Spatial Variation In Response Research Articles

Variation in Grassland Fuel Curing in South Africa

Fire is critical to the maintenance of ecological function in many ecosystems worldwide, especially mesic sub-Saharan rangelands. But most rangeland fire research occurs in a wildfire context, is focused on fire effects, or simply assumes that grass-dominated fuelbeds are homogeneous. In this study, we sampled fuel moisture from several species in two grassland locations in South Africa to determine (1) if grassland fuels cure differently among species or across locations, (2) whether differences in curing meaningfully affect fire behaviour, and (3) if fuel moisture is associated with soil moisture. Data were characterised by high variability among sampling sites and dates, which highlights the importance of accounting for—rather than averaging out—variation with hierarchical analysis. Variability among locations and species indicates that broad similarities among plant communities do not adequately describe fuelbed dynamics. We observed patterns in the C3 Festuca costata that deviated from general patterns in C4 grasses, particularly in grasslands at the edge of environmentally determined transitions. These differences might have landscape-level implications under global environmental change. The temporal breadth and species-level specificity of our study constitute novel data that identify further research to improve the understanding of fuelbed ecology in grasslands worldwide, beyond the context of extreme fire weather and behaviour. Our data suggest that managers in South Africa and abroad should consider heterogeneity within grassland fuelbeds and recognize seasonal changes to ensure that objectives are obtainable ahead of burns, and to explain spatial variation in response within what might have appeared to be a homogeneous grassland fuelbed.

Spatial and ecological variation in dryland ecohydrological responses to climate change: implications for management

AbstractEcohydrological responses to climate change will exhibit spatial variability and understanding the spatial pattern of ecological impacts is critical from a land management perspective. To quantify climate change impacts on spatial patterns of ecohydrology across shrub steppe ecosystems in North America, we asked the following question: How will climate change impacts on ecohydrology differ in magnitude and variability across climatic gradients, among three big sagebrush ecosystems (SB‐Shrubland, SB‐Steppe, SB‐Montane), and among Sage‐grouse Management Zones? We explored these potential changes for mid‐century for RCP8.5 using a process‐based water balance model (SOILWAT) for 898 big sagebrush sites using site‐ and scenario‐specific inputs. We summarize changes in available soil water (ASW) and dry days, as these ecohydrological variables may be helpful in guiding land management decisions about where to geographically concentrate climate change mitigation and adaptation resources. Our results suggest that during spring, soils will be wetter in the future across the western United States, while soils will be drier in the summer. The magnitude of those predictions differed depending on geographic position and the ecosystem in question: Larger increases in mean daily spring ASW were expected for high‐elevation SB‐Montane sites and the eastern and central portions of our study area. The largest decreases in mean daily summer ASW were projected for warm, dry, mid‐elevation SB‐Montane sites in the central and west‐central portions of our study area (decreases of up to 50%). Consistent with declining summer ASW, the number of dry days was projected to increase rangewide, but particularly for SB‐Montane and SB‐Steppe sites in the eastern and northern regions. Collectively, these results suggest that most sites will be drier in the future during the summer, but changes were especially large for mid‐ to high‐elevation sites in the northern half of our study area. Drier summer conditions in high‐elevation, SB‐Montane sites may result in increased habitat suitability for big sagebrush, while those same changes will likely reduce habitat suitability for drier ecosystems. Our work has important implications for where land managers should prioritize resources for the conservation of North American shrub steppe plant communities and the species that depend on them.

Improved eigenfilter-based time-domain wideband beamforming

An improved eigenfilter-based wideband beamforming method with frequency invariance and nulls was proposed. Based on the optimization model formed by maximum energy array cost function and linear constraints of array response in main great direction,array spatial response variation was integrated into the cost function to achieve frequency invariance. Two methods,integrating the extended sidelobe energy into cost function and using linear constraints of array response in the direction of inference,were designed to achieve nulls,so that two new constraint optimization models were formed,which could be solved by eigenfilter. Simulation results show that frequency invariance and nulls of beam response are achieved at the specified angle region in the frequency passband,and the gain of the sidelobe is small,the effectiveness and satisfactory performance of the proposed method are proved.

