Abstract
Abstract. 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.
Highlights
IntroductionRayleigh lidar is a well established technique used to determine atmospheric temperature profiles from the midstratosphere (∼30 km) to the lower thermosphere (∼95 km), (Chanin, 1984; Sica et al, 1995)
Rayleigh lidar is a well established technique used to determine atmospheric temperature profiles from the midstratosphere (∼30 km) to the lower thermosphere (∼95 km), (Chanin, 1984; Sica et al, 1995).Rayleigh lidars measure the intensity of light backscattered by the atmosphere, as a function of altitude, from a pulsed laser
The algorithm used in this work explicitly determines a relative pressure profile from the relative mass-density profile, which is determined from the photon-count profile
Summary
Rayleigh lidar is a well established technique used to determine atmospheric temperature profiles from the midstratosphere (∼30 km) to the lower thermosphere (∼95 km), (Chanin, 1984; Sica et al, 1995). Inherent in the determination of temperature profiles using the Rayleigh lidar technique is the assumption that measured photon-count profiles are proportional to the atmospheric mass-density profile. Equation (4) shows that the signal measured by a Rayleigh lidar is proportional to the atmospheric mass density, so long as the above assumptions are valid, i.e. the composition of the atmosphere does not change. In order to determine an atmospheric temperature profile, a Rayleigh lidar measured photon-count profile is first corrected for range (Eq 4) and is scaled to an atmospheric model so that it represents a relative mass-density profile, ρrel, i.e. the model is used to estimate the proportionally constant applicable to Eq (4).
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