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  • 1
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    Taxonomy of Pfiesteria (Dinophyceae) (2006)
    In:  EPIC3Harmful Algae, 5(5), pp. 481-496
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    Spatial Variability of SWE in Alpine Areas - How do variability patterns change with grid designs? (2011)
    In:  EPIC3AGU American Geophysical Union - fall meeting, San Francisco, 2011-12-05-2011-12-09
    Details
    Publication Date: 2019-07-17
    Description: Estimation of the total amount of water stored as snow in a catchment area during the winter season is a major driver for successful modeling and managing of water resources as well as for accurate predictions of mass balances and changes thereof on glaciated areas. As a comprehensive measurement of the entire catchment is usually impossible, the main difficulty is to link scales. Point measurements of snow depth and density must be combined to estimate the distribution of snow water equivalent (SWE) in a slope, and various slopes are combined to estimate in the average amount of SWE in a catchment. However, especially in mountainous areas, wind redistribution in combination with variable precipitation and complex surface topography, reduce the representativeness of single point data of SWE to sometimes less than a few meters. Therefore, the estimated variability pattern will highly depend on the applied measurement grid and its spatial resolution. For the present study, we employed radar technology to increase the resolution of measurement points to tens of centimeters and less. These radar measurements were performed at three different locations: (i) a relatively low slope, high Alpine glacier in Tirol, Austria, (ii) a non glaciated, high Alpine site in SW Colorado, USA and (iii) a highly wind influenced middle elevation site in Idaho, USA. A regular grid of circles subdivides the respective measurement area in several parts. The variability patterns of the two-way travel time (TWT) of the radar signal are analyzed for each circle separately utilizing geostatistical methods. These patterns are compared with the results using different spatial resolutions and to the results of the respective probings in the circles. At site (i) the observed snow depths were very homogeneous on a scale of hundreds of meters, and the variability patterns of the radar data stay fairly constant and correspond well with the probings. Site (ii) and (iii), however, are characterized by high variabilities in snow depth on a relatively small spatial scale. Therefore, the variability pattern changed significantly with varying spatial resolutions and the probings don't correspond to the radar measurements.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 3
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    Seasonal and diurnal cycles of liquid water in snow-Measurements and modeling (2015)
    In:  EPIC3Journal of Geophysical Research: Earth Surface, 120(10), pp. 2139-2154, ISSN: 21699003
    Details
    Publication Date: 2016-12-20
    Description: Evaluating and improving snow models and outflow predictions for hydrological applications is hindered by the lack of continuous data on bulk volumetric liquid water content (θw) and storage capacity of the melting snowpack. The combination of upward looking ground-penetrating radar and conventional snow height sensors enable continuous, nondestructive determinations of θw in natural snow covers from first surficial wetting until shortly before melt out. We analyze diurnal and seasonal cycles of θw for 4 years in a flat study site and for three melt seasons on slopes and evaluate model simulations for two different water transport schemes in the snow cover model SNOWPACK. Observed maximum increases in θw during a day are below 1.7 vol % (90th percentile) at the flat site. Concerning seasonal characteristics of θw, less than 10% of recorded data exceed 5 vol % at the flat site and 3.5 vol % at slopes. Both water transport schemes in SNOWPACK underestimate maximum θw at the flat site systematically for all observed melt seasons, while simulated θw maxima on slopes are accurate. Implementing observed changes in θw per day in outflow predictions increases model performance toward higher agreement with lysimeter measurements. Hence, continuously monitoring θw improves our understanding of liquid water percolation and retention in snow, which is highly relevant for several aspects of the cryosphere such as avalanche formation, catchment hydrology, and ice sheet mass balances.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    upGPR technology for continuous snowpack monitoring to calibrate and validate remote sensing data (2014)
    In:  EPIC3ESA Workshop on Novel Mission Concepts for Snow and Cryosphere Research, Noordwijk, The Netherlands., 2014-09-16-2014-09-17
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    Publication Date: 2014-09-22
