Shipboard Acoustic Doppler Current Profiler Research Articles

The front on the Northern Flank of Georges Bank in spring: 1. Tidal and subtidal variability

During March–April 1999, 2 weeks of undulating CTD and shipboard acoustic Doppler current profiler surveys revealed the variability of the intense internal tide on the northern edge of Georges Bank. The nature of the internal tide was modulated by episodic surface intrusions of cool, fresh Scotian Shelf Water (SSW), stratifying the otherwise vertically well‐mixed outer bank. The introduction of SSW created a system analogous to that in summer, when the outer bank is thermally stratified and separated from well‐mixed regions by a tidal mixing front. During SSW intrusions, internal tidal behavior is characterized by tidal advection that is significantly faster than internal wave propagation speeds on the bank (supercritical flow) and slower than the lowest internal modes in deeper water to the north (subcritical flow). A large‐amplitude internal lee wave develops over the slope during off‐bank tidal flow. This stalled energy is released to propagate on‐bank as a high‐frequency internal wave when the tide reverses. It is suggested, by analogy with the summer case, that a portion of this energy is used by mixing at the on‐bank limit of SSW. The presence of SSW thus modifies the internal tidal response, enabling a mechanism that contributes to its assimilation with ambient bank water. The off‐bank‐propagating internal tide is dominated by a mode 1 internal wave at the M2 frequency, with cross‐bank velocities comparable to the barotropic tide.

Characterization of the mean and seasonal flow regime on Georges Bank from shipboard acoustic Doppler current profiler data

From 1995 through 1999 the Northwest Atlantic GLOBEC program sponsored over 100 oceanographic cruises to Georges Bank and the surrounding waters. About 12,000 hours of shipboard acoustic Doppler current profiler (ADCP) data were collected during the program on more than 80 of these cruises, forming one of the most extensive three‐dimensional current measurement data sets ever collected. These data have been used here to examine the seasonal variability of the bank’s barotropic flow field. The variability has been described using the 5 years of ADCP observations to derive both small area statistics and seasonal least squares fits, and a more flexible description based upon interpolating functions describing the spatial and temporal dependence of the bank‐wide stream functions. Both methods show the seasonal acceleration of the bank gyre in the summer with larger velocities along the north flank and smaller seasonal variations over the southern flank. The stream functions show the seasonal change from a winter condition with on‐bank flow from the northwest through to the acceleration and ecologically critical closure of the anticyclonic Georges Bank gyre during the summer. On the basis of annual and semiannual decompositions of the seasonal progression, the closure of the gyre in the area of the Great South Channel appears to occur by June, first in the shallow waters and then progressively southward, but it does not extend as far as the middle of the southern flank. A series of monthly Lagrangian drift predictions based upon the stream function analysis, suggest that the observed seasonal movement of the larval fish from their spawning grounds over the Northeast Peak in March, through to their late summer concentration over the central bank, can generally be ascribed to the seasonal barotropic flow over the inner portion of the bank. The analysis also showed that those larvae found over the outer part of the bank are, almost certainly, doomed to be swept out of the banks’ ecosystem, to either the west or south.

Surveying the Upper Ocean with the Ocean Surveyor: A New Phased Array Doppler Current Profiler

Abstract A new shipboard current profiler, a 75-kHz ocean surveyor, was operationally used during two research cruises in the tropical Atlantic and the subpolar North Atlantic, respectively. Here, a report is presented on the first experience with this instrument in two very different current regimes, in the Tropics with large vertical shears, and in the subpolar regime with mainly barotropic flow. The ocean surveyor continuously measured currents in the upper ocean from near the surface to about 500–700-m depth. The measurement range showed a dependence on the regional and temporal variations of scattering particles and on the intensity of swell and wind waves. Statistical comparisons are performed with on-station lowered acoustic Doppler current profiler (LADCP) profiles and underway measurements by classic shipboard acoustic Doppler current profiler (ADCP) measurements. Accuracy estimates for hourly averaged ocean surveyor currents result in errors of about 1 cm s–1 for on-station data and of 2–4 cm s–...