Uncertain hydrological modelling: application of the Pitman model in the Great Ruaha River basin, Tanzania

Uncertainty analysis has become the standard approach to hydrological modelling, but has yet to be effectively used in practical water resources assessment. This study of the Great Ruaha River basin in Tanzania is based on the use of regional estimates of mean runoff, groundwater recharge and three flow points on flow duration curves (FDCs) to constrain ensemble outputs from the Pitman monthly model using Monte Carlo parameter sampling. The constraint bounds were quantified from gauged data available for 26 sub-basins together with assumptions about the spatial variations in hydrological response using limited physical sub-basin property and climate data. The results are encouraging in that the simulated FDC ranges bracket the observed curves at two gauging stations downstream of many ungauged sub-basins that are important sites for water resources development decision making. Further work is required to refine the constraint bounds, the input parameter sets and climate data and achieve a more robust model of the basin.Editor D. Koutsoyiannis; Guest editor G. Mahé

Effect of intra‐specific competition, surface chlorophyll and fishing on spatial variation of gadoid's body condition

Fish condition indices can be used as biological indicators of the health of individuals and are influenced by numerous external and internal drivers. Like most essential biological traits, they are very sensitive to the spatial heterogeneity occurring in marine ecosystems, which appears at many observational scales. This brings out different ecological processes that can only be revealed either regionally or locally. The scale‐dependent spatial variability concerns not only environmental factors, but also anthropogenic activities such as fishing. Understanding these relationships is crucial for improving the spatial management of marine resources, because fish condition considerably affects the sustainability of populations. We explore the influence of density‐dependent (intra‐specific competition) and density‐independent variables (surface chlorophyll a concentration and fishing impact) on fish condition of three species of harvested gadoids (Merluccius merluccius, Phycis blennoides and Micromesistius poutassou) of the benthopelagic communities off the Balearic Islands (western Mediterranean). This area is characterized by high spatial heterogeneity in the environmental processes and fishing impact. Results show contrasting responses in body condition to the investigated covariates, with species‐specific and ontogenetic differences sensitive to the spatial scale of analysis. Some of these responses occur at regional level, while others are more sensitive to local variation. Intra‐specific competition shows a very clear effect, which depends on the ontogeny, identifying aggregation areas for recruits and limitation of resources for older individuals. Surface chlorophyll a has always a species‐specific regional effect, despite gadoids have a more benthic behavior. Fishing effort displays a heterogeneous impact on fish condition. While spatially contrasting effects are observed at local scale, non‐ linear regional patterns occur, with positive effects of fishing pressure at intermediate levels. Models analyzing the influence of external drivers in essential fish biological traits such as body condition should consider the spatial variation in responses, especially in highly heterogeneous areas where anthropogenic activities occur. Failing to do so may hide local ecological processes that can be crucial for the persistence of fish populations, which is of paramount relevance for the regional assessment and spatial management of marine exploited resources.

Pore pressure sensitivities to dynamic strains: Observations in active tectonic regions

