Near-bottom seismic profiling: High lateral variability, anomalous amplitudes, and estimates of attenuation

For almost a decade the Marine Physical Laboratory of Scripps Institution of Oceanography has been conducting near‐bottom geophysical surveys involving quantitative seismic profiling. Operating initially at 4 kHz and more recently at 6 kHz, this system has provided a wealth of fine scale quantitative data on the acoustic properties of ocean sediments. Over lateral distances of a few meters, 7‐dB changes in overall reflected energy as well as 10‐dB changes from individual reflectors have been observed. Anomalously high amplitudes from deep reflectors have been commonly observed, suggesting that multilayer interference is prevalent in records from such pulsed cw profilers. This conclusion is supported by results from sediment core physical property work and related convolution modeling, as well as by the significant differences observed between 4‐ and 6‐kHz profiles. In general, however, lateral consistency has been adequate in most areas surveyed to permit good estimates of acoustic attenuation from returns from dipping reflectors and sediment wedges

A look at profiler performance

Since about 1974, Doppler radars operating in UHF and VHF ranges have been used increasingly to study atmospheric winds. Historically, large systems capable of obtaining data from high altitudes have focused attention on the mesosphere and stratosphere, rather than on the troposphere wherein abides most of the weather considered by most meteorologists. Research address some questions the meteorologist must logically ask first, viz., what is the actual performance capability of these systems, how accurate is the wind data of interest to meteorologists, and from what altitudes in the troposphere are the data reliably obtained

Interpretation of combined wind profiler and aircraft-measured tropospheric winds and clear air turbulence

In the first experiment, it was found that wind profilers are far better suited for the detailed examination of jet stream structure than are weather balloons. The combination of good vertical resolution with not previously obtained temporal resolution reveals structural details not seen before. Development of probability-derived shear values appears possible. A good correlation between pilot reports of turbulence and wind shear was found. In the second experiment, hourly measurements of wind speed and direction obtained using two wind profiling Doppler radars during two prolonged jet stream occurrences over western Pennsylvania were analyzed. In particular, the time-variant characteristics of derived shear profiles were examined. Profiler data dropouts were studied in an attempt to determine possible reasons for the apparently reduced performance of profiling radar operating beneath a jet stream. Richardson number and wind shear statistics were examined along with pilot reports of turbulence in the vicinity of the profiler

Combined VHF Dopplar radar and airborne (CV-990) measurements of atmospheric winds on the mesoscale

Hourly measurements of wind speed and direction obtained using two wind profiling Doppler radars during two prolonged jet stream occurrences over western Pennsylvania were analyzed. In particular, the time-variant characteristics of derived shear profiles were examined. To prevent a potential loss of structural detail and retain statistical significance, data from both radars were stratified into categories based on the location data from the Penn State radar were also compared to data from Pittsburgh radiosondes. Profiler data dropouts were studied in an attempt to determine possible reasons for the apparently reduced performance of profiling radars operating beneath a jet stream. Temperature profiles for the radar site were obtained using an interpolated temperature and dewpoint temperature sounding procedure developed at Penn State. The combination of measured wind and interpolated temperature profiles allowed Richardson number profiles to be generated for the profiler sounding volume. Both Richardson number and wind shear statistics were then examined along with pilot reports of turbulence in the vicinity of the profiler

Scientific cruise report Elisabeth Mann-Borgese SUMMIX-MESO

Objectives: It was intended to investigate the meso-scale and sub-meso-scale dynamics of the upper layers (upper 80 m) in the central Baltic Sea, using towed instruments and acoustic profilers, to better understand the physical conditions for cyanobacteria blooms. Under optimal weather conditions, we intended to carry out 10 one-day quasi-synoptic surveys by cruising in large meandering patterns (see fig. 1) covering areas of 15 X 15 nautical miles or 8 X 8 nautical miles, depending on the survey mode, see below. This cruise was the meso-scale component of the two-ship SUMMIX experiment together with RV Meteor (Physical and biochemical exchange-, mixing- and transformation processes in the central Baltic Sea during summer stratification and their controls on the cyanobacterial summer bloom) which was intended to be located at a fixed position nearby RV Elisabeth Mann Borgese in order to survey the water column in high vertical, spatial and parameter resolution, including biogeochemical experiments on board. In addition to the physical parameters, also vertical and horizontal zooplankton net tows as well as water samples taken by CTD bottles were planned

