So much non-science about transfer of energy between different temperature objects.
So many state that it is impossible for a cool object to heat a hotter object.
But both bodies emit radiation corresponding to their temperatures. Each body obviously does not know of the existence of the other before it releases its radiation.
The cold body obviously receives radiation from the hot body and therefore warms
The hot body obviously receives radiation from the cold body and therefore cools slower than if the cold body were at 0K.
Specification for a thermal imaging camera
http://www.flir.com/cs/emea/en/view/?id=41964
Imaging Performance
IR resolution 640 x 480 pixels
Spectral range 7.5 – 13 µm
Image frequency 30 Hz
Focus Automatic or manual
Focal Plane Array (FPA)
Uncoooled microbolometer
Measurement
Temperature range
-40°C to +500°C (optional up to +2000°C)
Environmental specifications
Operating temperature range -15 °C to
+50 °C
This thermal imaging camera will operate at +50
°C ambient This means the imagaging device (a micro bolometer array) is at at least 50
°C since it is uncooled.
How can it measure -40
°C when it is at 50
°C?
How does a microbolometer work:
http://www.laserfocusworld.com/articles/print/volume-48/issue-04/features/microbolometer-arrays-enable-uncooled-infrared-camera.html
Modern microbolometers measure temperature changes caused by IR absorption in individual pixels, which are thermally isolated and assembled into focal-plane arrays (FPAs).
Each pixel in an array is a very low-mass IR-absorbing structure supported by thin legs, which limit heat conduction to the underlying substrate, as shown in Fig. 1. The lower the mass of the illuminated pixel, the less IR energy is needed to increase its temperature a given amount, and the more sensitive it is.
FIGURE 1. One pixel in a microbolometer array. An infrared-absorbing surface is elevated above the substrate and thermally isolated from adjacent pixels. Low mass increases the temperature change from heat absorption. Read-out circuits typically are in the base layer, which may be coated with a reflective material to reflect transmitted IR and increase absorption of the pixel.
Two classes of IR-absorbing materials are used in microbolometers. Pyroelectric or ferroelectric crystals generate electrical signals that are directly proportional to the temperature increase caused by IR absorption; the most common material now in use is barium-strontium titanate. Other materials act as thermistors, in which the electrical resistance changes with temperature. As in the original 19th century bolometer, measuring the resistance of a microbolometer pixel measures the incident IR intensity. The leading materials today are the semiconductors amorphous silicon and vanadium oxide (often abbreviated VOx), which are compatible with the standard semiconductor processing technology used to fabricate the read-out circuits that generate images.
The sensitivity depends on how much the resistance or other electrical signal changes with temperature, and this depends on the absorbing material. The pixel response time also is important; absorbers should collect heat quickly and hold it long enough for measurement, then dissipate it before the next frame is recorded. A typical rule of thumb is that the time response should be no longer than one-third of the interval per frame, about 10 ms for a 3 Hz frame rate. Response time and performance also depend on the read-out integrated circuit (ROIC), which collects temperature data from all pixels for each frame. Noise usually is measured as noise-equivalent temperature difference (NETD), with lower being better, and 50 mK a desirable target.
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So there we have it the receiver plate is heated by the IR
Heat from the bolometer will be radiated away in all directions there can be NO imaging of the object from this radiation leaving the bolometer. Radiation leaves the bolometer before it knows where it will land so will be equal from all parts of the bolometer even if it eventually lands on a cooler object beyond the lens.
Unless you postulate negative energy rays (cold rays - this would be a new concept on me!) from the cold object that can be FOCUSED onto the bolometer then I cannot understand how statements suggesting that cold cannot heat warm can be a feature of the explaination of a bolometer’s operation.
If you assume normal physics applies then the thermal imaging camera can be understood.
Point the camera at 100
°C the bolometer receives radiation focused on it and its temperature raises above its ambient.
Point the camera at 0K the bolometer receives no radiation so will stay at its ambient.
Point the camera at -20
°C the bolometer receives radiation focused on it and its temperature will rise but too a lower value than in the 100
°C case.
A -20
°C object will therefore produce an image in the bolometer’s output
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An Iceberg at night by IR
.
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Note that thermal imaging to give exact temperatures is not simple the emissivity of the object under inspection affects the temperature calculated. Also a IR reflective surface may actually show a temperature of a reflected object rather than the reflector
