adaptation of prestack migration to multi offset ground penetrating radar gpr data in adapting the prestack migration technique used in seismic imaging to the inversion of ground penetrating radar gpr from time to depth sections we show that the theoretical integral formulation of the inversion can be applied to electromagnetic problems albeit with three assumptions the first two assumptions concern the electromagnetic characteristics of the medium primarily that the medium must be perfectly resistive and non dispersive and the third concerns the antennae radiation pattern which is taken to be 2d the application of this adaptation of the inversion method is confirmed by migrating actual gpr measurements acquired on the test site of the laboratoire central des ponts et chaussees the results show good agreement with the geometry of the structures in the medium and confirm that the possible departure from the assumption of a purely resistive medium has no visible effect on the information concerning the geometry of scattering and reflecting structures the field experiments also show that prestack migration processing is sufficiently robust with regard to the assumption of a non dispersive medium the assumption of a 2d antennae radiation pattern however produces artefacts that could be significant for laterally heterogeneous media nevertheless where the medium is not highly laterally heterogeneous the migration gives a clear image of the scattering potential due to the geometry of structural contrasts in the medium the scatterers are well focused from diffraction hyperbolae and well localized spatial geometry has limited dimensional accuracy and positions are located with a maximum error equal to the minimum wavelength of the signal bandpass objects smaller than one wavelength can nevertheless be detected and well focused if their dielectric contrasts are sufficiently high as in the case of iron or water in gneiss gravels furthermore the suitability of multi offset protocols to estimate the electromagnetic propagating velocity and to decrease the non coherent noise level of measurements is confirmed our velocity estimation is based on the semblance calculation of multi offset migrated images and we confirmed the relevance of this quantification method using numerical data the signal to noise ratio is improved by summing multi offset results after the addition of random noise on measurements thus the adaptation of prestack migration to multi offset radar measurements significantly improves the resolution of the scattering potential of the medium limitations associated with the methods used here suggest that 3d algorithms should be applied to strongly laterally heterogeneous media and further studies concerning the waveform inversion are necessary to obtain information about the electric nature of the medium

a global view of stratospheric gravity wave hotspots located with atmospheric infrared sounder observations 1 the main aim of this study is to find and classify hotspots of stratospheric gravity waves on a global scale the analysis is based on a 9 year record 2003 to 2011 of radiance measurements by the atmospheric infrared sounder airs aboard nasa s aqua satellite we detect gravity waves based on 4 3 m brightness temperature variances our method focuses on peak events i e strong gravity wave events for which the local variance considerably exceeds background levels we estimate the occurrence frequencies of these peak events for different seasons and time of day and use the results to find local maxima or hotspots in addition we use airs radiances at 8 1 m to simultaneously detect convective events including deep convection in the tropics and mesoscale convective systems at middle latitudes we classify the gravity wave sources based on seasonal occurrence frequencies for convection but also by means of time series analyses and topographic data our study reproduces well known hotspots of gravity waves e g the andes and the antarctic peninsula however the high horizontal resolution of the airs observations also allows us to locate numerous mesoscale hotspots which are partly unknown or poorly studied so far most of these mesoscale hotspots are found near orographic features like mountain ranges coasts lakes deserts or isolated islands this study will help to select promising regions and seasons for future case studies of gravity waves

a semianalytical ocean color inversion algorithm with explicit water column depth and substrate reflectance parameterization a semianalytical ocean color inversion algorithm was developed for improving retrievals of inherent optical properties iops in optically shallow waters in clear geometrically shallow waters light reflected off the seafloor can contribute to the water leaving radiance signal this can have a confounding effect on ocean color algorithms developed for optically deep waters leading to an overestimation of iops the algorithm described here the shallow water inversion model swim uses pre existing knowledge of bathymetry and benthic substrate brightness to account for optically shallow effects swim was incorporated into the nasa ocean biology processing group s l2gen code and tested in waters of the great barrier reef australia using the moderate resolution imaging spectroradiometer modis aqua time series 2002 2013 swim derived values of the total non water absorption coefficient at 443 nm at 443 the particulate backscattering coefficient at 443 nm bbp 443 and the diffuse attenuation coefficient at 488 nm kd 488 were compared with values derived using the generalized inherent optical properties algorithm giop and the quasi analytical algorithm qaa the results indicated that in clear optically shallow waters swim derived values of at 443 bbp 443 and kd 443 were realistically lower than values derived using giop and qaa in agreement with radiative transfer modeling this signified that the benthic reflectance correction was performing as expected however in more optically complex waters swim had difficulty converging to a solution a likely consequence of internal iop parameterizations whilst a comprehensive study of the swim algorithm s behavior was conducted further work is needed to validate the algorithm using in situ data

