Rough Seafloor Research Articles

Geomorphology and mechanisms of subduction erosion in the sediment-starved Mariana convergent margin

Subduction erosion, commonly occurring in convergent margins, serves as a key mechanism for effective recycling of materials into the deep subduction. Subduction of bathymetric highs is widely recognized as a critical factor of subduction erosion of the forearc. The Mariana margin is an often-cited example of a tectonically erosive zone, with numerous topographic features such as seamounts, ridges, horsts, and grabens. However, few studies have attempted to determine the regional subduction erosion regime. By combining high-resolution bathymetric data and multichannel seismic profiles, this study analyzed the seafloor roughness, forearc taper angle, accretionary prism, and forearc topography to reveal evidence of subduction erosion at the Mariana margin. The subduction of rough seafloor (seamounts, horsts, and grabens) has accelerated the erosion process of the sediment-starved (<1 km) Mariana margin. In addition to causing depressions and landslides on the inner trench slope, this erosive process resulted in a flat forearc topography, which in turn may have induced a steeper forearc slope and taper angle. The arc-trench distance also shows a strong negative correlation with subduction erosion along the Mariana margin. The involvement of fluid inhibits the erosive process by favoring the development of a smooth surface along the plate interface. Our results suggest that tectonic erosion at the Mariana margin is jointly due to three mechanisms: seamount subduction, horst and graben subduction, and hydrofracturing. This integrated erosive process corresponds to a long-term subduction erosion rate of the submerged forearc of 7–8 km3/km/Myr, significantly lower than those calculated along the other global convergent margins.

Imaging the shallow velocity structure of the slow‐spreading ridge of the South China Sea with downward continued multichannel seismic data

AbstractHigh‐resolution shallow oceanic crust velocity models provide crucial information on the tectonothermal history of the oceanic crust. The ocean bottom seismometers record wide‐angle seismic reflection and refraction data to image deeper structures compared with streamer data set. However, most ocean bottom seismometers experiments produce low‐resolution velocity models with limited shallow crustal structure due to sparse ocean bottom seismometers spacing. Multichannel seismic data recorded by towed streamers provide complementary seismic images of the oceanic crust but yield little information on subseafloor velocity because most subseafloor refractions are masked by seafloor reflections. Therefore, it is difficult to obtain fine‐scale velocity structure of shallow upper oceanic crust with both ocean bottom seismometers and multichannel seismic data. Downward continuation technique redatumed the shots and receivers to the seafloor to collapse the seafloor reflections to the zero offset and extract refractions as first arrivals from nearly zero offset, enabling dense ray coverage at the shallow crust. We applied the downward continuation and traveltime tomography methods to two synthetic models, Marmousi and SEAM Phase I Salt models, to demonstrate the performance of the strategy in the situations of flat seafloor and rough seafloor topography. We conducted the first‐arrival traveltime tomography on downward continued towed‐streamer multichannel seismic data across a slow‐spreading ridge of the South China Sea, providing unprecedented details of shallow velocity structure in the sediments. The low velocity sediments revealed by traveltime tomography match well with the prestack depth migration profile.

Acoustic scattering modeling and sound field characteristics of rough seafloor in shallow sea

Acoustic scattering is an important part of ocean acoustics, and the acoustic scattering caused by the unevenness of the seafloor surface is one of the reasons for the fluctuation of acoustic propagation in the ocean. In order to solve the acoustic scattering problem of sea bottom surface roughness, normal wave theory is used to model the acoustic field. To simplify the problem, Lambert’s law is used to establish the seafloor rough scattering model in horizontal layered shallow sea waveguides, and the scattering field is assumed to be isotropic in the horizontal direction. Based on this model, the amplitude distribution and the phase distribution of the scattered sound pressure are obtained, and the intensity of the scattered sound field and its spatial correlation coefficient are simulated numerically. The prediction of the scattered sound field under rough interface conditions is realized, and the variation of the spatial characteristics of the scattered sound field with the roughness of the seafloor is revealed. The results show that when Lambert’s law is used to describe the rough interface acoustic scattering and when the seafloor roughness is smaller than the wavelength, the spatial correlation coefficient of the scattered sound field at two different positions in space has a change rule of periodic oscillation attenuation with the increase of spatial distance, and in the vertical direction, the oscillation period is larger and the attenuation is slower. When the roughness increases, the oscillation amplitude of the horizontal and the vertical correlation coefficient gradually increase, the oscillation period of the horizontal correlation coefficient gradually decreases, and the vertical correlation coefficient no longer attenuates in the direction near the seafloor, which is the result of the weakening of the seafloor acoustic scattering. The model theory in this paper can also be extended to the acoustic scattering modeling of rough sea surface. For the case of non-horizontal seabed, the scattered sound field of the rough interface in the waveguide can be obtained by using coupled normal wave or adiabatic normal wave theory.

