Optical Sensors for Planetary Radiant Energy (OSPREy): Calibration and Validation of Current and Next-Generation NASA Missions

A principal objective of the Optical Sensors for Planetary Radiance Energy (OSPREy) activity is to establish an above-water radiometer system mounted on an offshore-platform as a lower-cost alternative to existing in-water buoys for the collection of ground-truth observations. The goal is to be able to make high-quality measurements satisfying the accuracy requirements for the vicarious calibration and algorithm validation of current and nextgeneration ocean color satellites. This means the measurements will have a documented uncertainty satisfying the established performance metrics for producing climate-quality data records (CDRs). The activity is based on enhancing commercial-off-the-shelf (COTS) fixed-wavelength and hyperspectral sensors to create thermally regulated hybridspectral instruments with an improved accuracy and spectral resolution, as well as a dynamic range extended into shorter and longer wavelengths. Greater spectral diversity in the ultraviolet (UV) will be exploited to separate the living and nonliving components of marine ecosystems; UV bands will also be used to flag and improve atmospheric correction algorithms in the presence of absorbing aerosols. The short-wave infrared (SWIR) is expected to improve atmospheric correction, because the ocean is radiometrically blacker at these wavelengths. The cost savings are derived not only from using existing technologies as a foundation of the instrument designs, most notably recently developed microradiometers, but also from the above-water approach itself. From the oceanographic perspective, above-water radiometry involves the use of offshore platforms, which have several advantages: a) offshore platforms and towers already exist, b) a tower provides a very stable platform and deterministic solar geometry, c) biofouling is a significantly lesser problem compared to an in-water instrument system, d) acquiring high-quality data at longer wavelengths is easier to achieve, and e) the offshore structure offers a great deal of protection for the instruments. In addition to the relevance to NASA Earth Science, the OSPREy approach significantly impacts the state of the art of optical calibration technology, which is in transition. The production of a transfer radiometer and demonstration of its utility should help interrupt the cycle of escalating costs associated with lamp standards, because it encourages the transition toward detectorbased standards. The world ocean is immense and it is not possible for one agency or one country to produce global CDRs of a uniform quality without strong partners from other nations. Establishing a high-quality and cost-effective sampling capability that is readily reproduced—because it can be purchased as a COTS system—is an important first step towards establishing a global calibration and validation paradigm. This report describes the overall design of OSPREy; the documented uncertainty will be presented in a subsequent report.