The retrieval of surface emissivity in the 8-14-mum region from remotely sensed thermal imagery requires channel-averaged values of atmospheric transmittance, path radiance, and downwelling sky flux. Band-pass resampling introduces inherent retrieval errors that depend on atmospheric conditions, spectral region, bandwidth, flight altitude, and surface temperature. This simulation study is performed for clear sky conditions and moderate atmospheric water vapor contents. It shows that relative emissivity retrieval errors can reach as much as 3% for broadband sensors (1-2-mum bandwidth) and 0.8% for narrowband instruments (0.15 mum), even for constant surface emissivity. For spectrally varying surface emissivities the relative retrieval error increases for the broadband instrument by similar to2% in channels with strong emissivity changes of 0.05-0.1. The corresponding retrieval errors for narrowband sensors increase by approximately 3-4%. The channels in the atmospheric window regions with lower transmittance, i.e., 8-8.5 and 12.5-14 mum, are most sensitive to retrieval errors. (C) 2002 Optical Society of America. [References: 23]
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