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1.
Radar backscatter measurements from the ocean were made at 13.9 GHz from Skylab. The radar signal increased rapidly with wind speed over the entire range of winds encountered, and for angles of incidence of30deg and larger. Signals observed were normalized to a nominal incidence angle (from values withinpm2deg of the nominal) and to a nominal upwind observation direction, using a theoretical model that has been verified as approximately true with aircraft experiments. The wind speed was regressed against the resulting scattering coefficientssigma^{0} and the values ofbeta in windpropto sigma^{0beta} were obtained for incident angles of1deg , 17deg , 32deg , 43deg, and50deg , and for vertical, horizontal, and cross polarizations. For the three larger angles,beta varies from 0.3 to 0.6. Observations during the summer and winter Skylab missions were treated separately because of possible differences caused by an accident to the antenna between the two sets of observations. The results are in general agreement with the theory [26] in all cases, with the winter and cross-polarized agreement somewhat better than that for summer like-polarized data. The "objective analysis" method used for determining "surface-truth" winds in the Skylab experiment was tested by comparing results obtained at weather ships (using all other ship reports to produce the analysis) with the observations made by the weather ships themselves. In most cases, the variance about the regression line between objective analysis and weather-ship data actually exceeded that about the regression line between objective analysis and backscattcr data! 相似文献
2.
海面的曳力系数和空气动力学粗糙度长度是计算海气动量、感热和水汽通量交换必需的参数。基于在“黑格比”和“灿都”台风期间收集的涡动相关系统观测数据, 文章研究了10m风速和摩擦速度之间、10m风速和曳力系数之间、以及10m风速和动力粗糙度长度之间的参数化关系。结果表明: 曳力系数和摩擦速度及10m风速之间存在抛物线关系, 动力粗糙度长度与摩擦速度及10m风速之间存在自然指数关系; 临界摩擦速度为0.83m·s-1, 临界10m级风速为23.69m·s-1。 相似文献
3.
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
4.
Comprehensive wind tunnel measurements have been made of the drag coefficients of both the body and the faired cable of a towed system. The drag data has been embodied in theoretical calculations of the depth attained in tow, at speed up to 3 m s−1 (6 knots) with scopes up to 135 m (440 ft). The agreement with sea trial observations is excellent.The work has highlighted the importance of accounting for the variation of faired cable drag with cable angle and has shown that the drag increments due to gaps and misalignments between individual fairing elements cannot be ignored.Methods are derived for estimating these effects for application to other faired cable towed systems. 相似文献
5.
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
6.
SWAN模型中不同风拖曳力系数对风浪模拟的影响 总被引：1，自引：1，他引：0
本文以荷兰哈灵水道海域为实验区域,通过敏感性实验,研究了在14 m/s、31.5 m/s和50 m/s（分别代表一般大风、强热带风暴和强台风的极端条件）定常风速下SWAN模型中不同风拖曳力系数对风浪模拟的影响程度。结果表明,对于近岸浅水区域（水深小于20 m）,风拖曳力系数计算方案的选择对有效波高影响较小,而且当风速增加到一定程度后,波浪破碎成为影响波高值的主要因素;对于深水区域（水深大于30 m）,一般大风条件下风拖曳力系数计算方案的选择对有效波高影响仍然较小,随着风速的继续增大,风拖曳力系数计算方案的选择对有效波高的影响逐渐显著。对于平均周期,风拖曳力系数计算方案的选择和风速的改变对其影响均较小,而由水深变浅导致的波浪破碎对其影响较为显著。根据敏感性实验结果,本文对SWAN模型中风拖曳力系数计算方案的选择做出如下建议:计算近岸浅水区域风浪场或深水区域一般大风条件风浪场时,其风拖曳力系数可以直接采用模型默认选项;而对于深水区域更大风速条件,可首先采用模型默认选项试算,然后结合当地海域实测波浪资料进行修正。 相似文献
7.
《Oceanic Engineering, IEEE Journal of》2009,34(4):407-422
8.
Experimental results from an array of moored current meters and an HF ocean surface radar support the idea that line broadening on the radar spectra is caused by the velocity distribution within the radar target cell. The experiment was done in the wake of a small island where the velocity variations were severe. An estimate is made of the line broadening which can be expected. In a turbulent flow with dissipation rate of the orderepsilon sim 10^{-10}m^{2}s^{-3} and target cell size 1 3000 m, the line broadening isDeltaf sim 10^{-3} Hz. This would be resolved with a radar time series ofsim 20 min and indicates that the HF ocean surface radar technique has potential in the observation of surface velocity distributions. 相似文献
9.
On the parameterization of drag coefficient over sea surface 总被引：1，自引：0，他引：1
Six parameterization schemes of roughness or drag coefficient are evaluated on the basis of the data from six experiments. They present great consistency with measurement when friction velocity u*<0.5 m/s (approximately corresponding to 10 m wind speed U10 <12 m/s) and large deviation from measurement when u*≥0.5 m/s (approximately U10≥12 m/s). In order to improve the deviation, a new parameterization of drag coefficient is derived on the basis of the similarity theory, Charnock relationship and Toba 3/2 power law. Wave steepness and wind-sea Reynolds number are considered in the new parameterization. Then it is tested on the basis of the measurements and shows significant improvement when u*≥0.5 m/s. Its standard errors are much smaller than the ones of the other six parameterizations. However, the new parameterization still needs more tests especially for high winds. 相似文献
10.