    Description: One missing link in ground truth observations for remote sensing data of snow is continuous snowpack monitoring over the course of a season. While conventional snow pits represent only snapshots in time, which not necessarily coincident with satellite overpasses, continuous observations at short time intervals allow for direct relation of current snowpack conditions with recorded remote sensing data. Furthermore, such monitoring enables tracking of changes in adjacently recorded satellite signals to settling or disappearance/ appearance of specific snow layers or liquid water occurrences. The combination of upward-looking ground-penetrating radar (upGPR) and automatic weather station (AWS) allows for continuous monitoring of changes in snowpack stratigraphy, snow water equivalent (SWE) and bulk volumetric liquid water content (Theta_w) within the snowpack. Results thereof are not biased through spatial variability of pit locations, since upGPR is a non-destructive monitoring technique. Other non-destructive instruments recording snow parameters are usually measuring from above the snow surface. Above snow installations, however, are not capable in monitoring layer specific settling and depth of liquid water infiltrations into the snowpack. Even surface wetting cannot be clearly identified by above snow instrumentation. In addition, to monitor changes in Theta_w in snow, only non-destructive methods will produce reliable data. Here, we present upGPR data recorded over three consecutive winter season at the test site Weissfluhjoch, Davos Switzerland together with data from a slope sites above Davos, and a test site above Boise, Idaho, USA. We can show that upGPR continuously monitors major changes in snowpack stratigraphy, liquid water appearance/ disappearance and SWE within the snowpack. SWE determinations by radar were always within or close to a 5% range in comparison to manual measurements. While comparing estimated diurnal liquid water outflow with lysimeter records at the test site WFJ, the knowledge of the variations in residual water content from one day to another from the radar reduces deviations between measured and modeled outflow remarkably. The installation of upGPR systems in sheltered, spatially homogenous high Alpine areas will allow for continuous calibration and/or validation of snow retrieval algorithms for remote sensing (satellite and airborne) data. Data thereof can be used to assimilate model outputs and may help to improve and consolidate remote sensing retrieval algorithms for various kinds of snowpack conditions.
    Repository Name: EPIC Alfred Wegener Institut
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  • 5
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    South China Sea internal tide/internal waves-impact on the temporal variability of horizontal array gain at 276 Hz (2006)
    IEEE
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © IEEE, 2004. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 29 (2004): 1292-1307, doi:10.1109/JOE.2004.836794.
    Description: The temporal variability of the spatial coherence of an acoustic signal received on a bottomed horizontal array has been calculated for 276-Hz narrow-band signals. A conventional plane wave beamformer was applied to the received signals. The temporal variability of the array's omnipower, beam power, and array gain are related to variability in the sound-speed field. The spectral characteristics of array omnipower are nonstationary and changed as the spectral characteristics of the temperature field varied. The array omnipower and beam-power variability tracked each other in time and varied by as much as 15 dB over time intervals as short as 7 min. Array gain varied up to 5 dB and usually tracked the omnipower variability. A contiguous 24-h section of data is discussed in detail. This data section is from a time period during which the high-frequency fluid dynamic perturbation of the sound-speed field was of smaller amplitude than other sections of the 16-d data set. Consequently, this section of data sets an upper bound for the realizable array gain. The temporal variability of array gain and spatial coherence at times appears to be correlated with environmental perturbation of the sound-speed field, but are also correlated with changes in the signal-to-noise ratio. The data was acquired during the Office of Naval Research's South China Sea Asian Seas International Acoustics Experiment. The 465-m 32-channel horizontal array was placed on the bottom in 120 m of water at the South China Sea shelf break. The acoustic source was moored in 114 m of water /spl sim/19 km from the receiving array.
    Description: This work was supported by the Office of Naval Research.
    Keywords: Array signal gain ; Coherence ; Internal waves ; Narrow-band conventional beamforming ; Shallow-water arrays
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: 1254863 bytes
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  • 6
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    Non-destructive quantification of snowpack properties (2009)
    In:  EPIC3Proceedings ISSW International Snow Science Workshop 2009, Davos, Switzerland
    Details
    Publication Date: 2019-07-17
    Description: A temporal observation of the stratigraphy of seasonal snowpacks is only possible with noninvasive methods. Electromagnetic waves, specifically radar waves, proved to be the most appropriate technique to estimate internal snow parameters and media transitions non-destructively. Thereby, it is possible to estimate quantitatively snowpack stratigraphy and observe the snowpack evolution with time. Radar systems work as an active wave transmitter, which records reflection intensities with travel-time. Either the system modulates the signal on a defined frequency range, such as frequency modulated continuous wave systems (FMCW) or a short impulse is radiated at a center frequency and bandwidth. The stratigraphic resolution and the penetration depth of both systems depends on the system parameters. The frequency determines the penetration depth and sensitivity and the bandwidth determines the vertical resolution. In previous studies FMCW X- and Ku-band frequencies failed to penetrate a moist snowpack, butprovided convincing results in resolving the snowpack stratigraphy. Pulsed 900 MHz antennas, as well as L- and C-band FMCW systems penetrated a wet snowpack up to one meter and measured adequate gradients in snow density. Current research in pulsed and modulated systems show that electromagnetic wave systems are convincing methods to quantitatively measure snow stratigraphy non-destructively.
