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Adhesion properties of metal-composite bonds are crucial in defining composite capability with other metallic components, and failures could lead to severe accidents. Hence, the study is aimed at the development and characterization of metal-composite bonds using different rigid adherends and adhesive materials (thermoset and thermoplastics). Among natural fibers, jute was used, while aramid, carbon, and glass woven reinforcements were employed from synthetic fibers. A simultaneous comparison of both thermoset and thermoplastic matrices was done using epoxy, polypropylene (PP), and polyvinyl butadiene (PVB) as adhesive materials. Floating roller delamination characterization proved variation in adhesion qualities governing different failure modes by varying adhesive even in a single rigid adherend. The highest fracture toughness was observed for aluminum-jute bonds made with PP and PVB that was due to toughness of matrix and intralaminar failure. Carbon being brittle in nature showed the most fluctuated performance with a 90% difference between the highest value of carbon-PVB and the lowest value of carbon-epoxy. Thermoplastic matrices owing to plasticity offered overall more fracture toughness than brittle thermoset resin. Furthermore, intralaminar was the dominant failure mechanism in the jute-based bond made with thermoplastic matrix.

This paper presents a collection of lidar-derived aerosol intensive optical properties for several aerosol types, namely the particle linear depolarization ratio, the extinction-to-backscatter ratio (lidar ratio) and the Ångström exponent. The data collection, named DeLiAn, is based on globally distributed, long-term, ground-based, multiwavelength, Raman and polarization lidar measurements, conducted mainly with lidars that have been developed at the Leibniz Institute for Tropospheric Research. The intensive optical properties are presented at two wavelengths, 355 and 532 nm, for 13 aerosol categories. The categories cover the basic aerosol types (i.e., marine, pollution, continental European background, volcanic ash, smoke, mineral dust), as well as the most frequently observed mixtures they form. This extensive collection also incorporates more peculiar aerosol categories, including dried marine aerosol that, compared to marine aerosol, exhibits a significantly enhanced depolarization ratio (up to 15 %). Besides Saharan dust, additional mineral dust types related to their source region were identified due to their lower lidar ratios (Central Asian and Middle Eastern dust). In addition, extreme wildfire events (such as in north America and Australia) emitted smoke into the stratosphere showing significantly different optical properties, i.e., high depolarization values (up to 25 %), compared to tropospheric smoke. The data collection reflects and underlines the variety of aerosol mixtures in the atmosphere and can be used for the development of aerosol-typing schemes. The paper contains the most up-to-date and comprehensive overview of optical properties from aerosol lidar measurements and, therefore, provides a solid basis for future aerosol retrievals in the frame of both spaceborne and ground-based lidars. Furthermore, DeLiAn can assist the efforts for the harmonization of satellite records of aerosol properties performed at different wavelengths.

The eVe dual-laser/dual-telescope lidar system is introduced here, focusing on the optical and mechanical parts of the system's emission and receiver units. The compact design of the linear–circular emission unit along with the linear–circular analyser in the receiver unit allows eVe to simultaneously reproduce the operation of the ALADIN lidar on board Aeolus as well as to operate it as a traditional ground-based polarisation lidar system with linear emission. As such, the eVe lidar aims to provide (a) ground reference measurements for the validation of the Aeolus L2A aerosol products and (b) the conditions for which linear polarisation lidar systems can be considered for Aeolus L2A validation, by identifying any possible biases arising from the different polarisation state in the emission between ALADIN and these systems, and the detection of only the co-polar component of the returned signal from ALADIN for the L2A products' retrieval. In addition, a brief description is given concerning the polarisation calibration techniques that are applied in the system, as well as the developed software for the analysis of the collected signals and the retrieval of the optical products. More specifically, the system's dual configuration enables the retrieval of the optical properties of particle backscatter and extinction coefficients originating from the two different polarisation states of the emission and the linear and circular depolarisation ratios, as well as the direct calculation of the Aeolus-like backscatter coefficient, i.e. the backscatter coefficient that Aeolus would measure from the ground. Two cases, one with slightly depolarising particles and one with moderately depolarising particles, were selected from the first conducted measurements of eVe in Athens in September 2020, in order to demonstrate the system's capabilities. In the slightly depolarising scene, the Aeolus-like backscatter coefficient agrees well with the actual backscatter coefficient, which is also true when non-depolarising particles are present. The agreement however fades out for strongly depolarising scenes, where an underestimation of ∼18 % of the Aeolus like backscatter coefficient is observed when moderately depolarising particles are probed.