engineering geological mapping of tropical soils for land use planning and geotechnical purposes a case study from jamaica west indies abstract an area of a tertiary and cretaceous deposits 100 310 m above sea level and on predominant 20 45 highly dissected concave slopes was investigated to assess its geotechnical characteristics and land use planning implications lithologies include turbidites fluvial conglomerates breccias sandstones mudrocks carbonates granodiorite acid dykes chloritized and epidotized volcanics andesite and holocene fluvial deposits bedrock is highly fractured and sheared hydrothermally altered and highly weathered soils are quite variable with a strong geological control on soil properties soils are generally sandy to gravely with local silts and clays in mudrocks within holocene alluvium or in hydrothermally altered and sheared granodiorites the soils are composed of 0 14 80 00 gravel 5 36 62 50 sand 2 33 50 55 silt 0 17 51 50 clay and total fine content between 2 50 and 94 50 with natural moisture between 4 and 44 during the dry season plastic limit between 6 and 35 liquid limit between 19 and 83 and plasticity index between 1 and 59 sandy soils have residual friction angles between 19 and 39 pi values less than 35 with cohesion between 1 00 and 5 27 kn m 2 for cohesive samples astm classification of soils include soil groups gc gm gw gp sp sm sc sm sc ml cl and ch based on the characteristics of the terrain the geotechnical and land use planning problems include high landslide frequency and susceptibility soil erosion fluvial and reservoir sedimentation high debris flow hazard cut slope failures potentially expansive clays and silts seepage erosion and soil piping differential settlement in interlayered competent and incompetent lithologies high solution erosion and potential subsidence over limestones waste water disposal problems and groundwater pollution and seismic induced settlement and ground failures these phenomena suggest that systematic site investigations should be conducted prior to the utilization of these areas for construction and development in order to minimize the deleterious effects resulting from ground failure

geological and geotechnical constraints for urban planning and natural environment protection a case study from mekelle city northern ethiopia the study was conducted in the rapidly expanding city of mekelle located in the northern part of ethiopia east africa an integrated approach including geomorphological geological and engineering geological geotechnical and hydrogeological methods were used to characterize the natural urban environment to be used as a baseline for protection and rational planning of development conventional field observation test pits and drilled boreholes were used to collect soil rock and water samples and standard laboratory procedures were applied the results revealed that the main geologic constraints to sustainable development of the city are active erosion instability of slopes flood hazard cyclic alternating hard and weak rock layers high swelling shrinkage soils shallow and unconfined groundwater with variable composition and high susceptibility to corrosion and pollution it is recommended to avoid development and expansion of the city in areas of steep land forms at the foot of steep slopes and in areas covered by black alluvial soil deposits development of a systematic multidisciplinary database aided by gis with continuous monitoring and updating is also highly recommended and will be useful for further refined geotechnical microzonation it is the authors belief that this study highlights the basic constraints and hazards the city is facing and provides baseline information and awareness to the city planners decision makers geo environmentalists engineers and the community for future expansion and rehabilitation plans and to tackle the existing hazards

direct measurements of ocean surface velocity from space interpretation and validation the median doppler shift of radar echoes is analyzed in measurements by envisat s advanced synthetic aperture radar asar over the ocean this doppler centroid differs from a predicted signal based on the predicted motion of the satellite and earth this anomaly converted to a surface doppler velocity u d appears to be of geophysical origin two wide swath images over the gulf stream around cape hatteras suggest that u d contains high resolution information on surface currents while on a global scale u d is found to vary with the wind speed in the range direction a simple quantitative forward model is proposed based on a practical two scale decomposition of the surface geometry and kinematics the model represents the effect of the wind through the wave spectrum and gives u d u 10 u c with u 10 and u c as the 10 m wind speed and quasi eulerian current in the line of sight of the radar projected on the sea surface respectively and as a coefficient function of the wind speed wave development and radar geometry it is found that for an incidence angle of 23 0 3 for moderate winds and fully developed seas this model is validated with a global data set of asar wave mode observations with colocated model winds acquired over the global ocean during the years 2003 and 2004 the doppler signal therefore provides the signed parameter u d that can be used to reduce the wind direction ambiguity in the inversion of high resolution wind fields from sar imagery a qualitative validation of current effects is shown for the english channel where tidal currents dominate thus it should be possible to combine this previously ignored geophysical doppler signal with traditional information on sea surface roughness in order to provide very high resolution wind and current fields

