共查询到20条相似文献,搜索用时 31 毫秒
1.
《Oceanic Engineering, IEEE Journal of》2009,34(4):407-422
2.
《Oceanic Engineering, IEEE Journal of》2009,34(1):83-92
3.
《Oceanic Engineering, IEEE Journal of》2008,33(2):69-88
4.
《Oceanic Engineering, IEEE Journal of》2009,34(4):451-458
5.
《Oceanic Engineering, IEEE Journal of》2009,34(4):485-494
6.
Evaluation of Laser Scanning and Stereo Photography Roughness Measurement Systems Using a Realistic Model Seabed Surface 总被引:1,自引:0,他引:1
《Oceanic Engineering, IEEE Journal of》2009,34(4):466-475
7.
8.
9.
《Oceanic Engineering, IEEE Journal of》2009,34(4):476-484
10.
《Oceanic Engineering, IEEE Journal of》1980,5(1):17-21
The ratiosZ_{K,t} of electrical conductivities of potassium chloride (KCI) solutions of known concentration (K ) to standard seawater at the same temperature have been measured at15deg C and24deg C for solutions withZ_{k,15} between 0.96 and 1.04. The "normal" concentration (N or K_{N} ) givingZ_{N,15}= 1 was found to beK_{N} = 32.4356 gKCI/kg solution. The effect of temperature onZ_{N,t} was measured over the range15deg C to30deg C. Equations are given for KCI concentration as a function ofZ_{15} and the inverse function, forZ_{15}/Z_{24} as a function ofZ_{24} (to allow use of a laboratory salinometer for the KCI-seawater comparisons), andZ_{N,t} as a function of temperature. 相似文献
11.
Systems of identical precisely spaced bubbles or similar monopole scatterers in water-e.g., inflated balloons or thin-walled shells-insonified at frequenciesomega_{SR} dose to their fundamental radial resonanceomega_{0} (bubble) frequency may themselves display resonance modes or superresonances (SR's) [1]. Ordinary single-bubble resonances magnify the local free-field pressure amplitudep_{1} by a factor(ka)^{-1} ,a being the radius andk the wavenumber in water: for air bubbles or balloons in water, this factor is of the order of 70. Under SR conditions each member of the system amplifies the local free-field amplitude by a further factor of order(ka)^{-1} . Depending upon geometry and other constraints, the pressure fieldP_{SR} on the surface and in the interior of each scatterer will then be in the range of10^{3}p_{1} to5 times 10^{3} p_{1} . This paper investigates the sensitivity of this phenomenon to small departures from the ideal model. In particular, it examines the effect of small differences in scatter positioning and volumes in the context of an SR system consisting of two bubbles/balloons close to the boundary of a thin elastic plate overlying a fluid half-space. It is found that, to observe the SR phenomenon, radii and positions should be controlled to within approximately 1/2 percent.P_{SR} is also sensitive to the angle of incidence of the plane wave train. For the simple system examined here, this sensitivity is considerable for either flexural wave trains or volume acoustic waves incident upon the bubble/ balloon pair (doublet). Practical uses of the phenomenon may range from the design of passive high-Q acoustical filter/amplifiers and acoustical lenses to improved source efficiencies. 相似文献
12.
The ratiosR_{s,t,o} of electrical conductivity of seawater samples of precisely known salinity to standard seawater at the same temperature have been measured over a wide range of salinities from 0 to42permil S and over the full range of oceanic temperatures from -2 to35deg C. The samples withS<35permil were prepared by accurate weight dilution of standard seawater with distilled water. High salinity samples were prepared by fast evaporation of standard seawater and subsequent weight dilution into the already determined <35permil range. An equation was derived which expresses the S versusR_{s,t,o} relationship very precisely from1-42permil and at all temperatures, i.e.,S = f_{1}(R_{s,t,o}) + f_{2}(R_{s, t,o},t) =Sigma_{n=0}^{5} a_{n}R^{n/2}+ frac{Delta t}{1+kDelta t} Sigma_{n=0}^{5} b_{n}R^{n/2} whereDelta t = t-15deg C,R = R_{s, t.o} ; only the first termf_{1} is required at15deg C. The effeet of temperature on the electrical conductivity of standard seawater was also measured. The ratior_{t} of the conductivity at temperaturet to the conductivity at15deg C (C_{35,t, o}/C_{35,15,o} ) is very aeenrately expressed by a fourth degree equation int . i.e,r_{t}=Sigma_{n=0}^{4} c_{n}t^{n} These two equations are sufficient for all salinity determinations at normal atmospheric pressure. 相似文献
13.
Channel capacity in bits per joule 总被引:1,自引:0,他引:1
Underwater acoustic telemetry has a total input energy constraint, since the energy is stored in the transmitter's batteries. This work is primarily rephrasing the work in channel capacity in terms ofC_{J} bit/J as compared toC bit/s, to emphasize the energy efficiency and to deemphasize the speed of the telemetry. The energy channel capacityC_{J} , for any waveform channel with well-defined capacityC bit/s at signal powerS watts, is defined asC/S bit/J. It is shown that for coherent binary frequency shift keying (BFSK) and waveform channels, the supremum ofC_{J} overS is approached asS approaches zero. For the Gaussian channel the best coding uses narrow bands with the highest S/N. 相似文献
14.
