Depolarization channel for barcelona lidar. Implementation and preliminary measurements

A new depolarization channel has beenimplemented in the BarcelonaTech University(UPC) multi-wavelength lidar system. The opticaland mechanical designs are presented. The specialconfiguration of the total power channel is alsodetailed, with the relevant aspects in measurement inversion. Some preliminary measurements arepresented for Saharan dust intrusion events.Peer ReviewedPostprint (published version

Current research in lidar technology used for the remote sensing of atmospheric aerosols

Lidars are active optical remote sensing instruments with unique capabilities for atmospheric sounding. A manifold of atmospheric variables can be profiled using different types of lidar: concentration of species, wind speed, temperature, etc. Among them, measurement of the properties of aerosol particles, whose influence in many atmospheric processes is important but is still poorly stated, stands as one of the main fields of application of current lidar systems. This paper presents a review on fundamentals, technology, methodologies and state-of-the art of the lidar systems used to obtain aerosol information. Retrieval of structural (aerosol layers profiling), optical (backscatter and extinction coefficients) and microphysical (size, shape and type) properties requires however different levels of instrumental complexity; this general outlook is structured following a classification that attends these criteria. Thus, elastic systems (detection only of emitted frequencies), Raman systems (detection also of Raman frequency-shifted spectral lines), high spectral resolution lidars, systems with depolarization measurement capabilities and multi-wavelength instruments are described, and the fundamentals in which the retrieval of aerosol parameters is based is in each case detailed.Peer ReviewedPostprint (published version

Remote sensing mediante LIDAR en la UPC

Peer Reviewe

Diffuse sunlight based calibration of the water vapor channel in the UPC Raman lidar

A method for determining the calibration factor of the water vapor channel of a Raman lidar, based on zenith measurements of diffuse sunlight and on assumptions regarding some system parameters and Raman scattering models, has been applied to the lidar system of Universitat Politècnica de Catalunya (UPC; Technical University of Catalonia, Spain). Results will be analyzed in terms of stability and comparison with typical methods relying on simultaneous radiosonde measurements.Peer ReviewedPostprint (published version

Speed measurements with a continuous wave lidar prototype

The UPC lidar group is developing a Doppler wind lidar based on the “edge-technique” [1]. Such systems use the slope of a high resolution optical filter as frequency discriminator. A laboratory prototype, able to measure the speed of solid targets emitting continuous wave radiation and using a Fabry-Perot interferometer as optical filter, has been built. A tuning control has been included to compensate drifts between the emitted frequency and the filter resonance frequencies in order to assure maximum sensitive measurements. The design of the system and different results concerning the performance of the tuning control system and speed measurements will be presented.Peer ReviewedPostprint (published version

Considerations about the determination of the depolarization calibration profile of a two-telescope lidar and its implications for volume depolarization ratio retrieval

We propose a new method for calculating the volume depolarization ratio of light backscattered by the atmosphere and a lidar system that employs an auxiliary telescope to detect the depolarized component. It takes into account the possible error in the positioning of the polarizer used in the auxiliary telescope. The theory of operation is presented and then applied to a few cases for which the actual position of the polarizer is estimated, and the improvement of the volume depolarization ratio in the molecular region is quantified. In comparison to the method used before, i.e., without correction, the agreement between the volume depolarization ratio with correction and the theoretical value in the molecular region is improved by a factor of 2–2.5.Peer ReviewedPostprint (published version

Remote sensing mediante LIDAR en la UPC

Peer Reviewe

Calibration of Raman lidar water vapor mixing ratio measurements using zenithal measurements of diffuse sunlight and a radiative transfer model

This is a postprint (author final draft) version of article that has been accepted for publication. A fully version can be found at: https://doi.org/10.1109/TGRS.2018.2851064 © 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Among the different techniques available for measuring the atmospheric water vapor content, Raman lidars stand out as accurate instruments providing detailed profiles with high temporal and altitude resolution. Their principle is based on obtaining the range-resolved ratio of the lidar signals corresponding to Raman returns from water vapor and nitrogen molecules, which is proportional to the water vapor mixing ratio. To do this, it is necessary to determine a calibration factor, specific of each lidar instrument. A method for obtaining this parameter, based on zenith measurements of diffuse sunlight, on Raman scattering models and on simulations, using a radiative transfer model, to estimate sky radiances at the wavelengths of interest, has been applied to the lidar system of Universitat Politècnica de Catalunya (UPC; Technical University of Catalonia, Barcelona, Spain). A set of calibrations, performed between 2016 and 2017, has permitted assessing the calibration procedure and analyzing the stability of the calibration factor in the UPC instrument. Results show that although the calibration factor can remain stable for long periods of time, it can suffer sudden variations that make indispensable to implement a convenient and reliable procedure to perform regular calibrations. We show that the method, which can be applied to any lidar with water vapor and nitrogen Raman channels, can completely dispense with radiosonde data. The calibration method is validated by comparison with simultaneous radiosonde water vapor measurements. Limitations of radiosondes for validating--and eventually calibrating--water vapor Raman lidars have been revealed.Peer ReviewedPostprint (author's final draft

Sistema lidar elástico incoherente para sondeo de la atmósfera

The main features of the incoherent elastic lidar operating at the premises of the Department of Signal Theory and Communications' Electroinagnetic and Photonics Engineering Group, in the Campus fiord of the Polytechnic University of Catalonia, are presented. The system is able to detect atmospheric acrosols (dust, haze, smoke...) and to prende data about the structure of clouds. Its performance is shown in the forro of results concerning the measurement of atmospheric extinction and backscatter coefficients for severa' atmospheric conditions.Peer ReviewedPostprint (published version