Mapping soil water content under sparse vegetation and changeable sky conditions: comparison of two thermal inertia approaches

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A critical analysis of a thermal inertia approach to map surface soil water content onbare and sparsely vegetated soils by means of remotely sensed data is reported. The study area isan experimental field located in Barrax, Spain. In situ data were acquired within the Barrax 2011research project. An advanced hyperspectral scanner airborne imager provides images in thevisible/near-infrared and thermal infrared bands. Images were acquired both in day andnight times by the Instituto Nacional de Técnica Aeroespacial between 12th and 13th ofJune 2011. The scene covers a corn irrigation pivot surrounded by bare soil, where a set ofin situ data have been collected both previously and simultaneously to overpasses. To validateremotely sensed estimations, an ad hoc dataset has been produced by measuring spectra, radiometrictemperatures, surface soil water content, and soil thermal properties. These data werecollected on two transects covering bare and sparsely vegetated soils. This ground datasetwas used (1) to verify if a thermal inertia method can be applied to map the water contenton soil covered by sparse vegetation and (2) to quantify a correction factor accounting forsolar radiation reduction due to sky cloudiness. The experiment intended to test a spatially constantand a spatially distributed approach to estimate the phase difference. Both methods werethen applied to the airborne images collected during the following days to obtain the spatialdistribution of surface soil water content. Results confirm that the thermal inertia methodcan be applied to sparsely vegetated soil characterized by low fractional cover if the solarradiation reaching the ground is accurately estimated. A spatially constant value of thephase difference allows a good assessment of thermal inertia, whereas the comparison withthe three-temperature approach did not give conclusive responses. Results also show thatclear sky, only at the time of the acquisition, does not provide a sufficient condition to obtainaccurate estimates of soil water content. A corrective coefficient taking into account actualsky cloudiness throughout the day allows better estimates of thermal inertia and, thus, ofsoil water content. © 2013 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.JRS.7.073548]
Lingua originaleEnglish
pagine (da-a)073548-1-073548-17
Numero di pagine17
RivistaJournal of Applied Remote Sensing
Stato di pubblicazionePublished - 2013

All Science Journal Classification (ASJC) codes

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