The origin of deep ocean microseisms in the North Atlantic Ocean

Oceanic microseisms are small oscillations of the ground, in the frequency range of 0.05–0.3 Hz, associated with the occurrence of energetic ocean waves of half the corresponding frequency. In 1950, Longuet-Higgins suggested in a landmark theoretical paper that (i) microseisms originate from surface pressure oscillations caused by the interaction between oppositely travelling components with the same frequency in the ocean wave spectrum, (ii) these pressure oscillations generate seismic Stoneley waves on the ocean bottom, and (iii) when the ocean depth is comparable with the acoustic wavelength in water, compressibility must be considered. The efficiency of microseism generation thus depends on both the wave frequency and the depth of water. While the theory provided an estimate of the magnitude of the corresponding microseisms in a compressible ocean, its predictions of microseism amplitude heretofore have never been tested quantitatively. In this paper, we show a strong agreement between observed microseism and calculated amplitudes obtained by applying Longuet-Higgins' theory to hindcast ocean wave spectra from the North Atlantic Ocean. The calculated vertical displacements are compared with seismic data collected at stations in North America, Greenland, Iceland and Europe. This modelling identifies a particularly energetic source area stretching from the Labrador Sea to south of Iceland, where wind patterns are especially conducive to generating oppositely travelling waves of same period, and the ocean depth is favourable for efficient microseism generation through the ‘organ pipe’ resonance of the compression waves, as predicted by the theory. This correspondence between observations and the model predictions demonstrates that deep ocean nonlinear wave–wave interactions are sufficiently energetic to account for much of the observed seismic amplitudes in North America, Greenland and Iceland

Comparing Correlations Between Four-Quadrant And Five-Factor Personality Assessments

For decades,some of the most popular devices used in educating students and employees tothe values of diversity are those that are based on a four-grid identification of behavior style. The results from the scoring of the instruments provide individual profiles in terms of a person’s assertiveness, responsiveness, and preferred tone of interacting with his environment. In the past decade, a five-factor framework has gained in popularity as an assessment instrument. The scope of the current paper is a comparison of a four-factor instrument (questionnaire)to a five-factor instrument (questionnaire) to establish correlations between the two. If the information can be seen as being complimentary rather than disconnected, then users will benefit from synergy as they encounter different instruments throughout their careers. Also, duplication of effort in terms of using multiple instruments may be reduced

An alternative approach for calculating the SAR damping ratio of verified oil slicks

Source: https://ieeexplore.ieee.org/xpl/conhome/1000307/all-proceedings.The damping ratio is a calculated feature that measures the contrast between oil-slicked water and the open ocean in SAR data. To implement the damping ratio, the current literature suggests estimating the open water backscatter by taking strips of undefined width across the range direction, obtaining the damping ratio as a function of incidence angle. We show in this paper that the method proposed in the literature can be improved by instead sampling open water pixels randomly. The method is tested on RADARSAT-2 quad-polarimetric SAR imagery of a verified oil slick acquired during the 2013 NOFO oilon-water exercise conducted in the North Sea. The results suggest that deviations in the derived damping ratio encountered by implementing the method proposed in the literature can be reduced from of order 100 – 10-1 to 10-3

Measurement of Oil Slick Transport and Evolution in the Gulf of Mexico using L-band Synthetic Aperture Radar

Source at https://www.vde-verlag.de/proceedings-en/454636104.htmlThe transport and evolution of a mineral oil slick originating at a seep in the Gulf of Mexico approximately 16 km offshore of the mouth of the Mississippi River is measured using a series of images acquired at 40 minute intervals with the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR), an L-band, high resolution, high signal-to-noise instrument operated by the U.S. National Aeronautics and Space Agency (NASA). A series of four images acquired over a 2-hour time period is used in the study. Both VV-intensity images and the VVintensity contrast between the slick and clean water (damping ratio) are used. The intensity images show the spatial development and transport of the slick within an area extending from the source northward to near the Louisiana (USA) coast. The slick initially spreads to the northeast from the origin site, then become entrained in an along-shore current. From there, the direction of transport changes by nearly 180º, and the oil from the slick moves west along a path much closer to the Louisiana shoreline. Concentration of the oil within the slick is observed along fronts and internal waves. The oil that remains on the surface the longest shows increasing damping, which could indicate the formation of more stable emulsions that can persist in the environment

An investigation on the damping ratio of marine oil slicks in synthetic aperture radar imagery

The damping ratio has recently been used to indicate the relative internal oil thickness within oil slicks observed in synthetic aperture radar (SAR) imagery. However, there exists no well-defined and evaluated methodology for calculating the damping ratio. In this study, we review prior work regarding the damping ratio and outline its theoretical and practical aspects. We show that the most often used methodology yields damping ratio values that differ, in some cases significantly, for the same scene. Three alternative methods are tested on multi-frequency data sets of verified oil slicks acquired from DLR's F-SAR instrument, NASA's Unmanned Aerial Vehicle Synthetic Aperture Radar (UAVSAR) and Sentinel-1. All methods yielded similar results regarding relative thickness variations within slick. The proposed damping ratio derivation methods were found to be sensitive to the proportion of oil covered pixels versus open water pixels in the azimuth direction, as well as to the scene size in question. We show that the fully automatable histogram method provides the most consistent results even under challenging conditions. Comparisons between optical imagery and derived damping ratio values using F-SAR data show good agreement between the relatively thicker oil slick areas for the two different types of sensors

Studies of the Deepwater Horizon Oil Spill With the UAVSAR Radar

On 22- 23 June 2010, the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) L band radar imaged the Deepwater Horizon oil spill and the effects of oil that was transported within the Gulf of Mexico. We describe the campaign and discuss the unique contributions of the UAVSAR radar to the study of the detection, migration, and impact of oil from the spill. We present an overview of UAVSAR data analyses that support the original science goals of the campaign, namely, (1) algorithm development for oil slick detection and characterization, (2) mapping of oil intrusion into coastal wetlands and intercoastal waterways, and (3) ecosystem impact studies. Our study area focuses on oil-affected wetlands in Barataria Bay, Louisiana. The results indicate that fine resolution, low-noise, L band radar can detect surface oil-on-water with sufficient sensitivity to identify regions in a slick with different types of oil/emulsions and/or oil coverage; identify oil on waters in inland bays and differentiate mixed/weathered oil from fresh oil as it moves into the area; identify areas of potentially impacted wetlands and vegetation in the marshes; and support the crisis response through location of compromised booms and heavily oiled beaches