, Unwin M. Sensing Ocean, Ice and Land Reflected Signals from Space: Results from the UK-DMC GPS Reflectometry Experiment. ION GNSS 18th International Technical Meeting of the Satellite Division.2005.1679-1685
[48]Camps A, Park H, Valencia E, et al. Preliminary error budget of a GNSS-R spaceborne mission. Geoscience and Remote Sensing Symposium, IEEE International.2011:3444-3447.
[49]关止,赵凯,宋冬生.利用反射GPS信号遥感土壤湿度.地球科学进展.2006,21(007)：747-750.
[50]王迎强,严卫,符养,等.机载GPS反射信号土壤湿度测量技术.遥感学报.2009,13(4)：670-685
[51]邵连军,张训械,孙强,等.GPS信号海面散射特性和初步实验结果.电波科学学报.2008,23(4).699-703
[52]王波,王红光,赵振维,等.GPS海面反射信号特性仿真分析.全球定位系统.2008,33(6)：13-16
[53]http://baike.baidu.com/view/628443.htm
[54]王惠南.GPS导航原理与应用.北京：科学出版社,2003.
[55]http://baike.baidu.com/view/152877.htm.
[56]http://baike.baidu.com/view/45519.htm.
[57]http://baike.baidu.com/view/590829.htm.
[58]Auber J C, Bibaut A, Riga] J M. Characterization of multipath on land and sea at GPS frequencies Alexandria, VA:Institute of Navigation,1994:1155-1171.
[59]Katzberg S J, Garrison J L. Utilizing GPS to determine ionospheric delay over the ocean. NASA Tech. Memo,1996.
[60]Masters D. GPS signal scattering from land for moisture content determination. Geoscience and Remote Sensing Symposium, IEEE International.2000.7:3090-3092
[61]Larson K M, Braun J J, Small E E, et al. GPS multipath and its relation to near-surface soil moisture content. Selected Topics in Applied Earth Observations and Remote Sensing, IEEE Journal of.2010,3(1):91-99
[62]李紫薇,于暘GNSS-R海洋微波遥感前沿技术进展.遥感学报.2009：13,250-254.
[63]Garcia-Fernandez M, Egido A, Caparrini M. StarGym, a GNSS-R end-to-end simulator.
[64]Larson K M, Gutmann E D, Zavorotny V U, et al. Can we measure snow depth with GPS receivers?. Geophys. Res. Lett.2009,36:17.
[65]Jacobson M D. Inferring Snow Water Equivalent for a Snow-Covered Ground Reflector Using GPS Multipath Signals. Remote Sensing.2010,2(10):2426-2441.
[66]Jacobson M D. Snow-covered lake ice in GPS multipath reception-Theory and measurement. Advances in Space Research.2010,46(2):221-227.
[67]Komjathy A, Maslanik J, Zavorotny V U, et al. Sea Ice Remote Sensing Using Surface Reflected GPS Signals. Geoscience and Remote Sensing Symposium, IEEE International 2000, 7:2855-2857.
[68]Komjathy A, Maslanik J A, Zavorotny V U, et al. Towards GPS surface reflection remote sensing of sea ice conditions.6th International Conference on Remote Sensing for Marine and Coastal Environments, Charleston, SC, United States,2000.
[69]Wiehl M, Legresy B, Dietrich R. Potential of reflected GNSS signals for ice sheet remote sensing. Progress In Electromagnetics Research.2003,40:177-205.
[70]Gleason S, Adjrad M, Unwin M. Sensing Ocean, Ice and Land Reflected Signals from Space: Results from the UK-DMC GPS Reflectometry Experiment. ION GNSS 18th,2005.
[71]Nunziata F, Migliaccio M. An Electromagnetic Bistatic Scattering Model for GNSS Sea Surfactant Monitoring. Proceedings of the European Navigation Conference-Global Navigation Satellite Systems, Napoli,Italy,2009
[72]Treuhaft R N, Lowe S T, Zuffada C, et al.2-cm GPS altimetry over Crater Lake. Geophys. Res. Lett.2001,28(23):4343-4346.
[73]Ulaby F T, Moore R K. Fung A K. Microwave remote sensing:Active and passive. Volume 1-Microwave remote sensing fundamentals and radiometry. Artech House, Dedham, MA.1981.
[74]Ulaby F T, Moore R K, Fung A K. Microwave Remote Sensing:Active and Passive. Artech House, Dedham, MA,1982.
[75]Ulaby F T, Moore R K, Fung A K. Microwave Remote Sensing:Active and Passive, vol.Ⅲ, Volume Scattering and Emission Theory, Advanced Systems and Applications. Inc., Dedham, Massachusetts.1986:1797-1848.
[76]Chen K S, Wu T D, Tsang L, et al. Emission of rough surfaces calculated by the integral equation method with comparison to three-dimensional moment method simulations. Geoscience and Remote Sensing, IEEE Transactions on.2003,41(1):90-101.
[77]Fung A K, Chen K S. Microwave scattering and emission models and their applications. Norwood, MA:Artech House,1994.