AbstractTriggered seismicity arising from dynamic stresses is often explained by the Mohr‐Coulomb failure criterion, where elevated pore pressures reduce the effective strength of faults in fluid‐saturated rock. The seismic response of a fluid‐rock system naturally depends on its hydromechanical properties, but accurately assessing how pore fluid pressure responds to applied stress over large scales in situ remains a challenging task; hence, spatial variations in response are not well understood, especially around active faults. Here I analyze previously unutilized records of dynamic strain and pore pressure from regional and teleseismic earthquakes at Plate Boundary Observatory (PBO) stations from 2006 to 2012 to investigate variations in response along the Pacific/North American tectonic plate boundary. I find robust scaling response coefficients between excess pore pressure and dynamic strain at each station that are spatially correlated: around the San Andreas and San Jacinto fault systems, the response is lowest in regions of the crust undergoing the highest rates of secular shear strain. PBO stations in the Parkfield instrument cluster are at comparable distances to the San Andreas Fault (SAF), and spatial variations there follow patterns in dextral creep rates along the fault, with the highest response in the actively creeping section, which is consistent with a narrowing zone of strain accumulation seen in geodetic velocity profiles. At stations in the San Juan Bautista (SJB) and Anza instrument clusters, the response depends nonlinearly on the inverse fault‐perpendicular distance, with the response decreasing toward the fault; the SJB cluster is at the northern transition from creeping‐to‐locked behavior along the SAF, where creep rates are at moderate to low levels, and the Anza cluster is around the San Jacinto Fault, where to date there have been no statistically significant creep rates observed at the surface. These results suggest that the strength of the pore pressure response in fluid‐saturated rock near active faults is controlled by shear strain accumulation associated with tectonic loading, which implies a strong feedback between fault strength and permeability: dynamic triggering susceptibilities may vary in space and also in time.

Spatial and temporal variations in ecosystem response to monsoon precipitation variability in southwestern North America

AbstractDue to its marked vegetation phenology and precipitation gradients, the North American Monsoon Region (NAMR) is a useful domain for studying ecosystem responses to climate variability and change. To this end, we analyze long‐term dynamics (1982–2004) in monsoon precipitation (Pr), time‐integrated Normalized Difference Vegetation Index (TINDVI) used as proxy of net primary productivity, and rain‐use efficiency (RUE). The analysis focuses on six ecoregions, spanning from desert environments to tropical dry forests, to investigate (1) how net primary productivity and rain‐use efficiency vary along a precipitation gradient, (2) if interannual variability in net primary productivity is linked to the interannual variability in precipitation, and (3) if there is evidence of a long‐term signal imposed on the interannual variability in rain‐use efficiency. Variations in TINDVI and RUE with Pr along the NAMR precipitation gradient differ among ecoregions exhibiting intensive or extensive water use strategies. We explain the nonlinear behaviors along the precipitation gradient as resulting from different physiological responses to climatological means and the impact of topographic effects. Statistical analysis indicates that the interannual variability in vegetation response is significantly related to the interannual variability in Pr, but their correlation declines with time. A long‐term positive signal in RUE imposed on its interannual variability is identified and results from a constant TINDVI under negative long‐term trends of Pr. This important finding suggests the combined long‐term effects of ecosystem acclimation to reduced water availability and increasing CO2 concentration across the varied ecosystems of the North American Monsoon Region.

Spatial and seasonal variation in chemical composition and toxicological response of ambient particulate matter

Spatial and seasonal variation in chemical composition and toxicological response of ambient particulate matter

A stratigraphical basis for the Last Glacial Maximum (LGM)

The Last Glacial Maximum (LGM) is widely used to refer to the episode when global ice volume last reached its maximum and associated sea levels were at their lowest. However, the boundaries of the interval are ill-defined and the term and acronym have no formal stratigraphical basis. This is despite a previous proposal to define it as a chronozone in the marine records on the basis of oxygen isotopes and sea levels, spanning the interval 23–19 or 24–18 ka and centred on 21 ka. In terrestrial records the LGM is poorly represented since many sequences show a diachronous response to global climate changes during the last glacial cycle. For example, glaciers and ice sheets reached their maximum extents at widely differing times in different places. In fact, most terrestrial records display spatial variation in response to global climate fluctuations, and changes recorded on land are often diachronous, asynchronous or both, leading to difficulties in global correlation. However, variations in the global hydrological system during glacial cycles are recorded by atmospheric dust flux and this provides a signal of terrestrial changes. Whilst regional dust accumulation is recorded in loess deposits, global dust flux is best recorded in high-resolution polar ice-core records, providing an opportunity to define the LGM on land and establish a clear stratigraphical basis for its definition. On this basis, one option is to define the global LGM as an event between the top (end) of Greenland Interstadial 3 and the base (onset) of Greenland Interstadial 2, spanning the interval 27.540–23.340 ka (Greenland Stadial 3). This corresponds closely to the peak dust concentration in both the Greenland and Antarctic ice cores and to records of the global sea-level minima. This suggests that this definition includes not just the coldest and driest part of the last glacial cycle but also the peak in global ice volume. The later part of the LGM event is marked by Heinrich Event 2, which reflects the onset of the collapse of the Laurentide at c. 24 ka, together with other ice sheets in the North Atlantic region. A longer and later span for the LGM may be desirable, although defining this in chronostratigraphical terms is problematic. Whichever formal definition is chosen, this requires the contribution of the wider Quaternary community.

