Manual revision 041
Section 6: Troubleshooting
SBE 37-SM RS-232
69
Problem 4: Salinity Spikes
Salinity is a function of conductivity, temperature, and pressure, and must be
calculated from C, T, and P measurements made on the same parcel of water.
Salinity is calculated and output by the 37-SM if
OutputSal=Y
. Alternatively,
salinity can be calculated in SBE Data Processing’s Data Conversion module
from the data uploaded from memory (.hex file) or in SBE Data Processing’s
Derive module from the converted (.cnv) file.
[
Background information
: Salinity spikes in
profiling
(i.e., moving, fast
sampling) instruments typically result from misalignment of the temperature
and conductivity measurements in conditions with sharp gradients. This
misalignment is often caused by differences in response times for the
temperature and conductivity sensors, and can be corrected for in post-
processing if the T and C response times are known.]
In
moored,
free-flushing instruments such as the 37-SM MicroCAT, wave
action, mooring motion, and currents flush the conductivity cell at a faster rate
than the environment changes, so the T and C measurements stay closely
synchronized with the environment (i.e., even slow or varying response times
are not significant factors in the salinity calculation). More typical causes of
salinity spikes in a moored 37-SM include:
Cause/Solution 1
: Severe external bio-fouling can restrict flow through the
conductivity cell to such an extent that the conductivity measurement is
significantly delayed from the temperature measurement.
Cause/Solution 2
: For a MicroCAT moored at shallow depth, differential
solar heating can cause the actual temperature inside the conductivity cell to
differ from the temperature measured by the thermistor. Salinity spikes
associated mainly with daytime measurements during sunny conditions may
be caused by this phenomenon.
Cause/Solution 3
: For a MicroCAT moored at shallow depth, air bubbles
from breaking waves or spontaneous formation in supersaturated conditions
can cause the conductivity cell to read low of correct.
