0 Infrared Spectral Sensitivity Bands. 0 Image Resolution and Field-of-View. 1 Detector arrays and pixel sizes 2. 2 Infrared lens characteristics. 0 High Velocity Camera Features.
1 Brief exposure times 3. 3 Dynamic section expansion 3. 4 Function triggering 3. 5 Calibration: Non-uniformity correction and radiometry. 0 Infrared Camera Applications.
IR Inspection in Design,Test and Manufacturing. Hyperspectral and Gas Imaging, Remote Sensing. Target Signature Measurement andTracking. Research and Development. BodyTemperature Detection, Health related Imaging.
Non-DestructiveTest NDT. Recent developments in cooled mercury cadmium telluride MCT or HgCdTe infrared detector cutting edge designs have created likely the development of high performance infrared cameras for use in a large variations of demanding thermal imaging applications. These infrared cameras are now available with spectral sensitivity within the shortwave, mid-wave and long-wave spectral bands or alternatively in 3 bands. In addition, a variations of camera resolutions are available like a result of mid-size and large-size detector arrays and different pixel sizes. Also, camera features now with high frame rate imaging, adjustable exposure time and function triggering enabling the capture of temporal thermal events.
Sophisticated processing algorithms are available that result in an expanded dynamic section to stay away from saturation and optimize sensitivity. These infrared cameras shall be calibrated such that the output digital values correspond to object temperatures. Non-uniformity correction algorithms are included that are independent of exposure time. These performance capabilities and camera features enable a large section of thermal imaging applications that were previously not possible. At the heart regarding the high velocity infrared camera is a cooled MCT detector that delivers extraordinary sensitivity and versatility for viewing high velocity thermal events.
0 Infrared Spectral Sensitivity Bands. Due to availability of a variations of MCT detectors, high velocity infrared cameras have been drafted to operate in multiple distinct spectral bands. The spectral band shall be manipulated by varying the alloy composition regarding the HgCdTe and the detector set-point temperature. The result is a lone band infrared detector with extraordinary quantum efficiency typically above 70% and high signal-to-noise ratio can detect extremely tiny grades of infrared signal. As shown in Figure 2, look link below for a done post referencing all figures and tables, single-band MCT detectors typically fall in one regarding the 5 nominal spectral bands shown:.
Short-wave infrared SWIR cameras - visible to 2. Broad-band infrared BBIR cameras - 1. Mid-wave infrared MWIR cameras - 3-5 m. Long-wave infrared LWIR cameras - 7-10 m response. Very Long Wave VLWIR cameras - 7-12 m response.
In addition to cameras that utilize monospectral infrared detectors that hold a spectral response in one band, new processes are being developed that utilize infrared detectors that hold a response in 3 bands known as 3 color or dual band. Examples with cameras possessing a MWIR or LWIR response covering most 3-5 m and 7-11 m, or alternatively sure SWIR and MWIR bands, or even 3 MW sub-bands. There are a variations of reasons motivating the selection regarding the spectral band for an infrared camera. For sure applications, the spectral radiance or reflectance regarding the objects below observation is what determines the greatest spectral band. These applications with spectroscopy, laser beam viewing, detection and alignment, target signature analysis, phenomenology, cold-object imaging and surveillance in a marine environment.
Additionally, a spectral band should be selected due to the fact that regarding the dynamic section concerns. Figure 3, look link below for a done post referencing all figures and tables, shows the infrared image obtained with an LWIR infrared camera resulting from the test firing of a solid rocket booster. The intra-scene dynamic section within the plume and the background is about 2200K. Such an extended dynamic section should not be likely with an infrared camera imaging within the MWIR spectral range. The large dynamic section performance regarding the LWIR system is with no problems explained by comparing the flux within the LWIR band with that within the MWIR band.
As calculated from Planck's curve, the distribution of flux due to objects at widely varying temperatures is smaller within the LWIR band than the MWIR band when observing a scene possessing similar object heat range. In other words, the LWIR infrared camera can image and measure ambient heat objects with high sensitivity and resolution and at similar time extremely warm objects i. Imaging large heat ranges with an MWIR system should have significant challenges due to the fact that the signal from high heat objects should should be drastically attenuated resulting in poor sensitivity for imaging at background temperatures. 0 Image Resolution and Field-of-View. 1 Detector Arrays and Pixel Sizes.
