A dual mode camera is a type of camera that has two modes of operation – thermal imaging and visible light imaging. This allows the camera to capture both thermal images, which detect heat signatures, and regular visible light images. Having both capabilities in one camera makes dual mode cameras very versatile for a range of applications. Some key things to know about dual mode cameras:
How do they work?
Dual mode cameras contain two separate image sensors – one for detecting infrared radiation (heat signatures) and one for capturing visible light like a regular digital camera. The infrared sensor detects infrared radiation emitted from objects in the scene and forms a thermal image. The visible light sensor functions like a normal camera, capturing a visible light image from the same viewpoint. The two images can then be overlaid and fused together.
Use cases
Some common use cases for dual mode cameras include:
- Surveillance – the thermal imaging allows for monitoring in low light conditions or for detecting warm bodies
- Inspections – identifying heat leaks, electrical faults, moisture etc. in buildings or machinery
- Search and rescue – detecting living subjects in challenging environments
- Wildlife monitoring – detecting and identifying animals at night
- Firefighting – seeing through smoke to find people and identify hotspots
- Maritime navigation – spotting debris and obstacles in the water at night
Benefits
Key benefits of dual mode cameras:
- Operate in all conditions – the thermal camera works in total darkness and through smoke/fog
- Combination of vision modes provides more situational context
- Heat signatures are detectable even for hidden or camouflaged objects
- Thermal imaging allows temperature measurements
How thermal imaging works
Thermal cameras can see heat that is invisible to the naked eye. All objects emit infrared radiation as a function of their temperature. The hotter an object is, the more infrared radiation it emits. Thermal cameras detect this infrared radiation and convert it into an electronic signal that is then processed into a thermal image.
Infrared energy
Infrared energy sits between the visible light and microwave portions of the electromagnetic spectrum. It has longer wavelengths than visible light, meaning lower frequencies and lower energy. Infrared radiation is emitted by all objects based on their temperature. Even very cold objects like ice cubes emit infrared. As an object heats up, it emits more infrared radiation.
Infrared detection
Thermal camera sensors detect infrared radiation using materials that are sensitive to IR wavelengths. They convert the infrared energy into electrical signals that can be processed into thermal images. Common IR detector materials include:
- Microbolometers – made of materials that change resistance based on temperature. Detect IR by changes in resistance.
- InSb – indium antimonide semiconductors transform incoming infrared photons into electrons.
- InGaAs – indium gallium arsenide semiconductors also convert infrared into electrons.
Modern thermal cameras use detector arrays with thousands or tens of thousands of tiny infrared sensitive pixels to form high resolution thermal images. Sophisticated image processing is used to turn the raw electrical signals into precise temperature measurements.
Emissivity
The emissivity of an object describes how efficiently it emits infrared energy compared to a perfect blackbody at the same temperature. This must be accounted for to measure absolute temperatures accurately. Most natural materials like wood, water, skin etc. have emissivities of 0.90 to 0.98. Shiny metals can have lower emissivities.
Types of thermal imaging cameras
There are different types of infrared/thermal cameras optimized for different applications:
Cooled thermal cameras
Use cryogenic cooling to get the sensor array down to extremely low temperatures. This reduces thermal noise, improving sensitivity to detect the smallest temperature differences. Mainly used for research and high precision applications.
Uncooled thermal cameras
Use an uncooled infrared detector array that operates at room temperature. More convenient as they require no cooling system. Used in most applications outside of specialized science/research uses.
Shortwave infrared (SWIR) cameras
Sensitivity to shorter IR wavelengths from 0.9-1.7μm. Can see some visible light in addition to heat signatures. Used for imaging through fog, smoke and other particulates.
Midwave infrared (MWIR) cameras
Operate in the 3-5μm wavelength range. Best for detecting heat signatures of room temperature objects like human bodies. Common for thermography and surveillance uses.
