1. NSF Gulfstream-V VCSEL hygrometer in START08 Mark A. Zondlo (1), Mark E. Paige (2), and Joel A. Silver (2) 1-Civil and Environmental Engineering Princeton, University 2-Southwest Sciences, Inc. H2OH2O 14.9 km; NSF Gulfstream-V; July 30, 2007

2. VCSEL hygrometer specifications Specifications: Range: 1-40,000 ppmv Accuracy: 5% Precision: <3% (1 Hz) Mass: 5 kg Power: 10 W Unattended operation Test flights in NSF PACDEX, HEFT 07, and HEFT 08

3. 1. Vertical cavity surface emitting laser (VCSEL) near 1854 nm 2. Wavelength modulation spectroscopy (250 kHz) 3. Fiber optic system 4. Digital signal processing microchips 5. External, open-path design Experimental: VCSEL hygrometer 29 cm

4. Near-IR water spectroscopy  1854 nm 1.5  stronger than 1370 nm, 100  stronger than 944 nm Paige, 2005

5. Vertical cavity surface emitting laser (VCSEL) relatively new devices at 1854 nm (Vertilas) consume very low power (15 mW) large current tuning range probe multiple bands with one laser) probe stronger absorption band than existing TDL systems (sufficient sensitivity for tropopause measurements)

6. Other design attributes open path cell minimizes sampling issues 1.9 cm diameter, Au-coated mirrors, 14.95 cm apart, 25 passes = 3.74 m pathlength wavelength modulation spectros. - full spectral fit - 250 kHz modulation - modulation ampl. Adjusted to P, T fiber optic (no purging) - calibrate at T, P, mixing ratios Temp. Press. input (fiber) output (detector)

7. Lab experiments: ~ 1 ppmv, -79.0°C f.p. Note: 2 hour precision < 1 Hz (22 hour experiment) slopes = -1/2 25 Hz: raw data, fits; 1 Hz: linelocking, T, P factor of 5 between y-values signal averaging to ~ 500 s ~ 2 hr. drift is << 1 Hz data

8. HEFT #04: Overview Except around 23:00 UTC, VCSEL did well from surface-tropopause

9. TF #04: segment at tropopause (14.9 km)  25 Hz deviation (2  ) = 4.3%

10. VCSEL hygrometer summary START08/Pre-HIPPO specifications: 3% or less precision (1 Hz) 5% accuracy 25 Hz sampling Status: Accuracy: Intercompared at Aqua-VIT in Oct. 2007 10% higher than mean @ 5, 65, 150 ppmv (within error) Precision: In-flight precision demonstrated HEFT-08: Refine calibrations, spectroscopy; laser control

11. 7640 ppmv: 0°C frost point (weak line) 1 Hz: 38 ppmv = 0.5% slopes = -1/2 25 Hz: raw data, fits; 1 Hz: linelocking, T, P factor of 5 between y-values signal averaging to ~ 60 s ~ 10 min. drift is < 1 Hz data

12. Multilinear regression fit  fit entire spectral peak to Voigt fit, adjust modulation / scan width  normalized Voigt shapes constant vs. T,P (<3%)

13. Roles of atmospheric water vapor “standard” atmosphere

14. Outline I. Introduction A. Climate B. Chemistry C. Dynamics II. VCSEL Hygrometer for NSF G-V A. Measurement challenges B. Experimental C. Flow modeling studies D. Flight results III. Laboratory studies A. Calibrations B. Precision / noise / drift IV. Future directions Ackowledgements: Mark E. Paige (SWS), Joel A. Silver (SWS), Jack Fox (NCAR), Michael D. Curry (St. John’s College), Kate Brubaker (St. John’s College), Armin Afliche (Jülich), Martina Krämer (Jülich), Cindy Twohy (Oregon St.), Elliot Weinstock (Harvard), NCAR EOL aircraft/flight crew, PACDEX Science team, NSF HAIS, NSF Atm. Chem.