High velocity infrared cameras are available possessing different resolution capabilities due to their use of infrared detectors that have different array and pixel sizes. Multiple common array formats are shown in Figure 4, look link below for a done post referencing all figures and tables. For applications that don't ever want high resolution, high velocity infrared cameras based on QVGA detectors release excellent performance. Figure 4a, look link below for a done post referencing all figures and tables, shows a 320x256 array of 30 m pixels. Such cameras are known for their extremely large dynamic section due to use of relatively large pixels with deep wells, little noise and extraordinarily high sensitivity.
Infrared detector arrays are available in different sizes, the greatest common are QVGA, VGA and SXGA as shown. The VGA and SXGA arrays hold a denser array of pixels and consequently deliver higher resolution. The QVGA is economical and exhibits excellent dynamic section due to the fact that of large sensitive pixels. More recently, the cutting edge designs of smaller pixel pitch has resulted in infrared cameras possessing detector arrays of 15 micron pitch, delivering some regarding the greatest impressive thermal images available today. For higher resolution applications, cameras possessing larger arrays with smaller pixel pitch deliver images possessing high contrast and sensitivity.
In addition, with smaller pixel pitch, optics should possibly grow to smaller distant reducing cost. A 640x512 VGA format pixel array is depicted in Fig. 4b and a 1280x1024 SXGA format pixel array is depicted in Fig. A sample image from an SXGA camera is shown in Figure 5. Look link below for a done post referencing all figures and tables.
2 Infrared Lens Characteristics. Lenses drafted for high velocity infrared cameras have their own special properties. Primarily, the greatest relevant specifications are focal length field-of-view, F-number aperture and resolution. Focal Length: Lenses are normally identified by their focal length e. The field-of-view of a camera and lens combination depends on the focal length regarding the lens as well as the overall diameter regarding the detector image area.
As the focal length increases or the detector volume decreases, the field of view for that lens shall decrease narrow. Since the field-of-view depends on the detector physical size, if a lens that is drafted to be used on the detector depicted in Fig. 4c is used on neither regarding the detectors depicted in Figs. 4a or 4b, the resulting field-of-view should be 1/2 that regarding the 4c detector. Look link below for a done post referencing all figures and tables.
Table1, look link below for a done post referencing all figures and tables, shows common lens or camera combinations and their resulting field-of-view for the 4a and 4b sized detectors. Shown are the commonly available lens focal lengths for mid-wave MWIR, broadband BBIR and long-wave LWIR imaging. A convenient online field-of-view calculator for a section of high-speed infrared cameras is available within the comprehensive post at the link below:. In addition to common focal lengths, infrared close-up lenses are also available that make high magnification 1X, 2X, 4X imaging of tiny objects, as shown in Figure 6, look link below for a done post referencing all figures and tables. Infrared close-up lenses give a magnified view regarding the thermal emission of tiny objects for example electronic components.
F-number: Unlike high velocity visible light cameras, objective lenses for infrared cameras that utilize cooled infrared detectors should be drafted to be compatible together with the internal optical creation regarding the dewar the cold housing in which the infrared detector FPA is located. As shown in Figure 7, look link below for a done post referencing all figures and tables, this is due to the fact that the dewar is drafted with a cold stop or aperture inside that prevents parasitic radiation from impinging on the detector. Due to the fact that of thecold stop, the radiation from the camera and lens housing are blocked, infrared radiation that should distant exceed that received from the objects below observation. Like a result, the infrared life captured by the detector is primarily due to object's radiation. The location and volume regarding the exit pupil regarding the infrared lenses and the f-number should be drafted to match the location and diameter regarding the dewar cold stop.
Actually, the lens f-number can always be decreased than the effective cold stop f-number, as long as it is drafted for the cold stop within the real position. Lenses for cameras possessing cooled infrared detectors should be specially drafted not only for the critical resolution and location regarding the FPA but also to accommodate for the location and diameter of a cold stop that prevents parasitic radiation from hitting the detector. Resolution: The modulation transfer function MTF of a lens is the characteristic that helps determine the ability regarding the lens to resolve object details. The image produced by an optical system shall be somewhat degraded due to lens aberrations and diffraction. The MTF describes how the contrast regarding the image varies together with the spatial frequency regarding the image content.
