An improved dark-object subtraction technique for atmospheric scattering correction of multispectral data

Consideration is given to the effects of canopy closure, understory vegetation, and background reflectance on the relationship between Landsat TM data and the leaf area index (LAI) of temperate coniferous forests in the western U.S. A methodology for correcting TM data for atmospheric conditions and sun-surface-sensor geometry is discussed. Strong inverse curvilinear relationships were found between coniferous forest LAI and TM bands 3 and 5. It is suggested that these inverse relationships are due to increased reflectance of understory vegetation and background in open stands of lower LAI and decreased reflectance of the overstory in closed canopy stands with higher LAI.

Remote sensing of temperate coniferous forest leaf area index The influence of canopy closure, understory vegetation and background reflectance

https://pubag.nal.usda.gov/download/37771/PDF

Relationship of Thematic Mapper Simulator Data to Leaf Area Index of Temperate Coniferous Forests

Many important ecological questions concern eco? system processes occurring over large areas. However, our understanding of ecosystem functions is derived primarily from research executed on small, intensively studied sites, and extrapolation to large areas is diffi? cult. For example, it is not known definitively whether the land biota act as a source or a sink in the global carbon cycle, or whether increases in carbon dioxide concentrations and the subsequent predicted global warming would stimulate or suppress land vegetation (Bolin 1977, Woodwell et al. 1983). Much of this indecision results from our inability to directly measure important vegetation properties on large spatial scales. Estimates of the global carbon content of terrestrial plant biomass range from 450 x 1015 to 1000 x 1015 g. These estimates are derived by extrapolation of data from sites of intensive study to the areal coverage of vegetation assumed to be equivalent; hence no direct means of verification exist. As a consequence, no defensible estimate of energy and mass exchange rates is possible for large areas of terrestrial vegetation. Four recent workshops have evaluated the potential of advanced satellite technology for direct measure? ment of critical vegetation characteristics over large areas (Botkin 1982, 1985,Goody 1982, Wittwer 1983). Each workshop ultimately identified leaf area index (LAI, the area of leaf over a given area of ground) as the single variable both amenable to measurement by satellite and of greatest importance for quantifying en? ergy and mass exchange by plant canopies over landscapes. Characterizing vegetation in terms of LAI, rath? er than species composition, is a critical simplification for regional and global comparison of different terres? trial ecosystems. Previous research in crops and grass? lands has shown leaf area and biomass to be correlated with reflectance values measured by satellite-based sensors (Wiegand et al. 1979). We report here the first attempt to measure the LAI of coniferous forests using optical scanners of satellite resolution.

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Remote Sensing of Coniferous Forest Leaf Area

Factors affecting the remotely sensed response of coniferous forest plantations.

An analysis is presented of the magnitude and variability of the effect of the atmosphere on high-altitude Daedalus Airborne Thematic Mapper data. By regressing ATM radiances against ground radiances (from measurements by a helicopter-mounted Barnes Modular Multiband Radiometer), it was possible to account for atmospheric conditions and variability across a 250 km transect in Oregon to estimate coniferous forest leaf area index. The technique permitted scene contrast to be increased, providing an improved capability for measurement of ground feature radiance.

M. J. Hall

Papers

Atmospheric effects on the remote sensing estimation of forest leaf area index