role of a low viscosity zone in stabilizing plate tectonics implications for comparative terrestrial planetology 1 earth s near surface layer its lithosphere is broken into quasi rigid plates that form the upper thermal boundary layer for mantle convection since the discovery of plate tectonics it has been widely conjectured but only recently demonstrated that this peculiar style of convection may be facilitated by an upper mantle low viscosity zone lvz over which the plates glide easily the lvz or asthenosphere concept dates from 19th century investigations of isostatic support of mountain belts and is supported by modern evidence for a seismic low velocity zone and by studies of postglacial rebound and dynamic compensation of the earth s gravity field here we show in both two dimensional 2 d cartesian and 3 d spherical earth models that combining a pronounced lvz and a plastic yield stress to allow localized weakening of the cold thermal boundary layer results in a distinctly plate tectonic style of convection with 30 toroidal surface motion for the 3 d case recycling of water into the upper mantle at subduction zones is a plausible cause of earth s lvz whereas venus is dry and lacks both an lvz and plate tectonics

estimating advective near surface currents from ocean color satellite images abstract improved maximum cross correlation mcc techniques are used to retrieve ocean surface currents from the sequential ocean color imagery provided by multiple newer generations of satellite sensors on hourly scales in the yellow sea and the u s east and gulf coasts the mcc calculation is validated in a series of bio optical forecasting biocast experiments with predetermined synthetic velocities and its products are evaluated by examining the errors and biases with respect to the high frequency radar hfradar measurements the root mean square rms errors in our best current products derived from the overlap of satellite sensor swath between the viirs sequential orbits are less than 0 17 m s 1 in the evaluation area outside of the chesapeake bay the most accurate current products are those derived from the imagery data of r rs 551 b b 551 and c 551 while the image sequences of b b 551 and z eu lee are identified as the most suited products for the retrieval of currents because of their best production capacities of valid velocity vectors mechanisms between the advective processes and the dynamic changes of bio optical properties are discussed regarding the performances of various color products on the retrieval of currents similarities of velocity distribution in the retrieved vector arrays are collected across different mcc products derived from ocean color datasets that are of different types and derived from different spectral channels of satellite overpasses the inter product similarities themselves can be used to characterize the near surface advection as well and usually have smaller errors than each of the individual mcc currents moreover efforts are also under way to improve the ocean color derived currents by merging several of the mcc products with similarities to increase the total spatial coverage this study not only seeks the image derived products best representing the sea surface current structures in coastal areas but also exploits how these currents can be improved or optimized to support the ocean forecasts

predicting plate velocities with mantle circulation models 1 we predict plate motions from a comprehensive inversion of theoretical estimates of tectonic forces in order to evaluate the relative importance of these and the uncertainties of such models plate driving forces from the mantle are calculated using global flow models that are driven by tomography and subduction derived density fields observed and predicted plate velocities agree well for a variety of models leading to varied conclusions about the relative importance of forces the dominance of the subduction related density pattern in the mantle is confirmed it appears that p wave models do not satisfactorily image all of the slab associated anomalies in the upper mantle furthermore lower mantle structure always improves the plate motion fit with respect to models that are based on upper mantle anomalies and lithospheric thickening only we show that the average torques from the lower mantle scale with the radial flow through the 660 km phase transition the amplitude of the lower mantle torques will be significant for a range of models if there is mass flux through 660 km we also evaluate parameterized edge forces and find that the additional inclusion of such torques does not significantly improve the model fit the main reason for the nonuniqueness of the inversions is plate boundary geometry since all plate motions are dominated by the trench ridge system and plates move from ridges to trenches

computing coastal ocean surface currents from infrared and ocean color satellite imagery many previous studies have demonstrated the viability of estimating advective ocean surface currents from sequential infrared satellite imagery using the maximum cross correlation mcc technique when applied to 1 1 km resolution advanced very high resolution radiometer avhrr thermal infrared imagery applied only to infrared imagery cloud cover and undesirable viewing conditions gaps in satellite data and edge of scan distortions limit the spatial and temporal coverage of the resulting velocity fields in addition mcc currents are limited to those represented by the displacements of thermal surface patterns and hence isothermal flow is not detected by the mcc method the possibility of supplementing mcc currents derived from thermal avhrr imagery was examined with currents calculated from 1 1 km resolution moderate resolution imaging spectroradiometer modis and sea viewing wide field of view sensor seawifs ocean color imagery which often have spatial patterns complementary to the thermal infrared patterns statistical comparisons are carried out between yearlong collections of thermal and ocean color derived mcc velocities for the central california current it is found that the image surface patterns and resulting mcc velocities complement one another to reduce the effects of poor viewing conditions and isothermal flow the two velocity products are found to agree quite well with a mean correlation of 0 74 a mean rms difference of 7 4 cm s and a mean bias less than 2 cm s which is considerably smaller than the established absolute error of the mcc method merging the thermal and ocean color mcc velocity fields increases the spatial coverage by approximately 25 for this specific case study