As expected, larger objects have relatively high contrast when compared to smaller objects. Normally, little spatial frequencies have an MTF close to two or 100%? as the spatial frequency increases, the MTF eventually drops to zero, the ultimate limit of resolution for a provided optical system. 0 High Velocity Infrared Camera Features: variable exposure time, frame rate, triggering, radiometry. High velocity infrared cameras are necessary for imaging fast-moving thermal objects as well as thermal events that occur in a very brief time period, too brief for standard 30 Hz infrared cameras to capture precise data. Well-known applications with the imaging of airbag deployment, turbine blades analysis, dynamic brake analysis, thermal analysis of projectiles and the read of heating effects of explosives.
In each of these situations, high velocity infrared cameras are effective tools in performing the compulsory analysis of events that are otherwise undetectable. It is due to the fact that regarding the high sensitivity regarding the infrared camera's cooled MCT detector that there is the possibility of capturing high-speed thermal events. The MCT infrared detector is implemented in a snapshot mode where all the pixels simultaneously integrate the thermal radiation from the objects below observation. A frame of pixels shall be exposed for a very brief interval as brief as and lt;1 microsecond to as long as 10 milliseconds. Unlike high velocity visible cameras, high velocity infrared cameras don't ever want the use of strobes to view events, so there is no should synchronize illumination together with the pixel integration.
The thermal emission from objects below observation is normally sufficient to capture fully-featured images regarding the object in motion. Because regarding the benefits regarding the high performance MCT detector, as well as the sophistication regarding the digital image processing, it is likely for today's infrared cameras to perform many regarding the functions compulsory to enable detailed observation and testing of high velocity events. As such, it is useful to review the usage regarding the camera within the effects of variable exposure times, full and sub-window frame rates, dynamic section expansion and function triggering. 1 Brief exposure times. Selecting the greatest integration time is usually a compromise between eliminating any motion blur and capturing sufficient life to make the desired thermal image.
Typically, most objects radiate sufficient life during brief intervals to still make a very high quality thermal image. The exposure time shall be increased to integrate more regarding the radiated life until a saturation position is reached, usually multiple milliseconds. On the other hand, for moving objects or dynamic events, the exposure time should be kept as brief as likely to remove motion blur. Tires running on a dynamometer shall be imaged by an above velocity infrared camera to determine the thermal heating effects due to simulated braking and cornering. One relevant application is the read regarding the thermal characteristics of tires in motion.
In this application, by observing tires running at speeds in excess of 150 mph with an above velocity infrared camera, researchers can capture detailed heat data during dynamic tire testing to simulate the loads associated with turning and braking the vehicle. Heat distributions on the tire can indicate potential difficulty parts and security concerns that want redesign. In this application, the exposure time for the infrared camera wants to be sufficiently brief sequential to remove motion blur that should reduce the resulting spatial resolution regarding the image sequence. For the set-up shown in Figure 8, look link below for a done post referencing all figures and tables, for a desired tire resolution of 5mm, the desired maximum exposure time shall be calculated from the geometry regarding the tire, its volume and location with respect to camera, and together with the field-of-view regarding the infrared lens. The exposure time compulsory is determined to be shorter than 28 s.
Creating use of a Planck's calculator, one can calculate the signal that should be obtained by the infrared camera adjusted with critical F-number optics. The result indicates that for an object heat estimated to be 80C, an LWIR infrared camera shall deliver a signal possessing 34% regarding the well-fill, while a MWIR camera shall deliver a signal possessing only 6% well fill. The LWIR camera should be necessary for this tire testing application. The MWIR camera should not perform as well since the signal output within the MW band is many decreased requiring neither a detailed exposure time or other changes within the geometry and resolution regarding the set-up. The infrared camera response from imaging a thermal object shall be predicted based on the black body characteristics regarding the object below observation, Planck's law for blackbodies, as well as the detector's responsivity, exposure time, atmospheric and lens transmissivity.
