Manual

June 2004 Isis® Sonar User's Manual, Volume 2 114
Appendix G How Isis Processes CTD Data
Conductivity, turbidity, and density of water play an important role in determining the velocity
of sound. Water’s CTD can vary significantly from place to place and time to time, as can the
speed of sound. This appendix describes how Isis interacts with CTD when those parameters
are processed through a SeaBird or Falmouth Scientific device.
G.1 Overview
Isis reads the file ISIS.CTD when you first start Isis. ISIS.CTD contains calibration data used
in computing values from CTD data. The file is ASCII and can be readily changed with any
editor.
Different devices, such as SeaBird or Falmouth Scientific, require different input from the
ISIS.CTD file. Consequently, you will want to tailor the contents of ISIS.CTD to match the
needs of the different devices.
Instead of modifying the original isis.ctd file, it is best to copy isis.ctd to
another file and then use the copy as your working ctd file. After you
modify the copy, you would then copy it back onto isis.ctd so that Isis
can use it when you next run the software.
For example, the file SIS7000.CTD contains the calibration coefficients for that sonar’s CTD.
Change the data in that file and copy SIS7000.CTD to ISIS.CTD before running Isis.
G.2 How Isis Treats SeaBird CTD Data
Data from a SeaBird CTD device is entered into Isis via the serial port. The following serial
template characters relate to the various raw CTD parameters:
Q Conductivity Frequency (Hz)
{pf} Pressure Frequency (Hz) or Fish Depth (m)
b Temperature Frequency (Hz)
; Pressure Temperature (Degrees C)
| Turbidity (0 to +5 volts) (optional; use “pipe” symbol)
After Isis gets the serial port information above, the following steps are performed:
1. If a manual depth has
not been set (in Configure, Transducer Depth), and both
pressure frequency and pressure have been received as non-zero values, then
the towfish depth (in meters) is computed. The depth computation is based on
pressure frequency and pressure temperature. The result is Towfish Depth.
Appendix G: How Isis Processes CTD Data