Optimizing three-frequency Na, Fe, and He lidars for measurements of wind, temperature, and species density and the vertical fluxes of heat and constituents

Measurements of metastable helium in Earth's atmosphere by resonance lidar

Monitoring and predicting space weather activity is increasingly important given society’s growing reliance on space-based infrastructure but is hampered by a lack of observational data. Airglow at 1083 nm from metastable helium He(2³S) in the thermosphere has long been a target for remote-sensing instruments seeking to fill that gap; however, passive measurements of He(2³S) fluorescence are limited by low brightness, and interpretation of these observations is complicated by the > 500 km depth of the He(2³S) layer. Here, we demonstrate a lidar instrument that is able to stimulate and detect He(2³S) fluorescence, and we present measured profiles of He(2³S) density. These measurements provide crucial validation to space weather models, support predictions of peak number density ( ~ 1 cm⁻³) and the dependence of density on altitude, solar zenith angle, and season, and extend by a factor of 4 the maximum probed altitude range by an atmospheric profiling lidar. These measurements open the door for the development of more sophisticated lidars: by applying well-established spectroscopic lidar techniques, one can measure the Doppler shift and broadening of the He(2³S) line, thereby retrieving profiles of neutral wind speed and temperature, opening a window for studying space weather phenomena.

Metastable helium is a promising target for remote-sensing observations of Earth’s thermosphere. This paper reports on the development of a resonance lidar capable of resolving metastable helium density profiles and presents initial results

Simulation and optimization of Fe resonance fluorescence lidar performance for temperature-wind measurement

Fe resonance fluorescence lidar (Fe lidar) is considered an ideal candidate for temperature and wind measurement in the mesosphere and lower thermosphere region. However, considering the complexity of it, only a few Fe lidars have been operated in a few locations. To develop a Fe lidar with high performance, simulation work is the first important step. A simulation model is built in this paper. The expressions for the temperature-wind uncertainties are derived using the error propagation method. Within the limit of saturation effect, an index decomposition of the lidar and atmospheric parameters are performed. When the dwell time and central frequency shift are optimized to 0.205 and 932 MHz at night and 0.212 and 687 MHz during the day, night and daytime calibration curves are acquired, and after confirming the simulation parameters, the performance of Fe lidar is also evaluated. The simulation model could provide a valuable guidance for Fe lidar design.

Demonstration of an iron fluorescence lidar operating at 372 nm wavelength using a newly-developed Nd:YAG laser

We report on the development of a pulsed neodymium-doped yttrium aluminum garnet (Nd:YAG) laser operating at a 1116 nm wavelength. Because the third harmonic is within a few gigahertz of the 372 nm absorption line of iron, this laser system represents an alternative to alexandrite lasers commonly used in iron fluorescence lidars. With our prototype, we achieved a 0.5 W at 372 nm wavelength and a 100 Hz pulse repetition frequency. As a proof of concept, we show iron density measurements, which have been acquired using the novel lidar transmitter.