Atmospheric Effects of Star Imaging (I): Sky Polarization

The rapid development of aerospace technology, such as GPS satellite navigation system, represented by high precision and sensitivity, is gradually gaining wide attention from researchers and replacing traditional radio navigation systems, playing an important role in military defense, space exploration, engineering surveying, air-to-air combat and other fields. However, due to the limitations of traditional electromagnetic theory, satellite navigation technology has relatively weak anti-electronic deception and electromagnetic jamming capabilities. In order to enhance the autonomy and reliability of the navigation system, a passive and strong counter-jamming navigation method, which is named as starlight navigation, has been proposed. In the 1950 s, the advent of star sensors has greatly improved the accuracy of starlight navigation. Star sensors are high-precision attitude-sensitive measuring instruments that measure the star vector component in the star sensor coordinate system by conducting the stellar observation, and determine the three-axis attitude of the carrier relative to the inertial coordinate system using known precise star positions. The high accuracy, strong counter-jamming ability, and independence from other systems of star sensor navigation technology have a wide range of applications and important military value on various airborne, shipborne, and vehicle-mounted platforms in near-earth space. However, as the development of observation platforms and the decrease in the observation height of star sensors in the atmosphere, a star sensor operating in the terrestrial space will inevitably be affected by sky background radiation, atmospheric turbulence, and atmospheric refraction during the observation. This three-part paper aims to extensively reveal these atmospheric effects on stellar observation. In Part I, we investigate how to reduce the effect of sky background radiation on star imaging by using polarization filtering technique. Based on the LIDAR measured data, we calculate the distribution and scattering characteristics of the entire atmospheric particles in typical regions. Concretely, we stratify the entire atmosphere based on specific calculation needs, taking into account the aerosol extinction profile, atmospheric density, and weather conditions of typical regions. We then calculate the aerosol particle number density, extinction coefficient, and scattering phase matrix, using the near-surface visibility, complex refractive index, and distribution type of aerosol particles, in conjunction with the Mie scattering theory. By combining the preprocessing data of atmospheric particles with the vector radiation transfer model, we employ the doubling and adding method and set the fixed parameters in this calculation model to study the polarization characteristics of the sky background in the near infrared band and obtain the polarization distributions of the sky background under different atmospheric and observation conditions. Furthermore, we analyze the effects of observation and solar position on the polarization distribution of the sky background under different values of wavelength. We show that using near-infrared light with a large value of wavelength and located in the absorption band for observation or increasing the observation altitude of the star sensor can suppress the sky background light to some extent by using polarization filtering technique. Other than that, we find that when the observing azimuth angle is certain, choosing a suitable observing angle can ensure the possibility of using polarization filtering technique at lower solar altitude to reduce the effect of sky background radiation on the star imaging. This research sheds light on the atmospheric effects on star imaging and provides insights into how polarization filtering technique can be used to reduce the impact of sky background radiation on stellar observation. Moreover, this study's findings have significant implications for the development of more effective and reliable star sensor navigation technology.