Offsetting effects of aerosols on Arctic and global climate in the late 20th century

Abstract. We examine the impacts of atmospheric aerosols on Arctic and global climate using a series of 20th century transient simulations from Community Climate System Model version 4 (CCSM4). We focus on the response of surface air temperature to the direct radiative forcing driven by changes in sulfate and black carbon (BC) concentrations from 1975 to 2005 and we also examine the response to changes in sulfate, BC, and organic carbon (OC) aerosols collectively. The direct forcing from sulfate dominates the aerosol climate effect. Globally averaged, simultaneous changes in all three aerosols produce a cooling trend of 0.015 K decade−1 during the period 1975–2005. In the Arctic, surface air temperature has large spatial variations in response to changes in aerosol concentrations. Over the European Arctic, aerosols induce about 0.6 K decade−1 warming, which is about 1.8 K warming over the 30-year period. This warming is triggered mainly by the reduction in sulfate and BC emissions over Europe since the 1970s and is reinforced by sea ice loss and a strengthening in atmospheric northward heat transport. Changes in sulfate concentrations account for about two thirds of the warming and BC for the remaining one third. Over the Siberian and North American Arctic, surface air temperature is likely influenced by changes in aerosol concentrations over Asia. An increase in sulfate optical depth over Asia induces a large cooling while an increase in BC over Asia causes a significant warming.

Developing a model for effects of climate change on human health and health–environment interactions: Heat stress in Austin, Texas

Human health and well-being are and will be affected by climate change, both directly through changes in extreme weather events and indirectly through weather-induced changes in human and natural systems. The goal of this study was to develop and apply a broadly applicable modeling and support platform for decisions at the local scale that consider potential climate change health effects and the effectiveness of mitigation options. The model’s first application examined how climate change induced heat stress could affect morbidity and mortality in Travis County, Texas (Austin and vicinity) and how increased vegetation coverage, applied in several different ways, could quantitatively mitigate heat stress effects. The model was developed in a manner which will allow ready adaptation to other locations and health endpoints. The model followed the logical steps: (1) determine spatial and temporal variation in hazard exposure; (2) analyze spatial variation in population vulnerability to hazards; (3) estimate health outcome risk for population groups through hazard exposure and hazard response functions; (4) examine how mitigation options may affect health outcomes and their links to other ecosystem services. Demonstration runs explored spatial and temporal variation in health effect responses and effects of potential urban forestry mitigation options.

Biomarker records of phytoplankton productivity and community structure changes in the Central Yellow Sea mud area during the Mid-late Holocene

The Yellow Sea (YS) environmental and ecological changes during the Holocene are driven by the interactions between the Yellow Sea Warm Current (YSWC), the East Asian Winter Monsoon (EAWM) and the Kuroshio Current (KC). We report marine biomarker records of brassicasterol, dinosterol and C37 alkenones in core ZY1 and core ZY2 from the South Yellow Sea (SYS) to reconstruct the spatial/temporal variations and possible mechanisms of phytoplankton primary productivity and community structure changes during the Mid-late Holocene. The contents of the corresponding biomarkers in the two cores are similar, and they also reveal broadly similar temporal trends. From 6 kyr to 3 kyr, the biomarker contents in the two cores were relatively low with small oscillations, followed by a distinct increase at about 3 kyr indicating productivity increases caused by a stronger EAWM. The alkenone/brassicasterol ratio (A/B) is used as a community structure proxy, which also showed higher values in both cores since 3 kyr, indicating increased haptophyte contribution to total productivity. It is proposed that the YS community structure has been mainly influenced by the YSWC, with stronger YSWC influences causing an increase in haptophyte contribution since 3 kyr. Some differences of the biomarker records between ZY2 and ZY1 suggest spatial variations in response to YSWC and KC forcing. When the KC was intensified during the periods of 6–4.2 kyr and 1.7–0 kyr, the YSWC extended eastward, exerting more influence on core ZY1. On the other hand, when the KC weakened during 4.2–1.7 kyr, the YSWC extended westward, exerting more influence on the ZY2.

