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Progress in water vapour spectroscopy at RAL Dr Robert McPheat CAVIAR Progress Meeting UCL, 13/05/2010.

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Presentation on theme: "Progress in water vapour spectroscopy at RAL Dr Robert McPheat CAVIAR Progress Meeting UCL, 13/05/2010."— Presentation transcript:

1 Progress in water vapour spectroscopy at RAL Dr Robert McPheat CAVIAR Progress Meeting UCL, 13/05/2010

2 Previous MSF Measurements Measurements in the mid- and near-IR. These measurements were intended to target the weak water vapour continuum. –Long path lengths. Measurements carried out at moderate (0.01cm -1 ) & high resolution (0.002cm -1 ) using the Bruker IFS125 HR FTS. Initial measurements revealed a need for better line data too. –High resolution measurements cm -1 using the Bruker IFS120/5 HR –Long integration times (~ 12 hours) in mid-IR

3 SPAC White OpticsInnerCooling Jacket

4 High temperature pressure gauge & filling line Temperature & pressure logging Temperature control Outer vacuum jacket Transfer optics vacuum tank Detector box Electrical feedthroughs

5 Example Spectra at 160 ° C Background 3000 hPa Water vapour 1600Wavenumber / cm

6 Self Broadened Spectra 3000 hPa Water vapour at 160 °C 2000Wavenumber / cm % Transmittance

7 Example Spectra Air Broadened Spectra 600 mbar water vapour in 5 bar total pressure mixture with air at 160 deg. C 100 % 2500Wavenumber / cm

8 Pure H 2 O measurements (self-continuum): 1) empty cell 2) Argon (same pressure as H 2 O in step 3) 3) pure H 2 O (same pressure as in step 2) 4) Argon (same pressure as H 2 O in step 3) 5) empty cell (quick measurement) H 2 O + Air measurements (foreign-continuum): 1) empty cell 2) Air (5 atm) 3) Air + H 2 O (5 atm total) 4) Same as in 2) 5) empty cell SPAC measurement procedure

9 F Foreign (H 2 O + Air; 5atm total pressure) measurements, in addition to the pure H 2 O (F)Only foreign (5 atm total pressure) measurement All air broadened measurements 0.1 cm -1. Near-IR SPAC measurements Saturated P H2O (mb) ! T (K)P H2O (mb) (F) (F), 300 F (F), 400, 600 F, F,1000, 1500 F, F,1000, 1500,2000, 3000, ,2000, 3000, 4000, 5000 Resolution (cm -1 ): N of scans: : – cm -1, 5 – 1 µm

10 Saturated P H2O (mb)! T (K)P H2O (mb) F (F) (F)1000, , , 3000, , 5000 Resolution (cm -1 ): N of scans: 0.05 (0.2 foreign) 0.1 | 0.2 (0.2 foreign) 0.2 | 0.3 -> 500 F Foreign (H 2 O + Air; 5atm total pressure) measurements, in addition to the pure H 2 O (F) Only foreign (5 atm total pressure) measurement Near-visible SPAC measurements 8500 – cm -1, 1.18 – µm

11 SPAC reconfiguration Measure pathlength Install BaF 2 windows Maximum pressure 1.5 bar ~ 800 cm -1 long wavelength cut off.

12 Plan for mid-IR SPAC measurements 800 – 2100 cm -1, 12.5 – 4.8 µm Saturated P H2O (mb) ! T (K)P (mb) ? 10 F , 15 F (F) 10, 15 F, (F) No Argon steps are needed for LPAC measurements (F) , 150, , 150, 200, 350 Resolution (cm -1 ): N of scans: | ? (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


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