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It has long been assumed that Rayleigh lidar can be used to measure atmospheric temperature profiles up to about 90 or 100 km and that above this region the technique becomes invalid due to changes in atmospheric composition which affect basic assumptions on which Rayleigh lidar is based. Modern powerful Rayleigh lidars are able to measure backscatter from well above 100 km requiring a closer examination of the effects of the changing atmospheric composition on derived Rayleigh lidar temperature profiles. The NRLMSISE-00 model has been used to simulate lidar signal (photon-count) profiles, taking into account the effects of changing atmospheric composition, enabling a quantitative analysis of the biases and errors associated with extending Rayleigh lidar temperature measurements above 100 km. The biases associated with applying a nominal correction for the change in atmospheric composition with altitude has also been investigated. The simulations reported here show that in practice the upper altitude limit for Rayleigh lidar is imposed more by the accuracy of the temperature or pressure used to seed the temperature retrieval algorithm than by accurate knowledge of the atmospheric composition as has long been assumed.

Light detection and ranging (Lidar) is a remote sensing technique that is used for measuring atmosphere parameters, such as temperature, composition, and wind. Lidar, like radar, operates by transmitting a beam of electromagnetic radiation and subsequently detecting any radiation scattered back to the instrument. The scattered radiation is analyzed in order to determine some property, or properties of the medium through which the radiation traveled. The range of atmospheric parameters that can be measured with lidar include: temperature, wind velocity, atomic and molecular species concentration, and aerosol and cloud properties.

A well-established technique for the determination of temperature in the middle atmosphere is the retrieval of temperature profiles from density profiles of air. The measurement of air density profiles from the ground and from space are typically determined from measurements of Rayleigh-scattered light. Most researchers using the Rayleigh-scatter temperature technique do not state whether they correct their measurements for the absorption of light due to ozone in the upper stratosphere. Such corrections may have been less significant for initial studies of temperature, but with the current need for temperature measurements of sufficient quality to access atmospheric change, these corrections take on an added importance. Significant improvement to the temperature measurements in the stratosphere are shown to result by including this effect for any reasonable choice of ozone profile. Simple correction functions are presented for temperature measurements, appropriate for low, middle, and high latitu...

Two new techniques have been developed to estimate the densities of N2, O2, and O from Rayleigh lidar backscatter photocount profiles and from independent temperature determinations. Both techniques involve solving initial value problems for the N2, O2, and O densities. These initial value problems are derived from the lidar equation, the ideal gas law, and the assumption of hydrostatic equilibrium. Their solutions are valid in regions where the Rayleigh lidar backscatter can be fully isolated from other scattering sources, e.g., aerosol scattering and where independent temperature determinations can been made. Estimates of the N2 and O2 density profiles in the upper mesosphere and lower thermosphere have been performed on three nights using simultaneous sodium-resonance-fluorescence lidar measurements to independently determine the temperature profile. The available measurements are of insufficient quality to retrieve O density profiles. The resulting N2 and O2 density retrievals appear reasonable when compared with previous determinations from sounding rockets and give hope that this method will allow routine ground-based measurements of major constituent density in the middle atmosphere. A detailed error analysis is described which shows that the primary source of random errors is the Rayleigh photocounts, while the most important systematic errors are uncertainties in the N2 and O2 Rayleigh backscatter cross sections and in the normalization of the lidar density profiles in the upper stratosphere and lower mesosphere.

Rayleigh and Raman scatter measurements from The University of Western Ontario Purple Crow Lidar (PCL) have been used to develop temperature climatologies for the stratosphere, mesosphere, and thermosphere using data from 1994 to 2013 (Rayleigh system) and from 1999 to 2013 (vibrational Raman system). Temperature retrievals from Rayleigh-scattering lidar measurements have been performed using the methods by Hauchecorne and Chanin (1980; henceforth HC) and Khanna et al. (2012). Argall and Sica (2007) used the HC method to compute a climatology of the PCL measurements from 1994 to 2004 for 35 to 110 km, while Iserhienrhien et al. (2013) applied the same technique from 1999 to 2007 for 10 to 35 km. Khanna et al. (2012) used the inversion technique to retrieve atmospheric temperature profiles and found that it had advantages over the HC method. This paper presents an extension of the PCL climatologies created by Argall and Sica (2007) and Iserhienrhien et al. (2013). Both the inversion and HC methods were used to form the Rayleigh climatology, while only the latter was adopted for the Raman climatology. Then, two different approaches were used to merge the climatologies from 10 to 110 km. Among four different functional identities, a trigonometric hyperbolic relation results in the best choice for merging temperature profiles between the Raman and Low level Rayleigh channels, with an estimated uncertainty of 0.9 K for merging temperatures. Also, error function produces best result with uncertainty of 0.7 K between the Low Level Rayleigh and High Level Rayleigh channels. The results show that the temperature climatologies produced by the HC method when using a seed pressure are comparable to the climatologies produced by the inversion method. The Rayleigh extended climatology is slightly warmer below 80 km and slightly colder above 80 km. There are no significant differences in temperature between the extended and the previous Raman channel climatologies. Through out this study, we discuss the data collected by PCL for a long term (1994–2013) up to 110 km. Moreover, different merging functions in various methods were used to merge the temperature climatologies for different channels.

