Conference Agenda

Atmospheric particles have a remarkable impact on the global environment and climate change. The mineral dust, marine, polluted marine, absorbing, and other types of aerosols are important parts of the global biogeochemical cycles. The land-sea-wind circulation, different heights of boundary layers over sea and continents, the thermal and mechanical turbulence and the pollution emissions in the coastal zones have pronounced impact on the optical properties of the aerosols. In view of these, vertical resolved measurements of optical aerosol properties with calibrated and QA/QC checked lidar systems are necessary. Hence, evaluation and calibration of the data quality of observation equipment are needed urgently. The proposed project tasks are to intercalibrate the lidars from both partners by using EARLINET QA/QC procedures side by side. For this, the lidars from China are scheduled to be transported to Europe. The intercalibration and intercomparison will be conducted at TROPOS in Leipzig/Germany (http://www.tropos.de/) since often particle layers of dust, polluted marine aerosol and other types of aerosol had been observed at TROPOS, the technical infrastructure at TROPOS together with the running systems there is well established. Afterwards, the lidars will be theoretically and experimentally analyzed (including the determination of Müller Matrixes) to determine the contributions of the optical parts to the total system parameters and their uncertainties. With this system calibration and validation results, the optical particle parameters like the extinction coefficient, the backscatter coefficient, the lidar ratio, the aerosol optical thickness, the depolarization ratio, and the Ångström exponent will be measured at TROPOS during a following intensive measurement campaign of about 3 months. The mentioned intensive particle parameters will be used for aerosol type characterization from the observed data.

After this crosscheck, also the intercomparison of the measurement results from the ground-based lidars and from spaceborne lidars (carried by EARTHCARE, ADM-Aeolus, CALIPSO) will be conducted. Furthermore, the wind profiles, the turbulence, and the dynamic structure inside the atmospheric boundary layer will also be observed, which will support the research on the vertical mixing and lateral transport (including sea-land-wind) of aerosols. Through vertical wind speed detection, aerosol flux will be calculated, and thus the strength and deposition of aerosols can be estimated. After the transportation of the lidar systems to Changdao Island / China, a second joint intensive joint measurement campaign will be carried out in this project. This task will enhance the cognition of aerosols like polluted marine, polluted dust, dust, and other aerosol types. It is expected that the aerosols consist mainly of mixtures of mineral dust, pollution, and marine within the planetary boundary layer and in the lofted layers (above) at Changdao Island.

After its launch in autumn 2018, the spaceborne wind lidar ALADIN (Atmospheric LAser Doppler INstrument) on-board ESA’s Earth Explorer satellite Aeolus will allow for global observation of atmospheric wind profiles. Being the first ever satellite-borne Doppler wind lidar instrument, ALADIN will significantly contribute to the improvement in numerical weather prediction by providing one component of the wind vector along the instrument’s line-of-sight (LOS) from ground throughout the troposphere up to the lower stratosphere. The vertical resolution is 0.25 km to 2 km depending on altitude, while the precision in wind speed is envisaged to be between 1 m·s^-1 to 3 m·s^-1.

Over the past years, an airborne prototype of the Aeolus payload, the ALADIN Airborne Demonstrator (A2D), has been developed at DLR (German Aerospace Center) and deployed in several field experiments, aiming at pre-launch validation of the satellite instrument and at performing wind lidar observations under various atmospheric conditions. The A2D features a high degree of commonality with ALADIN in terms of laser source and Doppler lidar receiver design. Thus, it represents the key instrument for the planned calibration and validation activities during the Aeolus mission, as it allows validating the instrument concept, operating procedures as well as wind retrieval algorithms.

In autumn 2016, the A2D was engaged in the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX). Based in Keflavík, Iceland, this international field campaign had the overarching goal to investigate the influence of diabatic processes, related to clouds and radiation, on the evolution of the North Atlantic jet stream. Apart from providing accurate wind observations for quantifying effects of disturbances on the downstream propagation of the jet, the research flights performed during NAWDEX considerably extended the wind dataset obtained with the A2D as well as with the 2-µm coherent wind lidar on-board the same aircraft – the DLR-Falcon F20. Hence, NAWDEX was an ideal platform for assessing the performance of the two wind lidar systems in heterogeneous atmospheric scenes including strong wind shear and varying cloud conditions.

Besides the DLR-Falcon, three additional aircraft were involved in the campaign being equipped with diverse state-of-the art remote sensing instruments which enabled the observation of a large set of atmospheric parameters, while ground stations delivered a comprehensive suite of further measurements to complement the meteorological analysis. For the first time, coordinated flights were conducted involving the DLR-Falcon, the German HALO deploying an aerosol lidar, a cloud radar and dropsondes as well as the French Falcon SAFIRE with an on-board cloud radar and a UV Doppler lidar instrument. Comparative analysis of the wind data obtained during the collocated flight legs allowed quantifying the accuracy and the precision of the various instruments and demonstrated the complementarity of the different technologies for measuring wind speeds. This work will provide an overview of the NAWDEX campaign and present the results from the wind data analysis both from a meteorological and an instrument point-of-view.