Rip Currents Off Rocky‐Shore Surge Channels

AbstractMore than half the world's coastlines are rocky, but rip‐current dynamics on these topographically complex shores have not been studied. Field experiments on a typical rocky shore using video, drifters, and in‐situ current meters and pressure sensors reveal that incoming narrow‐banded swells result in incident wave groups that force breakpoint low‐frequency (LF) waves, which act in phase inside the surf zone to generate set‐up, run‐up, overtopping, and mass flux, pooling water atop the shore. Set‐up is enhanced by the change in momentum of the LF waves owing to dissipation by bottom friction over the rough seafloor, and by depth‐limited breaking, evidenced by low reflection. A 1D momentum balance results in a mean bottom‐drag coefficient of 1 owing to the rough bottom and vegetation. During wave‐group minima, the hydraulic head of the pooled water forces a return flow through a network of incised feeder channels that converge to a primary surge channel, directing flow offshore. The rip current extends three surf‐zone widths offshore with a maximum velocity of 1 m/s, and (in contrast to sandy shores) flow exits the surf zone, augmenting cross‐shore transport. Rip current strength is a function of channel hypsometry, overtopping, and exit constriction, factors that vary with the tide. As the tide rises, the mean flow decreases as the hydraulic head decreases and the constriction diminishes. Similar to rip currents on sandy beaches, rip currents on rocky shores are modulated by tides and sea‐swell, but they differ in geometric scale and forcing mechanism.

Monitoring Deep Sea Currents With Seafloor Distributed Acoustic Sensing

AbstractUnderwater fiber optic cables commonly traverse a variety of seafloor conditions, which leads to an uneven mechanical coupling between the cable and the ocean bottom. On rough seafloor bathymetry, some cable portions might be suspended and thus susceptible to vortex‐induced vibrations (VIV) driven by deep ocean currents. Here, we examine the potential of distributed acoustic sensing (DAS) to monitor deep‐sea currents along suspended sections of underwater telecom fiber optic cables undergoing VIV. Oscillations of a seafloor fiber optic cable located in southern France are recorded by DAS along cable sections presumably hanging. Their characteristic frequencies are lower than 1 Hz, at different ocean depths, and have an amplitude‐dependency consistent with the driving mechanism being VIV. Based on a theoretical proportionality between current speed and VIV frequencies, we derive ocean current speed time series at 2,390 m depth from the vortex shedding frequencies recorded by DAS. The DAS‐derived current speed time series is in agreement with recordings by a current meter located 3.75 km away from the hanging cable section (similar dominant period, high correlation after time shift). The DAS‐derived current speed time series displays features, such as characteristic periods and spectral decay, associated with the generation of internal gravity waves and weak oceanic turbulence in the Mediterranean Sea. The results demonstrate the potential of DAS along hanging segments of fiber optic cables to monitor a wide range of oceanography processes, at depths barely studied with current instrumentation.

Large-scale impacts of small-scale ocean topography

While large-scale seafloor features (e.g. continental slopes, mid-ocean ridges) help shape the broad patterns of ocean circulation, small-scale rough topography (e.g. seamounts, abyssal hills) can also impact the large-scale dynamics in two significant ways. First, they impact the momentum budget through flow steering, flow blocking and drag force, non-local momentum transfer via the generation of radiating internal waves and momentum dissipation by topographically induced turbulence. Second, they impact the density budget. Turbulence induced by flow–topography interactions facilitates ocean overturning circulation by upwelling dense, deep waters which form in polar oceans and sink to the abyss. Rough topography and its associated dynamics are of subgrid scale in Earth systems models (ESMs) and need parameterization for the foreseeable future. A parameterization of the intertwined impacts of flow–topography interactions on momentum and density budgets is currently non-existent, although its importance is well established. Radko (J. Fluid Mech., vol. 961, 2023, A24) provides a novel analytical model for representing the impact of rough seafloor on larger-scale flows, spanning slow to fast flow-speed regimes in homogeneous and multilayer models. The proposed ‘closure’ is in remarkable agreement with high-resolution numerical simulations and provides a crucial step forward in parameterizing the impact of rough topography in coarse-resolution ocean models. Extending the model to the full Navier–Stokes equations, linking it to the density budget and considering more realistic ocean topography are three critical future steps towards implementing Radko's theory in operational ESMs.

