Calculating NDVI

Question

I would like to calculate the NDVI for an area to identify vegetation cover over a 32 year period using. However, I am having challenges with the calculations I have attempted with Raster Calculator. I am using images acquired from the USGS Earth Explorer for the years 1988, 2000, 2017, 2018 and 2020. I have created the Multi Band Composites for each year and used the Bands from those Composite images to perform the calculation for NDVI in Raster Calculator.
For the first image 1988 (Landsat 4) I used Band 4 (NIR) and Band 3 (Red), using the equation
Float("1988compo_1988 - Band_4" - "1988compo_1988 - Band_3") / Float("1988compo_1988 - Band_4" + "1988compo_1988 - Band_3")

However, I got the following message in in the screenshot.

I have read some of the previous submissions, but none of those adequately address this issue.

user2856 · Accepted Answer

Start the filename of the output raster with a character not a number, i.e NDVI_1988_1 instead of 1988_NDVI_1
From the Esri FAQ: What characters should not be used in ArcGIS for field names and table names?

Do not start field or table names with an underscore or a number.

And Geodatabase table properties -> Defining feature class properties
shows you can only start a GDB featureclass or table name with the letters A-Z (also applies to rasters in GDBs):

Calculating NDVI

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