Fog, friend or foe?.

Seeing as though most of the macho lot out there have night vision tubes strapped to their ‘M’ whatever. You should note that night vision can’t see through smoke, fog, heavy rain, snow, or other obscurants. Thermal can see through smoke and other obscurants, but can be  stopped by window and wind shield glass.

OK, all you have to do is yell out “night vision or thermal?” to whoever is following you and you know how safe you are.

Thermal works in fog (sort of with a reduced range) only the chances of a user positively identifying friend or foe is remote. Unless you have IR emitting tags fitted to your clothes.
I tried this a while ago. Simple IR emitters pulsing at 5 beats a second.

It worked BUT it made me stand out on EVERYONE’S  night vision.
Whoops, so much for being covert.

Then you have the smart arse.
Knows night vision is in use so has a pocket full of flares.
This will be highly effective in fog, heavy rain, or snow as the light spill from the flares is usually enough to swamp lesser grades of NV. Gen 0 to 2 for instance with 3-4 still unable to clearly differentiate targets if the flare is between them and you.

Fog. What other benefits has it?
Sound attenuation.
Yep, it does that. Except you have to think about what noise you are generating.
Attenuation by sound waves in fog is all about the  frequency, or pitch of the sound.
Higher the pitch, the better the attenuation. This is why fog horns have a very low pitch.
Now it’s not perfect but you can dig a generator into the ground, this reducing scatter noise and it’s IR signature. Get close enough though and you’ll still be able to zero in on it. Or if you have a dog, and they will lead you straight to it.
Their hearing being way better than ours.

Are there many types of fog?
You bet there are and in low lands it all depends on a low if nil wind speed. Fog forms when the difference between air temperature and dew point is generally less than 2.5 °C or 4 °F.

Now I had absolutely no idea that there were so many “official” types of fog.

Radiation (Winter) fog.
Clear cold night sky’s.
The ground chills down, the moisture condenses.
Rather than fog I tend to treat this like a heavy dew.

Valley or basin fog.
Think temperature inversion.
You have a cold basin of air and the wind blows warmer moisture laden air across it.
It’s a bitch as unless the wind picks up a lot or the temperature increases (sunlight), it can last for days.

Advection fog is sort of the same thing without the need for valley’s or basins.
If you have snow cover which hasn’t melted, warm moisture laden air over it will chill down and drop its moisture.
You also get this a lot at sea or (unfortunately) for those who live on water.

Evaporation fog.
Evaporation fog is caused by cold air passing over warmer water or moist land.
Slightly different and again an inland boaters fog.
Warm river evaporating away and a cold wind over it causes the water laden moisture to condense. Thus is it possible to be on a river in fog, walk a couple of hundred yards in land and it’s gone. Your day starts damp and wet until the sun warms everything up.

Up slope fog.
That wind blowing across hills.
Warm air from below rises, it gets cold, it “rains”.

Now here’s a thought and a sort of fog.
High rise apartments and low altitude clouds. Fog for the top few dwellings.
Sort of useful for collecting water on drip clothes and nets but nearly always short lived as the streets warm up, hot air rises and drives away the moisture laden air.

Freezing fog.
Composed of supercooled water droplets
This forms rime.
Fluffy ice that forms on all posts and lines on the windward side of things.
Living in an aluminum boat, I really hate this type of fog!

And finally.
I do love a good pea-souper.
Dulling noise, reducing visibility, making prey less jumpy for some reason.
Like they feel safe wrapped up in the gloom I suppose.
As for foraging / scavenging. Even with IR supported CCTV security, fog is your friend.
Only don’t forget some nice hot, bright, flares for when you get into the mire.

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One Response to Fog, friend or foe?.

  1. Interesting, different sorts of fog the same as different kinds of rain.
    Just as an aside: ‘Last of the Summer Wine’ on how Foggy got his nickname: Thick and Wet.

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