comparison of radar and video observations of shallow water breaking waves simultaneous microwave and video measurements of shallow water breaking waves are presented a comparison of the data from the two sensors shows that short duration spikes in the measured x band radar cross section are highly correlated with the presence of breaking waves in the video imagery in addition the radar backscatter from shallow water breaking events is responsible for 40 to 50 of the total cross section which is a much larger contribution than typically observed for deepwater breaking events based on estimates of the area of individual breaking regions determined from digitized video images the radar cross section per unit area of the turbulent breaking region is shown to be well approximated by a value of 1 9 db at 31 spl deg grazing finally there are some differences between the radar and video signals that suggest that microwave radar may be less sensitive than video techniques to relict foam not associated with active wave breaking in general the results indicate that radar is a very good detector of shallow water breaking waves and suggest that radar can be used for the measurement of the spatial and temporal variations of wave breaking

rapid wavelet based bathymetry inversion method for nearshore x band radars abstract a wavelet based method for bathymetry retrieval from x band radar images is proposed the method combines traditional fast fourier transform techniques for retrieving peak frequency maps by evaluating the spectral peaks in the time domain and a localized 2d continuous wavelet transform for retrieving the corresponding peak wavenumbers the main improvements of the new method compared to conventional fft based methods are as follows a the wavelet based approach is localized naturally fitting the inhomogeneous conditions typically found in the nearshore environment b it is continuous and uses wave phase information providing smooth bathymetry maps with good accuracy rmse in the range 2 6 6 6 of the maximum water depth c it requires relatively small number of successive images without the limitation of requiring a uniform time step in order to verify the proposed method 2d simulations of wave shoaling and refraction were performed for different sea conditions and over several bottom topographies a radar image model including tilt and shadowing modulations together with speckle noise was applied to the simulated surface elevations to provide synthetic radar images the method s ability to reconstruct the original bathymetry is shown to be robust in intermediate to shallow water depths kph

video estimation of subaerial beach profiles abstract a technique is presented that allows estimation of the subaerial beach profile using video imagery using either a shadow from a pole or the light from a narrow slit a line can be drawn across the beach at a known origin and angle when viewed from the longshore direction the line will appear as a visible beach profile that can be digitized from the image and the ground coordinates of the profile uniquely determined the theoretical pixel vertical footprint is about one thousandth of the range from the camera or for a typical camera about 10 cm at the 100 m range accuracies can be up to 1 2 pixel or 5 cm at this range a field test using a fire hose as a proxy for the shadow proved the technique with an average accuracy of 68 of the theoretical footprint size being found the success of this technique suggests that profile data may be routinely collected using an automated system without the need for a survey team thus allowing the ready collection of long time series for climatological studies

application of marine radar to monitoring seasonal and event based changes in intertidal morphology this paper demonstrates the application of marine radar and a newly developed waterline mapping technique to the continued surveillance and monitoring of inter and intra annual intertidal morphological change thus capturing new detail on coastal system behaviours marine radar data from 2006 to 2009 are used to create a sequence of waterline elevation surveys that show clear morphological evolution of two different sites in the dee estuary uk an estimate of volumetric change was made at two locations west hoyle sandbank and the nw wirral beach both sites exhibited a similar cyclic pattern of volumetric change with lowest volumes in autumn and winter respectively the average beach elevations above admiralty chart datum clearly reflect the observed change in sediment volume with reduced elevations in winter and increased elevations in summer suggesting a trend of high energy storm waves in autumn and winter that remove sediment and simultaneously moderate the vertical dimension of bedforms in the intertidal area data at this temporal and spatial scale are not easily obtainable by other current remote sensing techniques the use of marine radar as a tool for quantifying coastal change over seasonal and event timescales in complex hydrodynamic settings is illustrated specifically its unique application to monitoring areas with dynamic morphology or that is vulnerable to erosion and or degradation by storm events is exemplified

remote sensing of breaking wave phase speeds with application to non linear depth inversions abstract a number of existing models for surface wave phase speeds linear and non linear breaking and non breaking waves are reviewed and tested against phase speed data from a large scale laboratory experiment the results of these tests are utilized in the context of assessing the potential improvement gained by incorporating wave non linearity in phase speed based depth inversions the analysis is focused on the surf zone where depth inversion accuracies are known to degrade significantly the collected data includes very high resolution remote sensing video and surface elevation records from fixed in situ wave gages wave phase speeds are extracted from the remote sensing data using a feature tracking technique and local wave amplitudes are determined from the wave gage records and used for comparisons to non linear phase speed models and for non linear depth inversions a series of five different regular wave conditions with a range of non linearity and dispersion characteristics are analyzed and results show that a composite dispersion relation which includes both non linearity and dispersion effects best matches the observed phase speeds across the domain and hence improves surf zone depth estimation via depth inversions incorporating non linearity into the phase speed model reduces errors to o 10 which is a level previously found for depth inversions with small amplitude waves in intermediate water depths using linear dispersion considering the controlled conditions and extensive ground truth this appears to be a practical limit for phase speed based depth inversions finally a phase speed sensitivity analysis is performed that indicates that typical nearshore sand bars should be resolvable using phase speed depth inversions however increasing wave steepness degrades the sensitivity of this inversion method

