NSF Gulfstream-V VCSEL hygrometer

in START08Mark A. Zondlo (1) , Mark E. Paige (2), and Joel A. Silver (2)

1-Civil and Environmental EngineeringPrinceton, University

2-Southwest Sciences, Inc. H2O

14.9 km; NSF Gulfstream-V; July 30, 2007

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

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

Near-IR water spectroscopy

1854 nm 1.5 stronger than 1370 nm, 100 stronger than 944 nm

Paige, 2005

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)

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)

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 betweeny-values

signal averagingto ~ 500 s

~ 2 hr. driftis << 1 Hz data

HEFT #04: Overview

Except around 23:00 UTC, VCSEL did well from surface-tropopause

TF #04: segment at tropopause (14.9 km)

25 Hz deviation (2) = 4.3%

VCSEL hygrometer summarySTART08/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

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 betweeny-values

signal averagingto ~ 60 s

~ 10 min. driftis < 1 Hz data

Multilinear regression fit

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

Roles of atmospheric water vapor

“standard”atmosphere

OutlineI. Introduction

A. ClimateB. ChemistryC. Dynamics

II. VCSEL Hygrometer for NSF G-VA. Measurement challengesB. ExperimentalC. Flow modeling studiesD. Flight results

III. Laboratory studiesA. CalibrationsB. 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.