Shuttle lidar resonance fluorescence investigations 2: Analysis of thermospheric Mg^+ measurements

Abstract

Shuttle lidar measurements of magnesium-ion (Mg+) number density in the ionosphere (80-500 km) have been numerically simulated. A set of recently defined system parameters are used to assess the system performance. These simulations take into account the saturation effect of atomic absorption due to the high intensity of the laser, which is seen to be important in making near-field or daytime measurements. When the saturation is important, a calibration procedure must be used to correct the systematic error introduced by this effect. Both the nadir- and zenith-viewing configurations have been considered because the altitude of the Shuttle was assumed to be 300 km. The background level in these two configurations is discussed, and we show that the background level for zenith-viewing with the assumed lidar system parameters is negligible. The calibration of the lidar system parameters by means of Rayleigh backscattering from atmospheric molecules in the stratosphere is examined. This method is shown to require extra care because of the wavelength used (2796 A), which lies within a strong absorption band of ozone causing large transmission errors. The Shuttle lidar capability for Mg(+) measurement is compared with the requirements for conducting scientific investigations in the thermosphere.