Absorption Measurements from the Gulf of Maine: An Inter-Comparison of Instruments

The goal of remote sensing is to obtain quantitative and qualitative information about the constituents of natural waters from measurements of reflectance or ocean color. The shape and magnitude of these spectral measurements are related to the inherent optical properties of the water. The three main water constituents that contribute to the bulk inherent optical properties: phytoplankton, chromophoric dissolved organic matter (CDOM), and non-algal particles. In order to develop algorithms that derive information about these constituents from radiometric measurements, a large amount of in situ data must be collected from the region of interest. These measurements can be difficult to obtain due to instrumental constraints. This study focused on the inter-comparison of three different instruments designed to make absorption measurements: a Liquid Waveguide Capillary Cell (LWCC) coupled to a miniature spectrometer; multi- and hyperspectral in-situ attenuation and absorption sensors; and a benchtop spectrophotometer. Natural samples were measured in situ, on the ship, and on shore as part of the monitoring effort of the Coastal Ocean Observation and Analysis (COOA) center at the University of New Hampshire. Laboratory experiments were performed to further investigate inter-instrument differences. Preliminary results of CDOM absorption measurements made with the benchtop spectrometer and using the waveguide setup exhibited a strong correlation (R=0.993).