nearshore subtidal bathymetry from time exposure video images time averaged over many wave periods nearshore video observations show the process of wave breaking as one or more white alongshore bands of high intensity across a known depth profile similar bands of dissipation can be predicted with a model describing the time averaged cross shore evolution of organized wave and roller energy this close correspondence between observed and modeled dissipation proxies is used to develop a new remote sensing technique termed subtidal beach mapper sbm to estimate nearshore bathymetry sbm operates on a time series of cross shore intensity profiles to resolve the pattern in depth change on a morphological timescale including overall gain or loss of sediment rather than to focus on the particular change induced by a single intensity profile from each intensity profile the breaking induced component is isolated by removing the contribution of background illumination and persistent foam the depth profile is updated based on a comparison between this video derived dissipation proxy and a cross shore profile of the dissipation of the roller energy this updating is implemented through time dependent mass balance equations for the seabed and a buffer layer above the bed sbm was tested using 1 year of hourly video data collected at egmond aan zee netherlands the dominant morphological changes observed from ground truth data were reproduced reasonably well including the shoreward migration of the outer bar and the net sediment gain in the profile root mean square differences between surveyed and sbm derived depth after 1 year of video based depth updating with an average of about 70 intensity profiles per month were smallest 0 2 m on the inner bar and largest 0 6 m in the outer bar trough with a profile average value of about 0 4 m despite the many processes included in sbm the implementation of a heuristic scaling function in the mass balance equations to spatially adjust morphological growth rates was essential to these results in particular near the shoreline where otherwise the profile is prone to an unrealistic deepening

ocean surface determination from x band radar image sequences 1 an empirical inversion method is presented for determination of time series of ocean surface elevation maps from nautical radar image sequences the method is based on the determination of the surface tilt angle in antenna look direction at each pixel of the radar images thereby in situ sensors are not required an external calibration is not necessary a conventional nautical x band radar operating at grazing incidence and horizontal polarization in transmit and receive is used as a sensor radar image sequences with their high spatial resolution and large coverage offer a unique opportunity to derive and study individual waves and wave fields in space and time and therefore allow the measurement of individual wave parameters and wave groups for validation of the inversion scheme the significant wave heights derived from the inverted radar data sets and from colocated wave records are compared it is shown that the accuracy of the radar retrieved significant wave height is within the accuracy of the in situ sensors furthermore a wave elevation time series is directly compared to a buoy record to show the capabilities of the proposed method

shallow water bathymetry derived from an analysis of x band marine radar images of waves image sequences of surface gravity waves are readily produced by standard marine x band radars these image sequences contain a great deal of information regarding wave parameters and their variation over an area by approaching the analysis of such data using image analysis techniques it is possible to map the variations in wave behaviour in a shallow water area wave celerity and direction can be mapped and inversion algorithms based on linear wave theory used to infer the underlying bathymetry knowledge of the period of the waves is necessary for the analysis and this can also be calculated from the radar data although there is some discrepancy between the figures derived from radar data and from an offshore s4dw instrument these discrepancies are investigated and the results presented three days of data from the holderness ii deployment during 1995 have been analysed and estimates of the bathymetry produced the calculated depths show a mean water level comparable to that read off an admiralty chart for the area and a tidal signal is also clearly superimposed on the data giving confidence in the water depths derived using this technique

island evolution and stepwise retreat late holocene transgressive barriers mississippi delta coast limitations of a model abstract several vital components of a new three stage barrier shore development model on delta coasts require further scrutiny to be acceptable even with modifications solid evidence for a proposed continuous evolutionary sequence involving genetic relationship between islands associated with erosional headlands and firmly established island arcs as well as between these detached arcs and inner shelf shoals has not yet been demonstrated convincingly in the few examples that were presented the range of probable roles of erosional or prograding headlands active or inactive subdeltas subtidal shoals and barrier spits in barrier island formation variable rates of island evolution and decomposition in different settings and genetic alternatives of shelf shoal formation introduce many more possible variables than could be harnessed into the rather restrictive three stage model the highly changeable south chandeleur islands are unsuitable analogs for a model of barrier and primary surf overstep during relative sea level rise alternating erosion accretion cycles during recorded history of the islands as a whole cast doubt on the likelihood of their future total elimination even in absence of the barrier chain wave dampening across shallow chandeleur sound would be expected to prevent a primary surf zone from forming along the mainland shore

