期刊名称：ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences
印刷版ISSN：2194-9042
电子版ISSN：2194-9050
出版年度：2007
卷号：XXXVI-7/C50
出版社：Copernicus Publications
摘要：Sun and sensor geometry cause directional effects in remotely sensed reflectance data which can influence the estimation of biophysical and biochemical variables. Previous studies have indicated that bidirectional measurements contain added information with which the accuracy of derived plant structural parameters can be increased. Because accurate biochemistry mapping is linked to vegetation structure, nitrogen concentration (C N ) estim ates might be indirectly improved w ith multiangular information. We analyzed data of the spaceborne ESA - mission CHRIS on - board PROBA - 1, which provides hyperspectral and multiangular data. The images were acquired in July 2006 over a forest study site in Sw itzerland and were subsequently preprocessed. From each of the five CHRIS images (five different viewing zenith angles) we extracted 60 crown spectra, which correspond to field - sampled trees. Then we developed four - term models by regressing lab - measured C N on four datasets either consisting of original reflectance values (SPEC) or continuum - removed data. The wavebands used in the regression models were determined with a subset selection algorithm. For the data of all view angle combinations particular mode ls were generated, in total 31 equations were evaluated per spectral dataset by comparing the coefficients of determination (R 2 ) and cross - validated root mean square errors. The results of this study indicate that added information contained in multiangula r data improved regression models for C N estimation and lowered RMS errors . Considerable contribution can be achieved with data of a second and third viewing zenith angle. Models based on combinations of off - nadir data performed best. These findings suppor t the potential of multiangular Earth observations for ecological monitoring and modeling studies
