Determination of instantaneous sea surface,wave heights,and ocean currents using satellite observations of the global positioning system

Abstract

Using GPS phase observations in the kinematic mode, we are able to achieve centimeter accuracy in relative three‐dimensional coordinates. This could be verified even for fast‐moving sensors in aircraft, such as airborne photogrammetric cameras, at the time of exposure. Sophisticated kinematic software has been developed resolving cycle slips and carrier‐phase ambiguities during motion. To determine the instantaneous sea surface, the GPS receiver is placed in a free‐drifting buoy with the antenna on top. Differencing the 1‐Hz observations, wave heights can be determined as well as velocity and direction of ocean (tidal) currents.

This article deals with the experiences from a test for the practical realization of this proposal. Hardware installation, software, and data analysis are described. Plans to use such an observational scenario of a GPS buoy array in the North Sea for the calibration of the radar altimeter of the European satellite ERS‐1 are presented.     

Intertidal sand‐dwelling Peracarid fauna of North Island,New Zealand

Abstract

Substrate and infauna samples were taken at four tidal levels (mean high water springs, high mid beach, low mid beach, and mean low water neaps) with a 0.0625 m² quadrat at 14 North Island beaches in New Zealand. The distributions of Peracarida (Crustacea) were correlated with sediment type, tidal height, and degree of exposure; sampling began in March 1972 and was completed in November 1973.

Substrate samples were sieved and median diameter of the particles ranged from very coarse sand of — 0.60? to very fine sand of + 3.259?. Substrates were variously sorted: ? quartile deviation ranged from 0.14? to 0.66?, skewness from ‐ 0.08? to + 0.07?.

Peracarid fauna was moderately abundant; the maximum value was 720 animals per square metre on a fully exposed beach. Highest average abundance (303 per square metre) for the 14 beaches was recorded from the mean low water neap station. Amphipoda was the dominant group (54% of all Peracarida recorded), followed by Isopoda (33%) and Cumacea (13%). Frequency of occurrence at the 56 stations was headed by Amphipoda (64%), followed by Isopoda (46%), and Cumacea (20%).

The results are compared with data from Stewart Island beaches, and the biogeographical distributions of recorded Peracarida are discussed. An unexpectedly high degree of endemism exists for a warm‐temperate region, caused by the isolation of New Zealand, which has no direct shallow water contact with tropical or cold temperate regions.     

Circulation in Tasman Bay

Direct current measurements at four locations in Tasman Bay and numerical model results are used to analyse the mean flow in Tasman Bay. The mean circulation conforms to that previously found from drift card experiments: a clockwise circulation in Golden Bay, and an anti‐clockwise flow in Tasman Bay, with a return south‐westerly flow on the coast near Nelson. Typical mean speeds are 0.02–0.05 m.s^‐1. The circular flow appears asymmetrical in both bays, with a stronger outflow along Farewell Spit in Golden Bay and near D'Urville Island in Tasman Bay.

An analytical tidal solution is used to exhibit the influence of Cook Strait in producing smaller tidal amplitudes in eastern Tasman Bay. Tidal speeds of 0.15–0.30 nus^‐1 are typical, with tidal ellipses having degenerated into north‐east, south‐west lines.     

Tidal observations on the West Coast,South Island,New Zealand

Harmonic tidal constants, calculated from sea surface elevation observations at Jackson Bay on the West Coast of the South Island, are consistent with available semi‐diurnal and diurnal tidal phase distributions. Current observations taken over a 111 day period at mid‐depth in 1505 m of water on the southern flank of the Challenger Plateau and over a 240 day period in 1430 m of water on the South Island western coast continental slope, are subject to tidal analysis. At both sites there is a component of energy flux directed across the isobaths and only at the northern site for the M2 tide is the phase consistent with a dominant progressive barotropic tide. The successive 30 day harmonic constants at the southern continental slope site exhibit a trend in the M2 tidal ellipse speed and ellipticity suggesting the presence of a regular internal tide. Superposition of ‘internal tidal’ and barotropic tidal flows, as prescribed from progressive‐ and standing‐wave elevations, to fit the observations indicates that the ‘internal tide’ is probably associated with the first baroclinic mode. At the current‐meter depths the speeds of the ‘internal tide’ for the M2 tide are about the same as the barotropic speeds, whereas, the S2 ‘internal tide’ speeds are larger than those of the barotropic tide. The consistency of the trend in ellipse parameters lends support to the theoretical progressive trapped barotropic tidal flows being a good approximation to the actual barotropic tide. Some support for the hypothesis that the S2 tide on the West Coast of New Zealand has a substantial standing wave contribution is given by the northern observations, where the ratio of the S2: M2 internal tidal ellipse current amplitudes are substantially larger than the ratio of the elevations, the internal tide being generated by across‐isobath flows.     

