Estimation of roughness length and sensible heat flux from WiFS and NOAA AVHRR data

Abstract

Development of representative NOAA AVHRR data based Land Surface Processes (LSP) parameters, towards incorporation into GCMs in quasi-dynamic mode, was undertaken by using (i) Normalized Difference Vegetation Index (NDVI) for the computation of roughness length (Z o), and (ii) Land Surface Temperature (T s) along with air density, specific heat of air at constant pressure, air temperature and aerodynamic resistance data to compute Sensible Heat Flux (SHF). NDVI was corrected for sensor degradation and atmospheric errors. Surface temperature (T s) was computed for the pixel by weighted mixing of the temperatures computed for the assumed bare soil (T g) and full canopy (T v) conditions, using respective emissivity values in AVHRR channels 4 and 5 and split window algorithm, based on relative normalized distance of NDVI (for the pixel) from NDVI (soil) and NDVI (full canopy). The results reported in this study compared well with the Z o and SHF computed from tower-based meteorological measurements. This paper also discusses Z o computed with 188 m resolution IRS-1C/WiFS data and validation of results obtained from the AVHRR data with those derived from WiFS data