Teledyne 440, System Manual, Page: 73 / 256

5 – Operating Software
DPN 402196 Issue 4.1 © Teledyne TSS 5- 7
NOTE
When a Target Scaling value of greater than 2000uV is used, the RunView display
colour scheme is modified. See section 5.3.2 "View Menu" on page 5-14 for a
detailed explanation of the relevant changes.
5.2.3.2 Threshold
Set an appropriate value for threshold.
High settings will make the 440 System less sensitive to noise but will also decrease its operating
range. The default setting of 15µV has proved to be suitable for the majority of survey operations.
However, Teledyne TSS recommend using 25µV to minimise noise sensitivity and maximise operating
range.
If the recommended threshold value of 25µV does not provide the performance requirements from the
system or it is not clear what the required threshold value should be, always use the default value of
15µV.
5.2.3.3 Seawater Compensation
The 440 System uses a compensation method to distinguish signals arising from seawater and the
target.
To do this, it is necessary for the software to know the conductivity of the seawater surrounding the
coils and ROV during the survey. The conductivity is strongly determined by the water temperature,
and for convenience this has been grouped into bands of 0-10
o
C, 10-25
o
C and >25
o
C.
Select a suitable band.
This assures that salinity is between 30 and 33 psu, in areas where salinity is high (e.g. Mediterranean)
or river outfalls reduce salinity (e.g. Black Sea) then manual compensation may be necessary. Refer to
Appendix A "Operating Theory" for further details.
Note that surface water temperature may be considerably higher than the temperature at depth. Below
200m, the water temperature is typically 4
o
C.
NOTE
The seawater rejection algorithm only functions correctly for ROV altitudes below
approximately 4m. Above this height the target signal may ‘jump’ even if no target
is present. This is not a deficiency in the system.
The seawater rejection algorithm has proven reliable, and gives only small errors
(30µV at 3m altitude) if the incorrect temperature band is selected. However, in
shallow or fresh water, performing a manual seawater compensation as explained
in appendix A may be beneficial.