An investigation of seafloor and oceanographic characteristics in deep-water of north Labuan Bajo, Indonesia

On 12 December 1992, an earthquake, followed by a tsunami, occurred on Flores Islands, creating massive damage in the northern area and resulting in an early warning tsunami for the Labuan Bajo region. This area is a high-priority tourist designation in Indonesia with busy offshore activities and infrastructure development. Thus, earthquake and tsunami mitigation strategies are mandatory. Part of the mitigation effort is mapping the seafloor and characterizing oceanographic conditions in the deep-water north of this area. This paper describes the seafloor and oceanographic conditions using a multibeam echosounder (MBES) survey, conductivity-temperature-depth (CTD) measurement, and current observation. Results show that the rough and complex seafloor topography is revealed in the study area. Seafloor topography consists of a steep slope on the nearshore, flat topography in the sublittoral and shelf, a steeper slope in the bathyal zone, and relatively flat in the abyssal zone found from the south to north in the area. In addition, physical oceanographic properties are observed in two locations with a maximum depth measurement of 3,029 m. The result indicates that the water column is divided into three layers based on gradient changes: surface layer, thermocline layer, and colder depth layer. Moreover, two single-point current measurements at the exact locations are carried out at water depths of 3,029 m and 1,880 m. Result also describes that both stations have current directions of 128.14° and 124.49°, with current magnitudes of 0.1693 m/s and 0.3724 m/s, respectively. This investigation could serve as primary data and information in the study area. Furthermore, it could support the government and other stakeholders related to the development of Labuan Bajo, e.g., infrastructure (submarine cable, port, etc.) and resilience program (e.g., tsunami early warning system) that region

A Scaled Tank Experiment for the Stochastic Rough Interface Scattering

Bottom reverberation is an important limitation that affects the detection performance of active sonar in shallow water. The stochastic rough seafloor surface scattering is one of the main scattering sources of the bottom reverberation. Since there are much uncertainties, such as propagation fluctuation, unstable station of transmit and receive equipment, it is difficult to investigate the quantitative relationship between the random rough interface parameters and the statistical property by processing the experimental reverberation data collected in the ocean In this paper, the statistical characteristics of the irregular 3D printed interface scattering field are studied by a scaled tank experiment, and the detailed results are presented by the comparison between the COMSOL simulations and the recorded data, the feasibility of the random rough interfaces experiment is verified well. Because the relationship between parameters is precisely controllable, it lays a foundation for the subsequent experimental research of target extraction under the background of interface scattering.

Seismic Multiple Attenuation in the Continent–Ocean Transition Zone of the Northern South China Sea

In this study, we process four new multichannel reflection seismic profiles acquired in 2015 and 2016 in the continent–ocean transition zone (COT) of the northern South China Sea (SCS). We apply a multi-domain, progressive, and seabed-controlled denoising technique and obtain a good denoising effect. Combining velocity analysis in the multi-round time domain and forward modeling, we analyze the types and characteristics of multiples in the study area and formulate an effective demultiple technique to attenuate strong seabed multiples, diffracted multiples from rough seafloor, and other multiples from deep reflectors. The processing results show that the sea surface-related multiple elimination technique predicts the sea surface-related multiples accurately by data convolution, and has a good effect in attenuating seabed multiples. Diffracted multiple attenuation method extracts high-frequency and high-energy diffracted multiples, and suppresses multiples by the energy ratios of multiples to primary events. To attenuate deep multiples, we select predictive deconvolution to attenuate periodic deep multiples after many trials and detailed analysis. The combination of these different techniques in sequence proves to be quite effective in attenuating different seismic multiples in the COT. The imaged crustal structures near the COT often show strong magmatism and/or basement uplifting. The faulted and thinned continental crust adjacent to the COT corresponds to the lowest free-air gravity anomalies. Gravity anomalies often increase from the COT to the oceanic crust. An exception is to the northeast of the SCS, where the relatively wide COT shows very high gravity anomalies, likely induced by mantle upwelling and serpentinization.

