close range airborne structure from motion photogrammetry for high resolution beach morphometric surveys examples from an embayed rotating beach abstract the field of photogrammetry has seen significant new developments essentially related to the emergence of new computer based applications that have fostered the growth of the workflow technique called structure from motion sfm low cost user friendly sfm photogrammetry offers interesting new perspectives in coastal and other fields of geomorphology requiring high resolution topographic data the technique enables the construction of topographic products such as digital surface models dsms and orthophotographs and combines the advantages of the reproducibility of gps surveys and the high density and accuracy of airborne lidar but at very advantageous cost compared to the latter three sfm based photogrammetric experiments were conducted on the embayed beach of montjoly in cayenne french guiana between october 2013 and 2014 in order to map morphological changes and quantify sediment budgets the beach is affected by a process of rotation induced by the alongshore migration of mud banks from the mouths of the amazon river that generate spatial and temporal changes in wave refraction and incident wave angles thus generating the reversals in longshore drift that characterise this process sub vertical aerial photographs of the beach were acquired from a microlight aircraft that flew alongshore at low elevation 275 m the flight plan included several parallel flight axes with an overlap of 85 between pictures in the lengthwise direction and 50 between paths targets of 40 40 cm georeferenced by rtk dgps were placed on the beach spaced 100 m apart these targets served in optimizing the model and in producing georeferenced 3d products rtk gps measurements of random points and cross shore profiles were used to validate the photogrammetry results and assess their accuracy we produced dense point clouds with 150 to 200 points m from which we generated dsms and orthophotos with respective resolutions of 10 cm and 5 cm compared to the gps control points we obtained a mean vertical accuracy less than 10 cm with a maximum of 20 cm in marginal sectors with sparse vegetation and in the lower intertidal zone where water saturated surfaces generated lower resolution data as a result of a lack of coherence between photographs the overall results show that sfm photogrammetry is a robust tool for beach morphological and sediment budget surveys our sfm workflow enabled the discrimination of beach surface features at a scale of a few tens of centimetres despite the low textural contrasts exhibited by the quartz beach sand and the relatively uniform upper beach topography as well as the calculation of beach sediment budgets 66 000 m of sand were removed from the northern sector of the beach of which 22 000 m were transferred to the southern sector in the course of rotation finally we briefly highlight 1 the advantages of sfm photogrammetry compared to other high resolution survey methods 2 the advantages and disadvantages of respectively a microlight aircraft and an unmanned aerial vehicle uav in undertaking sfm photogrammetry and 3 areas of potential future improvement of the sfm workflow technique these concern more extensive cross shore deployment of ground control points to reduce possible tilt and oblique cross shore photography to improve parallax

modeling the precision of structure from motion multi view stereo digital elevation models from repeated close range aerial surveys the accuracy of digital elevation models dems derived from structure from motion sfm multi view stereo mvs 3d reconstruction is commonly computed for a single realization of model elevations this approach may be adequate to estimate an overall measure of systematic error however it cannot provide a good estimation of measurement precision knowing measurement precision is crucial for measuring elevation surface changes observed by dem comparisons in this paper we illustrate an approach to characterize spatial variation in the precision for sfm mvs derived dems we use a snow covered surface of an active rock glacier located in the southern french alps as the case study a spatially varying precision estimate is calculated from repeated close range aerial surveys for a single acquisition period by calculating the standard deviation per grid cell between the dems created for each flight repetition regression analysis using a generalized additive model gam is performed to model the estimated precision and provide insights regarding how sensor survey design and field site conditions may spatially influence the measurement precision additionally we define how dem error can be described differently depending on the available validation data in our study image height above ground level and distance to ground control points had the greatest explanatory power for spatial variation in dem precision image overlap mean reprojection error and saturation were also useful for explaining spatially varying measurement precision of the dems field site characteristics such as slope angle and shading had the least importance in our model of precision from a practical point of view regression modeled relationships between precision and image and site characteristics can be utilized to design future surveys with similar sensing platforms and site conditions for improved dem precision

accounting for permafrost creep in high resolution snow depth mapping by modelling sub snow ground deformation abstract snow depth estimation derived from high resolution digital elevation models dems can lead to improved understanding of the spatially highly heterogeneous nature of snow distribution as well as help us improve our knowledge of how snow patterns influence local geomorphic processes slope deformation processes such as permafrost creep can make it challenging to acquire a snow free dem that matches the sub snow topography at the time of the associated snow covered dem which can cause errors in the computed snow depths in this study we illustrate how modelling changes in the sub snow topography can reduce errors in snow depths derived from dem differencing in an area of permafrost creep to model the sub snow topography a surface deformation model was constructed by performing non rigid registration based on b splines of two snow free dems seasonal variations in creep were accounted for by using an optimization approach to find a suitable value to scale the deformation model based on in situ snow depth measurements or the presence of snow free areas corresponding to the date of the snow covered dem this scaled deformation model was used to transform one of the snow free dems to estimate the sub snow topography corresponding to the date of the snow covered dem the performance of this method was tested on an active rock glacier in the southern french alps for two surveys dates which were conducted in the winter and spring of 2017 by accounting for surface displacements caused by permafrost creep we found that our method was able to reduce the errors in the estimated snow depths by up to 33 an interquartile range reduction of 11 cm compared to using the untransformed snow free dem the accuracy of the snow depths only slightly improved root mean square error decrease of up to 3 cm greater reductions in error were observed for the snow depths calculated for the date that was furthest i e the winter survey in time from the snow free dem additionally we found that our approach to scaling the deformation model has promising potential to be adapted for monitoring seasonal variations in permafrost creep by combining in situ snow depth measurements with high resolution surface deformation models