The Practical Salinity Scale (PSS) 1978 is defined only for salinities within the range 2-42. We have investigated the relationship between mass-determined salinity, electrical conductivity, and temperature for salinities between 0 and 2 with the aim of developing an extension to the Practical Salinity Scale 1978. The paper presents our data, on the basis of which the following correction is proposed to extend the validity of the equations defining the scale to the entire 0-42 range:S=summin{i=0}max{5} (a_{i}+b_{i}f(t))R_{t}^{i/2}-frac{a_{0}}{1 + 1.5x + x^{2}}-frac{b_{0}f(t)}{1+y^{1/2} + y + y^{3/2}} wheref(t)=frac{(t-15)}{1 + k(t-15) x=400R_{t} y=100R_{t} and the constanta_{i}, b_{i} , andk are defind by the Practical Salinity Scale 1978. 相似文献
15.
Rationale for the measurement of open-ocean tsunami signatures are presented, and available pertinent data are reviewed. Models for tsunami signature and background noise are proposed in order to synthesize an optimum tsunami receiver. Using these models, the minimum tsunami amplitude (in cm) to yield the probability of correct tsunami detectionP_{D} = 0.999 and probability of false alarmP_{F} = 10^{-3} is found to be0.718/sqrt{f_{0}} , wheref_{0} is the tsunami dominant frequency (in cycles/h). A realizable receiver is proposed and its performance is evaluated using actual tsunami signatures. It is demonstrated that the detection of a tsunami with an average amplitude as small as 0.7 cm is possible for theP_{D} andP_{F} as above. Simulation results using synthesized background noise are shown. Tidal effects on the receiver performance also are considered and are found negligible for a certain range of the receiver parameters, resulting in a considerable reduction of the signal processing required. 相似文献
16.
In this paper, the effect of channel phase coherence upon a matched filter envelope detector output is investigated for a pulsed radar or active sonar. A novel model for the correlated channel phases allows the explicit calculation of the loss in detection performance using the deflection criteria. The theoretical model yields good agreement with simulations when the phase correlation coefficients between the first and last pulses are between 0.1 and 1.0. It is shown that a 3-dB loss in performance, as compared to the optimum detector for perfect coherence, requires phase correlation between adjacent pulses ofrho_{i,i+1} = 0.91 , 0.96, and 0.96 for 10, 20, and 30 pulses, respectively. On the other hand, the same performance is obtained with a noncoherent combiner of the matched filter pulse returns when correlation between adjacent pulses,rho_{i,i+1} = 0.8 , 0.835, and 0.84 for 10, 20, and 30 pulses, respectively. Ifrho_{i,i+1} is smaller than these quantities, one is better off performing noncoherent detection. 相似文献
17.
Dauphinee T. Klein H. Kirby C. Kathnelson J. 《Oceanic Engineering, IEEE Journal of》1983,8(4):288-292
A new portable salinometer has been developed which is based On a direct determination of the conductivity ratioR_{t} = (C_{x}/ C_{s})_{t} of sample(x) to standard(s) seawater in a dual-cell, continuous-flow system. The new salinometer requires only 10 ml of unknown and much less of standard, drawn from the source bottles through fine Teflon tubes, to obtain complete flushing and several repeat readings to the order ofpm0.001 , in salinity. The system is autobalancing over the full range of conductivity ratio from 0 to 1.3 and in the future will be direct reading in salinity units. The amount of standard water required is so low that standard water ampoules, at the rate of l/day, can be used as the source. The method used offers a possibility of a direct measurement of salinity in the ocean by measuringR_{t} in situ. 相似文献
18.
The direction of the mean surface wind field in the North Pacific Ocean was mapped on September 25 and 26, 1973, over an area of3 times 10^{6} (km)2by OTH-B HF radar. A spatial resolution of 60 km in range and 15 km in cross range was used at points spaced by 150 km in range and 80 km in cross range. Wind directions were inferred from the upwind/downwind first-order Bragg ratio and the measure of the maximum ratio occuring for radial winds at points near each observation. Over 90 percent of the recorded data were usable for this purpose.High spatial resolution is essential to make detailed measurements of the wind speed and direction across and along an atmospheric cold front. The location of the atmospheric cold front derived from the wind field agreed well with the ESSA VIII satellite frontal location. 相似文献
19.
An echo sounder has been developed with features ideally suited to oceanographic and fisheries research. Instruments commonly used for such research are inaccurate, limited in dynamic range, unstable, and generally inflexible. An effort has been made to overcome these deficiencies with the sonar system discussed here. The echo sounder to be described has a time-varied-gain receiver (20 log_{10} R or40 log_{10} R + 2alphaR ) accurate to withinpm0.5 dB over a 100-dB range. The equivalent dynamic range is 140 dB (the ratio of the maximum signal at minimum gain to the equivalent input noise at maximum gain in a 4-kHz bandwidth). The temperature stability ispm0.5 dB from10deg to35deg C at any range. Operating parameters, including frequency, can be easily altered to accommodate a variety of needs. 相似文献
20.
Microwave scattering signatures of the ocean have been measured over a range of surface wind speeds from 3 m/s to 23.6 m/s using the AAFE RADSCAT scatterometer in an aircraft. Normalized scattering coefficients are presented for vertical and horizontal polarizations as a function of incidence angle (nadir to55deg ) and radar azimuth angle (0deg to360deg ) relative to surface wind direction. For a given radar polarization, incidence angle, and azimuth angle relative to the wind direction, these scattering data exhibit a power law dependence on surface wind speed. The relation of the scattering coefficient to azimuth angle obtained during aircraft circles (antenna conical scans) is anisotropic and suggests that microwave scatterometers can be used to infer both wind speed and direction. These results have been used for the design of the Seasat-A Satellite Scatterometer (SASS) to be flown in 1978 on this first NASA oceanographic satellite. 相似文献