Radiometric Calibration for Multispectral Imagery- Support for Reflectance Panels?

Alasdair

Hi All! I'm using drone mapping for research on a university project in Scotland. I would really like to be using WebODM for this to keep everything open source and accessible, but I am finding the radiometric calibration of multispectral images to be a sticking point. I understand the software can calibrate using EXIF data from the sensor on supported models (I am using a P4P M and a Micasense Red-Edge P). I have reflectance panels that I image for each flight and need to use to calibrate the images and generate accurate reflectance maps in addition to the EXIF data. I was wondering if there are plans to implement support for reflectance panels in WebODM, or other open source alternatives? I know its possible in in e.g. Pix4D, but want to steer away from them!
As a fun note- I tried processing the same data set on Pix4D and it couldn't even complete it, whereas it took only an hour, with great results on WebODM with the same machine and data set, an amazing piece of open source software!

3 Replies

pierotofy Best answer

Hey, yes in theory it's possible to add support for reflectance panels, but currently if you want to use them, you'll need to pre-calibrate the images yourself. There's some scripts available on the internet that can do it if you do a search.

👍 1
ImaPlayfair

To add on to the previous response, I ran into this limitation with my multispectral workflow recently as well. The solution I came to for efficiency's sake was to use Metashape to do reflectance calibration and then import the calibrated image set to be run in WebODM. Since you have access to Pix4D, you may be able to do something similar, although I have personally veered away from Pix4D because I'm not a fan of its overall workflow.
To address your opensource preferences: I didn't encounter any standalone tools, but there is pretty good documentation from MicaSense available at the following webpage and you might be able to develop your own tool or simply build out the scripts necessary for standalone reflectance calibration. https://support.micasense.com/hc/en-us/articles/115000351194-Radiometric-Calibration-Model-for-MicaSense-Sensors
For the P4P, it looks like DJI has a few tools, but I'm completely unfamiliar with them and their pay structure.
Somewhat related - I'm also working at a University and we're always looking for opportunities for collaboration, so feel free to reach out if you are inclined!

Alasdair OP

Thanks both for the help. I'll look into what I can do with a custom script, that mica sense repo looks like a good starting point. I think Pix4D unfortunately does the calibration at the orthomosaic stage, but I'll check if it outputs corrected images too. My end goal is to use these maps to find tree seedlings and look at river restoration in the Scottish Highlands, if that's something you're interested in let me know!

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