28 research outputs found
Airborne hydromapping area-wide surveying of shallow water areas
River engineeringInnovative field and laboratory instrumentatio
Double ring-closing approach for the synthesis of 2,3,6,7-substituted anthracene derivatives.
A method for the synthesis of 2,3,6,7-substituted anthracene derivatives, one of the most challenging anthracene substitution patterns to obtain, is presented. The method is exemplified by the preparation of 2,3,6,7-anthracenetetracarbonitrile and employs a newly developed, stable, protected 1,2,4,5-benzenetetracarbaldehyde as the precursor. The precursor can be obtained in two scalable synthetic steps from 2,5-dibromoterephthalaldehyde and is converted into the anthracene derivative by a double intermolecular Wittig reaction under very mild conditions, followed by a deprotection and intramolecular double ring-closing condensation reaction
Free-Space distribution of entanglement and single photons over 144 km
Quantum Entanglement is the essence of quantum physics and inspires
fundamental questions about the principles of nature. Moreover it is also the
basis for emerging technologies of quantum information processing such as
quantum cryptography, quantum teleportation and quantum computation. Bell's
discovery, that correlations measured on entangled quantum systems are at
variance with a local realistic picture led to a flurry of experiments
confirming the quantum predictions. However, it is still experimentally
undecided whether quantum entanglement can survive global distances, as
predicted by quantum theory. Here we report the violation of the
Clauser-Horne-Shimony-Holt (CHSH) inequality measured by two observers
separated by 144 km between the Canary Islands of La Palma and Tenerife via an
optical free-space link using the Optical Ground Station (OGS) of the European
Space Agency (ESA). Furthermore we used the entangled pairs to generate a
quantum cryptographic key under experimental conditions and constraints
characteristic for a Space-to-ground experiment. The distance in our experiment
exceeds all previous free-space experiments by more than one order of magnitude
and exploits the limit for ground-based free-space communication; significantly
longer distances can only be reached using air- or space-based platforms. The
range achieved thereby demonstrates the feasibility of quantum communication in
space, involving satellites or the International Space Station (ISS).Comment: 10 pages including 2 figures and 1 table, Corrected typo
Применение технологии Airborne Hydromapping и многолучевого эхолотного исследования в округе Рейнфельден
Applying terrestrial lidar for evaluation and calibration of airborne lidar-derived shrub biomass estimates in Arctic tundra
Analyzing near water surface penetration in laser bathymetry – A case study at the River Pielach
Recent developments in sensor technology yielded a major progress in airborne laser bathymetry for capturing shallow water bodies.
Modern topo-bathymetric small foot print laser scanners do no longer use the primary near infrared (NIR) signal (λ=1064 nm) but
only emit and receive the frequency doubled green signal (λ= 532 nm). For calculating correct water depths accurate knowledge of the
water surface (air-water-interface) is mandatory for obtaining accurate spot positions and water depths. Due to the ability of the green
signal to penetrate water the first reflections do not exactly represent the water surface but, depending on environmental parameters like
turbidity, a certain penetration into the water column can be observed. This raises the question if it is even feasible to determine correct
water level heights from the green laser echoes only.
In this article, therefore, the near water surface penetration properties of the green laser signal are analyzed based on a test flight of the
River Pielach (Austria) carried out with Riegl's VQ-820-G (532 nm) and VQ-580 (1064 nm) scanners mounted on the same airborne
platform. It is shown that within the study area the mean penetration into the water column is in the range of 10–25 cm compared to the
NIR signal as reference. However, as the upper hull of the green water surface echoes coincides with the NIR signal with cm-precision,
it is still possible to derive water surface models from the green laser echoes only via statistical analysis of aggregated neighboring
echoes and robustly keep the underestimation of the water level below 6 cm. This especially holds for still and stationary flowing water
bodies
HIGH RESOLUTION AIRBORNE SHALLOW WATER MAPPING
In order to meet the requirements of the European Water Framework Directive (EU-WFD), authorities face the problem of repeatedly performing area-wide surveying of all kinds of inland waters. Especially for mid-sized or small rivers this is a considerable challenge imposing insurmountable logistical efforts and costs. It is therefore investigated if large-scale surveying of a river system on an operational basis is feasible by employing airborne hydrographic laser scanning.