ground penetrating radar a near face experience from washington county arkansas digital ground penetrating radar gpr is an emerging technology for detecting locating and or mapping features in the shallow subsurface it has application to geology civil engineering environmental science engineering soil science and many other fields this case history describes a high quality gpr survey performed in very close proximity to a vertical limestone rock face at a roadcut site in northwest arkansas the configuration allowed interpretation of the gpr results with the maximum of amount of geologic control the rock face itself our experience suggests that gpr has significant potential as a high resolution tool for mapping shallow structure and stratigraphy in carbonate rocks

multifold borehole radar acquisition and processing the multifold acquisition principle was applied to a borehole radar survey performed in a granitic site grimsel test site switzerland two multifold coverage acquisitions 40 fold and 20 fold were carried out in a subhorizontal borehole instrumental drifts transmission time and sampling frequency fluctuations were corrected in order to remove shifts observed on cmp gathers and to optimize velocity analysis and trace stacking computation of velocity spectra was adapted in order to take into account the features of the medium investigated homogeneous velocity various reflector orientations the nmo velocities were then interpreted as angles between reflectors and the survey line the processing based on the computation of several constant velocity stacked sections performed with different nmo velocities leads to better results than the standard dmo nmo processing the signal to noise ratio of the stacked profile is improved in comparison with the single fold section which results from a standard acquisition from a practical point of view the implementation of a multifold radar survey within a borehole is difficult but a greater investigation range is obtained more reflectors are detected and the mapping of geological discontinuities is improved

gravity wave characteristics in the southern hemisphere revealed by a high resolution middle atmosphere general circulation model abstractgravity wave characteristics in the middle to high latitude southern hemisphere are analyzed using simulation data over 3 yr from a high resolution middle atmosphere general circulation model without using any gravity wave parameterizations gravity waves have large amplitudes in winter and are mainly distributed in the region surrounding the polar vortex in the middle and upper stratosphere while the gravity wave energy is generally weak in summer the wave energy distribution in winter is not zonally uniform but it is large leeward of the southern andes and antarctic peninsula linear theory in the three dimensional framework indicates that orographic gravity waves are advected leeward significantly by the mean wind component perpendicular to the wavenumber vector results of ray tracing and cross correlation analyses are consistent with this theoretical expectation the leeward energy propagation extends to several thousand kilometers which explains part of the gravity wave distribution aro

acquisition and processing of wide aperture ground penetrating radar data a 40 channel wide aperture ground penetrating radar gpr data set was recorded in a complicated fluvial aeolian environment in eastern canada the data were collected in the multichannel format usually associated with seismic reflection surveys and were input directly into a standard seismic processing sequence filtering static corrections common midpoint gathering velocity analysis normal and dip moveout corrections stacking and depth migration the results show significant improvements over single channel recordings in noise reduction and depth of penetration by stacking and in spatial positioning and reduction of diffraction artifacts by migration these characteristics increase the potential for reliable interpretation of structural and stratigraphic details thus without having to develop any new software gpr data processing technology is brought to the same level of capability flexibility and accessibility that is current in seismic exploration