M.M. Zdravkovich 《Applied Ocean Research》1985,7(4):197-201
The drag and lift force are measured on circular cylinders fitted with end plates in a wind tunnel. The gap between the cylinder and the wall, G, the thickness of the turbulent boundary layer along the wall, δ, and the Reynolds number, Re, are varied in the following ranges: 0 < G/D < 2, 0.12 < δ/D < 0.97 and 4.8 × 104 Re 3 × 105. The lift and drag coefficients are presented in terms of a new variable G/δ.
It is found that the lift coefficient is governed by the gap to diameter ratio G/D while the drag coefficient is dominated by the ratio of gap to thickness of the boundary layer, G/δ. 相似文献
11.
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
12.
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
13.
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
14.
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
15.
The B/Ca ratio of planktonic foraminifer shells has been used as a proxy for reconstructing past ocean carbonate chemistry. However, recent studies have revealed significant uncertainties associated with this proxy, such as whether seawater temperature or [ CO_3~(2-)] is the dominant control on the partition coefficient(K_D) of planktonic foraminiferal B/Ca. To address these uncertainties and thus improve our understanding of the planktonic foraminiferal B/Ca proxy, we analysed B/Ca ratios in the tests of Neogloboquadrina dutertrei(300–355 μm) and Pulleniatina obliquiloculata(355–400 μm) in surface sediment samples from the tropical western Pacific and South China Sea. The relationship between these B/Ca ratios and bottom water calcite saturation states(Δ[ CO_3~(2-)]) is weak, thus suggesting only a small dissolution effect on the B/Ca of the two species. The correlation coefficients(R~2) between the B/Ca ratios of N. dutertrei and P. obliquiloculata and environmental parameters(e.g., temperature, salinity, phosphate, DIC and ALK) in the tropical western Pacific and South China Sea are not high enough to justify using B/Ca ratios as a palaeoenvironmental proxy in the study areas. The significant correlation between K_D values of N. dutertrei and P. obliquiloculata and carbonate system parameters(e.g.,[ CO_3~(2-)], DIC, ALK, pH and [ HCO_3~-]) in the study area reflect chemical links between the K_D denominator and these variables. Based on our surface sediment calibration, an empirical relationship between the K_D of N.dutertrei and temperature is proposed in the tropical western Pacific. We also generated a record of B/Ca ratios in N. dutertrei(300–355 μm) from Core MD06-3052 in the tropical western Pacific over the past 24 ka to evaluate the application of the revised B/Ca proxy method. Based on the reconstructed empirical relationship for B/Ca and subsurface seawater ALK, we estimated subsurface seawater carbonate system parameters in the tropical western Pacific since 24 ka. In general, the estimated subsurface seawater pH and [ CO_3~(2-)] show an increase with time, and the record of subsurface seawater pCO_2 shows a decrease with time, in the tropical western Pacific over the past 24 ka. The consistent trends in subsurface seawater pCO_2 and opal flux during deglaciation may imply that the reported increase in subsurface water pCO_2 in the study area was promoted by enhanced upwelling in the Southern Ocean. 相似文献
16.
A method is described for measuring the sound speed and the sound-speed gradient of surficial sea floor sediment from bottom-reflected signals recorded in marine seismic experiments. The technique makes use of the ocean-bottom impulse responses that are deconvolved from the data by means of a novel curve-fitting algorithm based on thel_{1} norm (least absolute value) criterion. The algorithm constructs the impulse response by extracting spikes one at a time in a manner that causes thel_{1} error to decrease by the maximum amount possible as each spike is chosen. Thel_{1} curve-fitting approach is a completely general strategy for deconvolution, and our algorithm can be used with data obtained from any type of marine seismic source. Since our experiments have been carried out with small explosive charges, we have also developed a method for estimating the bubble-pulse wavelet directly from the recorded bottom-reflected signal. In this paper, thel_{1} algorithm is used to deconvolve impulse responses for data obtained in an experiment in the Alaskan Abyssal Plain. The sediment-sound-speed gradient determined from these results is typical of other values reported for turbidite abyssal plains where the surficial sediments are composed of unconsolidated silty deposits. 相似文献
17.
《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
18.
Richard W. Sternberg 《Marine Geology》1976,20(4):M25-M31
Aseries of boundary-layer measurements was made at three anchor stations on Campeche Bank, Yucatan. Measurements consisted of current speed at six levels within 1.5 m of the bed, current direction, and stereophotographs of boundary. Analysis of the drag coefficient revealed that the boundary-layer flow was hydrodynamically transitional and the magnitude of the drag coefficient varied between 2·10−3 and 6·10−2 as a function of the flow conditions and bed configuration. These data appear to be representative of flows of an intermediate nature, not only in the observed variations of the drag coefficient with respect to Reynolds number but in the way that the drag coefficient correlates with other measurements made in low- and high-velocity environments, respectively. 相似文献
19.
20.
The design and ultimate performance of an extremely low-frequency (ELF) superconducting quantum interference device (SQUID) antenna that is mounted in a submarine-towed buoy depends critically on the motion spectrum of the buoy. Motion spectrum measurements from near dc to 100 Hz were conducted on a hydrodynamically stabilized buoy while being towed in the 650-m towing basin of the David Taylor Naval Ship Research and Development Center, Carderock, MD. The spectra show that the angular motion of the buoy can be held to4 times 10^{-6} rad/sqrt{Hz} or less within the ELF receiver bandwidth of 30-130 Hz, as long as properly streamlined fairings are used on the hydrofoil trailing edges in order to prevent oscillations from vortex shedding. Low-frequency oscillations of the buoy were3 times 10^{-3} rad/sqrt{Hz} or less for frequencies down to 0.025 Hz. This performance of the buoy is sufficient to permit it to serve as a towed platform for the NRL prototype SQUID receiver. 相似文献