The electrical conductivity of weight diluted and concentrated standard seawater as a function of salinity and temperature

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 to42permilS and over the full range of oceanic temperatures from -2 to35degC. The samples withS<35permilwere 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 <35permilrange. An equation was derived which expresses the S versusR_{s,t,o}relationship very precisely from1-42permiland 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-15degC,R = R_{s, t.o}; only the first termf_{1}is required at15degC. The effeet of temperature on the electrical conductivity of standard seawater was also measured. The ratior_{t}of the conductivity at temperaturetto the conductivity at15degC (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.     

The effect of concentration and temperature on the conductivity ratio of potassium chloride solutions to standard seawater of salinity 35 ‰(Cl 19.3740 ‰)

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 at15degC and24degC for solutions withZ_{k,15}between 0.96 and 1.04. The "normal" concentration (N or K_{N}) givingZ_{N,15}= 1was found to beK_{N} = 32.4356gKCI/kg solution. The effect of temperature onZ_{N,t}was measured over the range15degC to30degC. 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.     

Matched-Filter Envelope Detector Deflection Performance for a Correlated Phase Channel

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.     

Properties of superresonant systems of spherical scatterers

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},abeing the radius andkthe 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-Qacoustical filter/amplifiers and acoustical lenses to improved source efficiencies.     

The extension of the Practical Salinity Scale 1978 to low salinities

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}, andkare defind by the Practical Salinity Scale 1978.     

Tsunami detectability using open-ocean bottom pressure fluctuations

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} = 0.999and 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.     

A portable salinometer based on direct measurement of the conductivity ratioR_{t}

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.     

Sparse Cylindrical Sonar Arrays

Sparse arrays offer a means for reducing the cost and complexity of beamforming systems. Most of the work in the literature has focused on sparse linear arrays with isotropic transducer elements, which simplifies analysis greatly. In this paper, we will focus on multibeam cylindrical arrays using highly directive elements for use in fishery applications, which requires a directionally independent imaging performance in the azimuth direction as well as beam steerability in the elevational direction. To populate such an array, we suggest a low periodicity in the azimuth direction of the array, which ensures a (near) directionally independent imaging performance in this direction. At the same time it reduces the complexity of the problem so that a suggested iterative method can find the optimal layout under the given constraints, within reasonable time. The optimality of the constrained solution is verified using a stochastic optimization procedure, with a “loosened” periodicity constraint. Simulations then show that the proposed layout, having low periodicity in the azimuth direction, has a reduced peak sidelobe level compared to the fully sampled array. All of the layouts have been required to support beam steering from $-$30 $^{circ}$ to 0$^{circ}$ in elevation and in all 360$^{circ}$ in azimuth, without deterioration in performance.      

A versatile sonar system for ocean research and fisheries applications

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} Ror40 log_{10} R + 2alphaR) accurate to withinpm0.5dB 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 ispm0.5dB from10degto35degC at any range. Operating parameters, including frequency, can be easily altered to accommodate a variety of needs.     

Seasat altimeter sensor file algorithms

The Seasat altimeter is designed to measure three parameters important to oceanography: height of the spacecraft above the ocean surface (h), significant wave height (H_{1/3}), and ocean backscatter coefficient (sigmadeg) from which surface winds may be inferred. Since the measurement process is indirect, and the measurement environment is complicated by many factors affecting the instrument readings, corrections to the raw data are needed before they are used to compute geophysical parameters. These corrections are accomplished by the Seasat altimeter sensor file algorithms. The purpose of this paper is to describe these algorithms, why they are needed, how they are implemented, and their evaluation using in-flight data.     

Static and dynamic modeling of a SAR imaged ocean scene

A number of models exist that attempt to explain wave imagery obtained with a synthetic aperture radar (SAR). These models are of two types; static models that depend on instantaneous surface features and dynamic models that employ surface velocities. Radar backscatter values (sigma_{0}) were calculated from 1.3- and 9.4-GHz SAR data collected off Marineland, FL. Thesigma_{0}data (averaged over many wave trains) collected at Marineland can best be modeled by the Bragg-Rice-Phillips model which is based on roughness variation and the complex dielectric constant of oceans. This result suggests that capillaries on the surface of oceanic waves are the primary cause for the surface return observed by a SAR. Salinity and temperature of the sea at small and medium incidence angles produce little effect upon sea-surface reflection coefficients atX-band, for either of the linear polarizations. The authors' observation of moving ocean, imaged by the SAR and studied in the SAR optical correlator, support a theory that the ocean surface appears relatively stationary in the absence of currents. The reflecting surface is most likely moving slowly (i.e., capillaries) relative to the phase velocity of the large gravity waves.     

Attenuation Measurements Across Surface-Ship Wakes and Computed Bubble Distributions and Void Fractions

A surface ship's wake is composed of several hydrodynamic phenomena. A large part of that wake contains a mixture of air bubbles of various sizes in turbulent water. Eventually, as the wake ages, the turbulence subsides and bubbles begin to rise at rates that are determined by their sizes. These bubbles of various sizes and concentrations control the propagation of acoustic signals inside and across a wake. To further our understanding of these phenomena, a series of three continuous-wave (CW)-pulsed signals were transmitted across a wake as the wake aged. Each transmission contained a set of four 0.5-ms-long pulses. The 12 pulses ranged over frequencies from 30 to 140 kHz in 10-kHz steps. The acoustic attenuations across wakes that were due to varying bubble-size densities within the wakes were determined experimentally. From those data, estimates of the bubble densities as functions of the speed of the wake-generating ship, the wake's age, and acoustic frequency were calculated. From the bubble-density results, power-law fits and void fractions are calculated. The attenuation measurements were taken at 7.5-m intervals behind the wake-generating ship and continued for about 2 km. The experiment was run for wakes generated at ship speeds of 12- and 15-kn wakes, and the 15-kn run was repeated for consistence determination. The bubble densities were observed to have power-law forms with varying parameters with the strongest, for early ages, having an exponent of ${-}$3.6 and a void fraction of 4 $times$ 10$^{-7}$ , and with both diminishing for older wakes, as might be expected.      

