Latest Contributions by MervynLotter

Hi there   I would like to include the output of a raster function into the Tabulate Area GP tool, but my raster function output does not have an attribute table. If it were a traditional raster, then I would have run the  Build Raster Attribute Table gp tool to create one.  Is there a raster function equivalent or is there a different approach to follow? I need to work with categorical data.   Thanks. ... View more

Hi there I have a 16 bit raster which has an attribute table with several numerical fields (density of several invasive species). I would like to to run the Zonal Statistics as Table GP tool to extract the average density of various invasive species for each of our reserves. Unfortunately, when running this tool, a user cannot specify which attribute field to use in this GP tool. The tool uses the default value field.  I am guessing there is no simple workaround? The Tabulate Areas GP tool only considers categorical classes, so it is not an option (and not the ideal output). I suspect the way forward would be to create individual rasters from each of the attribute field names. And then use these in the Zonal Stats as Table tool.  This sounds simple but i can't find a tool to do so.  Any advice?  Thank you.  ... View more

The background is that I need to provide an opinion on the impact of grazing on an area using satellite imagery. I need to look at impacts after 2008 so I want to compare imagery taken before 2008 with imagery taken in 2021. I want to use the Normalized Difference Vegetation Index (NDVI) to do so and so I opted to use the Landsat imagery from Landsat 5 TM and Landsat 8 OLI. A quick analysis of the AGOL Living Atlas Multispectral Landsat imagery, comparing June of 2005 with June of 2021, showed that for my study area the average NDVI value June 2005 was 0.3374 and in June 2021 it was 0.3989. So based on this, I was thinking that there had not been any significant impacts. However, I chose to download additional Landsat imagery from Earth Explorer and their Landsat Collection 2 Level-2 datasets. After doing so and manually computing these indices, I realised that the differences in values is actually much larger and attributed to differences in sensors, and not so much to grazing (as the impact would have been reversed – lower NDVI values in 2021). Using the Earth Explorer datasets, the mean NDVI value for 2007 is 0.1877, while for 2021 it is 0.5343. This leads me to the purpose of my query. 1) Are the NDVI values from the Multispectral Landsat image service actually comparable across time as they are derived from different sensors measuring slightly different parts of the spectral range? Or has Esri applied some form of normalisation or correction to make them comparable? The metadata did not state anything like this from what I could tell. 2) Are there any approaches I can consider to standardise or correct the bands so that they are comparable? If I can’t correct for these differences, then I cannot use this approach to quantify changes. I am thinking of moving across to the coarser-scale MODIS NDVI imagery at 250 m as they use the same sensor throughout. Any assistance would be much appreciated. Best wishes Mervyn ... View more