Recordings from the downward-pointing cameras on commercial airliners that provide inflight belly-cam views could be downloaded after landing to use for research, for example on vegetation cover, traffic density on roads, night-time light which measures economic development. The flight paths are saved on flight tracking websites anyway, which enables localising the video at any point of time to the GPS coordinates the flight was at. The recordings are not much use for military spying because countries ban overflights of sensitive sites anyway. Thus security and privacy arguments should not stop research in this case.
The resolution of the belly cameras is low and the wavelengths cover only visible light, not infrared which would be useful for vegetation measurements. The compensating upside is the frequent overflights of many parts of the globe, thus the dense temporal coverage. The videos are almost costless to obtain – just plug an external hard drive into the existing inflight entertainment system to and later upload its contents at the airport. The low cost contrasts with specialised satellite and aerial surveys.