Atmospheric absorption and scattering impact on optical satellite-ground links

Free-space radio-frequency (RF) communication links for intersatellite or satellite-to-ground communications are getting increasingly constraint by the insufficient spectrum availability and limited data rate of RF technology. With the advent of large satellite mega-constellation networks for global communications coverage, this limitation of classical RF communication becomes even more critical. Therefore, the establishment of point-to-point free-space optical link technology (FSO) in space will become of paramount importance in future systems, where the application will be for data-relays links, or for mega-constellations inter-satellite links, as well as for direct data downlinks, or from deep-space probes to ground. Further advantages of optical FSO-besides spectrum availability-is its increased power efficiency, higher data rates, avoidance of interference, and inherent protection against interception. When, however, these optical communication links have to pass through Earth's atmosphere, attenuation and scattering effects do influence the signal transmission. In this publication, we investigate the effects of atmospheric attenuation, including the effects of molecular absorption as well as aerosol scattering and absorption, for typical wavelength regions used for FSO, dependent on the link geometries. Based on transmission-simulation databases, we show useful spectral ranges and their specific attenuation strength. Free spectral transmission windows dependent on atmospheric quality and elevation angle are identified for reliable and efficient use of the optical transmission technology in space applications.