Seasonal variation of volume transport in the major inflow region of the Taiwan Strait: the Penghu Channel

Abstract Eight cruises of current measurements along a zonal transect (∼31.84 km) across the major inflow region of the Taiwan Strait, the Penghu Channel, were carried out using the shipboard Acoustic Doppler Current Profiler during 1999–2001. On each cruise, the measurement was repeated twice along the transect with a time lag of 6 h and 12 min, and the repeated data were averaged to eliminate the dominant semidiurnal tidal currents. Velocities, after removing semidiurnal tides, suggest a strong northward flow in the channel, with a speed of about 100 cm/s in the upper 50 m in summer. The northward flow becomes much weaker in winter. The calculated throughflow transports vary seasonally and are correlated with the change of the East Asia monsoon. The estimated transport is around 0 during the peak northeast monsoon in winter, increases from 0.5 to 1 Sv (1 Sv=106 m3/s) as the northeast monsoon weakens in spring, peaks to 1.5 Sv at the end of southwest monsoon in summer, and decreases rapidly from 1.5 to 0 Sv when the northeast monsoon intensifies in fall. The error, mostly induced by unfiltered diurnal tidal currents, is estimated to be±0.20 Sv in the transport calculation.

Upper-ocean currents around Taiwan

Abstract Current velocity, measured by Shipboard Acoustic Doppler Current Profiler (Sb-ADCP) during 1991–2000, was used to study the upper-ocean ( The composite and moored currents revealed a branch of the Kuroshio that intruded steadily and persistently into the South China Sea. Part of the intruded Kuroshio flowed out of the South China Sea through the northern Luzon Strait and re-united with the main stream Kuroshio. The Kuroshio had two velocity maximum cores southeast of Taiwan, but gradually combined into one as the Kuroshio flowed north. The Kuroshio was deflected by the I-Lan Ridge east of Taiwan and the zonal-running shelf break northeast of Taiwan. At the shelf break, the Kuroshio split, with one branch intruding onto the shelf. West of the Luzon Strait, the Kuroshio intruded into the South China Sea. Some water flowed northward into the Taiwan Strait and re-joined the Kuroshio. Currents in the Taiwan Strait flowed primarily in a northward direction, except for the southward current near the coast of Mainland China. North of the Taiwan Strait, a branch of the northward flow followed the northern coast of Taiwan to join the Kuroshio. The composite current varied consistently from season to season. There was generally poor correlation between currents and local winds, especially in the deep-water regime. Remote forces were important in the currents around Taiwan.

Dynamic Structure of the Kuroshio South of Kyushu in Relation to the Kuroshio Path Variations

The variation of velocity and potential vorticity (PV) of the Kuroshio at the PN line in the East China Sea and the TK line across the Tokara Strait were examined in relation to the path variations of the Kuroshio in the southern region of Japan, using quarterly data from a conductivity-temperature-depth profiler and a shipboard acoustic Doppler current profiler during 1987–97. At the PN line the Kuroshio has a single stable current core located over the continental slope and a significant maximum of PV located just onshore of the current axis in the middle part of the main pycnocline. On the other hand, the Kuroshio at the TK line has double current cores over the two gaps in the Tokara Strait; the northern core has a much larger velocity than the southern core on average during periods of the large meander of the Kuroshio, while the difference in strength between the double cores is small during the non-large-meander (NLM) period. At the TK line, PV in the middle pycnocline is variable; it is small and nearly uniform throughout the section for 40% of the total observations, while it has a significant maximum near the northern core for 30% and two maxima corresponding to the double current cores for 23%. The small, nearly uniform PV occurs predominantly during the NLM period, and is closely related to the generation of the small meander of the Kuroshio southeast of Kyushu.

Detailed structure of the Subtropical Front over Chatham Rise, east of New Zealand

