A global end-member approach to derive <i>a</i><sub>CDOM</sub>(440) from near-surface optical measurements

Abstract

This study establishes an optical inversion scheme for deriving the absorption coefficient of colored (or chromophoric, depending on the literature) dissolved organic material (CDOM) at the 440 nm wavelength, which can be applied to global water masses with near-equal efficacy. The approach uses a ratio of diffuse attenuation coefficient spectral end-members, i.e., a short-and long-wavelength pair. The

Airborne Radiometry for Calibration, Validation, and Research in Oceanic, Coastal, and Inland Waters

“…This approach is fundamentally different from traditional calibration methods which typically rely on fixed location and custom-built above-and in-water optical sensor packages maintained in one location, e.g., the Marine Optical Buoy (MOBy) and Bouée pour l'acquisition de Séries Optiques à Long Terme (BOUSSOLE) projects (Clark et al, 2003;Antoine et al, 2008, respectively) which cannot be opportunistically deployed across different regions and are generally not optimized for measurement of shallower and more complex inland water bodies. The approach described here provides calibration-level performance for ocean color from fixed platforms as well as airborne observatories; when flown at LSA, the requirement for complex atmospheric correction is removed, while the 10decade dynamic range allows the same sensors to operate equally effectively in water ranging from extremely clear to highly turbid, including red tides (Hooker et al, 2018a,b,c;Kudela et al, 2019), and across an expanded spectral range that improves algorithm performance for a global range of water bodies (Hooker et al, 2020;Houskeeper et al, 2021). The 15 Hz version of C-AERO already met or exceeded all recommendations for SNR from the aquatic remote sensing community (Kudela et al, 2019), while the recent upgrade to 30 Hz sampling for the downward-viewing (L T ) radiometer has substantially increased the realized SNR for coastal waters.…”

“…The thrusters improve the planar and solar geometry of the light apertures, as well as increasing surface loitering while decreasing descent rate. The net effect of these improvements is a vertical sampling resolution (VSR) that is frequently 1 mm or less (Hooker et al, 2020), whereas C-OPS without C-PrOPS typically has a VSR of 1 cm (Hooker et al, 2013).…”

“…OCEANIA did not include the HIS or AATS-14 sensors. C-OPS was upgraded to include small digital thrusters (Hooker et al, 2018a) that improve the VSR to 1 mm or less (Hooker et al, 2020). Driving requirements for flight planning emphasized C-AIR observations without competing requirements from another sensor, as experienced with AATS-14 in COAST and C-AIR E s , L i , and L T radiometer configuration and integration was unchanged.…”

“…In-water validation data were collected aboard the R/V John Martin for COAST and OCEANIA, and from the Santa Cruz Municipal Wharf for C-HARRIER. Instrumentation (Table 1) included the C-OPS and HyperPro II profiling radiometers, MicroTOPS II sun photometer, and ancillary measurements of water quality parameters including total chlorophyll a (TChl a; Van Heukelem and Thomas, 2001), phytoplankton composition via microscopy (Lund et al, 1958), CDOM (Hooker et al, 2020), IOP, and standard oceanographic parameters (temperature, salinity) as described in Bausell and Kudela (2019) and Hooker et al (2020). Suspended Particulate Material (SPM) was not collected, but a United States Geological Survey (USGS) cruise in San Francisco Bay provided a range of concentrations from the same time period of 14.6-126.3 mg L −1 (n = 6) for San Pablo and Suisun bays (Grizzly Bay is in northern Suisun; Figure 1).…”

The MALINA oceanographic expedition: how do changes in ice cover, permafrost and UV radiation impact biodiversity and biogeochemical fluxes in the Arctic Ocean?

“…THAAs were determined as the sum of 18 dissolved amino acids using an Agilent high-performance liquid chromatography system equipped with a fluorescence detector (excitation: 330 nm; emission: 450 nm). Samples (100 µL) of filtered seawater were hydrolyzed with 6 mol L −1 hydrochloric acid using a microwave-assisted vapor-phase method (Kaiser and Benner, 2005). Free amino acids liberated during the hydrolysis were separated as o-phthaldialdehyde derivatives using a LiCrospher RP-18 or Zorbax SB-C18 column (Shen et al, 2012).…”