Description: The objective of this Phase I project is to assess the feasibility of a compact wavelength-scanning hyperspectral transmissometer to measure in-situ beam attenuation, a critical ocean inherent optical property (IOP), in support of oceanographic research. The instrument will perform measurements from ultraviolet to near-infrared wavelengths (approximately 360-750 nm) and at a resolution that meets the needs of NASA remote sensing satellite missions such as PACE, GLIMR, and SBG for hyperspectral ocean color remote sensing model development and data product validation. The instrument will utilize a broadband light source coupled to a continuous variable filter to selectively scan through source wavelength ranges to transmit to the sample. A reference detector will monitor source output to calibrate for instability. Upon passing through the sample volume, the transmitted light will be coupled to a spectral detector for measurement. The detector architecture will be defined from outcomes of a trade study in Phase I. By utilizing a wavelength-discriminating detector, we can simultaneously measure transmitted light (at the same wavelengths as the source wavelength range entering the sample volume) and inelastically-scattered light (at wavelengths greater than the source wavelength range entering the sample volume), increasing the scientific capabilities of the instrument and simplifying in-field calibrations. During Phase I we will perform optical and mechanical simulations of different instrument geometries to optimize SWaP and performance. We will design, assemble, and test an optical breadboard with different detector architectures to understand the tradeoffs (engineering and science) between different detectors and measurement configurations. We will assess measurement accuracy and reproducibility by measuring different sample standards and will ultimately benchmark our performance against commercially-available transmissometers to validate our breadboard to TRL 4.

Benefits: Current and future NASA missions for hyperspectral ocean sensing, such as PACE, GLIMR, and SBG, require in-situ instrumentation to measure inherent optical properties (IOPs) for model development and to ground truth remotely-sensed measurements for algorithm and data product validation. A robust in-situ hyperspectral transmissometer with comparable spectral bandwidth and resolution to these missions would directly support validation efforts by increasing the accuracy of and confidence in remote sensing data products. The proposed hyperspectral transmissometer would also complement other in-situ hyperspectral IOP instrumentation developed by our team for absorption and backscattering measurements, enabling full IOP closure from ultraviolet to near-infrared wavelengths. Along with this, simultaneous inelastic scattering measurements made by the instrument would simplify and improve in-the-field calibration procedures and enable new data product outputs to support science investigations in biogeochemistry, environmental monitoring, and other areas of Earth Science research within NASA. Scientists and researchers in government, academic, and industrial institutions studying ocean IOPs or using optical sensors for ocean science (e.g. biogeochemistry, radiometry, environmental monitoring) research would benefit from the proposed hyperspectral transmissometer. Complementary inelastic scattering measurements made by the sensor would improve upon the offerings of current transmissometers and increase the scientific potential of in-situ instrumentation.