Equatorial Box GP506 ac-s Processing Notes

Setup
For the Equatorial Box GP506 cruise, the WET Labs ac-s (s/n 007) was connected to a WET Labs DH-4 data logger. The logger
was connected to a PC laptop and configured to save WAP data stream to the PC hard disk. Files were logged hourly by the
WLHost software.

The ac-s was plumbed in a system containing an computer-controlled, electronically-actuated valve, diverting the flowing seawater
through a 0.2 micron filter for the first 10 minutes of every hour.

Data Processing
WET Labs WAP software (version 4.22) was used to extract binary WAP files into ASCII format.

Extracted data were divided into Transects (one for each leg of the cruise).

Each extracted ac-s ASCII hourly file was then run through an automatic processing routine, which performs the following processing:

a. removes data during the transition periods between filtered and unfiltered seawater;
b. discards spectra with "filter wheel discontinuity" values in a or c > 0.002 1/m.
c. discards any spectra containing value outside of high and low thresholds; thresholds are calculated (based on 5th and 95th ptile) for each wavelength independently over 1 minute bins
d. bins data to 1-minute intervals, with a MATLAB datenum time assigned to the leading edge of each bin; and
e. saves data as hourly files containing 1-minute binned data.

Timeseries of binned a,c are loaded from file using Load_ACS_Binned and further processed using Calc_ACS_apcp:

a. Separate filtered water measurements
b. Calculate particle ap,cp by difference using linear interpolation between filtered measurements
c. Residual temperature and scattering correction applied to absorption spectra (described in Slade et al 2008 in prep)
d. Calculate bp by difference (note that apcorr and bp wavelengths do not match cp wavelengths)

Whole transects of data were then saved to .mat format (TransectX\ACS_apcp_TransectX.mat).