Effects of aerosol phase function and other atmospheric parameters in radiometric calibration of hyperspectral visible/NIR satellite instruments above test sites of different altitudes

To verify data obtained by a satellite instrument a systematic calibration of the instrument is carried out. In addition to an internal calibration using on–board lamp or reflected solar radiation, the external calibration based on a comparison of radiance measurements above special ground test sites and calculated radiances is often employed. Radiances at the top of the atmosphere can be calculated using a radiative transfer model basing on measurement of the atmospheric properties and surface characteristics at the test sites. External calibration of hyperspectral instrument is sensitive to the spectral structure of absorbing and scattering of atmospheric species and, as a consequence, has a specific spectral structure of errors. We compared theoretical errors of a satellite hyperspectral instrument radiometric calibration using two test sites one of which is located in downcountry at 200 m a.s.l. and another one in highlands at 2000 m a.s.l. We suppose that both stations are equipped by the same set of instruments for measurements of the properties of the atmosphere and surface reflectance. The aerosol vertical profile and the aerosol phase function are supposed as not measured characteristics. The analysis is performed for an instrument with the spectral resolution of 1-8 nm which is typical for special regime of payload GSA of Russian satellite Resurs-P. The errors related with the atmospheric composition (including possible scenarios of the aerosol phase function and the aerosol vertical profile) and albedo measurement errors were theoretically examined. The errors strongly depend on aerosol loading. In case of low aerosol loading (corresponding to aerosol optical depth of 0.1 at 0 m a.s.l.) errors are less than 10% at both sites for all the wavelengths between 400 nm and 1000 nm with the exception of the absorption band of water vapor about 950 nm, where errors reach 35% at downcountry and 14% at highlands. For aerosol optical depth of 1 at 0 m a.s.l. the errors can reach 45% at downcountry and 18% at highlands.