1. Progress in water vapour spectroscopy at RAL Dr Robert McPheat CAVIAR Progress Meeting NPL, 29/09/2010

2. Plan for mid-IR measurements 800 – 2100 cm -1, 12.5 – 4.8 µm Saturated P H2O (mb) ! T (K)P (mb) 13.8285 ? 10 F 19.1290 10, 15 F 27.8296 20(F) 10, 15 F, 20 62310 50 20(F) No Argon steps are needed for LPAC measurements 135325 100 20(F) 270340 100, 150, 200 510355 100, 150, 200, 350 Resolution (cm -1 ): N of scans: 0.01 0.02 | 0.050.003 ? (to ensure good S/N) | SPAC, 20m | LPAC, 512m (F) Only foreign measurement: H 2 O + Air(  1.5atm) F Foreign measurement: H 2 O + Air(  1.5atm), in addition to the pure one

3. LPAC measurements 512 m path length, 31 images High accuracy Baratrons & PRTs Room kept at 297 K Initial problems stable WV pressure

4. LPAC Window problems

5. LPAC Measurements New water vapour injection system Sample Gauge Air

6. LPAC S/N Measurements 700 – 2100 cm -1 0.003 cm -1 resolutionSet aperture for 1300 cm -1 LWP filter 1300 cm -1 0.006 cm -1 resolution