Sonar images of bodies: What they actually look like and why it matters

If you’ve spent any time on true crime forums or deep-sea recovery threads, you’ve probably seen them. Those grainy, neon-yellow or ghostly blue shapes on a dark background. People claim they see a shoulder, a limb, or a torso. But here is the thing: sonar images of bodies rarely look like what you see in the movies. It’s not a clear photograph. It’s sound.

Most people expect a medical X-ray. Instead, they get a smudge.

Understanding how we find things underwater has changed radically in the last decade. It’s a mix of high-end physics and a weird kind of "eye" that recovery experts develop over years of staring at static. When a person goes missing in a lake or an ocean, the clock starts ticking, and the technology used to find them is both incredible and frustratingly limited.

The weird physics of seeing with sound

Sonar stands for Sound Navigation and Ranging. It’s basically screaming into the dark and timing how long it takes for the echo to bounce back. Simple, right? Not really. When you’re looking for sonar images of bodies, you aren't looking for the body itself. You're looking for the acoustic shadow.

Imagine holding a flashlight against a textured wall in a pitch-black room. If there is a small bump on that wall, the light hits it, and a long shadow stretches out behind it. Side-scan sonar works the exact same way. The "towfish" (the device dragged behind a boat) sends out a fan-shaped beam. When that beam hits a human shape, the sound bounces back—that’s the bright spot. But behind that shape, where the sound couldn't reach, is a dark void.

That shadow is where the detail lives.

Experts like Gene Ralston, who is legendary in the search and recovery world, don't just look at the bright "return." They look at the shape of the shadow. A shadow might show the bend of a knee or the extension of an arm in a way the actual reflection doesn't. It’s eerie. It’s precise. And it takes a massive amount of mental processing to translate those blobs into a "target" for a dive team.

Why bodies are so hard to spot

Water is a nightmare for sensors. You’ve got thermoclines—layers of different water temperatures—that can literally bend sound waves. If a body is lying in a forest of sunken trees or a field of boulders, the sonar images of bodies become almost impossible to distinguish from the debris.

Human beings are "soft targets." Unlike a sunken aluminum boat or a steel pipe, a body doesn't reflect sound particularly well. We are mostly water. This means the density of a body is sometimes too close to the density of the surrounding water for the sonar to get a "hard" hit.

Then there is the decomposition factor.

As time passes, gasses build up. A body might bloat and rise, or it might settle into the silt. If it’s buried in mud, sonar won't see it at all. You’d need sub-bottom profiling for that, which is a whole different ballgame. In places like Lake Tahoe, which is incredibly deep and cold, bodies can be preserved for decades, maintaining a distinct shape that sonar can pick up. In warmer, shallower water? You might only have a few days before the "shape" becomes unrecognizable to the equipment.

High-Frequency vs. Low-Frequency

Not all sonar is created equal. If you use a low-frequency 100 kHz unit, you can see a long way—maybe 500 meters on each side—but the resolution is garbage. You’ll see a sunken ship, but you won't see a person.

To get actionable sonar images of bodies, searchers usually crank it up to 600 kHz or even 1200 kHz. The range drops significantly, sometimes to just 20 or 30 meters, but the "pixel" size shrinks. This is where you start seeing the "human" outline.

Real-world tech: SAR and ROVs

In the 2014 search for the Sewol ferry in South Korea, or the tragic recovery efforts following the Baltimore bridge collapse in 2024, sonar was the frontline. In Baltimore, divers were working in "zero visibility." They couldn't see their own hands. They relied on "imaging sonar" mounted on their helmets or handheld units that provided a real-time top-down view of the wreckage.

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These aren't the side-scan units towed behind boats. These are "multibeam" or "scanning" sonars.

Think of it like this:

• Side-Scan: Good for mapping a large area of a lake bed quickly.
• Multibeam: Provides a 3D-like topographical map.
• Sector Scanning: Stationary, high-res "photograph" of a specific spot.

