1. A shell monitoring system for providing information for performing a registration correction for artillery, the system comprising: (a) a first optical imaging system deployed at a first location; (b) a second optical imaging system deployed at a second location, spaced apart from said first location; and (c) a processing system in data communication with said first and second optical imaging systems, said processing system being configured to: (i) monitor outputs from said first and second imaging systems to detect potential shell trajectory events viewed by said imaging systems; (ii) correlate said potential shell trajectory events to eliminate potential shell trajectory events not viewed by both of said optical imaging systems and to determine locations for potential shell trajectory events viewed by both of said optical imaging systems; (iii) receive shell firing data relating to firing of at least one shell, said shell firing data being sufficient to determine at least one predicted trajectory time point for the shell; (iv) identify one of said potential shell trajectory events as a detected shell trajectory event corresponding to the predicted trajectory time point; and (v) retrieve the time and location of said detected shell trajectory event for use in determining a registration correction for the artillery.