Growth of biomass occurs through the mechanisms of photosynthesis and carbon
assimilation, which needs light in the visible part of the spectrum, besides carbon dioxide
and water as the major inputs. Chlorophyll absorbs light from 0.4 to 0.7 mm and this
photosynthetic active radiation (PAR) can be approximated from the total solar radiation.
The Absorbed PAR (APAR) varies with the vegetation density, as well as with PAR. The
ratio of APAR/PAR can be computed on a pixel-by-pixel basis using NDVI from remote
sensing data (Asrar et al., 1992). Satellite measurements of clouds (for PAR) being
combined with NDVI (for APAR/PAR) can thus give us estimates of APAR. Monteith
(1972) pioneered the concept of calculating net primary biomass production as a function
of APAR and introduced the growth efficiency e as the biomass production/APAR
fraction. This method will give the biospheric growth including forests, wetlands,
rangelands, rain-fed cropped areas and irrigated cropped areas. As the river basin is
becoming the major framework for decision making on water management issues, and
water has to be shared by competing users, this method allows us to get the biomass
productivity of the entire area, rather than of the crops alone (e.g., Prince and Goward,
1995).
Growth of biomass occurs through the mechanisms of photosynthesis and carbonassimilation, which needs light in the visible part of the spectrum, besides carbon dioxideand water as the major inputs. Chlorophyll absorbs light from 0.4 to 0.7 mm and thisphotosynthetic active radiation (PAR) can be approximated from the total solar radiation.The Absorbed PAR (APAR) varies with the vegetation density, as well as with PAR. Theratio of APAR/PAR can be computed on a pixel-by-pixel basis using NDVI from remotesensing data (Asrar et al., 1992). Satellite measurements of clouds (for PAR) beingcombined with NDVI (for APAR/PAR) can thus give us estimates of APAR. Monteith(1972) pioneered the concept of calculating net primary biomass production as a functionof APAR and introduced the growth efficiency e as the biomass production/APARfraction. This method will give the biospheric growth including forests, wetlands,rangelands, rain-fed cropped areas and irrigated cropped areas. As the river basin isbecoming the major framework for decision making on water management issues, andwater has to be shared by competing users, this method allows us to get the biomassproductivity of the entire area, rather than of the crops alone (e.g., Prince and Goward,1995).
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