Energy balance and momentum budgets due to the internal tides generated by a group of submarine canyons

A field multibeam survey discovered a group of regularly-spaced submarine canyons on the continental shelf in the northern South China Sea. However, they are not included in the bathymetry datasets commonly used by the oceanographic community. In this study, we employ a very-high-resolution (as fine as 54 m) numerical model that resolves these submarine canyons to investigate their impacts on the local internal tide generation and propagation. Results show that the barotropic to internal tidal conversion rate exhibits an alternating distribution on each flank of submarine canyons. Rotational direction of the tidal flow determines a positive conversion rate on the west flank and a negative rate on the east flank. The rough seafloor due to the submarine canyons does not appreciably change the dissipation of barotropic tides, but significantly affects the dissipation of internal tides, leading to an averaged dissipation rate of 1.2 × 10−9 W kg −1. Internal tides also induce a bottom intensified mean flow, which causes westward mean transport on the continental slope and a clockwise circulation inside each submarine canyon. The mean flow satisfies a momentum budget between the Coriolis force, pressure gradient and divergence of momentum flux of barotropic and internal tides. We highlight that the divergence of the pseudo-momentum flux of internal tides acts as a stress and is especially reinforced near the sea bottom and surface. Its effect on the sea surface is even comparable with moderate winds (∼13 m s−1).

Numerical modeling of T-wave generation in a horizontally inhomogeneous ocean

T-waves are generated by earthquakes and travel horizontally with the speed of sound. They are the most common earthquake sounds in the ocean and make strong contributions to the ambient sound field. However, the mechanisms of their generation remain poorly understood. Recent theoretical paper [O. A. Godin, J. Acoust. Soc. Am. 150, 3999–4017 (2021)] argues that scattering of ballistic waves from the earthquake focus by the ocean surface is a strong source of T-waves, which should be considered on par with previously identified generation mechanisms of wave diffraction on large bathymetric features and scattering by the rough seafloor. This paper compares the T-waves due to ocean surface roughness and a seamount in deep water. 3-D surface scattering and wave interaction with large-scale bathymetric features are modeled rigorously using time-domain spectral-element code SPECFEM3D, with the ocean surface being shaped by wind waves and sea swell and a large seamount located off the earthquake epicenter. These simulations are complemented by a normal-mode code to propagate the sound field from the generation region to long ranges. A mode projection technique is developed to efficiently couple SPECFEM3D to the normal mode code. The two mechanisms are found to generate T-waves of comparable amplitudes.

Numerical modeling of low-frequency scattering from targets buried under rough seafloors

The acoustic backscattering of elastic bodies lying across the seafloor is a problem of great interest in many underwater applications, such as detecting and classifying buried objects. In this work, the backscattered wavefield of meter-sized targets is investigated numerically in the 1–50 kHz frequency band. The simulator solves the three-dimensional linearized equations of continuum mechanics. The computations are performed through a multi-GPU solver based on a multi-grid staggered finite-difference time-domain method (cf. Sabatini et al., 181st ASA Meeting, Seattle, Washington, 2021). The effects of the seafloor roughness and the target burial depth on the spectrum of the scattered field are more specifically analyzed. This study demonstrates the usefulness of direct numerical simulations of acoustic scattering from realistic elastic objects in complex underwater environments to improve the capabilities of sonar systems in detecting and identifying buried objects.

The Hidden History of the South‐Central Cascadia Subduction Zone Recorded on the Juan de Fuca Plate Offshore Southwest Oregon

AbstractNew seismic reflection data collected and processed as part of early career scientist training at sea and in classroom projects fill gaps in seismic coverage of the Cascadia subduction zone and provide new insights into anomalous subduction behavior and mass wasting along the south‐central Cascadia Subduction Zone (CSZ) between 42°20’N and 44°15’N. The data reveal at least six distinct buried horizons of folded and faulted sediments similar to strata recently interpreted to result from in situ deformation induced by the load imposed by a large blocky mass transport deposit known as the 44°N slide. Although our results support prior studies indicating that the south‐central CSZ has experienced large slope instabilities, they indicate that the slides were more frequent but volumetrically smaller than previously thought. Similar strata have not been observed elsewhere beneath the abyssal plain adjacent to the Cascadia subduction zone. The structure of the deformation front along this segment is also indistinct, in contrast to the clear frontal faults outboard of folded trench strata observed immediately to the north and south (and generally throughout the rest of Cascadia). We attribute the anomalous nature of this segment of the margin to past subduction of shallow and rough seafloor, which resulted in greater uplift of the forearc than elsewhere along the margin. A consequence of this postulated history would be the shedding of older, more consolidated blocks onto the Juan de Fuca plate, resulting in the observed distinctive stratigraphy offshore southern Oregon.

