Understanding the Limitations of Thermal Imaging Cameras Underwater

Thermal imaging cameras are widely used across industries for their ability to visualize heat signatures and detect anomalies invisible to the naked eye. However, their performance in underwater environments is fundamentally restricted. This white paper explores the scientific limitations of thermal imaging technology in aquatic applications, discusses why conventional thermal cameras are unsuitable for underwater use, and outlines practical alternatives for underwater detection and diagnostics.

 

1. Introduction to Thermal Imaging Technology

Thermal cameras operate by detecting Infrared Radiation.  Electromagnetic waves emitted by objects based on their temperature. Unlike visible light, infrared energy reveals heat patterns, which can be converted into digital images known as Thermograms.

While this capability has proven invaluable in fields such as electrical diagnostics, building inspections, and search and rescue, it is essential to recognize the boundaries of this technology in specific environments, particularly underwater.

 

2. Why Thermal Imaging Fails Underwater

a) Infrared Absorption by Water

Infrared Radiation is almost entirely absorbed by water within the first few millimeters. This means that even in crystal-clear water, thermal radiation from submerged objects cannot travel far enough to be detected by the camera. As a result, the camera cannot "see" heat through water in the way it can through air.

b) Lack of Infrared Transmission

Unlike visible light, which can pass through water to a limited extent, infrared wavelengths do not transmit effectively underwater. This physical limitation renders thermal imaging ineffective for detecting subsurface temperature variations.

 

3. Equipment Vulnerability to Water

Most commercially available thermal imaging cameras are not built to withstand submersion. They are typically designed for dry, terrestrial environments and are not waterproof unless explicitly specified.

Even brief exposure to water can damage the sensitive electronics within the device. While rugged or IP-rated models offer water resistance to some extent (e.g., splashes or rain), full submersion requires specialized waterproof housings, and even then, the optical limitations of infrared in water still apply.

 

4. Surface-Level Use Cases

Thermal cameras can still be useful above water for detecting temperature variations on:

• Water surfaces (e.g., leaks, discharge points)
• Objects at or just above the surface (e.g., wildlife, human bodies, vessel engines)
• Pipes or tanks containing hot fluids, where heat is transferred to the external surface

These cases are limited to line-of-sight, above-surface applications where heat is emitted or reflected.

 

5. Alternatives for Underwater Detection

For underwater inspection or detection tasks, other technologies are recommended:

• Sonar imaging – Ideal for structural or object detection underwater.
• Underwater cameras (optical) – Useful in clear water and well-lit conditions.
• Diver-held instruments – Including contact thermometers or probes for specific temperature readings.

 

6. Conclusion

While thermal imaging offers unparalleled diagnostic capabilities in many industrial and environmental applications, its use underwater is severely constrained by the physics of infrared transmission in water and equipment design limitations. Professionals requiring underwater diagnostics should seek appropriate tools tailored to aquatic environments, rather than relying on thermal imaging.