three dimensional properties of andes mountain waves observed by satellite a case study the southern andes region has been clearly identified in previous satellite and balloon observations and in global models as a hot spot of small scale gravity wave activity with monthly mean momentum fluxes exceeding 10 times background values in fall winter and spring seasons this makes this region a focus of interest for global circulation and climate studies we analyze a case study on 8 may 2006 combining observations from the atmospheric infrared sounder instrument on the aqua satellite and the high resolution dynamics limb sounder instrument of the aura satellite to form a three dimensional picture of the wave field the observations show a widespread wave pattern over the southern andes extending eastward over the south atlantic simulations with the weather research forecasting model clearly identify the waves as orographic in origin but the observed wave pattern is far from the simple two dimensional wave field forced by steady flow over a mountain ridge the morphology of the pattern is consistent with three dimensional linear theoretical calculations of downstream propagation and latitudinal focusing of mountain waves into the stratospheric jet the observations confirm the importance of this process in the stratosphere and we find the process also occurring in the global analysis and forecasts from the european centre for medium range weather forecasting our analysis evaluates some strengths and weaknesses of current orographic wave drag parameterizations in global models and the relevance of parameterization assumptions in global models with high resolution copyright 2011 by the american geophysical union

interpolating wide aperture ground penetrating radar beyond aliasing abstractmost of the data acquisition in ground penetrating radar is done along fixed offset profiles in which velocity is known only at isolated points in the survey area at the locations of variable offset gathers such as a common midpoint we have constructed sparse heavily aliased variable offset gathers from several fixed offset collinear profiles we interpolated those gathers to produce properly sampled counterparts thus pushing data beyond aliasing the interpolation methodology estimated nonstationary adaptive filter coefficients at all trace locations including at the missing traces corresponding positions filled with zeroed traces this is followed by an inversion problem that uses the previously estimated filter coefficients to insert the new interpolated traces between the original ones we extended this two step strategy to data interpolation by employing a device in which we used filter coefficients from a denser variable offset gather to interpolate the missing traces on a few

a three dimensional mountain wave imaged in satellite radiance throughout the stratosphere evidence of the effects of directional wind shear swath scanned thermal radiances from the advanced microwave sounding units amsu a on the noaa and aqua satellites are used to image the horizontal temperature structure of a long wavelength mountain wave that formed over southern scandinavia on 14 january 2003 data from all six stratospheric channels show this wave propagating through the full depth of the stratosphere in channels 9 11 altitudes 20 90 hpa the imaged wave has a phase structure broadly consistent with a stationary wave radiated by the southeastward flow over and above the quasi elliptical terrain of southern norway channel 12 radiances at 10 hpa however show a remarkable abrupt change in imaged wave structure the horizontal wavelength contracts phase lines rotate anticlockwise by 30 40 and peak activity migrates to the south to lie over denmark and northern germany similar structure persists in channels 13 and 14 at 2 5 hpa with progessively increasing radiance amplitudes these features are stable over the 10 hours of amsu a measurements from five separate overpasses and are validated against independent radiances acquired by the atmospheric infrared sounder airs and retrieved airs amsu a temperature profiles from the aqua overpass this change at the channel 11 12 interface coincides with an onset of anticlockwise rotation backing and intensification of background stratospheric winds with height fourier ray and spatial ray modelling incorporating these directionally sheared winds and simplified orographic forcing reproduce the salient features of the observations but only after wave induced temperature perturbations have been converted to channel radiances using a forward model the differential visibility of various components of this three dimensional mountain wave to the amsu a channel weighting functions has a first order impact on the observations at heights above 10 hpa once that is factored in the combined observations and modelling provide direct experimental support for the shutts model s predictions of how backing wind vectors affect the vertical evolution of three dimensional mountain waves implications of these observations for orographic gravity wave drag parametrization are briefly discussed copyright 2007 royal meteorological society

