Sentera Double 4K - ODM Orthophoto for NDVI and NDRE

[CL_Argentina]

Hi! I am a new WebODM user starting with the image processing of some flights. I have a DJI Phantom 4Pro and a Sentera Double 4K NDVI - NDRE sensor.

I got all the orthophotos GeoTIFF through WebODM and when I open them in QGIS for the NDVI / NDRE index acquisition I see that each orthophoto has 4 bands.

I just want to ask if bands 1, 2, 3 and alpha corresponds to R,G,B and NIR (in case of NDVI orthophoto) and to R,G,B and RE in case of NDRE orthophoto.

I know it might be a simple question but I could not find the bands detail.

Thanks in advance,
C.

[Saijin_Naib]

Welcome!

The bands should be in the order that they came from the sensor in.

Do you have any samples you can share? We can help you check them in QGIS so you know for the future.

[CL_Argentina]

Hi Saijin, thanks for your quick reply.

Here is a link to NDVI and NDRE samples: NDVI and NDRE samples - Google Drive

I think that band 1 corresponds to Red and band 3 to NIR (NDVI sample) and RE (NDRE sample)

Thanks for your help in advance,
C.

[Saijin_Naib]

So, if you load them into QGIS, righ click, go to Layer Properties, and then Information and scroll down, you’ll get the bands as they’re labeled when created:
odm_orthophoto_NDVI.tiff

odm_orthophoto_NDRE.tiff

This can be a great way to double-check, and also allow you to make custom display/indicies by mixing bands to output RGB display channels (things like False-Color Composites, like LANDSAT does):

Why is that Forest Red and That Cloud Blue?

[CL_Argentina]

Thank you Saijin,

I saw the same in QGIS, but I find it weird since it should be using NIR and RE for NDVI and NDRE calculation. Also, according to Sentera Support band 1 is red, band 2 green, band 3 NIR and band alpha should be dismissed. Anyway, I’ll keep looking for more information.

Thank you again!
C.

[Saijin_Naib]

Could you put a “raw” image from each sensor there to to compare?

[CL_Argentina]

Sure! So the sensor gives after the flight 2 folders: “NDVI” and “NDRE”. Raw images are inside of each folder.

You will find in the previous link 2 images (one from NDVI and the other from NDRE folder).

[Saijin_Naib]

So it looks like we’re mapping band 3 from the raw images to band 3 in the composite TIFF. So, that should be consistent with the images from the sensors. We are likely not naming them according to the manufacturer since they don’t seem to be putting the band names into the EXIF.