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Image Intensifier Vs Thermal Imager | Difference between Image Intensifier and Thermal Imager

This page compares Image Intensifier vs Thermal Imager and mentions difference between Image Intensifier and Thermal Imager. Image intensification principle is used in image intensifier and thermal imaging principle is used in thermal imager.

Introduction:
Both of these are techniques used in night vision devices which make them possible to see in the low light conditions. As we know it is difficult to see in low light conditions due to lower spectral range and lower intensity range. Following techniques enhance these two parameters.

Both of these approaches are employed in night vision devices used in surveillance, security, navigation, hunting, wild life etc. The devices which use these techniques include cameras, goggles, scopes, binoculars etc.

Image Intensifier based on image intensification

• Image intensifier uses image intensification principle.
• Image intensification works on the principle of collecting small quanta og light reflected off the target scene in order to be viewed in visible and near infrared bands of EM (Electromagnetic) spectrum in low light conditions.
• Collected photons are amplified through the processes of photon to electron conversion, electron multiplication and electron-photon conversion. All these processed are carried out in image intensifier tube.
• Image intensifier tube based night vision devices use other components such as lens, eye piece and power supply. Lens is used to collect the photons, eye piece is used to view intensified image and power supply is used to generate required DC voltages for electron acceleration.

Image Intensifier tube

Image Intensifier

➤ Image intensifier tube amplifies low light images to the levels which can be seen with naked eye or detected by digital image sensor. As shown low level light of photons enters night vision device through input window and strikes the photo-cathode.
➤ The photo electrons released by photocathode are accelerated and focused by high magnitude electric field towards MCP (Microchannel Plate).
➤ The MCP has millions of small channels and electrons entering these channels are both accelerated by another high magnitude electric field within the MCP and multiplied by secondary emission resulting from electrons bouncing off the inner walls of these channels.
➤For each electron entering the MCP, approx. about 1000 electrons are generated and subsequently accelerated from the output of MCP by third electric field towards the phosphor screen (i.e. thin light emitting layer).
➤Phosphor screen deposited on inside of the output window converts impinging electrons back to photons.
➤For every photon entering the input window of the intensifier tube, tens of thousands of photons will come out of the output window after emission from the phosphor screen. At the output CCD, EMCCD or ICCD is used based on the technical requirements.
➤The multi-stage process explained above produces an intensified or amplified image of the object which is brighter than original image.

As night vision technology is in existence since many years, there are many generations of image intensifier technology such as generation-0, generation-1, generation-2, generation-3, generation-3+ and generation-4. The figure-1 depicts Generation-3 image intensifier architecture.

Thermal Imager based on thermal imaging

• Thermal Imager uses thermal imaging principle. It does not require visible light for its operation and hence the device can see in the total darkness.
• IR (Infrared) energy radiated by the object to be imaged is incident on the thermal imaging sensor which uses complex algorithms to construct the image visible to the viewer.
• Thermal imaging sensors are more expensive compare to their visible spectrum counterparts (e.g. CCD/CMOS sensors). CCD/CMOS sensors have spectral response sensitive to visible region of the EM spectrum.

Thermal imaging principle

Thermal Imager Principle

➤As shown Thermal imager consists of lens, 2 dimensional array of photo sensors, signal conditioning and signal processing modules. The figure-2 depicts thermal imaging principle used in thermal imager. Let us understand working of these modules.
➤The front end lens focuses IR radiation emitted by all the objects in view on 2D array of IR detector elements, which creates a detailed temperature pattern of it known as thermogram.
➤The thermal Imager measures very small relative temperature differences and converts invisible heat patterns into clear, visible images.
➤Sensors used in the thermal imager scan at the rate of 30 times per second. They can sense temperatures in range from -20 degreeC to +2000 degreeC. It can sense temperature changes as small as 0.1 degreeC.
➤Next, the temperature pattern is translated into electronic impulses. The signal processing unit converts these impulses into data for display. The thermal imaging principle is used in thermal camera >>.



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