How does night vision and thermal works in rain?

In this article, we will look at how night vision devices and thermal imaging equipment work. Let's decide which of them will work better in rainy weather. We also investigate the factors that should be considered when choosing in favor of night vision optics or thermal imaging devices.

NV and TV technologies - how they work.

NV technology involves capturing and enhancing weak night light reflected from objects. The lenses of the device are capable of capturing the most inefficient light radiation invisible to the eye. The collected light enters the photocathode, where it is converted into electrons. Electrons enter the microchannel plate and cause an additional emission of electrons. That is, an increase in the amount of energy occurs. The latter bombard the phosphor screen, which causes the emission of photons of light. This light forms an image on the screen of night vision equipment.
TV technology uses an entirely different principle. It is based on the property of any object with a temperature above absolute zero to emit thermal energy. In simpler terms, you can measure the temperature of any object, even a cold one. All thermal imaging devices are capable of recording this temperature. The lenses of the thermal imager capture the minor heat radiation. The thermal sensor measures and the processor processes the data and forms a picture. It is a heat map of the area to which the device is directed.

How do NV and TV works in the rain?

How does a night vision device work when it rains?
Night vision equipment and a thermal imager display the picture on the screen differently. On a night vision monitor, we see the light reflected from objects. The light travels the distance from the subject to the lens of the night vision goggles. For a perfect image, nothing should interfere with the passage of light photons. But in reality, this is not the case. Light travels in the atmosphere, not in a vacuum.
Consequently, impurities of gases, dust, the smallest particles of water will interfere with the passage of light. They create the effect of partial absorption of light by the atmosphere and cause the photons to scatter. The clearer the air and less saturated with water vapor, the more precise the image on the screen. For example, let's take the air of the sea coast and alpine air. A more contrasting and clearer picture will be on night vision binoculars in the mountains. Near the sea, the contours of objects will be softer and blurred on the screen of the same night vision binoculars. Now let's make the situation worse - it's raining. Each particle of water will interfere with the passage of photons of light. Some of them will be absorbed, and some will bounce off the surface of the drops and create visual "noise" on the monitor of the night vision monocular. The reflectivity of the water is very high. The more it rains, the denser the "noise" on the screen looks. Sometimes, it is almost impossible to see anything due to the thick wall of rain, using a night vision device. In this case, it is much more effective to use any thermal imaging equipment instead of night vision devices.

How does thermal imaging equipment work when it rains?
The thermal imager does not pick up reflected light. It measures the temperature of the environment and builds an image based on the temperature difference. In our example of rain, the droplets are negligible for the device to register changes in their temperature. If the rain is not heavy and does not fall like a dense wall, then the thermal imager will not "see" the rain in the air. But, at the same time, it will be possible to notice large drops on the ground or other objects. Water evaporates from surfaces and cools them. Sensitive thermal imaging binoculars detect changes in surface temperatures and display the data as a picture of a running droplet. It is very curious to watch how rain, invisible through thermal imaging binoculars, leaves drops and streams of water on the ground. Light rain will not affect the operation of the thermal imaging equipment in any way. But, when it's raining cats and dogs, the streams of water act as a protective shield. They will hide everything behind them. Water perfectly absorbs thermal radiation from objects, and therefore a thermal imaging device cannot correctly measure the temperature of surfaces.
Consequently, anything behind the rain wall will be poorly displayed. Therefore, heavy pouring rain with a dense structure, will interfere with observation with thermal glasses or a rifle scope. And light rainfall will not interfere with viewing with thermal binoculars or monocular.

When should you use NV or TV?

In order to make a decision about the use of a particular equipment, several factors must be taken into account. First, you need to consider the height of the terrain above sea level where you are. This will affect the density of the ambient air. The higher the altitude, the thinner the atmosphere and the better the image. Secondly, it is worth considering the type of area: a large industrial center or a small village. The air in the villages is clean and transparent, in contrast to the polluted cities. Third, we take into account air humidity, atmospheric pressure and temperature. When it is extremely dry, high pressure and cold, the transparency of the air will be maximum. As a rule, under such conditions, nights are more often illuminated by the moon or cloud cover is very low. These conditions are ideal for a night vision device. In the case of dense clouds, an increase in the generation of a night vision device to the third generation or infrared illumination can help. If it is raining lightly, then the choice is obvious in favor of thermal imaging binoculars or thermal imaging sight. They will come in handy on an absolutely impenetrable night, with fog or blizzard. But with heavy, heavy rain, let's be realistic, thermal glasses or night vision goggles will not be effective.

Night vision manufacturers and thermal imaging equipment manufacturers have filled the market with high-tech products. In order not to get lost in the face of a huge offer, we recommend that you take a few simple steps. The first step is to decide on the tasks. The second step is to find out your climatic conditions and make friends with a portable weather station. Of course, the weather forecast will help you. We will give the third place to the collection of information from trusted sources about the models you like. In the event that one of the technology options does not cover all your needs, you should pay attention to the tandem of NV and TV. For example, thermal imaging binoculars detect a target, but do not give an accurate indication of the distance. Then the use of a night vision sight will give more information for orientation. In fourth place, we put the principle of expediency. Ask yourself, "How many times a year will I use this gadget?" In most cases, this will protect you from spontaneous purchases. But if this is a lifelong dream, then we are always in favor. Dreams should come true, and technology should expand our capabilities!