Broad classification of New Zealand inlets with emphasis on residence times

Thirty‐two New Zealand coastal inlets are tentatively classified into seven groups with probable similar circulation patterns, based on ratios of their physical parameters: volume, tidal compartment, entrance width, surface area, length, and average width. Eighteen of these have a predominant tidal flow, shown from their small ratio (ß < 4) of tidal compartment to total volume, and the cross‐sectional areas of their entrances are controlled by the tidal flow: Moutere, Waimea, Aotea, Whanganui, Avon‐Heathcote, Tauranga, Parengarenga, Porirua‐Pauatahanui, Kawhia, Nelson, Rangaunu, Raglan, Whangarei, Bluff, Otago, Hokianga, Manukau, and Whangaruru. The other fourteen range from long narrow sounds with probable strong vertical circulation (e.g., Pelorus Sound) to large bays with strong mean horizontal circulations (e.g., Tasman and Hawke Bays).

Examples of residence time calculated in inlets with ß > 4 are given for Tasman Bay, a bay with a mean horizontal circulation, which has a residence time of 1–3 months, and Pelorus Sound, an inlet with a vertically complex circulation, which has a residence time of about 20 d.     

M2 model of the global ocean tide derived from SEASAT altimetry

Abstract

The recovery of ocean tides from satellite altimetry, an attractive alternative to the hydrodynamical‐numerical approach, is investigated to create a global model of the M2 tide. From the outline of the difficulties faced in altimetry interpretation, we bring out general guidelines to extract the tidal information from a short span of measurements. In particular, we discuss the choice of a reference surface and the effect of the orbit error and tidal aliasing on the recovery. From space‐time harmonic analyses of twenty‐four days of SEASAT altimetry, we derive M2 solutions expanded into series of surface spherical harmonics for the Indian, Pacific, and Atlantic Oceans separately and for the world ocean. The M2 cotidal maps we obtain feature qualitatively realistic tidal patterns and are consistent with the deep sea gages data. We then cast the bases to estimate the error budget of the altimeter tide solutions. The M2 fundamental harmonics involved in tidal energetics are evaluated from a spectral convolution of the global solutions with the ocean function and are used to test and discuss our results.

The present tidal recoveries must still be considered as preliminary trials because they are strongly dependent on the limits of the SEASAT mission and subject to improvements via an updating of our analysis procedure. But the altimeter approach of the open ocean tide modelling proves to be efficient, and the objective—to produce highly reliable models with the support of the next generation of satellite altimeters—is reasonably optimistic.     

An improved method for mapping tidal waterways based on remotely sensed waterlines: A case study in the Yellow River Delta,China

Abstract

Tidal waterways perform as the paths through which seawater invades. Their spatial-temporal variation with the shift in Yellow River’s route requires the accurate measurement of their status. Visual interpretation for delineating tidal waterways is inefficient due to a substantial amount of work. Buffer analysis provides an alternative to visual interpretation. However, it is difficult to use the buffer distance threshold to identify tidal waterways from other freshwater bodies. In this study, we present a straightforward method for mapping tidal waterways. First, we adopted the normalized difference water body index (NDWI) to extract water bodies. Waterlines were subsequently delineated based on a morphological opening filter with a kernel of 9?×?9. Finally, tidal waterways were mapped based on the proposed topological relation in ArcGIS. We showed the utility of this approach by mapping tidal waterways in the Yellow River Delta, China. The proposed method enables tidal waterways be mapped precisely and was replicable and universal in other similar studies.     

Variations of the age of tides in the global oceans

Abstract

Earlier studies on the age of tide dealt mostly with the age of the semi‐diurnal tide in the Atlantic and Pacific Oceans. In these studies, the variations of the age of tide were determined making use of recorded tidal data up to and including the 1960s. In the present study, all available tidal data till the mid 1980s are utilized and the computations were done for the four global oceans: Atlantic, Pacific, Indian, and Arctic. Also, in addition to the age of the semi‐diurnal tide, the age of the parallax and the age of the diurnal tide were determined. The distribution patterns for the positive and negative ages for the semi‐diurnal tide, parallax, and diurnal tide were related whenever possible with the tidal amphidromic point locations and the amplitude ratios S₂/M₂, N₂/M₂, and O₁/K₁.     

