fog model inconsistency
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here a serial of screenshots which shows the inconsistency of fog model
I used the FMAP generated from F4Wx
I take off with low visibility ( < 2km ) and higher I go, the more the fog disappears : the fog-shrouded area is expanding to well over 2kms … you can even see the runway in the middle of a breakthrough in the clouds. It doesn’t make sense there…
we should have a layer that does not allow the terrain to be viewed …
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Wait U4 for more information on this…
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@suhkoi69 hi, we need to double check but for now this is working as intended. This is a bit counterintuitive.
There are two fog layers in BMS: lower (more dense) and higher. In between, we have a transition between both which is not relevant to this discussion.
When you go inside the lower layer, you have more fog blocking your forward view, hence you see less. When you go higher, the fog layer is actually smaller.
Notice how the ray of light that goes to the upper plane goes through a lot less fog than the lower plane. So, essentially, when you are inside the lower layer, most of your view forward will be pure fog.
Of course, there could be a math error in the code as well, but I believe if you put both planes in my picture in the same pitch angle, then, the lower plane will be able to see a bit more than the upper one at the point straight ahead.
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@Seifer I agree but if you look at the second picture from the top, the fog layer is fully invisible when I m high …
Now, if visibility is less than 2km, this implies that the fog is rather dense… it’s inconceivable that from the sky it would appear as clear as it does on the 2nd screenshot…it should be milkier as we can see on 4th screenshot
if the visibility > alt fog, we move as if there is like a cylinder without fog below us
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I use this fog ‘feature’ to spot ground targets when they are otherwise completely invisible.
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@suhkoi69 said in fog model inconsistency:
@Seifer I agree but if you look at the second picture from the top, the fog layer is fully invisible when I m high …
Now, if visibility is less than 2km, this implies that the fog is rather dense… it’s inconceivable that from the sky it would appear as clear as it does on the 2nd screenshot…it should be milkier as we can see on 4th screenshot
if the visibility > alt fog, we move as if there is like a cylinder without fog below us
As a matter of fact , I fly very very regularly (2/3 flights a month) and I have witnessed this exact phenomenon many times and that is explained by seifer’s drawing
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@suhkoi69
In the image above, the fog layer allows you to see 500m out while you’re inside the layer looking forward, but if the layer is only 499m or less high, you will be able to see the ground just fine from above.I remember one time I had to close the airport I work at because we had less than 100m horizontal visibility, but one aircraft came overhead at 1400ft (±425m) and he could see the airport clear as day, just like we could see him flying from the ground just as well. Caused a bit of friction between myself and the pilot because he didn’t understand why I didn’t allow him to land, because he too didn’t understand there can be a distinct difference between vertical and horizontal visibility.
In many (most?) situations, fog will indeed be a layer that you can clearly spot from up high, like the first video below, but there are also situations where you have clear visibility from “higher” altitudes, but see absolutely nothing once you’re in the thick of it, as in video 2. I know the second video is rain, but the same effect applies to fog.
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So the idea should be that dense fog (or cloud cover) is invisible from up high, but not when inside it ?
I love a good IFR scenario so if this is wrong I would hope that it can get some attention
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I remember once going into EDDH at night time with low fog. We could see every lamp in the city and from the approach and runway lighting beautifully.
Just until at about 200 ft when we entered the fog and all was gone in a second, leaving us in a bright white mess from our landing light.
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@Mav-jp Very interesting, I thought fog appeared as a transparent milky layer seen from above.
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@suhkoi69 said in fog model inconsistency:
@Mav-jp Very interesting, I thought fog appeared as a transparent milky layer seen from above.
Not really , you need to think as an accumulation of particles , the more particule accumulated in your LOS , the more fog. So when looking from above you don’t see many particles if ground is close whereas if you are in the layer and look horizontally , you don’t see shit LOL
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@Mav-jp So are you saying that in this case shown here, with LSOs barely being able to see the stern, a jet up high looking down will be able to see the carrier clear as day ?
