Estimating clear-sky all-wave net radiation from combined visible and shortwave infrared (VSWIR) and thermal infrared (TIR) remote sensing data

Abstract

The surface radiation budget is characterized by the all-wave net radiation. Existing parameterization methods of estimating surface net radiation require the input of many surface and atmospheric parameters and rely heavily on the availability and accuracy of such data. Other methods involve retrieval of the shortwave (0.3-3.0μm) and longwave (3.0-100.0μm) components separately from visible and shortwave infrared (VSWIR) and thermal infrared (TIR) data, respectively. The proposed HyspIRI mission will carry a VSWIR spectrometer and a TIR multispectral imager with a nadir spatial resolution of 60m. The broad range of spectral information will provide a unique opportunity to directly estimate the surface net radiation from the high-resolution HyspIRI data. In this study, we propose a new algorithm to estimate the clear-sky instantaneous all-wave net radiation over the land surface by combining VSWIR and TIR remote sensing data. The new method is based on extensive modeling of atmospheric radiative transfer over the entire solar spectrum. The algorithm is first tested with MODIS data. Validation with 1-year measurements at seven Surface Radiation Budget Network (SURFRAD) sites in 2013 demonstrates that the new method can accurately estimate clear-sky instantaneous all-wave net radiation with a root mean square error (RMSE) of 70.6W/m2, which is better than the method of separating shortwave and longwave components. MODIS/ASTER Airborne Simulator (MASTER) data from the HyspIRI preparatory airborne campaign are also used as a proxy to demonstrate the suitability of the algorithm for data from the future HyspIRI mission.