Mega‐Depressions on the Cocos Ridge: Links Between Volcanism, Faults, Hydrothermal Circulation, and Dissolution

AbstractHigh‐resolution bathymetry and three‐dimensional seismic data along the Cocos Ridge reveal a 245 km2 field of ∼1–4 km in diameter seafloor depressions. The seafloor depressions are part of a two‐tiered honeycomb pattern. The lower‐tier depressions have steep faults that truncate strata with chaotic internal reflections consistent with sediment collapse into the depression. These extend into a lens shaped interval just above igneous basement. Overlying these depressions is a second broader set with rough seafloor morphology with gently dipping boundaries defined by pinch‐out stratigraphic patterns. Drilling results indicate that the lens‐shaped zones that host the deeper depressions represent anomalous regions of high porosity, low velocity, and low density within calcareous rich sediment. Analysis of nannofossils from IODP Site U1414 suggests the collapse structures formed during the late Miocene, whereas the younger shallower depressions likely formed between the early Pliocene and the Pliocene‐Pleistocene boundary. Geochemical and petrological analysis at Site U1414 suggests that hydrothermal circulation during the late Miocene led to carbonate dissolution and collapse. Following collapse, focused fluid‐flow and bottom current scouring resulted in formation of the overlying set of depressions and a honeycomb seafloor morphology. Similar sets of depressions along the Carnegie Ridge to the south support the hypothesis that two‐tiered depressions formed in response to processes that occurred broadly across the Panama Basin between the late Miocene and the Pliocene‐Pleistocene transition. Geochemical results at Site U1414, combined with geophysical data, suggest this two‐tiered system of depressions currently guides ongoing fluid outflow.

Diurnal Coastal Trapped Waves and Associated Deep‐Ocean Mixing Near the Head of Suruga Trough

AbstractCoastal submarine canyons are expected to be sites of enhanced turbulent mixing which create productive fishing areas in coastal waters. Recent studies suggested the potential role of diurnal coastal trapped waves (CTWs) in inducing significant turbulent mixing in coastal submarine canyons poleward of 30° where the diurnal tide becomes subinertial. Nevertheless, the detailed physical processes responsible for the generation and dissipation of CTWs in such submarine canyons have hardly been investigated so far. In the present study, to investigate the turbulent mixing processes associated with diurnal CTWs in submarine canyons, we carry out high‐resolution (Δx, Δy = 1/240°) non‐hydrostatic three‐dimensional numerical experiments focusing on Suruga Bay located at the north end of Suruga Trough, Japan. The numerical experiments show that diurnal (subinertial) tidal currents over the Izu Ridge generate CTWs which propagate cyclonically along the coast of Suruga Bay. In the middle of Suruga Bay, bottom‐intensified flow due to the diurnal CTWs interacts with rough seafloor topography to excite upward propagating internal lee waves, which create mixing hotspots extending high above the seafloor. The resulting diurnal (subinertial) tidal energy dissipation in Suruga Bay is found to be much larger than that associated with semidiurnal (superinertial) internal tides. Furthermore, it is found that baroclinic energy flux based on a simple barotropic‐baroclinic decomposition severely underestimates the wave energy flux in areas with high CTW activity. These results strongly indicate that the existence of CTWs might be a key factor to clarify the dissipation/mixing processes in submarine canyons.

A numerical model for geometrically nonlinear analysis of a pipe-lay on a rough seafloor

Despite a detailed assessment of a potential route for offshore oil and gas transport pipelines, the pipelines are still often being subjected to a pipe-lay on a rough seafloor, which can substantially increase the internal forces within the pipeline.To ensure pipeline integrity during the installation, it is essential to obtain internal force envelope diagrams, which provide the historical maximum and minimum force bounds at every location along the pipeline throughout the entire pipe-lay proceeding.This paper provides a simple numerical technique for calculating the internal force envelope diagrams. The entire pipeline is modeled as a single continuous segment considering geometrical nonlinearity induced by large deformations. The solution technique is based on consistent minimization of the total potential energy of the system discretized as a Riemann sum and the solution of the subsequent algebraic system of nonlinear finite difference equations with a Newton-Raphson technique.The feasibility of the proposed technique is demonstrated through several scenarios of a pipe-lay across the basic types of seafloor irregularity. The results have revealed that, in general, any seafloor irregularity leads to an increase in maximum internal force values at certain locations.The proposed technique provides a time-saving alternative to commercial special-purpose finite element software.

