Measuring land surface temperature, near-infrared and short-wave infrared reflectance for estimation of water availability in vegetation

Abstract

The vegetation water status is a crucial variable for modelling of drought impact, vegetation productivity and water fluxes. Methods for spatial estimation of this variable still need to be improved. The integration of remotely sensed data of land surface temperature (LST) and water vegetation indices based on near-infrared (NIR) and short-wave infrared (SWIR) reflectance for estimation of vegetation water content and water available for evapotranspiration require more analysis. This study contains a detailed method and measurements of LST, NIR and SWIR reflectance of soybean, corn and barley taken in field campaigns in central Argentine Pampas and laboratory with a ST PRO Raytek (8–14 µm) and a spectrometer SVC HR-1024i (0.35 and 2.5 µm). Also, relative water content of leaves was measured in laboratory during the dehydration process. This method and dataset could be also used for researching other wavelengths between 0.35 and 2.5 µm as indicator of water vegetation status (e.g. solar-induced chlorophyll fluorescence, photosynthesis). Procedures useful to measure field spectra of vegetation are presented. Not only the traditional method to measure leaves spectra in laboratory, but also in field were applied. The method allows the integration of spectra and thermal data as a proxy of vegetation water status.

Relationship between TIR and NIR-SWIR as Indicator of Vegetation Water Availability

“…This spectrometer can acquire spectra with a sampling interval of ≤0.0033 µm, 0.7 µm; ≤0.0095 µm, 1.5 µm; ≤0.0065 µm, 2.1 µm. A reference reflectance spectralon panel (99%) was used to convert raw incident radiance to spectral reflectance [35]. All spectral measurements were made in a nadir orientation of the spectrometer, with a distance of about 0.4 m between the spectrometer and the canopy.…”