a simplified close chamber technique will be useful if you are planning to calculate (and before that sample the air) the methane. its comparatively easy to sample the air (i.e. surface emission of methane, if any) with a closed chamber mounted on the land surface. enough of the literature and "how to operate" videos are also available. simply search for, Closed chamber technique + methane estimation.
the best part is, one can prepare the chamber with minimum expenses and minimum complications.
the sample collected nevertheless shall be analysed using standard methods avalable (I would suggest GC with and FID detector)