Evolution of the microstructure and reflectance of the surface scattering layer on melting, level Arctic sea ice

The microstructure of the uppermost portions of a melting Arctic sea ice cover has a disproportionately large influence on how incident sunlight is reflected and absorbed in the ice/ocean system. The surface scattering layer (SSL) effectively backscatters solar radiation and keeps the surface albedo of melting ice relatively high compared to ice with the SSL manually removed. Measurements of albedo provide information on how incoming shortwave radiation is partitioned by the SSL and have been pivotal to improving climate model parameterizations. However, the relationship between the physical and optical properties of the SSL is still poorly constrained. Until now, radiative transfer models have been the only way to infer the microstructure of the SSL. During the MOSAiC expedition of 2019–2020, we took samples and, for the first time, directly measured the microstructure of the SSL on bare sea ice using X-ray micro-computed tomography. We show that the SSL has a highly anisotropic, coarse, and porous structure, with a small optical diameter and density at the surface, increasing with depth. As the melting surface ablates, the SSL regenerates, maintaining some aspects of its microstructure throughout the melt season. We used the microstructure measurements with a radiative transfer model to improve our understanding of the relationship between physical properties and optical properties at 850 nm wavelength. When the microstructure is used as model input, we see a 10–15% overestimation of the reflectance at 850 nm.This comparison suggests that either a) spatial variability at the meter scale is important for the two in situ optical measurements and therefore a larger sample size is needed to represent the microstructure or b) future work should investigate either i) using a ray-tracing approach instead of explicitly solving the radiative transfer equation or ii) using a more appropriate radiative transfer model

Sea Ice Melt Pond Fraction Derived From Sentinel‐2 Data: Along the MOSAiC Drift and Arctic‐Wide

Melt ponds forming on Arctic sea ice in summer significantly reduce the surface albedo and impact the heat and mass balance of the sea ice. Therefore, their areal coverage, which can undergo rapid change, is crucial to monitor. We present a revised method to extract melt pond fraction (MPF) from Sentinel-2 satellite imagery, which is evaluated by MPF products from higher-resolution satellite and helicopter-borne imagery. The analysis of melt pond evolution during the MOSAiC campaign in summer 2020, shows a split of the Central Observatory (CO) into a level ice and a highly deformed ice part, the latter of which exhibits exceptional early melt pond formation compared to the vicinity. Average CO MPFs are 17% before and 23% after the major drainage. Arctic-wide analysis of MPF for years 2017–2021 shows a consistent seasonal cycle in all regions and years

Simultaneous measurements of sound, vibration, and flow, as well as determination of acoustic transfer functions in the context of air water heat pumps

Luft-Wasser-Wärmepumpen haben zahlreiche ökologische und ökonomische Vorteile, jedoch sind die damit verbundenen Lärmemissionen problematisch. Ziel dieser Arbeit war der Aufbau eines Messsystems zur simultanen Erfassung von Schall, Vibration und Luftströmung, um damit die Entwicklung leiserer Wärmepumpen zu unterstützen. Das System wurde an einer kommerziell erhältlichen Wärmepumpe praktisch angewandt, und mehrere Arten der Datenauswertung und -visualisierung wurden beschrieben. Übertragungsfunktionen von akustischen Absorbermaterialien und luftseitigen Wärmetauschern wurden gemessen, und die Effekte der Luftströmung auf diese Übertragungsfunktionen wurden untersucht. Diese Arbeit wurde im Kontext des SilentAirHP Projekts am Austrian Institute of Technology (AIT) ausgeführt.Air-to-water heat pumps provide numerous ecological and economical gains, but the associated noise emissions proved to be problematic. The aim of this thesis was to create a measurement system for simultaneous detection of sound, vibration and air flow, to aid the development of quieter heat pumps. The system was used on a commercially available heat pump and several ways of data evaluation and visualization have been described. Transfer functions of acoustic absorber materials and air-side heat exchangers were measured, and the effects of air flow on these transfer functions were investigated. This thesis was carried out at the Austrian Institute of Technology (AIT), in the context of the SilentAirHP project.6

Water colour spectro-radiometry platform raw data (cau_boeoetle_1) from pack ice during legs 4 and 5 of the MOSAiC expedition with POLARSTERN to the Arctic Ocean