A detailed description of the Subtropical Front (STF) over Chatham Rise is presented. Information is provided by conductivity‐temperature‐depth (CTD) profiler temperature and salinity transects, high‐resolution (3–4 km spacing), near‐synoptic expendable bathythermograph surveys, shipboard acoustic Doppler current profiler measurements, a 160 km constant depth undulator tow, and satellite SST measurements in austral autumn and spring (April and October) near 178°30′E. Detailed sections across the front reveal that the STF can be divided into northern and southern fronts (NSTF and SSTF) separated by a frontal zone, consistent with observations of the STF elsewhere. Comparison with a western CTD section along 176°E reveals that this structure breaks down close to the New Zealand landmass. The dominant impact of seasonally is the formation and decay of a seasonal thermocline of fairly constant depth over the entire region. Velocity measurements indicate eastward zonal flows on the northern and southern flanks of Chatham Rise. The flow over Chatham Rise is complicated by stirring processes but has a mean southward trend consistent with the less dense, warm, salty subtropical water (STW) overriding the more dense, cold, fresh subantarctic water (SAW) to the south. Horizontal‐length‐scale analyses of the temperature field for a constant depth tow at 21 m indicate a k−2.4 spectral falloff with no proof of preferential length scales. The temperature salinity gradients are largely density compensated in this mixed layer tow. The horizontal temperature standard deviation shows subsurface maxima concentrated at the locations of the NSTF and SSTF. Vertical length scales vary across the front, with large scales (80–100 m) in the STW north of the STF and smaller scales (20–40 m) in the subtropical frontal zone and SAW to the south. The surface vertical length scales are dominated by the presence of a seasonal thermocline.

The Cross-Stream Potential Vorticity Front and Its Role in Meander-Induced Exchange in the Gulf Stream

Abstract The potential vorticity (PV) front observed in the upper thermocline at the northern edge of the Gulf Stream has been thought of as an inhibitor to lateral motion of parcels on isopycnals. The role of the PV front in relation to lateral motion and cross-stream exchange was investigated by monitoring the evolving PV field in the vicinity of Lagrangian parcels at the northern edge of the stream. The observational study involved shipboard acoustic Doppler current profiler (ADCP) and conductivity–temperature–depth surveys to sample the velocity and density fields around water parcels as they flowed through meanders. The observations reveal that the PV field in the vicinity of parcels moves laterally across the stream and evolves as parcels negotiate meander crests and troughs, allowing parcels to move across the stream without changing their Lagrangian PV. This lateral motion of the PV front suggests that it is more a response to than an inhibitor of the lateral motion of parcels in the meanders. The...

Absolute geostrophic velocity within the Subantarctic Front in the Pacific Ocean

Velocity measurements from a shipboard acoustic Doppler current profiler (ADCP) are used as a reference for geostrophic current calculations on six sections across the Subantarctic Front (SAF) in the Pacific Ocean. The resulting cross‐track velocity estimates near the bottom range from 4 to 10 cm s−1 to the east in the eastward jet at the SAF; in adjacent regions of westward surface flow, the near‐bottom velocity is usually to the west. On one section where simultaneous lowered ADCP velocity profiles are available, they confirm the results from the shipboard ADCP. Annual mean velocity sections from the Parallel Ocean Program numerical model also show near‐bottom velocities exceeding 5 cm s−1, with the same tendency for the zonal velocity component near the bottom to match the direction of the surface jets. Transport across the entire Antarctic Circumpolar Current (ACC) cannot be estimated accurately from ADCP‐referenced geostrophic sections because even a very small cross‐track bias integrates to a large error. A preliminary look at the 1992 model transport stream function shows that the effect of bottom‐referencing varies from section to section; it can cause 40‐Sv recirculations to be missed, and can cause net transport to be underestimated or overestimated by O (30 Sv).

Mean Structure and Dynamics of the Shelfbreak Jet in the Middle Atlantic Bight during Fall and Winter*

Using a collection of high-resolution shipboard acoustic Doppler current profiler (ADCP) velocity sections that cross the Middle Atlantic Bight shelfbreak jet near 70°W, the mean structure of the frontal jet is described and the dominant modes of variability of the jet are examined. A mean section is constructed in a translating coordinate frame whose origin tracks the instantaneous position of the core of the jet, thereby minimizing variability associated with the lateral meandering of the current. The mean jet so constructed extends to the bottom, tilting onshore with depth, with near-bottom flow exceeding 0.10 m s−1. The corresponding cross-stream flow reveals a clear pattern of convergence that extends along the tilted axis of the jet, with enhanced convergence both near the surface and near the bottom. This convergence is largely attributed to the locally convergent topography and is shown to drive an ageostrophic circulation dominated by downwelling at, and offshore of, the jet core. The collection of ADCP sections also suggests a previously undetected mode of variability, whereby the jet systematically fluctuates between a convergent, bottom-reaching state and a surface-trapped state with weaker cross-stream velocities. This variability is associated with significant variations in the southwestward transport of the jet and does not seem to be related to simple meandering of the current.

