The Comprehensive Test Ban Treaty (CTBT) permits Multi-Spectral and InfraRed Imaging (MSIR) to be performed as part of an On-Site Inspection (OSI) for the purpose of reducing the search area for the location of a possible underground nuclear explosion (UNE). Dedicated airborne MSIR measurements have not been made in conjunction with historical or recent UNE's. Satellite data has been used to show that MSIR observables can be used to reduce the search area, but the satellite data do not have the spatial resolution or spectral and thermal capabilities desired to fully characterize the MSIR observables. Consequently, there is insufficient information currently available to confidently specify an MSIR instrument to be used on an Additional Overflight as part of an OSI.