Met Office instrument measuring water vapour by using a tunable diode laser absorption technique, reported as a volume mixing ratio (ppmv).

The WVSS-II measures atmospheric water vapour using a near-infrared tunable diode laser absorption spectrometer. Two instruments are fitted to the aircraft, one which uses a flush inlet and the other which uses a modified Rosemount inlet mounted on a short pylon.

The data frequency is measured in 1Hz and be found in this frequency in both the 32Hz and 1Hz data files.

Parameters in the data files are: WVSS2F_VMR(Water Vapour Measurement from Flush inlet WVSSII serial no. 4229 linearly interpolated to 1Hz, ppmv),WVSS2R_VMR(Water Vapour Measurement from Rosemount inlet WVSSII serial no. 0388 linearly interpolated to 1Hz, ppmv)