Abstract:

Optical absorption and scattering are the primary determinants of the flow of radiant energy in the ocean’s surface waters. Particles in the water are the principle source of scattering, and the scattering measurements can indicate the amount and/or type of particles present. While a complete measurement of the scattered light field is complex and cumbersome, a measurement of the backscattering at particular angles can usually be related to the total backscattering of light. The backscattering of light not only provides information about the particles present, it is important for understanding variations in remote sensing reflectance. We measure backscattering in the water with 6 channels (442, 488,532,589,620, 680 nm at ~140°) and 700 nm (at ~117°) scattering meters. These instruments also measure chlorophyll fluorescence. The instruments are lowered through the upper portion of the water column to obtain vertical profiles of the in-situ chlorophyll and CDOM fluorescence, as well as the amount and spectral shape of the backscattering. These profiles were made at most of the CTD sampling stations, but instrument constraints limit the depth of the scattering profiles to <300 m. This data was collected 2017-05-02 - 2017-05-12, during the same cruise (R/V Point Sur cruise PS17-21) as GRIIDC CTD dataset R4.x257.230:0013 (https://doi.org/10.7266/N7GM85P1).

Suggested Citation:

Chuanmin Hu. 2018. Near surface fluorescence and optical scattering profiles at CTD sampling stations, cruise DP05 (R/V Point Sur PS17-21), 2017-05-02 - 2017-05-12. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7TX3CQ8

Purpose:

The combination of in-situ backscattering and fluorescence measurements can be used to examine the amount and type of particles is the water column. Profiles of the measurements through the upper 200 m of the water column allow estimation of the vertical distribution of phytoplankton particles with little chlorophyll-a, and the concentration of dissolved colored material in the water column.

Data Parameters and Units:

Cruise ID Hydroscat; Cast ID; Cast time (DD-MMM-YY HH:MM); Latitude (decimal degrees); Longitude (decimal degrees); Station ID; Comment; Nominal depth bin (m); Average depth recorded for all measurements in depth bin (m); Columns (bb405-bb700) contain the particulate backscattering attenuation coefficient (per m) at the 6 wavelengths measured by the HOBILabs HS6 (405, 442, 448, 532, 590, and 700 nm); Estimate of in-situ chlorophyll a concentration (mg Chl/m^3) derived by scaling the HS6 700 nm fluorescence measurements with the chlorophyll concentration measured in water samples collected during the cruises' CTD casts (HS6 chlFl); Estimate of CDOM absorption (a/m at 400 nm) of 400nm light derived from the HS6's 532 nm fluorescence measurements scaled to water sample measurements (HS6 fl532 ag 400). The particulate backscattering estimate (1/m) for 700 nm light from the ECO-FLNT (FLNT-bbp700) Chlorophyll fluorescence (mg Chl/m^3) from the FLNT that have been scaled to measured values from CTD water samples (FLNT ChlFl) -999 = lack of comments; NAN = missing value

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