frequency wavenumber modelling and migration of 2d gpr data in moderately heterogeneous dispersive media an algorithm for modelling and migrating ground penetrating radar gpr data in moderately heterogeneous dispersive media is presented the method is based on wavefield extrapolation in the frequency wavenumber f k domain from the solution of the 2d maxwell s equations the wavefield is extrapolated by a phase shift technique using a constant relative permittivity k and a quality factor q it is then modified by a correction term to handle the lateral k and q variations the spatial distribution of the k and q factor values representing the given model parameters is introduced into the algorithm by a regular grid parametrization the radar wave dispersion and attenuation induced by relaxation processes are taken into account by a linear frequency dependent q model and expressed by a complex wavenumber in the propagation equation a synthetic case and a field data set illustrate the potential of the method for frequencies of 300 500 and 900 mhz in the first case a typical civil engineering problem is considered the frequency dependence of the wave velocity and attenuation is well illustrated the synthetic data are afterwards migrated using the initial model parameters the results show the importance of using spatially varying model parameters in the migration processes the second case concerns an application of the method to a real data set in order to adjust the model parameters a forward modelling sequence is performed until the best match between the measured and the synthetic data is achieved a depth migration is then applied to the data and the result is compared with the initial model parameters in conclusion we assess the contributions of the method to industrial applications by discussing the performance of the algorithm compared with its limitations

mountain waves and wakes generated by south georgia implications for drag parametrization high resolution simulations of flows over south georgia south atlantic are used to increase understanding of the likely influence of small isolated mountainous islands on the large scale flow and to ascertain the extent to which parametrization schemes can account for the missing drag in models where such islands are only partially resolved long duration 1 month austral winter forecasts with a horizontal grid spacing of 1 5 km are used to quantify the mountain wave momentum fluxes generated by the island and the low level drag associated with flow blocking dynamics the characteristics of the drag such as the occurrence of high and low drag states its dependence on wind direction and the spectral contributions to the mountain wave momentum flux are considered flow splitting and low level wave breaking are shown to be responsible for wake regions that extend for hundreds of kilometres from the island regions of deceleration are also evident in the stratosphere due to mountain wave dissipation the extent to which an orographic drag parametrization scheme can reproduce the drag is investigated by comparison with coarse resolution 15 km grid spacing simulations in which the orography is poorly resolved and a large proportion of the drag is parametrized it is demonstrated that the total of the resolved plus parametrized drag in these simulations closely resembles that at high resolution although it is underpredicted during instances of high drag simple modifications to the scheme which enhance the drag when the low level flow is approximately normal to the major axis of the subgrid orography are shown to rectify this the study demonstrates that at least for relatively simple isolated mountain ranges the drag and mountain wave momentum fluxes can be predicted in a deterministic sense by a well tuned parametrization scheme of suitable complexity although inclusion of stochastic effects might lead to yet further improvements

velocity analysis from common offset gpr data inversion theory and application to synthetic and real data we implemented a procedure to estimate the electromagnetic em velocity using common offset ground penetrating radar gpr data the technique is based on the inversion of reflection amplitudes to compute the series of reflection coefficients used to estimate the velocity in each interpreted layer the proposed method recursively calculates the incident angles at any interface taking into account the offset between antennas and needs as input in addition to the picked amplitudes values a reference amplitude for each analysed gpr trace and a velocity value for the first shallowest layer the latter two parameters can be estimated directly from the available data or can be better constrained by further dedicated gpr acquisitions or by additional direct measurements we critically evaluated the performances for both synthetic and real data acquired with different antenna frequencies and we demonstrated that the new method can be applied in several real situations despite the necessary approximations and simplifying hypotheses the velocity values calculated for each layer are consistent with direct information and with cross validations obtained considering profiles acquired using different antennas and various path directions tests of the method on synthetic and real data sets show that the errors in the calculated velocity fields are quite low and comparable with more demanding velocity analysis techniques the obtained em velocity field is crucial in many processing steps such as for example true amplitude recovery depth conversion and imaging and provide essential information to characterize the subsurface materials

