I am really interested in working with some of my farmer friends to monitor crops using NDVI. I get the concept, but what I am struggling with is using the reading to reflect nitrogen needs vs irrigation needs. I have been reading scholarly articles, but I was hoping someone would be able shed some light.
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just tried mapknitter and it does not work in IE. Tried in Chrome, it works but what an unusable software ! After one image it's already a pain to use. What would it be with hundreds of images to stich, rotate, scale, distort one by one !? No wonder it 's free.
Try MS ICE. It's free and generally good for most job. dronemapper is a good online service provider with reasonable price. I use Agisoft for my job. It's great
NDVI gives a general impression of crop health. Briefly, plants are green because the chromaphores that collect light energy, chlorophylls, collect blue and red light. The energy from this light is used to generate biomass from air and water. Infrared light, however, is not high enough energy to participate in this reaction so plants do their best to reflect this wavelength. This is accomplished through the spongy layer that collapses when the plant is under stress. Thus, a ratio of visible to infrared reflectivity is an excellent gauge of plant health.
These ratios do not by themselves indicate why the plant is stressed. It could be due to water, fertilizer, or some other reason entirely. Agribotix's experience with corn growers in Missouri is that fertilizer deficiency is almost always the cause of plant stress. This experience is echoed by users of the Trimble GreenSeeker (http://www.trimble.com/agriculture/greenseeker.aspx), a device that fertilizes in real-time by using an NDVI signal. I wrote a brief blog post on that idea here: http://agribotix.com/blog/2014/4/25/nitrogen-sensing-technologies-a....
The imaging won't be much use on its own. Unless you collaborate with an agronomist with fairly extensive knowledge of the crop/s in question, you would ideally measure foliar N levels and correlate with water application or uptake in some way.
I don't know what crops you're dealing with but the relationship between N and irrigation often easy enough to quantify but doesn't tell the whole story. If foliar N is closely related to yield you might find a series of NDVIs (or other veg indices) over the course of a couple of seasons might allow you to draw some conclusions about irrigation versus yield and refine the application of water in subsequent seasons.