the application of a radar based depth inversion method to monitor near shore nourishments on an open sandy coast and an ebb tidal delta abstract coastal management in the netherlands has the aim to defend coastal zones by preventing flooding and mitigating erosion to that end large scale nourishments are placed in the nearshore which are supposed to dynamically preserve the coastal zone over a timescale of years to assess their effectiveness these nourishments are monitored over large areas and long durations as repetitive in situ measurements become too expensive remote sensing offers an attractive alternative mapping depth and near surface current fields via depth inversion algorithms dia however the information that can be derived from remotely sensed data is subject to improvement in this study a 3d fft based dia named xmfit x band matlab fitting is introduced which is robust accurate and fast enough for operational use focusing on depth estimates the algorithm was validated for two case studies in the netherlands 1 the sand engine a beach mega nourishment at a uniform open coast and 2 the tidal inlet of the dutch wadden sea island ameland characterizing a more complex coast considering both sites the algorithm performance was characterized by a spatially averaged depth bias of 0 9 m at the sand engine and a time varying bias of approximately 2 0 m at the ameland inlet when compared to in situ depth surveys the accuracy was lower but the time resolution higher depth estimates from the ameland tidal inlet were produced every 50 min by an operational system using a navigational x band radar to monitor the placement of a 5 million m3 ebb tidal delta nourishment a pilot measure for coastal management volumetric changes in the nourishment area over the year 2018 occurring at 7 km distance from the radar were estimated with an error of 7 depth errors statistically correlated with the direction and magnitude of simultaneous near surface current estimates additional experiments on sand engine data demonstrated that depth errors may be significantly reduced using an alternative spectral approach and or by using a kalman filter

estimation of the nearshore bathymetry from high temporal resolution sentinel 1a c band sar data a case study abstract the study of the changes in swell properties in the nearshore domain due to interaction with the sea bottom to infer the bathymetry has deserved some attention in the last few years satellite remote sensing images in particular synthetic aperture radar sar have been used to produce a directional wave spectrum by fast fourier transform fft from which the wavelength and wave direction of the ocean surface waves can be retrieved these wave properties can be directly used in the linear dispersion relation to estimate the water depth the present work takes advantages from the very short revisit times of the sentinel 1a with c band 5 405 ghz sar images with 10 m of spatial resolution to study the repeatability of this methodology for deriving the nearshore sea bottom morphology using a case study in the aveiro region located in the portuguese west coast this site is exposed to high energetic wave climate of the north atlantic ocean overall a set of four images were selected for the analysis the robustness of the fft methodology to calculate the wavelength and wave direction from sar images was analysed through calculating their standard deviations the errors of estimating the local bathymetry from these quantities was accessed which allowed to quantify the water depth limits of application of this methodology the set of images was used to establish a bathymetric estimation that merges the derived bathymetry of each image the computed bathymetry was quantitatively compared with the measurements made in 2013 and available at raia observatory the relative error of the water depth ranges between 6 and 10 but increases for the higher depths and depends on the accuracy of the computed wavelength at deep waters the merged derived bathymetry also provides a better approximation for the measured bathymetry than those derived from the individual images

application of the linear dispersion relation with respect to depth inversion and remotely sensed imagery remote sensing methods have been developed to estimate bathymetry through the use of a theoretical relationship between wave speed and water depth known as the linear finite depth dispersion equation for surface gravity waves the authors describe a validation effort encompassing several hundred observations of wavenumber magnitude for sea swell frequencies obtained over a wide variety of conditions to investigate possible error sources resulting from the practical application of this relationship these wavenumber estimates were computed from pressure gauge signals using signal processing algorithms that can be equivalently applied to measurements of wave phase as imaged through remote sensors the major goal was to determine the accuracy of the dispersion relation while attempting to minimize errors associated with sensor positioning tidal variations and doppler shifts due to mean currents for water depths outside the surf zone the linear dispersion relation is highly accurate with average depth estimation errors on the order of 3 9 of the observed depth in shallower regions nominally less than 4 m for this field site where wave breaking is evident and nonlinear shoaling effects are more pronounced normalized depth errors of over 50 were commonly observed with most predictions being deeper than observations strong correlation between these bias errors and measured wave heights emphasizes the importance of accounting for wave amplitude in the calculation of shallow water phase speeds for depth estimation a simple depth correction is provided to allow for bathymetry estimation within the surf zone

