Literature
Thermal Imager Distance Calculator
Calculator for blood type expected for a given population sample
Marking for Night Vision Devices and Thermal Imaging Devices
Optimized Parameters for Stitching Micro-prismatic Films
Thermal Imager Distance Calculator
Download Spreadsheet of the Thermal Imager Distance Calculator here.
Sample of the Spreadsheet |
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|---|---|---|---|
| Charateristics of IR imager | |||
| Angular Resolution | 1 |
mR | |
| Spectral Response | 7.5 to 12.5 | um | |
| Magnification | 2X | ||
| Scene Characteristics | |||
| Distance to object ® | 200 |
m | |
| Resolving Power Calculation | Horizontal | Vertical | Units |
| IFOV (Given by manufacturer) | 8.6 |
6.4 |
Degrees |
|
0.150 |
0.112 |
radians |
| Pixels (Given by manufacturer) | 160 |
120 |
ea |
|
|||
|
|||
| "L (at ""distance to object"" from above)" | 30.020 |
22.340 |
m |
|
|||
| L/pixel | 0.188 |
0.186 |
m |
|
|||
| Pixel req | 2 |
2 |
|
|
|||
| Resolving Power | 0.375 |
0.372 |
m |
|
1.231 |
1.222 |
ft |
|
15 |
15 |
in |
| Therefore, a rectangular object with the following dimensions should be detectable. | 15 |
15 |
in |
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Blood Type Calculator
Calculator showing the number of each blood type expected for a given population sample.
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Angles and Dangles
Understanding and evaluating NVG markers requires the understanding of two different angles. They are called the entrance angle and the observation angle. The Entrance angle is the angle between the viewing device and the Illuminating device. The observation angle is the angle between the NVG and the perpendicular from the marker. For NVGs the entrance angle is a function of the physical separation between the imager and illuminating device. When optimizing an NVG marker, the acceptable entrance angle should be as small as possible for covertness. The acceptable observation angle should be as large as possible so that identification can be made from any or almost any angle.
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Marking for Night Vision Devices and Thermal Imaging Devices
There are fundamental differences between Night Vision Goggles or Devices (NVGs) and Thermal Imaging Devices or Forward Looking Infrared Devices (FLIRs), which lead to fundamental differences in the methods of marking individuals and assets for users of these devices. If we do not understand these fundamental differences we are at risk for not effectively identifying people and assets that rely on us for help.
Key differences between the two technologies lie in the wavelengths of energy used, amount of amplification, and the nature of the energy to which they are sensitive. NVGʼs are sensitive to both visible and near infrared energy. Near infrared encompasses those wavelengths from .7μm to 3μm. These are not visible to the naked eye, although excessive energy from a laser or led in these wavelengths can damage the eye. Additionally, NVGʼs amplify the light and near infrared energy (NIR) that enter it. FLIRs are sensitive to energy from 3μm to 5μm (midwave infrared) and from 8μm to 14μm (long wave infrared). The energy from 5μm to 8μm is absorbed in the atmosphere and not available to us. With the technology we possess, we do not have a single useful system that can allow us to analyze energy in the midwave and long wave infrared simultaneously. Therefore, every FLIR is designated to work in one band or the other. FLIRs do NOT amplify energy at all. They are sensitive to the wavelengths of energy listed above but they cannot amplify the way night vision can. Another significant difference is the natural occurrence of the energy the device is sensitive to. The majority of visible and NIR energy in the atmosphere is from the Sun, moon, and stars. There is minimal NIR otherwise occurring naturally in the environment. On the other hand, midwave IR and long wave IR consist of energy which is naturally emitted by all things, organic and nonorganic, living and dead, which are at a temperature above absolute zero (-273°C). Therefore there are an infinite number of sources of thermal infrared all the time day and night in our environment. As a result, NVG users will often require artificial illumination sources while FLIR users will not require any illumination. That is good because we do not have effective thermal infrared illumination sources. It is very useful to know that as energy wavelength increases the ability for the energy to cut through obscurants such as dust and fog increases. Therefore, you can “see through” obscurants best with a thermal imager, better with night vision, and the least with the naked eye.
The differences above lead to differences in the technology and methods of marking individuals and assets. The first and most significant difference is the difference between reflectivity and retro-reflectivity. Figure 1 shows retroreflectivity at the left and reflectivity at the right. Retro-reflectivity energy bounces directly back in the direction from which it came. A bicycle reflector works like this. If a vehicleʼs headlights shine on a bike reflector from any direction, there is light that comes back directly at the vehicle. In reflectivity energy bounces off the surface as light does off a mirror. The principals that govern images we see in a mirror all apply. Markers for NVGʼs are retro-reflective while markers for FLIRs are reflective. The surface effects of the markers are different. Markers for FLIRs are a function of around 10 microns (.01mm or .0004in) of thickness at the surface whereas markers for NVG are a function of multiple complementary layers working together. This is fundamentally very significant. Because thermal reflection occurs only at the surface, thick protective layers cannot be applied to FLIR markers such as are applied to NVG markers. Therefore, FLIR markers are fundamentally less durable than NIR markers. Manufacturers use very specialized techniques to minimize this inequality, but until a new game-changing technology is developed, we expect this inequality to remain.
