tocThe Bidirectional Polarized Reflectance Model of SoilWu Taixia and Zhao YunshengI. I NTRODUCTIONII. P OLARIZATION C HARACTERISTIC OF S OILA. Influence of Incidence AngleFig. 1. 0 $^{\circ}$ and 90 $^{\circ}$ polarized reflectance of Fig. 2. 0 $^{\circ}$ and 90 $^{\circ}$ polarized reflectance of Fig. 3. 0 $^{\circ}$ and 90 $^{\circ}$ polarized reflectance of B. Influence of Relative Azimuth and Viewing Zenith AngleC. Physical Reasons of the Soil Surface Showing Polarization ChaIII. B IDIRECTIONAL R EFLECTANCE AND B IDIRECTIONAL P OLARIZED RIV. M ODEL D EVELOPMENTA. Hapke ModelB. Soil BPDF ModelFig.€4. Measurement model comparison of BPDF.C. Model ComparisonV. C ONCLUSIONL. Xiaowen and A. H. Strahler, Geometric-optical modeling of a cF. Maignan, F.-M. Bréon, and R. Lacaze, Bidirectional reflectancW. Lucht, C. B. Schaaf, and A. H. Strahler, An algorithm for theB. Pinty, M. M. Verstraete, and R. E. Dickson, A physical model S. Liang and J. R. G. Townshend, A modified hapke model for soilS. Jacquemond, F. Baret, and J. F. Hanocq, Modeling spectral andD. S. Kliger, J. W. Lewis, and C. E. Randall, Ploarized Light inM. Chami and R. Santer, Aerosol remote sensing using ground-baseI. Csiszar, G. Gutman, P. Romanov, M. Leroy, and O. Hautecoeur, C. Leroux, J. Lenoble, G. Brogniez, J. W. Hovenier, and J. F. deJ. Xifeng, Q. Delin, and Z. Dexiang, The measuring device for biZ. Yunsheng, H. Fang, and J. Lun, Study on polarization reflectaZ. Hongying, Z. Hu, Y. Lei, and Z. Yunsheng, Model of reflectionB. G. Henderson, J. Theiler, and P. Villeneuve, The polarized emR. M. A. Azzam and N. M. Bashara, Ellipsometry and Polarized LigH. G. Berry and A. E. Livingston, Measurement of the stokes paraB. W. Hapke, Bidirectional reflectance spectroscopy 1, Theory, JB. Hapke, Theory of Reflectance and Emitance Spectroscopy . Camb2854 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 43, NO. 12, DECEMBER 2005The Bidirectional PolarizedReflectance Model of SoilWu Taixia and Zhao YunshengAbstract—Soil albedo is a critical parameter affecting theEarth’s climate and environment. In remote sensing data, analysisof the soil bidirectional reflectance distribution function (BRDF)has to be known. Several models for bidirectional reflectance oversoil have been developed. The Hapke bidirectional reflectancemodel has been widely used for soil modeling. Polarization ofradiation reflected by soil carries important information of soilproperties. The polarized light always goes with the bidirectionalreflectance. Therefore, polarization reflectance of a ground targetcarries equivalent important information as bidirectional re-flectance. Detecting multiangle polarization information of soilbecomes a new method in quantitative remote sensing. In thispaper, we analyzed the existence of polarization on the soil surfacein a2space and compared the bidirectional reflectance withthe bidirectional polarized reflectance. We then developed a newpolarized BRDF model of soil as the bidirectional polarizationdistribution function (BPDF) model. The BPDF model helps toimprove classification and quantitative analysis of soil.Index Terms—Bidirectional polarization distribution function(BPDF), bidirectional reflectance distribution function (BRDF),model, polarization reflectance, soil.I. INTRODUCTIONWHEN using remote sensing data to increase the discern-ment capability of the Earth’s surface, angle informationwas found to have influence and contribution to the identity andclassification of objects in remote sensing images [1]. In fact,the full angle information of an object is its three-dimensionalspectrum characteristics inspace. Two approaches havebeen used to characterize the angle spectrum. The first oneemphasizes applications only. It assumes that a ground targetis a Lambert object and ignores the angle differences. Theother approach emphasizes the verity and difference of angleinformation. The bidirectional reflection distributing function(BRDF) has been used in information extraction. Bidirectionalreflectance is the basic macroscopically phenomenon of elec-tromagnetic wave reflection in nature [2], [3]. The reflectionand emission radiation of ground targets are closely related tothe surface structural characteristics and material compositions.Land surface radiates incidence electromagnetism wave in alldirections except absorption and forms different fringing fluxfunction of material spectrum characteristics. The BRDF effectover soil has been widely studied. Analyses in laboratory andManuscript received April 28, 2005; revised July 11, 2005. This work wassupported in part by the Science and Technology Innovation Foundation ofChinese Academy of Science and in part by the National Natural ScienceFoundation of China.The authors are with the College of Urban and Environmental Sciences,Northeast Normal University, 130024 Jilin, China (e-mail: [email protected];[email protected]).Digital Object Identifier 10.1109/TGRS.2005.857905field measurements have shown the anisotropic effect of soildepending on the constituents such as mineral composition,organic matter, iron oxides, and soluble salts. The surfaceroughness and soil moisture are important factors as well[4]–[6].In the process of reflecting, scattering, and transmitting ofelectromagnetic waves, surface targets can produce polarizedcharacteristics that related to the nature of the surface mate-rials. Since polarization reflectance is always bidirectional, wecan attain the polarized three-dimensional spatial distributionof the targets by a polarizer when detecting its bidirectionalreflectance. Different object or the same object in different con-dition such as structural characteristics, roughness, moisturecontents, etc., brings different states of polarization (SOP). Thepolarization spectrum is closely relevant to the wavelength [7].Therefore, detecting the polarization information of an objectbecomes a new method in remote sensing. The polarizationof the radiation reflected by the soil may contain importantinformation that can be observed by satellite instrumentssuch as Polarization and Directionality of Earth Reflectance(POLDER). In this paper, based on the Hapke model [8]–[10],we present a new polarized BRDF model of soil, the BPDFmodel, that aims to know more about the soil optical propertiesand its interactions with the plants.II. POLARIZATION CHARACTERISTIC OFSOILIn this paper, we measured multiangle polarization re-flectance and bidirectional