Spatial variability of hydrological processes and model structure diagnostics in a 50 km2catchment

In this paper, we develop diagnostic methods to assess spatial variability in hydrological processes, particularly those relevant to catchment modelling. We target a range of catchment responses, including runoff volume, runoff timing, storage–discharge relationships, and threshold responses to rainfall and soil moisture. The diagnostics allow us to map the scales and patterns of process variability, to test whether climate or physical catchment characteristics can be used to predict patterns in processes, and to explore the implications for appropriate spatial variability in hydrological model structures or parameters. We apply the diagnostic tests to the mid-sized (50 km2) Mahurangi catchment in Northland, New Zealand, combining data from 28 flow gauges, 13 rain gauges, and 18 soil moisture measurement sites to build a comprehensive description of spatial variation in catchment response. The results show a complex picture: different diagnostics reveal different patterns of hydrological processes, and large variations in processes occur, even over the short length scales involved (~10 km). Catchment and climate characteristics almost all show the same pattern, i.e. that subcatchments in the far North and South of the Mahurangi are similar to each other (higher elevation, steep, forested), but contrast with central subcatchments (lower elevation, shallower slopes, pasture). Surprisingly, this pattern is not reflected in the patterns of diagnostic indices, demonstrating the difficulty of defining realistic a priori estimates of spatial variability in processes. We discuss how process variations correspond to the design of components of a simple lumped conceptual model. In the Mahurangi catchment, we find that spatial variations in multiple aspects of the hydrological response imply a need for spatial variation in both model structures and parameters. Copyright © 2013 John Wiley & Sons, Ltd.

Internal flow variations and diachronous sedimentation within extensive, sustained, density-stratified pyroclastic density currents flowing down gentle slopes, as revealed by the internal architectures of ignimbrites on Tenerife

During a protracted explosive eruption, at least four laterally extensive and sustained pyroclastic density currents radiated across the flanks of Las Cañadas volcano, Tenerife. Each pyroclastic current developed marked local and regional spatial variations in response to the incised, gently concave substrate topography. The locations of these variations shifted in space as rapid sedimentation from the current progressively buried and modified the topography. This complex, shifting response of the density currents to minor topographic variations has been reconstructed in high-resolution over a wide area (>500 km2) using the internal architecture of cryptic time-surfaces (entrachrons) marked by compositional zoning in the deposit, including variations in clast types. Valley-side field relations reveal that the currents were density-stratified. Yet, at a single instant in time, the lower levels of each current comprised a granular-fluid at some locations but were fully dilute and turbulent at others. Moreover, the locations of these variations shifted geographically as the topography changed during the eruption. The variations within the current are recorded by numerous superbly exposed gradational transitions from various stratified to massive lithofacies, both laterally and in the downcurrent direction. Individual currents were regionally widespread and travelled >15 km, but deposited only in longitudinally restricted, localised zones that spanned several small valleys and interfluves. The currents bypassed slopes up- and downcurrent of the restricted depositional zones, without depositing. The locations of deposition then gradually shifted with time, such that the extensive deposit sheet was gradually assembled beneath the sustained current in a diachronous fashion. Onlap relationships of internal entrachrons reveal that the base of the ignimbrite sheet and even the bases of individual flow-units are markedly diachronous. Deposition of a flow-unit commenced and ceased at different times in different places. This study suggests that in hazard assessments: (a) models of density currents that incorporate only pre-existing topography (e.g. from DEMs) may give misleading results in the case of sustained currents because sedimentation from these significantly modifies the topography during emplacement, altering flow paths; (b) frequencies and scales of previous pyroclastic currents determined from pyroclastic successions are likely to be significantly under-estimated because currents commonly bypass without leaving a deposit record; and (c) even where preservation appears to be complete, an ignimbrite at a single exposure commonly will not record the current’s entire flow history at that site.