Having gained a greater understanding of the technology, we must now apply the information and see how it affects operations. Because illumination is needed for NIR markers to retro-reflect you need illumination when using NVGs. This is very significant because of more NVGs and FLIRs in the hands of the enemies. As our enemies acquire more and more NVGs, using illumination will become more risky. FLIR markers are therefore more covert than NVG markers. NVGs are also more accessible than are FLIRs due to limitations on sale and due to the expense of these units. For these reasons we anticipate friendly militaries using more and more FLIRs and consequently more FLIR markers. Infrared Tools provides NVG, FLIR, and fusion markers which combine both technologies into a single product. The amplification which is inherently part of NVGs and not FLIRs makes NVG markers much more detectable than an equivalent size FLIR marker. In use we recommend that a FLIR marker should be 10X to 50X the area of an NVG marker for similar detectability. Many factors affect this, primarily the quality of the imaging equipment. Another concept that must be considered is detection versus identification. Because of the lack of amplification, FLIR markers of a certain shape or with a certain marking on it can be more easily identified than a similar marker for NVGʼs. Printing on NVG markers generally disappear after about 30m. On the other hand, NVG markers are best for detection. Because of the amplification, you can detect a properly illuminated similar sized marker more effectively with NVGs.
Reflection and retro-reflection have a significant impact on detection. For a
- NIR marker to be detected the viewer should preferably
- View the position using NVGs and illuminate the marker from their viewing position
- Be positioned within 30° of perpendicular from the marker.
For a FLIR marker to be detected, the viewer should
- View the marker using a FLIR without any illumination
- Be positioned such that the marker reflects back to the viewer an object having a temperature different from the object being marked.
The ideal cold object is the sky, because on a clear night, the sky temperature is less than -40°C (-40°F). For fixed asset marking, this means that all markers should be situated so that they angle upwards at about 15° or more.
Consider carefully positioning, imaging technology, marker size, and the technology of the enemy. When we understand the limitations, advantages, and disadvantages we are able to make wiser decisions about implementing marking technologies. With that understanding we can build an SOP to effectively save lives.
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Optimized Parameters for Stitching
Micro-prismatic Films
Infrared Tools has converted its production of 3/4” sewable IFF squares from glass bead technology to micro-prismatic technology. This change is predicated upon the following section of draft specification IR PD-06-05 which covers IFF tape:
3.3.1 Basic material. The material is a micro-prismatic retroreflective flexible polymeric film, black in color. The film shall be durable to weather and launderable. The material is a micro-prismatic retroreflective flexible polymeric film designed for near infrared vision systems commonly known as Night Vision Goggles (NVG). When printed as a flag, Military Police (MP) or Criminal Investigation Division (CID) brassard, it shall adhere to the upper sleeve of the coat by means of a hook and loop attachment. the flag and brassards shall have the hook portion affixed to the back by means of a high heat resistant, water insoluble, pressure sensitive adhesive.
The micro-prismatic films are thinner with less adhesive and therefore require different sewing parameters than their glass bead counterparts. The following table will give some guidance.
Parameter |
Direction |
|---|---|
| Needle | #16 (preferred) or #18, non-cutting |
| Pitch | (stitches/in) 9 (GL/PD 07-13 requires 9-12) |
| Stitches | 5 in each direction to create at .55 by .55 square similar to Figure below. |
| Thread tension | Use tension as low as possible without causing any sewing issues. |
| Tacking | It is preferred, if possible, for the needle to use previous holes rather than new holes when back tacking. |
Figure - Sewn IFF Tape
Should you have problems implementing our new product, please contact us and we will assist in any way possible. You can contact us via phone at 443-292-8885 or engineering@InfraredTools.com
Because we would actually prefer no more than 8 stitches/in for the film, we have been in contact with ACU program management about allowing a lower pitch for the IFF square. They were receptive to our feedback. We would welcome any of our customers to request an engineering modification to use 8 stitches per inch on the IFF tape. As the ACU program management is already aware of this, you could expect relatively fast resolution.
If 8 stitches per inch is used, the preferred parameters would be:
Parameter |
Direction |
|---|---|
| Needle | #16 (preferred) or #18, non-cutting |
| Pitch | (stitches/in) 8 |
| Stitches | 4 in each direction to create at .5 by .5 square. |
| Thread tension | Use tension as low as possible without causing any sewing issues. |
| Tacking | It is preferred, if possible, for the needle to use previous holes rather than new holes when back tacking. |
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Tale of Two Thermal Films
Infrared Tools has two different types of thermal films and the difference is key to making a choice for a given use. There are three primary aspects for consideration: emissivity, gloss, and abrasion resistance. Emissivity is functionally the apparent coldness of the film in a thermal imaging device (FLIR). Therefore, lower emissivity improves detection. Emissivity is measured on a scale from 1 to 0 and most materials in our world are about .95.
| Characteristic | T Film | C Film |
| Emissivity | Very Low (~.1) | Low |
| Detectability | Very High | Good |
| Gloss | Medium | Low |
| Abrasion Resistance | Moderate | High |
Both films are made with a highly tear resistant film. Additionally the film is very quiet compared to another competitive film. In fact, third party testing confirmed that our film is approximately 10X as quiet as another competitive film. For a given project, the primary consideration is the relative importance of detectability compared to abrasion resistance. Once an understanding is reached, the ideal film for a given product or project can be logically determine.
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