GiViP: A Visual Profiler for Distributed Graph Processing Systems

Analyzing large-scale graphs provides valuable insights in different application scenarios. While many graph processing systems working on top of distributed infrastructures have been proposed to deal with big graphs, the tasks of profiling and debugging their massive computations remain time consuming and error-prone. This paper presents GiViP, a visual profiler for distributed graph processing systems based on a Pregel-like computation model. GiViP captures the huge amount of messages exchanged throughout a computation and provides an interactive user interface for the visual analysis of the collected data. We show how to take advantage of GiViP to detect anomalies related to the computation and to the infrastructure, such as slow computing units and anomalous message patterns.Comment: Appears in the Proceedings of the 25th International Symposium on Graph Drawing and Network Visualization (GD 2017

Applications of MST radars: Meteorological applications

Applications of mesosphere stratosphere troposphere radar to mesoscale meteorology are discussed. The applications include using the radar either as a research tool to improve our understanding of certain dynamical systems or as part of a network used to provide input data for weather forecasting. The workhorse of the operational observing network is the radiosonde balloon which provides measurements of pressure, temperature, humidity, and winds up to heights of 16 to 20 km. Horizontal and vertical measurement capabilities, reflectivity data, derivable quantities and parameters, and special operational requirements are surveyed

Seasonal and spatial structure of the gravity waves and vertical winds over the central USA derived from the NOAA Profiler Network data

Data from the National Oceanic and Atmospheric Administration wind profiling radar network for the period 2002 2005 were used to investigate the effects of precipitation, topography and gravity waves on the measurements of winds by wind profilers, and to study the climatology and sources of atmospheric gravity waves. The comparison of the profiler winds to the NCAR/NCEP reanalysis and MM5 model winds revealed that monthly averaged wind profiler vertical velocities are strongly affected by precipitation in the lowest 3 km of the troposphere, both directly by hydrometeor velocity and indirectly via gravity wave activity produced by convection. We have determined that presence of downward wind velocities with magnitudes larger than 0.25 m/s is the sign of precipitation-affected data. This velocity threshold was used for identifying and correcting the contaminated data. The characteristics of the gravity waves in three period bands (6 min - 1 hour, 1 - 3 hours and 3 - 12 hours) and three orthogonal spatial components were obtained using spectral analysis of the profiler winds. The most kinetic energy was found to be associated with the low-frequency horizontal component of gravity waves. A consistent seasonal pattern and geographical distribution of kinetic gravity wave energy were observed in the troposphere, with maxima reaching ~25 J/kg in winter at 8 - 10 km altitude. A technique for quantifying the topography variance near the measurement sites was developed and applied to evaluate the effects of topography on gravity wave generation. We have determined that topography is an important source of the medium- and high-frequency waves in the middle troposphere. Correlation and regression analyses were used to study sources of the gravity waves. Convection was found to explain a significant part of the vertical component of the kinetic gravity wave energy throughout the troposphere and total kinetic energy in the lower troposphere, while vertical shear of the zonal wind was the predominant source in the upper troposphere. The results of this study are important for interpreting the wind measurements by wind profiling radars and for improving gravity wave parameterizations in global circulation models.Ph.D.Committee Chair: Dr. Robert G. Roper; Committee Member: Dr. Derek Cunnold; Committee Member: Dr. Irina Sokolik; Committee Member: Dr. Paul Steffes; Committee Member: Dr. Robert Blac

Lessons learned from developing turbulence profilers for telescopes' instruments Lessons learned from developing turbulence profilers for telescopes' instruments

International audienceThis article presents the results obtained during three years of developing turbulence profilers for two different telescopes; namely Gemini South and the future Adaptive Optics Facility (AOF). The profilers are embedded in a facility instrument that provides the data from the Shack-Hartmann wavefront sensors which feed the SLODAR approach used to generate the profiles. The main results focused on two unsolved problems: dealing with the dome seeing and the effect of the atmosphere outer scale on the accuracy of the profilers