That depends on what platform you are using for ISR (aerial manned vs UAS vs space based). Most of my guys are GIS or SATCOM since we primarily use space based systems, although I have one who works with aerial LIDAR and has a few deployments for it. A good GIS degree is always helpful, several cities need GIS personnel so that is always a market outside of Government work (and the merger of Digital Globe and GeoEye didn't help those working in the US Government sector). Another path to look into is some of the UAS programs that are starting up due to the usage of UAS platforms by LEOs. You can also get into some sort of commo degree due for the command links/freqs that are used by most ISR systems.