Lidar is an active remote sensing technique similar in principle to radar, except that it utilizes light rather than radio waves. Lidar finds applications in many areas, including atmospheric and oceanic research, digital mapping, chemical and biological agent detection, speed measurement, and targeting. This chapter describes the principles of lidar and provides examples of the application of lidar in measuring the properties of the Earth's atmosphere. Keywords: lidar; laser–radar; laser; atmospheric optics; Rayleigh; aerosol; DIAL; Raman

Temperature measurements from the PCL Rayleigh lidar located near London, Canada, taken during the 11 year period from 1994 to 2004 are used to form a temperature climatology of the middle atmosphere. A unique feature of the PCL temperature climatology is that it extends from 35 to 95 km allowing comparison with other Rayleigh lidar climatologies (which typically extend up to about 85 km), as well as with climatologies derived from sodium lidar measurements which extend from 83 to 108 km. The derived temperature climatology is compared to the CIRA-86 climatological model and to other lidar climatologies, both Rayleigh and sodium. The PCL climatology agrees well with the climatologies of other Rayleigh lidars from similar latitudes, and like these other climatologies shows significant differences from the CIRA-86 temperatures in the mesosphere and lower thermosphere. Significant disagreement is also found between the PCL climatology and sodium lidar climatologies measured in the central and western United States at similar latitudes, with the PCL climatology consistently 10 to 15 K cooler in the 85 to 90 km region.

Sodium resonance-fluorescence lidar is an established technique for measuring atmospheric composition and dynamics in the mesopause region. A large-power-aperture product (6.6-W m(2)) sodium resonance-fluorescence lidar has been built as a part of the Purple Crow Lidar (PCL) at The University of Western Ontario. This sodium resonance-fluorescence lidar measures, with high optical efficiency, both sodium density and temperature profiles in the 83-100-km region. The sodium lidar operates simultaneously with a powerful Rayleigh- and Raman-scatter lidar (66 W m(2)). The PCL is thus capable of simultaneous measurement of temperature from the tropopause to the lower thermosphere. The sodium resonance-fluorescence lidar is shown to be able to measure temperature to an absolute precision of 1.5 K and a statistical accuracy of 1 K with a spatial-temporal resolution of 72 (km s) at an altitude of 92 km. We present results from three nights of measurements taken with the sodium lidar and compare these with coincident Rayleigh-scatter lidar measurements. These measurements show significant differences between the temperature profiles derived by the two techniques, which we attribute to variations in the ratio of molecular nitrogen to molecular oxygen that are not accounted for in the standard Rayleigh-scatter temperature analysis.

A lidar system has been built to measure atmospheric-density fluctuations and the temperature in the upper stratosphere, the mesosphere, and the lower thermosphere, measurements that are important for an understanding of climate and weather phenomena. This lidar system, the Purple Crow Lidar, uses two transmitter beams to obtain atmospheric returns resulting from Rayleigh scattering and sodium-resonance fluorescence. The Rayleigh-scatter transmitter is a Nd:YAG laser that generates 600 mJ/pulse at the second-harmonic frequency, with a 20-Hz pulse-repetition rate. The sodium-resonance-fluorescence transmitter is a Nd:YAG-pumped ring dye laser with a sufficiently narrow bandwidth to measure the line shape of the sodium D(2) line. The receiver is a 2.65-m-diameter liquid-mercury mirror. A container holding the mercury is spun at 10 rpm to produce a parabolic surface of high quality and reflectivity. Test results are presented which demonstrate that the mirror behaves like a conventional glass mirror of the same size. With this mirror, the lidar system's performance is within 10% of theoretical expectations. Furthermore, the liquid mirror has proved itself reliable over a wide range of environmental conditions. The use of such a large mirror presented several engineering challenges involving the passage of light through the system and detector linearity, both of which are critical for accurate retrieval of atmospheric temperatures. These issues and their associated uncertainties are documented in detail. It is shown that the Rayleigh-scatter lidar system can reliably and routinely measure atmospheric-density fluctuations and temperatures at high temporal and spatial resolutions.