continuous profiles of electromagnetic wave velocity and water content in glaciers an example from bench glacier alaska usa we conducted two dimensional continuous multi offset georadar surveys on bench glacier south central alaska usa to measure the distribution of englacial water we acquired data with a multichannel 25 mhz radar system using transmitter receiver offsets ranging from 5 to 150 m we towed the radar system at 5 10 km h 1 with a snow machine with transmitter receiver positions established by geodetic grade kinematic differentially corrected gps nominal 0 5 m trace spacing for radar velocity analyses we employed reflection tomography in the pre stack depth migrated domain to attain an estimated 2 velocity uncertainty when averaged over three to five wavelengths we estimated water content from the velocity structure using the complex refractive index method equation and use a three phase model ice water air that accounts for compression of air bubbles as a function of depth our analysis produced laterally continuous profiles of glacier water content over several kilometers these profiles show a laterally variable stratified velocity structure with a low water content 0 0 5 shallow layer 20 30 m underlain by high water content 1 2 5 ice

seasonal cycle of orographic gravity wave occurrence above small islands in the southern hemisphere implications for effects on the general circulation 1 orographic gravity waves generated by flow over the topography of small islands in the southern oceans have been observed from orbit with the atmospheric infrared sounder on the aqua satellite we examine the occurrence frequencies of these waves in the stratosphere at 40km above 14 islands and examine geographical and seasonal changes our results show that these small island mountain waves occur commonly in the stratosphere in the may september season though not every day differing seasonal variations are evident at different islands and the seasonal variations are closely related to latitude and prevailing wind patterns we also examine interannual variability in 2years of data and the relationships between occurrence frequencies momentum fluxes and stratospheric and surface winds the results suggest that stratospheric winds have a first order limiting effect on the observations of these island mountain waves in atmospheric infrared sounder airs data surface wind direction and island orographic relief have an additional but secondary influence on the island mountain wave occurrence frequencies in airs data the implications are that these wave events are extremely common and that on many days when the waves are not observed in airs data they have likely dissipated and induced a drag force on the atmosphere below the 40km observation level observations of momentum flux during these wave events also permit a first estimate of their importance to the general circulation of the southern hemisphere

determination of water depth with high resolution satellite imagery over variable bottom types a standard algorithm for determining depth in clear water from passive sensors exists but it requires tuning of five parameters and does not retrieve depths where the bottom has an extremely low albedo to address these issues we developed an empirical solution using a ratio of reflectances that has only two tunable parameters and can be applied to low albedo features the two algorithms the standard linear transform and the new ratio transform were compared through analysis of ikonos satellite imagery against lidar bathymetry the coefficients for the ratio algorithm were tuned manually to a few depths from a nautical chart yet performed as well as the linear algorithm tuned using multiple linear regression against the lidar both algorithms compensate for variable bottom type and albedo sand pavement algae coral and retrieve bathymetry in water depths of less than 10 15 m however the linear transform does not distinguish depths 15 m and is more subject to variability across the studied atolls the ratio transform can in clear water retrieve depths in 25 m of water and shows greater stability between different areas it also performs slightly better in scattering turbidity than the linear transform the ratio algorithm is somewhat noisier and cannot always adequately resolve fine morphology structures smaller than 4 5 pixels in water depths 15 20 m in general the ratio transform is more robust than the linear transform

diffuse reflectance of oceanic shallow waters influence of water depth and bottom albedo we used simplifying assumptions to derive analytical formulae expressing the reflectance of shallow waters as a function of observation depth and of bottom depth and albedo these formulae also involve two apparent optical properties of the water body a mean diffise attenuation coefficient and a hypothetical reflectance which would be observed if the bottom was infinitely deep the validity of these approximate formulae was tested by comparing their outputs with accurate solutions of the radiative transfer obtained under the same boundary conditions by monte carlo simulations these approximations were also checked by comparing the reflectance spectra for varying bottom depths and compositions determined in coastal lagoons with those predicted by the formulae these predictions were based on separate determinations of the spectral albedos of typical materials covering the floor such as coral sand and various green or brown algae the simple analytical expressions are accurate enough for most practical applications and also allow quantitative discussion of the limitations of remote sensing techniques for bottom recognition and bathymetry as early as 1944 duntley used a spectrograph mounted in a glass bottomed boat or flown in an airplane to analyze radiances emerging from the ocean and shallow waters he evidenced the influence of the water depth on the spectral composition of the upward flux duntley 1963 using a monte carlo technique plass and kattawar 1972 calculated the radiative field in the atmosphere cean system and in particular examined the dependence of the upward flux on the albedo of the ocean floor gordon and brown 1974 studied the diffuse reflectance of a shallow ocean using monte carlo simulations and a probabilistic approach gordon and brown provided an analysis based on photon history of the light field as modified by the presence of a reflecting bottom in addition ackleson and klemas 1986 developed a two flow model that simulated the light field within a canopy of bottom adhering plants a single scattering approximation for irradiance reflectance was also

