- المجال: Education
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Founded in 1876, Texas A&M University is a U.S. public and comprehensive university offering a wide variety of academic programs far beyond its original label of agricultural and mechanical trainings. It is one of the few institutions holding triple federal designations as a land-, sea- and ...
The delay, usually a day or two, between full and new moons (when the equilibrium semi-diurnal tide is maximum) and the following spring tides. This terminology was first used to refer to this phenomenon by Whewell in 1883, although Defant referred to it as ``spring retardation'' in 1961 and Wood later (in 1978) used the terms ``age of the phase inequality'' and ``age of the diurnal equality'' to refer to, respectively, the ages of the semi-diurnal and diurnal tides. This delay is caused by frictional energy dissipation in coastal seas, although a localized increase in the age of tide is also a good indication of resonances at that location.
Industry:Earth science
The elapsed time since a given water mass was last at the sea surface.
Industry:Earth science
Part of the southeastern Australasian Mediterranean Sea centered at about 10° S and 137° E. It is bounded by Irian Jaya and Papua/New Guinea to the north and northeast, the Timor Sea to the west, and Australia and the Gulf of Carpenteria to the south and the southeast. It is mostly a large shelf (covering about 650,000 km<sup>2</sup>) ranging from 50 to 80 m deep, although it can get as deep as 3650 m to the northwest in the Aru Basin.
There is a steady westward flow along the southern side of the Sunda Islands that is part of the larger pattern of throughflow through the Australasian Mediterranean from the Pacific to the Indian Ocean. South of this the circulation varies with the monsoon and trade winds that drive it. The deep water is renewed from the northwest via the Timor Trough.
Sea surface temperatures range from a maximum of 28. 4° in Dec. -Feb. to a minimum of 26. 1° in Jun. -Aug. , while salinities annually range from 34. 2-34. 8 in the deeper parts to the north to 34. 2 to 35. 0 on the Arafura Shelf.
Industry:Earth science
A scientific collaboration between the U. S. , China, Korea, Japan, Taiwan, Russia and Singapore. The ASIAEx major field experiments began in 2000, one focusing on acoustic bottom reverberation and the other on acoustic cross-shelf progagation.
Industry:Earth science
One of three major components of deep sea sediments, the other two being detrital and biogenic. Authigenic minerals are those formed by spontaneous crystallization within the sediment or water column, and make up only a small fraction of the total sediment volume. The most important of this type of sediment is the iron-manganese oxide material formed by reduction of these metals deep in the sediment column. The resultant material migrates upwards and is deposited in the oxygenated upper layers of sediment. It can also be produced as a by-product of hydrothermal activity near ridge crests.
Industry:Earth science
An instrument used to measure ocean currents. It transmits high frequency acoustic signals which are backscattered from plankton, suspended sediment, and bubbles, all of which are assumed to be traveling with the mean speed of the water. The ADCP estimates horizontal and vertical velocity as a function of depth by using the Doppler effect to measure the radial relative velocity between the instrument and scatterers in the ocean.
Three acoustic beams in different directions are the minimum number required for measuring the three velocity components, with a fourth adding redundancy and an error estimate. A ping is transmitted from each transducer about once per second, with the echo returning over an extended period. Echos from shallow depths return before those from greater depths. Profiles are produced by range-gating the echo signal, i.e. breaking the echo into successive segments called depth bins corresponding to successively deeper depth ranges. The noisy velocity estimates from each ping are vector-averaged into 1- to 10-minute ensembles, and the resulting relative velocities are rotated from the transducer's to the earth's reference frame using the ship's gyrocompass.
A navigation calculation is performed to obtain absolute currents, which are obtained by subtracting the average of the ship velocity relative to a reference layer (i.e. ADCP velocities) from the absolute ship velocity over the ground (from GPS navigation). The raw absolute current velocities relative to the reference layer are then smoothed to reduce the effect of noise in the position fixes, and combined with the navigation data to obtain the best estimates of ship positions and velocities. Thus, absolute currents at any depth can be determined from the ship navigation data and the relative ADCP measurements.
The ADCP measures the ocean current velocity continuously over the upper 300 m of the water column, usually in 8 m depth increments. It is also used to estimate the abundance and distribution of biological scatterers over the same depth range and in the same depth increments.
ADCP data collection requires that four instruments work together. These are the ADCP itself, the ship's gyrocompass, a GPS receiver, and a GPS Attitude Determination Unit (ADU).
Industry:Earth science
The northern branch of the subtropical gyre in the North Atlantic Ocean. This carries around 15 Sv of water along 35-40° N to the western part of the gyre, i.e. the Canary Current.
Industry:Earth science
A joint U. S. and Russian program started in 1995. The main objective of ACOUS is to establish a long-term, real-time Arctic Ocean observing system using cabled moorings that integrate point measurements with acoustic remote sensing measurements. The remote sensing is used to monitor basin-scale changes in the ocean temperature and the thickness of the Arctic ice cover.
Industry:Earth science
One of the three plains that comprise the Pacific-Antarctic Basin (the others being the Bellingshausen and Mornington Abyssal Plains). It is located at around 150° W.
Industry:Earth science
