Finishing Date: 2020-02-12
Content Reference: FLIR TechNote
1. Users will often ask a thermal imaging can see how far?
A: The role of distance depends on many factors. Comprising: a lens, if the detector cooling, temperature sensitivity, detection target size, target and background. Of course, before this all the factors, and the other is the weather.
2. The user will then ask, sunny, rain fog were visible range is how many?
A: It is certain that definitely affected in this foggy rainy weather. Specifically how the impact, had to get to know the quantitative evaluation of transmission and haze of infrared radiation.
1) the transmittance of the infrared radiation
even blue skies, inherent atmospheric absorption rate will be restricted from a particular thermal imaging detectable. Thermal imaging generates an image according to the difference of the target circulated.
In fact, the further transmission of the transmission distance from the target to the thermal imager, the more loss along the way. Therefore, we must consider the attenuation coefficient. And the ratio of the incident radiation while the radiation transmitted through the material after occlusion.
Further, the greater the humidity of the air, the greater the attenuation.
2) Fog, how quantitative evaluation?
Fine mist water droplets suspended in the earth's surface or near the earth's surface from the accumulation atmosphere. When nearly saturated vapor in the air, i.e. a relative humidity of 100%, if a sufficient number of condensation nuclei can fog. Aggregation core may be smoke and dust particles.
Fog type: radiation fog and advection fog.
Advection fog: mixing two different temperatures and humidity air flow created.
Radiation fog: radiation gas stream cooled to near the cloud point temperature of the formation.
Classification fog: ICAO ICAO method used, according to this system, the mist can be divided into four classes:
Class I: visual distance of 1220 m
Class II: visual distance of 610 m
IIIa categories: visual distance of 305 m
Class IIIb: visual distance of 92 m
Causes of reduced visibility the fog are: absorption and scattering fog particles of natural or artificial light.
The amount of scattering and absorption depends on how much mist particles (or suspended particulate) microphysical structure.
3. how to answer it? US Air Force's resolution propagation model
A: Actually, the best way is measured and dependent on experience. But MODTAN can help save you the trouble of complicated field test, ahead of simulation results.
MODTAN is prepared and supported by the Air Force one atmospheric radiative transfer code. It is capable of a variety of atmospheric conditions under model weather conditions, and also for various spectral wavelengths solutions predicted irradiation optical path, the optical transmission path, the brightness of the sky, sun and moon to the atmosphere wherein the surface irradiance and the like.
MORTAN model offers six climate model also defines six types of suspended particles can occur at the climatic conditions.
- Six kinds of species including Climate:
tropical, mid-latitude summer, mid-latitude winter, summer sub-Arctic, sub-Arctic winter, the US standard. - Six kinds of aerosols categories include:
rural, urban, maritime, advection fog, radiation fog, desert.
End. . .