Messages

1

General / Re: Reflectance/Radiometric Calibration on MicaSense Sequoia

« on: March 11, 2018, 09:44:22 PM »

Hi Selimerguden,

I've tried processing the images as you suggested, but I still get get some odd results.

1. If I process the images without applying any reflectance corrections then the data values for each band in my site range from:

Green: 5875 to 32348
Red: 3408 to 43059
Red Edge: 6214 to 55145
NIR: 5765 to 56416

Which all seem pretty reasonable.

2. Processing using the calibration values only (with just the 'use reflectance panel' option ticked) gives the ranges:

Green: 61731 to 65586
Red: 63224 to 65573
Red Edge: 65516 to 65536
NIR: 65515 to 65536

Which surely cannot be correct?

3. Processing using the calibration values and the sun sensor (both the 'use reflectance panel' and 'use sun sensor' options ticked) gives the ranges:

Green: 1197 to 9005
Red: 884 to 12678
Red Edge: 2190 to 29271
NIR: 2359 to 36428

Although these seem a bit more realistic in terms of the ranges, the values themselves seem odd.

It seems to me as though something is fundamentally wrong here. Any thoughts?

Mark

2

General / Re: Reflectance/Radiometric Calibration on MicaSense Sequoia

« on: March 11, 2018, 07:41:11 PM »

Hi Gustavo,

Sorry about the late reply. Yes,  I do have the reflectance values for the Airinov target:

Green 17.1%
Red 21.5%
Red Edge 26.6%
NIR 36.9%

Mark

3

General / Re: Reflectance/Radiometric Calibration on MicaSense Sequoia

« on: March 06, 2018, 10:07:08 PM »

Hi selimerguden,

Sorry, a further extension to my last post:

If the image values are still in DN units (even if calibrated), then then workflow from MicaSense suggests than the values from the reflectance panel haven't been used yet:

https://micasense.github.io/imageprocessing/MicaSense%20Image%20Processing%20Tutorial%201.html

As the suggested workflow is:

• Calibrated digital numbers are converted to radiance units by B1/(2^16) (for 16-bit images)
• The radiance image is converted into reflectance using the radiance values of the panel image of known reflectance to determine a scale factor between radiance and reflectance. With the final values usually in the range between 0 and 1.

If this is the case, then what is Photoscan actually giving us?

I think i'm even more confused!

Cheers
Mark

4

General / Re: Reflectance/Radiometric Calibration on MicaSense Sequoia

« on: March 06, 2018, 09:31:13 PM »

Hi selimerguden,

Thanks for the info. I am a bit confused though, as I thought that the whole point of going through this process of calibrating the reflectance (using the target) was to end up with reflectance values. I also assumed that these results would be normalised, and that we wouldn't have to use the raster calculator to do this. But then I'm still trying to find my feet with the software.

I really appreciate any insight that you can give us though, as it sounds like you're someone who knows what they're talking about!

Cheers
Mark

5

General / Re: Reflectance/Radiometric Calibration on MicaSense Sequoia

« on: March 06, 2018, 08:31:35 AM »

Hi gtalckmin,

Yes, I've tried two different scenarios, running the reflectance calibration both at the start of the processing workflow, and also at the end, just before making the orthomosaic. I think that Alexey said that you can actually do this at any stage, as long as it was done before the orthomosaic. In both cases though I get the same result. It's as if the DN numbers haven't been changed at all. Hopefully Alexey can perhaps check this out for us?

Cheers
Mark

6

General / Re: Reflectance/Radiometric Calibration on MicaSense Sequoia

« on: March 05, 2018, 06:13:06 PM »

Hi selimerguden,

Thanks for your reply, I really appreciate people trying to help me out. I've tried your tip with the brightness setting, but this doesn't really seem to help. Instead I went through the normal processing flow, but left the Reflectance Calibration until just before making the orthomosaic. This makes working with the GCPs easier, but I still end up with very white images/orthomosaic. If I go into the Raster Calculator and just graph the B1 (green) band, then you can see that rather than being between 0 and 1, the values are huge (around 65500). It seems like something is going wrong in the calculation somewhere, but I'm stuck as the workflow is pretty straightforward. This seems like the same thing the gtalckmin was saying in the original post.

Any thoughts?

Cheers
Mark

7

General / Re: Reflectance/Radiometric Calibration on MicaSense Sequoia

« on: March 05, 2018, 01:02:33 PM »

Hi Alexey,

Many thanks for the updated procedure.

I'm still having a few issues though. Adding the photos, the manual masks and reflectance values is fine, and when I hit OK on the Calibrate Reflectance dialog it seems to do something, so that the 'Normalize band sensitivity' option in the Camera Calibration dialog is automatically enabled. But, my images all seem to then turn white.

Any ideas on what might be causing this?

A few images are attached.

Thanks
Mark

8

General / Re: Reflectance/Radiometric Calibration on MicaSense Sequoia

« on: March 05, 2018, 11:09:58 AM »

Hi gtalckmin,

I am trying to figure out how to use the 'Calibrate Reflectance' option with a Sequoia in 1.4.1 too. There were a couple of earlier posts about this, most notably by Sean, but these tend to relate to 1.4.0:

http://www.agisoft.com/forum/index.php?topic=8362.0

Somewhere along the line Alexey (Agisoft Technical Support) produced a procedure which I've attached.

I'm using the Airinov QR reflectance targets, but these aren't getting automatically recognized either, although the images are automatically put into a Calibration folder, presumably because of some information in the metadata. This isn't such a problem, as the procedure tells you how to mask out the non-target area for each band, and manually enter the calibration values. You can then see if things have been successful if the 'normalize band sensitivity' option has been enabled in the Camera Calibration dialog.

However, having gone through the procedure I end up with almost totally white images, which seem to be over-exposed. This also seems to have been encountered by a couple of other users (Nenad  and school):

http://www.agisoft.com/forum/index.php?topic=7730.msg38070#msg38070

I'm now going down the road of trying to correct the images outside of Photoscan using python and some information provided by Micasense, but this is a challenge:

https://micasense.github.io/imageprocessing/MicaSense%20Image%20Processing%20Tutorial%201.html

Hopefully someone will be able to explain where we are going wrong, or if there is an issue with the software.

Cheers