The objective of this Phase II proposal is to build a new submersible hyperspectral absorption spectrophotometer for ocean color biogeochemical and optical closure research. The proposed instrument will employ an integrating cavity design with spectral filters for removal of fluorescence effects from absorption, and excitation-emission measurement. The integrating cavity has distinct advantages over current commercial in-situ 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 dominant in-situ absorption instrument currently on the market, the WET Labs AC-s. While absorption spectra are the primary inversion product of ocean color remote sensing, providing a direct link to net primary production, the oceanographic community currently has no in-situ sensor for algorithm development and validation that measures absorption spectra with acceptable accuracy.
The proposed instrument employs the following components: (i) an integrating sphere to maintain accuracy in the presence of particle scattering; (ii) broadband Xe arc lamp source to cover spectral range from 300nm to 750nm; (iii) spectral filters for rejection of fluorescence by phytoplankton pigments and dissolved organic material; (iv) dual spectrometers for measuring signal within integrating sphere as well as the source spectrum; (v) integrating sphere is designed with continuous fluid flow and bubble clearance in mind; and (vi) a solid absorption standard calibration is proposed to make highly accurate measurements in the field.
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 in preparation for the hyperspectral PACE 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.