Update: We are no longer selling the BG3 filter glass as we’ve got a new set of custom filters which do a better job of separating NIR and visible light. The links below are pointing to the new filter product pages.
I’ve been experimenting with multispectral imagery lately and recently got some special filter glass that makes it possible to perform NDVI analysis on a single image. The filter, Schott BG3 glass, blocks out light in the red spectrum but allows blue, some green and near infrared light to pass. As a result, a camera modified with this filter will record NIR light in its red channel instead of red light, resulting in an NGB image. We’re now selling converted NGB SX260 HS cameras at Event 38 as well as the individual filters so you can do the modification yourself!
After adjusting the color balance, the images come out looking something like this, which is a pretty cool effect in itself:
I was a bit worried that these images might cause problems for the post-processing stitching algorithms. So I mounted my modified SX260 onto an Aphex to make a quick map. The images self-geotagged and, happily, were stitched together easily by Agisoft Photoscan! The NGB map is shown, in very low detail, below:
The image shows part of a local R/C flying field. Most of the area is short grass. The paved runway, access road and a small shack are visible as well as a small treeline, though it is a bit difficult to see. Using the Fiji version of ImageJ plus the Photomonitoring plugin as described at FlightRiot, I ran a single camera NDVI analysis on the ortho image which resulted in the false color NDVI image below:
This image appears to do a great job of depicting where the densest vegetation is. The runway is mostly dark red with some cracks of green where grass has overgrown. The dirt access road is largely covered by small patches of grass that poke through the gravel, leaving it a lighter shade of red. The shack is completely devoid of vegetation, as expected. In the lower right corner, two lighter green turnoffs are visible which match up to the aisles of an occasionally used grass parking lot.
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