scholarly journals Near-Surface Current Mapping by Shipboard Marine X-Band Radar: A Validation

2018 ◽  
Vol 35 (5) ◽  
pp. 1077-1090 ◽  
Author(s):  
Björn Lund ◽  
Brian K. Haus ◽  
Jochen Horstmann ◽  
Hans C. Graber ◽  
Ruben Carrasco ◽  
...  
Keyword(s):  
Mississippi River ◽  
Oil Spills ◽  
Surface Current ◽  
Current Profile ◽  
Near Surface ◽  
Sea Surface Roughness ◽  
X Band ◽  
Effective Depth ◽  
The Mean ◽  
Potential Impact

AbstractThe Lagrangian Submesoscale Experiment (LASER) involved the deployment of ~1000 biodegradable GPS-tracked Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE) drifters to measure submesoscale upper-ocean currents and their potential impact on oil spills. The experiment was conducted from January to February 2016 in the Gulf of Mexico (GoM) near the mouth of the Mississippi River, an area characterized by strong submesoscale currents. A Helmholtz-Zentrum Geesthacht (HZG) marine X-band radar (MR) on board the R/V F. G. Walton Smith was used to locate fronts and eddies by their sea surface roughness signatures. The MR data were further processed to yield near-surface current maps at ~500-m resolution up to a maximum range of ~3 km. This study employs the drifter measurements to perform the first comprehensive validation of MR near-surface current maps. For a total of 4130 MR–drifter pairs, the root-mean-square error for the current speed is 4 cm and that for the current direction is 12°. The MR samples currents at a greater effective depth than the CARTHE drifters (1–5 m vs ~0.4 m). The mean MR–drifter differences are consistent with a wave- and wind-driven vertical current profile that weakens with increasing depth and rotates clockwise from the wind direction (by 0.7% of the wind speed and 15°). The technique presented here has great potential in observational oceanography, as it allows research vessels to map the horizontal flow structure, complementing the vertical profiles measured by ADCP.

A THREE-YEAR BASELINE SAMPLING AND ANALYSIS STUDY OF PETROLEUM POLLUTANTS IN COASTAL LOUISIANA

2005 ◽  
Vol 2005 (1) ◽  
pp. 201-206 ◽  
Author(s):  
David Gisclair ◽  
Javed Iqbal
Keyword(s):  
Oil Spill ◽  
Aromatic Hydrocarbons ◽  
Mississippi River ◽  
Oil Spills ◽  
Biological Effects ◽  
Dry Weight ◽  
Average Concentration ◽  
Polynuclear Aromatic Hydrocarbons ◽  
The Mean ◽  
Coastal Louisiana

ABSTRACT The Louisiana Oil Spill Coordinator's Office (LOSCO) conducted a three-year study of baseline levels of oil spill constituents in South Louisiana as mandated by Act 740 of the Louisiana Legislature. The act mandated an environmental inventory concentrating on areas with a high probability of oil spills. The main goal of the project was to streamline restoration efforts in Coastal Louisiana, the Mississippi River, major tributaries and reduce associated risks to habitat. The study consisted of 3,540 composite sediment samples collected at 1,180 sites each year from 1997 through 1999. Results indicate that the mean level of total unresolved petroleum hydrocarbons (TUPH) in coastal Louisiana and major rivers during 1997 to 1999 was 44,608ng/g based on dry weight sediment. The mean total saturated hydrocarbons n-alkanes level (nC9-nC35) was 5,444ng/g. and mean total polynuclear aromatic hydrocarbons (PAH) level was 587ng/g. Results indicate chronic/degraded and recent input of petroleum contamination in coastal areas and the Mississippi river. These results indicated that petroleum constituents in Louisiana sediments are bio-available reservoirs of polynuclear aromatic hydrocarbons posing some risk to the ecosystem. Approximately 5% of the sites investigated have TPAH levels more than 1,000ng/g in three consecutive years while 51% of the samples have TPAH levels less than 100ng/g indicating low pollution. More than 98% of the samples were below NOAA sediments quality guidelines ERL (Effects Range – Low) values for PAHs. About 159 hot spots in 17 parishes (counties) were identified where all TUPH, TPAH and T-Sat exceeded the average concentration in at least one sampling year. The data suggests that current concentrations of contaminants in Louisiana are basically not in the toxic range to produce biological effects. However efforts would be necessary to monitor, control, and alleviate contaminants of concern especially in hotspot areas.

