Exploration of a Whole Atmosphere LIDAR Concept for Whole Atmosphere Science: Advances in Resonance Doppler LIDAR Technologies
Although resonance Doppler lidars have made significant contributions to our understanding of the mesosphere and lower thermosphere (MLT), today's whole atmosphere models demand a more complete picture, requiring mobile instruments with superior resolution and coverage (0-200+ km). Higher resolution is needed to capture smaller scale impacts on transport of energy and momentum in the MLT, greater coverage to understand the ways in which disturbances originating in the lower atmospheres can govern both large and small scale dynamics, and wind to complete the picture of dynamic transport and energy/momentum flux. A whole atmosphere lidar is needed and we have a two-pronged approach to address this need in the community.
First, existing resonance lidar receivers with fully realized efficiency will improve temporal and spatial resolutions, fill in the Rayleigh gap and lower the detection threshold for tenuous layers of metal in the thermosphere. We show how certain design considerations have improved the lidar sensitivity by several factors, as demonstrated by cases of the implementation at Boulder, Colorado, Cerro Pachón, Chile and Arecibo, Puerto Rico. The performance of these resonance lidars is now sufficient to directly resolve seasonal vertical eddy flux in the MLT region for the first time and detect previously unstudied thermospheric Na layers above Cerro Pachón up to 170 km.
Second, we developed a Major Research Instrumentation Fe Doppler lidar which includes substantial innovations. With this lidar as the platform for a novel receiver design concept, we investigate a field-widened Mach-Zehnder interferometer (MZI) to enable this resonance lidar to conduct wind measurements below the MLT. We show how the MZI can be integrated with the Fe Doppler lidar to make measurements nearly as sensitive as the most sensitive implementations of the MZI, yet insensitive to aerosol load, temperature, pressure and turbulence of the scatter volume. Summation of the two channels recovers the original signal, which can be used harmoniously with MLT measurements, enabling routine wind profiling from the near surface to more than 115 km with a single lidar. The implications are an improved understanding of whole atmosphere thermal structure and dynamics and gravity wave spectrum, source and dissipation.