The spaceborne Aerosol and Carbon dioxide Detection Lidar (ACDL) will measure the global column concentrations of carbon dioxide (CO₂) and aerosols profiles simultaneously . The column concentrations of carbon dioxide are measured by 1572 nm double-pulsed integrated path differential absorption (IPDA) lidar technique. The aerosols and clouds profiles are obtained by 532 nm high resolution spectrum lidar (HRSL) technique. Both techniques are combined in the ACDL lidar payload. The dedicated atmosphere and environment monitoring satellite will carry the ACDL lidar and is scheduled to launch in 2020. The spaceborne lidar prototype is being developed. An airborne Aerosol and Carbon dioxide Detection Lidar (AACDL) is developed and high altitude flight validation experiments are scheduled to implement in 2018.

For a double-pulsed 1.57-μm integrated path differential absorption (IPDA) lidar, the transmitted laser pulse energy is an important factor which can influence the uncertainty of the CO₂ Column concentrations measurement. Designing an 1.57μm double-pulsed laser energy monitor and to improve the accuracy of the normalized energy ratio of the transmitter pulse energies to returned echo pulse energies are presented. In the experiments, each pulse is divided into two parts .One is received by the detector directly and the other is delayed by the 200 m multimode fiber. Ground glass diffusers in front of the integrating sphere are used to reduce speckles generated by integrating sphere. Ground glass diffusers with different grits and the rotational speeds are compared. The results show that the rotated ground glass diffuser with 120 grits has the minimum standard deviation of the normalized energy ratio after a moving average. Compared to the situations without the ground glass diffuser or with static ground glass diffuser, the slopes of the Allan deviations of normalized energy ratio with rotated ground glass diffusers are more close to -0.5 in logarithmic coordinates.

In preparation of ESA’s upcoming Earth Explorer mission Aeolus which strives for the global observation of wind profiles from the ground to the lower stratosphere deploying the first-ever satellite-borne wind lidar system ALADIN, the ALADIN airborne demonstrator (A2D) has been developed at DLR (German Aerospace Center). Due to its representative design and operating principle, the A2D provides valuable information on the wind measurement strategies of the satellite instrument as well as on the optimization of the wind retrieval and related quality-control algorithms. Hence, it represents an essential testbed for the planned calibration and validation activities after the launch of Aeolus which is scheduled for end of August 2018.

The A2D was successfully employed for wind observations in the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) conducted in Iceland in autumn 2016. Within the scope of the campaign, which aimed to study the influence of diabatic processes on the evolution of the North Atlantic jet stream, 14 research flights were performed extending the wind and calibration dataset of the A2D. In particular, the recording of very high wind speeds above 80 m·s^-1 and strong wind shear of 10 m·s^-1·km^-1 was obtained by sampling an intensified jet stream close to Scotland on 27 September 2016. Broad vertical and horizontal coverage across the troposphere was achieved thanks to the complementary design of the A2D receiver comprising a Rayleigh and Mie channel for analysing both molecular and particulate backscatter signals. Validation of the instrument performance and retrieval algorithms was conducted by comparison with DLR’s coherent wind lidar which was operated in parallel on-board the same aircraft. The systematic error of the A2D line-of-sight (LOS) wind speeds was determined to be less than 0.5 m·s^-1 for both receiver channels, while the random errors range from 1.5 m·s^-1 (Mie) to 2.7 m·s^-1 (Rayleigh). This work will present the operation principle of the A2D and demonstrate selected wind results obtained during NAWDEX.

Ground-based measurements were carried out during field campaigns in April–June of 2010, 2011 and 2012 over northwestern China at Minqin, the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) and Dunhuang, respectively. In this study, three dust cases were examined, and the statistical results of dust occurrence, along with physical and optical properties were analyzed. The results show that both lofted dust layers and near-surface dust layers were characterized by extinction coefficients of 0.25–1.05 km⁻¹ and high particle depolarization ratios (PDRs) of 0.25–0.40 at 527 nm wavelength. During the three campaigns, the frequencies of dust occurrence retrieved from the lidar observations were all higher than 88%, and the highest frequency was in April. The vertical distributions revealed that the maximum height of dust layers typically reached 7.8–9 km or higher. The high intensity of dust layers mostly occurred within the planetary boundary layer (PBL). The monthly averaged PDRs decreased from April to June, which implies a dust load reduction. Comparing the relationship between the aerosol optical depth at 500 nm (AOD₅₀₀) and the Angstrom exponent at 440–870 nm (AE_440–870) confirms that there is a more complex mixture of dust aerosols with other types of aerosols when the effects of human activities become significant.