I get that the in-the-fog perspective is different from the above-the-fog perspective, but still.
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@jayb said in fog model inconsistency:
So are you saying that in this case shown here, with LSOs barely being able to see the stern, a jet up high looking down will be able to see the carrier clear as day ?
According to my understanding, we need to know 2 criteria longitudinal visibilty and fog altitude …if the altitude fog is lower than the longitudinal visibility , then you are right , a jet up high looking down will be able to see the carrier clear as day
Otherwise, the fog layer will cover the carrier and it will be hidden by fog …
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METARS report fog with 2 distinct categories, MIFG=shallow fog a few meters thick, Gustav_Guns described it in his post, ground features and lights visible from direcly above and slant until entering the layer. The other is FG=fog a thick layer, several hundreds of feet, no ground or lights visible from neither directly above nor slant.
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@luke777 said in fog model inconsistency:
METARS report fog with 2 distinct categories, MIFG=shallow fog a few meters thick, Gustav_Guns described it in his post, ground features and lights visible from direcly above and slant until entering the layer. The other is FG=fog a thick layer, several hundreds of feet, no ground or lights visible from neither directly above nor slant.
Interesting, thanks. If you set up fog in the mission editor, you set up fog from the ground up to an altitude you choose. So that could give a fog layer of hundreds of feet, ie FG conditions. But would BMS then make that see-through at slant or up high? Hm, gotta test
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@suhkoi69 said in fog model inconsistency:
@jayb said in fog model inconsistency:
So are you saying that in this case shown here, with LSOs barely being able to see the stern, a jet up high looking down will be able to see the carrier clear as day ?
According to my understanding, we need to know 2 criteria longitudinal visibilty and fog altitude …if the altitude fog is lower than the longitudinal visibility , then you are right , a jet up high looking down will be able to see the carrier clear as day
So, shallow (low altitude but perhaps widespread) fog can be see-through from a distance and/or up high. Not sure if this is a BMS construct or a real-life feature, although Mav-jp hinted to it being a thing in real-life.
A thick layer of fog (up to a high altitude) on the other hand should not be see-through from any vantage point, right ?
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@jayb said in fog model inconsistency:
@Mav-jp So are you saying that in this case shown here, with LSOs barely being able to see the stern, a jet up high looking down will be able to see the carrier clear as day ?
I get that the in-the-fog perspective is different from the above-the-fog perspective, but still.
it just depends on the fog depth
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@jayb said in fog model inconsistency:
A thick layer of fog (up to a high altitude) on the other hand should not be see-through from any vantage point, right ?
Right! If the vertical layer of the fog is thick enough, you should not be able to see the ground.
On the other hand, if the vertical layer is thin (like MIFG on METAR), you will be able to see the ground direct bellow you.I fly very often and this really happens
Greetings from Brazil!
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@luke777
yes, MIFG translates into mist / fog, meaning fog surrounded by mist or FG meaning fog surrounded by clear air. -
@Gustav_Guns said in fog model inconsistency:
meaning fog surrounded by clear air.
Yep, i remember a day when the airport was closed for VFR operations due to MIFG, but when i look up, the sky was CRYSTAL CLEAR and BLUE AS WATER!
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@Gustav_Guns said in fog model inconsistency:
@luke777
yes, MIFG translates into mist / fog, meaning fog surrounded by mist or FG meaning fog surrounded by clear air.MIFG means shallow fog (MI from the French word “mince”, which means thin; FG from FG)
Mist would be BR (again from a French word, “brume”)The official difference according ICAO is in the visibility:
Mist (BR) is used when visibility > 1km
Fog (FG) is used when visibility < 1km
Both BR and FG happen because of the presence of water droplets in the air, unlike haze - abbreviated as HZ - which happens when there are pollutants in the air (e.g. dust particles)
