Is anyone using the VARI image to measure Leaf Area Index variation in field crops


#1

Hi there, I am looking to use the VARI image of wheat crops mapped in early/mid spring to assess the Leaf Area Index (LAI) of crops to aid nitrogen application, I have read that VARI is actually very good for this purpose which also means this can be done with an RGB camera (whilst NDVI flattens out once plants start extending in the spring due to the angle of leaves). Has anyone else got experience of using the VARI images produced by drone deploy to relate to LAI? Regards, Sam


#2

Yes! We use it in pine plantations. It’s OK for identifying differences on a stand or field level. TGI is also a useful RGB metric for chlorophyll content in plants as well. In pine we have a tool for measuring LAI on the ground from below, what we have found is the calculation is close, but not always perfect if there is a plethora of ground vegetation (think weeds in farm field), that can skew the results, also the differences are harder to tease out since the spectral ranges are much closer. So, is it useful: in our application it is, I don’t know much about wheat. We use a different processing software (ArcGIS Pro) that allows us to take the 3 band TIFF file and run it, you could also consider using other image processor or raster calculation program (ERDAS Imagine comes to mind).


#3

Nice, thanks @E_Poole!


#4

Thanks @E_Poole, I have been reading a number of papers on the topic of late and feel that both VARI and TGI (as you mention) would probably both serve a common purpose all be it in slightly different ways, i.e. one is a measure purely of Leaf Area and the other chlorophyll, but what I need to do (as you have done) is find a way (piece of software) of converting the VARI image produced into a measure of LAI or TGI to allow estimation of N in the crop canopy (that isn’t too expensive or maybe even free… At the moment I am not charging for a service with my drone but am obviously paying for use of DD, etc as I wish to ground truth concepts before offering a service… you mention ArcGIS Pro and ERDAS can you shed anymore light on these programmes…? Regards :slight_smile:


#5

Sorry for the tardy reply, I was tied up with Thanksgiving family stuff. OK, ESRI stands for Environmental Systems Research Institute. They are the prementent Geographic Information Systems company on the market, think Google Earth on super steroids. They offer a wide range of software and applications from server to desktop to mobile. Their software can process photos for VARI and TGI, as well as other multispectral images at the touch of a button, they used to be a vector (point/line/polygon) specialists, now they are more raster friendly. ERDAS is a company that has been around for a while, they were the go to raster (imagery) processing and analysis folks since the late 90’s. They used to be part of Leica Geosystems, but I think they either changed names or were bought out. Their package can be used to identify tree species by canopy classes, extrapolate land use from sat images, or just about any other thing you can think of. Neither of these software suites are free, in fact they are the exact opposite: they are incredibly expensive (1000’s per year per user). In your case an out of the box pay for play service like is offered in DD is a much better use of resources in my opinion. I work with Terabytes of aerial imagery on 600,000 acres, for my applications it makes sense, probably not for yours. If your going to offer services like this in the future and your client base is large enough I’d invest in these types of platforms and get some training, if this is a start-up and a side job, I’d probably just run with a canned system like Drone Deploy uses…


#6

Thanks for the info @E_Poole :slight_smile: I’m learning fast with all this, with time I would hope to add the use of the drone with crop imagery to my service as an agronomist to make better decisions for and add additional services to my customers (and new ones). I’m still getting my head round raster calculators since looking these up following your previous reply… I have signed up to DD for a year to look at how i can use this and so far it is looking promising , but I would like to take the VARI images generated within DD and translate them into LAI or the Orthomosaic images and convert them into TGI to aid with nitrogen application in the spring, rather than just looking at the VARI image and trying to interpret this. I don’t believe DD offer this service currently, hence I’m looking at other avenues but as you say at this point there’s no justification for big investment, as I am just testing the water and would like to find a way of doing so at much smaller cost whilst experimenting… Thanks again for taking the time to reply to me, this has been of great help pointing me down the right avenues to investigate…