Engineering topics
Publications and source records attributed to Mcllrath, T. J..
The physics of fluorescence lidar is reviewed, with emphasis placed on understanding the features which determine its applicability to particular species and environments. The successful applications of fluorescence lidar to date are covered, and a range of proposed measurements is considered. Attention is given to stratospheric applications.
A ground-based differential absorption lidar (DIAL) system is described which has been developed for vertical range-resolved measurements of water vapor. The laser transmitter consists of a ruby-pumped dye laser, which is operated on a water vapor absorption line at 724.372 nm. Part of the ruby laser output is transmitted simultaneously with the dye laser output to determine atmospheric scattering and attenuation characteristics. The dye and ruby laser backscattered light is collected by a 0.5-m diam telescope, optically separated in the receiver package, and independently detected using photomultiplier tubes. Measurements of vertical water vapor concentration profiles using the DIAL system at night are discussed, and comparisons are made between the water vapor DIAL measurements and data obtained from locally launched rawinsondes. Agreement between these measurements was found to be within the uncertainty of the rawinsonde data to an altitude of 3 km. Theoretical simulations of this measurement were found to give reasonably accurate predictions of the random error of the DIAL measurements. Confidence in these calculations will permit the design of aircraft and Shuttle DIAL systems and experiments using simulation results as the basis for defining lidar system performance requirements
A technique is proposed for remote sensing of atomic oxygen by laser excitation of a two-photon transition. Excitation at 2256 A and subsequent fluorescence at 8447 A allow probing of the mesosphere and lower thermosphere without interference by absorption. The two-photon excitation rate is calculated, and its dependence on laser power, duration, and linewidth is discussed. Values are given for remote sensing from a spacecraft at 200 km ranging down to 80 km with 1-km range resolution. Accuracies of better than 10% are expected with a 1 J, a 20-psec excitation pulse and a 1-sq-m collecting telescope.