ocean wind fields retrieved from radar image sequences 1 the dependency of radar backscatter on the surface wind field is investigated using a nautical x band radar operating at grazing incidence and horizontal polarization in transmit and receive this resulted in development of an algorithm for wind retrieval from nautical radar image sequences the algorithm consists of two parts in the first part wind directions are extracted from wind induced streaks that are in line with the mean surface wind direction these streaks are visible in the temporal integrated radar images at scales between 100 and 500 m the orientation of the streaks is determined from the local gradients which are derived from the radar images smoothed and reduced to the appropriate scales in the second part wind speeds are derived from the backscatter of the temporal integrated radar image sequence and the radar retrieved wind direction the dependency of the radar backscatter on the local surface wind and geometry of the radar is parameterized by training a neural network the algorithm is applied to radar image sequences acquired by a nautical x band radar mounted aboard an offshore platform in the north sea the radar derived winds are validated by comparison to in situ wind data measured at the platform the comparison of wind directions resulted in a correlation of 0 99 with a standard deviation of 14 2 for wind speeds the correlation is 0 97 with a standard deviation of 0 85 m s 1 in contrast to traditional offshore wind sensors the retrieval of the wind field from the backscatter of the ocean surface makes the system independent of the sensors motion and installation height and reduces the effects due to platform induced blockage and turbulence effects

high resolution bathymetry estimates via x band marine radar 2 effects of currents at tidal inlets abstract in this second of two papers the high spatial resolution cbathy depth estimate algorithm is extended to account for the existence of currents aligned with the wave directions the extended algorithm is applied using x band radar image time series collected at two hydrodynamically and morphologically complex environments an ebb tidal shoal new river inlet nc and an estuarine river mouth columbia river or wa even without accounting for doppler effects the depth estimates are capable of discerning the location of channels and shoals over domain sizes of 4 km2 at the ebb tidal shoal and 25 km2 at the estuary mouth however the tidal currents at these sites are shown to strongly modulate depth estimate accuracy when only the intrinsic linear wave dispersion relation neglecting doppler shift effects is inverted low pass filtering of the depth estimate time series via an uncertainty weighted tidal average explicitly attenuates the error oscillations beyond that of the uncertainty weighted kalman filter this post hoc method of compensating for the unmodeled doppler term achieves 0 35 m rmse and 0 02 m shallow bias at the shallow ebb tidal shoal as compared to a concurrent sounding survey but substantial bias remains at the estuary mouth due to asymmetric doppler effects for large following or opposing currents at large relative water depths simultaneous estimation of depth and currents via inversion of the dispersion relation including doppler shifts is more effective at the deep estuary mouth where currents more strongly affect the incident wave field in the estuary channel with locations as deep as 27 m kalman filtered depths achieve 0 92 m rmse and 0 38 m deep bias as compared to a concurrent sounding survey 95 of estimates are within 10 of those surveyed independent of the doppler compensation technique kalman filtered depths can be used to more tightly constrain high resolution current velocity estimates

a temporal waterline approach to mapping intertidal areas using x band marine radar abstract mapping the morphology of intertidal areas is a logistically challenging time consuming and expensive task due to their large expanse and difficulties associated with access a technique is presented here that uses standard marine navigational radar operating at x band frequency the method uses a series of time exposure radar images over the course of a two week tidal cycle to identify the elevation of the wetting and drying transitions at each pixel in the radar images thereby building up a morphological map of the target intertidal area this temporal waterline method is applied to a dataset acquired from hilbre island at the mouth of the dee estuary uk spanning march 2006 to january 2007 the radar gathered data with a radial range of 4 km and the resulting elevation maps describe the intertidal regions of that area the results are compared with airborne lidar data surveyed over the same area and within the radar survey time period the residual differences show good agreement across large areas of beach and sandbanks with concentrations of poor estimations around points that are shadowed from the radar or likely to suffer from pooling water this paper presents the theoretical framework of the method and demonstrates its stability and accuracy the temporal waterline radar method is aimed at providing a useful tool for the monitoring and operational management of coastlines

accuracy of bathymetric assessment by locally analyzing radar ocean wave imagery february 2008 in this paper the error source in assessing the bathymetry by a recently presented method the dispersive surface classificator is discussed this method is based on the analysis of x band radar image sequences of sea surface waves to determine spatial maps of hydrographic parameters to implement this objective the radar deduced bathymetry is validating by multibeam echosounder data the accuracy of the method is high in homogeneous areas and reduced at the areas of bathymetric gradient and lower but comparable with multibeam echosounder data under the assumption of the spatial resolution the identification of systematic correlation of the absolute value of the error with the slope is significant and insignificant with the actual depth itself the spatial correlation of the error illustrates that the direction of the wave field influences the neighboring grid cell in the same direction the application of the method during crucial weather conditions is the main advantage and permits the accurate operational nearshore monitoring for several applications

depth inversion in shallow water based on nonlinear properties of shoaling periodic waves abstract two depth inversion algorithms dia applicable to coastal waters are developed calibrated and validated based on results of computations of periodic waves shoaling over mild slopes in a two dimensional numerical wave tank based on fully nonlinear potential flow fnpf theory in actual field situations these algorithms would be used to predict the cross shore depth variation h based on sets of values of wave celerity c and length l and either wave height h or left right asymmetry s2 s1 simultaneously measured at a number of locations in the direction of wave propagation e g using video or radar remote sensing techniques in these dias an empirical relationship calibrated for a series of computations in the numerical wave tank is used to express c as a function of relative depth koh and deep water steepness koho to carry out depth inversion wave period is first predicted as the mean of observed l c values and ho is then predicted either based on observed h or s2 s1 values the celerity relationship is finally inverted to predict depth h the algorithms are validated by applying them to results of computations for cases with more complex bottom topography and different incident waves than in the original calibration computations in all cases root mean square rms errors for the depth predictions are found to be less than a few percent whereas depth predictions based on the linear dispersion relationship which is still the basis for many state of the art dias have rms errors 5 to 10 times larger

