FOG HORN

Thermal imaging is a technology where informed buyers make better decisions so this article is intended to provide you with a basic foundation of thermal imaging and introduce you to 2 variants of FLIR’s outstanding commercial imagers, the PS24 and PS32. So, lets rough it out together.

When discussing thermal imaging you’ll hear references made to wave length. As average users, we probably don’t understand  what wave length is and how it relates to anything tangible. So,  let’s gain a foundation so you approach your purchase decision better informed.

Wavelength refers to the distance between the peak of one wave to the next. When we say that something has a longer or shorter wavelength we are saying that the distance between electromagnetic wave peaks is either longer or shorter, and it’s expressed in meters.

Frequency refers to the number of cycles occurring within a specified period of time; expressed in cycles per second. You’ll often see this symbol  used (Hz) or Hertz to express frequency. A cycle is represented in my figure by points AB. The higher the frequency the more cycles occur in a 1 second slot. So, a 1 MHz (pronounced mega hertz) signal  represents 1 million cycles per second, and a 1 KHz (pronounced kilo hertz) signal represents one thousand cycles per second. Which do you think has the longer wave length?Wavelength relates to frequency in that an emission with a longer wavelength will have a lower frequency than one with a shorter wavelength.

When you add energy to molecules they vibrate at a higher rate, or frequency, so by default those emissions will have a shorter wave length. When the molecule is cooled, they vibrate at a lower rate (frequency), so their emissions will have a longer wavelength. This is how thermal imaging works.

In thermal imaging we don’t detect temperatures, we detect the electromagnetic emissions associated with molecular activity and from those emissions we infer temperature relationships that we translate into contrasts. An old friend, now deceased, Chief Petty Officer, would have expressed it like this, “a man that eats pussy is a cock sucker by default” – an inference no one in my group agreed with – ; however, thermal imagers detect electro magnetic energy and internally translate it to varying levels of contrast to form an image, within a given band. My next to last sentence in this paragraph has one hugely important modifying clause and that is – “within a given band”

If you need imaging that is going to give you superior detail and range you look for equipment using sensors with a  larger frame size; in other words a greater pixel count. The higher the pixel count the greater detail and greater range, with costs rising proportionally. If your requirements are less demanding, a lower pixel count will give you slightly lower resolution and subsequent lower range at a correspondingly  lower price.

The figure above does an excellent job of pictorially representing what I verbalized earlier. Note that as temperature increases wave length decreases. So, taking a look at the graphic, if you were designing a thermal imager to detect game, personnel and material would you have it operate in the short wave, medium wave or long wave band? Clearly the long wave end of the spectrum. Why?  – because that’s where the relevant temperature ranges are.

Another conclusion that you can reach from simple examination of the graphic is that each of the three bands are in their own right a broad space. So as a designer you would pick a subset of that band to design for. Something resulting in a good performance to cost ratio. In FLIR’s case their SCOUT PS handheld imager, operates in the 7.5 – 13.5 µm (pronounce micron, or you can get away with micrometer) region of the long wave. Note, this is only a 6µm band, which makes sense because we are detecting targets who themselves have a “relatively” small temperature differentials.

What makes thermal imaging such a powerful tool is that unlike Image Intensified technologies, thermal does not require light nor is it adversely impacted by light. If you’ve ever walked into an illuminated space wearing NVDs you’ve experienced “white outs”. All things, living or not, have an electromagnetic signature that can be measured, and a thermal imager will reveal a target where a night vision device will not. Can thermal imaging be defeated? Yes and countermeasure designers focus on altering the emissivity of the target, usually with coatings or covers, but it won’t be long before we actually see active thermal countermeasure. Nature has its own countermeasure in the form of dense fog and heavy rainfall.

So, keep in mind that night vision relies on light being reflected from the subject; for example, star light, moon light and ambient light. A night vision device amplifies, many times over, reflected light so we can see the subject and its surroundings in what would otherwise be darkness. In the absence of ambient light or where ambient light is very limited such as indoors, or a cave, we must use illuminators. The illuminator is nothing more than a flashlight operating just outside of the visible light spectrum. Thermal imaging can be used in total darkness.

So let’s talk about FLIR’s commercial offerings, the PS Scout (PS24 and PS32)

Specifications for FLIR PS24 Scout Digital Thermal Camera:

• Detector Type: 240 x 180 VOx Microbolometer
• Focal Length: 19mm Fixed Focus
• Field of View (H ~ W): 24° ~ 18°
• Waveband: 7.5 – 13.5 Micrometers
• Start-up: < 5 Seconds
• Diopter Adjustment: +/- 2
• USB Port: Software Updates/Upgrades/Charging
• Tasklight: LED
• Built-In Viewfinder Display: Color LCD Display
• Polarity / Detection Palettes: White Hot; Black Hot; InstAlert
• Image Optimization: FLIR Proprietary Digital Detail Enhancement
• Video Format: 9 Hz Refresh Rate
• Weight (with battery): 12 oz (340 g)
• Size (L ~ W ~ H): 6.70″ x 2.31″ x 2.44″
• Fixed Use: Standard Tripod Mount
• Standard Warranty: 2 Years
• Battery Type: Internal Battery/Li-Ion
• Battery Recharging: USB Cable for Internal Battery; Optional Charging Cradle
• Battery Life (Operating): 5+ Hours Typical
• Rating: IP-67 (submersible)
• Operating Temp.: -4°F to 122°F (-20°C to +50°C)
• Detect Man-Sized Target (1.8 m ~ 0.5 m): ~350 yds (~320 m)
• M.S.R.P.: $1999

Specifications for FLIR PS32 Scout Rechargeable Thermal Sight:

• Resolution: 320×240 pixels
• Focal Length: 19mm Fixed
• Digital Zoom: 2x
• Field of View: 24° height x 18° width
• Diopter Adjustment: +/- 2
• Tasklight Bulb: LED
• Viewfinder Display: Color LED
• Polarity Palettes: White Hot, Black Hot, InstAlert
• Refresh Rate: 9 Hz
• Weight: 12 oz (with battery)
• Dimensions: 6.7″ x 2.31″ x 2.44″
• Tripod Adaptable: Yes, 1/4-20 mount
• Batteries: Internal lithium-ion
• Battery Life: 5+ hours
• Interface: USB
• Waterproof Rating: IP-67
• Operating Temperature: -4°F to 122°F
• Human Detection Range: ~500 yards
• M.S.R.P. $2999