Study area was clipped by using the shape file from Band 3 and Band 4. First, Band 3 and Band 4 were converted to at-satellite brightness temperature by using the built-in function in semi-automated tool in QGIS (semi-automatic classification plug-in). NDVI was calculated by b4-b3/b4+b3 in landsat 5 images, the range of NDVI was 0.0968299 - 0.433846. Green Vegetation fraction were also needed to examine the role of vegetation in mix land cover that was derived from the equation:
GVF = NDVI - NDVImin / NDVImax - NDVImin
but the problem here was as you would see the range of the fraction is -0.631684 - -0.0011024) that is due to some abnormalities in the data that don't know how to remove it. Is there something wrong in "NDVI" values as there is no data values (no data values = -3.4020 + 38) by seeing the properties of image in QGIS. I have taken the NDVImin and NDVImax as 0.0968299 and 0.433846 respectively but literature has shown that the values 0.05 and 0.70 as NDVI threshold values that were derived by global Advanced Very High Resolution Radiometer (AVHRR) 10-day composite data (Zeng et al. 2000).