Raster functions have been around in ArcGIS Pro for some time now. They work slightly differently to traditional raster data processing. Instead of writing out a new raster image with each step, they create a virtual raster (that only exists “in memory”) which is calculated based on the input raster(s) values. This allows output to be created very quickly. Some functions require Spatial Analyst (SA) or Image Analyst (IA) extensions, while others are available without extensions. A full list of the Raster Functions can be found here.
For this example, I used some Sentinel 2 imagery which can be downloaded from the Copernicus Open Access Hub. I then loaded some of the image bands to ArcGIS Pro. Go to the Imagery tab and click Raster Functions. This will open the Raster Functions Pane. Expand Math and choose the Calculator function. (Note: Calculator requires SA or IA extension).
This will open the dialog for the Calculator. It allows you to define raster data or layers as variables and then use those defined variables to construct an algorithm.
In this example, I am doing a simple ratio between Sentinel 2 bands 12 and 8 (these are similar wavelength ranges to Landsat TM7 bands 7 and 4). Once a variable is defined in the calculator, it will appear in intellisense (you can see the popup in the image below showing b8 and b12 as options), along with various other available mathematical functions.
Once you have completed the formula, it is possible to either create the result in the current map “in memory” or save it out as a permanent raster file.
Click Create new layer to add the resulting processed image to your map.
It is then possible to create a series of ratio images and make a composite of those ratio images. This can highlight features of interest to your study.
The image below is RGB Sentinel2 band ratios 4/3, 11/3, 12/8 (Landsat TM7 band ratios 3/2, 5/2, 7/4). It was created using the Composite Bands raster function.
Posted by Ben Holmes, GIS Consultant, Exprodat