http://www.fsnau.org..._Index_NDVI.pdf (from wiki)
I like how they always state Value X 'commonly' represents Y.
There are tonnes of references listed in those two links that may point to something interesting.
Look at the first link in particular, they reference actual Case Studies where NDVI was used.
One of the earliest applications of NDVI was in:
Rouse, J. W., R. H. Haas, J. A. Schell, and D. W. Deering (1973). Monitoring vegetation
systems in the Great Plains with ERTS, Third ERTS Symposium, NASA SP-351 I, 309-
If you can get your hands on that, it might be helpful.
Thanks for the speedy response. Sorry I didn't get back to you until now. I thought I signed up for email notifications of responses, but I didn't get one, so I need to double check that.
So I went through the pdf you pulled f/ Wiki, and it was a useful overview explanation of NDVI, but I wasn't able to make sense of the last sentence.
"Theoretically, NDVI values are represented as a ratio ranging in value from -1 to 1 but in practice extreme negative values represent water, values around zero represent bare soil and values over 6 represent dense green vegetation."
Did the author mean 0.6, instead of 6? That was a tad confusing; I just assumed it meant 0.6.. I have only been reading that NDVI goes from -1 to +1, and anything under zero "do not have any ecological meaning" (quote f/ other article you linked). And if >0.6 means "dense green vegetation", then does my NDVI filter of 0.38 not count?
So the link from Rangeland Methods
had some great links at the very bottom under Additional Information. This site from NASA
provided the best explanation of NDVI yet. The quote on the right, "If there is much more light in NIR waves than in visible wavelengths, then the vegetation in that pixel is likely to be dense", in concert with the nice diagram of NIR and Visible light bouncing off a green and withered tree made a lot of sense.
This FAQ on Vegetation in Remote Sensing
is written by a Caltech prof in '94, but the information is extensively thorough and concise.
So that FAQ alone practically answered all my questions. The "Problems" section near the bottom (27-33) proved especially helpful. What I gathered was...
27) How well do these vegetation indices work in areas with low
A) Generally, very badly. (more details on the website)
31) How low a plant cover is too low for these indices?
A) These are rules of thumb, your mileage may vary:
RVI, NDVI, IPVI = 30%
SAVI, MSAVI1, MSAVI2 = 15%
DVI = 30%
PVI, WDVI, GVI = 15%
SUMMARY: In order of preference for each type of sensor:
TM or MSS (or any broad-band sensor)
1: NDVI (or IPVI)
3: SAVI (top of list for low vegetation)
Since this is my first foray into remote sensing, I can't verify the accuracy of FAQ on Vegetation in Remote Sensing
. Are there any remote sensors out there who would be will to take a quick gander and tell if this is all up to date methodology? Particularly the bit on SAVI (#16).
I'm going to see if I can run a SAVI (Soil Adjusted Vegetation Index) on the LandSat data. FAQ on Vegetation in Remote Sensing
contains the equations and a lot of good jazz. It recommends NDVI for denser vegetated areas, while SAVI is better for dealing with "soil noise".
I read back to my original post, and I neglected to mention that I'm studying vegetation in an urban area (Pasadena, CA), so these indices might not be as well suited? Yikes. Again, any remote sensors, please, please chime in.
This is the where the data is from, the LAR-IAC program run in LA County to gather various remotely sensed data. This page
details how it has been used to get NDVI indices, but used a tolerance of >0.1, while we went with >0.38 because we're looking at the tree canopy. My bad for not mentioning the urban environment. I didn't take that into account until I started reading the FAQ and how it focuses primarily on remote regions w/ interference f/ roads and glare f/ buildings.
Anyway, this FAQ gave me a good understanding of various vegetation indexes and which to use. Next step is to determine which is preferable for urban environments like Pasadena. I think I'll call the Mark Greninger in LA County tomorrow. Thanks for your help thus far!
Edited by htomita, 13 May 2011 - 12:03 AM.