Measurement of spray drift with a specifically designed lidar system

Field measurements of spray drift are usually carried out by passive collectors and tracers. However, these methods are labour- and time-intensive and only provide point- and time-integrated measurements. Unlike these methods, the light detection and ranging (lidar) technique allows real-time measurements, obtaining information with temporal and spatial resolution. Recently, the authors have developed the first eye-safe lidar system specifically designed for spray drift monitoring. This prototype is based on a 1534 erbium-doped glass laser and an 80 mm diameter telescope, has scanning capability, and is easily transportable. This paper presents the results of the first experimental campaign carried out with this instrument. High coefficient of determination (R2>0.85) were observed by comparing lidar measurements of the spray drift with those obtained by horizontal collectors. Furthermore, the lidar system allowed an assessment of the drift reduction potential (DRP) when comparing low-drift nozzles with standard ones, resulting in a DRP of 57%(preliminaryresult) for the tested nozzles. The lidar system was also used for monitoring the evolution of the spray flux over the canopy and to generate 2-D images of these plumes. The developed instrument is an advantageous alternative to passive collectors and opens the possibility of new methods for field measurement of spray drift.Peer ReviewedPostprint (published version

Aerosol lidar intercomparison in the framework of SPALINET- the SPAnish LIdar NETwork: methodology and results

A group of eight Spanish lidars was formed in order to extend the European Aerosol Research Lidar Network-Advanced Sustainable Observation System (EARLINET-ASOS) project. This study presents intercomparisons at the hardware and software levels. Results of the system intercomparisons are based on range-square-corrected signals in cases where the lidars viewed the same atmospheres. Comparisons were also made for aerosol backscatter coefficients at 1064 nm (2 systems) and 532 nm (all systems), and for extinction coefficients at 532 nm (2 systems). In total, three field campaigns were carried out between 2006 and 2007. Comparisons were limited to the highest layer found before the free troposphere, i.e., either the atmospheric boundary layer or the aerosol layer just above it. Some groups did not pass the quality assurance criterion on the first attempt. Following modification and improvement to these systems, all systems met the quality criterion. The backscatter algorithm intercomparison consisted of processing lidar signal profiles simulated for two types of atmospheric conditions. Three stages with increasing knowledge of the input parameters were considered. The results showed that all algorithms work well when all inputs are known. They also showed the necessity to perform, when possible, additional measurements to attain better estimation of the lidar ratio, which is the most critical unknown in the elastic lidar inversion

Lidar-Radiometer Inversion Code (LIRIC) for the retrieval of vertical aerosol properties from combined lidar/radiometer data: Development and distribution in EARLINET

This paper presents a detailed description of LIRIC (LIdar-Radiometer Inversion Code) algorithm for simultaneous processing of coincident lidar and radiometric (sun photometric) observations for the retrieval of the aerosol concentration vertical profiles. As the lidar/radiometric input data we use measurements from European Aerosol Research Lidar Network (EARLINET) lidars and collocated sun-photometers of Aerosol Robotic Network (AERONET). The LIRIC data processing provides sequential inversion of the combined lidar and radiometric data. The algorithm starts with the estimations of column-integrated aerosol parameters from radiometric measurements followed by the retrieval of height dependent concentrations of fine and coarse aerosols from lidar signals using integrated column characteristics of aerosol layer as a priori constraints. The use of polarized lidar observations allows us to discriminate between spherical and non-spherical particles of the coarse aerosol mode. The LIRIC software package was implemented and tested at a number of EARLINET stations. Intercomparison of the LIRIC-based aerosol retrievals was performed for the observations by seven EARLINET lidars in Leipzig, Germany on 25 May 2009. We found close agreement between the aerosol parameters derived from different lidars that supports high robustness of the LIRIC algorithm. The sensitivity of the retrieval results to the possible reduction of the available observation data is also discussed

EARLINET instrument intercomparison campaigns: Overview on strategy and results

This paper introduces the recent European Aerosol Research Lidar Network (EARLINET) quality-assurance efforts at instrument level. Within two dedicated campaigns and five single-site intercomparison activities, 21 EARLINET systems from 18 EARLINET stations were intercompared between 2009 and 2013. A comprehensive strategy for campaign setup and data evaluation has been established. Eleven systems from nine EARLINET stations participated in the EARLINET Lidar Intercomparison 2009 (EARLI09). In this campaign, three reference systems were qualified which served as traveling standards thereafter. EARLINET systems from nine other stations have been compared against these reference systems since 2009. We present and discuss comparisons at signal and at product level from all campaigns for more than 100 individual measurement channels at the wavelengths of 355, 387, 532, and 607 nm. It is shown that in most cases, a very good agreement of the compared systems with the respective reference is obtained. Mean signal deviations in predefined height ranges are typically below ±2 %. Particle backscatter and extinction coefficients agree within ±2  ×  10−4 km−1 sr−1 and ± 0.01 km−1, respectively, in most cases. For systems or channels that showed larger discrepancies, an in-depth analysis of deficiencies was performed and technical solutions and upgrades were proposed and realized. The intercomparisons have reinforced confidence in the EARLINET data quality and allowed us to draw conclusions on necessary system improvements for some instruments and to identify major challenges that need to be tackled in the future

Lidar sensing of the atmosphere: receiver design and inversion algorithms for an elastic system