2 Variable frame rates for full frame images and sub-windowing. While standard velocity infrared cameras normally deliver images at 30 frames or 2nd with an integration time of 10 ms or longer, high velocity infrared cameras are can deliver many more frames per second. The maximum frame rate for imaging the entire camera array is limited by the exposure time used and the camera's pixel clock frequency. Typically, a 320x256 camera shall deliver up to 275 frames or 2nd for exposure times shorter than 500 s? a 640x512 camera shall deliver up to 120 frames or 2nd for exposure times shorter than 3ms. The high frame rate capability is highly desirable in many applications when the function occurs in a brief no.
One example is in airbag deployment testing where the effectiveness and security are evaluated sequential to make creation changes that shall improve performance. As shown in Figure 9, look link below for a done post referencing all figures and tables, an above velocity infrared camera reveals the thermal distribution during the 20-30 ms period of airbag deployment. Like a result regarding the testing, airbag manufacturers have created changes to their designs within the inflation time, fold patterns, tear patterns and inflation volume. Had a standard IR camera been used, it shall have only delivered two or 3 frames during the initial deployment, and the images should be blurry due to the fact that the bag should be in motion during the long exposure time. Airbag effectiveness testing has resulted within the should make creation changes to improve performance.
A high velocity infrared camera reveals the thermal distribution during the 20-30ms period of airbag deployment. Like a result regarding the testing, airbag manufacturers have created changes to their designs within the inflation time, fold patterns, tear patterns and inflation volume. Other sequences are available for viewing online. Even higher frame rates shall be achieved by outputting only portions regarding the camera's detector array. This is necessary when there exists smaller parts of interest within the field-of-view.
By observing just sub-windows possessing fewer pixels than the full frame, the frame rates shall be increased. Some infrared cameras have minimum sub-window sizes. Commonly, a 320x256 camera has a minimum sub-window volume of 64x2 and shall output these sub-frames at almost 35Khz, a 640x512 camera has a minimum sub-window volume of 128x1 and shall output these sub-frame at faster than 3Khz. Because regarding the complexity of digital camera synchronization, a frame rate calculator is a convenient tool for determining the maximum frame rate that shall be obtained for the different frame sizes. 3 Dynamic section expansion.
One regarding the complications of possessing a very high sensitivity infrared detector is that the overall scene dynamic section shall be limited. For example, if a raw count corresponds to six mK or digital count, a 14-bit signal section shall deliver fewer than 80C in dynamic range. This section is distant reduced due to the fact that of pixel non-uniformity. Like a consequence, the section of object temperatures that shall be viewed in one frame should be too narrow for the application. To increase the apparent dynamic range, an one of a kind solution shall be implemented which allows the user to artificially expand the dynamic section without sacrificing the high sensitivity performance regarding the camera.
This mode is sometimes called Dynamic Section ExtendIR, DR-X, superframing, multi-IT. When the dynamic section expansion mode is engaged, the camera sequentially captures multiple frames, each frame possessing an alternate exposure time. The brief sequence includes frames that are highly sensitive due to the fact that of long exposure times and also fewer sensitive frames for imaging objects at higher temperatures due to the fact that of shorter exposure times. For the method to be effective, the overall time for the frame sequence should be brief enough to stay away from motion blur. If this is the case, then camera software combines the frames into one image frame possessing the entire dynamic section for the sequence.
As an example, think about the following sequence of images showing the process of mixing a cold fluid to a flask of boiling liquid. If an exposure time was selected based on the full heat range, the thermal resolution regarding the cooler objects shall be poor. Conversely, if the exposure time is selected to improve the thermal resolution regarding the cold fluid, the hotter objects shall cause saturation. Like a result, with dynamic section expansion, multiple integration times shall be selected that span the entire scene dynamic range. Exposure time 110 s or Frames 1,4,7 or Object Heat Section 65-150C.
Exposure time 600 s or Frames 2,5,8 or Object Heat Section 35-70C. Exposure time 1375 s or Frames 3,6,9 or Object Heat Section 5-40C. In this example, 3 exposure times have been selected 1375 s, 600 s, and 110s to close a large scene temperature. The camera then cycle through each exposure time at the full frame rate. If the camera is operating at 240 frames or second, first frame shall be at first exposure time, the 2nd frame shall be at the 2nd exposure time, the third at the third exposure time.
