Description: The objective of this Phase I proposal is to assess the feasibility of a new submersible hyperspectral absorption spectrophotometer for ocean color and biogeochemistry research. The proposed instrument will employ an integrating cavity design with high resolution spectral discrimination from 300 nm to the 750 nm for both source light and detector to mitigate the effects of scattering error and fluorescence contamination. The integrating cavity has distinct advantages over current commercial in-water spectrophotometers in having enhanced sensitivity in a compact form factor associated with a very long pathlength, while also eliminating substantial scattering errors that are the largest source of bias for the existing instrument currently on the market (SeaBird/WET Labs ac-s). While absorption spectra are a primary inversion product of ocean color remote sensing, providing a direct link to primary production, the ocean science community currently lacks an in-water sensor for algorithm development and validation with acceptable accuracy and needed spectral range. Indeed, the PACE Science Team has identified this as a key technology gap related to their mission Our objective in Phase I is to examine design tradeoffs to achieve high SNR, uniformity of light field in the cavity, and high sample throughput, while eliminating scattering and fluorescence contamination in a compact, low power embodiment. Modeling and bench top experimentation will be used to optimize light source selection, coupling to spectral dispersion elements and cavity, and configuration of the integrating sphere. Our ultimate accuracy target is 2%, consistent with state-of-the-art bench top systems. This is the accuracy required for PACE ocean biogeochemistry research and is at least an order of magnitude better than any current in-water sensor. The result of Phase I will be a thoroughly vetted design concept for a submersible absorption spectrometer for in-water and lab use to be built in Phase II.

Benefits: NASA scientists and funded researchers working on ocean color algorithm development and cal/val, are currently hindered by a lack of ground truth spectral IOP data. The oceanographic community currently has no in-situ sensor for algorithm development and validation that measures absorption spectra with acceptable accuracy. As hyperspectral remote sensing becomes more widespread and given the push within NASA programs in preparation for the hyperspectral PACE, GEOCAPE, and GLIMR ocean color missions, development of this system is very timely.

Like the NASA applications, the target market for the proposed instrument is government scientists and agency-funded researchers utilizing optical measurements in ocean science, biogeochemistry, and ocean color algorithm development and cal/val. An in-situ instrument for measuring hyperspectral absorption without the confounding effects of scattering and fluorescence would see wide applicability.