An analysis and interpretation of the current data collected in the strait of Juan de Fuca in 1973

Abstract

We evaluate a set of current measurements done in a section of the Strait of Juan de Fuca. The flow is of estuarine character, the upper layer flow usually being directed seaward. The RMS value of steady current exceeds its mean value appreciably in the upper layer; it also exceeds the mean near the bottom. The near‐surface currents do change their direction on occasions and can run landward for over five consecutive days, especially in the southern part of the channel. The lower layer flow (landward) and the upper layer flow (seaward) varied in magnitude from 90 to 160 thousand m³/sec, and their fluctuations were in phase; their difference, the net flow, is of the order of 5% to 10% of these flows and could not be calculated with any confidence. Tidal motion is barotropic in the section, with some deformation in the vertical caused by bottom friction and internal stresses. The M₂ tide in the system Juan de Fuca‐Georgia Strait can be represented by a standing Kelvin wave influenced by friction. The K₁ tide can also be represented by a standing Kelvin wave if some leakage is allowed in the northern end of Georgia Strait. Topographic effects mask the Coriolis influence on the intensity of tidal currents.     

Tidal estimation in the pacific with application to SEASAT altimetry

Abstract

The techniques for computing the eigenfunctions of the velocity potential (Proudman functions) set out in Sanchez et al. (1986) in relation to the Atlantic‐Indian Ocean are here applied to the Pacific Ocean, using a 6° × 6° grid of 510 points (455 points for the associated stream functions). Normal modes are computed from the first 150 Proudman functions and have natural periods from 43.9 hours downwards. Tidal syntheses are derived from these modes by direct application of the (frictionless) dynamic equations and by least‐squares fitting of Proudman functions to the dynamically interpolated tide‐gauge data of Schwiderski (1983). The modes contributing most energy to the principal harmonic tidal constituents are different in the two computations; their natural periods are typically in the range of 9–16 hours for semidiurnal, 14–43 hours for diurnal tides. The RMS of fit for Proudman functions is in all cases better than the corresponding value for the same number of spherical harmonics.

Before fitting the Proudman functions to the altimetry from the 3‐day repeat cycle of Seasat, the data are processed by novel methods. The geoid component is eliminated by taking collinear differences at a fixed time‐lag of two repeat cycles. Orbit errors are reduced by extracting the 1 rev^?1 component at every ascending node; this component varies slowly and nonlinearly in time. The spatial fitting process includes M₂ and O₁ frequencies, both of which emerge with significant and realistic tidal mapping, but residual noise in the data limits the number of Proudman functions to about 50–60 before showing signs of “over‐fitting.”; Fitting the same data by spherical harmonics gives marginally lower predicted variance for the same number of parameters.     

Ocean tides for satellite geodesy

Abstract

Spherical harmonic tidal solutions have been obtained at the frequencies of the 32 largest luni‐solar tides using prior theory of the author. That theory was developed for turbulent, nonglobal, self‐gravitating, and loading oceans possessing realistic bathymetry and linearized bottom friction; the oceans satisfy no‐flow boundary conditions at coastlines. In this theory the eddy viscosity and bottom drag coefficients are treated as spatially uniform. Comparison of the predicted degree‐2 components of the Mf, PI, and M2 tides with those from numerical and satellite‐based tide models allows the ocean friction parameters to be estimated at long and short periods. Using the 32 tide solutions, the frequency dependence of tidal admittance is investigated, and the validity of sideband tide models used in satellite orbit analysis is examined. The implications of admittance variability for oceanic resonances are also explored. By extending the theory to include a second constraint derived from tide observations or data‐constrained tide models, it is possible to assess those models from a fluid dynamic perspective. One general conclusion from such exercises is that the large higher‐degree admittances of current short‐period tide models are dynamically incompatible with their degree‐2 admittances. Eventually it may prove possible to produce dynamically sound, observationally consistent tide models by combining the author's tide theory with satellite orbit determination.     

虾池纳潮期日本刺沙蚕幼虫数量及其沉降的研究

于1992年2月27日－5月30日在文登市高岛盐场养虾场，对日本刺沙蚕（卵、各期胚胎和幼虫）的纳潮数量和幼虫的沉降进行现场调查和实验研究。结果表明，对养虾生产有意义的纳潮期有3个。3月上旬的新月潮，持续12d，数量为（25－50）×103个／m3，主要组成是受精卵、各期胚胎和担轮幼虫。3月甲旬的满月潮持续7d，数量为（2－5）×103个／m3。4月上旬的新月潮持续8d，数量为（2－3．5）×103个／m3。纳潮量与潮汐关系密切，但与平均潮高无显著的相关。各潮期的纳潮数量比应是4：4：2。对16个纳潮虾池测试的平均沉降量为4492个／m2。据现场调查和实验研究，日本刺沙蚕幼虫的沉降期可划为暂时沉降（5－6刚节）和变态沉降（7—10刚节）。出现暂时沉降（4月15日以后），便可执行纳潮后的排水等虾池早期管理。纳潮的定量监测方法简单、快速和准确，可用来指导虾池的纳潮。     

