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A Laser Doppler Anemometer system designed to measure two components of the velocity vector in fluids is presented. The scheme followed is the differential technique with backward scattering configuration. The scheme uses three laser beams crossing at the point of measure. Two of the beams pass through frequency shifters in order to displace the zero reference of each velocity component. The bursts reflected by the particles in the fluid are detected and mixed on the surface of an APD, which is used as an optical detector. The system can work in real time with a rate of 30 measurements per second. It has been designed to detect velocities up to 3 m/s which is a current limit in hydrodynamic experiments. The error committed is about 1% and both signs of the velocity are distinguished.

Presentamos un prototipo de un sistema lidar (radar láser) de onda continua heterodino de baja potencia, para la medida de la velocidad de desplazamiento de superficies. Ofrece simplicidad y fácil alineación de todos los dispositivos ópticos. Permite medir la velocidad de blancos a distancias de más de 6 m y, empleando una frecuencia intermedia de 160MHz, obtener información del signo de la velocidad. Esta frecuencia intermedia se consigue mediante la inserción de un modulador acusto óptico (AOM). La detección se real iza sobre la superficie activa de un fotodiodo de avalancha (APD). En este artículo presentamos la descripción del sistema y medidas de laboratorio de potencia, anchura espectral y tolerancia en distancia.

El objetivo fundamental de esta tesis es el estudio y desarrollo de sistemas de bajo coste desistemas lidar para detección y medida de velocidad de blancos sólidos.

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.

The short-wave (SW) direct radiative effect (DRE) during the summer 2019 heatwave produced partly by a mod erate, long-lasting Saharan dust outbreak over Europe is anal ysed in this study. Two European sites (periods) are consid ered: Barcelona, Spain (23 30 June), and Leipzig, Germany (29 and 30 June), 1350 km apart from each other. Major data are obtained from AERONET and polarised Micro-Pulse Li dar (P-MPL) observations. Modelling is used to describe the different dust pathways, as observed at both sites. The coarse dust (Dc) and fine dust (Df) components (with total dust, DD = Dc + Df) are identified in the profiles of the total par ticle backscatter coefficient using the POLIPHON (POlarisa tion LIdar PHOtometer Networking) method in synergy with P-MPL measurements. This information is used to calculate the relative mass loading and the centre-of-mass height, as well as the contribution of each dust mode to the total dust DRE. Several aspects of the ageing of dust are put forward. The mean dust optical depth and its Df/DD ratios are, re spectively, 0.153 and 24 % in Barcelona and 0.039 and 38 % in Leipzig; this Df increase in Leipzig is attributed to a longer dust transport path in comparison to Barcelona. The dust produced a cooling effect on the surface with a mean daily DRE of-9.1 and-02.5 Wm-2 , respectively, in Barcelona and Leipzig, but the Df/DD DRE ratio is larger for Leipzig (52 %) than for Barcelona (37 %). Cooling is also observed at the top of the atmosphere (TOA), although less intense than on the surface. However, the Df/DD DRE ratio at the TOA is even higher (45 % and 60 %, respectively, in Barcelona and Leipzig) than on the surface. Despite the predominance of Dc particles under dusty conditions, the SW radiative im pact of Df particles can be comparable to, even higher than, that induced by the Dc ones. In particular, the Df/DD DRE ratio in Barcelona increases by +2.4 % d-1 (surface) and +2.9 % d-1 (TOA) during the dusty period. This study is completed by a second paper about the long-wave and net radiative effects. These results are especially relevant for the next ESA EarthCARE mission (planned in 2022) as it is de voted to aerosol cloud radiation interaction research., This research was funded by the Spanish Ministry of Science, Innovation and Universities (CGL2017-90884-REDT and PRX18/00137 “Salvador de Madariaga” programme), the Spanish Ministry of Science and Innovation (PID2019-104205GB-C21 and PID2019-103886RB-I00), the H2020 programme from the European Union (ACTRIS, GA no. 654109, 778349, and 871115), and the Unity of Excellence “María de Maeztu“ (MDM-2016-0600) financed by the Spanish State Research Agency (AEI). MPZ has been partially funded by the AEI (Unity of Excellence “María de Maeztu” - Centro de Astrobiología (CSIC-INTA), MDM-2017-0737). MALC is supported by the INTA predoctoral contract programme.