Analysis of Debris Signature Characteristics and Evolution in the 24 May 2016 Dodge City, Kansas, Tornadoes

2020 ◽  
Vol 148 (12) ◽  
pp. 5063-5086
Author(s):  
Zachary B. Wienhoff ◽  
Howard B. Bluestein ◽  
Dylan W. Reif ◽  
Roger M. Wakimoto ◽  
Louis J. Wicker ◽  
...  
Keyword(s):  
Doppler Radar ◽  
Surface Sampling ◽  
Mean Flow ◽  
Near Surface ◽  
Significant Growth ◽  
X Band ◽  
The Mean ◽  
Anomalous Nature ◽  
Direct Correspondence ◽  
Rapid Scanning

AbstractOn 24 May 2016, a supercell that produced 13 tornadoes near Dodge City, Kansas, was documented by a rapid-scanning, X-band, polarimetric, Doppler radar (RaXPol). The anomalous nature of this storm, particularly the significant deviations in storm motion from the mean flow and number of tornadoes produced, is examined and discussed. RaXPol observed nine tornadoes with peak radar-derived intensities (ΔVmax) and durations ranging from weak (~60 m s−1) and short lived (<30 s) to intense (>150 m s−1) and long lived (>25 min). This case builds on previous studies of tornado debris signature (TDS) evolution with continuous near-surface sampling of multiple strong tornadoes. The TDS sizes increased as the tornadoes intensified but lacked direct correspondence to tornado intensity otherwise. The most significant growth of the TDS in both cases was linked to two substantial rear-flank-downdraft surges and subsequent debris ejections, resulting in growth of the TDSs to more than 3 times their original sizes. The TDS was also observed to continue its growth as the tornadoes decayed and lofted debris fell back to the surface. The TDS size and polarimetric composition were also found to correspond closely to the underlying surface cover, which resulted in reductions in ZDR in wheat fields and growth of the TDS in terraced dirt fields as a result of ground scouring. TDS growth with respect to tornado vortex tilt is also discussed.

On Shipboard Marine X-Band Radar Near-Surface Current ‘‘Calibration’’

2015 ◽  
Vol 32 (10) ◽  
pp. 1928-1944 ◽  
Author(s):  
Björn Lund ◽  
Hans C. Graber ◽  
Katrin Hessner ◽  
Neil J. Williams
Keyword(s):  
Surface Current ◽  
Differential Gps ◽  
Near Surface ◽  
The Pacific ◽  
X Band ◽  
Correction Technique ◽  
Order Of Magnitude ◽  
Cross Track ◽  
The Impact ◽  
Ship Speed

AbstractThe ocean wave signatures within conventional noncoherent marine X-band radar (MR) image sequences can be used to derive near-surface current information. On ships, an accurate near-real-time record of the near-surface current could improve navigational safety. It could also advance understanding of air–sea interaction processes. The standard shipboard MR near-surface current estimates were found to have large errors (of the same order of magnitude as the signal) that are associated with ship speed and heading. For acoustic Doppler current profilers (ADCPs), ship heading errors are known to induce a spurious cross-track current that is proportional to the ship speed and the sine of the error angle. Conventional mechanical gyrocompasses are very reliable heading sensors, but they are too inaccurate for shipboard ADCPs. Within the ADCP community, it is common practice to correct the gyrocompass measurements with the help of multiantenna carrier-phase differential GPS systems. This study shows how a similar multiantenna GPS-based ship heading correction technique stands to improve the accuracy of MR near-surface current estimates. Changes to the standard MR near-surface current retrieval method that are necessary for high-quality results from ships are also introduced. MR and ADCP data collected from R/V Roger Revelle during the Impact of Typhoons on the Ocean in the Pacific (ITOP) program in 2010 are used to demonstrate the MR currents’ accuracy and reliability.