The fourth frame shall begin the sequence repeatedly at first exposure time. The system shall effectively generate 3 sequences, 3 frames apart, each at a rate of 80 frames or 2nd together with the 3 exposures times. Through image processing, the sequential frames shall be recombined into one done sequence creating a pixel by pixel determination as to apparent signal, distant increasing the dynamic range. The resulting image is shown within the post link referenced below with a 5-150C object heat scale?. The exposure times correspond to different camera sensitivities as shown in Figure 10.
In operation, the camera is programmed to select the appropriate exposure time frame by frame. The resulting data shall neither be multiple sequences created from multiple integration times, or a combined sequence that takes the greatest appropriate data based upon the scene. In addition, the user can decide to vary the many frames per integration time, as well as have the choice to utilize an internal filter mechanism for attenuation or spectral data. Certain applications want very large thermal dynamic ranges, which shall not be likely with a lone integration time. The high velocity infrared camera's dynamic section expansion mode shall let the user to cycle through exposure times at the fastest rate likely for the camera.
4 Function Triggering. In order to capture high velocity events, infrared cameras should be properly synchronized. Within the tire-testing example in Section 3. 1 above, it is likely to have an optical encoder on the rotating tire that allows precise position location. The TTL signal generated by the optical encoder shall be fed into the infrared camera to trigger the begin regarding the recording sequence for the camera.
The result is that every time the encoder sends the pulse, the camera exposes the infrared detector for a sure exposure time creating an image. This allows a real-time stop image sequence to be created via software. In addition to ability to accept an external TTL trigger, infrared cameras have other capabilities that improve their ability to capture high velocity events. For example, sure trigger features permit the infrared camera to synchronize the trigger together with the desired image capture. Due to the fact that digital image frames are captured in real time, a pre-trigger permits the software to identify the beginning of a desired sequence that actually occurs prior to the trigger signal! Post-trigger delays are also available for aligning the frame capture with an function that follows the trigger subsequent to a programmable delay.
In addition, most high velocity thermal cameras currently have the ability to give a trigger output to let external devices to be synchronized together with the thermal camera. That is why the camera can slave or be slaved. Possessing most a trigger input and output is useful in an application that involves creating use of multiple cameras to view similar target from different angles. In this case, the data shall be assembled via software into a 3-dimensional rendering regarding the thermal profile. 5 Calibration: non-uniformity correction and radiometry.
One regarding the challenges in obtaining the greatest data from an above performance infrared camera system was in maintaining a real calibration. Calibration many times refers to 3 different operations. One, non-uniformity correction, is compulsory to calibrate the sensor for optimal image quality. The other calibration has to do with determining the heat of objects based on their image brightness. Non-uniformity correction is compulsory to assure that the infrared detector array delivers the greatest likely image quality.
Each pixel within the detector array inevitably has a slightly different gain and offset value. In addition, some pixels shall have other anomalous properties that deviate from the norm. The gain and offset for all the pixels within the array should be adjusted such that each pixel performs identically to others. Variations can occur for a variations of reasons, within detector non-uniformity and optical affects for example the lens illumination non-uniformity that attenuates the apparent radiance near the edge regarding the image. Anomalous pixel signals should be replaced with nearest neighbor averages as is appropriate for the application.
To correct for the gain and offset, a calibration called Non Uniformity Correction NUC should be created. The process typically requires that the user expose the detector to a cold and warm blackbody source. An algorithm then corrects the detector signal non-uniformity. A similar process called Bad Pixel Replacement BPR is compulsory for any pixels that are regarded bad which means they deviate from sure thresholds set for evaluating uniformity or due to noisy behavior. Non-uniformity correction is complicated due to the fact that there exists variations in pixel performance for each integration time.
Therefore, this process should should be performed for every integration time that the user selects. As high performance cameras can operate from 1us to and gt;10ms, this means that in theory 10,000 calibrations should be made. However, due to the fact that regarding the linear response regarding the detector, recent advances have been likely to make this process transparent to user. A process called TrueThermal allows the user to select any integration time and the camera shall automatically reference a look up table of most NUC and BPR properties that were established neither at the factory or at the user's site. In this situation, once a user selects the appropriate integration time, the camera system applies a predefined NUC and BPR table to let instant and seamless operation.
