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A precise pulsed ranging method using long laser pulses was developed and tested experimentally. It is based on direct analog–digital sampling of both the reference and received pulses and their software processing by digital filtering, pulse shape retrieving, selections, pulse center calculation, and averaging. The method is effective for pulse widths longer than the sampling step, including the case when only one sample exceeds the threshold. A temporal accuracy on the order of 10−2 of the sampling step and better can be realized in the optimal receiving regime. The method offers an approach for the creation of precise ranging instruments by using relatively long laser pulses. This was demonstrated on a 10.6 μm range-finding system emitting 500 ns laser pulses with time instability with respect to the triggering pulses. A ranging accuracy on the order of (3–5) cm was achieved using traditional 10 MHz/8 bit analog/digital converters. The method enlarges the set of prospective laser sources suitable for p...

A novel wide‐band Doppler LIDAR detection technique (up to GHz range), by using two sets of digitally selected reference frequencies, is developed. It combines the advantages of two well‐known approaches—the analog quadrature detection (low sampling frequency and data rate, highly dynamic range) and the direct digitizing (fully digital controlling and processing without coherent oscillator minimum analog stages, very easy tuning) at the same accuracies as the Doppler estimates. This technique may be applied in airborne and satellite Doppler LIDARs as well as in low‐cost ground‐based systems using CO2 or solid‐state laser sources.

A new scheme for Doppler lidar detection by frequency shifted tracking of the reference frequency is described. The main advantages of the scheme are wide tolerable range of the laser instabilities (in principle more than 100 MHz), easy wideband tuning of the tracking frequency, one analog output by A/D converter with a sampling rate of only several times higher then the maximum expected Doppler frequency. It is shown how to account for the chirp history. The use of frequency synthesis for Doppler detection in wide frequency band of laser instabilities is considered.

Analytical estimates for the limiting temporal resolution of the photoreceiving system based on the spectral analysis of the interference signal from single-frequency decayed oscillations excited by the secondary electron train are given. It is shown that the resolution limit is defined by the r.m.s. fluctuations of the photoemission time and time-jitter of the secondary electron packets divided by the square root of the number of photoelectrons within the resolution cell at arbitrary intensities, and does not depend on the time-broadening of the electron packets excited by individual photoelectrons. Numerical estimates show the possibility of obtaining resolutions of the order of 10−12–10−14 s. The achieving of such resolutions is due to the interference of a great number of oscillations with phase differences smaller than π giving a resultant signal of very small phase variance. The product of the limiting resolution interval and the square root of the signal energy is a constant, depending on ...

Within the framework of the project "EARLINET-ASOS (European Aerosol Research Lidar Network - Advanced Sustainable Observation System)" Contract No 025991 of European Commission's Framework Program 6 (EC FP6) (http://www.earlinet.org), transportation of Saharan dust over Europe has been observed in the sky over Sofia, during the last week of May, 2008. This phenomena, predicted by the Atmospheric Modeling and Weather Forecasting Group of National Technical University of Athens (NTUA) (http://forecast.uoa.gr/) and the Forecast system of Barcelona Supercomputing Center (BSC) (http://www.bsc.es/projects/ earthscience/DREAM), was interesting with its relatively long-time existence and large scale of propagation over the continent. In this work, we present the results and some comments of the measurements of the atmospheric backscatter coefficient made in Sofia, using aerosol lidar with CuBrvapor laser.

In this work we developed a method for estimation of the ratio of aerosol to molecular backscattering coefficients in lidar sounding of the atmosphere. We presented our first results of such analysis of lidar measurement carried out in June- July 2008, using lidar system with a CuBr-laser and two receiving channels. The laser emits simultaneously two closely disposed wavelengths λ 1 =510.6 nm and λ 2 =578.2 nm of similar output powers. The spectral distance between these wavelengths provides well distinguished molecular scattering signal. From the other side the both wavelengths are too close to accept (in the first order of approximation) a similarity in the aerosol scattering conditions. Both lidar channels have very similar technical parameters (as overlapping functions, photon detector sensitivity, optical transmission, etc.) and thus, provide similar output signal levels for both wavelengths. The preliminary results from the analysis of experimental data demonstrated the opportunity to detect and to process well distinguished lidar signals in clear atmosphere. The operational heights exceed 9 km at accumulation time 30 min, that is typical for the adopted integration time in European lidar network EARLINET.

The Doppler detection schemes, effective at high frequency instabilities of laser sources are of great interest for lidar performance. The stability of ≈ 10−9 is required to realize ≈ ± 1 m/s accuracy of wind speed [1,2]. Doppler detection schemes on the intermediate frequency opera ting at stabilities of order of 10−7 ÷ 10−6 are described here, based on the so-called tracking heterodyne [3,4] and the proper lidar synchronization.

A method has been developed whereby near-photon-counting performance can be achieved at high signal levels in gated optical systems of long coherence time. The method involves converting the received photoelectrons into single-frequency secondary waves. Linear performance has been demonstrated even when the photon-counting pulses greatly overlap. Furthermore, the effect of a non-stationary background may be taken into account simply as the square root of its intensity, without recourse to chopping at the signal overlap and in the background spectra.