“…For a satellite in low-Earth orbit we expect similar polarimetric behaviours (after correcting for orbit orientation differences: geostationary satellites are located in a fairly narrow equatorial belt, whereas low earth orbit satellites cover a wide range of inclinations), with the key difference that they traverse the range of solar phase angles over a much shorter timespan, compressing the relevant timescales, which makes obtaining diagnostic data more challenging. Kosaka et al (2020) observed geostationary satellite Express-AM5 using a much larger telescope, the 2m Nayuta telescope, and a polarimeter, for ∼ 5 hours at a cadence of 90 seconds, forming one of the highest quality and highest cadence polarimetric datasets of a geostationary satellite to date. In their data, they see a minimum in the optical polarisation (P lin ∼ 1%) around the time of the minimum phase angle, with rapidly increasing linear polarisation after the minimum phase angle (with values increasing up to P lin ∼ 14% in the phase angle interval covered by their observations).…”