Surface emissivity primary influences the accuracy of land surface temperature retrieval using remote sensing methods. This parameter is important in thermal infrared remote sensing. This paper aims to investigate the effects of soil water content and roughness on the thermal infrared emissivity of bare soil through an experimental method. This work can provide useful information for developing a soil emissivity retrieval method via remote sensing. The spectral emissivity of two soils（loam and sandy loam） with different soil water contents was measured by a Nicolet IS10 Fourier-transform infrared spectrometer with an integrating sphere. Data were used to analyze the effects of soil water content on soil spectral emissivity. The average emissivity of both soil types with different particle sizes of 8—14 μm was determined using an active-passive diffuse emissivity measuring device. This device can determine the effects of soil water content on the average soil emissivity for 8—14 μm particles. Soil emissivity increases with increasing soil water content because of the high emissivity of water.The average emissivity of loam soil with water contents of 0%, 13.7%, 26.1%, and 43.4%are 0.81, 0.92, 0.93, and 0.95, respectively, for wavelengths from 3 μm to 11 μm, as well as 0.73, 0.89, 0.93, and 0.96, respectively, for wavelengths from 3.3 μm to 5.3 μm. Moreover, the average emissivity of sandy loam soil with water contents of 0%, 8.8%, 25.3%, and 28.6% are 0.82, 0.92, 0.94, and 0.95,respectively, for the wavelengths from 3 μm to 11 μm, as well as0.75, 0.89, 0.95, and 0.96, respectively, for wavelengths from 3.3 μm to 5.3 μm. For the effects of soil roughness on emissivity, the results show that the average emissivities from 8—14 μm are 0.916, 0.934, and 0.937 for particles with sizes less than 0.6, 0.6—1, and 1—2 mm, respectively, for the dry sandy loam soil, as well as 0.936, 0.951, and 0.959, respectively, for the dry loam soil. Soil emissivity increases with increasing soil moisture. Wavelengths from 3.3 μm to 3.5 μm are the most affected by soil moisture. In this wavelength range, the band-average difference in soil emissivity between dry and wet soils is higher than 0.2. The wavelengths with minimal effect include 11 μm to 15 μm, when the band-average difference in soil emissivity between dry and wet soils is lower than 0.015. For the thermal infrared atmospheric window waveband（8—14 μm）, wavelengths from 8 μm to 9.5 μm are the most influenced by soil moisture. In this range, the band-average difference for soil emissivity is 0.05. Soil emissivity slightly increases with increasing particle size for dry and wet soils. Furthermore, soil emissivity increases by more than 0.05 for bands 10, 11, and 12 of ASTER data with increasing soil water content.

soil emissivity;soil water content;soil roughness;soil spectrμm