干旱区生态环境知识资源中心

Absolute sensor calibration is the basis on which measured radiance from multiple sensors can be compared with each other or with time. Despite the increasing sophistication and reliability of on-board satellite sensor calibration systems, vicarious (or ground-look) calibration methods remain an important component of calibration validation. These methods, particularly the surface reflectance method, typically involve intensive measurements, at the time of satellite over-flight, of the surface and atmospheric properties (such as, surface reflectance and temperature, atmospheric pressure, water vapor and temperature profiles, and aerosol optical properties) that are ideally uniform, stable, and well defined. Such conditions are found, for example, in the desert southwest of the United States or in the atmosphere above high altitude lakes. A key measurement that has been often neglected and one that is becoming increasingly important due to rapid industrialization of developing countries, is the single scattering albedo of aerosols a measure of the fraction of light that is scattered from the total amount extinguished from the direct beam; typical values range from close to 1 to 0.8 or lower for highly absorbing aerosols. It is obtained from a measurement of aerosol absorption for which many techniques are available. The error in the measurement of absorptance disproportionately impacts the error in the scattered radiance as seen by the remote sensor. Here we describe the sensitivity of sensor calibration to aerosol absorption and illustrate why it should be an important measurement in the field calibration campaigns, including those planned for the next generation satellites of the US National Polar-Orbiting Operational Environmental Satellite System.