The Use of Empirical Orthogonal Functions for Deriving Response Based Extreme Current Profiles

2012 ◽  
Author(s):  
Gus Jeans ◽  
Liam Harrington-Missin ◽  
Andrew Watson ◽  
Jon Upton
Keyword(s):  
Surface Current ◽  
Empirical Orthogonal Functions ◽  
Current Profile ◽  
Orthogonal Functions ◽  
Data Set ◽  
Near Surface ◽  
Orthogonal Function ◽  
Large Current ◽  
Traditional Assumption

Coherent extreme current profiles are derived to reduce the over-conservatism associated with the traditional assumption that extreme currents occur at all depths through the water column simultaneously. Empirical Orthogonal Function (EOF) analysis has proven effective for derivation of coherent extreme current profiles in regions where it effectively captures the dominant characteristics of the flow regime. This is despite the questionable suitability of EOF for Current Profile Characterisation, which reduces a large current profile data set into a much smaller set of profiles for riser fatigue studies. EOF Mode 1 and 2 are used to represent six years of in-situ current profiles accounting for 97.75% of the original variance. With the assumption that depth integrated speed squared is proportional to drag on a simple riser, three sets of extreme current profiles were derived. A) Profiles associated with extreme near surface current speeds, B) Profiles associated with extreme mid-depth current speeds and C) Profiles associated with extreme drag on a riser.

Passive Optical Sensing of the Near-Surface Wind-Driven Current Profile

2017 ◽  
Vol 34 (5) ◽  
pp. 1097-1111 ◽  
Author(s):  
Nathan J. M. Laxague ◽  
Brian K. Haus ◽  
David G. Ortiz-Suslow ◽  
Conor J. Smith ◽  
Guillaume Novelli ◽  
...  
Keyword(s):  
Surface Wind ◽  
Tidal Flow ◽  
Surface Current ◽  
Current Profile ◽  
Material Transport ◽  
Near Surface ◽  
Oil Transport ◽  
Wave Flume ◽  
Current Characteristics ◽  
The University

AbstractEstimation of near-surface current is essential to the estimation of upper-ocean material transport. Wind forcing and wave motions are dominant in the near-surface layer [within O(0.01) m of the surface], where the highly sheared flows can differ greatly from those at depth. This study presents a new method for remotely measuring the directional wind and wave drift current profile near to the surface (between 0.01 and 0.001 m for the laboratory and between 0.1 and 0.001 m for the field). This work follows the spectral analysis of high spatial (0.002 m) and temporal resolution (60 Hz) wave slope images, allowing for the evaluation of near-surface current characteristics without having to rely on instruments that may disturb the flow. Observations gathered in the 15 m × 1 m × 1 m wind-wave flume at the University of Miami’s Surge-Structure-Atmosphere Interaction (SUSTAIN) facility show that currents retrieved via this method agree well with the drift velocity of camera-tracked dye. Application of this method to data collected in the mouth of the Columbia River (MCR) indicates the presence of a near-surface current component that departs considerably from the tidal flow and may be steered by the wind stress. These observations demonstrate that wind speed–based parameterizations alone may not be sufficient to estimate wind drift and to hold implications for the way in which surface material (e.g., debris or spilled oil) transport is estimated when atmospheric stress is of relatively high magnitude or is steered off the mean wind direction.

Comparisons of Scatterometer and TAO Winds Reveal Time-Varying Surface Currents for the Tropical Pacific Ocean*

2005 ◽  
Vol 22 (6) ◽  
pp. 735-745 ◽  
Author(s):  
Kathryn A. Kelly ◽  
Suzanne Dickinson ◽  
Gregory C. Johnson
Keyword(s):  
Southern Oscillation ◽  
Surface Current ◽  
Current Data ◽  
Surface Currents ◽  
Radar Altimeter ◽  
Near Surface ◽  
The Mean ◽  
Divergence Pattern ◽  
Acoustic Doppler Current Profilers ◽  
Good Agreement

