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

Anthony Mallama

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.