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The Satellite for Estimating Aquatic Salinity and Temperature, or SEASALT, is a 6U CubeSat designed to acquire coastal images to measure Sea Surface Temperature (SST) and to develop and utilize an algorithm to estimate Sea Surface Salinity (SSS). SSS can be retrieved in coastal zones by utilizing atmospherically corrected optical images to retrieve remote sensing reflectance (Rrs). Rrs and SSS can then be empirically related through algorithms specific to different aquatic bodies. Current satellite instruments used for SSS calculations, such as MODIS and VIIRS, have limited revisit times and low spatial resolutions that make it challenging to implement SSS retrieval algorithms. The Planet constellation imagers have lower revisit times and higher spatial resolution than MODIS and VIIRS, but lack the optical bands to enable retrieval of SSS. SEASALT is designed to address both of these limits. SEASALT utilizes bands centered at 412 nm, 470 nm, 540 nm, and 625 nm in the visible (VIS), and 746 nm, and 865 nm in the Near Infra-Red (NIR) to provide accurate atmospheric corrections related to aerosols. A constellation of SEASALT instruments would be feasible to launch and operate, allowing for SSS to be retrieved frequently on a global scale. The SEASALT mission requires a two-year development phase from its current post-instrument PDR state. The SEASALT instrument design has multiple detectors and corresponding optical paths to capture the science bands. The instrument has a large primary catadioptric Ritchey-Chrétien based telescope covering the 412 nm, 746 nm, and 865 nm bands, with the RGB and LWIR cameras each on their own optical paths. The instrument has two custom-designed calibrators, one for the 412, 746, and 865 nm wavelength cameras, which have both a light source and a shutter mechanism. The payload assembly also integrates an additional calibrator for the LWIR camera. Finally, a dual-redundant Raspberry Pi flight computer, based on the MIT DeMi and BeaverCube missions, monitors and controls all payload operations. In this work, we discuss design trades for payload and instrumentation, covering overall optical design, telescope design, electronic interfaces, and structural design requirements for fitting in a 6U Cubesat and performing its mission. We also present a detailed radiometric performance analysis of the optical path to determine each band’s signal-to-noise ratio (SNR) and ensure it will meet mission SSS retrieval requirements. |