A low-power hypsometer-type barometer for remote weather stations

The paper describes a low-power barometer intended for remote weather stations, but also meeting the requirements for manned stations and airports, in which the condensation temperature of carbon disulphide (CS2) is used to determine the barometric pressure(p). A heated cylindrical bulb with a re-entrant well for a thermistor through the bottom and an internal radiation shield is 1/3 filled with CS2. Helical springs assist CS2migration on wetted surfaces and allow liquid and vapor to pass one another in the small diameter exit-condenser tube. A miniature Dewar flask gives thermal insulation and a 0.01-mm beryllium-copper diaphragm transmits the external pressure. The condensation temperature is read with a simple Wheatstone bridge and dc amplifier giving an outputV_{0} = 0.5(p- 100 Pa)V. Pulsed power with the pulse length controlled by a second thermistor on the outlet tube is used for efficiency. Long term tests of a number of barometers have given power levels around 40 mW at20degC and indicated maximum drifts ofpm50Pa/year,pml0Pa/day, andpm2Pa short term.     

Digital waveform codings for ocean acoustic telemetry

M-sequence waveform coding with a single long codeword has been considered as the basis for long-range underwater acoustic telemetry for one user. (An m-sequence is a periodic, binary, linear-law maximal-length sequence. If the span of the law is n, the maximal length L-2ⁿ=1). For a given law, a single m-sequence transmits a maximum of log₂ (L) bits of source information per channel word. To increase the number of bits per word, families of m-sequences and Gold codes are considered and compared to a single m-sequence. A hypothetical idealized multipath channel with added white Gaussian noise is assumed. Coding using families of m-sequences is recommended because it requires a smaller bit-energy-to-noise ratio than other waveform codes to achieve an equivalent codeword error probability     

A physical radar cross-section model for a wind-driven sea with swell

A new spectrum model for the ocean surface is proposed. We determine the two unknown parameters in this spectrum by fitting it to radar observations. We find that this spectrum combined with two-scale scattering theory can predict much of the observed dependence of the radar cross section on radar frequency, polarization, angle of incidence, and wind velocity at incidence angles in the0deg-70degrange. The spectrum model is combined with a model for swell to examine the effect of swell on the radar cross section. We find that the effect of swell is significant for low radar frequencies (Lband) and near normal incidence but can be nearly eliminated by using higher frequencies (K_{u}band) and large angles of incidence (approx 50deg).     

Acoustic Observation of the Time Dependence of the Roughness of Sandy Seafloors

A statistical model for the time evolution of seafloor roughness due to biological activity is applied to photographic and acoustic data. In this model, the function describing small scale seafloor topography obeys a time-evolution equation with a random forcing term that creates roughness and a diffusion term that degrades roughness. When compared to acoustic data from the 1999 and 2004 Sediment Acoustics Experiments (SAX99 and SAX04), the model yields diffusivities in the range from 3.5$,times {hbox {10}} ^{-11}$ to 2.5 $,times {hbox {10}} ^{-10}~{hbox {m}}^{2} {hbox {s}} ^{-1}$ (from 10 to 80 cm$^{2} {hbox {yr}}^{-1}$), with the larger values occurring at sites where bottom-feeding fish were active. While the experimental results lend support to the model, a more focused experimental and simulation effort is required to test several assumptions intrinsic to the model.      

Active microwave measurement from space of sea-surface winds

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 of30degand larger. Signals observed were normalized to a nominal incidence angle (from values withinpm2degof 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 ofbetain 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,betavaries 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!     

High-resolution mapping of oceanic wind fields with skywave radar

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.     

Dissipation observations of drag coefficients over the open ocean

Forty-three open-ocean observations of drag coefficients observed at Argus Island Tower near Bermuda by the dissipation technique resulted in constant drag coefficients for mean horizontal wind velocities between 7.8 and10.4 m .s^{1}in good agreement with the larger near-neutral data set of DeLeonibus and Simpson [1] and the neutral data of Large and Pond [2], both of whom observed10^{3}C_{10} = 1.2whereC_{10}is the drag coefficient at l0 m. Ratios of vertical-to-horizontal wind velocity spectral densities averaged over an inertial subrange of 0.8 to 1.6 Hz ranged from 0.7 to 1.07 in agreement with the Busch and Panofsky [3] result that isotropy is approached only when the observation height is much greater than the Nyquist wavelength.     

Seasat-A satellite scatterometer instrument evaluation

The Seasat-A satellite scatterometer (SASS) was designed to measure ocean surface wind speed and direction in twenty-four (24) independent cells over a 1000-km swath. It operated in the interrupted CW mode at a frequency of 14.6 GHz with four (4) fan beam antennas and used Doppler filtering in the receiver for resolving the cells on the surface. The instrument began operating in space on July 6, 1978, and gathered normalized radar cross section (sigma^{0}) data for approximately 2290 h. The purpose of this paper is to describe the in-orbit evaluation of the SASS hardware and its compatibility with the spacecraft. It has been determined that the scatterometer operated flawlessly throughout the mission, met all design requirements, and established a good data base for geophysical processing.