west florida continental shelf response to upwelling favorable wind forcing 2 dynamics dynamics analyses are presented for the west florida continental shelf response to upwelling favorable alongshore or offshore winds using a three dimensional time dependent primitive equation model these analyses complement the kinematics analyses of li and weisberg 1999 results are provided on four topics 1 the response evolutions to quasi steady states 2 the across shelf distributions of the vertically integrated alongshore and across shelf momentum balances 3 the three dimensional structures of the terms composing the momentum balance closures and 4 the model sensitivity to vertical friction parameterization the response evolution starts with a local wind driven acceleration and it transitions over the inner shelf into a primary balance between the pressure gradient coriolis and vertical friction terms thus the inner shelf spin up takes a classical ekman geostrophic route the middle shelf takes longer because it also depends on coastal boundary effects notably the partial closure of the domain in the south by the florida keys the outer shelf never achieves a steady state because of topographic wave effects coastline and isobath geometries result in fully three dimensional flow fields thus a two dimensional model that ignores alongshore variations cannot account for the results obtained the inner shelf is the transition region between ekman and ekman geostrophic balances where the surface slope results from mass adjustments through overlapping surface and bottom ekman layers across the inner shelf the vertically integrated momentum balance shows a gradual trade off between the coriolis pressure gradient and bottom friction terms and with the inner shelf frictionally determined its scale is sensitive to vertical friction parameterization

an upwelling case study on florida s west coast using a combination of satellite sea surface temperature imagery in situ currents temperature and sea level data and a numerical circulation model we describe an upwelling event observed along florida s west coast although ubiquitous features of continental shelves descriptions of coastal upwellings or downwellings are generally complicated by the continuum of processes in which they occur for the case study presented the winds were light and the baroclinic background currents were steady for several days prior to the event these conditions allow the evolution of a specific winddriven upwelling event to be viewed as an initial value problem the data and the numerical model analysis show that the route of adjustment by the sea level and currents is a classical ekman geostrophic one sea level drops due to an offshore ekman transport causing a geostrophic alongshore jet and the associated onshore flow within the bottom ekman layer accounts for the appearance of cold water at the surface this surface manifestation occurs as an elongated feature centered about the 25 m isobath that spans roughly half of the florida peninsula from just north of tampa bay to key west the coldest water is observed offshore from tampa bay and we explain this region of locally maximum upwelling on the basis of the coastline and isobath geometries

bottom pressure and sea level measurements in the gulf of lions abstract bottom and atmospheric pressure sea level wind current and temperature measurements have been obtained during summer in the coastal zone of the gulf of lions relations between these parameters are estimated mainly with coherence analysis first it is shown that the atmospheric pressure forcing is small and that the sea level and bottom pressure spectra are very similar then the characteristics of tides are computed with a least squares method removing the tidal signal from the original time series allows us to study in a clearer way the inertial frequency band arguments for the possible occurrence of sea surface oscillations at this frequency are discussed at lower frequencies large sea level variations are due to the wind at frequencies higher than the tidal ones very energetic signals are connected with natural oscillations of the gulf of lions induced by atmospheric pressure perturbations of a relatively small scale this paper is concerned with regional oceanograhy but the result

west florida shelf response to upwelling favorable wind forcing kinematics the barotropic responses of the west florida continental shelf to idealized upwelling favorable alongshore and offshore wind stresses are studied using the three dimensional time dependent primitive equation princeton ocean model pom when forced with uniform winds the shelf circulation evolves quickly to a quasi steady state a southeastward alongshore wind lowers sea level along the coast and drives a southeastward coastal jet with a relatively weak northwestward return flow farther offshore a southwestward offshore wind lowers sea level along the west florida coast and raises sea level along the panhandle coast two independent circulation gyres are set up in association with these regionally different sea level distributions an anticyclonic gyre off the west florida coast consisting of a southeastward coastal jet and a broad return flow over the middle shelf and a cyclonic gyre off the panhandle coast consisting of a strong northwestward coastal jet and an adjacent narrow southeastward undercurrent these gyres are separated by the big bend region in both cases alongshore and offshore wind forcing the circulations are fully three dimensional with opposing surface and bottom boundary layer flows accounting for the across shelf transports the shapes of the coastline and the isobaths are important determinants of the shelf wide responses several locally maximum upwelling regions are identified for geometrical reasons these include the panhandle coast south of apalachicola bay the west florida coast south of tampa bay along the florida keys and at the shelf break where topographic rossby waves are evident

ground based multi view photogrammetry for the monitoring of landslide deformation and erosion recent advances in multi view photogrammetry have resulted in a new class of algorithms and software tools for more automated surface reconstruction these new techniques have a great potential to provide topographic information for geoscience applications at significantly lower costs than classical topographic and laser scanning surveys based on open source libraries for multi view stereo photogrammetry and structure from motion this study investigates the accuracy that can be obtained from several processing pipelines for the 3d surface reconstruction of landslides and the detection of changes over time two different algorithms for point cloud comparison are tested and the accuracy of the resulting models is assessed against terrestrial and airborne lidar point clouds change detection over a period of more than two years allows a detailed assessment of the seasonal dynamics of the landslide the possibility to estimate sediment volumes and 3d displacement are illustrated for the most active parts of the landslide algorithm parameters and the image acquisition protocols are found to have important impacts on the quality of the results and are discussed in detail

reproducibility of uav based earth topography reconstructions based on structure from motion algorithms combination of uav based aerial pictures and structure from motion sfm algorithm provides an efficient low cost and rapid framework for remote sensing and monitoring of dynamic natural environments this methodology is particularly suitable for repeated topographic surveys in remote or poorly accessible areas however temporal analysis of landform topography requires high accuracy of measurements and reproducibility of the methodology as differencing of digital surface models leads to error propagation in order to assess the repeatability of the sfm technique we surveyed a study area characterized by gentle topography with an uav platform equipped with a standard reflex camera and varied the focal length of the camera and location of georeferencing targets between flights comparison of different sfm derived topography datasets shows that precision of measurements is in the order of centimetres for identical replications which highlights the excellent performance of the sfm workflow all parameters being equal the precision is one order of magnitude higher for 3d topographic reconstructions involving independent sets of ground control points which results from the fact that the accuracy of the localisation of ground control points strongly propagates into final results 2015 elsevier b v

west florida shelf mean circulation observed with long term moorings 1 the mean circulation on the west florida continental shelf is described using long term current measurements bounded by the florida peninsula to the east and the gulf of mexico to the west the west florida continental shelf mean flow is oriented approximately along isobath and southward the mean velocity vectors veer systematically with depth shoreward over shallow water and seaward over deeper water this polarization change implies that the mean flow is upwelling over shallow water and downwelling seaward from the inner shelf such a well organized three dimensional coastal ocean circulation pattern revealed by an unprecedented set of observations and explained on the basis of wind forcing and density field adjustment has important implications for both fisheries and red tide occurrences

