About the potential of lidars with different photodetectors under daytime sky radiation

Results of theoretical analysis and experimental developments implemented as advanced methods and means to improve a noise-immunity of lidar systems for practical applications are discussed. A particular attention is paid to assessing the developed methods and technical solutions effectiveness and their comparison with existing lidar systems and real receivers. © 2016 Owned by the authors, published by EDP Sciences.Peer ReviewedPostprint (published version

Assessment of capabilities of lidar systems in day-and night-time under different atmospheric and internal-noise conditions

As an application of the dimensionless parameterization concept proposed earlier for the characterization of lidar systems, the universal assessment of lidar capabilities in day and night conditions is considered. The dimensionless parameters encapsulate the atmospheric conditions, the lidar optical and optoelectronic characteristics, including the photodetector internal noise, and the sky background radiation. Approaches to ensure immunity of the lidar system to external background radiation are discussed. © The Authors, published by EDP Sciences, 2018.Peer ReviewedPostprint (published version

Compact lidar system using laser diode, binary continuous wave power modulation, and an avalanche photodiode-based receiver controlled by a digital signal processor

We analyze the practical limits of a lidar system based on the use of a laser diode, random binary continuous wave power modulation, and an avalanche photodiode (APD)-based photereceiver, combined with the control and computing power of the digital signal processors (DSP) currently available. The target is to design a compact portable lidar system made all in semiconductor technology, with a low-power demand and an easy configuration of the system, allowing change in some of its features through software. Unlike many prior works, we emphasize the use of APDs instead of photomultiplier tubes to detect the return signal and the application of the system to measure not only hard targets, but also medium-range aerosols and clouds. We have developed an experimental prototype to evaluate the behavior of the system under different environmental conditions. Experimental results provided by the prototype are presented and discussed.Peer ReviewedPostprint (published version

Spatial filtering efficiency of monostatic biaxial lidar: analysis and applications

Results of lidar modeling based on spatial-angular filtering efficiency criteria are presented. Their analysis shows that the low spatial-angular filtering efficiency of traditional visible and near-infrared systems is an important cause of low signal background-radiation ratio SBR at the photodetector input. The low SBR may be responsible for considerable measurement errors and ensuing the low accuracy of the retrieval of atmospheric optical parameters. As shown, the most effective protection against sky background radiation for groundbased biaxial lidars is the modifying of their angular field according to a spatial-angular filtering efficiency criterion. Some effective approaches to achieve a high filtering efficiency for the receiving system optimization are discussed.Postprint (published version

Error analysis for the lidar backward inversion algorithm

Here we depart from the inhomogeneous solution of a lidar equation using the backward inversion algorithm that is nowadays generally referred to as the Klett method. In particular, we develop an error sensitivity study that relates errors in the user-input parameters boundary extinction and exponential term in the extinction-to-backscatter relationship to errors in the inverted extinction profile. The validity of the analysis presented is limited only by the validity of application of the inversion algorithm itself, its numerical performance having been tested for optical depths in the 0.01–10 range. Toward this end, we focus on an introductory background about how uncertainties in these two parameters can apply to a family of inverted extinction profiles rather than a single profile and on its range-dependent behavior as a function of the optical thickness of the lidar inversion range. Next, we performed a mathematical study to derive the error span of the inverted extinction profile that is due to uncertainties in the above-mentioned user calibration parameters. This takes the form of upper and lower range-dependent error bounds. Finally, appropriate inversion plots are presented as application examples of this study to a parameterized set of atmospheric scenes inverted from both synthesized elastic-backscatter lidar signals and a live signal.Peer Reviewe

Sistemas Lidar para control de tráfico

Peer Reviewe

Contribución de la red de lidares EARLINET a la infraestructura europea de investigación atmosférica ACTRIS (Aerosols, Clouds, and Trace Gases Infrastructure Network).

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Assessment of lidar inversion errors for homogeneous atmospheres

The inversion of lidar returns from homogeneous atmospheres has been done customarily through the well-known slope method. The logarithmic operation over the range-corrected and system-normalized received signal used in this method introduces a bias in the statistics of the noise-affected processed signal that can severely distort the estimates of the atmospheric attenuation and backscatter coefficients under measurement. It is shown that a fitting of the theoretically expected exponential signal to the range-corrected received one, using as the initial guess the results provided by the slope method and a least-squares iterative procedure, can yield enhanced accuracy under low signal-to-noise ratios and especially in moderate-to-high extinction conditions.Peer Reviewe

Compact and Simple X 3 (9 to 27 GHz) Pll Frequency Multiplier Using Harmonic Phase Detection

Frequency multiplication in the microwave and millimeter-wave range can be performed in compact form using harmonic phase detectors, in which the veo phase is directly compared to a multiple of the reference frequency internally generated in the same device. In this paper we present a x3 P.l.L. frequency multiplier following this technique that phase-locks a 27 GHz Gunn diode VCO to a 9 GHz reference, in a simple and compact arrangement. The Gunn diode frequency is controlled vía the voltage applied to it. The phase detector used is a balanced mixer, ímplemented with a 90• microstrip hybrid ring and Schottky diodes, and designed at the 9 GHz referente frequency. This system can be employed through the microwave and millimeter-wave ranges to obtain low arder odd-index frequency multiplications.Peer ReviewedPostprint (published version

Multiplicador de frecuencias PLL con detector de fase armónico

An indirect synthesis frequency multiplier at microwave frequencies is presented. A microstrip balanced mixer implemented with a 90 hybrid is used as phase detector, to compare directly phases of signals at 9 and 27 GHz. In this way it is possible to remove the frequency dividers on the feedback loop. This technique will be used for synthesizing the 1st. L.O. of the 30 GHz channel in a coherent receiver for the propagation package of the Olympus satellite.Peer ReviewedPostprint (published version