Please could you give me some clarity regarding the calibration of the DJI Phantom 4 Multispectral. Whilst the purchase of the P4 MS does not come with a calibration target but within DJI Terra software, there is an option for radiometric calibration.

  

I am trying to source a calibration target from various sources, but I would be grateful if you would advise me. I have seen others asking this question, but it has not clearly advised upon. So please could you give me a definite answer.

  

1.      What % of reflectance target works best. I have been advised the Sentera reflectance target may be about a 20% reflectance, DJI please comment.

  

2.      The band average for a reflectance target from a particular company for a 50% reflection target for each wavelength is shown below, but there is very little or no variance (+/- 0.05) between the wavelength from the calibration report is that correct? :-

  

  

Blue (B): 450 nm ± 16 nm; - 0.51

  

Green (G): 560 nm ± 16 nm; - 0.52

  

Red ®: 650 nm ± 16 nm; - 0.52

  

Red edge (RE): 730 nm ± 16 nm; - 0.52

  

Near-infrared (NIR): 840 nm ± 26 nm - 0.51

  

Please could I get some clarity on this subject. If I were to purchase reflectance target what vales should I expect. And what is the best target reflective value (%).

Thank you

Hi there, thank you for reaching out. Currently, DJI does not define the best reflectance of the reflectance target. For the second question, you may need to confirm with the reflectance target manufacturer.
If you need to buy a reflectance target, it is recommended that you buy three types with different materials with an even reflectance distribution (eg 20%, 50%, 70%). Hope this is informative for you.

Hi DJI Susan, thanks for your reply. Unfortunately, this just confuses the whole concept. Why when other drone multispectral sensor manufactures only have one reflector calibration panel are you now suggesting 3 different material types at 3 different reflectance distributions 20%, 50%, 70%. And this without any explanation?  Why do DJI who are or were in my eyes the superior drone manufacturer, now seem to be extremely cryptic in your reply’s, and do not actually solve the problem of calibration target. Is it a ploy to get users to stay with the DJI Terra? From your other replies to other users of DJI P4 MS on this forum to this issue you have never mentioned 3 types of material and 3 reflectance value. You don’t seem to be consistent? Why?
I am asking a rudimental question to the ability of your drone; I would expect a decent answer that answers the issue in question. You seem to be skirting around the issue rather than answering it. Please could I get a definite answer. Please outline make, material and reflectance value of a calibration target I can use for my DJI MS drone? If you are unable to answer it please could I speak with someone who can, or someone in a higher position please who can give me a more informative answer.
Dare I say I use Pix4D with my DJI P4 RTK for mapping purposes and they state that Sentara sensor or Microsence calibration panels are workable with DJI workflow. If you do not become more transparent, I will have to widen my research and go onto my global network and involve many more potential users of DJI multispectral, who will not purchase DJI and go with a competitor of this type of sensor.

I have now sourced a suitable reflectance target, which is extremely compatible. I can source it on several reflectance distributions (eg 20%, 50%, 70%) if required or  similar to another well known  branded target. Who would I need to speak to in DJI to possibly arrange supplying your customers?  

Hi  fans259ef885,

DJI have done one unique RADIOMETRIC CALIBRATION for the P4M multispectral sensor (NOT for each camera as far as I know); the radiometric correction coefficients are stored inside the header of each image. SfM softwares like Pix4Dmapper and Agisoft Metashape are able to use those values to obtain something "close" to  the TRUE radiometric REFLECTANCE.

If you only need to use Vegetation Indexes (VI) (e.g. NDVI) you DO NOT need to care about radiometric calibration at all due to the fact that all VIs are based on ratios.

If you do scientific research and you need to publish TRUE REFLECTANCE values I think you need just ONE calibration panel and I suggest to choose the % reflectance on the base of the characteristics of your environment (i.e. incoming sun light intensity - average irradiance in the sites you have to survey).

When buying  the calibration target be sure to get from the company its Calibration Certificate. It should report both a table with the reflectances measured in the lab along the spectrum from blue to NIR (i.e. spectral signature) and the accuracy of the above measurements. The best Radiometric Calibration panels are quite expensive and their price increase with size, consequently when choosing the size take into account the height Above Ground Level (AGL) you use to fly or just buy a 20x20cm target if you want to shoot the target before and after the flight.

Maurizio

Hi,
I agree with mbuonanno #5
I compared dataset of P4M and Tetracam microADC which has a reflectance target and a calibration file. Quite honestly, the P4M works very well and produces quality data. With Agisoft Metashape. We gave up Pix4D for research work a long time ago.
After all it depends on what research you need to do. If you need something very precise I recommend a hyperspectral camera, it's more serious than a P4M in terms of volume of data available.
I encourage people not to focus on the reflectance target, remember that there is a solar sensor integrated to the drone and that does its job well.

To address the some of the common issues with processing multispectral data we are looking to support the Multispectral. If you have a couple of sample images laying around we would love to add support for this camera.

Some advantages of using TerrainDrop would include faster coverage since only 5-10% overlap needs to be used (non-photogrammetry approach), built-in image to image comparisons, zero wait time and it is free.

5-10%! the line-up must certainly be fantastic. It's not a serious solution.