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  • 1
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    In:  EPIC3Aquatic Ecology, 40(4), pp. 481-492, ISSN: 1386-2588
    Publication Date: 2017-03-06
    Description: In a laboratory flume, a comparative study on the near-bottom performance of the Acoustic Doppler Velocimeter (ADV) was conducted. Two different ADV systems were tested for different configurations and two flow velocities (9 cm s−1, 18 cm s−1). The results were compared with synchronous measurements with a Laser Doppler Anemometer (LDA). Near-bottom velocity measurements with the ADV have to be interpreted carefully as the ADV technique underestimates flow velocities in a zone close to the sediment. The height of this zone above the sediment varies with different ADV systems and configurations. The values for nominal sampling volume height (SVH) given by the software often underestimate the true, effective sampling volume heights. Smaller nominal SVH improve the ADV near-bottom performance, but the vertical extent of the zone in which the ADV underestimates flow by more than 20% may be larger than true SVH/2 by a factor of 2 (=true SVH). When the measurement volume approaches the bottom, ADV data quality parameters (signal-to-noise-ratio (SNR) and signal amplitude) exceeding the average ‘open water’ level, are clear indicators that the ADV has begun to underestimate the flow velocity. Unfortunately, this is not a safe indicator for the range of reliable measurements as the ADV may begin to underestimate velocities even with unchanged ‘open water’ data quality parameters. Thus, one can only recommend avoiding measurements below a distance from the bottom that was defined empirically comparing the ADV and the LDA velocity profiles. This distance is 2.5 times nominal sampling volume height for the tested ADV systems and experimental settings.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    In:  EPIC315th International Circumpolar Remote Sensing Symposium (ICRSS), Potsdam, Germany, 2018-09-10-2018-09-14
    Publication Date: 2022-09-29
    Description: For a responsible development of the Arctic, new remote sensing technologies and services are of great importance. Many of such innovations are based on scientific research. However, it is not trivial that they find their way into application. In order to ease this kind of transfer across the interface between academia and industry, the Alfred Wegener Institute has established a technology transfer office (TTO). The TTO takes up inventions and business ideas emerging from scientific research and supports innovators and entrepreneurs to progress them into the respective markets. The other way round, the TTO serves as the contact point for stakeholders from industry, governmental and non-governmental bodies to forward specific problems into the scientific community. Here we present two examples to illustrate the AWI technology transfer approach: 1) Planned for 2022, the German hyperspectral earth observation satellite EnMAP (Environmental Mapping and Analysis Programme) will measure the reflected radiance from the earth’s surface over a wide hyperspectral wavelength range (from visible to short wave infrared). In order to provide correct hyperspectral satellite products such as land cover (natural surfaces, urban), surface waters, surface mineralogy, hydrology (snow, moisture) etc. in a correct manner, it is necessary to normalize for the incidence and the reflection of light depending on the zenith and azimuth viewing geometries. This is performed by providing the bidirectional reflectance distribution function BRDF for different materials. Determination of BRDFs for terrestrial surfaces is very challenging especially for high latitudes due to the low solar altitude. For Arctic vegetation mapping, a specific satellite field goniometer was developed at AWI to perform such ground truthing (Buchhorn et al., 2013). The goniometer allows for mobile ground-based measurements in order to determine the BRDF for different vegetation types. It consists of an azimuth angle adjustment module mounted on a tripod with a zenith arc with sensor sled equipped with two portable spectro-radiometers, a GPS receiver, an NC-Eye camera system and a white reference panel. The goniometer was prototyped, patented and licensed to a precision mechanics manufacturer. The commercial system in this case addresses the scientific community and specialized service providers. 2) Starting with geophysical ice thickness measurements on sea-ice and using air-borne electromagnetic measuring systems (Krumpen et al. 2011) a group of AWI scientists developed specific sea-ice related services for scientific, governmental and private sector customers operating in Arctic sea-ice. Subsequently the AWI spin-off Drift & Noise Polar Services was established in 2014. The new business was developed towards near real-time remote sensing ice information products and sea-ice consultancy for safer and faster navigation through ice-covered waters. Ice charts and weather information are generated from SAR and optical imagery (e.g. Sentinel 1 and 2). Since reliable broadband data transfer channels do not exist, particularly for high latitudes, the start-up also develops appropriate data compaction and transfer protocols combined with hand-held mobile systems for nautical officers which allow for near real-time access to latest ice data onboard ship. Thus shipping companies are able to save time and fuel by adapting their route while increasing safety. Fig. 1: Portable field spectro-goniometer for EnMAP ground truthing (a). Hand-held sea-ice information system “Ice Pad” using merged optical and SAR imagery (b). References 1. M. Buchhorn, R. Petereit & B. Heim (2013) A Manual Transportable Instrument Platform for Ground-Based Spectro-Directional Observations (ManTIS) and the Resultant Hyperspectral Field Goniometer System. Sensors, 13 (12), 16105-16128, doi:10.3390/s131216105. 2. T. Krumpen, L. Rabenstein, & J. Hoelemann (2011) Quantifying Sea Ice Formation Rates in the Laptev Sea by Means of ENVISAT SAR Scenes and Airborne Ice Thickness Measurements. International Union of Geodesy and Geophysics (IUGG) General Assembly, Melbourne, Australia, 29 June 2011 - 7 July 2011, hdl:10013/epic.38551.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Format: application/pdf
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