Airborne forward pointing UV Rayleigh lidar for remote clear air turbulence (CAT) detection: system design and performance

A high-performance airborne UV Rayleigh lidar system was developed within the European project DELICAT. With its forward-pointing architecture it aims at demonstrating a novel detection scheme for clear air turbulence (CAT) for an aeronautics safety application. Due to its occurrence in clear and clean air at high altitudes (aviation cruise flight level), this type of turbulence evades microwave radar techniques and in most cases coherent Doppler lidar techniques. The present lidar detection technique relies on air density fluctuations measurement and is thus independent of backscatter from hydrometeors and aerosol particles. The subtle air density fluctuations caused by the turbulent air flow demand exceptionally high stability of the setup and in particular of the detection system. This paper describes an airborne test system for the purpose of demonstrating this technology and turbulence detection method: a high-power UV Rayleigh lidar system is installed on a research aircraft in a forward-looking configuration for use in cruise flight altitudes. Flight test measurements demonstrate this unique lidar system being able to resolve air density fluctuations occurring in light-to-moderate CAT at 5 km or moderate CAT at 10 km distance. A scaling of the determined stability and noise characteristics shows that such performance is adequate for an application in commercial air transport.Comment: 17 pages, 19 figures. Pre-publish to Applied Optics (OSA

A survey of preference-based reinforcement learning methods

Reinforcement learning (RL) techniques optimize the accumulated long-term reward of a suitably chosen reward function. However, designing such a reward function often requires a lot of task- specific prior knowledge. The designer needs to consider different objectives that do not only influence the learned behavior but also the learning progress. To alleviate these issues, preference-based reinforcement learning algorithms (PbRL) have been proposed that can directly learn from an expert's preferences instead of a hand-designed numeric reward. PbRL has gained traction in recent years due to its ability to resolve the reward shaping problem, its ability to learn from non numeric rewards and the possibility to reduce the dependence on expert knowledge. We provide a unified framework for PbRL that describes the task formally and points out the different design principles that affect the evaluation task for the human as well as the computational complexity. The design principles include the type of feedback that is assumed, the representation that is learned to capture the preferences, the optimization problem that has to be solved as well as how the exploration/exploitation problem is tackled. Furthermore, we point out shortcomings of current algorithms, propose open research questions and briefly survey practical tasks that have been solved using PbRL

A survey of preference-based reinforcement learning methods

Reinforcement learning (RL) techniques optimize the accumulated long-term reward of a suitably chosen reward function. However, designing such a reward function of ten requires a lot of task-specific prior knowledge. The designer needs to consider different objectives that do not only influence the learned behavior but also the learning progress. To alleviate these issues, preference-based reinforcement learning algorithms (PbRL) have been proposed that can directly learn from an expert\u27s preferences instead of a hand-designed numeric reward. PbRL has gained traction in recent years due to its ability to resolve the reward shaping problem, its ability to learn from non numeric rewards and the possibility to reduce the dependence on expert knowledge. We provide a unified framework for PbRL that describes the task formally and points out the different design principles that affect the evaluation task for the human as well as the computational complexity. The design principles include the type of feedback that is assumed, the representation that is learned to capture the preferences, the optimization problem that has to be solved as well as how the exploration/exploitation problem is tackled. Furthermore, we point out shortcomings of current algorithms, propose open research questions and briefly survey practical tasks that have been solved using PbRL

Latent Heat Flux Profiles from Collocated Airborne Water Vapor and Wind Lidars during IHOP_2002

Latent heat flux profiles in the convective boundary layer (CBL) are obtained for the first time with the combination of the DLR water vapor differential absorption lidar (DIAL) and the NOAA high resolution Doppler wind lidar (HRDL). Both instruments were integrated nadir viewing on board the DLR “Falcon” research aircraft during the International H2O Project (IHOP_2002) over the U.S. Southern Great Plains. Flux profiles from 300 – 2500 m AGL are computed from high spatial resolution (150 m horizontal and vertical) two-dimensional water vapor and vertical velocity lidar cross sections using the eddy covariance technique. All cospectra show significant contributions to the flux between 1 and 10 km wavelength, with peaks between 2 and 6 km, originating from large eddies. The main flux uncertainty is due to low sampling (55 % rmse at mid-CBL), while instrument noise (15 %) and systematic errors (7 %) play a minor role. The combination of a water vapor and a wind lidar on an aircraft appears as an attractive new tool that allows measuring latent heat flux profiles from a single over-flight of the investigated area

Development and application of an airborne differential absorption lidar for the simultaneous measurement of ozone and water vapor profiles in the tropopause region

