Abstract
Aerosol refractive index and size distribution estimations based on polarized atmospheric irradiance measurements are proposed together with its application to reflectance based vicarious calibration. A method for reflectance based vicarious calibration with aerosol refractive index and size distribution estimation using atmospheric polarization irradiance data is proposed. It is possible to estimate aerosol refractive index and size distribution with atmospheric polarization irradiance measured with the different observation angles (scattering angles). The Top of the Atmosphere (TOA) or at-sensor radiance is estimated based on atmospheric codes with estimated refractive index and size distribution then vicarious calibration coefficient can be calculated by comparing to the acquired visible to near infrared instrument data onboard satellites. The estimated TOA radiance based on the proposed method is compared to that with aureole-meter based approach which is based on refractive index and size distribution estimated with solar direct, diffuse and aureole (Conventional AERONET approach). It is obvious that aureole-meter is not portable, heavy and large while polarization irradiance measurement instruments are light and small (portable size and weight).
Highlights
Earth observation satellites have a long history of being characterized by vicarious methods
This paper describes at-sensor radiance of ASTER/VNIR with the estimated aerosol parameters derived from AERONET and SKYNET as well as the proposed method together with a sensitivity analysis
Reflectance based vicarious calibration method proposed here is based on MODTRAN with the following input parameters, Measured surface reflectance (Lambertian surface), Calculated molecule scattering based on a measured atmospheric pressure, Calculated aerosol scattering with the aerosol parameters, refractive index and size distribution which are estimated with measured polarized irradiance at several scattering angles based on the proposed method, Calculate absorbance due to water vapor and ozone with measured column water and ozone
Summary
Earth observation satellites have a long history of being characterized by vicarious methods. Ozone absorption is taken into account based on MODTRAN with measured column ozone using atmospheric extinction measurements This sun-to-ground-to-sensor transmittance is multiplied by the at-sensor radiance output from the radiative transfer code to correct the radiances for this strong absorption. While this approach is an approximation that excludes interactions between diffusely scattered radiances and absorption, it does not cause large uncertainties for ASTER applications because of the small absorption effect within most of the bands, and the typically high surface reflectance of the test sites used in this work. AERONET (Holben B.N. et al, 1998) and SKYNET Aoki, K. et al, 2005) allows for the estimation of aerosol parameters at the specific locations They use aureole-meters and sky-radiometers which allow solar direct, diffuse and aureole irradiance. This paper describes at-sensor radiance of ASTER/VNIR with the estimated aerosol parameters derived from AERONET and SKYNET as well as the proposed method together with a sensitivity analysis
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