ground based and uav based photogrammetry a multi scale high resolution mapping tool for structural geology and paleoseismology this contribution reviews the use of modern 3d photo based surface reconstruction techniques for high fidelity surveys of trenches rock exposures and hand specimens to highlight their potential for paleoseismology and structural geology we outline the general approach to data acquisition and processing using ground based photographs acquired from standard dslr cameras and illustrate the use of similar processing approaches on imagery from unmanned aerial vehicles uavs it is shown that digital map and trench data can be acquired at ultra high resolution and in much shorter time intervals than would be normally achievable through conventional grid mapping the resulting point clouds and textured models are inherently multidimensional x y z point orientation colour texture archival and easily transformed into orthorectified photomosaics or digital elevation models dems we provide some examples for the use of such techniques in structural geology and paleoseismology while pointing the interested reader to free and commercial software packages for data processing visualization and 3d interpretation photogrammetric models serve to act as an ideal electronic repository for critical outcrops and observations similar to the electronic lab book approach employed in the biosciences this paper also highlights future possibilities for rapid semi automatic to automatic interpretation of the data and advances in technology

monitoring and modelling morphological change in a braided gravel bed river using high resolution gps based survey recent research in fluvial geomorphology has emphasized the direct monitoring of channel topography as a useful tool to better understand the interrelationship between river form and process and in particular to estimate bedload transport rates and reach scale sediment budgets until recently however this morphometric approach has been limited to comparison of repeatedly surveyed cross sections with the associated problems of low frequency sampling and an emphasis on cross stream as opposed to downstream morphological dynamics recent advances in analytical photogrammetry have however permitted the acquisition of data at sufficient resolutions to represent macroform 101 m and microform 10 m channel geometry in fully three dimensions while inherently spatially distributed the photogrammetric approach to land surveying is however restricted to observable areas of the channel and is thus of limited use in the subaqueous zone especially if flows are turbid or highly coloured this paper presents an alternative approach to the study of three dimensional morphological dynamics of a divided reach of the gravelly river feshie scotland in which topographic survey of both exposed and submerged areas of the reach was undertaken using the global positioning system gps survey results from two field programmes in 1998 and 1999 are presented in which a geotronics geotracer 2000 real time kinematic gps receiving unit was used to survey a 200 80 m reach rapid radial survey methods were employed permitting the collection of 2000 survey points per day giving a mean density over the 13 ha reach of 1 1 points per square metre a detailed assessment of survey errors and dem quality is presented and a limit of detection of c 10 cm proposed as an upper threshold for the identification of significant change between dems preliminary interpretation of channel dynamics in 1998 99 reveals relatively little change to the overall macroscale reach structure dem differencing techniques however highlight important local changes including the progradation of submerged bar fronts bar head aggradation and scour along major channel thalwegs and the erosion of fines from sloughs copyright 2000 john wiley sons ltd

estimating groundwater discharge into the northeastern gulf of mexico using radon 222 abstract submarine groundwater discharge sgd may provide important chemical constituents to the ocean but the dispersed nature of this process makes locating and quantifying its input extremely difficult since groundwater contains 3 4 orders of magnitude greater radon than seawater 222rn may be a useful tracer of this process if all other sources of radon to bottom waters can be evaluated we report development of a sgd tracing tool based on radon inventories in a coastal area of the northeastern gulf of mexico we evaluated factors that influence the concentration of radon in the water column i e production decay horizontal transport and loss across the pycnocline using a linked benthic exchange horizontal transport model total 222rn benthic fluxes 2420 dpm m 2 day 1 measured with in situ chambers are of the magnitude required to support measured sub pycnocline 222rn inventories while estimates of molecular diffusion show that this input is relatively small 230 dpm m 2 day 1 using this model approach together with measurements of the radon inventory we estimated a regional subsurface fluid flow ranging from 180 to 710 m3 sec 1 into the 620 km2 study area this discharge equivalent to an upward advective velocity of approximately 2 10 cm day 1 dispersed over this entire study area is equivalent to approximately 20 first magnitude springs

the erosion and suspended matter seawater interaction during and after the 1996 outburst flood from the vatnajokull glacier iceland abstract the gjalp subglacial eruption 1996 within the vatnajokull glacier iceland triggered a catastrophic outburst flood bringing at least 180 million tonnes of suspended solids to the sea in only 42 h this amounts to 1 of the total annual global river suspended flux to the oceans the specific bet surface area of the suspended solids was measured to be 11 8 18 9 m2 g translating to the average total bet surface area of 2 8 10 9 km2 providing enormous potential for adsorption desorption and precipitation dissolution fluxes at the suspended solids ocean water interface altered basalt glass was the major constituent of the suspended matter 80 secondary minerals such as zeolites and calcite amounted to 11 but only 5 was fresh volcanic glass the suspended grains were generally rounded the glass carried by the flood is different in chemical composition from the glass produced by the gjalp eruption the gjalp material has higher feototal tio2 and tio2 p2o5 ratios than the suspended glass in the flood waters the majority of the flood samples match the composition of the volcanic system down stream from the eruption site the large amount of altered material in the flood and its chemical composition suggests erosion conforming to a 2 m deep 1000 m wide and 50 000 m long channel in less than 42 h the behaviour of 28 elements on the surface of the suspended solids exposed to seawater was quantified by experiments in the laboratory the altered basaltic glass dissolved in seawater as recorded by the si release from the glass the dissolved concentrations of na ca si ba cd co cu hg mn ni and total dissolved inorganic n increased considerably when the suspended solids come into contact with the seawater but the concentrations of mg k s sr fe pb and zn decreased the experimental seawater solutions were supersaturated with respect to calcite mg montmorillonite and amorphous iron hydroxide the rate of release mol m2 s of si mn ba co ni and cd decreased continuously during the one week exposure to sweater after one week the logarithm of the dissolution rate of the altered basaltic glass was 11 9 to 11 6 si mole m2 sec significantly lower than the steady state rates for fresh basaltic glass at similar conditions calculated one day desorbed dissolution suspended material fluxes are greater than the integrated dissolved flood fluxes for mn ba ni co and cd but the si dissolved food flux was greater than the one day desorbed dissolved suspended material flux

