I got the following annoying-scaring experience.

I decided to fly my Spark close to an approaching patch of fog. I took off and climbed at just 60 meters, above the patch of fog, and flew around for a few minutes, still in sight of my drone.

In the meantime the patch of fog approached my location and I ended up flying over it.

I decided to descend but, approaching the top of fog layer, at about 50meters, the altitude sensed by my Spark dropped to ZERO, as if the fog was seen as a solid surface, and I suddenly got the message “landing”. However no landing was actually performed as my Spark was not able to sense a real consistent solid surface, so its status freezed in a landing status with an hovering at a sensed 0.1-0.2 meters, although the real altitude was 50m. There was no way to unfreeze it. The only possible option for me was to command a light climb with the left stick up, which cleared the landing status. However, by trying to lower it, I continued to get a landing status with no possible control authority.

I also tried to select sport mode, hoping to remove any issue related to a false obstacle avoidance. However I found no way to remove the bottom sensors obstacle avoidance.

I stayed minutes trying to lower my Spark, without success.

Finally I decided to climb and control the lateral-longitudinal position to let it eventually crash-land on a desired target when the batteries would have been depleted. At the final battery low status warning, when the propeller rotation speed was not enough to keep it in a hovering position, it finally descended and impacted the terrain nicely, without any damage, just ad a slightly higher speed with respect to the standard landing manoeuvre.

Is there any way to bypass this issue in case a similar situation occurred again with false bottom obstacle avoidance sensing?

I think they key here is that you flew in fog and it is definitely not recommended. I had similar issues as you did but had some clear areas where I could guide it through. Fog as I understand is like a ground layer to the spark sensors so it sees it and senses that is ground level, hence your problems. DJI obviously doesn't recommend flying in these conditions.

I think they key here is that you flew in fog and it is definitely not recommended. I had similar issues as you did but had some clear areas where I could guide it through. Fog as I understand is like a ground layer to the spark sensors so it sees it and senses that is ground level, hence your problems. DJI obviously doesn't recommend flying in these conditions. I personally really enjoyed flying in and above fog but knew I had an escape route if things went pear shaped.

I wonder if turning off obstacle avoidance in the settings would of allowed you to land ?

larrymull Posted at 2017-10-17 13:57
I think they key here is that you flew in fog and it is definitely not recommended. I had similar issues as you did but had some clear areas where I could guide it through. Fog as I understand is like a ground layer to the spark sensors so it sees it and senses that is ground level, hence your problems. DJI obviously doesn't recommend flying in these conditions.

Of course, one should not fly with such an alien condition as.... fog.  Because it would be terribly difficult to implement a software option that would avoid these situations....

What a scary situation, i hope never to get throught this.

Had the same scenario a few days ago. Also I was aware that fog will throw of the sensors so I flew with great care. How ever I was fully capable of maneuvering the craft through the fog.
As someone pointed out in my post that sport mode will do the trick.
As of now sport mode is my failnsave in case the spark goes rogue or disobeys my orders.
If you get the chance again, try to fly close to you and test the fog / auto landing with sport mode engaged. (Please be careful )
This is a good exercise for a pilot as weather conditions sometimes can turn bad quickly and it catches you by surprise, this way you now how to react and what to do.  

Larrymull is right. Please take our user manual as reference, we are not recommend you fly in bad weather including fog.

Rawsome Posted at 2017-10-17 15:30
Had the same scenario a few days ago. Also I was aware that fog will throw of the sensors so I flew with great care. How ever I was fully capable of maneuvering the craft through the fog.
As someone pointed out in my post that sport mode will do the trick.
As of now sport mode is my failnsave in case the spark goes rogue or disobeys my orders.

Thanks. However, as mentioned, I did try the Sport mode but it is only disabling forward obstacle avoidance. Nothing changes to the behaviour of the bottom obstacle sensor and even in Sport Mode I had the same issue while trying to descend: landing was always triggered without the change to accomplish it.

Jetline737 Posted at 2017-10-18 04:07
Thanks. However, as mentioned, I did try the Sport mode but it is only disabling forward obstacle avoidance. Nothing changes to the behaviour of the bottom obstacle sensor and even in Sport Mode I had the same issue while trying to descend: landing was always triggered without the change to accomplish it.

Just had the same problem in a low cloud situation. I was going to report this until I saw this post.
It is autumn and i think a lot of people may get caught out in murky weather conditions.
Can DJI confirm that in sport mode the vertical down facing collision avoidance system is still active.?

I often use full down stick to force a landing on my hand this then shuts off motors after landing. If the spark gets a false ground detection there is a real possibility of it thinking it has arrived on 'terra firma' when it hasn't and shutting down whilst airborne .

Can dji confirm this is a possibillity
thanks

In fog its normal - also someone here wrote somewhere that he flew to high and low clouds made same as fog for u - but dron felt from 100m + If u are not sure u have a clear view in fog - dont fly - today i made few shots but in case of your accident i made photo from 20m from fog not flown in it.

Sensors are not perfect - last week my spark in gesture control by my dad hover above armrest of the balcony - it was long but only 3cm width object - guess what happened - he detected it as plain bigger surface and landed (tried to ladn ) on armrest.  unfortunetly ofc felt down to  pavement from 2m xD

In such a situation I will try to do something like emergency autorotation , will try to mantain forward motion descending at high rate . Some one tryed it ? As I remember if you fly at high pitch it goes down a little by itself.

drones wth downward sensors don't like to fly in fog.  Throws the sensors off and/or get fogged up and can't do their job properly.  DJI doesn't recommend flying your drone on a foggy day or in fog.

