Daytime lidar measurements of the stratosphere and mesosphere at the alomar observatory

Abstract

The Rayleigh/Mie/Raman (RMR) Lidar at the ALOMAR Observatory in Northern Norway (69°N, 16°E) has been equipped with special filters to make daytime measurements of the Rayleigh back-scattered lidar signal at 532 nm, 355 nm and 1064 nm. At the high latitude location of ALOMAR, the sun is on or above the horizon for approximately 10 weeks around the summer solstice. Despite this, the ALOMAR RMR lidar measures temperature profiles up to middle mesosphere altitudes (75 km) at any local time, throughout the summer period. These “daytime” lidar observations have been made possible by combining several important features: a powerful and stable laser, a very small field-of-view for the lidar receiving telescope, and narrow-band filters, using double-etalon Febry-Perot interferometers, in front of the photon counting detectors. Special highlights of this novel capability of the RMR Lidar include a daytime wind capability and three-colour observations of noctilucent clouds (NLCs) at all local times throughout the 1997 and 1998 mid-summer NLC “seasons”. The major features of the ALOMAR RMR system, including the special double-etalon Fabry-Perot interferometers which are required to produce efficient daytime detection filter systems for each of the lidars, will be presented and discussed.