On the skewness of vorticity in the upper ocean

Conservation of potential vorticity suggests that when the magnitude of relative vorticity approaches the planetary vorticity, cyclonic vorticity should be preferred. Small‐scale, 3‐km relative vorticity is examined using shipboard Acoustic Doppler Current Profiler (ADCP) velocity measurements and P‐code Global Positioning System (GPS) navigation from a cruise in the North Pacific. The skewness of relative vorticity in the mixed layer is positive, consistent with theory. The probability density function of vorticity reveals that positive skewness occurs because large vorticities are more likely to be cyclonic than anticyclonic. The skewness is shown to be significant relative to measurement and random errors. In contrast, skewness in the thermocline has no preferred sign. The skewness peaks at the surface and decays to zero at the base of the mixed layer.

Lateral dispersion over the continental shelf: Analysis of dye release experiments

Lateral dispersion over the continental shelf was examined using dye studies performed as a part of the Coastal Mixing and Optics experiment. Four experiments performed at intermediate depths, each lasting 2.5–5 days, were examined. In some cases the dye patches remained fairly homogeneous both vertically and horizontally throughout an experiment. In other cases, significant patchiness was observed on scales ranging from 2 to 10 m vertically and a few hundred meters to a few kilometers horizontally. The observations showed that the dye distributions were significantly influenced by shearing and straining on scales of 5–10 m in the vertical and 1–10 km in the horizontal. Superimposed on these larger‐scale distortions were simultaneous increases in the horizontal second moments of the dye patches, with corresponding horizontal diffusivities based on a Fickian diffusion model of 0.3–4.9 m2 s−1. Analysis of the dye data in concert with shear estimates from shipboard acoustic Doppler current profiler observations showed that the existing paradigms of shear dispersion and dispersion by interleaving water masses cannot account for the observed diffusive spreading of the dye patches. This result suggests that some other mechanisms provided an additional diffusivity of order 0.2–4.6 m2 s−1. An alternative mechanism, dispersion by vortical motions caused by the relaxation of diapycnal mixing events, may explain the observed dispersion in some cases.

Currents in the Celebes and Maluku Seas, February 1999

Upper ocean currents in the Celebes Sea, the northern Maluku Sea, and the adjacent region to the east were measured during February 1999 using a shipboard acoustic Doppler current profiler (ADCP) on R/V Kaiyo. The new data provide the first quasisynoptic observations of the circulation within the central Celebes Sea. South of Mindanao, the Mindanao Current split into three branches. Only the westernmost branch entered the Celebes Sea, where part retroflected around a cyclonic eddy in the western Celebes Sea and part took a shorter route through the eastern basin before the two paths joined and returned to the Pacific. The remainder of the Celebes Sea branch of the Mindanao Current continued toward Makassar Strait. In the central and eastern Celebes Sea, the circulation pattern below 150 m differed substantially from that at the surface. The strongest feature was a northward flow that exceeded 60 cm s−1 near 230 m in the center of the basin, where shallower currents were weak. A northward transport of 6 Sv in the top 300 m was measured across 1.75°N in the Maluku Sea, carrying Indonesian Seas waters northeast toward the Pacific. Water properties and other current sections in the northern Maluku Sea confirm shallow northeastward flow.

Flow structure and seasonalityin the Hebridean slope current

The intensity, structure and variability of the slope current have been determined from 16 months of observations with Acoustic Doppler Current Profilers (ADCP) and conventional current meters on a cross-slope section at the Hebridean shelf edge during the Shelf Edge Study (SES) programme. After removal of the tidal signals, the mean flow over the upper slope is found to be closely parallel to the topography with speeds of ≈ 20 cm·s –1. The flow extends down to a depth of 500 m and is predominantly barotropic, especially in winter when the flow is practically uniform between 350 m and the surface. In summer, there is a significant baroclinic component with a pronounced maximum in current at a depth of about 200 m but more than 80% of the kinetic energy is in the barotropic component. Flow in the core of the current is highly persistent with the Neumann’s steadiness St > 0.8 in summer. In winter the flow is generally more energetic and variable and extends onto the adjacent shelf. The cross-slope profile of sea surface elevation, computed from the mean barotropic currents, shows a consistent relation to seabed topography through the seasonal cycle. Long-term averages of the cross-slope components are generally small (≈ 2 cm·s –1) with some indication of persistent down-slope flow in the bottom Ekman layer. Measurements with shipboard ADCP on sections at intervals along the slope show a high degree of continuity in the structure of the flow. The core of the flow appears to be related to a weak positive salinity anomaly and a depression of the 9.5 °C isotherm near the shelf, but there is no strong correlation between the core of the slope-current and the core of the salinity anomaly. It is proposed that this may be due to differences in the cross-stream diffusion of salt and momentum which have different boundary conditions at the slope. The observed cross-stream structure of the current supports the hypothesis that JEBAR is the principal forcing mechanism but the result cannot be regarded as conclusive since a uniform potential vorticity model of the flow produces a similar cross-sectional structure of the current.