waves at holderness from x band radar abstract during the holderness experiment of 1994 1995 and 1995 1996 data were collected by a coastal deployment of an x band radar with simultaneous deployments of various moored and bottom mounted wave measurement devices the radar data consist of sequences of images of the sea surface at intervals of 1 5 h over several months three dimensional wave number frequency spectra were derived from the sequences of captured images using an analysis method developed by young et al j geophys res 90 c1 1985 1049 some aspects of this analysis were refined an empirical transfer function was derived relating the radar image spectra to the wave spectra measured by other instruments a new calibration procedure for obtaining wave height from the radar spectra was also derived the radar spectra were compared with directional spectra collected by a bottom mounted interocean s4dw directional wave current meter and with datawell waverider data the capabilities of x band radar in a coastal situation are discussed including the derivation of water depth required to optimise the analysis

model parameterization and experimental design issues in nearshore bathymetry inversion 1 we present a general method for approaching inverse problems for bathymetric determination under shoaling waves we run the korteweg de vries kdv model for various bathymetric representations while collecting data in the form of free surface imagery and time series the sensitivity matrix provides information on the range of influence of data on the parameter space by minimizing the parameter variances three metrics based on the sensitivity matrix are derived that can be systematically used to make choices of experiment design and model parameterization this analysis provides insights that are useful irrespective of the minimization scheme chosen for inversion we identify the characteristics of the data time series versus snapshots early time measurements versus long duration measurements nearshore measurements versus offshore measurements and model bathymetry parameterizations for inversion to be possible we show that bruun dean and exponential bathymetric parameterizations are preferred over polynomial parameterizations the former can be used for inversion with both time series and snapshot data while the latter is preferably used only with snapshot data also guidelines for time separation between snapshots and spatial separation between time series measurements are derived index terms 4560 oceanography physical surface waves and tides 1255 4546 oceanography physical nearshore processes 4594 oceanography physical instruments and techniques 4255 oceanography general numerical modeling keywords experimental design model parameterization bathymetric inversion

wind retrieval from shipborne nautical x band radar data in this paper we study the retrieval of wind information from nautical x band radar data in contrast to previous studies where data from stationary research platforms were used this study focuses on data from a moving platform encountering a larger variety of conditions than a platform at a fixed location compared to traditional in situ sensors wind data derived from nautical radar images are much less susceptible to air flow distortion by the platform since the images cover a large area around the ship images collected with a standard nautical hh polarized x band radar operating at grazing incidence exhibit a single intensity peak in upwind direction the wind retrieval method developed here uses a harmonic function that is least squares fitted to the radar backscatter intensity as a function of antenna look direction the upwind direction is given by the direction that corresponds to the peak of the fitted function an empirical model function is derived to retrieve the wind speed from the average radar backscatter intensity contrary to wind retrieval methods that have been proposed before this approach is well suited for data acquired from a moving platform as it functions well even if the radar field of view is partially shadowed and does not require ship motion correction here we focus on data that were collected during two storms using the first storm to derive and the second to test the empirical model functions the method is validated using measurements from two ship based anemometers

video observations and model predictions of depth induced wave dissipation time averaged video observations of the nearshore zone show the process of wave breaking as one or more white alongshore bands of high intensity corresponding to the preferential location of breaking wave dissipation on one or more sandbars across a known depth profile similar bands of dissipation can be predicted with existing wave transformation models based on the wave energy balance this opens up possibilities for estimating bathymetry from video observations by processing observed intensities into a model predicted proxy of wave dissipation and the inverse modeling of this dissipation proxy into depth the objectives of this paper are 1 to present a technique for processing time averaged cross shore image intensity profiles into profiles that solely contain the contribution due to wave breaking and 2 to empirically determine which modeled wave dissipation proxy relates best to the cross shore shape of the obtained breaking induced intensity the processing technique involves the removal of background illumination and noise and most importantly a correction for white foam that after being generated in the breaking process remains floating at the water surface this foam thus contributes to high image intensities but is not predicted by wave transformation models based on video and bathymetric data collected at the double barred beach at egmond aan zee the netherlands and a standard wave transformation model containing the wave and roller energy balances we find that the modeled cross shore distribution of the dissipation of the energy of the surface roller the white aerated mass of water at the breaking wave front matches the observed cross shore shape of breaking induced intensity well other hypothesized dissipation proxies result in a larger 10 m seaward bias in the locations of maximum breaking induced intensity and model predicted dissipation or do not predict the cross shore change in the area below the breaking induced intensity bands correctly

