I am working on a species distribution model for a lizard species in the American Southwest, from northern Utah to middle of Mexico, middle California east to middle New Mexico. One of the variables I need is an MSAVI as a vegetative proxy for those desert areas. I am working exclusively in R and ArcGIS Pro, so I have no experience coding in Google Earth Engine, JavaScript, Python, etc. I have read that Google Earth Engine is the easiest way to compile that sort of file. I need a raster layer with MSAVI for across the whole region so I can clip it to my study area and run my model. The layer needs to be from LandSat 7 from the year 2000 and extend through that whole area as mentioned above. Can anyone assist me in how to build and run the code for that in Google Earth Engine?
I have attempted compiling individual tif tiles from Earth Explorer and laying them all out in ArcGIS Pro, then running the mosaic raster function to blend them into one layer for Red band and one for the NIR band. Not only was this time consuming, but it ultimately didn't work in my code in R when I got it there, the tif tiles had not been cleared of cloud cover and so on, so the layer was unusable. I was expecting to build one layer in red than one in NIR and run the MSAVI layer with R code. Can anyone help explain how to build that file and then also export it as a raster file, or two raster files (one Red and one NIR)?