observations and numerical simulations of mountain waves in the presence of directional wind shear three research aircraft observed small amplitude gravity waves over the south western french alps on 13 november 1999 during the mesoscale alpine programme map radiosonde ascents and global positioning system dropsondes deployed by map research aircraft indicate that the upstream flow was characterized by topographic blocking below 2 km and low level directional wind shear associated with a synoptic scale depression that extended above the alpine crest the in situ vertical velocity data from the three research aircraft and backscatter from lidar onboard the low level and upper level aircraft exhibit gravity wave signatures in the lower troposphere that are characterized by relatively short horizontal wavelengths on a scale of 5 km or less the in situ flight level and backscatter data also suggest a rapid decrease in the wave amplitude with height due to a directional critical layer that partially absorbs wave energy in the lower to middle troposphere in concert with a decrease in the scorer parameter with height that traps the wave energy numerical simulation results obtained from the non hydrostatic coupled ocean atmosphere mesoscale prediction system model using a horizontal resolution of 556 m indicate the presence of low level wave breaking above the highest peaks and confirm the presence of trapped waves and a directional critical level results based on linear theory and nonlinear model simulations suggest that the absorption of wave energy associated with the directional critical layer has an important impact on the wave characteristics including the momentum flux copyright 2006 royal meteorological society

stratospheric trailing gravity waves from new zealand abstractgravity waves are frequently observed in the stratosphere trailing long distances from mid to high latitude topography two such trailing wave events documented over new zealand are exami

multi band spectral matching inversion algorithm to derive water column properties in optically shallow waters an optimization of parameterization abstract deriving inherent optical properties iops and other water quality parameters from satellite remote sensing data covering optically shallow environments has historically been problematic due to difficulties in separating the benthic signal from that of the water column while recent advances have improved such retrievals most methods have high uncertainties for very shallow

examples of reverse time migration of single channel ground penetrating radar profiles a single channel ground penetrating radar gpr profile portrays a distorted unfocused image of subsurface structure due to apparent position shifts associated with dipping reflectors and to diffractions from corners and edges a focused image may be produced from such data by using any of the migration algorithms previously developed for seismic data we use reverse time migration based on the scalar wave equation field work was performed over a simple stratigraphic soil sequence and a complicated fluvial environment in the migrated images reflector continuity is enhanced and the level of detail available for high resolution interpretation is significantly increased

density muon radiography of la soufriere of guadeloupe volcano comparison with geological electrical resistivity and gravity data density muon radiography is a new method to determine the average density of geological bodies by measuring the attenuation produced by rocks on the flux of cosmic muons we present such density radiographies obtained for the soufri ere of guadeloupe lava dome both in the north south and east west planes these radiographies reveal the highly heterogeneous density structure of the volcano with low density regions corresponding to recognized hydrothermally altered areas the main structures observed in the density radiographies correlate with anomalies in electrical resistivity cross sections and a density model obtained from gravity data

velocity variations and water content estimated from multi offset ground penetrating radar the common midpoint cmp processing technique has been shown to be effective in improving the results of ground penetrating radar gpr profiling when radar data are collected with the cmp multioffset geometry stacking increases the signal to noise ratio of subsurface radar reflections and results in an improved subsurface image an important aspect of cmp processing is normal moveout velocity analysis our objectives are to show the effect of multiple velocity analyses on the stacked radar image and particularly to demonstrate that this velocity information can also be used to determine subsurface water content most gpr surveys are very limited in spatial extent and assume that within the survey range radar velocity structure in the shallow subsurface can be adequately approximated by a single velocity function in data processing in this study we show that variation in radar velocity can be quite significant and that the stacked profile improves as the number of velocity analysis locations is increased interval velocities can be calculated from the normal moveout velocities derived in the cmp velocity analysis with some reasonable assumptions about subsurface conditions necessary for radar propagation interval velocity can be converted to an estimate of volumetric water content therefore by collecting gpr data in the multioffset cmp geometry not only is the radar profile improved but it also allows for an interpretation of subsurface variation in water content we show the application of these techniques to multioffset gpr data from the chalk river test area operated by atomic energy of canada limited

