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We report airborne measurements of CO_2 column abundance conducted during two 2009 campaigns using a 2.05?μm laser absorption spectrometer. The two flight campaigns took place in the California Mojave desert and in Oklahoma. The integrated path differential absorption (IPDA) method is used for the CO_2 column mixing ratio retrievals. This instrument and the data analysis methodology provide insight into the capabilities of the IPDA method for both airborne measurements and future global-scale CO_2 measurements from low Earth orbit pertinent to the NASA Active Sensing of CO_2 Emissions over Nights, Days, and Seasons mission. The use of a favorable absorption line in the CO_22?μm band allows the on-line frequency to be displaced two (surface pressure) half-widths from line center, providing high sensitivity to the lower tropospheric CO_2. The measurement repeatability and measurement precision are in good agreement with predicted estimates. We also report comparisons with airborne in situ measurements conducted during the Oklahoma campaign.

The Bernoulli solution of the lidar equation with the assumption of a constant extinction/backscattering ratio can lead to errors in the derived aerosol extinction and backscattering profiles. This paper presents a general theoretical analysis of the errors that result from differences between the assumed and actual extinction/backscattering ratio profiles. Examples of the influence of the constant extinction/backscattering ratio assumption on the lidar derived aerosol extinction profile are presented for various laser wavelengths.

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 Å), 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.

A Shuttle lidar technique based on the detection of backscattered resonance fluorescence radiation has been numerically modeled and applied to the measurements of sodium (Na) and potassium (K) number density in the upper atmosphere (80–110 km). The simulations use recently defined lidar system parameters and take into account the effect of saturation of atomic absorption due to the high intensity of laser pulses. Such an effect is shown to be important in daytime measurements, when there is a need to narrow the laser beam divergence in order to reduce the background light. When the saturation effect is important, an optimal laser beam divergence can usually be found as a result of a trade off between the reduction of signal return (due to saturation) and the reduction of background level (by narrowing the receiver field of view). A procedure for calibration of the saturation effect is discussed. The Shuttle lidar measurement capability for Na and K is compared to conventional techniques and requirements for conducting scientific investigations in the mesosphere.

The differential absorption lidar (DIAL) technique generally assumes that atmospheric optical scattering is the same at the two laser wavelengths used in the DIAL measurement of a gas concentration profile. Errors can arise in this approach when the wavelengths are significantly separated, and there is a range dependence in the aerosol scattering distribution. This paper discusses the errors introduced by large DIAL wavelength separations and spatial inhomogeneity of aerosols in the atmosphere. A Bernoulli solution for determining the relative distribution of aerosol backscattering in the UV region is presented, and scattering ratio boundary values for these solutions are discussed. The results of this approach are used to derive a backscatter correction to the standard DIAL analysis method. It is shown that for the worst cases of severe range dependence in aerosol backscattering, the residual errors in the corrected DIAL O_3 measurements were <10 ppbv for DIAL wavelengths at 286 and 300 nm.