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
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    Non-Destructive Characterization of Snowpack Properties (2009)
    In:  EPIC3ISSW International Snow Science Workshop, 27.09. - 02.10.2009, Davos, Switzerland.
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    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 8
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    Remote acoustic sensing of oceanic fluid and biological processes (2018)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: High frequency acoustic backscattering systems are being used in monostatic modes to evaluate the use of acoustic techniques to detect and study a variety of fluid processes in the oceanic environment. A short outline of those research programs actively evaluating and using acoustic techniques is presented, followed by a detailed review of this investigator's program. This program uses a multifrequency high frequency acoustic system to study a variety of processes including turbulent mixing, air-sea interactions, internal waves, interleaving water masses, natural particulate dispersion and distribution, the dispersion of particulates associated with deep ocean disposal of industrial chemical waste, and biological response to a variety of stimulae including fluid motion, predators, and oceanographic instrumentation. Graphic acoustic data records of several of the above phenomena are described.
    Description: Prepared for the Office of Naval Research under Contract N00014-77-C-0196; NR 083-004, for the National Oceanic & Atmospheric Administration under Grants NA79AA-D-00030 (Ocean Dumping Program) and NA79AA-D-00102 (Office of Sea Grant) and for the National Science Foundation under Grant OCE 77-08682.
    Keywords: Underwater acoustics ; Oceanography ; Marine biology
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
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  • 9
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    A towed, multi-frequency H.F. sonar system for scattering and ocean dynamics studies (2018)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: The system described provides wide operational flexibility at any operating frequency from 5 kHz to over 800 kHz (except for a small band around 455 kHz) limited mainly by the availability of transducers. Variable pulse width, variable receiver bandwidth, low receiver noise, various time variable gain functions and wide system dynamic range characterized the system. Built-in time-sharing controls maximize flexibility of graphics display on either dry-paper or fibre-optic CRT recorders.
    Description: Prepared for the NORDA under Contract N00014-77-C-0196; and for the National Oceanic and Atmospheric Administration under Grant 04-8-MO1-43.
    Keywords: Underwater acoustics ; Sonar ; Oceanographic instruments ; Scientific apparatus and instruments
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
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  • 10
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    Remote acoustic sensing of the particulate phase of industrial chemical wastes and sewage sludge : report on the seasonal variability of the dispersion of the particulate phase as observed from three cruises, July 1977, January-February 1978, and April 1978 (2018)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: The seasonal variability of the dispersion of the particulate phase of industrial chemical waste has been studied with acoustic backscattering techniques at Deep Water Dumpsite 106 (DWD 106). The vertical dispersion of the particulates has been found to be strongly dependent on the depth of the mixed layer and the magnitude of the density gradient associated with the seasonal thermocline. The horizontal dispersion of the particulates as a function of depth has been found to be strongly dependent on the shear present in the water column. Entire waste plumes have been found to be advected out of the dumpsite in less than 24 hours when the area is occupied by a warm core ring. Simple calculations based upon Stoke's law are presented to reveal the impact of variable oceanic density structure on the sink rate of particles and to indicate the need for incorporating these considerations into numerical models. A short discussion is presented on (1) the need to make field measurements on the magnitude of both turbulence and shear in the water column and (2) the need to incorporate shear and turbulence-dependent calculations for the sink rates of particles into those numerical models which may be used to predict the particulate and effluent dispersion rates at DWD 106.
    Description: Prepared for the National Oceanic and Atmospheric Administration under Grants 04-7-158-44054, NA79AA-D-00030 and Ocean Dumping Grant 04-8-MOl-43.
    Keywords: Waste disposal in the ocean ; Factory and trade waste ; Sewage disposal
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
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