Systems and methods for monitoring a sample or a sample flow associated with a process or an environment. The systems and methods transmit terahertz signals at the sample, receive a resulting spectral response, perform a spectral analysis, and display a result or choose a course of action. The analysis compares the sample's absorption or reflection spectral response to known spectrums to determine composition; or to determine if the sample flow has deviated from “normal”. In one embodiment, the systems and methods use reflection terahertz on a contained sample; in another it uses transmission terahertz to look at a sample flow outside the vehicle. In this embodiment the analysis is used to determine sample composition. In other embodiments, the analysis is used to discern or warn of changes, or to choose a course of action.