Airborne all-solid-state DIAL for water vapour measurements in the tropopause region: system description and assessment of accuracy

• Published in: Applied physics. B, Lasers and optics Vol. 75; no. 2-3; pp. 165 - 172
• Main Authors: Poberaj, G., Fix, A., Assion, A., Wirth, M., Kiemle, C., Ehret, G.
• Format: Journal Article
• Language: English
• Published: 01.09.2002
• Subjects: Assessments; Dials; Error detection; Intrusion; Lasers; Spectra; Tropopause; Vapour
• ISSN: 0946-2171; 1432-0649
• DOI: 10.1007/s00340-002-0965-x

A novel airborne all-solid-state DIAL system for water vapour measurements in the upper troposphere and lower stratosphere has been developed at DLR. Its transmitter is based on an injection-seeded KTP optical parametric oscillator (OPO) pumped by the second harmonic of a Q-switched, diode-pumped single-mode Nd:YAG laser at a repetition rate of 100 Hz. The OPO is optimised for operation in the spectral region between 920--950 nm with an average output power of 1.2 W and a spectral purity higher than 99%. The latter is controlled on a pulse-by-pulse basis during in-flight operation. The system is also designed to perform simultaneous polarisation-sensitive backscatter measurements at 532 nm and 1064 nm for aerosol detection. For the first time, daytime measurements of two-dimensional water vapour cross sections with high vertical (500--750 m) and horizontal (6--20 km) resolution were performed in the tropopause region. Very low mixing ratios (10--50 ppmv) and strong gradients were observed inside stratospheric intrusions. The sensitivity (1-*s error) of the DIAL in the centre of the stratospheric intrusions ranges from 3% (0.6 ppmv) in the near field to 12% (5 ppmv) in the far field (~4 km). First comparisons with in situ measuring instruments show very good agreement.