Retrieval of the canopy leaf area index in the BOREAS flux tower sites using linear spectral mixture analysis

This paper reports on the use of linear spectral mixture analysis for the retrieval of canopy leaf area index (LAI) in three flux tower sites in the Boreal Ecosystem-Atmosphere Study (BOREAS) southern study area: Old Black Spruce, Old Jack Pine, and Young Jack Pine (SOBS, SOJP, and SYJP). The data used were obtained by the Compact Airborne Spectrographic Imager (CASI) with a spatial resolution of 2 m in the winter of 1994. The convex geometry method was used to select the endmembers: sunlit crown, sunlit snow, and shadow. Along transects for these flux tower sites, the fraction of sunlit snow was found to have a higher correlation with the field-measured canopy LAI than the fraction of sunlit crown or the fraction of shadow. An empirical equation was obtained to describe the relation between canopy LAI and the fraction of sunlit snow. There is a strong correlation between the estimated LAI and the field-measured LAI along transects (with R 2 values of 0.54, 0.71, and 0.60 obtained for the SOBS, SYJP, and SOJP sites, respectively). The estimated LAI for the whole tower site is consistent with that obtained by the inversion of a canopy model in our previous study where values of 0.94, 0.92, and 0.63 were obtained for R 2 for the SOBS, SYJP and SOJP sites, respectively. The CASI 2-m summer data over the SOBS site was also employed to investigate the possibility of deriving canopy LAI from the summer data using linear mixture analysis. At a spatial resolution of 10 m, the correlation between the field-measured LAI and the estimated LAI along transects is small at R 2 less than 0.3, while R 2 increases to 0.6 at a spatial resolution of 30 m. The difficulty in canopy LAI retrieval from the summer data at a spatial resolution of 10 m is likely due to the variation of the understory reflectance across the scene, although spatial misregistration of the CASI data used may also be a possible contributing factor.

[1]  Baoxin Hu,et al.  Retrieval of Leaf Area Index and Canopy Closure from CASI Data over the BOREAS Flux Tower Sites , 2000 .

[2]  A. Rencz,et al.  Remote sensing for the earth sciences , 1999 .

[3]  Brian L. Markham,et al.  Variability of boreal forest reflectances as measured from a helicopter platform , 1997 .

[4]  Alan H. Strahler,et al.  A hybrid geometric optical-radiative transfer approach for modeling albedo and directional reflectance of discontinuous canopies , 1995, IEEE Transactions on Geoscience and Remote Sensing.

[5]  Paul E. Johnson,et al.  A semiempirical method for analysis of the reflectance spectra of binary mineral mixtures , 1983 .

[6]  Wallace M. Porter,et al.  The airborne visible/infrared imaging spectrometer (AVIRIS) , 1993 .

[7]  R. Rummel.  Applied Factor Analysis , 1970 .

[8]  W. Verhoef.  Light scattering by leaf layers with application to canopy reflectance modelling: The SAIL model , 1984 .

[9]  Richard A. Fournier,et al.  Seasonal change in understory reflectance of boreal forests and influence on canopy vegetation indices , 1997 .

[10]  Paul J. Gemperline,et al.  Target transformation factor analysis with linear inequality constraints applied to spectroscopic-chromatographic data , 1986 .

[11]  R. Fernandes,et al.  A multi-scale approach to mapping effective Leaf Area Index in Boreal Picea mariana stands using high spatial resolution CASI imagery , 2002 .

[12]  Karl Fred Huemmrich,et al.  Remote Sensing of Forest Biophysical Structure Using Mixture Decomposition and Geometric Reflectance Models , 1995 .

[13]  D. Peddle.  Spectral Mixture Analysis and Geometric-Optical Reflectance Modeling of Boreal Forest Biophysical Structure , 1999 .

[14]  Robert E. Dickinson,et al.  Land processes in climate models , 1995 .

[15]  S. T. Gower,et al.  Leaf area index of boreal forests: theory, techniques, and measurements , 1997 .

[16]  Jessica A. Faust,et al.  Imaging Spectroscopy and the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) , 1998 .

[17]  J. Boardman.  Automating spectral unmixing of AVIRIS data using convex geometry concepts , 1993 .

[18]  A. Strahler,et al.  Winter boreal forest canopy BRF results: comparisons between airborne data, laboratory simulations and geometrical-optical model data , 1995, 1995 International Geoscience and Remote Sensing Symposium, IGARSS '95. Quantitative Remote Sensing for Science and Applications.

[19]  Wout Verhoef,et al.  A new forest light interaction model in support of forest monitoring , 1992 .

[20]  Edwin T. Engman,et al.  Status of remote sensing algorithms for estimation of land surface state parameters , 1995 .

[21]  P. Sellers.  Canopy reflectance, photosynthesis and transpiration , 1985 .

[22]  J. Chen,et al.  Retrieving Leaf Area Index of Boreal Conifer Forests Using Landsat TM Images , 1996 .

[23]  John R. Miller,et al.  Atmospheric Correction Validation of casi Images Acquired over the Boreas Southern Study Area , 1997 .

[24]  Edmund R. Malinowski,et al.  Factor Analysis in Chemistry , 1980 .

[25]  Characterization and Calibration of the CASI Airborne Imaging Spectrometer for BOREAS , 1997 .

[26]  P. Sellers.  Canopy reflectance, photosynthesis, and transpiration. II. the role of biophysics in the linearity of their interdependence , 1987 .

[27]  Derek R. Peddle,et al.  Remote sensing of biophysical variables in boreal forest stands of Picea mariana , 1996 .

[28]  N. Goel.  Models of vegetation canopy reflectance and their use in estimation of biophysical parameters from reflectance data , 1988 .

[29]  Alan H. Strahler,et al.  Geometric-optical bidirectional reflectance modeling of the discrete crown vegetation canopy: effect of crown shape and mutual shadowing , 1992, IEEE Trans. Geosci. Remote. Sens..