Teledyne 440, System Manual, Page: 120 / 256

6 – Operating Procedure
6-16 © Teledyne TSS DPN 402196 Issue 4.1
If the signal strength on any channel exceeds 5µV, perform another background compensation
procedure as described in
section "Background Compensation Procedure" on page 6-14 and then
continue the survey.
6.3.4 Seawater Compensation
The 440 system is based on being able to separate the different signals arising from seawater and
target. This allows the range to the target to be determined from two coils.
This is achieved by means of a signal processing routine, which differentiates the target signal from the
unwanted seawater signal on the basis of its slower decay rate. This process requires the provision of
two calibration parameters by the user. For convenience, they are pre-programmed into DeepView and
are selected on the basis of the approximate water temperature.
The seawater algorithm can reject the signals arising from the seawater to levels of approximately 5µV.
If the incorrect temperature band is selected, then this rejection worsens to perhaps 20µV. This error
voltage is still small in relation to target voltages at all but the most extreme ranges, so the impact of
selecting the incorrect band is not great. Further, the seawater error voltage increases as the ROV is
lifted off the sea floor. Generally, when tracking a target which is deeply buried the vehicle will be close
to the seabed, reducing the error voltage still further.
Select a band based on the approximate water temperature at the survey depth. Although surface
water temperature varies widely, below 200m the temperature is usually 4°C.
A manual compensation routine is available (see section 6.2.2.4 "Seawater ‘Active’ Compensation" on
page 6-24 and Appendix A "Operating Theory" ). This may be used if there is reason to suspect that the
pre-programmed parameters are not giving sufficient performance. This may occur in regions of
atypical salinity (such as the Black Sea) or in the presence of fresh water outfalls or vents. Teledyne
TSS recommends the use of the pre-programmed bands for the majority of surveys.
The parameters can also be affected slightly by the total water column depth. In situations where the
water depth is shallow and changing, manual compensation may be required. Please contact Teledyne
TSS for advice on this point.
6.3.5 Background Noise Profile
The Background Noise Profile allows the surveyor to measure spurious signals in the surveying vicinity
and identify if they will have an effect on the quality of the survey data. It also allows for identification of
areas that could be problematic during the survey.
This data can be logged to assist post-survey data processing and identification of any anomalies in
the survey data gathered. It also allows for the logged data to be replayed to highlight any problems
that occurred during a survey.
6.3.6 The Survey Operation
Normally, survey operations conducted using the 440 System will require only the Run Display screen
and other selections from the Operation Menu.
The following paragraphs describe how you should use the facilities of the 440 System during a survey.
They assume that you have completed the full target scaling and background compensation
procedures successfully.
6.3.6.1 Interpreting the Run Display Screen
The Run Display screen is the most informative screen available from the 440 System and would
normally be on permanent view during a survey operation.