Reson Seabat 8101

System OperationBoth the absorption (α) and spreading loss values can be changed by the operatorat the Ocean Menu using the menu items ABSORB and SPREAD. Whenswitching between FIXED and TVG gain modes, the last gain value in each categoryis restored upon selection.3.4.7 AutoGainThe automatic receiver gain function analyzes the bottom return and automaticallyincreases or decreases the receiver gain accordingly. The AutoGain menuitem controls the level of signal amplitude threshold to which the sonar return iscompared.Operator settings are OFF and 1 to 10. The lower the selected number, the lowerthe threshold and therefore, the lower the gain setting selected by the SonarProcessor. A typical setting is 4. However, the optimal setting will vary with bottomtype and other environmental conditions.NOTEGood bottom detect conditions must be present before the AutoGain function willperform properly.3.5 Ocean MenuThe Ocean Menu allows the operator to enter various correction factors to compensatefor changing environmental conditions. Menu selections are:3.5.1 SpreadThis selection allows the operator to enter the amount of cylindrical and sphericalspreading loss that is expected through the ambient water medium. This coefficientvalue is used in conjunction with the absorption loss value (ABSORB) torecompute the TVG curve that will be applied to the returned signal (see theGainMode menu selection). The range available is from 0 to 60. An initial valueof 30 is recommended.3.5.2 AbsorbThis selection allows the operator to enter the amount of loss expected throughthe ambient water medium. This value is used in conjunction with the spreadingloss value (SPREAD) to recompute the TVG curve as described above. Therange available is from 0 to 120 dB/km. If the exact value is not known, a value of70 dB/km for salt water and 20 dB/km for fresh water is recommended.3.5.3 VelocityThe displayed value is the speed of sound through the local water at the SonarHead (in meters per second) that the Sonar Processor will use in projector steeringcomputations. Output data packets are not corrected for a sound velocity pro-______________________________________________________________________SeaBat 8101 Operator's Manual 3-7 Version 3.02