video based depth inversion techniques a method comparison with synthetic cases abstract applications of video based depth inversion in the near shore coastal environment are growing in numbers video based capabilities in nearshore monitoring are improving and coastal monitoring programs are expanding due to greater availability and reduced costs video derived beach state indicators such as beach width bar position and wave and current parameters are supplemented by accurate depth estimations through inversion video based depth inversion knows two main approaches a spectral and temporal method of celerity estimation the two methods have so far never been compared as video systems are often tailored for the chosen celerity estimation method here a spectral and temporal method are compared using controlled synthetic datasets obtained using the serre1d boussinesq model to estimate celerity and invert depth the assessment is carried out on a set of wave boundary conditions with over linear and barred bottom profile both methods invert depth with a similar accuracy for the most realistic jonswap cases an evident correlation is found between wave skewness non linearity and depth estimation error linked to the limits of the linear dispersion relation a residual sensing error is linked to method based parameters and a changing wave shape as incident waves propagate inshore the inversion error can be reduced significantly including a wave height dependent non linear correction importantly a method based error is introduced for the temporal method to increase the suitability for data assimilation likewise the spectral method has its own existing depth error estimation to feed into the kalman filter however these method based error estimates show very weakly or no relation to the observed error between estimated cross shore profile and bottom profile used for the model input

artificial neural network correction of remotely sensed sandbar location abstract this contribution details an accurate method for the remote sensing of submerged sandbar location through the application of an artificial neural network to video data lippmann and holman lippmann t c holman r a 1989 quantification of sandbar morphology a video technique based on wave dissipation j geophys res 94 c1 995 1011 have shown that the intensity maxima seen in time averaged video images of the nearshore zone provide a reasonable proxy for sandbar location however recent studies have indicated that there may be a large deviation up to 30 40 m between the measured bar position and predictions based on the intensity maximum in the cross shore direction these deviations occur largely due to modulations of the breakpoint by the tide and variations in the incident wave energy this paper utilises an artificial neural network to model the cross shore movement in the intensity maximum due to tides and waves the resulting signal is then removed from the video estimates to provide an accurate estimation of the sand bar location unique field data sets collected as part of the coast3d experiment are used to train and test the neural network model these data consist of simultaneous measurements of the nearshore bathymetry and video imagery of the double bar system at egmond aan zee the netherlands the resulting model yields accurate estimates of sandbar location with residual errors of less than 5 m for the outer bar and less than 10 m for the inner bar the artificial neural network model is utilised to extend the bathymetric data set for egmond aan zee for times when wave conditions were too large to allow physical measurement

accuracy of bathymetry and current retrievals from airborne optical time series imaging of shoaling waves a sequence of visual images of shoaling ocean waves collected from an aircraft can be used to retrieve maps of water depth and or currents the data are mapped to rectilinear coordinates on the mean ocean surface and three dimensional 3d cubes of these data typically 2 min dwell and 256 m spl times 256 m square area are fourier transformed to provide the 3d frequency wavenumber spectrum of the modulations the spectrum is fitted by the theoretical two dimensional dispersion surface for linear gravity waves with the depth and current vector as free parameters and the errors determined by comparison with simultaneously collected in situ data very little attention has been focused on the limitations and inherent errors in this approach for retrieving these parameters in the past this paper examines the dependence of these errors upon various instrumental and collection geometry parameters in order to estimate the achievable retrieval accuracy and provide collection guidelines significant errors occur when the mapping is inaccurate and when the data cubes are too small either spatially or temporally data cubes of the size given above or larger are required to contain the relative errors within 5 to 10 of the ground truth values the spatial resolution and temporal sampling rate are less critical and pixel sizes of spl sim 3 4 m and framing rates of spl sim 0 5 hz for depth and 1 2 hz for currents are sufficient for providing adequate results with the data examined here finally we show that the covariance matrix from the functional fit provides a quantitative measure of the retrieval accuracy independent of in situ data

seismic and acoustic signals detected at lo ihi seamount by the hawai i undersea geo observatory 1 the hawai i undersea geo observatory hugo is an ocean bottom observatory located on the summit of lo ihi seamount hawai i an electro optical cable connects the hugo junction box to a shore station on the big island of hawaii thereby enabling the first real time monitoring of a submarine volcano hugo was active for 3 months in 1998 collecting nearly continuous real time data on a high rate hydrophone signals detected during that time include local as well as teleseismic earthquakes t phases from pacific wide earthquakes landslides on the submarine flank of kilauea and eruption sounds from the current kilauea eruption the data do not indicate a lo ihi eruption during the time that hugo was active the variety and quality of signals detected by the hugo hydrophone confirms that a real time observatory can serve a valuable role in studies of oceanic acoustics local and teleseismic earthquakes and submarine eruption mechanics

