Technical note Description of a computer code to simulate the satellite signal in the solar spectrum: the 5S code

TLDR

The 5S code estimates pixel apparent reflectance by combining Lambertian ground reflectance with gaseous absorption, molecular and aerosol scattering, and ground inhomogeneity, using selectable observation geometry, atmospheric, ground, and spectral band parameters, and outputs reflectance, gaseous transmittance, surface irradiance, and component contributions to the satellite signal. Benchmark calculations demonstrate the 5S code accurately simulates solar radiation backscattered by the Earth‑surface‑atmosphere system as observed by satellite sensors.

Abstract

Abstract A computer code (acronym 5S) has been developed that allows estimation of the solar radiation backscattered by the Earth-surface-atmosphere system, as it is observed by a satellite sensor. Given the Lambertian ground reflectance, the apparent reflectance of the observed pixel is estimated by taking into account the effects of gaseous absorption, scattering by molecules and aerosols and, to some extent, inhomogeneity in the ground reflectance. The input parameters (observation geometry, atmosphere model, ground reflectance and spectral band) can be either selected from some proposed standard conditions (e.g. spectral bands of a satellite sensor) or user-defined. Besides the pixel apparent reflectance, the code provides the gaseous transmittance, the irradiance at the surface and the different contributions to the satellite signal according to the origin of the measured radiance. Some complementary results are also available; among others, benchmark calculations permit assessment of the code accuracy.