Influence of delta growth on paleo‐tidal flow: Fraser River delta,British Columbia—Part 2: Tidal model

Abstract

The paleo‐tidal flows in the waters in the vicinity of Point Roberts and the Fraser River delta were numerically simulated through the development of a coarse grid model (2 km mesh size) and a fine grid model (2/3 km mesh size). The basic hydrodynamic equations, the numerical grid layout, and the finite‐difference forms are given. Special attention was given to transferring the boundary grid data generated from coarse grid model to the boundaries of the fine grid model. Diagrams are presented to show that the fine grid model yields much superior results in the sense of providing a greater amount of detail, in the current patterns and the eddy structure, than is provided by the coarse grid model, in the application to estimating sedimentary patterns.     

A numerical tidal and storm surge model of the North Sea

Abstract

A two‐dimensional, vertically integrated, numerical model has been used to compute the M₂ and S₂ tidal components for the North Sea. The model has also been applied for simulation of two storm surge situations. The results of the computations are compared with sea level observations from coastal stations, and for one of the simulations a comparison with current measurements is also performed.     

Intertidal sand‐dwelling Peracarid fauna of Stewart Island

Abstract

The distributions of infaunal Peracarida (Crustacea) and their correlation with sediment type, tidal height, and degree of exposure were studied in winter (June) at five beaches on Stewart Island, New Zealand. The beaches were selected lo cover a range of exposures to wind and wave action and substrate sorting. Substrate and infauna samples were taken at four tidal levels from each, with a 0.0625 m² quadrat.

Sieve separation and statistical analysis of the substrate samples indicated predominantly sand‐sized particles from all beaches, with median diameters in the range +1.52 to +2.92 ? (phi) units. Substrates were well sorted throughout the size range: ? quartile deviation ranged from 0.26 to 0.71, skewness from —0.18 to +0.07 ?.

Peracarid fauna was generally abundant, with a maximum of 29 136 per m²sampled in a more sheltered beach. Cumacea was the most abundant group, followed by Amphipoda, Isopoda, and Tanaidacea; dominance followed a similar sequence, being 78%, 19%, 2% and 1% respectively. Frequency of occurrence at the 19 stations was headed by Amphipoda (100%), with Isopoda 53%, Cumacea 32% and Tanaidacea 11%.     

Sediment transport near the Tauranga entrance to Tauranga Harbour

Abstract

Sediment transport at the Tauranga Entrance was studied in relation to tidal currents and waves. Bedforms resulting from tidal flow were investigated with scuba divers and echo‐soundings. The alignment and scale of bedforms indicated the direction and approximate rate of sediment transport. Sediment transport was measured directly using sediment traps, and results were compared with rates calculated by another method. Maximum sediment transport rates of 20 000–30 000 g.m^?1 per half tidal cycle occur near the inlet gorge, but rates vary considerably in time and space, depending mainly upon power of tidal currents. A model of sediment transport for this inlet has been evolved based on tidal flow streamlines, bedform features, and the measured and calculated rates of sediment transport.     

胶州湾水交换及湾口潮余流特征的数值研究

利用基于普林斯顿海洋模式建立的胶州湾及临近海域潮汐潮流数值模型,结合胶州湾口走航式声学多普勒海流剖面仪(ADCP)测流资料,研究了胶州湾口的潮(余)流特征,并在潮流模型的基础上耦合建立了水质模块,模拟了胶州湾的水交换过程。考虑M2,S2,K1,O1,M4和MS4六个主要分潮,胶州湾口潮流场的模拟与ADCP观测数据吻合较好。外湾口水道上的潮流非常强,大潮期间观测到201 cm/s的峰值流速。团岛岬角的两侧分别存在一个流向相反的余流涡旋,两涡旋在团岛附近辐合,形成了57 cm/s的离岸强余流。整个胶州湾平均水体存留时间为71 d,平均半交换时间为25 d。胶州湾水体交换能力在空间分布上有很大差异:湾口海域最强,向湾顶逐渐减弱。湾内存在两个弱交换区,分别位于湾的西-西南部和东北端,水体存留时间多超过80 d,湾西局部水域最长达120 d,而半交换时间也大多超过40 d。潮流场的结构、强度,以及与湾口距离的远近是造成湾内水交换能力空间差异的主要原因。     

