Dataset: Biofloat_48 Wetlabs FLNTU chlorophyll sensor Profiles

Chlorophyll fluorescence (parameter name chl_raw_float) is reported as raw instrument counts without subtraction of dark counts.  Parameter name chl_raw is reported as instrument voltage output minus dark voltage (median in situ dark voltage = 0.083 volts); this parameter was intercalibrated with ship CTD, float and glider fluorometers and is reported as ship CTD volts.  

Chlorophyll a from fluorescence (parameter name chl_a_derived): Comparison of the chlorophyll fluorometers on the Knorr CTD and on float 48 with extracted chlorophyll from the R/V Knorr 193-03 water samples show clear depth and time dependences. Accordingly, a linear relationship between chlorophyll and fluorescence is abandoned in favor of a more complex, albeit empirical scheme. Counts from the float 48 fluorometer are converted to chlorophyll using a dark offset and a gain that has dependences on temperature, PAR, depth and yearday, with the gain and offset adjusted so that the float best matches the extracted chlorophyll at the R/V Knorr –float calibration casts (where nearly simultaneous profiles of the R/V Knorr CTD and float 48 were performed to 250 m). The resulting float 48 chlorophyll matches the bottles from both the R/V Knorr process cruise and R/V Bjarni deployment cruises with an error of 30-50%.  For more details see
Chlorophyll_Calibration-NAB08.pdf.