Monitoring Earth's shortwave reflectance: GEO instrument concept

In this paper we present a GEO instrument concept dedicated to monitoring the Earth's global spectral reflectance with a high revisit rate.Based on our measurement goals, the ideal instrument needs to be highly sensitive (SNR>100) and to achieve global coverage with spectral sampling (::S1Onm) and spatial sampling (::Slkm) over a large bandwidth (380-2510 nm) with a revisit time (3x/day) sufficient to fully measure the spectral-radio metric-spatial evolution of clouds and confounding factor during daytime. After a brief study of existing instruments and their capabilities, we choose to use a GEO constellation of up to 6 satellites as a platform for this instrument concept in order to achieve the revisit time requirement with a single launch. We derive the main parameters of the instrument and show the above requirements can be fulfilled while retaining an instrument architecture as compact as possible by controlling the telescope aperture size and using a passively cooled detector.