I calculated the percent vegetation cover in a given study area using NDVI method and just to want make sure that my method was correct and the result is reliable. I just did this through simply calculation of NDVI and then I reclassified my map (I used +0.2 as the threshold to separate vegetation and non-vegetation) and finally calculated the proportion of the green to whole area. However, someone recommended me using Green Vegetation Fraction to produce the vegetation map and calculation the percent vegetation cover. Any ideas?
Your method assumes that a pixel is either fully vegetated (> 0.2) or not vegetated (< 0.2). However, even for vegetated pixels you surely have different coverage. Consider that a fully vegetated pixel should have NDVI > 0.8 (circa).
You should compute for each pixel a fraction vegetation coverage (following on of the relationships proposed in the literature) and then average these values on the whole area.
See the attached publication for one of the possible relationships (eq. 1) to use.
Article Physical based retrieval of crop characteristics for improve...
you can use some other image data source. it can help you to find more accuracy
The NDVI is very sensitive to soil colour, soil moisture, shading effects caused by solar and viewing angle geometry, so it would be wise to start by making sure the NDVI is appropriate for your study conditions. There are dozens of alternative vegetation indexes. Also, the value of the NDVI, as of other vegetation indexes, is affected by other factors than vegetation cover: leaf area index, phenology and physiological status of the vegetation, vertical structure of the plant community (e.g. open grassland vs. multi-layered forest). Thresholding the NDVI at 0.2 and considering that anything above that is vegetation, and equivalent in terms of projected cover over the entire range of above-threshold values is a very crude approach. However, it may be enough for your purposes, but that is impossible for me to assess, given the lack of information on your study conditions.
Maybe that comes too late. Which kind of vegetation do you want to derive the percent of cover? and which NDVI method are you refering to? could you provide a reference for the NDVI method you mention?
If you want to derive pecentage of TREE cover and you have access to very high resoultion imagery (at least in google earth) you could derive training areas with calculated percentage tree cover (digitazing the canopy cover) and use a Random Forest regresion model to derive the percentage of tree cover for all your pixels. This method was used to derive the global percentage of tree cover "VCF" product either MODIS or Landsat based. The method is described in the references attached by Hansen et al.
Another alternative (I think would probably be the most accurate approach) is calculate the fraction cover by (GREEN) vegetation through Spectral Unmixing. It will require you: -1st know which are the main "components" that cover your pixels( normally: soil, green vegetation, non-green vegetation (bark, etc), water?, and SHADE!), 2nd build your spectral library for enmembers of these components (you need training areas of pure pixels representings the spectral signature of those), 3rd calculate each fraction cover (could be implemented in many softwares, ENVI, or open source softwares are available). There are many references following spectral (un)mixing approach to map vegetation cover. If you have only multispectral data (e.g. Landsat) I found useful the reference by Rogan et al. (see ref. attached)
Article Continuous fields of land cover for the conterminous United ...
Article Towards an operational MODIS continuous field of percent tre...
Article A comparison of methods for monitoring multitemporal vegetat...
Values of NDVI (or any other spectral vegetation index) can't be directly related to % vegetation cover for a scene of interest unless there has been some calibration study performed between the spectral index values and ground truth measurements of % foliage cover. In other words, you need to predict the level of foliage cover using a calibration model (prediction model) that is suitable for the scene of interest. Note that NDVI 'saturates' at high cover and is not useful for distinguishing between different levels of foliage cover at high levels of foliage cover. You will find some articles on my ResearchGate publications page that relate to vegetation indices and the estimation of % foliage cover.
I agree with @Jose Gonzalez de Tanago Menaca (Alternative method)
Kindly tell me that I want to know how much is the vegetation area and how much is the barren land in my study area. How can I do that. Regards
Could anyone please share, the processing (may be in Arcmap or Erdas) for computing NDVI for Soil and NDVI for Vegetation covers. I need to work with Fractional Vegetation Cover (FVC)
@Jahangir Khan
Hello, we just published a paper about estimation of FVC based on a simple physical method.Article Estimating fractional vegetation cover and the vegetation in...
If you have any question about it, please let me know.
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