inversion for the density depth profile of polar firn using a stepped frequency radar 1 translating satellite measurements of ice sheet volume change into sea level contribution requires knowledge of the profile of density as a function of depth within the ice sheet and how this profile changes over time this paper describes an interferometric method of inverting ground penetrating radar returns for the profile of firn density as a function of depth the method is an interferometric implementation of the common midpoint approach performed using a stepped frequency phase sensitive ground penetrating radar by recording the phase difference of returns with a range of antenna separations the different path lengths through the firn allow recovery of a smoothed representation of the density profile this density model is characterized by three parameters surface density and two decay lengths for porosity each operating over a different density range our results suggest that the stepped frequency radar used here can accurately recover differences in two way traveltime and produce useful estimates of the density profile in a test of the method performed at summit station in greenland the recovered density depth profile agreed with independent density measurements from an ice core and a neutron probe to within 6 root mean square error

effects of optically shallow bottoms on upwelling radiances inhomogeneous and sloping bottoms if the benthic boundary in optically shallow waters is spatially inhomogeneous or sloping the underwater light field is inherently three dimensional 3d numerical simulations of 3d underwater radiances were made for environmental conditions observed in shallow bahamian waters the simulations show that if the pattern of bottom reflectance for an inhomogeneous but level bottom has a spatial scale much smaller than the bottom area seen by a radiometer the inhomogeneous bottom can be replaced by a homogeneous bottom whose reflectance is the areaweighted average of the actual bottom reflectances for large scale patterns of bottom reflectance the 3d light fields near the edges of bottom patches of different reflectances can be predicted from analytical models incorporating the sensor geometry and one dimensional 1d light fields computed for homogeneous bottoms with errors of order 10 when compared to the exact 3d solutions the same holds true for uniformly sloping bottoms whose 3d light fields can be modeled in terms of the 1d light fields computed for level bottoms with errors of less than 10 for bottom slopes of 20 or less

applying reflection tomography in the postmigration domain to multifold ground penetrating radar data acquisition and processing of multifold ground penetrating radar gpr data enable detailed measurements of lateral velocity variability the velocities constrain interpretation of subsurface materials and lead to significant improvement in image accuracy when coupled with prestack depth migration psdm reflection tomography in the postmigration domain was introduced in the early 1990s for velocity estimation in seismic reflection this robust accurate method is directly applicable in multifold gpr imaging at a contaminated waste facility within the u s department of energy s hanford site in washington the method is used to identify significant lateral and vertical velocity heterogeneity associated with infilled waste pits using both the psdm images and velocity models in interpretation a paleochannel system that underlies the site and likely forms contaminant migration pathways is identified

gravity waves over the eastern alps a synopsis of the 25 october 1999 event iop 10 combining in situ and remote sensing measurements with a high resolution simulation in situ and lidar data acquired during six repetitive flight legs across grossglockner 3797 m highest summit of the eastern alps reveal a coherent structure of the mountain wave field generated by a south westerly cross alpine flow on 25 october 1999 during intensive observing period iop 10 of the mesoscale alpine programme map the downward looking laser system sampling at 100 hz provides distinct wave induced signatures in the layered clouds below the cruising altitude of about 11 km data obtained from three sondes dropped from the aircraft hint at mid tropospheric wave breaking in the lee of the main alpine crest the measurements are juxtaposed with results from a nested non hydrostatic simulation 2 km horizontal resolution for the finest grid wave cloud signatures in satellite images from meteosat and the national oceanic and atmospheric administration satellites are used for comparisons with the simulation in a region away from the aircraft track sensitivity experiments reveal the regular wave response to be induced by the background profile and re enforced by the suitably spaced terrain copyright 2003 royal meteorological society