LIDAR es un acrónimo de LIght Detection And Ranging. En la presente tesis, se usan técnicas basadas en lidar elástico para monitorizar la atmósfera remotamente y derivar información cuantitativa acerca de sus parámetros ópticos. Esta tesis doctoral comprende el diseño y operación de una estación lidar elástica basada en un láser pulsado de Nd:YAG operando a las longitudes de onda de 1064 y 532 nm, en lo que se refiere a los sistemas de recepción, control y diseño de algoritmos de inversión. Básicamente, puede dividirse en tres partes bien diferenciadas: La primera (Caps. 1, 2 y 3) comprende el estudio de la dispersión elástica (Rayleigh y Mie) en la atmósfera, orientada al cálculo del balance de enlace, e intenta vislumbrar la interrelación entre variables físicas tales como la temperatura, la presión y la humedad, y el fenómeno de dispersión, dejando de lado su posible extrapolación a modelos meteorologicos. Partiendo de esta base, se estiman valores de extinción y retrodispersión para diferentes condiciones atmosféricas y, como resultado, se presenta un balance de enlace para el sistema. El mismo incluye el estudio del alcance lidar, la estimación de la relación señal a ruido, y la evaluación de fotodiodos para diferentes librerías del usuario. Esta primera parte se cierra con las especificaciones globales del sistema. La segunda parte de este trabajo (Caps. 4, 5 y 6) atiende al diseño e implemen-tación del receptor, sistemas de sincronización y control. El receptor optoelectrónico se basa en amplificadores realimentados en corriente y cuenta con un excelente producto ganancia ancho de banda. Por lo que respecta al subsistema de sincronismo, se presentan dos unidades distintas con vistas a un futuro sistema lidar de escaneo, lo cuál ofrece la posibilidad de realizar scans entrelazados. Para terminar, el sistema de control diseñado se basa en el software de control LabView, que ofrece una filosofía de control distribuido. Con este propósito, se han especificado e implementado protocolos de bus lidar y su señalización para la presente estación lidar. Finalmente, la tercera parte comprende el diseño de algoritmos de inversión con y sin memoria (Caps. 7 y 8). Los algortimos sin memoria para atmósferas homogéneas se basan en procedimientos de ajuste por regresión como son el método de la pendiente y el de mínimos cuadrados y, en el caso de atmósferas inhomogéneas, se basan en el método de Klett y calibraciones adecuadas. Los algortimos con memoria se basan en diferentes modelos estocásticos para la atmósfera y filtrado de Kalman no lineal. Además de los algortimos de inversión, también se calculan y discuten las curvas del error de inversión. El Cap. 9 describe las medidas llevadas a cabo con el sistema que este trabajo ha permitido construir así como el resultado de aplicar los algoritmos de inversión presentados en los capítulos precedentes. La inversión de escenas reales comprende estudios de la estructura de polución, estudios de nubes (ceilometría, básicamente desplazamiento y estructura de las nubes) y señala posibles fuentes de error en el factor de solapamiento.LIDAR is an acronym of LIght Detection And Ranging. In the present case, the elastic lidar techniques are used to remotely sense the atmosphere and to derive quantitative information about its optical parameters.This thesis comprises the design and operation of an elastic lidar station based on a pulsed Nd:YAG laser operating at the 1064- and 532-nm wavelengths, in the parts concerning receiver, control systems, and inversion algorithms.Basically, it can be divided in three different parts: The first one (Chaps. 1, 2, and 3) encompasses the study of the elastic scattering (Rayleigh and Mie) in the atmosphere for link-budget purposes and gives some insight into the interweaving between physical variables such as temperature, pressure and humidity, and the scattering phenomena, letting apart any possible extrapolation to meteorological models. From this basis, extinction and backscatter figures for different atmospheric conditions can readily be assessed and, as result, a system link budget is presented. This includes lidar range study, signal-to-noise ratio assessment, and photodiode evaluation from custom-made libraries. At the end of the first part, the system specification is made. The second part of this work (Chaps. 4, 5, and 6) is concerned with the design and implemen-tation of receiver, synchronization, and control systems. The optoelectronic receiver is based on current-feedback amplifiers and features a very large gain-bandwidth product. As for the synchronization subsystem, two different units are presented with a view to a future scanning lidar system, which makes room for interspersed scans. Eventually, the control system designed is LabView based and features a distributed control philosophy. For that purpose, lidar bus protocols and signals are specified and built for the actual lidar station. Finally, the third part encircles the design of inversion algorithms with and without memory (Chaps. 7 and 8). Non-memory algorithms for homogeneous atmospheres are based on regression curve-fitting procedures, such as the slope-method and the least squares while in instances of inhomogeneous atmospheres they are based on Klett's method and appropriate calibrations. Memory algorithms are based on different stochastic models for the atmosphere and on non-linear Kalman filtering. In addition to these inversion procedures, error assessment plots are also derived and discussed. Chap. 9 describes the measurements carried out with the system this work has contributed to build and the results of applying to them the inversion algorithms discussed in the preceding chapters.The inversion of live-scenes involves pollution structure studies, cloud studies (ceilometry, cloud motion and wave clouds, basically), and hints overlap factor error sources

Adaptive Estimation of the Stable Boundary Layer Height Using Combined Lidar and Microwave Radiometer Observations

A synergetic approach for the estimation of stable boundary-layer height (SBLH) using lidar and microwave radiometer (MWR) data is presented. Vertical variance of the backscatter signal from a ceilometer is used as an indicator of the aerosol stratification in the nocturnal stable boundary-layer. This hypothesis is supported by a statistical analysis over one month of observations. Thermodynamic information from the MWR-derived potential temperature is incorporated as coarse estimate of the SBLH. Data from the two instruments is adaptively assimilated by using an extended Kalman filter (EKF). A first test of the algorithm is performed by applying it to collocated Vaisala CT25K ceilometer and Humidity-and-Temperature Profiler (HATPRO) MWR data collected during the HD(CP)2 Observational Prototype Experiment (HOPE) campaign at Julich, Germany. The application of the algorithm to different atmospheric scenarios reveals the superior performance of the EKF compared to a non-linear least-squares estimator especially in non-idealized conditions.Peer ReviewedPostprint (author's final draft