Water vapour spectroscopy in the MSF

Dr Robert McPheat

CAVIAR Progress Meeting

NPL 02/06/2008

SPAC

• Short path-length absorption cell (SPAC) – 1.2 to 20 metres – Multi-pass reflective optics (White)– Being upgraded for CAVIAR

• -200 to 200ºC temperature range• 5 bar maximum pressure• No cold spots (including valves, feedthroughs etc.)• Mirrors adjustable from outside• Accurate temperature & humidity measurement• Corrosion resistant

• Made first measurements• Problems with thermal expansion

– Can be used for hot measurements

SPAC upgrade

Optics Inner Cooling Jacket

High temperature pressure gauge & filling line

Temperature & pressure logging

Temperature control

Outer vacuum jacket

Transfer optics vacuum tank

Detector box

SPAC upgrade modifications

Second High Resolution Spectrometer

• Bruker IFS120 HR Upgrade– Upgraded electronics /

moving mirror to same specification as IFS125

– Maximum spectral resolution of 0.0015 cm-1

– Spectral range of 10 to 40,000 cm-1

LPAC Vacuum Upgrades

• Replace unreliable pumps & gauges (dating from early 1970s)

• Oil free to avoid contamination– 3 large dry pumps– 1 dry backing pump– 6 new gauges

Future Work• Measurement of unsaturated strong lines• Finish SPAC modifications

– Measurements covering visible to FIR• Need window & detector box modifications for FIR

– Up to 450 K• LPAC vacuum upgrade

– Measurement conditions– 243K to 293K – water pressures up to 0.75 SVP– resolution up to possible 0.0015cm-1 but mainly at 0.03cm-1

– water/air mixtures at total pressures of 150, 500 & 1000 hPa