We report a summary of the experience and results from one-year unattended operation of an automatic backscatter lidar. The backscatter lidar is realized for measurements at altitudes of Planetary Boundary Layer (PBL) and the troposphere. Such lidar has been developed and tested to answer the necessity for operation at remote sites an/or during atmospheric measurement campaigns. The results are from one year of urban boundary layer height measurements in the city of Basel (Switzerland). During this one-year of operation the lidar was remotely controlled via Internet, including also the data transfer. Here we present examples of lidar measurements of diurnal cycles of the urban boundary layer development and its height. We also present cases of lidar measurements performed in clear and cloudy sky, where the lidar observations are compared with the visual control of the sky documented by automatic camera. The results and the experience are discussed in view of the application of such automatic lidar for long-term operation as part of aerosol lidar network.
Ecological monitoring and analysis of the planetary boundary layer (PBL) dynamics require determination of the mixing layer height (MLH) on a continuous basis. In a number of cases it is necessary to determine the MLH with sufficiently high resolution - both altitude and temporal. The backscatter lidar provides a convenient tool for such determination, using the aerosol as tracer and determining its vertical profile and its time-evolution, with the capability for continuous measurements. Although methods already exist, based on the altitude derivative of the backscatter lidar signal (altitude Gradient method) and its time-variance (Variance method), the application of these methods with high resolution is limited by the background noise presence. We report here a further development of backscatter lidar gradient and variance methods for MLH determination, allowing higher resolutions. In it, the MLH determination from the gradient and the variance of the lidar signal is supported by a convenient filter technique. Time scale of increased temporal resolution allows the investigation of the fine atmospheric dynamic structures like convective motion. A number of examples in MLH retrieval are presented. The examples are based on backscatter lidar measurements performed in the PBL above Neuchatel, Switzerland (47.00°N, 6.95°S, 485m asl). The examples show the applicability and the usefulness of the reported technique in measurements of the daily cycle of the MLH dynamics.
We report the upgraded version of two compact, airborne, automatic lidars, installed on the stratospheric research aircraft M55 "Geophysica". The lidars (named MAL1 and MAL2) are depolarisation backscatter instruments. They are installed on the aircraft for probing independently upwards and downwards with respect to the aircraft altitude, providing the possibility to detect the cloud presence simultaneously above and below the aircraft. The cloud parameters determined from the lidar signals are the followings: the altitude of the cloud base and cloud top, the backscatter ratio and the depolarisation ratio of the subvisible clouds. The measurements are at a single wavelength of 532 nm (the second harmonics of the Nd:YAG laser). The combination of the photon counting signal acquisition system, the pulse duty cycle and the output power of the micro-pulsed laser, leads to a high dynamic range of detection. Objectives of the lidar installation on this stratospheric aircraft are the measurements of high-altitude cirrus and polar stratospheric clouds, as well as aerosol layers in the middle and high troposphere. We present examples of measurements of backscatter and depolarisation ratio of sub-visible clouds performed with these lidars, during recent field campaigns: ESA ENVISAT Validation and EC projects EUPLEX (European Polar Stratospheric Clouds and Lee Wave Experiment). and TROCCINOX (Tropical Convection, Cirrus and Nitrogen Oxides Experiment).
In a number of measurement scenarios it is necessary to operate a lidar in remote sites with a minimum personnel attendance on the spot. This requires a stability of operation, automatic functioning and remote control of the instrument status, and data downloading. Such backscatter/depolarisation lidar is realised by Observatory of Neuchatel and was operated for one year in Basel, Switzerland as part of Urban Boundary Layer study (BUBBLE project). The lidar is optimal for measurements at altitudes of planetary boundary layer (PBL) and troposphere. The operation was remotely controlled via internet from the premises of Observatory of Neuchatel. The lidar measurements covered a large number of the diurnal cycles of PBL development. We present a brief description of the lidar and its operation. We also present a preliminary results for PBL diurnal cycle measurements. These results include: determination of the aerosol mixed layer height using the altitude derivative of the lidar backscatter range-corrected signal and determination of the aerosol backscatter coefficient with a lidar signal inversion procedure.
Backscatter lidar measurements were performed in the atmospheric boundary layer and the troposphere above Neuchatel, Switzerland (47.00°N, 6.95°S, 485m asl). The backscatter lidar is based on Nd:YAG laser. The lidar measurements are done in the period from June 2000 till February 2002 as part of the EU project EARLINET (http://lidarb.dkrz.de/earlinet/). From the lidar measurements, we determine the following values vertical profile of the aerosol backscatter coefficients, the gradient of the range-corrected lidar signal and the variance of the range-corrected lidar signal. These values are used to determine the aerosol mixed layer (AML) height in the atmospheric boundary layer (ABL). In this work, we present a comparison of these different lidar methods to determine the AML height. The lidar-obtained values are also compared with the values for ABL top, as determined from upper air weather parameters. This comparison is performed and presented for various seasons and time in the diurnal cycle.