imaging: down, side and live sonar
How to read down imaging, side imaging and live sonar to find structure, confirm fish and get back to the right spot.
what each technology does
Traditional sonar (2D) shows echoes from a cone. Imaging uses high frequencies in a thin beam, like a slice, and builds an almost photographic image. Live sonar shows in real time what is in front of or below the boat, including the bait. Each answers a different question.
tips
- Down imaging (DownVü, DownScan, DI): a thin slice under the boat. It shows the drawing of branches, rock, fallen trees and vegetation. Fish appear as a clear dot or streak, not as an arch.
- Side imaging (SideVü, SideScan, SI): slices to both sides of the boat. It sweeps a wide strip and is the best tool for finding new structure.
- Live sonar (Garmin LiveScope, Lowrance ActiveTarget, Humminbird MEGA Live): real-time imaging, with the fish moving and reacting to the bait.
- In imaging, a lower frequency (about 455 kHz) reaches farther; a higher one (800 kHz or more) gives more detail and reaches less.
how to read down imaging
The bottom appears as a light band. Everything rising from it takes shape: a branch becomes a thin branched line, rock becomes a light block, vegetation looks like fur. Fish are white dots or streaks inside or near the structure. Use it in split screen with the 2D: the 2D shows there is fish, down imaging shows which structure it is in.
tips
- Travel at a steady speed, usually 5 to 10 km/h. Faster, and the image loses definition.
- Adjust the contrast until the bottom is clear without washing out.
- A fish touching a branch appears as a brighter spot than the branch itself.
how to read side imaging
The boat is in the middle of the screen and the image scrolls as it moves. The dark band in the center is the water column under the boat: the distance from the center to where the bottom begins, on each side, equals the depth. From there outward comes the bottom. Objects rising from the bottom reflect strongly (light) and cast a dark shadow outward. The longer the shadow, the taller the object.
tips
- Fish: a loose white dot in the water column or on the bottom, sometimes with a small shadow separate from it. A school becomes a cloud of dots.
- Range: in water up to about 6 m, start with 25 to 30 m on each side; in deeper water, increase it. Too much range in shallow water worsens the definition.
- Speed: a steady 5 to 10 km/h. Too slow stretches the image; too fast squashes it.
- Travel in a straight line. A turn distorts the image and makes the same object look crooked or doubled.
- Riverbanks and depth drop-offs appear as sudden changes in texture and long shadows.
- Hard bottom reflects brighter; mud and loose sand look darker.
live sonar
The transducer goes on the axis of the electric motor or on a swivel pole. You point to where you will cast and see structure, fish and bait in real time. The useful range is usually between 15 and 30 m, depending on the water and the model. The beam is wide vertically and narrow horizontally: only what is in that slice appears.
tips
- Forward mode: a vertical slice ahead of the boat. Best for finding suspended fish and casting to them.
- Downward mode: for vertical fishing; you see the jig falling and the fish rising.
- Perspective mode: a view from above, like a map. Good in shallow water for watching fish move around.
- Apparent size deceives: the same fish looks bigger near the transducer and smaller farther away.
- A fish moves and changes shape; a branch stays still.
- Cast past the target and bring the bait into the beam. If the fish follows and gives up, change the pace or the bait.
common mistakes
- Getting stuck on the screen and forgetting navigation and safety.
- Working the same fish dozens of times. Pressured fish learn; give the spot a rest.
from the image to the waypoint
The workflow is to sweep with side imaging, mark, confirm with down imaging and 2D, and only then fish.
- On the map, choose change areas: points, channels, depth drop-offs, bay and igarapé mouths.
- Make passes parallel to the bank or the channel, in a straight line and at steady speed, with side imaging on.
- When you see an object with a shadow, don't stop on top of it. Finish the pass.
- Pause the screen or scroll back in history, put the cursor over the object and create the waypoint at the cursor's position, not the boat's.
- Give it a name that says what it is, like timber 4 m or rock 7 m.
- Go back over the spot with down imaging and 2D to confirm the structure and see if there is fish.
- Position the boat at casting distance, with the wind or current in your favor, and use the virtual anchor if you have one.
- Cast, bringing the bait past the structure from several angles.
tips
- GPS is off by a few meters. When you return to the spot, confirm it on the screen before casting.
- Remember the lag: what appears in the middle of the screen has already passed.
- Mark places where nothing happened too. Knowing what to rule out saves the day.
checklist
Check off what's ready. Saved on this device.
sources and references
- technical Humminbird — Understanding Transducer Frequencies and Cone AnglesSide and downward imaging at 455 kHz, 800 kHz and MEGA, with the range of each; 2D at 50, 83 and 200 kHz.
- technical Garmin — ECHOMAP UHD2 6/7/9 sv Owner's Manual: Garmin SideVü Sonar ViewHow the side imaging view is displayed and read.
- technical Garmin — LiveScope Plus LVS34 Transducer Installation InstructionsVersion 4, Apr./2025. Mounting on the shaft and tube of the electric motor, on a pole and on the Perspective mode bracket.
keep reading
basic sonar: how to read the fishfinder
Understand how sonar sees underwater, what each mark on the screen means, and how to adjust the unit to find bottom, structure and fish.
boating and travelGPS and marking spots
Waypoints, routes, tracks, nautical charts, and how to save and share fishing spots without losing secrecy or safety.
boating and travelbow-mount electric motor
What it's for, how to use the virtual anchor, sizing the battery and range, and reaching structure without spooking fish.