Mavic 3M AgMultispectral - Is calibration required in Pix4D mapper?

PIX4Dmapper
1

Hi,

I am processing AgMultispectral data captured with a Mavic 3M. Everything has been great thus far, however I am wondering if within Pix4D mapper stage 3 output processing if Radiometric Calibration is required for this drone?
To my understanding this drone features a sun irradiance sensor on top, and calibrates “on-the-go”, and as such I have never taken calibration reflectance pad images prior to flight. Do I set the radiometic calibration to “No Correction”? Or do I leave it as default on “Camera and Sun Irradiance” and just assume that Pix4D Mapper will read the .tif image data and calibrate accordingly to produce accurate index outputs and reflectance maps?

Any help would be appreciated.

Cheers!

2

Hi Corey,
I cannot comment on what corrections the M3M is doing while in flight. However, we recommend not manipulating the images in any way before bringing them into Mapper. This includes some of the dewarp settings DJI also has.

Once you bring the images into Mapper, the program will read what Exif data has been stored on the images. When generating the reflectance map, Pix4Dmapper uses the values present in the Exif. Depending on what is present will determine what type of correction you can perform ( Camera only, Camera and Sun Irradiance, or Camera, Sun Irradiance and Sun angle).

We also highly recommend using a radiometric calibration panel either immediately before or after the flight. This will allow you to generate a reflectance map that has absolute reflectance values. If you do not use a panel, then it is not possible to compare reflectance values from different acquisition periods.

3

Thankyou so much for the in depth reply.

Does this mean that without setting calibration pad images of known reflectance, then the ouput reflectance map is “useless” for lack of a better word? Furthermore, does this then have any negative effect on the index calculations and overall diminish the accuracy of the index maps such as NDVI?

4

Not using a calibration panel is okay if all you need to do is have relative reflectance values. Meaning, that you only need to compare areas within your field for that particular flight. However, if you want to compare your results day after day, or year after year, then you must use a calibration panel in order to produce absolute reflectance values.