detecting trend and seasonal changes in bathymetry derived from hico imagery a case study of shark bay western australia abstract the hyperspectral imager for the coastal ocean hico aboard the international space station has offered for the first time a dedicated space borne hyperspectral sensor specifically designed for remote sensing of the coastal environment however several processing steps are required to convert calibrated top of atmosphere radiances to the desired geophysical parameter s these steps add various amounts of uncertainty that can cumulatively render the geophysical parameter imprecise and potentially unusable if the objective is to analyze trends and or seasonal variability this research presented here has focused on 1 atmospheric correction of hico imagery 2 retrieval of bathymetry using an improved implementation of a shallow water inversion algorithm 3 propagation of uncertainty due to environmental noise through the bathymetry retrieval process 4 issues relating to consistent geo location of hico imagery necessary for time series analysis and 5 tide height corrections of the retrieved bathymetric dataset the underlying question of whether a temporal change in depth is detectable above uncertainty is also addressed to this end nine hico images spanning november 2011 to august 2012 over the shark bay world heritage area western australia were examined the results presented indicate that precision of the bathymetric retrievals is dependent on the shallow water inversion algorithm used within this study an average of 70 of pixels for the entire hico derived bathymetry dataset achieved a relative uncertainty of less than 20 a per pixel t test analysis between derived bathymetry images at successive timestamps revealed observable changes in depth to as low as 0 4 m however the present geolocation accuracy of hico is relatively poor and needs further improvements before extensive time series analysis can be performed

on the surface circulation in the western coral sea and residence times in the great barrier reef surface velocity observations from satellite tracked drifters made between 1987 and 2008 were used to resolve the surface circulation of the western coral sea west of 158 e and the great barrier reef gbr the mean surface current map depicts well the major circulation patterns of the region such as the position of the north vanuatu and north caledonia jets nvj and ncj and the western boundary currents the north queensland current nqc and the east australian current eac are well defined flowing at speeds greater than 50 cm s 1 to the north south of 15 s and 19 s respectively the nqc eac is mainly formed by the nvj ncj flows respectively the presence of the queensland plateau greatly affects the westward flow causing a zone of weak and highly variable currents that extends from 15 s to 18 s between the queensland plateau and the gbr shelf of the 235 drifters that crossed the western coral sea 75 entered the gbr analysis of the drifter trajectories inside the gbr reveals the presence of a northwestward circulation at speeds of 22 cm s 1 north of 18 s and 0 5 cm s 1 south of 18 s drifter travel times used to evaluate the water residence times within the gbr indicate residence times of a few weeks for most of the lagoon

subsurface radar propagation deconvolution the frequency dependence of attenuation is typically far greater for subsurface radar waves than for seismic waves since this frequency dependence causes the subsurface radar pulse shape to change as it propagates through the earth conventional wavelet deconvolution techniques are often inadequate to reconstruct the earth s reflectivity series the application of a time variant filter that undoes the effect of frequency dependent attenuation can substantially improve the resolution of subsurface radar data this filter is minimum phase with amplitude characteristics equal to the inverse of the attenuation function of the medium investigated preliminary tests on data from surveys over a water tank an underground mine stope and fractured granite suggest that good results can also be achieved by assuming attenuation is linearly proportional to frequency similar to a constant q model

the need to adapt the exploration model from the oil patch to contaminated site characterization a case from hill afb utah usa for decades the oil industry has employed a working model for hydrocarbon exploration in which large scale geophysical surveys are undertaken prior to a second phase of intensive targeted drilling this latter phase may be conducted in conjunction with further focused geophysical studies the geophysical surveys provide lateral coverage and continuity that are used to drive placement of drilling locations the reason for this approach is simple wells are expensive relative to geophysical surveys also practical limits on lateral coverage preclude optimization of exploration targets based on well information alone