Huailin Chen

Wind measurements with 355-nm molecular Doppler lidar

A Doppler lidar system based on the molecular double-edge technique is described. The system is mounted in a modified van to permit deployment in field operations. The lidar operates with a tripled Nd:YAG laser at 355 nm, a 45-cm-aperture telescope, and a matching azimuth-over-elevation scanner to permit full sky access. Validated atmospheric wind profiles were measured from 1.8 to 35 km with a 178-m vertical resolution. The range-dependent rms deviation of the horizontal wind speed is 0.4-6 m/s. The measured wind speed and direction are in good agreement with the rawinsonde wind measurements made simultaneously from the same location.

Single-frequency lasers for remote sensing

We have designed and built two versions of a space-qualifiable, single-frequency Nd:YAG laser. Our approach to frequency stabilization of the seeded oscillator is a variation of the “ramp and fire” technique. In this design, the length of the pulsed laser cavity is periodically varied until a resonance with the seed laser is optically detected. At that point the pulsed laser is fired, ensuring that it is in resonance with the seed laser. For one of the lasers the resulting single frequency pulses are amplified and frequency tripled. This system operates at 50 Hz and provides over 50 mJ/pulse of single-frequency 355 nm output. It has been integrated into the GLOW (Goddard Lidar Observatory for Winds) mobile Doppler lidar system for field testing. The second laser is a 20o Hz oscillator only system that is frequency doubled for use in the High Spectral Resolution Lidar (HSRL) system being built at NASA Langley Research Center. It provides 4 mJ of single-frequency 532 nm output that has a spectral purity of >10,000. In this paper we describe the design details, environmental testing, and integration of these lasers into their respective lidar systems.

Performance validation and error analysis for a direct-detection molecular Doppler lidar

In this paper we present a detailed analysis of the performance of the Goddard Lidar Observatory for Winds (GLOW) Doppler lidar. GLOW is a mobile direct detection Doppler lidar system which uses the double edge technique to measure the Doppler shift of the molecular backscattered laser signal at a wavelength of 355 nm. The lidar has been used in several recent field experiments to measure wind profiles from the surface into the lower stratosphere. Simulations of detected signal levels predicted using a realistic instrument model and representative atmospheric model will be presented and compared with range resolved signals detected with the photon counting data acquisition system. A detailed analysis of wind errors observed with the system will also be reported. The analysis begins by propagating ideal shot noise limited errors through the analysis algorithms used to calculate winds. The resulting shot noise limited errors are compared with statistical standard deviations obtained by averaging multiple independent wind profiles taken at various temporal and spatial sampling scales. An assessment of other instrumental and atmospheric effects contributing to the wind error will also be given.

Preliminary results of wind measurements by GLOW system in field campaigns

The Goddard Lidar Observatory for Wind (GLOW) has participated three field campaigns since Sept. 2000. Near 300 hours of wind measurement under a wide variety of conditions including day and night operation, high and low altitude, line of sight and horizontal winds, have been obtained from the GroundWinds intercomparison, Harlie-GLOW intercomparison ( HARGLO) and the International H2O Project (IHOP) field campaigns. The GLOW system has demonstrated the capability to atmospheric wind from ground up to 30 km with an accuracy of 0.4-6m/s.