Small-Scale Spatial Variation in Population Dynamics and Fishermen Response in a Coastal Marine Fishery

A major challenge for small-scale fisheries management is high spatial variability in the demography and life history characteristics of target species. Implementation of local management actions that can reduce overfishing and maximize yields requires quantifying ecological heterogeneity at small spatial scales and is therefore limited by available resources and data. Collaborative fisheries research (CFR) is an effective means to collect essential fishery information at local scales, and to develop the social, technical, and logistical framework for fisheries management innovation. We used a CFR approach with fishing partners to collect and analyze geographically precise demographic information for grass rockfish (Sebastes rastrelliger), a sedentary, nearshore species harvested in the live fish fishery on the West Coast of the USA. Data were used to estimate geographically distinct growth rates, ages, mortality, and length frequency distributions in two environmental subregions of the Santa Barbara Channel, CA, USA. Results indicated the existence of two subpopulations; one located in the relatively cold, high productivity western Channel, and another in the relatively warm, low productivity eastern Channel. We parameterized yield per recruit models, the results of which suggested nearly twice as much yield per recruit in the high productivity subregion relative to the low productivity subregion. The spatial distribution of fishing in the two environmental subregions demonstrated a similar pattern to the yield per recruit outputs with greater landings, effort, and catch per unit effort in the high productivity subregion relative to the low productivity subregion. Understanding how spatial variability in stock dynamics translates to variability in fishery yield and distribution of effort is important to developing management plans that maximize fishing opportunities and conservation benefits at local scales.

Measurements of spatial variations in response of ionization chambers

Measurements of the spatial variations in the response of three ionization chamber (IC) designs were tested as a function of chamber bias voltage, incident X-ray flux and fill gas. Two components of spatial variation are seen. When the ionization chambers are near saturation, spatial variations exist that are tied to the chamber geometry. While the response of some chambers is relatively flat, others show significant variation across the IC. These variations appear to be inherent in the response of each IC at saturation. When the chamber is far from saturation, large spatial variations in response are present when N(2) is used as a fill gas, but not when ambient air is used as a fill gas. These appear to be tied to space charge effects.

Common garden experiments reveal uncommon responses across temperatures, locations, and species of ants

Population changes and shifts in geographic range boundaries induced by climate change have been documented for many insect species. On the basis of such studies, ecological forecasting models predict that, in the absence of dispersal and resource barriers, many species will exhibit large shifts in abundance and geographic range in response to warming. However, species are composed of individual populations, which may be subject to different selection pressures and therefore may be differentially responsive to environmental change. Asystematic responses across populations and species to warming will alter ecological communities differently across space. Common garden experiments can provide a more mechanistic understanding of the causes of compositional and spatial variation in responses to warming. Such experiments are useful for determining if geographically separated populations and co-occurring species respond differently to warming, and they provide the opportunity to compare effects of warming on fitness (survivorship and reproduction). We exposed colonies of two common ant species in the eastern United States, Aphaenogaster rudis and Temnothorax curvispinosus, collected along a latitudinal gradient from Massachusetts to North Carolina, to growth chamber treatments that simulated current and projected temperatures in central Massachusetts and central North Carolina within the next century. Regardless of source location, colonies of A. rudis, a keystone seed disperser, experienced high mortality and low brood production in the warmest temperature treatment. Colonies of T. curvispinosus from cooler locations experienced increased mortality in the warmest rearing temperatures, but colonies from the warmest locales did not. Our results suggest that populations of some common species may exhibit uniform declines in response to warming across their geographic ranges, whereas other species will respond differently to warming in different parts of their geographic ranges. Our results suggest that differential responses of populations and species must be incorporated into projections of range shifts in a changing climate.