This raw dataset contains in-situ hyperspectral and co-located water depth measurments from melt ponds on Legs 4 & 5 of the MOSAiC Expedition, collected by Böötle. The dataset allows to calculate remote sensing reflectance (R_rs) over melt ponds with associated melt pond water depth measurements.The small Böötle remote controlled water colour spectro-radiometry platform allows for the simultaneous collection of hyperspectral, bathymetric and temperature data in waters as shallow as 15cm. It is equipped with three OceanOptics STS-VIS spectro-radiometers (downwelling above-water and below-water irradiance, upwelling below-water radiance), a Tritech PA500 point sonar (water depth), and a DS18B20 temperature probe (subsurface water temperature). Propulsion is achieved by two air screws, thereby limiting the impact on the water column and the bottom substrate. The platform is remotely controlled by the operator with a maximum range of 100m. A web interface is provided via a wireless network, which allows for configuration and control of the sensor array. With a GPS receiver and two camera based systems, three independent localization systems are available. Data of each deployment is collected into a zip/tar file, holding a folder of plain text raw data (spectra, depth, GPS position) and image-based raw data (on-board all-sky camera; on-board and on-shore action cams (AC folders)). Digital copies of field notes (if any) are also included

Hyperspectral raw data (cau_stickle_1) from sea ice melt ponds during legs 4 and 5 of the MOSAiC expedition with R/V POLARSTERN

This raw dataset contains in-situ hyperspectral from Legs 4 & 5 of the MOSAiC Expedition, collected by Stickle. The dataset allows to calculate remote sensing reflectance (R_rs) as well as spectral albedo. For measurements over melt ponds, co-located water depth information was collected with a measuring ruler. The Stickle hyperspectral measurement platform is a hand-held gimbal-stabilized platform for three OceanOptics STS-VIS spectro-radiometers (downwelling upwelling irradiance, upwelling radiance). Position is logged with an included GPS receiver. Data of each deployment is collected into a zip/tar file, holding a folder of plain text raw data (spectra, depth, GPS position) and image-based raw data (co-deployed action cams (AC folders)). Digital copies of field notes (if any) are also included

Hyperspectral camera raw data (SPECIM_IQ_01) at the remote sensing site on the ice floe during MOSAiC expedition 2019/2020

The Hyperspectral camera Specim IQ measures relative reflectances for 512x512 pixels in 204 bands in a wavelength range from 400 nm to 1000 nm. Within the field of view, there was a white reference placed so that the reflectances can be compared to other datasets. During the MOSAiC expedition, the camera was installed at the remote sensing site on the ice. It was looking at the snow and ice, taking an image every 30 minutes for periods in April 2020 and July 2020. Each data record is a folder (compressed as one file) readable by the Specim IQ software, which is downloadable free of charge from the manufacturer (Specim) after registration. This dataset is from an experimental setup to explore the use of spatially resolved hyperspectral imaging of Arctic sea ice

Investigation of noise transmission of a machine tool enclosure

Machine tools are highly integrated mechatronic systems consisting of dedicated mechanic design and integrated electrical equipment – in particular drive systems and the CNC-control – to realize the complex relative motion of tool towards work piece. Beside the process related capabilities, like static and dynamic stiffness as well as accuracy behavior and deviation resistance against thermal influence, safety aspects are of major interest. The machine tool enclosure must fulfill multiple requirements like retention capabilities against the moving parts of broken tools, lose work pieces or clamping components. In regular use, the noise emission have to be inhibited at the greatest possible extent by the machine tool enclosure. Nevertheless, the loading door and the moving parts of the workspace envelope are interfaces where noise transmission is harder to be avoided and therefore local noise emissions increase. The aim of the objective investigation is to analyse the noise emission of machine tools to determine the local noise transmission of a machine tool enclosure by using arrays of microphones. By the use of this measuring method, outer surfaces at the front, the side and on the top of the enclosure have been scanned. The local transient acoustic pressures have been recorded using a standard noise source placed on the machine table. In addition, an exemplary manufacturing process has been performed to analyse the frequency dependent location resolved sound emissions