1. A method of correcting measurement data obtained from a multi-channel imaging system, comprising the steps of: a) producing a sub-image in each channel of the system using a predetermined wavelength; b) measuring a geometric distortion introduced by the system in each sub-image; c) determining a geometric correction matrix corresponding to said geometric distortion introduced by the system in each sub-image; and d) applying said geometric correction matrix to remove geometric distortion from measurement sub-images produced by the system.