A Study of Variation Characteristics of Surface Broadband Emissivity over Three Typical Bare Soil Underlying Surfaces in Northwestern China

A field observational experiment on ground surface downward longwave radiation (DLR),upward longwave radiation (ULR),and land surface temperature (LST) was conducted at three man-made sites at Gobi,desert,and bare loess zones in 2013 in Gansu Province.In the present study,variation characteristics of surface longwave radiation (LR),LST and surface broadband emissivity over Gobi (GbBE),desert (DeBE),and loess (LoBE) underlying surfaces are analyzed based on the observations collected in the experiment.Results show that the ULR and LST at the Loess site are lower than that at Gobi and desert sites.Surface broadband emissivity at each site has obvious variation characteristics,especially the diurnal cycle feature.Daily averages of surface broadband emissivity at GbBE,DeBE,and LoBE are approximately 0.926±0.0452,0.916±0.0419,and 0.881±0.049,respectively.The values and variation characteristics of observed land surface emissivity are not consistent with that in land surface models.Land surface emissivity can be affected by environmental factors and weather condition.Land surface soil moisture is a significant factor influencing surface emissivity in arid and semi-arid region.More relatively influential factors should be measured and analyzed in the future in field observational experiments.