Spectral Radiance Characterization of Starlink andOther Satellites for Terrestrial Optical Navigation

Compared to extensive studies on apparent magnitude and bi-directional reflectance functions (BRDFs) for Low Earth Orbit (LEO) satellites like Starlink, there has been a notable gap in the literature when it comes to spectral radiance characterization. Such characterization would be highly beneficial to the emerging Alternative Positioning, Navigation, and Timing (Alt-PNT) method of Terrestrial Optical Navigation (which involves collecting optical line-of-sight measurements to satellites in the presence of sky background, turbulence, and other atmospheric effects), as it could allow for careful design of optical filtering schemes to maximize signal-to-noise ratio (SNR) of the satellite measurements. To address the literature gap, the authors introduce a dataset resulting from a four-night observation campaign with the Magdalena Ridge Observatory’s 2.4-meter telescope. Spectra spanning 380–860 nm were collected for 50 satellites and orbital objects across LEO, Medium Earth Orbit (MEO), and Geostationary Orbit (GEO), with particular emphasis on all three generations of Starlink satellites. Analysis of the Starlink data reveals a local reflectance peak near 475 nm, a shape similar to the solar irradiance curve, and a distinct near-infrared spike for the v2 generation. Estimation of absolute spectral flux from relative flux density measurements is presented, as well as discussion on how near-infrared (NIR) or short wave infrared (SWIR) sensing could expand the operational envelope of terrestrial optical navigation. This dataset offers new insight into the feasibility of optical satellite tracking under challenging conditions, including daylight operations and onboard high-speed aerospace vehicles.