The Map View
The Map View provides a base-map over which the sonar track is displayed. If the sonar log contains side-scan, then the side-scan data is displayed in the appropriate location. By default, side-scan data is slant-range corrected, which means that the water-column is removed and the sonar returns are stretched so that they are shown in the correct geographical location. The current position of the sonar viewer playback is shown as a boat icon.
The Map View Control Panel
The map view control panel slides into view when the mouse pointer is held near the left edge of the map display and controls the display of side-scan data in the map view.
All options that are changed are saved on a per-log basis, and restored the next time that the sonar log is loaded. Changed options also become default options for when a new sonar log is loaded into the sonar viewer for the first time.
The overall brightness of the side-scan image can be adjusted using the brightness slider.
Contrast within the side-scan image can be adjusted using the contrast slider.
The ReefMaster Sonar Viewer includes a sophisticated auto-gain feature that equalises return strength across the sonar range. This reduces the darkening of the image with increasing sonar range:
Full auto-gain (left) versus no auto-gain
The auto-gain strength can be adjusted by using the auto-gain slider; with the slider at maximum (all the way to the right), auto-gain is fully enabled, whilst auto-gain is completely disabled when the slider is at minimum. Values between maximum and minimum result in an interpolated value.
4. Slant range correction
Slant-range correction is the process that removes the water column and stretches the remaining signal returns so that they are located in the correct geographical positions:
The same section of sonar log, with (left) and without slant-range correction
By default, side-scan is shown in the map view with slant-range correction enabled, as this places sonar returns in (approximately) the correct location. Slant-range correction can be disabled in the map view by clicking the slant-range correction toggle button. Disabling slant-range correction in the map view can be useful when reviewing tracks to observe the water column or features that would otherwise be obscured.
Note that when slant-range correction is disabled, side-scan signal returns in the map view are not correctly located.
Slant-range correction should always be enabled when marking the locations of features within the map view.
5. Side-scan signal priority
Side-scan signal priority controls how overlapping side-scan swaths are drawn:
Closest, Latest and Earliest signal priorities
·Closest signal gives priority to the signal return that is closest to the transducer. For example, if a side-scan swath overlaps so that returns at 10m and 25m distance from the transducer are located in the same position, the 10m signal return will be drawn. Closest signal usually provides the highest quality side-scan image and is the default.
·Latest signal draws later parts of the swath on top of earlier returns. Latest return can be useful when reviewing a track in conjunction with the Limit swath to position option (see below), as it ensures that the signal return at the current (latest) position is always visible.
·Earliest signal draws earlier parts of the swath on top of later returns.
The colour palette for the side-scan display can be chosen from the drop-down list. The palette list includes multi-colour palettes for 2D sonar as well as monochrome palettes more suitable for side-scan displays:
6. Noise reduction
Noise can be introduced into sonar returns as a result of electrical interference or other reasons, and can be particularly intrusive in areas of weaker returns.
Noise reduction removes individual sonar returns that conform to a particular noise "profile", and can dramatically improve the appearance of both side-scan and 2D sonar images:
No noise reduction, x1 noise reduction and x2 noise reduction
To enable noise reduction, select the Noise Reduction check-box (1). Noise reduction is available in two variants, x1 and x2, which can be selected using the drop-down list (2). x1 is the least aggressive, usually removing a substantial amount of noise with little affect on the integrity of the remaining sonar image. x2 is a more aggressive noise reduction technique that removes more noise, but may also produce a more noticeable effect on the sonar image.
8. Limit swath to position
Limit swath to position limits the drawing of the side-scan swath, so that it is only drawn up until the current position of the sonar viewer. In addition, the centre of the map view is locked to the current sonar position whilst this option is enabled:
The position can be updated using sonar playback or via the sonar control bar, or by panning the any of the individual sonar viewer channel views.