Vladimir A. Kovalev

Lidar measurement of the vertical aerosol extinction profiles with range-dependent backscatter-to-extinction ratios

An iterative lidar-signal inversion method is presented that is valid for two-component (molecular andaerosol) scattering atmospheres. The iterative procedure transforms the original lidar signal, thereby making it possible to use the lidar-equation solution for a single-component atmosphere. In a manner analogous to Fernalds approach, the molecular extinction profile is used as a foundation for the boundary-condition determination, but the inversion procedure can be performed with either constant or variable (range-dependent) phase functions. A specific region in the measured range is located at which the ratio of the aerosol to molecular extinction coefficients is a minimum as determined by an examinationof the lidar-signal profile; for this region boundary conditions are specified.

Distortion of particulate extinction profiles measured with lidar in a two-component atmosphere

Distortions of particular extinction-coefficient profiles measured with lidar in a two-component (molecular and aerosol) scattering atmosphere are analyzed. The error of the extinction coefficient measured at range r depends on the location of the point r(b), where a boundary value is specified, and the particulate optical depth of the atmosphere between r and r(b); the particulate backscatter-to-extinction ratio; and the ratio of particulate and molecular scattering extinction. If the near-end solution is used, small measurement errors can produce a significant divergence between the actual and the retrieved extinction-coefficient profiles, even if the boundary value and the particulate backscatter-to-extinction ratio are specified accurately. This effect is exacerbated at small values of the particulate scattering coefficient and the backscatter-to-extinction ratio. When reasonable criteria are used, feasible minimum and maximum boundary values can be specified to restrict the range of lidar equation solutions from below and from above.

Differential absorption lidar measurement of vertical ozone profiles in the troposphere that contains aerosol layers with strong backscattering gradients: a simplified version

A technique for determining approximate ozone-concentration profiles from differential absorption lidar (DIAL) data obtained in the troposphere with large gradients of aerosol backscattering is presented. The atmospheric interferences are defined as errors of the off-on DIAL signal ratio; the interferences are separated and removed before the ratio is differentiated. To facilitate the separation of the regular (subjected to differentiation) component of the signal ratio from random noise, the ratio is transformed into an intermediate function, and the measurement error is minimized by fitting of an analytical function to the transformed function. Simple criteria are used to demarcate atmospheric layering, for which a strong aerosol-backscattering gradient can result in an unacceptably large error in the measured ozone concentration.

Compensational three-wavelength differential-absorption lidar technique for reducing the influence of differential scattering on ozone-concentration measurements

A three-wavelength differential-absorption lidar (DIAL) technique for the ultraviolet spectral region is presented that reduces the influence of aerosol differential scattering on measured ozone-concentration profiles. The principal advantage of this approach is that, to a good first approximation, no correction for aerosol differential-extinction and backscattering effects are needed. Therefore, one avoids having to obtain an aerosol extinction-coefficient profile at a reference wavelength; nor does one have to invoke questionable assumptions regarding the spectral dependence of the aerosol total and backscatter coefficients.

Determination of vertical ozone profiles in the lower troposphere using estimates of the DIAL data quality

New algorithms are developed to improve the methodology of the ozone profile extraction from the signals measured by an ultraviolet DIAL system in a turbid troposphere. A routine procedure is developed to estimate the likely boundaries of the uncertainty in the retrieved ozone concentration profile caused both by the errors in the measured signals and by an uncertainty in the atmospheric characteristics used for the ozone concentration correction (specifically, by uncertainties in the assumed aerosol backscatter-to-extinction ratio and spectral dependence of the aerosol extinction and backscattering). The algorithms are integrated into a computer program, and a preliminary verification of the new technique for the ozone concentration derivation is made with one and two pairs of the signals, measured at the on and off wavelengths of the DIAL system.

Lidar-inversion technique for monitoring and mapping localized aerosol plumes and thin clouds

A new lidar-inversion technique is presented for the determination of the extinction-coefficient profile within a spatially restricted zone of atmospheric aerosol inhomogeneity such as a plume, thin cloud, etc. The return lidar signal is measured through the aerosol plume under investigation and also in a direction close to but outside the plume. By using the ratio of these signals, the constituent produced by the aerosol plume is separated from the aerosol background constituent. An iterative lidar- inversion technique is applied to the ratio of these signals rather than to the original signal. This technique is shown to be relatively insensitive to the assumed value of parameters used for the extinction-profile retrieval, and yields an acceptable measurement results even when the accuracy of the assumed parameters is poor.

Nonlinear-approximation technique for determining vertical ozone-concentration profiles with a differential-absorption lidar

A new technique is presented for the retrieval of ozone-concentration profiles (O(3)) from backscattered signals obtained by a multiwavelength differential-absorption lidar (DIAL). The technique makes it possible to reduce erroneous local fluctuations induced in the ozone-concentration profiles by signal noise and other phenomena such as aerosol inhomogeneity. Before the O(3) profiles are derived, the dominant measurement errors are estimated and uncertainty boundaries for the measured profiles are established. The off- to on-line signal ratio is transformed into an intermediate function, and analytical approximations of the function are then determined. The separation of low- and high-frequency constituents of the measured ozone profile is made by the application of different approximation fits to appropriate intermediate functions. The low-frequency constituents are approximated with a low-order polynomial fit, whereas the high-frequency constituents are approximated with a trigonometric fit. The latter fit makes it possible to correct the measured O(3) profiles in zones of large ozone-concentration gradients where the low-order polynomial fit is found to be insufficient. Application of this technique to experimental data obtained in the lower troposphere shows that erroneous fluctuations induced in the ozone-concentration profile by signal noise and aerosol inhomogeneity undergo a significant reduction in comparison with the results from the conventional technique based on straightforward numerical differentiation.