COAST (CubeSat Ocean Atmosphere Sensor Technology): A CubeSat for Measuring Sea Surface Salinity with Integrated Atmospheric Correction Capabilities
PI: Gawarkiewicz, Glen (Woods Hole Oceanographic Institute)
Co-PI(s): Cahoy, Kerri (MIT STAR Lab), Gould, Richard (NRL-SSC), McCarthy, Sean (NRL-SSC)
Start Year: 2019 | Duration: 2 years
Partners: MIT STAR Lab, NRL-SSC
Temperature and salinity are key oceanographic pr operties used to physically classify water masses. Determining density, they are the drivers of the large-scale thermohaline ocean circulation. Small- and meso-scale ocean features such as fronts and eddies can be identified and tracked solely using SST and salinity propertie s. The synoptic, simultaneous measurement of thermal, bio-optical ocean properties, and sa linity through an optical -proxy from a CubeSat could address a multitude of important oceanographic topics for both basic science and Naval applications. The algorithm to perform this from a nano-satellite leverages the statistical relationships between salinity and co-varying bio-optical properties such as absorption by colored dissolved organic matter.
Transiting over vast open ocean swaths far from any land mass, a satellite may provide observations otherwise unobtainable by terrestrial methods. With the introduction of the CubeSat format and its inherent capability to support a custom sensor(s) or data acquisition profile, the prospect for an ocean scientist to deploy a dedi cated satellite with orb ital and temporal scale capability has become a reality. Measurements do not necessarily have to be comparable with larger and far more expensive or capable orbiti ng platforms; the ability to make a fundamental determination of sea surface temperature and ocean color alone has considerable value. The direct benefit to the scientist is the previously unprecedented ability to develop an even broader context for site specific measurements.
The majority of space-borne optical oceanographic parameters observed from CubeSats rely on products related to atmospheric corrections to provide useful data. While there may be no acceptable alternative to using supplemental data, this appr oach may become extremely problematic. Time displacement, variances in orbital path, Earth-Sun orientation differences, local weather changes, and spacecraft to spacecraft sensor incompatibility may make acceptable analyses either difficult or impossible. Th e proposed COAST payload addresses this by employing five discrete overlayi ng imaging sensors that work fr om the visible deep blue and extend up into the long wave infrared (LWIR).
A CubeSat presents an interesting engineering challenge often where commonly available COTS components are either by careful integration or modification leveraged beyond their intended limit. Since primarily consumer grade sensors are used, validation of on-orbit performance beyond ground truthing corrections is extremely important. As with any remote radiometric measuring system, integral and autonomous calib ration is desirable. In addition to vicarious ground based calibration, COAST will introduce a combination on-orbit optical and thermal calibration feature. In coordination with custom ized algorithms, this platform will provide the data required to directly quantify littoral zone surface salinity without the need for additional products. In addition to the primary mission object ive of measuring sea surface salinity, some properties may serve as proxies for other phe nomena; for example CDOM can be used to indicate surface current patterns and sea surface temperature exhibits a close relationship with major ocean current features thus making this a comprehensive oceanographic surface sensing instrument.