Vol. 8, No. 2, 187-193, 2009

Abstract
The emissivity of natural surfaces is a required parameter in high accuracy land surface temperature (LST) determinations. Then, it is of great importance to know how thermal infrared (TIR) emissivity changes with the different factors. Soil type influence on emissivity is well known from experimental studies, whereas the effect of soil moisture (SM) on emissivity is one of the pending issues in thermal remote sensing. It is seen that the SM variation may cause a high systematic error in emissivity, e.g., about +0.1 in emissivity for an increase from 0.04 to 0.10 g/cm³ in SM for sandy soils. This study reveals a common emissivity increase with soil water content, higher for larger sand content and in the 8 to 9 μm range, but always significant considering the experimental uncertainty (δε~±0.5%). The emissivity increase is understood because of both the quartz contribution to decrease the emissivity of the material chiefly between 7.7 and 9.7 μm, and the decrease of the reflectivity by the water film on the soil particles. Emissivity-SM relationships were obtained with the aim of using them together with SM estimates from remotely sensed data in order to improve the TIR emissivity estimations and thus, the LST determination. Furthermore, the study showed the possibility of retrieving SM from TIR emissivities with a standard estimation error of about ±0.08 m³m^-3, when considering the OM content.

ISSN 1729-3782