Atlas of ocean tidal charts and maps,Part I: The semidiurnal principal lunar tide M2

Abstract

In this paper the author presents the NSWC ocean tide model of the semidiurnal principal lunar (M₂) tide in an atlas of ocean tidal charts and maps. The model is the computer result of a unique combination of mathematical and empirical techniques, which was introduced, extensively tested, and evaluated by Schwiderski (1978a, 1980a, b, 1983e). The computed M₂ amplitudes and phases are tabulated along with all specially labeled empirical input data on a 1° × 1 ° grid system in 42° × 71° overlapping charts covering the whole oceanic globe. Corresponding global and arctic corange and cotidal maps are included to provide a quick overview of the major tidal phenomena. Significant qualitative and quantitative features are explained and discussed for proper application. In particular, the charted harmonic constants may be used to compute instantaneous M₂ ocean tides with an accuracy of better than 5 cm any time and anywhere in the open oceans. Limitations of this accuracy in coastal waters and border seas are mentioned.

The following four sections of this paper deal with brief reviews, detailed evaluations, and simple improvements of general and special applications of the NSWC ocean tide model. In spite of the numerous and diverse applications with potential possibilities of erroneous interpretations, the results are gratifying without exceptions. For instance, it is concluded that the computed low‐degree spherical harmonic coefficients of the M₂ ocean tide model agree with recent empirical satellite solutions as closely as one could wish for within the elaborated nonmodel error bounds. Detailed computations of all significant tidal energy terms produced the following noteworthy results: The rate of supplied tidal energy of 3.50Z10¹² Watt matches Cartwright's (1977) estimate of 3.5Z10¹² Watt. The rate of energy loss by bottom friction and displacement over the shelves is 1.50Z10¹² Watt, which fits into Miller's (1966) estimated range of (1.4–1.7)Z10¹² Watt, with a clear bias toward his preferred lower bound. Perhaps most remarkably, the computed range (0.41–0.60)Z10¹² Watt for the rate of deep bottom friction work done by the unresolved fluctuating (internal or baroclinic) currents contains in its center Munk's (1966) estimate of 0.5Z10¹² Watt and lies safely below Wunsch's (1975) extreme upper bound of 0.7Z10¹² Watt, which both authors derived for the rate of energy needed to sustain the internal tidal circulations. As is commonly believed, the results substantiate the fact that the total rate of ocean eddy dissipation (into heat) by the averaged (surface or barotropic) currents and their fluctuating comotions is negligible within three significant figures. Finally, the total tidal energy budget of the oceans is perfectly balanced in realistic terms. Budget deficits in earlier tide models were traced to the following tacit assumptions: The ocean bottom tide is doing positive work on the oceans against the ocean tide. In fact, the bottom displacement work by the ocean tide against the bottom tide is an energy loss at the rate of 1.64Z10¹² Watt. The transfer of G. I. Taylor's quadratic bottom friction term from the Irish Sea to the global oceans without accounting for major differences in area resolution scales is directly responsible for significant budget deficits in semiempirical estimates. In contrast, the hydrodynamically more consistent and realistic linear law of bottom friction encountered no serious transplantation difficulties.     

Grain size parameters and sedimentary structures of a last Interglacial marine sand body,near Westport,New Zealand

Summary

Reids Rise is a remnant of a marine sand body that accumulated in the inner neritic zone of the continental shelf south‐west of Westport during the Last Interglacial. The sand body is notable for its spectacular sedimentary structures and consists of an upper unit that is characterised by trough cross‐lamination, locally forming mesoscopic ridges, and a lower unit that is characterised by horizontal lamination. The sand body is underlain by gravels of probable alluvial origin.

The trough cross‐laminated sets of the upper unit dip off near‐symmetrical ridges that probably formed as subaqueous bars. The dip azimuths of the cross‐laminae have a polymodal distribution with two bimodal maxima, one almost perpendicular to, and the second roughly parallel to the shoreline formed during the Last Interglacial. Magnitude of dip varies from horizontal to over 40°.

The sediment is clean, fine sand composed predominantly of angular grains. Sample to sample variation in grain size statistical parameters is small. The most notable feature is the extremely good sorting of the sand. Inclusive graphic standard deviation values range over 0.17–0.24? with 0.20? the modal value.

The mineralogy of the sand points to two main source areas, the Alpine metamorphic rocks to the south and south‐east, and the plutonic rocks of the Paparoa Range immediately east and south‐east of the study area.

The stratigraphic sequence is interpreted as being the product of deposition in a high energy, wave‐, tidal‐current‐, and longshore‐current‐dominated shallow neritic zone on an open coast during a transgressive cycle.