wind driven currents on the west florida shelf abstract three weeks of current meter wind and sea level data off cedar key florida are analyzed currents and sea level are found to be coherent with alongshore wind stress in the synoptic band 0 05 0 25 cycle per day and to lag it by approximately half a day little coherence is found with cross shelf wind stress at the inshore mooring 22 m depth currents are nearly barotropic for these winter 1978 data a linear parameterization of bottom stress in the barotropic alongshore current leads to a bottom friction parameter r of 0 01 0 02 cm s 1 using coastal wind stress no significant steady alongshore slope is found during this short interval the dominant momentum balance in the alongshore direction is between wind and bottom stress the offshore frictional length scale csanady 1978 is estimated to be 75 100 km which implies a seaward extent to a depth of about 30 m at the offshore mooring 44 m depth there is vertical shear between the currents at 9 and 39 m the upper cross shelf compon

seasonal modulation of the west florida continental shelf circulation velocity data from 28 n 84 w on the west florida continental shelf are presented the data were sampled from october 1993 through january 1995 at 1 m intervals between 3 m and 42 m in a total water depth of 47 m their monthly means suggest an annual cycle hypothesized to be driven by a seasonally varying shelf wide baroclinic structure motions at semi diurnal diurnal and synoptic time scales are seasonally modulated both by wind forcing and stratification that decouples fluid motions from the damping effects of bottom friction these motions are presented in the form of progressive vector plots with 16 months of data probability density and distribution functions for along shore and across shore particle displacements over specific time intervals are constructed for daily intervals particles are equally likely to travel approximately 5 km depending upon confidence interval in any direction for monthly intervals particles may travel a few hundred km primarily along shore

shelf circulation cells considerable insight has recently been gained into the dynamics of continental shelf circulation through a simplification of the governing equations resulting in a parabolic equation for the pressure field solutions of this equation appear to model realistically important flow phenomena notably the effects of winds and coastal geography in setting up half open coastal circulation cells and an associated trapped pressure field circulation cells should be established mainly on the inner shelf according to theory i e within about 30 km of the coast and should be important agents of mass exchange in the present paper the theory of shelf circulation is reviewed with an emphasis on its most general predictions then the question is examined of how a considerable body of evidence on coastal sea level variations in response to wind longshore sea level gradients longshore and cross shore currents can be interpreted in the theoretical framework

numerical model studies of the winter storm response of the west florida shelf abstract the wintertime wind driven ocean circulation on the west florida continental shelf is studied within the framework of a linearized storm surge model the model bathymetry incorporates a realistic shelf extending from new orleans to the southern tip of florida and a deep ocean region the boundary condition at the coast is that there is no normal flow at the open boundaries located off the shelf in deep water the adjusted sea level is fixed at zero it is found that 1 a coastally trapped response is achieved within one local inertial period following the imposition of the wind 2 the curved coast forces a mass exchange between the coastal water and the deep ocean 3 this exchange leads to the generation of a series of mesoscale eddies along the shelf edge and 4 these eddies give rise to long period shelf wide oscillations that persist beyond the local spin up time a hindcast of the wind driven flow on the west florida shelf for a particular period 11 25 march 1978 that contains the

the evaluation of unmanned aerial system based photogrammetry and terrestrial laser scanning to generate dems of agricultural watersheds article i nfo agricultural watersheds tend to be places of intensive farming activities that permanently modify their microtopography the surface characteristics of the soil vary depending on the crops that are cultivated in these areas agricultural soil microtopography plays an important role in the quantification of runoff and sedi ment transport because the presence of crops crop residues furrows and ridges may impact the direction of water flow to better assess such phenomena 3 d reconstructions of high resolution agricultural watershed to pographyareessential fine resolutiontopographicdatacollectiontechnologiescanbeusedtodiscernhighlyde tailed elevation variability in these areas knowledge of the strengths and weaknesses of existing technologies used for data collection on agricultural watersheds may be helpful in choosing an appropriate technology this study assesses the suitability of terrestrial laser scanning tls and unmanned aerial system uas photogrammetry for collecting the fine resolution topographic data required to generate accurate high resolution digital elevation models dems in a small watershed area 12 ha because of farming activity 14 tls scans 25 points m 2 were collected without using high definition surveying hds targets whic ha re generally used to mesh adjacent scans to evaluate the accuracy of the dems created from the tls scan data 1098 ground control points gcps were surveyed using a real time kinematic global positioning system rtk gps linear regressions were then applied to each dem to remove vertical errors from the tls point elevations errors caused by the non perpendicularity of the scanner s vertical axis to the local horizontal plane and errors correlated with the distance to the scanner s position the scans were then meshed to generate a demtls with a1 1m spatial resolution the agisoft photoscan and micmac software packages were used to process the aerial photo graphsand generate a dempsc agisoftphotoscan anddemmcm micmac respectively with spatial resolutions of 1 1 m comparing the dems with the 1098 gcps showed that the demtls was the most accurate data prod uct with a root mean square error rmse of 4 5 cm followed by the demmcm and the dempsc which had rmse values of 9 0 and 13 9 cm respectively the dempsc had absolute errors along the border of the study area that ranged from 15 0 to 52 0 cm indicating the presence of systematic errors although the derived demmcm was accurate an error analysis along a transect showed that the errors in the demmcm data tended to increase in areas of lower elevation compared with tls uas is a promising tool for data collection because of its flexibility and low operational cost however improvements are needed in the photogrammetric processing of the aerial photographs to remove non linear distortions

revealing the natural complexity of topographic change processes through repeat surveys and decision tree classification title revealing the natural complexity of topographic change processes through repeat surveys and decision tree classification short title decision tree classification of topographic change processes authors joshua r wyrick a gregory b pasternack b a lafayette college 740 high street easton pa 18042 b university of california davis one shields drive davis ca 95616 corresponding author tel 1 610 330 5735 e mail wyrickj lafayette edu fax 1 keywords topographic change dem differencing river morphology regulated rivers geomorphic change abstract topographic change processes tcps are the mechanisms by which a landscape is interpreted to be experiencing landform deformation and are defined by the specific actions occurring within a contiguous localized region that cause sediment to be either deposited or eroded past topographic change studies have mostly been focused at the site scale the goal of this study was to identify and delineate spatially explicit tcp