Northern Arabian Sea variability from TOPEX/Poseidon altimetry data: an extension of the US JGOFS/ONR shipboard ADCP study

Sea-level anomalies (SLA) derived from the TOPEX/Poseidon (T/P) altimetry and inferred geostrophic currents within the northern Arabian Sea were examined for the period from March 1993 through November 1996. The primary objective of this study was to confirm and extend our understanding of the upper-ocean mesoscale variability observed in the shipboard acoustic Doppler current profiler (ADCP) data collected during the US JGOFS/ONR Arabian Sea Expedition (September 1994–January 1996). The accuracy of the T/P altimetry data (∼3 cm rms) results in an uncertainty in the altimeter-derived velocities comparable to the ADCP measurement error. Thus the T/P data provide a reasonable method for extending studies of the mesoscale dynamics for the region. Comparison of the T/P-derived geostrophic velocities with concurrent ADCP data showed good correlation, with an r 2 between 0.7 and 0.9 and rms differences of 10 cm s −1. The T/P data confirm both the overall spatial and seasonal current patterns observed by the ADCP. The monsoonally averaged rms sea-level anomalies indicate a high degree of intraseasonal variation due to the generation of squirts, jets and eddies all along the coast, the variability of which increases in both intensity and areal extent during the Southwest Monsoon. The SLA data indicate a much reduced degree of variability over the shelf. The SLA-derived eddy kinetic energy (EKE) fields are consistent with those derived earlier from the ADCP data in both distribution and magnitude. There is a large increase in EKE to the west and southwest and to a lesser extent to the south and a large area of relatively reduced eddy activity over much of the eastern and northern Arabian Sea. The area of reduced eddy activity coincides with the location of the most intense portions of the oxygen minimum zone found in the northern Arabian Sea. The spatial scales of the eddies responsible for the EKE distribution over the study area range between 200 and 500 km in the nearshore region, decreasing to 100–200 km offshore. While there is significant energy variability in annual and semi-annual time scales, a substantial portion of the energy is found between 50 and 120 days, and the relative importance of this frequency band increases offshore. Spectra indicate a distinct break in the frequency content of the eddy field at about 15°N, with little energy at less than annual periods south of this latitude.

Nutrient Fluxes through the Taiwan Strait in Spring and Summer 1999

Transports of water and nutrients (N and P) through the Taiwan Strait were calculated using chemical hydrography and currents observed in May and August 1999. The surveys were conducted along a transect across the strait in the middle section. The velocity fields were determined by phase-averaging currents measured using shipboard Acoustic Doppler Current Profiler (ADCP) on two repeats, which were separated by 1.5 cycles of the dominant M2 tide. Nutrient distributions were also derived from phase-averaged data. The volume transports determined from the two surveys were similar (2.0 Sv and 2.2 Sv, respectively). By contrast, the nutrient fluxes obtained in August (1.82 kmol N/s and 0.34 kmol P/s) were significantly higher than those in May (0.96 kmol N/s and 0.16 kmol P/s), apparently due to coastal upwelling under southwest monsoon in summer. The rather low N/P ratios (6.0 and 5.4 by atoms) of the nutrient fluxes were attributed to the widespread N-deficiency in the upper water column of the North Pacific. The nutrient fluxes were fed mainly through a meridional deep channel off southwest Taiwan. The nutrient contributions from the Taiwan Strait to the East China Sea in spring and summer are comparable to the total riverine contributions from the Changjiang (also know as the Yangtze River) and other smaller rivers for nitrogen, but 8–17 times larger than the latter for phosphate. Therefore, the Taiwan Strait inflow may serve as an important supplement for the P-limiting condition in the huge coastal plume in the East China Sea.

