Publications (3)3.4 Total impact
Article: Field demonstration of simultaneous wind and temperature measurements from 5 to 50 km with a Na double-edge magneto-optic filter in a multi-frequency Doppler lidar.[show abstract] [hide abstract]
ABSTRACT: We report the first (to our knowledge) field demonstration of simultaneous wind and temperature measurements with a Na double-edge magneto-optic filter implemented in the receiver of a three-frequency Na Doppler lidar. Reliable winds and temperatures were obtained in the altitude range of 10-45 km with 1 km resolution and 60 min integration under the conditions of 0.4 W lidar power and 75 cm telescope aperture. This edge filter with a multi-frequency lidar concept can be applied to other direct-detection Doppler lidars for profiling both wind and temperature simultaneously from the lower to the upper atmosphere.Optics Letters 06/2009; 34(10):1552-4. · 3.40 Impact Factor
Article: Applications of spectral analysis and filter design in laser frequency locking for Na Doppler lidars[show abstract] [hide abstract]
ABSTRACT: A dye ring laser is stabilized to a D 2a Doppler-free feature of sodium vapor using a LabVIEW ® -based, phase-sensitive servo. Locking precision and stability, at better than ±1 MHz, are suitable for Na lidar applications. This performance was achieved with improved digital filter-ing and new approaches to the problem. The inverse type II Chebyshev discrete filter employed demonstrates superior filtering and computa-tional efficiency plus improved flexibility. New approaches include the determination of optimum modulation frequency, laser-tuning sensitivity, and bandwidth requirements via spectral analyses of the noise spec-trum, derivative scan, and modulated spectrum. This practice guides a user in selecting the system operation parameters and negotiating the trade-offs involved when expanding the filter's passband. Allan deviation plots provide a quantitative description of the short-and long-term fre-quency excursions. A comparison of Allan deviation plots before and after locking shows a substantial improvement in stability throughout time scales from 0.10 to 10 s.01/2009; 28.
Article: Role of gravity waves in the spatial and temporal variability of stratospheric temperature measured by COSMIC/FORMOSAT‐3 and Rayleigh lidar observations[show abstract] [hide abstract]
ABSTRACT: 1] This study utilizes COSMIC satellite and lidar observations to examine the spatial and temporal variability of stratospheric temperature at a number of scales. The geographic variation of the RMS temperature difference between pairs of COSMIC profiles shows a strong correspondence to previous climatologies of gravity wave activity. In addition, the second‐order structure functions we form can be directly related to the horizontal wave number power spectrum. These structure functions for different seasons and altitudes display a close correspondence to previous studies which examined the form of the horizontal wave number power spectra. Our analysis suggests that the wavefield may be particularly affected by changes in the zonal wind between 15 and 25 km and that the wind reversal between tropospheric westerlies and stratospheric easterlies in summer strongly contributes to critical‐level filtering. Inspection also shows that longer horizontal wavelength waves are preferentially removed in this region. At low altitudes, the variability related to gravity waves shows a remarkably similar pattern as a function of horizontal separation in both hemispheres but is quite different at higher altitudes. Such contrast implies that seasonal variability at higher altitudes may be dominated by changes in propagation conditions in the lower stratosphere. Examination of temperature variability as a function of spatial and temporal separation indicates that gravity wave activity dominates stratospheric temperature variability, and this has impacts on validation study site selection. For example, validation exercises in the summer hemisphere stratosphere are likely to be less affected by geophysical variability than those in the winter hemisphere. Citation: McDonald, A. J., B. Tan, and X. Chu (2010), Role of gravity waves in the spatial and temporal variability of stratospheric temperature measured by COSMIC/FORMOSAT‐3 and Rayleigh lidar observations, J. Geophys. Res., 115, D19128, doi:10.1029/2009JD013658.