Abstract

Narrow-band detection of the Raman water vapor spectrum using the lidar technique introduces a concern over the temperature dependence of the Raman spectrum. Various groups have addressed this issue either by trying to minimize the temperature dependence to the point where it can be ignored or by correcting for whatever degree of temperature dependence exists. The traditional technique for performing either of these entails accurately measuring both the laser output wavelength and the water vapor spectral passband with combined uncertainty of approximately 0.01 nm. However, uncertainty in interference filter center wavelengths and laser output wavelengths can be this large or larger. These combined uncertainties translate into uncertainties in the magnitude of the temperature dependence of the Raman lidar water vapor measurement of 3% or more. We present here an alternate approach for accurately determining the temperature dependence of the Raman lidar water vapor measurement. This alternate approach entails acquiring sequential atmospheric profiles using the lidar while scanning the channel passband across portions of the Raman water vapor $Q$-branch. This scanning is accomplished either by tilt-tuning an interference filter or by scanning the output of a spectrometer. Through this process a peak in the transmitted intensity can be discerned in a manner that defines the spectral location of the channel passband with respect to the laser output wavelength to much higher accuracy than that achieved with standard laboratory techniques. Given the peak of the water vapor signal intensity curve, determined using the techniques described here, and an approximate knowledge of atmospheric temperature, the temperature dependence of a given Raman lidar profile can be determined with accuracy of 0.5% or better. A Mathematica notebook that demonstrates the calculations used here is available from the lead author.

© 2013 Optical Society of America

Narrow-band, narrow-field-of-view Raman lidar with combined day and night capability for tropospheric water-vapor profile measurements

Scott E. Bisson, John E. M. Goldsmith, and Mark G. Mitchell
Appl. Opt. 38(9) 1841-1849 (1999)

Lamp mapping technique for independent determination of the water vapor mixing ratio calibration factor for a Raman lidar system

Demetrius D. Venable, David N. Whiteman, Monique N. Calhoun, Afusat O. Dirisu, Rasheen M. Connell, and Eduardo Landulfo
Appl. Opt. 50(23) 4622-4632 (2011)

Examination of the traditional Raman lidar technique. I. Evaluating the temperature-dependent lidar equations

David N. Whiteman
Appl. Opt. 42(15) 2571-2592 (2003)

Combined Raman lidar for the measurement of atmospheric temperature, water vapor, particle extinction coefficient, and particle backscatter coefficient

Andreas Behrendt, Takuji Nakamura, Michitaka Onishi, Rudolf Baumgart, and Toshitaka Tsuda
Appl. Opt. 41(36) 7657-7666 (2002)

Implementation and validation of a Raman lidar measurement of middle and upper tropospheric water vapor

Vanessa Sherlock, Anne Garnier, Alain Hauchecorne, and Philippe Keckhut
Appl. Opt. 38(27) 5838-5850 (1999)