Andrew Winkelman
 NOAA/GLERL
 2205 Commonwealth Blvd.
 Ann Arbor, MI  48105-2945
 Phone:    (734) 741-2336
 Fax:      (734) 741-2055
 e-mail:   andy.winkelman@noaa.gov

Surface transmissometry profiles were taken with a Sea-Bird Electronics Seacat Profiler 
(model # SBE 19) Sea-Bird Electronics, Inc. Bellevue, WA.  The Seacat Profiler has the 
ability to sample its sensors at a programmable rate of up to 2 hertz.  Because of the 
long time period over which these surface profiles were done (several hours), the 
sampling rate was reduced to 1 'scan' every 5 seconds. 

Water was pumped on board ship and into a flow through chamber which housed the 
transmissometer.  To reduce the size of the flow chamber, the transmissometer was 
detached from the CTD unit and placed by itself in the chamber.  While giving smaller 
turnover time, this setup did not allow for any of the other usual CTD parameters to 
be measured (temperature, conductivity, fluorescence, etc.).  A Cole-Palmer 
peristaltic pump was used to bring the water on board and was calibrated for flow 
speed before each transect (~4L per minute).  Tygon tubing was used as the transport 
hose and sampled the lake water from about 1m below the surface.  Approximately a 1 to 
2 minute lag time was needed for the water to travel from the lake to the transmissometer
sensor area.   

Data was downloaded from the CTD unit after each transect in the form of the scan number 
and transmissometry value.  Start and end times and locations were recorded from GPS 
receivers onboard the ship.  This data was then linked to PSS time, location, and depth 
data from the same transect (see Meta data file Met28).  

Transmissometry was measured using the in situ transmissometer  (Output is 0 - 5 Volts, 
5 Volts = 0/m, 0 Volts =  55.262/m).  Total suspended matter (TSM) is derived from 
transmissometry output of beam attenuation coefficient (Atten).  Regression developed 
by A. Winkelman (GLERL) using water samples and CTD transmissometry from surv-1999-067 
cruise for 1999 and surv-2000-063, -070, -101, -108, and -116 for 2000:

        For 1999:
        TSM (mg/L) = (2.39) * Atten - 1.98
        N = 44, r^2 = 0.99

        For 2000:
        TSM (mg/L) = (1.65) * Atten Ð 0.86
        N = 51, r^2 = 0.99