Following on from my last post on modifying the PowerShot S95 for NIR photography. I have ran a couple of test flights to collect some heathland data. The last flight produced 134 photos which were stitched with Agisoft Photoscan and then processed with the Fiji Photo monitoring plugin to produce the NDVI image shown. Original output files can be found here

Areas of green/higher chlorophyll containing vegetation can be seen on the processed photo as green and red areas.

The photos from the camera are a little blurred right now as the 2007 filter is thinner than the IR block that was removed from the camera causing some focusing issues. I have a replacement non blocking filter on order that should solve this problem.

I'm making progress, I now need how to analyse this to get some quantitative data...

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Comment by Jim Pullen on November 30, 2014 at 1:51am

Great stuff,

I have converted a ixus 220 and have been able to produce some images. I have found that getting the white balance correct is most important.

This image is of a salt marsh, muddy creek, sea wall plus an oil seed rape field which has just sprouted at the top of the image 

Comment by Bill Isenberger on November 30, 2014 at 6:21am

Cool drone application!

Comment by Rai on November 30, 2014 at 7:11am

Hi Mark (and Jim),

Thanks lot for your information. I would like to ask you a probably stupid question, but did you bring two cameras in a drone to get the NDVI images (one is still with IR block and the other one without)? Or you simply flew the UAV twice in the same area? As far as I understand (to the very limited knowledge of mine) we need to combine the true color images and NIR images to get NDVI? is it right or I am wrong? Please correct me if I am wrong. Thank you so much and would also love to share some results later on (I plan to use it to detect the algae blooming due to the eutrophication and high effluent of N and P in the river) if I can get far with this method. Thanks lot and good luck.

Best,

Rai

Comment by Mark Williams on November 30, 2014 at 11:39am
Rai. I used just one camera that captures both NIR and visible light. The public labs 2007 filter allows for this. If you are using a NIR only camera then you will need to also capture RGB from another camera at the same time. There may be benefits to doing this but it is beyond my budget at the moment. Using this to find algal blooms is a great idea. I look forward to hearing how you get on with it.
Comment by Mark Williams on November 30, 2014 at 11:40am
@Jim. What area of land is this covering? It looks great. Fixed wing or multicopter?
Comment by Jim Pullen on November 30, 2014 at 1:01pm

Hi Mark.

It's an area of saltmarsh over here in the UK. It was enwalled but reverted back to marsh after the seawall breached in the 1953 North Sea storm serge and was never mended.

Multicopter was an Iris with a 3d printed gimbal.

Area is around 70,000 m2.

Algae should show well. I have found green seaweed shows up very well. 

Comment by Rai on December 1, 2014 at 1:36am

Hi Mark,

Thanks lot for the info. Indeed I have tried to use the 2007 public lab filter but don't have idea yet how to analyze the result. I am now still collecting some papers to read. Thanks lot anyway Mark.

@ Jim, thanks for the information Jim, I will try to capture some micro-algae then.

I will definitely report the result once I can go further. Good luck

Best,

R

Comment by Chris Fastie on December 2, 2014 at 6:12am
Mark,
It looks like the S95 images that make up your stitched mosaic vary in focus. Was the camera on autofocus? Poor focus is a common result after converting a camera, but the new filter may not be to blame. The S95 makes it easy to adjust the final three screws holding the sensor plate, so it should be possible to get very good focus with the Rosco filter installed. A glass filter can give better results, but the big variable seems to be adjusting those screws. What new filter have you ordered?
Chris
Comment by Mark Williams on December 2, 2014 at 6:21am
Chris, I've played around with the screws a lot but can't improve the focus. They are currently tightened right down. The camera was focused at infinity so I'm expecting that the missing ir block is the problem. Have you got the S95 focus sharp with the IR block removed?

I have an optical window with the same dimensions as the IR block ordered. This will give full NGB wavelength transmittance and I can install the filter on top of this. Hopefully this will sharpen things up.
Comment by Chris Fastie on December 2, 2014 at 6:57am

Mark,

The only S95 I converted works pretty well. I put a Wratten 87 polyester filter inside and the focus is sharper on the right side of the photos (below). So I assume I can improve focus by adjusting one or more of the sensor screws. I will be really interested to learn how the optical glass helps. The first test to do might be with only the new glass to see if focus rivals the unmodified performance. Getting those screws right will be crucial.

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