A Bidirectional Reflectance Distribution Function for VisorSat Calibrated with 10,628 Magnitudes from the MMT-9 Database

TL;DR

This paper presents a calibrated bidirectional reflectance distribution function (BRDF) model for VisorSat satellites, derived from over 10,000 observations, improving brightness prediction accuracy in a satellite-centered coordinate system.

Contribution

The paper introduces a new BRDF model for VisorSat, calibrated with extensive observational data, in a coordinate system aligned with the satellite's physical shape and illumination conditions.

Findings

BRDF model reduces brightness prediction RMS from 1.05 to 0.51

Mean VisorSat magnitude at 1000 km is 6.84

Model parameters are based on least squares fitting to observational data

Abstract

A BRDF for the VisorSat model of Starlink satellites is described. The parameter coefficients were determined by least squares fitting to more than 10,000 magnitudes recorded by the MMT-9 robotic observatory. The BRDF is defined in a satellite-centered coordinate system (SCCS) which corresponds to the physical shape of the spacecraft and to the direction of the Sun. The three parameters of the model in the SCCS are the elevations of the Sun and of MMT-9 along with the azimuth of MMT-9 relative to that of the Sun. The mean VisorSat magnitude at a standardized distance of 1,000 km is 6.84 and the RMS of the distribution around that mean is 1.05. After the magnitudes are adjusted with the BRDF, the RMS reduces to 0.51. The set of MMT-9 observations transformed to the SCCS is available from the author.