TY - JOUR
T1 - Radiative transfer in shrub savanna sites in Niger
T2 - preliminary results from HAPEX-Sahel. 1. Modelling surface reflectance using a geometric-optical approach
AU - Franklin, Janet
AU - Duncan, Jeff
AU - Huete, Alfredo R.
AU - van Leeuwen, W. J.D.
AU - Li, Xiaowen
AU - Bégué, Agnès
N1 - Funding Information:
We are grateful to our colleagues Niall Hanan, Stephen Prince, and Alan Strahler for their contributions, including comments on the manuscript, and to Thierry Lebel and countless others who facilitated our HAPEX field work in Niger in 1991. This work was supported by NASA grants NAGW-2031 (to J. Franklin), NAGW-1949 (to A. Huete), NAGW-1967 and NAG 5-1471 (to S. Prince), and NSF grant INT-9014263 (to X. Li).
PY - 1994/7
Y1 - 1994/7
N2 - To use optical remote sensing to monitor land surface-climate interactions over large areas, algorithms must be developed to relate multispectral measurements to key variables controlling the exchange of matter (water, carbon dioxide) and energy between the land surface and the atmosphere. The proportion of the ground covered by vegetation and the interception of photosynthetically active radiation (PAR) by vegetation are examples of two variables related to evapotranspiration and primary production, respectively. An areal-proportion model of the multispectral reflectance of shrub savanna, composed of scattered shrubs with a grass, forb or soil understory, predicted the reflectance of two 0.5 km2 sites as the area-weighted average of the shrub and understory or 'background' reflectances. Although the shaded crown and shaded background have darker reflectances, ignoring them in the area-weighted model is not serious when shrub cover is low and solar zenith angle is small. A submodel predicted the reflectance of the shrub crown as a function of the foliage reflectance and amount of plant material within the crown, and the background reflectance scattered or transmitted through canopy gaps (referred to as a soil-plant 'spectral interaction' term). One may be able to combine these two models to estimate both the fraction of vegetation cover and interception of PAR by green vegetation in a shrub savanna.
AB - To use optical remote sensing to monitor land surface-climate interactions over large areas, algorithms must be developed to relate multispectral measurements to key variables controlling the exchange of matter (water, carbon dioxide) and energy between the land surface and the atmosphere. The proportion of the ground covered by vegetation and the interception of photosynthetically active radiation (PAR) by vegetation are examples of two variables related to evapotranspiration and primary production, respectively. An areal-proportion model of the multispectral reflectance of shrub savanna, composed of scattered shrubs with a grass, forb or soil understory, predicted the reflectance of two 0.5 km2 sites as the area-weighted average of the shrub and understory or 'background' reflectances. Although the shaded crown and shaded background have darker reflectances, ignoring them in the area-weighted model is not serious when shrub cover is low and solar zenith angle is small. A submodel predicted the reflectance of the shrub crown as a function of the foliage reflectance and amount of plant material within the crown, and the background reflectance scattered or transmitted through canopy gaps (referred to as a soil-plant 'spectral interaction' term). One may be able to combine these two models to estimate both the fraction of vegetation cover and interception of PAR by green vegetation in a shrub savanna.
UR - http://www.scopus.com/inward/record.url?scp=0028160348&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0028160348&partnerID=8YFLogxK
U2 - 10.1016/0168-1923(94)90027-2
DO - 10.1016/0168-1923(94)90027-2
M3 - Article
AN - SCOPUS:0028160348
SN - 0168-1923
VL - 69
SP - 223
EP - 245
JO - Agricultural and Forest Meteorology
JF - Agricultural and Forest Meteorology
IS - 3-4
ER -