observations of wave influence on alongshore ebb tidal delta morphodynamics at oregon inlet nc abstract a radar inlet observation system rios collected hourly x band radar data at the wave dominated oregon inlet nc for 9 months from september 2016 to may 2017 the intensity of the radar backscatter predominantly associated with surface wave shoaling and breaking was time averaged to provide an implied measure of bedforms superimposed on the ebb tidal delta eulerian and lagrangian motion tracking analyses determined the bedform alongshore migration rates over the study period these were found to be significantly correlated to estimates of longshore sediment flux based on offshore wave parameters given by ashton and murray 2006 although the exact magnitude of sediment transport cannot be directly estimated from bedform migration the correlation does support an underlying assumption that sediment transport varies proportionally in both magnitude and direction to average bedform movements the implications of these findings were further explored through application of the sediment transport model to a year long period of continuous offshore wave data 20 oct 2016 to 20 oct 2017 the predicted net transport of 90 000 m3 southward during this year is consistent with a previous estimate of inlet bypassing dolan and glassen 1973 however pronounced and opposing seasonal transport patterns were an order of magnitude higher than the yearly net and could lead to significant inter annual variability in alongshore sediment transport with similar dynamic response in ebb delta morphodynamics at oregon inlet

high resolution bathymetry estimates via x band marine radar 1 beaches abstract in this paired study we apply a recently developed high resolution bathymetry estimation algorithm cbathy to x band marine radar observations at two nearshore field sites the algorithm exploits observations of the spatial structure of wave phase to attain wavenumber estimates inverts the linear water wave dispersion relation for depth and then applies a kalman filter to objectively update the bathymetry estimates previously performance has only been tested using optical video observations in this first of two papers performance of the algorithm using x band radar image time series is tested at two disparate barred beach environments duck nc usa and benson beach wa usa each of the test beaches is either co located with duck nc or geographically close to benson beach wa those utilized in the original algorithm verification concurrent echosounder surveys are used as ground truth the bulk performance of the radar derived bathymetry estimate at duck nc achieves 0 49 m root mean square error rmse with 0 26 m bias deep this compares well with the bulk performance of the concurrent estimate derived using optical video 0 44 m rmse and 0 23 m bias deep the radar derived bathymetry estimate performance at benson beach is similar 0 35 m rmse and 0 11 m bias shallow and is comparable to that of an optical video derived estimate at a similar pacific northwest beach 0 56 m rmse and 0 41 m bias shallow at both beaches significantly higher performance is achieved at locations deeper than 2 m offshore of the surfzone than at locations shallower than 2 m surfzone where errors are often a large fraction of the total depth lastly several weeks of observations are utilized to assess the sensitivity of algorithm quality control to environmental conditions thresholds based on the shoreward component of wind stress and offshore wave steepness are identified and shown to impact the areal coverage of radar derived bathymetric estimates overall these results demonstrate the viability of marine radar observations as input to the cbathy algorithm and delineate some environmental constraints on algorithm performance in the companion paper the algorithm is extended to areas where tidal currents are important including an ebb tidal shoal and an estuary mouth

surf zone characterization for integration with remote sensing data abstract a numerical model that solves the unsteady incompressible reynolds averaged navier stokes equations has been utilized to simulate 57 cases of monochromatic breaking waves over a sloping bed the volume of fluid technique is used to track the complex discontinuous free surface and the renormalized group turbulence model is used for closure the model is validated by comparing predictions with particle image velocimetry data and other empirical results the model results are used to determine a relationship between the incipient wave breaking height and the maximum orbital velocity as well as a relationship between surf zone width and breaker type such expressions may be useful for remote sensing methods like synthetic aperture radar to derive breaker height and classification from image data

estimation of wave phase speed and nearshore bathymetry from video imagery a new remote sensing technique based on video image processing has been developed for the estimation of nearshore bathymetry the shoreward propagation of waves is measured using pixel intensity time series collected at a cross shore array of locations using remotely operated video cameras the incident band is identified and the cross spectral matrix is calculated for this band the cross shore component of wavenumber is found as the gradient in phase of the first complex empirical orthogonal function of this matrix water depth is then inferred from linear wave theory s dispersion relationship full bathymetry maps may be measured by collecting data in a large array composed of both cross shore and longshore lines data are collected hourly throughout the day and a stable daily estimate of bathymetry is calculated from the median of the hourly estimates the technique was tested using 30 days of hourly data collected at the sandyduck experiment in duck north carolina in october 1997 errors calculated as the difference between estimated depth and ground truth data show a mean bias of 35 cm rms error 91 cm expressed as a fraction of the true water depth the mean percent error was 13 rms error 34 excluding the region of known wave nonlinearities over the bar crest the accuracy of the technique improved and the mean rms error was 20 cm 75 cm additionally under low amplitude swells wave height h 1 m the performance of the technique across the entire profile improved to 6 29 of the true water depth with a mean rms error of 12 cm 71 cm

