A Lidar for the Region from the Stratosphere to the Thermosphere

Abstract:

At Utah State University (USU), in the Center for Atmospheric and Space Sciences (CASS), we are developing a lidar capable of making observations that would span the middle atmosphere from the lower stratosphere well into the lower thermosphere, 15 – 120 km. This would provide a new capability for observing this extended region with just one ground-based instrument. To do this, we are building upon extensive experience at CASS’s Atmospheric Lidar Observatory (ALO) with Rayleigh-scatter lidar. This new system uses two Nd:YAG lasers, operating at 532 nm and 30 Hz, with a combined power of 42 W, and four co-aligned, 1.25 m diameter, parabolic mirrors with a combined collecting area of almost 5 m². The resultant figure of merit, the power-aperture product (PAP), is 205 Wm², 65 times that of the original lidar. This increase is significant for both Rayleigh scatter at the highest altitudes and Raman scatter at the lowest altitudes. The light from the fibers from the four mirrors are combined and, at the moment, directed to the high-altitude Rayleigh detector channel. Observations have been obtained with this channel in the vicinity of summer solstice. The profiles, extending from 70 km to almost 120 km, show considerable structure, which changes from night to night and differs from the NRL-MSISe00 reference atmosphere. Improvements are under way to extend the maximum altitude. The next steps are to add a medium-altitude, Rayleigh detector channel and then a low-altitude, Rayleigh and Mie detector channel. They will be followed by a low-altitude, 607 nm, Raman detector channel. With what we learn from this extensive effort, we are planning a simpler system with more advanced technology that would be easier (and less expensive) to build and operate. The idea being that it could be fielded in many places in the world to contribute to an extensive ground-based network to observe the middle atmosphere. Much of this region represents a significant and challenging observational gap between aircraft and balloon-borne radiometers at the lower altitudes and combinations of ionosondes, meteor wind radars, resonance lidars, airglow imagers, Fabry-Perots, and incoherent-scatter radars at the higher altitudes.