What is a simple way to atmospherically correct Landsat 8 data using Erdas 9.3 or ArcGIS 9.3?
I would advise using the dark object subtraction (DOS) method for atmospheric correction. Essentially, you find a dark object in your scene--such as a deep, dark water body--where you know there is no reflectance. Any brightness values associated with the dark object in your scene are therefore likely the result of atmospheric effects. These values can then be subtracted from the other pixel values.
As far as i know there's no way of performing atmospheric correction for L8 images in Arcgis 9.3. but there's an plugin i QGIS called Semi-Automatic Classification that will perform DOS on Landsat 8 images. Check it out, it's pretty good.
You can find all the information here: http://fromgistors.blogspot.com/ and also in the Semi-automatic Classification Facebook group where you can find the author of the plugin, Luca Congedo.