Effect of Soil Moisture on the Angular Variation of Thermal Infrared Emissivity of Inorganic Soils

• Published in: IEEE geoscience and remote sensing letters 2014-06, Vol.11 (6), p.1091-1095
• Main Authors: Garcia-Santos, Vicente, Valor, Enric, Caselles, Vicente, Coll, Cesar, Angeles Burgos, Ma
• Format: Article
• Language: English
• Subjects: Angular emissivity; bare soil; Distance measurement; Radiometers; Remote sensing; Soil measurements; Soil moisture; soil moisture (SM); thermal infrared (TIR); Uncertainty
• ISSN: 1545-598X; 1558-0571
• DOI: 10.1109/LGRS.2013.2286747

Emissivity is influenced by different factors. This study deals with the effect of the soil moisture (SM) content on the zenithal (θ) variation of ratio-to-nadir emissivity (ε r ), for a wide variety of inorganic bare soils. To retrieve ε r , a goniometer assembly was used, together with two identical CIMEL Electronique CE312-2 radiometers working at six spectral bands within 7.7-14.3 μm, performing simultaneous radiance measurements at different combinations of zenith and azimuth angles. The results showed that the effect of SM upon ε r (θ) is different depending on the spectral range and textural composition of the sample. Sandy soils showed a decrease of ε r (θ) from nadir up to 0.132 for θ ≥ 40 ° at 8-9.4 μm under dry conditions, but this decrease was reduced to 0.093 with the increase of SM. Clayey samples did not present dependence of ε r (θ) on SM. Loamy texture samples presented a more sharp decrease of ε r (θ) with the increase of SM, reaching differences between nadir values and 70 ° up to 6%, at all spectral ranges studied. Finally, a parameterization of ε r with SM and θ was derived allowing to obtain ratio-to-nadir emissivities with an accuracy of ± 0.011.