|Title||Sources of variation in radiometric surface temperature over a tallgrass prairie|
|Publication Type||Journal Article|
|Year of Publication||1994|
|Authors||Friedl, MA, Davis, FW|
|Journal||Remote Sensing of Environment|
|Keywords||Biochemistry and Biophysics–Temperature) (Agronomy–Forage Crops and Fodder) (Soil Science–Physics and Chemistry (1970- )) Plants Vascular plants Spermatophytes Angiosperms Monocots Research Article Vegetation Index Soil Energy Balance Mathematical, Effects and Regulation–General Measurement and Methods) (Plant Physiology, Plantae-Unspecified Gramineae (Mathematical Biology and Statistical Methods) (Ecology Environmental Biology–Plant) (Biophysics–Biocybernetics (1972- )) (Metabolism–Energy and Respiratory Metabolism) (Temperature: Its Measurement|
Numerous studies have noted a strong negative correlation between radiometric surface temperature and spectral vegetation indices such as the NDVI, and have suggested that this relationship might be exploited in strategies to model land surface energy balance from satellites. These studies have been largely empirical in nature and the relationships among remotely sensed data, land surface properties, and land surface energy balance that produce this phenomenon remain unclear. We studied the relationship between radiometric surface temperature and NDVI over a tallgrass prairie in northeastern Kansas. The study site included a mix of landcovers, with fractional vegetation cover and exposed soil backgrounds over much of the site. We observed a persistent negative correlation between radiometric surface temperature and NDVI, but found that the relationship was highly date- and time-specific. In this context, the relationship between surface temperature and NDVI was observed to depend on landcover type, and a significant proportion of the total variance in both NDVI and radiometric surface temperature was explained by stratifying the data by landcover class. More importantly, our results show the relationship between surface temperature and NDVI to have little association with surface energy balance for data sets acquired from aircraft and helicopters on several dates during the growing seasons of 1987 and 1989. Based on results from a simulation model of the soil-canopy-sensor system, we hypothesize the observed covariance between radiometric surface temperature and NDVI to be largely caused by temperature differences between the soil background and vegetation canopy and by variation in fractional vegetation cover. This hypothesis is supported by evidence showing soil moisture to be an important secondary control on radiometric surface temperature due to its effect on soil thermal inertia, rather than as a limiting control on latent heat flux, as might be expected. These findings indicate that invertible surface energy balance models must account for the effects of landcover, soil background temperatures, and soil moisture before thermal infrared imagery can be effectively used to estimate land surface fluxes.