Different results due to different camera exposure settings


#1

Dear all

We’re doing a trial run for a project that involves plant health. We want to capture fields with two weeks in between to see what the difference is. So we took our DJI Phantom 4 Pro for a test flight over a field and repeated the same flight (copy of planned flight within the DroneDeploy app) twice.

The camera exposure settings were set to manual and I changed these for both flights due to lighting changes.

Now: The processed results with the option “Plant health” are severely different. But there was only 10min in between those two flights. In our opinion the results for both flights should be the same, regardless of the exposure settings. In two weeks from now the light will be completely different anyway, so we’re not sure what we’ll be comparing.

What would be the best approach for this issue? And is the Phantom 4 Pro the right tool to obtain information about plant health?

Any help is highly appreciated.

Thank you!


#2

Hi @J-5027,

Thanks for swinging by the DroneDeploy Forum. As far as I know, you should not be seeing drastic differences like this in your maps with slight camera exposure changes. Can you share the names of both of these maps so my team can further investigate?

Thanks,
Christina


#3

I am not a crops expert, but my understanding of ndvi is that it is purely a color analysis. Is it green or not green, so exposure has a huge effect on the results. If you look at these maps from that standpoint they are virtually the same. Just one is brighter than the other. If you add white light to red you get pink right? The more white light you apply to green the more like yellow it looks.


#4

Hi Christina,

Thank you very much for your reply and your help. The map names are:

Flight 1: Flight J-5027-A1
Flight 2: Flight J-5027-A2

Please let me know if there’s anyhting else you need.

Thanks!


#5

Hi Michael

Thank you very much for your reply. That’s an interesting point. I will try to conform the two maps with this approach and see if I can eliminiate the exposure mismatches.

Thanks!


#7

Thank you @J-5027. I’ve forwarded the info over to our team to review. I’ll report back if I need more info or if I have some to share. Thank you for your patience and cooperation! :slight_smile:


#8

Hi @J-5027,

@MichaelL is correct. When using an RGB camera you are measuring the “greenness” of a crop. Most plants are considered healthy when they are green due to their chlorophyll content.

So if you think about it. If you change the exposure on a camera that is capturing RGB data you will change the VARI map drastically. By increasing the exposure you will lose a lot of green in your images. Because of this, we say that VARI should be used to get a good idea of the surrounding area and used primarily for crop scouting. You should always ground truth your results.