Estimate Height from a Sonar Shadow

Use this when

A target on the side-scan image casts a visible acoustic shadow. You can measure that shadow to estimate how tall the target is above the bottom. The result is a calculated height based on the water depth, the horizontal range to the target, and the shadow length.

Before you start

• You must be viewing the side-scan channel. The Shadow Height tool is only available on side-scan views.
• The target needs a clear shadow that extends from its base toward nadir (the center line). Shadows pointing away from nadir, or targets with no visible shadow, cannot be measured this way.

Activate the Shadow Height tool

1. Click the Shadow Height button in the toolbar, or press H.
2. The cursor changes to indicate the tool is ready.

Take the measurement

1. Click the base of the shadow (the point where it meets the target body). A dot appears.
2. Click the tip of the shadow (the far dark end). The tool measures the slant range between the two points and computes the estimated height, showing a readout on the canvas.

The calculation uses the sonar's recorded water depth and the horizontal distance from nadir to the target. Targets closer to nadir (center of the swath) give more accurate results.

Save or dismiss the result

After the second click:

• Add Contact — click this in the readout to create a new contact at that position with the height pre-filled.
• Click elsewhere — clears the measurement and returns to cursor mode.

Saved measurements appear in the Measurements list in the sidebar with a height icon and the value in your current units.

What you should see

A dashed line across the shadow with a readout showing the estimated height (for example, "H 1.2 m"). The value adjusts based on where you clicked relative to the nadir line.

If it does not work

• H key does nothing — Shadow Height is only active on the side-scan view. Switch to a side-scan channel first.
• Readout shows 0 — the two points may be at the same horizontal position, or the target is at nadir where the denominator of the calculation is zero. Try a target further from the center line.
• Result is much larger than expected — check that you clicked the shadow base first and the tip second, not the reverse. If the shadow base is hard to identify, try placing the first point at the visible edge of the target's bottom.
• Target has no shadow — targets resting in the nadir zone or targets in very shallow water may not cast a measurable shadow. Use the Ruler to measure length instead.