Comprehensive investigation of the atmospheric Modulation Transfer Function (MTF) for satellite imaging payloads: considering turbulence and aerosol effects over Tehran

Abstract

In the realm of remote sensing using satellite imagery, real-time and region-specific estimation of Modulation Transfer Function (MTF) is critical for assessing, designing, and selecting optimal payloads, channels, and imaging conditions. The variability of Earth's atmosphere introduces uncertainties that complicate the development of a universally applicable MTF model, particularly challenging in urban areas that are prone to aerosol pollution and heat island effects. In this research, the atmosphere of the Tehran metropolitan area, which has not been extensively studied in terms of the MTF of overflying satellites, was investigated over five days in 2021 which were selected based on data availability and to cover a variety of different conditions. A general Small Angle Approximation (SAA) method is utilized to calculate the aerosol MTF, with Boundary Layer Heights (BLH) and Aerosol Layer Heights (ALH) validated against the literature, long-term observations, numerical models, and real-time observations. The turbulence MTF is calculated using a short-exposure isotropic Kolmogorov turbulence model. The refractive index structure parameter (Cn2) is determined using the general HMNSP99 model due to the absence of an established and calibrated model for Tehran. The assumptions for the turbulence MTF model are selected to cover a wide range of practical and widely used satellites over Tehran, while the uncertainties in the radiosonde data are taken into account by employing Monte Carlo simulations to model the effective Cn2 for Tehran. The results cover the effects of varieties in aerosol layer optical properties, particle types and size distribution, as well as variations in weather conditions and atmospheric state on the MTF and offer valuable insights for optimizing satellite imaging systems in urban atmospheric conditions and set the stage for further regional studies focused on enhancing image compensation and payload design.