Well over a decade ago, QMC Instruments made a small free standing wire polarizing grid which JPL's MIRO instrument on the Rosetta mission uses to separate incoming radiation into two channels: Two radiometers have been looking at 188 GHz (1.6 mm) and 562 GHz (0.5 mm). The lower band provides continuum measurements, giving subsurface temperature measurements, the higher frequency channel cover vibration lines which include H2O, CO, CH3OH, and NH3 and the isotopes H217O and H218O
Worth reading the ESA MIRO Blog here
Image thanks to ESA
MIRO has been measuring the rate of Water Loss from 67P/C-G. At its peak we are told here that the comet is losing 5 Liters a second...