Longwave infrared (LWIR) cameras
Used in the 8-14μm portion of the infrared spectrum. Sensitive to very small differences in heat making them ideal for detecting gases, moisture leaks, electrical faults etc.
| Camera Type | Wavelength Range | Key Applications |
|---|---|---|
| Cooled Thermal | MWIR or LWIR | Research, science |
| Uncooled Thermal | MWIR or LWIR | Thermography, surveillance, inspections |
| SWIR | 0.9 – 1.7 μm | Through smoke, agricultural monitoring |
| MWIR | 3 – 5 μm | People monitoring, firefighting |
| LWIR | 8 – 14 μm | Moisture detection, gas imaging |
Dual mode thermal/visible cameras
Dual mode cameras combine thermal and visible light imaging in one unit. This allows both infrared heat signatures and standard visible light images to be captured simultaneously from the same point of view.
Typical system design
There are two main approaches to building dual mode thermal/visible light cameras:
- Separate sensors – Two separate image sensors are used, one infrared and one visible light CMOS/CCD. The lenses are aligned side-by-side or in a beam splitting configuration to match the fields of view. Two separate images are generated and fused together in processing.
- Integrated sensor – A single integrated circuit contains both infrared and visible light pixels fused at the pixel level into a single combined detector array. Image processing provides a fused image. Requires sophisticated manufacturing.
Generally separate sensors allow higher resolution while integrated sensor chips are more compact. High end dual mode cameras even incorporate multiple different types of IR bands for advanced thermal imaging.
Key components
In addition to the infrared radiation sensor and visible light CMOS/CCD sensor, dual mode cameras include components like:
- Lenses – Made of IR transmitting materials. Can have coatings to equalize visible and IR light transmittance.
- Image processing – Combines the IR and visible images and provides image optimizations.
- Displays – Special displays are required to show both IR and visible images. Often OLED microdisplays.
- Camera housing – Rugged, stable platform to integrate components. Maintains alignment.
- Interfaces – Wired or wireless interfaces to transmit image data to external systems and displays.
- Power supplies – Provides stable power to the sensitive imaging systems.
Applications
As mentioned earlier, common applications of dual mode cameras include:
- Surveillance – monitored areas can be seen in all conditions
- Search and rescue – find people in darkness, fog, smoke etc.
- Inspections – get thermal and visual details on one image
- Public safety – police, firefighting
- Wildlife – identify and monitor animals at night
- Maritime – spot debris near ships to avoid collisions
Having both infrared and visible light images fused together provides far more situational information and context compared to single mode cameras. This makes dual mode thermal cameras ideal for public safety and security uses where visibility is limited and discerning warm bodies or hotspots is critical.
Choosing a dual mode camera
Key factors to consider when selecting a dual mode thermal/visible camera:
Infrared resolution
Thermal imaging resolution is much lower than visible light resolution. Typical IR resolutions range from 160×120 pixels up to 640×480 for high end cameras. Match resolution to your application’s needs.
Field of view
Narrow fields of view enable imaging at longer distances while wide fields are good for seeing the full area close-up. A good match between IR and visible FOV is important.
Thermal sensitivity
The camera’s ability to discern tiny temperature differences. Get the highest sensitivity your budget allows. Under 0.05°C is excellent.
Image detail
More expensive cameras have finer pixel sizes and better IR image processing for sharper, cleaner images.
Ruggedness
Important for outdoor applications. Look for ratings like IP67 water resistance and ability to withstand shock, vibrations, humidity etc.
Size and weight
Can range from handheld cameras to heavier stabilized gimbal mounts. Make sure it’s ergonomic for your uses.
Interfaces
Review options for power, data connectivity, onboard storage, displays etc. Wired or wireless.
Getting the right specifications for your particular application scenario is important to maximize the value from your dual mode camera investment.
Conclusion
Dual mode thermal/visible cameras provide the unique capabilities of thermal imaging while retaining the visual detail and context of visible light cameras in one powerful platform. They are becoming vital tools for surveillance, public safety, industrial inspections and more. As thermal sensor technology improves, dual mode cameras will keep getting lighter, smaller, easier to use and more affordable. They can provide critical imaging capabilities in the harshest conditions to save lives and ensure security.