on the effect of digital elevation model accuracy on hydrology and geomorphology this study compares published cartometric and photogrammetric digital elevation models dems of various grid spacings with a ground truth data set obtained by ground survey and studies the implications of these differences on key hydrologic statistics inferred catchment sizes and stream networks from published dems were found to be significantly different than those from the ground truth in most instances furthermore the width functions and cumulative area relationships determined from the published dems were found to fall consistently outside the 90 confidence limits determined from the ground truth for more than 60 of the relationship suggesting that these hydrologic properties are poorly estimated from published dems however the slope area relationships determined from published dems were found to be less sensitive to catchment shape size and stream network with the relationship falling outside the 90 confidence limits for less than 40 of the relationship for all catchments identified from the published dems a published relationship linking the horizontal resolution with the vertical accuracy of the dem was tested predicting a horizontal resolution of about 10 m for the published dems tested

variability of current temperature and bottom pressure across the west florida continental shelf winter 1981 1982 observations are analyzed from four current meter moorings deployed on the broad continental shelf in the northeastern gulf of mexico from november 29 1981 to february 8 1982 71 days consistent with recent modeling studies the shelf circulation responds within an inertial period to the alternating up and down coast synoptic scale wind forcing average response to a 0 5 dyn cm 2 alongshore wind stress as measured at the coast is 20 cm s 1 off cedar key and 40 cm s 1 in the north where the shelf narrows off cape san bias lower layer currents veer counterclockwise with depth as in a bottom ekman layer e folding scale 8 m the pressure field decays offshore e folding scale 160 km and yields a geostrophic current in good agreement with the observed alongshelf flow cross shelf and vertical variations of the tidal signals compare nicely with results from barotropic theory calculations indicate that most of the shoreward propagating tidal energy must be dissipated in depths of 20 m within 50 km of shore

role of river suspended material in the global carbon cycle the reaction of ca derived from silicate weathering with co2 in the world s oceans to form carbonate minerals is a critical step in long term climate moderation ca is delivered to the oceans primarily via rivers where it is transported either as dissolved species or within suspended material the relative importance for climate moderation of riverine dissolved ca vs suspended ca transport stems from the total ca flux and its climate dependence data in the literature suggest that within uncertainty global riverine dissolved ca flux is equal to suspended material ca flux to determine how these fluxes depend on temperature and rainfall a 40 yr field study was performed on 4 catchments

small scale variations of the wind driven coastal sea level response in the west florida bight abstract records from a number of temporary tide gage stations spaced an average of 20 km apart new cedar key florida are used to examine the alongshore pressure gradient over length scales much smaller than before possible in agreement with previous studies an alongshore stress of 1 dyn cm 2 will produce a large scale over distances of several hundred kilometers alongshore sea level gradient on the order of 10 6 sea level rising downwind however cross shore stress is also important and at short periods 3 5 days can be the more coherent forcing estimates of small scale level slope do appear to show systematic deviations from the larger scale slope some of which seem to be related to alongshore variations in nearshore bathymetry

summertime coastal currents in the northeastern gulf of mexico abstract observations of currents and temperature at a mooring on the 18 m isobath 30 km south of the florida shoreline are discussed for the 31 day period 15 august 15 september 1978 tidal currents having average amplitudes of 10 cm s 1 account for 85 of the observed kinetic energy low frequency currents with maximum speeds of 10 cm s 1 appear to be at least partly driven by local wind stress events of magnitude 0 2 dyn cm 2 frictional effects give rise to a veering with depth in the ekman sense of both the low frequency flow and the energetic counterclockwise rotating twice daily tidal currents propagation of both the tidal signal and low frequency coastal sea level fluctuations amplitudes 5 cm is westward through the study area

intrusion of loop current waters onto the west florida continental shelf an intrusion of loop current water up desoto canyon and onto the west florida continental shelf to within 8 km of the shore occurred in february 1977 boat aircraft and satellite data collected in the area for another purpose were used to estimate the space and time scales of the intrusion and the ultimate fate of the intruded waters the duration of the event was 18 days oceanic waters advanced across the shelf at speeds of 20 cm s sup 1 at maximum intrusion 6650 km sup 2 of shelf were affected approximately half the intruded water receded off the shelf and half appears to have been modified in situ

from experimental plots to experimental landscapes topography erosion and deposition in sub humid badlands from structure from motion photogrammetry in the last decade advances in surveying technology have opened up the possibility of representing topography and monitoring surface changes over experimental plots 10 m2 in high resolution 103 points m 1 yet the representativeness of these small plots is limited with structure from motion sfm and multi view stereo mvs techniques now becoming part of the geomorphologist s toolkit there is potential to expand further the scale at which we characterise topography and monitor geomorphic change morphometrically moving beyond previous plot scale work using terrestrial laser scanning tls surveys this paper validates robustly a number of sfm mvs surveys against total station and extensive tls data at three nested scales plots 30 m2 within a small catchment 4710 m2 within an eroding marl badland landscape 1 km2 sfm surveys from a number of platforms are evaluated based on i topography ii sub grid roughness and iii change detection capabilities at an annual scale oblique ground based images can provide a high quality surface equivalent to tls at the plot scale but become unreliable over larger areas of complex terrain degradation of surface quality with range is observed clearly for sfm models derived from aerial imagery recently modelled doming effects from the use of vertical imagery are proven empirically as a piloted gyrocopter survey at 50m altitude with convergent off nadir imagery provided higher quality data than an unmanned aerial vehicle uav flying at the same height and collecting vertical imagery for soil erosion monitoring sfm can provide data comparable with tls only from small survey ranges 5 m and is best limited to survey ranges 10 20 m synthesis of these results with existing validation studies shows a clear degradation of root mean squared error rmse with survey range with a median ratio between rmse and survey range of 1 639 and highlights the effect of the validation method e g point cloud or raster based on the estimated quality

