Literature Review
1.2. Remote Sensing of Leaf Area Index (LAI)
Leaf Area Index (LAI) defines an important structural property of a plant canopy, the number of equivalent layers of leaves the vegetation displays relative to a unit ground area. FPAR measures the proportion of available radiation in the specific photosynthetically active wavelengths of the spectrum 0.4 - 0.7microns that a canopy absorbs. Because LAI most directly quantifies the plant canopy structure, it is highly related to a variety of canopy processes, such as water interception, evapotranspiration, photosynthesis, respiration, and leaf litter fall. Hence the definition of LAI is used by terrestrial models to quantify the above ecosystem processes. LAI is an abstraction of a canopy structural property, a dimensionless variable that ignores canopy detail such as leaf angle distribution, canopy height or shape. FPAR is a radiation term, so it is more directly related to remotely sensed variables such as simple ratio, NDVI etc. than LAI. FPAR is frequently used to translate direct satellite data such as NDVI into simple estimates of primary production. It does not define plant canopies as directly as LAI, but is more specifically related to the satellite indices. Because the interrelationships between LAI and FPAR are high, and the utility of each is high we plan to produce both. Neither LAI or FPAR are critical variables themselves, rather they are both essential intermediate variables used to calculate terrestrial energy, carbon, water cycling processes and biogeo-chemistry of vegetation. The current consensus is that LAI will be used preferentially by ecological and climate modellers who desire a representation of canopy structure in their models.