In cooperation with the Bavarian Water Authority (WWA Weilheim) a pilot project was initiated by the Unit of Hydraulic Engineering at the University of Innsbruck and RIEGL Laser Measurement Systems exploiting the possibilities of a new LIDAR measurement system with high spatial resolution and high measurement rate to capture about 70 km of riverbed and foreland for the river Loisach in Bavaria/Germany and the estuary and parts of the shoreline (about 40km in length) of lake Ammersee. The entire area surveyed was referenced to classic terrestrial cross-section surveys with the aim to derive products for the monitoring and managing needs of the inland water bodies forced by the EU-WFD.
The survey was performed in July 2011 by helicopter and airplane and took 3 days in total. In addition, high resolution areal images were taken to provide an optical reference, offering a wide range of possibilities on further research, monitoring, and managing responsibilities. The operating altitude was about 500 m to maintain eye-safety, even for the aided eye, the airspeed was about 55 kts for the helicopter and 75 kts for the aircraft. The helicopter was used in the alpine regions while the fixed wing aircraft was used in the plains and the urban area, using appropriate scan rates to receive evenly distributed point clouds. The resulting point density ranged from 10 to 25 points per square meter. By carefully selecting days with optimum water quality, satisfactory penetration down to the river bed was achieved throughout the project.
During the data processing meshes for multiple purposes like monitoring sediment transport or accumulation and hydro-dynamic numeric modeling were generated. The meshes were professionally conditioned considering the adherence of, both, geometric and physical mesh quality criterions. Whereas the research is focused on the design and implementation of monitoring database structures, the airborne hydrographic data are also made available for classical processing means (cross sections, longitudinal section)
EVALUATION OF A NOVEL UAV-BORNE TOPO-BATHYMETRIC LASER PROFILER
We present a novel topo-bathymetric laser profiler. The sensor system (RIEGL BathyCopter) comprises a laser range finder, an Inertial
Measurement Unit (IMU), a Global Navigation Satellite System (GNSS) receiver, a control unit, and digital cameras mounted on an
octocopter UAV (RiCOPTER). The range finder operates on the time-of-flight measurement principle and utilizes very short laser
pulses (<1 ns) in the green domain of the spectrum (λ=532 nm) for measuring distances to both the water surface and the river bottom.
For assessing the precision and accuracy of the system an experiment was carried out in October 2015 at a pre-alpine river (Pielach in
Lower Austria). A 200 m longitudinal section and 12 river cross sections were measured with the BathyCopter sensor system at a flight
altitude of 15-20 m above ground level and a measurement rate of 4 kHz. The 3D laser profiler points were compared with independent,
quasi-simultaneous data acquisitions using (i) the RIEGL VUX1-UAV lightweight topographic laser scanning system (bare earth,
water surface) and (ii) terrestrial survey (river bed). Over bare earth the laser profiler heights have a std. dev. of 3 cm, the water surface
height appears to be underestimated by 5 cm, and river bottom heights differ from the reference measurements by 10 cm with a std.
dev. of 13 cm. When restricting the comparison to laser profiler bottom points and reference measurements with a lateral offset below
1 m, the values improve to 4 cm bias with a std. dev. of 6 cm. We report additionally on challenges in comparing UAV-borne to
terrestrial profiles. Based on the accuracy and the small footprint (3.5 cm at the water surface) we concluded that the acquired 3D
points can potentially serve as input data (river bed geometry, grain roughness) and validation data (water surface, water depth) for
hydrodynamic-numerical models
MULTI-WAVELENGTH AIRBORNE LASER SCANNING FOR ARCHAEOLOGICAL PROSPECTION
Airborne laser scanning (ALS) is a widely used technique for the sampling of the earth's surface. Next to the widely used geometric
information current systems provide additional information about the signal strength of each echo. In order to utilize this
information, radiometric calibration is essential. As a result physical observables that characterise the backscatter characteristic of the
sensed surface are available. Due to the active illumination of the surfaces these values are independent of shadows caused by
sunlight and due to the simultaneously recorded 3D information a single-channel true orthophoto can be directly estimated from the
ALS data. By the combination of ALS data utilizing different laser wavelengths a multi-wavelength orthophoto of the scene can be
generated. This contribution presents, next to the practical calibration workflow, the radiometric calibration results of the
archaeological study site Carnuntum (Austria). The area has been surveyed at three different ALS wavelengths within a very short
period of time. After the radiometric calibration of each single ALS wavelength (532 nm, 1064 nm and 1550 nm) a multi-channel ALS
orthophoto is derived. Subsequently, the radiometric calibration results of the single- and multi-wavelength ALS data are studied in
respect to present archaeological features. Finally, these results are compared to the radiometric calibration results of an older ALS
data acquisition campaign and to results of a systematic air photo interpretation