biases of srtm in high mountain areas implications for the monitoring of glacier volume changes because of its nearly global coverage the shuttle radar topographic mission srtm topography is a promising data set for estimating mountain glacier volume changes but first its absolute accuracy must be thoroughly investigated in a glacial environment we use topographic data available in the french alps to assess the usefulness of srtm for the monitoring of glacier volume variations we observe clear biases with altitude both on ice free and glacier covered areas at high altitudes srtm elevations are underestimated by up to 10 m these biases can have a significant impact on any estimate of glacier volume changes if srtm is the most recent of the two compared topographies the volume loss is overestimated and vice versa we cannot conclude definitively on the origin of these biases and whether they affect all high mountain areas but our findings invite reconsideration of previous estimates of glacier wastage based on srtm

mitigating systematic error in topographic models for geomorphic change detection accuracy precision and considerations beyond off nadir imagery unmanned aerial vehicles uavs and structure from motion photogrammetry enable detailed quantification of geomorphic change however rigorous precision based change detection can be compromised by survey accuracy problems producing systematic topographic error e g doming with error magnitudes greatly exceeding precision estimates here we assess survey sensitivity to systematic error directly correcting topographic data so that error magnitudes align more closely with precision estimates by simulating conventional grid style photogrammetric aerial surveys we quantify the underlying relationships between survey accuracy camera model parameters camera inclination tie point matching precision and topographic relief and demonstrate a relative insensitivity to image overlap we show that a current doming mitigation strategy of using a gently inclined 0 center dot 3 m representing accuracy issues an order of magnitude greater than precision based error estimates for higher relief topography and for nadir imaging surveys of the lower relief topography systematic error was 0 center dot 09 m modelling and subtracting the systematic error directly from the topographic data successfully reduced error magnitudes to values consistent with twice the estimated precision thus topographic correction can provide a more robust approach to uncertainty based detection of event scale geomorphic change than designing surveys with small off nadir camera inclinations and furthermore can substantially reduce ground control requirements c 2020 the authors earth surface processes and landforms published by john wiley sons ltd

a simple method for estimating barotropic tidal currents on continental margins with specific application to the m2 tide off the atlantic and pacific coasts of the united states abstract theory is developed to describe barotropic tidal currents on smooth continental shelves that is continental shelves with longshore scales much greater than the shelf width two models are considered one in which sea level don not vary significantly across the shelf and the other in which it does both models include longshore gradients and friction parameterized linearly in velocity the models were tested by calculating the m2 tidal currents off the atlantic and pacific coasts of the united states and then comparing the calculated currents to those measured results show that theory and observation are in very good agreement as far offshore as 300 km along the atlantic coast on account of the wide continental shelf current velocities are typically o 0 10 0 15 m s 1 north of cape hatteras and o 0 15 0 28 m s 1 off savannah georgia currents rotate anticyclonically and are highly elliptical ellipticity e 0 4 with the semi major axis oriented normal to the coast friction is sign

tides on the west florida shelf the principal semidiurnal m2 and s2 and diurnal k1 and o1 tidal constituents are described on the west florida continental shelf wfs using a combination of in situ measurements and a three dimensional primitive equation numerical model the measurements are of sea level and currents along the coastline and across the shelf respectively the model extends from west of the mississippi river to the florida keys with an open boundary arcing between it is along this open boundary that the regional model is forced by a global tide model standard barotropic tidal analyses are performed for both the data and the model and quantifiable metrics are provided for comparison based on these comparisons the authors present coamplitude and cophase charts for sea level and velocity hodographs for currents the semidiurnal constituents show marked spatial variability whereas the diurnal constituents are spatially more uniform apalachicola bay is a demarcation point for the semidiurnal tides that are well developed to the southeast along the wfs but are minimal to the west the largest semidiurnal tides are in the florida big bend and florida bay regions with a relative minimum in between just to the south of tampa bay these spatial distributions may be explained on the basis of local geometry a lagrangian stokes drift coherently directed toward the northwest is identified but is of relatively small magnitude when compared with the potential for particle transport by seasonal and synoptic scale forcing bottom stressinduced tidal mixing is examined and estimates are made of the bottom logarithmic layer height by the m2 tidal currents

digital terrain modeling abstract this article examines how the methods and data sources used to generate dems and calculate land surface parameters have changed over the past 25 years the primary goal is to describe the state of the art for a typical digital terrain modeling workflow that starts with data capture continues with data preprocessing and dem generation and concludes with the calculation of one or more primary and secondary land surface parameters the article first describes some of ways in which lidar and radar remote sensing technologies have transformed the sources and methods for capturing elevation data it next discusses the need for and various methods that are currently used to preprocess dems along with some of the challenges that confront those who tackle these tasks the bulk of the article describes some of the subtleties involved in calculating the primary land surface parameters that are derived directly from dems without additional inputs and the two sets of secondary land surface parameters that are commonly used to model solar radiation and the accompanying interactions between the land surface and the atmosphere on the one hand and water flow and related surface processes on the other it concludes with a discussion of the various kinds of errors that are embedded in dems how these may be propagated and carried forward in calculating various land surface parameters and the consequences of this state of affairs for the modern terrain analyst

role of river suspended material in the global carbon cycle comment and reply comment gislason et al 2006 1 make a claim that would significantly change our understanding of the long term carbon cycle they argue that reaction of basalt glass in seawater especially in what they call the fluidized bed reactors in the delta environment constitutes a significant

error in a usgs 30 meter digital elevation model and its impact on terrain modeling calculations based on us geological survey usgs digital elevation models dems inherit any errors associated with that particular representation of topography we investigated the potential impact of error in a usgs 30 m dem on terrain analysis over 27 km 2 the difference in elevation between 2652 differential global positioning systems measurements and usgs 30 m dem derived elevations provided the comparative error dataset analysis of this comparative error data suggested that although the global average error is small local error values can be large and also spatially correlated stochastic conditional simulation was used to generate multiple realizations of the dem error surface that reproduce the error measurements at their original locations and sample statistics such as the histogram and semivariogram model the differences between these alternative error surfaces provide a model of uncertainty for the unknown dem error spatial distribution these dem errors had a significant impact on terrain attributes which compound elevation values of many grid cells e g slope wetness index etc a case study using terrain modeling demonstrates that the result of error propagation is most dramatic in valley bottoms and along streamlines q 2000 elsevier science b v all rights reserved

