I wanted to share some of my results in comparing a modified consumer camera with a scientific grade multispectral camera when evaluating plant health with NDVI. This note is related to NDVI only as the modified consumer camera tested only has two bands to compare with(Red and NIR). I wanted to see if it was possible to get meaningful and comparable NDVI data from an affordable consumer grade camera vs a scientific multispectral camera and if the difference in price was really worth it.
NDVI is a vegetation index that uses a numerical indicator using visible and near-infrared bands to help analyze remote sensing measurements. It is often used in agriculture to measure general crop health and changes. It is calculated by dividing the difference in the near-infrared and red color bands by the sum of near-infrared and red bands for each pixel.
The consumer camera used was the Canon S100 with the internal IR filter removed and replaced with the MidOpt DB 660/850 filter(http://midopt.com/filters/db660850/) MidOpt Band info
The scientific camera used was the Micasense RedEdge 3(http://www.micasense.com/rededge/) RedEdge Band info
Canon S100 Red and NIR channels
RedEdge 3 Red and NIR channels
Both sets of camera images were calibrated against reflectance panels with known values. Only RAW images were used. The images were obtained on the same day at around solar noon. The flight with the Canon camera was flown within five minutes of landing with the RedEdge camera. The image sets were processed with Pix4D Pro with the only difference being a slight modification to the NDVI formula with the Canon to account for the NIR contamination in the red channel.
Side by side comparison
The results are very similar especially in terms of sensitivity. Can you tell which image set came from a near $7000 camera and which came from a camera that cost under $200? The Canon set is on the left of the above image and the RedEdge set is on the right. With the advances and availability of new filters to modify a consumer camera I think the gap is closing. Scientific cameras certainly have their abilities and value but the modified consumer cameras are proving their abilities and usefulness as well.
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Hi Claytonb, Really interesting analysis. I currently use a Canon S110 modified by Sensfly for NDVI and I wondered if there could be a big difference with a camera with separate sensors - I noticed now the accuracy that the camera can offer. Impressive! I also use Pix4D pro, what are the slight modification to the NDVI formula? (I imagine they will be different depending on the type of filter) And also, where did you find the calibration board? With known reflectance?
Thanks Alex
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Hi Alex, I would recommend contacting Charlie Langlois at Labsphere- clanglois@labsphere.com They can make affordable($300 range)targets that are smaller 2X2" pieces that work great with same quality and accuracy as the targets that cost thousands. The formula I used in the above comparison subtracted around 40% of the pixel value in the red channel. I imagine it can be very different with different sensors and filters. It also changes based on the shutter speed, ISO as well so you will have to play with it to see what you can get. Luckily I had the RedEdge camera and a Greenseeker to verify values and know what I was aiming for in the formula modification.
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