County collects monthly in situ water column profiles at its offshore monitoring
stations using a CTD. A CTD is a multi-sensor array that measures dissolved oxygen,
salinity, temperature, density (calculated), transmissivity, photosynthetically
active radiation, and fluorescence (as a measure of chlorophyll). The sensor array
is deployed on a rosette; a round metal frame that also holds 12 Niskin sampling
bottles. The CTD collects water quality measurements 16 times a second (16 Hertz)
as it is lowered through the water column from the surface to the bottom (downcast)
and back up again (upcast).
The CTD also triggers the closure of the 5-liter Niskin bottles on the upcast at pre-programmed depths
to collect discrete water-column samples for laboratory analysis of additional parameters.
The water column profile data for each cast are averaged, or binned, over each 0.5
meters of the total depth. Please click on the station map to the left to download
CTD data for both current and historic sampling stations. Detection limits and methods
are described in the following table.
Light Transmission data prior to May 19, 2014 were referenced to air. After this date,
all Light Transmission data are referenced to water. To convert the pre-May 19, 2014 data
to ‘referenced to water’, multiply the values by 1.095.
WET Labs WETStar Fluorometer
Seabird SBE 4 Conductivity Sensor
Seabird SBE 29 Pressure Sensor
Seabird SBE 43 Dissolved Oxygen Sensor
Calculated from conductivity, temperature, and depth sensors
Potential density (minus 1000) from conductivity, temperature, and depth
WET Labs C-Star Transmissometer
LI-COR Surface Light Intensity (PAR) LI-190-SA-50
PAR (Water Column)
LI-COR Light Intensity (PAR) LI-193-SA-50
Calculated from conductivity and temperature sensors