Field Emissivity Measurements during the ReSeDA Experiment

Emissivity measurements were made during the ReSeDA experiment. Emissivities are necessary for obtaining surface temperatures from remote sensing data in the thermal infrared, and they enter the radiative balance in the atmosphere-surface system. The objective of this study was to assess the spatial variation of surface emissivity in the area, with special regard to the spectral variation of emissivity in the 8-14 μm band. Field broadband (8-14 μm) measurements were performed for the main crops of the Alpilles experimental site (wheat, corn, sunflower and alfalfa). The box method was used for the field campaigns. This methodology is suitable for “in situ” emissivity measurements and permits covering the major crops and surface types, which gives us a good picture of the emissivity variability in the area In addition, laboratory spectral measurements were made to assess the spectral variation of emissivity. These measurements could only be made for soil samples, however, the spectral variation of green vegetation is known to be small. The field and laboratory measurements, together with estimates of plant dimensions and cover, were used in an emissivity model to derive effective spectral emissivities for various surface types and crops. In addition, we have shown that broadband (8-14 μm) integrated emissivities are a good approximation to equivalent hemispheric emissivities for the estimation of the longwave radiative balance.