multiyear subinertial and seasonal eulerian current observations near the florida big bend coast abstractmultiyear in situ eulerian acoustic doppler current profiler measurements were obtained at 5 10 and 19 m depths off the big bend coast and in 19 m off the florida peninsula to the south analysis on subinertial time scales dominated by weatherband frequencies led to the following conclusions at the 19 m big bend site k tower consistent with coastally trapped wave ctw theory the along isobath flow is not proportional to the local along isobath wind stress but rather to the alongshore wind stress to the south along the west florida shelf wfs at the southern 19 m site consistent with previous work the along isobath flow is driven by but is weakened by an alongshore pressure gradient brake via ctw dynamics this brake is due to the abrupt end of the wfs at the florida keys by contrast along isobath flow at the shallow 5 m site is driven by the local wind in a constant stress turbulent frictional layer because of the freshwater flux near the coast density usually increases s

structure from motion photogrammetry a low cost effective tool for geoscience applications abstract high resolution topographic surveying is traditionally associated with high capital and logistical costs so that data acquisition is often passed on to specialist third party organisations the high costs of data collection are for many applications in the earth sciences exacerbated by the remoteness and inaccessibility of many field sites rendering cheaper more portable surveying platforms i e terrestrial laser scanning or gps impractical this paper outlines a revolutionary low cost user friendly photogrammetric technique for obtaining high resolution datasets at a range of scales termed structure from motion sfm traditional softcopy photogrammetric methods require the 3 d location and pose of the camera s or the 3 d location of ground control points to be known to facilitate scene triangulation and reconstruction in contrast the sfm method solves the camera pose and scene geometry simultaneously and automatically using a highly redundant bundle adjustment based on matching features in multiple overlapping offset images a comprehensive introduction to the technique is presented followed by an outline of the methods used to create high resolution digital elevation models dems from extensive photosets obtained using a consumer grade digital camera as an initial appraisal of the technique an sfm derived dem is compared directly with a similar model obtained using terrestrial laser scanning this intercomparison reveals that decimetre scale vertical accuracy can be achieved using sfm even for sites with complex topography and a range of land covers example applications of sfm are presented for three contrasting landforms across a range of scales including an exposed rocky coastal cliff a breached moraine dam complex and a glacially sculpted bedrock ridge the sfm technique represents a major advancement in the field of photogrammetry for geoscience applications our results and experiences indicate sfm is an inexpensive effective and flexible approach to capturing complex topography

ocean currents and sea surface heights estimated across the west florida shelf abstract the across shelf structures of the ocean circulation and the associated sea surface height ssh variability are examined on the west florida shelf wfs for the 3 yr interval from september 1998 to december 2001 five sets of characteristic circulation patterns are extracted from 2 day low pass filtered data using the self organizing map extreme upwelling and downwelling structures with strong currents asymmetric upwelling and downwelling structures with moderate currents and a set of transitional structures with weak currents the temporal variations of these structures are coherent with the local winds on synoptic weather time scales on seasonal time scales they are related to both the local winds and the water density variations the circulation is predominantly upwelling during autumn to spring months october april and downwelling during summer months june september coastal sea level fluctuations are related to both the dynamical responses of the inner shelf circulation to meteorol

wind induced sea surface slopes on the west florida shelf abstract tidal and meteorological records at stations in the eastern gulf of mexico have been studied the sea level response is a maximum for winds along the coast and varies symmetrically with angle the coherence is maximum at periods of 4 10 days the horizontal coherence of sea level is high out to 500 km for 4 10 day periods the horizontal coherence for wind measured at coastal stations is high out to at least 500 km the amplitude of the response of sea level to winds is larger by a factor of 4 here on a broad shelf than on the oregon coast which is more narrow by about the same ratio a response of 16 cm is induced by 4 m s 1 wind this response or transfer function is uniform over the spectral range 4 100 days the sea level response to the longshore wind stress is not linear but to the power 0 8 0 1 and is attributed to the relatively low tidal currents in this region the large horizontal coherences of wind and sea level imply broad longshore flows extending 500 km or more along

straightforward reconstruction of 3d surfaces and topography with a camera accuracy and geoscience application topographic measurements for detailed studies of processes such as erosion or mass movement are usually acquired by expensive laser scanners or rigorous photogrammetry here we test and use an alternative technique based on freely available computer vision software which allows general geoscientists to easily create accurate 3d models from field photographs taken with a consumer grade camera the approach integrates structure from motion sfm and multi view stereo mvs algorithms and in contrast to traditional photogrammetry techniques it requires little expertise and few control measurements and processing is automated to assess the precision of the results we compare sfm mvs models spanning spatial scales of centimeters a hand sample to kilometers the summit craters of piton de la fournaise volcano with data acquired from laser scanning and formal close range photogrammetry the relative precision ratio achieved by sfm mvs measurement precision observation distance is limited by the straightforward camera calibration model used in the software but generally exceeds 1 1000 i e centimeter level precision over measurement distances of 10s of meters we apply sfm mvs at an intermediate scale to determine erosion rates along a 50 m long coastal cliff seven surveys carried out over a year indicate an average retreat rate of 0 70 0 05 m a 1 sequential erosion maps at 0 05 m grid resolution highlight the spatio temporal variability in the retreat with semivariogram analysis indicating a correlation between volume loss and length scale compared with a laser scanner survey of the same site sfm mvs produced comparable data and reduced data collection time by 80

estimation of nearshore tidal currents on nonsmooth continental shelves the theory of battisti and clarke 1982 to calculate analytically barotropic tidal currents across smooth continental margin topography is shown to be valid near shore on nonsmooth continental shelves the theory includes longshore gradients and friction and produces formulae easily evaluated with coastal sea level data the tidal currents across three such shelves west florida south of long island and vancouver island are calculated and compared with those observed

wind forced sea level variability along the west florida shelf winter 1978 abstract coastal tide gage and meteorological records from pensacola to key west for the period january april 1978 have been examined for low frequency fluctuations the dominant 6 day period signals in sea level alongshore wind stress and atmospheric pressure were coherent over the entire shelf and propagated southward consistent with the movement of cold fronts through the area sea level response tagged the local wind stress by 18 h in the north to 9 h in the south in response to a 1 dyn cm 2 alongshore stress sea level amplitudes were largest 60 cm where the shelf is widest 200 km and undergoes an abrupt bend and were 30 cm elsewhere large transient alongshore sea level slopes on the order of 10 6 were thus set up a linear steady state shelf circulation model hsueh 1980 is used to explore the sea level distribution that is in frictional equilibrium with a wind stress of given orientation for a bottom resistance coefficient of 0 014 cm s 1 a value suggested by an analysis of fe

