About this manual
The purpose of this publication is to provide the descriptions, procedures and detailed parameter explanations required to allow for safe and efficient use of the ST90 system. The publication also provides you with a thorough understanding of the parameters and adjustments provided by the ST90 system.
Simrad ST90
Operating procedures
- Getting started
- Choosing operating mode and key transmit parameters
- Controlling the gain and range settings
- Using the markers and tracking features
- Improving the recognition of fish and schools using receiver filters
  - About the receiver filter sequence in the ST90 system
    The filters in the ST90 system are implemented in “series�?. Any changes to a filter setting may therefore have an effect on subsequent filters.
  - Reducing noise and reverberation with the AGC (Automatic Gain Control) function
    Identifying echoes from fish and schools can often be challenging when they are hidden by noise and reverberation. When sonar conditions are poor, effective tuning of the filters in the ST90 system may be necessary to achieve a satisfactory result. Automatic Gain Control (AGC) is one of the tools provided to remove noise and reverberation from the echo presentation.
  - Reducing propeller noise and interference with the Noise Filter
    Unless you synchronize the transmissions from your other hydroacoustic systems you may have an issue with interference. Even with synchronization activated the noise from other nearby vessels may cause noise.
  - Reducing bottom and surface reverberation with the RCG (Reverberation Controlled Gain) function
    When you transmit an acoustic pulse into the water to search for a target, echoes will also be returned from any other objects in the beam. The energy reflected from these "unwanted" objects is referred to as reverberation. Reverberation is often a limiting factor, especially if you are searching for smaller targets.
  - Reducing noise and false echoes with the Ping-Ping Filter
    The Ping-Ping Filter analyses the historical information from previous consecutive pings in order to remove unwanted noise and interference from the echo presentation.
  - Reducing the strong bottom echo to see fish close to the seabed
    Fish close to the bottom can be hard to see because they may be hidden in the strong bottom echo.
  - Adjusting the intensity of the echo presentations
    The effect of the Gain adjustment is minimized if you apply RCG (Reverberation Controlled Gain) and AGC (Automatic Gain Control). The Display Gain is applied at the end of the filter sequence in the ST90 system. This means that you can use Display Gain if you are not completely satisfied with the results of the automatic gain functionality.
- Recording and replaying echo data
- Recording and exporting processed echo data
- Capturing the display presentation in image and video files
- Setting up presentation modes and views
- Defining the visual information in the sonar views
- Defining settings related to user preferences and individual customizing
- Saving, retrieving and maintaining user settings
- Defining the user-selected features on the Operating Panel
- Exporting sensor data, marker positions and technical information
Maintenance procedures
User interface
Menu system
Functions and dialog boxes
Concept descriptions
Technical specifications
The technical specifications summarize the main functional and operational characteristics of the ST90 system. They also provide information related to power requirements, physical properties and environmental conditions.
Datagram formats
The ST90 system can send and receive information to and from several different peripherals. All transmissions take place as datagrams with data sentences. Each datagram has a defined format and length.
***

Reducing the strong bottom echo to see fish close to the seabed

Fish close to the bottom can be hard to see because they may be hidden in the strong bottom echo.

The ST90 system provides a bottom filter to reduce the sometimes powerful echo from the seabed. This filter is useful if you try to find fish close to the bottom.

Procedure

Click in any view to make it active.
The active view is identified with a thicker border.
Open the Active menu.
Select Target Threshold.
Select a value from the options provided.
Select a Target Threshold value to control the "strength" of the filter. A higher numerical value increases the filter efficiency and reduces the bottom echo accordingly.
The choice you make is by default only applied to the currently selected (active) view.
Select the middle of the button to open a small menu with the available options. Select the left side of the button to select a "lower"' menu choice. Select the right side of the button to select a "higher"' menu choice.