[78]Ulaby F T, El-Rayes M A. Microwave dielectric spectrum of vegetation-Part II: Dual-dispersion model. Geoscience and Remote Sensing, IEEE Transactions on.1987(5):550-557.
[79]Matzler C, Sume A. Microwave radiometry of leaves. Microwave Radiometry and Remote Sensing Applications.1989:133-148.
[80]Karam M A, Fung A K, Antar Y. Electromagnetic wave scattering from some vegetation samples. Geoscience and Remote Sensing, IEEE Transactions on.2002,26(6):799-808.
[81]Fung A K. Microwave scattering and emission model and their applications. Norwood, MA: Artech House,1994..
[82]Stiles J M. A coherent polarimetric microwave scattering model for grassland structures and canopies[Dissertation], Univ. of Michigan,1996.
[83]Stiles J M, Sarabandi K. Electromagnetic scattering from grassland. Ⅰ. A fully phase-coherent scattering model. Geoscience and Remote Sensing, IEEE Transactions on.2000,38(1):339-348.
[84]Stiles J M, Sarabandi K, Ulaby F T. Electromagnetic scattering from grassland. Ⅱ. Measurement and modeling results. Geoscience and Remote Sensing, IEEE Transactions on.2000, 38(1):349-356.
[85]王芳.微波农作物相干和非相干理论散射模型及其应用研究：(博士学位论文).北京：北京师范大学,2006.
[86]Ulaby F T, Sarabandi K, Mcdonald K, et al. Michigan microwave canopy scattering model. International Journal of Remote Sensing.1990,11(7):1223-1253.
[87]Liang P, Pierce L E, Moghaddam M. Radiative transfer model for microwave bistatic scattering from forest canopies. Geoscience and Remote Sensing, IEEE Transactions on.2005,43(11): 2470-2483.
[88]庄钊文,肖顺平,王雪松.雷达极化信息处理及其应用.北京：国防工业出版社,1999.
[89]Ruck G T, Barrick D E, Stuart W D, et al. Radar Cross Section Handbook, vol.1 and 2. Plenum Press,1970.
[90]Elachi C, Kuga Y, Mcdonald K, et al. Radar polarimetry for geoscience applications.1990.
[91]Masters D, Axelrad P, Katzberg S. Initial results of land-reflected GPS bistatic radar measurements in SMEX02. Geoscience and Remote Sensing, IEEE Transactions on.2004,92(4): 507-520.
[92]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. Geoscience and Remote Sensing, IEEE Transactions on.2006,100(1):17-28.
[93]Caparrini M. Using reflected GNSS signals to estimate surface features over wide ocean areas. ESTEC Working Paper,1998.
[94]Ferrazzoli P, Guerriero L, Pierdicca N, et al. Forest biomass monitoring with GNSS-R: theoretical simulations. Advances in Space Research.2010,47(10):1823-1832.
[95]Anderson M. SMEX02 Watershed Vegetation Sampling Data, Walnut Creek, Iowa. Boulder, CO:Nat. Snow Ice Data Center. Digital media,2003.
[96]Anderson M. SMEX02 Watershed Vegetation Sampling Data, Walnut Creek, Iowa. Boulder, CO:Nat. Snow Ice Data Center. Digital media,2003.
[97]Jackson T J, Mckee L. SMEX02 land surface information:geolocation, surface roughness, and photographs. Boulder, CO:National Snow and Ice Data Center. Digital media.2004.
[98]Jackson T J, Cosh M H, Dulaney. W. SMEX02 land surface information:geolocation, surface roughness, and photographs. Boulder, CO:National Snow and Ice Data Center. Digital media.2004.
[99]Bracaglia M, Ferrazzoli P, Guerriero L. A fully polarimetric multiple scattering model for crops. Remote sensing of environment.1995,54(3):170-179.
[100]Laaperi A. Experimental results from oil thickness measurements with the microprocessor controlled microwave radiometer.1983 International Geoscience and Remote Sensing Symposium San Francisco, CA,United States.1983
[101]Dobson M C, Ulaby F T, Letoan T, et al. Dependence of radar backscatter on coniferous forest biomass. Geoscience and Remote Sensing, IEEE Transactions on.1992,30(2):412-415.
[102]Willis N J. Bistatic radar. Artech House,1991.
[103]Martinez-Vazquez A, Camps A, Duffo N, et al. Full polarimetric emissivity of vegetation-cov ered soils:Vegetation structure effects. Geoscience and Remote Sensing Symposium, IEEE International.2002,6:3542-3544.
[104]Egido A, Ruffini G, Caparrini M, et al. Soil Moisture Monitorization Using GNSS Reflected Signals.1ST Colloquium Scientific and Fundamental Aspects of the Galileo Programme.2008.
[105]Zuffada C, Zavorotny V. GPS reflections for Oceanography, ice and surface hydrology.2004: 29.
[106]Monerris,A, Rodriguez-Alvarez,N, Vall-llossera,M.,et al. The GPS and Radiometric Joint Observations experiment at the REMEDHUS site (Zamora-Salamanca Region, Spain). Proceedings of the IEEE international Geosciences and Remote Sensing Symposium. Cape Town, South Africa, 2009.