When a potential target is found on a side-scan tow, the team doesn't just send a diver down immediately. That’s dangerous. Instead, they drop an ROV (Remotely Operated Vehicle). These little underwater drones are equipped with their own sonar and high-def cameras. They get close. They verify. Only then does the recovery begin.

Misconceptions about "Blue" Sonar

You’ve seen the images on news reports. They look like high-contrast blue and white photos. Honestly, that’s just a color palette chosen by the operator. Most professional software like SonarWiz or SAR-HAWK allows you to toggle between "copper," "rainbow," or "grayscale."

Grayscale is often the best for finding sonar images of bodies. Why? Because the human eye is much better at detecting subtle changes in grey shading than in bright colors. A slight variation in the shadow of a rock might reveal the strap of a backpack or the curve of a skull.

The psychological toll of the image

There’s a reason you don’t see the raw files of these images released to the public often. They are haunting. Even though they are just "sound maps," the realization of what you are looking at hits hard. Search and rescue professionals talk about the "moment of recognition." It’s when a shape on the screen stops being a "topographical anomaly" and starts being a person.

It’s heavy work. It requires a clinical detachment to analyze the data points while maintaining the respect required for the recovery.

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How to actually read a sonar scan

If you ever find yourself looking at these files—perhaps as a hobbyist or someone interested in maritime history—there are three things to look for.

First, look for straight lines. Nature doesn't like straight lines. If you see a perfectly straight edge, it’s man-made. It’s a dock, a boat, or a piece of wreckage.

Second, look for symmetry. The human body is symmetrical. Even in a distorted sonar image, the presence of two similar shapes (legs or arms) protruding from a central mass is a huge red flag for searchers.

Third, look at the shadow length. By measuring the length of the shadow and knowing the height of the sonar sensor above the bottom, you can use basic geometry to calculate the height of the object. If the object is roughly 5'10", you’ve got a high-probability target.

$H_o = \frac{H_s \times L_{sh}}{L_{sh} + R}$

Where $H_o$ is the height of the object, $H_s$ is the height of the sensor, $L_{sh}$ is the length of the shadow, and $R$ is the range. Most modern software does this math for you instantly. You just click and drag a line from the base of the object to the end of its shadow.

The future of the search

We are moving into the era of AI-assisted detection. Synthetic Aperture Sonar (SAS) is the new gold standard. It provides resolution that is literally ten times higher than traditional side-scan. Companies like Kraken Robotics are creating systems that can "stitch" together sound pulses to create images that look almost like black-and-white photography.

In the past, a human had to stare at a scrolling screen for 12 hours straight. Fatigue leads to missed targets. Now, machine learning algorithms can flag "human-shaped anomalies" in real-time. It’s not replacing the expert, but it’s giving them a second set of eyes that never gets tired.

Actionable steps for maritime search or interest

If you are involved in a search, or if you are a diver interested in the tech, here is how you approach it properly:

1. Check the Frequency: Ensure you are using at least 600 kHz for SAR (Search and Recovery) operations. Lower frequencies will skip right over a body.
2. Control Your Speed: You cannot "speed" and get good sonar images of bodies. 2 to 3 knots is the sweet spot. Any faster and you get "motion blur" in the acoustic data.
3. Vary the Angle: If you see something suspicious, don't just pass it once. Circle back and image it from 90 degrees and 180 degrees. Shadows change based on the angle of the "light" (sound). A rock might look like a person from the north, but look like a rock from the east.
4. Manage Expectations: Sonar is a tool, not a miracle. It requires clear water (acoustically speaking), the right equipment, and an operator who knows that a "blob" isn't always just a blob.
5. Use Post-Processing: Don't rely on the tiny screen on the boat. Take the raw data and run it through software like ReefMaster or SonarTRX on a large, high-resolution monitor. The details you miss on the water will jump out at you in the office.

Understanding the limitations is just as important as understanding the capabilities. Sonar images of bodies provide closure for families and critical data for investigators, but they require a blend of high-tech hardware and very human intuition to interpret correctly.