Gravity current structure of the Chesapeake Bay outflow plume

Measurements made across the edge of the Chesapeake Bay outflow plume in September 1996 are examined for evidence of the frontal head structure expected for a buoyant gravity current. Shipboard acoustic Doppler current profiler and hydrographic data from two distinct, 2‐hour‐long sets of frontal transects are analyzed. One set of observations was acquired just south of the bay mouth (near Cape Henry, Virginia) during late flood tide in water depth of 8 m. These measurements show a nearly steady frontal structure and a frontal head that is approximately 5‐m deep and 20‐m wide. The second data set was acquired about 20‐km southeast of the bay mouth, where the plume bulges horizontally outward over the continental shelf. These measurements show a 9‐m‐deep frontal head (in water depth of 18 m) that ultimately dissipates during early flood tide. In both sets of observations, relative inflow of plume water into the frontal head is confined to a shallow surface layer estimated to be no more than about 2‐m deep. Referenced to this layer, frontal propagation is supercritical (Froude number greater than 1). Also measured was an expected sinking motion (of the order of 3 cm/s) along the front. Overall, the results are consistent with previous measurements made across smaller buoyant plumes and in the laboratory, and they are compatible with the use of fixed values of Froude number and entrainment parameter in two‐layer plume models. Additional study of the plume front during ebb tide is recommended.

Bottom Boundary Layer Structure and Detachment in the Shelfbreak Jet of the Middle Atlantic Bight*

The hydrographic properties of the bottom boundary layer (BBL) are investigated in a synoptic cross section of the Middle Atlantic Bight shelfbreak frontal jet. The dataset consists of closely spaced conductivity–temperature–depth stations and concurrent shipboard acoustic Doppler current profiler measurements. An extremum in BBL properties occurs in the frontal region where the layer becomes thinner (disappearing briefly), more stratified, and more strongly capped. These changes are apparently related to the significant cross-slope variation in interior stratification. Where the BBL vanishes, at the shoreward edge of the front, it detaches into the interior along an (nearly) isopycnal layer. This is revealed both by weak vertical stratification as well as weak isopycnal gradients of potential temperature (θ) and salinity (S) along the layer. An advective–diffusive model of the detachment in density space is used to explain the observed θ, S distribution as well as estimate the pumping speed along the detached BBL. The detided ADCP velocity fields are analyzed in light of the observed detached BBL. The mechanism of detachment is discussed in relation to existing models, and the secondary circulation in the cross-stream plane is inferred. This reveals a deep interior upwelling cell, apparently tied to the local bathymetry, which enhances the flow along the detached BBL.

Internal hydraulics and mixing in a highly stratified estuary

Shipboard acoustic Doppler current profiler and conductivity‐temperature‐depth data obtained during highly stratified conditions in the Hudson River estuary along a section of variable width and breadth are presented. The observations emphasize tidal period asymmetries in the vertical structure of current and salinity. However, these asymmetries exhibit significant along‐channel structure which is determined by channel morphology. During the ebb the flow is linearly sheared, and steep halocline slopes in the vicinity of channel contractions are maintained by momentum advection. A minimum in vertical shear across the pycnocline occurs in channel contractions. During food the pycnocline sharpens and flattens with a middepth velocity maximum embedded in the pycnocline which separates a stratified surface layer from a bottom mixed layer. The along‐channel structure in vertical shear is consistent with a lateral vorticity equation. Estimates of Richardson numbers suggest that vertical mixing across the pycnocline is enhanced downstream of channel contractions.

A Portable Retractable ADCP Boom-Mount for Small Boats

This paper describes the design, testing, and application of a portable and retractable shipboard acoustic Doppler current profiler (ADCP) boom-mount. The boom is specifically adapted for small fiberglass boats working with a minimal crew. The design permits the rapid collection of ADCP data on discontinuous transects which would be difficult or impossible using a large displacement hull vessel or with a towed vehicle. This capability is particularly useful in shallow wind-driven estuaries and in tidal channels where flow time scales are often on the order of several hours. Tests of the boom show that high quality ADCP data (as measured by percent good) can be obtained at boat speeds up to 4.0 m s−1 and that data quality depends on transducer depth. The utility of the retractable design is demonstrated with an 8 m boat on two nearly synoptic ADCP surveys of a shallow estuary. With minor modifications to accommodate different vessel geometries, the design could be readily adapted for use on similar vessels.