Am working with Landsat 5 TM and OLI images for time series and I need help on how to construct a model in calculating greenness index(G= Ref 554/Ref 677). Have tried several times and sometimes get inf in the metatdata and also dark images. Thank you for your help in advance
Hi Julius - use the raster calculator in ArcMap, but encapsulate the equation with a float(), e.g. float(green/red) or float(green)/float(red)
T. P. Robinson please I tried the float option using raster calculator in ArcMap but the image turns to be dark after i run the process. Is there any other option I could try. Thank you
Without seeing the output, it's difficult, but I assume it has a correct decimal range? Can you zoom into an area of interest, click properties and stretch "from current display extent" to see if it improves your contrast. If it does you can attempt to stretch it all to similar histogram distributions.
T. P. Robinson and Cheshini Malavipathirana. the float option worked when i used it in arcmap and tried to also create model to compare the metatdata in erdas which yielded the same results. But the challenge am now facing is that my image has water body which is showing higher green index above 1 than the vegetation (AOI).please what might be the problem since water is usually supposed to have low value of minus and 0 column. I tried using GNDVI under spectral in erdas and the water is having the values within the correct ranges of minus and 0. Please help me the challenge. Thanks in advance
Julius Bamah Did you get a clear satellite image? free from clouds?During drought season, vegetation canopy can be affected by water stress. This can have major impact on the plant development in general and can cause crop failure or lower crop production in agricultural areas.The Normalized Difference Water Index (NDWI) is known to be strongly related to the plant water content. It is therefore a very good proxy for plant water stress.
Julius Bamah - I suspect it's because you are using the simple ratio version of the greenness index. Try the normalised version - float(float(green)-float(red))/ float(float(green)+float(red))
Maybe more type conversion than needed, but it won't hurt.
Cheshini Malavipathirana Please I downloaded all the images in summer with image quality of 9 without clouds. Also the study area is a spring which flows through the vegetation so irrespective of rain there's always water available. NDWI as you said would have been good but am looking at pollution stress instead of water. I tried with NDVI but i want other index to validate the results of the NDVI. T. P. Robinson please when i tried the normalized version the water and my AOI which is the vegetation also turns black with values around 0.08. Am really grateful for how you are trying to help. Thank you so much
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