Once the sensor is calibrated for uniform image quality, the camera shall be calibrated for radiometry, or heat measurement. If an infrared camera is properly calibrated, the object heat shall be determined based on the radiance signal within the thermal images, the background ambient temperature, likely atmospheric effects and the objects emissive properties. It is many times particularly useful to be can use the infrared camera to measure the heat of objects for example projectiles traveling at high speeds. This finds applicability in multiple important situations, including: tracking of missiles, spacecraft and other objects, in determining the trajectory of bullets and projectiles and automatically identifying their origin based on trajectory information, and in creating thermal signatures for military targets. Some users want that the thermal data be calibrated for radiometry.
Again, this radiometric data shall be dependent upon a critical integration time and should with the NUC and BPR corrections. Within the past, for each integration time, an one of a kind radiometric calibration should be required. Today, the TrueThermal calibration function facilitates the process, not only correcting for NUC and BPR, but also applying the appropriate radiometric calibration table to data. This now allows the user to, in real time, change integration times and have fully corrected data for NUC, BPR and radiometric calibration. 0 Infrared Camera Applications.
IR Inspection in Design, Test and Manufacturing:. Thermal imaging has grow to an extremely valuable cutting edge designs in many industries like a tool to inspect and test different designs and processes. The thermal signatures shall be a result of electrical, electro-mechanical, chemical or other causes. Thermal images reveal heat dissipation, thermal conductance, non-uniformities as well as other important diagnostic factors. Hyperspectral and Gas Imaging, Remote Sensing:.
Broadband infrared cameras are very useful for hyperspectral imaging which involves the accumulation of a spectral set of times, gas imaging which occurs at an on occasion very narrow portion regarding the infrared spectrum and remote sensing imaging the backscatter, reflection and emission differences of different materials. Powerful image processing software is available to facilitate the analysis regarding the resulting infrared images. Target Signature Measurement and Tracking:. The spectral characteristics of vehicles, weapons and countermeasures have been located to be important for many applications. Broad spectral range, high resolution and high sensitivity are key features of infrared cameras for these applications.
We release multi-spectral imaging processes with a large section of optics. In addition, we release powerful data acquisition processes featuring real-time image capture and radiometric analysis. Research and Development:. Thermal imaging is used extensively in engineering and scientific studies centers around the world. Thermal imaging gives insight into critical details about an object's thermal and spectral characteristics.
In sure circumstances, details shall be obtained on high-speed events available with high frame-rate cameras as well as circumstances requiring large dynamic section available with variable integration cameras. Key to use of these imagers is many times application-specific software that permits the detailed analysis of most two-dimensional images as well as arrays of image sequences. Medical Imaging, Body Heat Detection:. Many physiological conditions make variations in body heat and heat distribution throughout the person body. As an example, the installation of thermographic cameras at airports has grow to a key Swine Flu and SARS screening tool for many parts around the world.
Thermography has also been used like a screening tool for applications for example breast cancer and pain management. Non-Destructive Test NDT?. Thermal imaging is a non-invasive technique which when applied with critical stimulus gives a view into subsurface defects in difficult test samples. Inspection of composite aircraft components is gaining large acceptance in airframe manufacture and service. Advanced fabrics are finding their method into automotive and consumer products and thermographic NDT is a fast and large region screening technique that is very cost effective.
Because regarding the impressive performance of MCT detector technology, high performance infrared cameras have grow to available that enable a large variations of demanding thermal imaging applications. A selection of infrared cameras are available possessing mid-format to large-format detectors and with spectral sensitivity ranging within the short, mid and long-wave spectral bands. The cameras owe their versatility to sure features that include: high frame rate imaging, adjustable exposure time, function triggering enabling the capture of temporal thermal events, dynamic section expansion, non-uniformity correction and radiometric calibration. These performance capabilities and camera features enable a large section of thermal imaging applications that were previously not possible, including: IR Inspection in design, test and manufacturing, hyperspectral imaging, gas detection, remote sensing, target signature measurement and tracking, R and amp;D, health related imaging and NDT. For a comprehensive post referencing all tables and figures please more infrared imagingWhite Papers see our online Knowledge.
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