water depth and surface current retrievals from airborne optical measurements of surface gravity wave dispersion visible images of nearshore ocean waves obtained from an aircraft have been utilized to estimate the surface currents and water depth below the waves a digital framing camera was mounted in a motion stabilized turret and used to obtain temporal sequences of high quality optical images of shoaling ocean waves data on the position and attitude of the camera turret were used to map the image data to a rectilinear coordinate system at the level of the surface effectively separating the spatial and temporal modulations due to the waves the resulting three dimensional 3 d space time data sets were fourier transformed to obtain frequency wave number spectra of these modulations these spectra contain information on the propagation characteristics of the waves such as their wavelengths and frequencies and their directions and speeds of propagation the water depth and current vector have been estimated by choosing these parameters so that a best fit is obtained between the theoretical dispersion relation for linear gravity waves and these 3 d wave spectra image data sets were acquired during the shoaling waves experiment showex along the quasi linear coastline in the vicinity of the army corps of engineers field research facility frf near duck on the north carolina outer banks summary wave parameters and bathymetry and current retrievals are typically within 10 of contemporaneous in situ measurements though outliers occur

accurate estimation of significant wave height with support vector regression algorithms and marine radar images abstract significant wave height h s is a basic parameter in wave characterization important for different problems in marine activities such as the design and management of vessels marine structures and wave energy converters h s is usually estimated using in situ sensors mainly buoys that record time series of wave elevation information in this paper we propose a method for h s estimation based on a support vector regression algorithm over non coherent x band marine radar images results for three different platforms fino 1 ekofisk and glas dowr at different locations of the north sea and south africa are presented showing that the svr obtains a better result than the existing standard method in h s prediction within different sea states observed at each location

comparison of optical and radar measurements of surf and swash zone velocity fields 1 surf zone bore celerities and swash zone surface currents were measured on a shallow sloping low energy beach using two remote sensing methods that differ fundamentally in their imaging mechanisms microwave doppler radar measures electromagnetic backscatter from small scale ocean surface roughness while video based particle image velocimetry piv relies on image texture resulting from variations in light reflectivity from the ocean surface imagery from the two methods showed high correlation in which regions of high radar backscatter corresponded to visibly identifiable waves and bores propagating across the surf zone correlation coefficients between radial velocity time series sampled using the two methods at multiple locations across the surf zone were typically greater than 0 5 for frequencies less than a noise cutoff of 0 25 hz similarly spectra were found to be coherent at the 95 level with a nearly zero phase shift between the two signals near the broad spectral peak between 0 02 and 0 25 hz however some significant differences were evident piv was capable of estimating both cross shore and alongshore surface velocities while the use of one microwave doppler radar system restricted surface velocity estimates from that technique to line of sight radial only piv was found to be more capable of estimating swash zone uprush and backwash surface velocities as a smoother water surface in the swash zone adversely affected radar reflectivity in contrast microwave doppler radar was found to be more capable of estimating the surface velocity between bores when insufficient image texture was recorded in the video imagery both techniques were capable of measuring surf zone bore celerities through comparison to a shallow water model and to independent celerity estimates extracted from the slope of individual bore trajectories typical normalized errors were roughly 25 for radar and 15 for piv

sensitivity of rip current forecasts to errors in remotely sensed bathymetry operational nearshore current forecasts based on numerical model simulations are gaining popularity as a measure to increase the safety of swimmers applying remotely sensed bathymetry in these model simulations is often proposed in order to cope with rapidly changing nearshore bathymetry errors in the remotely sensed bathymetry may negatively affect performance of the hydrodynamic model hence this study aims to determine the sensitivity of modelled nearshore currents with a strong focus on rip currents to errors in remotely sensed bathymetries the errors in the remotely sensed bathymetries depth inversion algorithm applied to video stream were quantified with a length scale aware validation technique providing useful insights in the contribution of pattern and amplitude errors to the total error throughout the analysis domain and over a range of bathymetric length scales subsequently simulations with a nearshore hydrodynamic model were performed using both in situ and remotely sensed bathymetries as an input a comparison of predicted rip currents on either bathymetry yielded performance statistics for operational current forecasts on remotely sensed bathymetries taking the model with in situ bathymetry as a reference linking these performance statistics back to the quantified errors in the remotely sensed bathymetry finally revealed the relation between errors in flow and bathymetry of all rip currents generated on an in situ bathymetry 55 were reproduced on the remotely sensed bathymetry showing that models predicting nearshore currents on remotely sensed bathymetry have predictive value positive rip current predictions were promoted significantly by accurate reproduction of the pattern and amplitude of nearshore bars at length scales between 200 and 400 m in contrast to the length scale aware validation technique applied here commonly used domain wide bulk error metrics lack important information about spatial variations in the quality of remotely sensed bathymetry