Abstract The differences between Tropical Atmosphere Ocean (TAO) anemometer and QuikSCAT scatterometer winds are analyzed over a period of 3 yr. Systematic differences are expected owing to ocean currents because the anemometer measures absolute air motion, whereas a radar measures the motion of the air relative to the ocean. Monthly averaged collocated wind differences (CWDs) are compared with available near-surface current data at 15-m depth from drifters, at 25-m depth from acoustic Doppler current profilers (ADCPs), and at 10-m depth from current meters and with geostrophic currents at the surface from the TOPEX/Poseidon radar altimeter. Because direct current observations are so sparse, comparisons are also made with climatological currents from these same sources. Zonal CWDs are in good agreement with the zonal current observations, particularly from 2°S to 2°N where there are strong currents and a robust seasonal cycle, with the altimeter-derived anomalous currents giving the best match. At higher latitudes there is qualitative agreement at buoys with relatively large currents. The overall variance of the zonal component of the CWDs is reduced by approximately 25% by subtracting an estimate of the zonal currents. The meridional CWDs are nearly as large as the zonal CWDs but are unpredictable. The mean CWDs show a robust divergence pattern about the equator, which is suggestive of Ekman currents, but with unexpectedly large magnitudes. Coefficients for estimating climatological zonal surface currents from the altimeter at the TAO buoys are tabulated: the amplitudes and phases for the annual and semiannual harmonics, and a linear regression against the Southern Oscillation index, are combined with the mean from the drifter currents. Examples are shown of the application of these estimators to data from SeaWinds on the Midori satellite. These estimators are also useful for deriving air–sea fluxes from TAO winds.

Remote measurement of near-surface currents via wave spectra: currents varying vertically and horizontally

2020 ◽  
Author(s):  
Benjamin K Smeltzer ◽  
Ida Seip Gundersen ◽  
Simen Ådnøy Ellingsen
Keyword(s):  
Surface Current ◽  
Window Size ◽  
Wave Dispersion ◽  
Remote Measurement ◽  
Wave Spectra ◽  
Surface Currents ◽  
Improved Method ◽  
Near Surface ◽  
X Band ◽  
Spatially Varying

&lt;p&gt;Remote sensing of ocean near-surface currents based on measurements of the wave spectrum is an attractive means of mapping currents over a large area simultaneously. The most common wave measurement method involves marine X-band radar (Lund et al. 2015), with optical video measurements using drones more recently being used as an alternative (Stre&amp;#223;er, Carrasco &amp; Horstmann, 2017). In both cases, analysis of the wave dispersion within a subset window of the spatial domain is performed to determine the spatially varying near-surface current. An improved method for determining the depth-dependence of sub-surface currents from measured wave spectra was recently developed by our group (Smeltzer et al 2019).&lt;/p&gt;&lt;p&gt;Our long-term goal is to develop methods whereby the best possible representation of the three-dimensional sub-surface current can be obtained from remote measurement of waves. Methods based on current retrieval from wave spectra must assume that horizontal current variations are slow compared to a typical wavelength, but this is not always so. To resolve horizontal space, retrieved images must be subdivided into windows and the velocity vector at the midpoint is determined from the 3D spectrum of the waves within the window only.&lt;/p&gt;&lt;p&gt;In this work we examine the dependence of the spatial window size on the results of the current reconstruction. When the window size is decreased, greater spatial resolution is achieved being able to capture currents that vary on a faster horizontal length scale, at the expense of lower resolution in wavevector spectral space which may decrease the accuracy of the reconstructed currents, especially when information as the depth-dependence of the flow is desired. When the window size is larger, the reconstructed current may not be representative of the average current within the window. We present experiments conducted in a laboratory where spatially varying currents and waves of can be well-controlled and measured in situ, a valuable test-bed setup compared to field measurements. We investigate the factors involved which determine the optimal choice of window size.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Lund, B., et al. A new technique for the retrieval of near-surface vertical current shear from marine X-band radar images. J. Geophys. Res.: Oceans (2015) &lt;strong&gt;120 &lt;/strong&gt;8466-8496.&lt;/p&gt;&lt;p&gt;Smeltzer, B.K., &amp;#198;s&amp;#248;y, E., &amp;#197;dn&amp;#248;y, A. and Ellingsen S.&amp;#197;., An improved method for determining near-surface currents from wave dispersion measurements. J. Geophys. Res.: Oceans. (2019) &lt;strong&gt;124&lt;/strong&gt;, https://doi.org/10.1029/2019JC015202.&lt;/p&gt;&lt;p&gt;Stre&amp;#223;er, M., Carrasco, R. and Horstmann, J., Video-based estimation of surface currents using a low-cost quadcopter, IEEE Geosci. Remote Sens. Lett. (2017) &lt;strong&gt;14 &lt;/strong&gt;2027-2031.&lt;/p&gt;

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