Put a small mirror in the down sensors ant give a try...

I've flown in foggy conditions, and had the same problem (DJI has the log-files).

DJI's advice is to not fly in fog, and my advice is the same, as for safety - you can't see sh*t in fog - just like the sensor...

But if you get into the situation again, try flying fast-forward, and to left or right circling. This helps me to get the birdy down, as the sensor seems to get bypassed a little bit.

You guys have to understand, the Spark uses infrared light to detect the landing surface (it's like the urinals that flush when you step away).  In the infrared light, the fog or a cloud looks exactly like a solid surface so the Spark "thinks" it can land.  The Spark can't fly through this "solid" surface so it just hovers.  It's simply a limitation of the sensor and that's why DJI says not to fly in fog or over clouds.  

But I see so simple solution? If the down vision sensor reads like 1m or so, and GPS says 100 the app/firmware should make more evaluation and at the and use last resort, ask the pilot if the spark is mid air or at the surface

The problem is GPS altitude measurement is not nearly as accurate as ground position accuracy.  It varies depending on GPS SAT position.  I've watched the altitude vary by 50 meters just sitting in one spot on a Garmin GPS Receiver.  As I recall altitude error is 1.5 times greater than ground position error by specification.  The position accuracy for civilian consumer customers (us) is guaranteed to only 5 meters best case.

50m with 15+ satellites 3d fix? My phone is better...

Phone guarantee is also 5 meters best case for ground position.  The 50 meters we are talking about is altitude changing not ground position.  Ground position also wanders in consumer devices but much less.  The GPS SATs are NOT stationary and so your device including Sparks also is constantly showing a new position.  If you have tracking you can see that the displayed location wanders around a central point constantly even when the GPS receiver is stationary.  Buildings, reflections, obstacles, etc. also degrade the GPS accuracy.  Position is far more accurate on a hill with clear sight in all directions than down in a narrow valley, city street or canyon.

I am curious now to know if also the Mavic and all the others have the same issue as they have a bottom sensor... I remember to have seen in the past clips of someone making its Phantom climbing and descending through clouds... with no issues...

The time when we are able to take "atmospheric" photos in fog or in snow with our drones will eventually come... but not with the current generation of drones. There are (at least) two problems. The first one is described in this thread - in fog, the optical sensors are not able to distinguish any ground pattern, hence spark is not able to calculate its distance from the ground. The other problem is that the consumer drones are generally not weather sealed. If one fly in fog, moisture can easily get inside the drone and once water condensates on fragile electronic, the drone will likely die.

It is possible to overcome both obstacles. The technology is out there: optical sensors can be backed up by ultrasonic "sonar" and this will solve the first issue. As for the second one, I'm sure one day we will witness weather-sealed drones. SLR cameras (mid-range and above) are weather-sealed for "ages". In the last about two years we witnessed appearance of rugged smart-phones  and even popular models (say iPhones) are now waterproof. Thus, one day competition will force producers to make their drones capable to work in fog/snow/etc. But not today. Introduction of any of these changes comes with increased production costs and so the drone producers will introduce them only if they are forced by competition.

Yesterday I tried to cover both the bottom sensors and the front sensor with black tape to see if it would take off, and how it eventually would fly.
It took off and was flying normally.  Both in OA, non-OA and sports mode. I felt no difference at all.
RTH was 3 meters off, and I set it down manually. No problem.
I believe the black tape on the bottom sensors will prevent it from being confused by fog.

That depends too on what they used to color the tape.  I was technical marketing for optical sensors at Honeywell, and it turns out that some black colors are totally transparent in infrared light.  In visible light the sensor is black, if you look at it in infrared the sensor looks like the housing is made of clear glass.

The electrician tape I used seems to block IR
Here it is hanging down from a table with a hand behind it as ir source.

Flyingstoo Posted at 2017-10-18 07:40
Just had the same problem in a low cloud situation. I was going to report this until I saw this post.
It is autumn and i think a lot of people may get caught out in murky weather conditions.
Can DJI confirm that in sport mode the vertical down facing collision avoidance system is still active.?

Had it once, yeah, it just shuts down and fell off if you do a force landing

old thread i know but

cant belive you would put tape over that bottom sensor , it is a wander it just didnt just keep flying to your max height and crash land when batteries drained .......

Looks like Sparky doesn't like the Fog...  Will try an avoid it

Hi, this happened to me. Sports mode etc, nothing worked. I then watched as the battery slowly ran out and it plummetted from the sky, into the water. They will not replace it.

If only i saw this before.
I just watched the battery slowly run out while it refused to descend even in sports mode. Then i saw it plummet into the water. They will not replace it. Kind of a big defect. There is no way to override the silly ground sensor. Why would software even take a ground sensor seriously when you are way above the take off point. I mean at least a simple override in sports mode would solve the problem.

Jose Ramos Posted at 2017-10-17 14:31
Of course, one should not fly with such an alien condition as.... fog.  Because it would be terribly difficult to implement a software option that would avoid these situations....

I'm a software developer. It is not a complex problem. Sports mode override problem solved. Also, if your height is above a threshold why take the ground sensor seriously? It's a no-brainer. How many years have Dji had to fix this?

djiuser_Thgw69AETdSw Posted at 7-16 17:21
I'm a software developer. It is not a complex problem. Sports mode override problem solved. Also, if your height is above a threshold why take the ground sensor seriously? It's a no-brainer. How many years have Dji had to fix this?

Are you a software developer, do you think flying in fog is wise?