A New Parameterization of Turbulent Mixing Enhanced Over Rough Seafloor Topography

AbstractExisting parameterizations of turbulent mixing enhanced over high‐wavenumber seafloor topography miss the fact that internal tidal waves emanating from the seafloor transform to internal lee waves as the tide‐topography interaction strengthens. This motivates us to replace the vertical decay scale of bottom‐enhanced turbulent mixing with the “vertical mean free path” of internal lee waves, namely, the average vertical distance over which internal lee waves propagate until they discharge their energy through interactions with the background internal waves. The resulting formula shows that the vertical extent of turbulent mixing becomes proportional to the abyssal barotropic tidal or steady flow amplitude squared and the inverse abyssal buoyancy frequency squared, but independent of the wavenumber of the seafloor, consistent with recent eikonal calculations and field observations. We propose a new parameterization of turbulent mixing enhanced over high‐wavenumber seafloor topography through incorporating the formulated vertical decay scale.

Measurement of Seafloor Acoustic Backscatter Angular Dependence at 150 kHz Using a Multibeam Echosounder

Acoustic seafloor measurements with multibeam echosounders (MBESs) are currently often used for submarine habitat mapping, but the MBESs are usually not acoustically calibrated for backscattering strength (BBS) and cannot be used to infer absolute seafloor angular dependence. We present a study outlining the calibration and showing absolute backscattering strength values measured at a frequency of 150 kHz at around 10–20 m water depth. After recording bathymetry, the co-registered backscattering strength was corrected for true incidence and footprint reverberation area on a rough and tilted seafloor. Finally, absolute backscattering strength angular response curves (ARCs) for several seafloor types were constructed after applying sonar backscattering strength calibration and specific water column absorption for 150 kHz correction. Thus, we inferred specific 150 kHz angular backscattering responses that can discriminate among very fine sand, sandy gravel, and gravelly sand, as well as between bare boulders and boulders partially overgrown by red algae, which was validated by video ground-truthing. In addition, we provide backscatter mosaics using our algorithm (BBS-Coder) to correct the angle varying gain (AVG). The results of the work are compared and discussed with the published results of BBS measurements in the 100–400 kHz frequency range. The presented results are valuable in extending the very sparse angular response curves gathered so far and could contribute to a better understanding of the dependence of backscattering on the type of bottom habitat and improve their acoustic classification.

The effect of seabed roughness on passive fathometer measurements

The seafloor is rough on a variety of horizontal scales spanning several orders of magnitude. This roughness, together with subbottom roughness and volume heterogeneities can play a role in scattering ambient sound. When the ambient sound pressure field is used to remotely sense the seafloor using passive fathometer techniques, scattering may cause a departure from the plane wave models that are commonly fit to passive estimates of the bottom reflection coefficient. Here, a model for the effect of scattering on passive reflection measurements is developed for an isovelocity water column. Results are shown for a rough half-space, and a rough layered seafloor. The bias introduced into geoacoustic inversions by the presence of seafloor scattering is investigated. [This work was supported by the U.S. Office of Naval Research.]

Rough seafloor and target far-field scattering prediction using numerically determined Green’s functions

Acoustic scattering from rough seafloor, and from targets on and buried within rough seafloor interfaces, is modeled using 3D finite elements to capture the effect of seafloor roughness and variability upon the far-field scattering. Though the model is necessarily small, far-field scattering prediction is achieved using Green’s functions determined numerically within the model. Comparisons to experimental measurements and between models demonstrate the effect that seafloor roughness and variation, as well as target orientation, burial, and asymmetry have upon the measured scattering. Numerically determined Green’s functions are an efficient method for obtaining long-range scattering prediction out of small, localized models, and are practical for complex geometry situations in which the exact Green’s function is difficult to estimate analytically. Best practice techniques for domain truncation in complex environments are also explored and compared in this work. [This work was supported by the Office of Naval Research and by the Strategic Environmental Research and Development Program.]