A new, combined, lidar system has been developed that is able to simultaneously measure profiles of ozone and water vapor onboard aircraft. The concurrent measurement of these complementary trace species in the upper troposphere and lower stratosphere allows inferring exchange processes in the tropopause region. Whereas an advanced H2O differential absorption lidar at 935 nm has successfully been developed and extensively tested at DLR in the past, we describe here an amendment of this lidar by the addition of an ultraviolet (UV) channel to measure ozone. The transmitter of the ozone differential absorption lidar (DIAL) is based on a near-IR optical parametric oscillator that is frequency-converted into the UV spectral range by intracavity sum frequency mixing. Hereby, a continuous UV tuning range of ∼297–317  nm has been achieved. The average output power in this range is higher than 1 W corresponding to more than 10 mJ per pulse at a repetition rate of 100 Hz. The ozone DIAL system has been carefully characterized both on the ground and in flight. The first simultaneously measured two-dimensional cross-sections of ozone and water vapor in the upper troposphere and lower stratosphere have been recorded during the Wave-driven Isentropic Exchange (WISE) field campaign in 2017 demonstrating the high potential of this system for studying exchange processes in this region of the atmosphere

Motility and Ultrastructure of Spirochaeta thermobhila

We analyze here for the first time the swimming behavior of a thermophilic, strictly anaerobic Spirochete, namely Spirochaeta thermophila using high temperature light microscopy. Our data show that S. thermophila very rapidly can change its morphology during swimming, resulting in cells appearing nearly linear, in cells possessing three different spiral forms, and in cells being linear at one end and spiral at the other end. In addition cells can rapidly bend by up to 180 degrees, with their ends coming into close contact. We combine electron with light microscopy to explain these various cell morphologies. Swimming speeds for cells with the various morphologies did not differ significantly: the average speed was 33 (+/- 8) mu m/s, with minimal and maximal speeds of 19 and 59 mu m/s, respectively. Addition of gelling agents like polyvinylpyrrolidone or methyl cellulose to the growth medium resulted in lower and not higher swimming speeds, arguing against the idea that the highly unusual cell body plan of S. thermophila enables cells to swim more efficiently in gel-like habitats

The TRY Database System

The TRY initiative (www.try-db.org) is a network of vegetation scientists providing curated plant trait data for the scientific community. The TRY Database currently contains about 7 million trait records for nearly 3000 different traits. The flexible database structure can hold any number of traits and a generic program can import any kind of data without requiring a template. About 10 million trait records for about 100 requests are released on a monthly basis. This is organized via the TRY Data Portal, which facilitates data contribution, exploration and customized requests. The Dataset Custodian Centre allows managing the status of contributed datasets and monitoring the use of these data from requests to scientific publications. The Request PI Centre allows managing and monitoring requests. Both centres facilitate direct contact of data contributors and users. In addition to the TRY Database we have established a file archive, which facilitates publication and DOIs for else unpublished plant trait datasets. The TRY Data Portal has evolved toward a long-term scientific data infrastructure, which combines the advantages of easy access to curated plant trait data almost ready for analyses, with direct contact of data providers and users, the opportunity for data providers to publish individual datasets and track the use of their data. This presentation will introduce details of the TRY database system

Spectroscopija 125Te (n,γ), (d,p) i (3He,α) reakcijama

Single γ-ray spectra and γγ-coincidences, following thermal neutron capture in 124Te, were measured with semiconductor detectors at the light-water reactor LWR - 15 at Řež. Intensities of g transitions in 125Te were normalized using the absolute intensity of 7.8% of the 6620 keV line in 36Cl. The high resolution (d,p) measurements were performed with 17 MeV deuterons, using the Q3D spectrograph at two scattering angles of 15° and 30°. Spectra were recorded in the range up to 3.3 MeV and calibrated using the proton peaks with l =1, and the corresponding level energies were determined in the thermal neutron capture reaction. The (3He,α) experiment was carried out with a 32 MeV He beam at the angle of 10°. The spectrum was recorded in one run by means of a large detector in a range up to approximately 4.7 MeV. The absolute intensities were determined by measuring the total beam current.Mjerili su se izravni γ- i sudesni γ-γ-spektri nakon uhvata termičkih neutrona u 124Te. Mjerenja (d,p) reakcija visokog razlučivanja na toj jezgri izvela su se s deuteronima 17 MeV na kutovima od 15° i 30° , pomoću Q3D spektrografa. Također se mjerio spektar u reakciji (3He,α) na 10° . Na osnovi tih mjerenja utvrđena su mnoga nova stanja 125Te na energijama uzbude do oko 4.5 MeV. Razlika grananja 403/443 keV iz izravnih i sudesnih γ-spektara ukazuje na jaku primjesu E2 u primarnom prijelazu od 6125 keV

Determination of the emission rates of CO2 point sources with airborne lidar

We report on CO2 emissions of a coal-fired power plant derived from flight measurements performed with the IPDA lidar CHARM-F during the CoMet campaign in spring 2018. Despite the results being in broad agreement with reported emissions, we observe strong variations between successive flyovers. Using a high-resolution large eddy simulation, we identify strong atmospheric turbulence as the cause for the variations and recommend more favorable measurement conditions for future campaign planning