Spatial variation in transient water table responses: differences between an upper and lower hillslope zone

AbstractTo better understand storage‐runoff dynamics, transient groundwater responses were examined in one of the steep watersheds in British Columbia's coastal mountains. Streamflow and piezometric data were collected for 1 year to determine the spatial and temporal relations between transient groundwater levels and discharge. Correlations between piezometer responses and lag‐time analysis were used to identify and better understand runoff generation mechanisms in this watershed. Results showed a large spatial and temporal variation in transient water table dynamics and indicated that two distinct zones existed: a lower hillslope zone and an upslope zone. Each zone was characterized by very different water table responses. The upper hillslope was disconnected from the stream for the majority of time, suggesting that during most events, it does not directly contribute to streamflow. Piezometers in the lower hillslope zone showed hydrologically limited responses, suggesting rapid subsurface flow, likely through the many macropores and soil pipes. The lag time between peak streamflow and peak groundwater level decreased with increasing antecedent moisture conditions and was more variable for piezometers further away from the stream than for piezometers close to the stream. The study results indicate that a single storage‐runoff model is not appropriate for this steep watershed and that a two‐ or three‐compartment model would be more suitable. Copyright © 2011 John Wiley & Sons, Ltd.

Rock topography causes spatial variation in the wave, current and beach response to sea breeze activity

We hypothesized that beach profiles that are perched on natural rock structures would be better protected from waves and currents than profiles that are not fronted by rock. In southwest Western Australia many beaches, such as at Yanchep, are perched on Quaternary limestone. Yanchep Lagoon is fronted by a low-crested limestone reef that partially encloses a coastal lagoon. The spatial variation of waves and currents around the rock structures were quantified during the sea breeze cycle at locations: (1) offshore; (2) 20 m seaward of the reef; (3) inside the lagoon; and (4) in the surf zone. The spatial variation in the beach profile response was measured at two beach profiles: (1) the Exposed Profile that was not fronted directly seaward by outcropping limestone; and (2) the Sheltered Profile which was fronted seaward by submerged limestone at 2 m water depth and that was near the lagoon exit at the end of the limestone reef. The Sheltered Profile had greater volume changes during the cycle of the sea breeze whilst the Exposed Profile recovered more by overnight accretion when wind decreased. The lagoonal current drove the strong response of the Sheltered Profile and may have contributed to the lack of overnight recovery of the beach together with the seaward rock formation impeding onshore sediment transport. The different direction and speed responses of bottom-currents in the surf zone fronting the two profiles reflected the local variation in geology, the influence of the jet exiting the lagoon, and wave refraction around the reef that was measured with GPS drifters and wave-ray tracing using XBeach. Major spatial variation in waves, currents and beachface behavior at this perched beach shows the importance of the local geological setting.

Time-Domain Implementation of Broadband Beamformer in Spherical Harmonics Domain

Most of the existing spherical array modal beamformers are implemented in the frequency domain, where a block of snapshots is required to perform the discrete Fourier transform. In this paper, an approach to real-valued time-domain implementation of the modal beamformer for broadband spherical microphone arrays is presented. The microphone array data are converted to the spherical harmonics domain by using the discrete spherical Fourier transform, and then steered to the look direction followed by the pattern generation unit implemented using the filter-and-sum structure. We derive the expression for the array response, the beamformer output power against both isotropic noise and spatially white noise, and the mainlobe spatial response variation in terms of the finite impulse response (FIR) filters' tap weights. A multiple-constraint problem is then formulated to find the filters' tap weights with the aim of providing a suitable tradeoff among multiple conflicting performance measures such as directivity index, robustness, sidelobe level, and mainlobe response variation. Simulation and experimental results show good performance of the proposed time-domain broadband modal beamforming approach.