analysis of current observations on the georgia shelf abstract an analysis is made of hf radar measurements of surface currents in shallow water near the georgia coast and also of vertical profile measurements of current and density the dominant structure is found to be a clockwise ellipse of semidiurnal periodicity the ellipses becoming smaller narrower and turning clockwise with depth there is a definite phase lead of the bottom currents with respect to the upper currents and some evidence of veering of the currents in the non ekman sense in order to explain the observed vertical variations a simple analytical expression is developed for periodic rotary currents in a barotropic ocean of constant eddy viscosity and depth h when the free surface elliptic motion is known the solution depends on the ratios f and h hekman and also on the sense of turning of the free surface ellipse the model is able to explain several features of the observed vertical variations as frictional effects

bottom currents and fluviomarine sedimentation on the mississippi prodelta shelf february may 1984 surface winds and currents temperature and water transparency at heights of 1 and 5 m above bottom in 60 m of water were measured during the period from february 23 to may 2 1984 at a site on the mississippi delta the objective was to better understand the influence of near bottom flow on the character of sedimentation on the prodelta shelf data analysis showed currents to be parabathic with periodicities of 5 and 20 days flow showed a strong east west polarization with net flow 0 4 cm s onshore at the lower level and 0 5 cm s offshore at the upper with easterly flow water temperature declined indicating upwelling and current veering between 1 and 5 m was 12 15 in the sense of a bottom ekman layer with westerly flow water temperature increased indicating downwelling and veering was of the same magnitude but in the sense of a surface ekman layer flow and suspended sediment data suggest that during the period of study deposition of sediment from the turbid plume of the mississippi river was continuous calculations of sediment settling velocities indicate that the surface plume of turbid river water transported in suspension particles with hydraulic equivalent diameters ranging from clay to fine sand size computations of friction velocity indicate that here on the outer prodelta shelf the observed bottom currents were not competent to erode bottom sediment short period 1 3 days fluctuations in mean bottom turbidity may be due to variations in the supply of suspended sediment as the surface plume moves laterally in response to the wind and in at least some cases to a vertical redistribution of sediment in suspension by currents too weak to initiate resuspension these fluctuations are probably responsible for the silty and sand laminae generally a millimeter thick or less observed in bottom cores the thickness of the annual flood deposit may approach 1 m in the vicinity of the plume

optimising uav topographic surveys processed with structure from motion ground control quality quantity and bundle adjustment structure from motion sfm algorithms greatly facilitate the production of detailed topographic models from photographs collected using unmanned aerial vehicles uavs however the survey quality achieved in published geomorphological studies is highly variable and sufficient processing details are never provided to understand fully the causes of variability to address this we show how survey quality and consistency can be improved through a deeper consideration of the underlying photogrammetric methods we demonstrate the sensitivity of digital elevation models dems to processing settings that have not been discussed in the geomorphological literature yet are a critical part of survey georeferencing and are responsible for balancing the contributions of tie and control points we provide a monte carlo approach to enable geomorphologists to 1 carefully consider sources of survey error and hence increase the accuracy of sfm based dems and 2 minimise the associated field effort by robust determination of suitable lower density deployments of ground control by identifying appropriate processing settings and highlighting photogrammetric issues such as over parameterisation during camera self calibration processing artefacts are reduced and the spatial variability of error minimised we demonstrate such dem improvements with a commonly used sfm based software photoscan which we augment with semi automated and automated identification of ground control points gcps in images and apply to two contrasting case studies an erosion gully survey taroudant morocco and an active landslide survey super sauze france in the gully survey refined processing settings eliminated step like artefacts of up to 50 mm in amplitude and overall dem variability with gcp selection improved from 37 to 16 mm in the much more challenging landslide case study our processing halved planimetric error to 0 1 m effectively doubling the frequency at which changes in landslide velocity could be detected in both case studies the monte carlo approach provided a robust demonstration that field effort could by substantially reduced by only deploying approximately half the number of gcps with minimal effect on the survey quality to reduce processing artefacts and promote confidence in sfm based geomorphological surveys published results should include processing details which include the image residuals for both tie points and gcps and ensure that these are considered appropriately within the workflow

modeling the topography of shallow braided rivers using structure from motion photogrammetry abstract recent advances in computer vision and image analysis have led to the development of a novel fully automated photogrammetric method to generate dense 3d point cloud data this approach termed structure from motion or sfm requires only limited ground control and is ideally suited to imagery obtained from low cost non metric cameras acquired either at close range or using aerial platforms terrain models generated using sfm have begun to emerge recently and with a growing spectrum of software now available there is an urgent need to provide a robust quality assessment of the data products generated using standard field and computational workflows to address this demand we present a detailed error analysis of sub meter resolution terrain models of two contiguous reaches 1 6 and 1 7 km long of the braided ahuriri river new zealand generated using sfm a six stage methodology is described involving i hand held image acquisition from an aerial platform ii 3d point cloud extraction modeling using agisoft photoscan iii georeferencing on a redundant network of gps surveyed ground control points iv point cloud filtering to reduce computational demand as well as reduce vegetation noise v optical bathymetric modeling of inundated areas and vi data fusion and surface modeling to generate sub meter raster terrain models bootstrapped geo registration as well as extensive distributed gps and sonar based bathymetric check data were used to quantify the quality of the models generated after each processing step the results obtained provide the first quantified analysis of sfm applied to model the complex terrain of a braided river results indicate that geo registration errors of 0 04 m planar and 0 10 m elevation and vertical surface errors of 0 10 m in non vegetation areas can be achieved from a dataset of photographs taken at 600 m and 800 m above the ground level these encouraging results suggest that this low cost logistically simple method can deliver high quality terrain datasets competitive with those obtained with significantly more expensive laser scanning and suitable for geomorphic change detection and hydrodynamic modeling