多普勒潮流仪(一)

多普勒潮流仪是利用超声波的多普勒效应来测定船速、潮流的一种设备。过去所用的螺旋桨式潮流仪和曳航式潮流仪必须在船舶停航时进行工作的。多普勒潮流仪在测定船速和希望获得某一深度潮流时,可以表层流作基准而测定。水深在300米以内的海域,以海底为基准来测定,所获的数值是对地船速及精度极高的绝对潮流值。

多普勒潮流仪(二)

1小时后,两者产生了7海里的差距,即表示船的速度比A 点的潮流速度快7海里。如果以A 点作为基准,则船的对水船速为7海里。因此,只要测定出船的对地速度和对水速度后,其差值就是以对地为基准的潮流速度。如果A 点的运动方向与图3所示方向相反时,则以A 点为基准的船速为13海里。

日本的鱼群监视潮流仪

近年来,日本开发了超声波式潮流仪,它的结构简单,测定精度高,而且在航行中可以在深层自动地测定潮流、船速.已在渔业界和其它海洋领域中广泛使用.最近,日本无线株式会社又开发了鱼群监视潮流仪.它不仅具有超声波式潮流仪的功能,而且具有多方向探鱼功能、以期大大提高渔获效率,节约燃费.

Observed Suspended Sediment Dynamics during a Tidal Cycle above Submerged Asymmetric Compound Sand Waves

The data from Acoustic Doppler Current Profiler （ADCP） of the three-dimensional current-field, echo intensity, modulation of Suspended Sediment Concentration （SSC）, and related water levels and wind velocities have been analyzed as a function of water depth above submerged asymmetric compound sand waves during a tidal cycle in the Lister Tiefofthe German Bight in the North Sea. Signatures of vertical current component, echo intensities and calculated SSC modulations in the water column depend strongly on wind and current velocity. Bursts of vertical current component and echo intensity are triggered by sand waves itself as well as by superimposed megaripples due to current wave interaction at high current ≥ 1.0 m＇s1 and wind speeds ≥ 10.0 m·s^-1, preferably of opposite directions, measured at high spatial resolution. The magnitude of currents and SSC modulations during ebb and flood tidal current phases are only weakly time dependent, whereas the local magnitudes of these parameters are variable in space above the sand waves. Some hydrodynamic parameters are further investigated and analyzed, showing a consistence of ADCP measurements in the applied theory.

Tide and Current Observations in the Central Chukchi Sea During the Summer of 2012

Current data from a moored Acoustic Doppler Current Profiler （ADCP） deployed at 69°30.155N, 169″00.654″W in the central Chukchi Sea during 2012 summertime is analyzed in the present paper. Characteristics of tidal and residual currents are obtained with Cosine-Lanczos filter and cross-spectral analyses. The main achievements are as follows： 1） Along with the local inertial frequency of 12.8 h, two other peaks at -12-h and -10-d dominate the time series of raw velocity; 2） The M2 dominates the 6 resolved tide constituents with significant amplitude variations over depth and the ratios of current speed of this constituent to that of the total tidal current are 54% and 47% for u and v components, respectively. All the resolved tidal constituents rotate clockwise at depth with the exception of MM and O1. The constituents of M2 and $2 with the largest major semi-axes are similar in eccentricity and orientation at deeper levels; 3） The maximum of residual currents varies in a range of 20-30 cm s-1 over depth and the current with lower velocities flow more true north with smaller magnitudes compared to the current in surface layer. The -10d fluctuation of residual current is found throughout the water column and attributed to the response of current to the local wind forcing, with an approximate 1.4 d lag-time at the surface level and occurring several hours later in the lower layer; 4） Mean residual currents flow toward the north with the magnitudes smaller than 7 cm s-1 in a general agreement with previous studies, which suggests a relatively weaker but stable northward flow indeed exists in the central Chukchi Sea.

Analysis of internal tidal characteristics in the layer above 450 m from acoustic Doppler current profiler observations in the Luzon Strait

The characteristics of internal tides in the upper layer of the Luzon Strait are investigated on the basis of direct-observation current data recorded on April 25 and September 26, 2008 by an acoustic Doppler current profiler. Spectral analysis and energy estimation show that the diurnals and semidiurnals carry most of the energy of internal tides. Values of the depth-integrated total energy E for the three frequency bands of diurnal, semidiurnal, and high frequencies are 31, 6.9, and 3.4 kJ. m, respectively. Near-inertial peaks are only present in the baroclinic component. The behavior of typical tidal frequencies （i.e., O1, K1, M2, MK3, and M4） and the near-inertial frequency is basically consistent with linear internal wave theory, which predicts E＋（ω）/E_（ω）=（ω-f）2/（ω＋f）2 at depths above 66 m, while not all prominent tidal components coincide well with the relation of the linear internal wave field at other depths. Examinations of depth structures of the baroclinic tides and temporal variations show that the surface tides and internal tides are both of mixed type, having diurnal inequality and spring-neap fortnight periods. The K1 and O1 tides have comparable cross- and along-shelf components, while the M2 and S2 tides propagate toward the shelf in the northern South China Sea as wave beams. The amplitude and phase of internal tides vary with time, but M2 and S2 tides appear to have structures dominated by the first mode, while the K1 and O1 tides resemble second-mode structures. The minor to major axis ratios are close to expected values of flω in the thermocline.