geological and geotechnical engineering aspects of low cost roads in mountainous terrain abstract the paper is concerned with design and construction of mountain roads in areas of high relief and steep mountain slopes where the principal soil types are transported rather than residual and the landscape is shaped mainly by active erosion processes in order to simplify the wide range of ground conditions encountered the geology and geomorphology of typical mountain terrain are described and related to a five zone model geotechnical features within each zone are then considered so that the application of various investigation and construction techniques can be appreciated the paper is primarily concerned with low cost but well trafficked primary roads where closure time due to slope failures or lack of maintenance are intended to be minimal village feeder roads and steep mountain haul roads for example those used in forestry are not the prime concern of the paper three aspects which distinguish mountain roads from typical lowland roads are the difficult ground access with numerous slope instability problems the greater use of very local construction materials and the greater need for off site drainage and erosion protection measures in remote rugged terrain access for wheeled traffic may not exist this severely curtails the use of conventional site investigation techniques such as drilling and means that greater emphasis is placed on remote sensing and on the surface assessment of ground conditions several relatively new low cost techniques applicable to the investigation of mountain regions are described a rational approach to alignment selection is developed which stresses the importance of stable ascent corridors and practical guidelines are offered on the selection of the road cross section and on the variety of techniques available to stabilise the cross section chosen the use of local construction materials is dictated largely on economic grounds and may place heavy constraints on construction standards and structural design the use of gabion structures is a major construction technique examined in the paper drainage and erosion protection methods are important in areas of high relief and erosion potential and a range of design approaches are described the bulk of stabilisation and control works described can only be attempted by labour

sar observation and numerical modeling of tidal current wakes at the east china sea offshore wind farm a terrasar x ts x synthetic aperture radar sar image acquired at the east china sea offshore wind farm presents distinct wakes at a kilometer scale on the lee of the wind turbines the presumption was that these wakes were caused by wind movement around turbine blades however wind analysis using spaceborne radiometer data numerical weather prediction and in situ measurements suggest that the prevailing wind direction did not align with the wakes by analyzing measurement at the tidal gauge station and modeling of the tidal current field these trailing wakes are interpreted to have formed when a strong tidal current impinged on the cylindrical monopiles of the wind turbines a numerical simulation was further conducted to reproduce the tidal current wake under such conditions comparison of the simulated surface velocity in the wake region with the ts x sea surface backscatter intensity shows a similar trend consequently turbulence intensity t i of the tidal current wakes over multiple piles is studied using the ts x observation it is found that the t i has a logarithmic relation with distance furthermore another case study showing wakes due to wind movement around turbine blades is presented to discuss the differences in the tidal current wakes and wind turbine wakes the conclusion is drawn that small scale wakes formed by interaction of the tidal current and the turbine piles could be also imaged by sar when certain conditions are satisfied the study is anticipated to draw more attentions to the impacts of offshore wind foundations on local hydrodynamic field

multi scale dynamics and rheology of mantle flow with plates fundamental issues in our understanding of plate and mantle dynamics remain unresolved including the rheology and state of stress of plates and slabs the coupling between plates slabs and mantle and the flow around slabs to address these questions models of global mantle flow with plates are computed using adaptive finite elements and compared to a variety of observational constraints the dynamically consistent instantaneous models include a composite rheology with yielding and incorporate details of the thermal buoyancy field around plate boundaries the local resolution is 1 km which allows us to study highly detailed features in a globally consistent framework models that best fit plateness criteria and plate motion data have strong slabs with high stresses we find a strong dependence of global plate motions trench rollback net rotation plateness and strain rate on the stress exponent in the nonlinear viscosity the yield stress is found to be important only if it is smaller than the ambient convective stress due to strong coupling between plates slabs and the surrounding mantle the presence of lower mantle anomalies affect plate motions the flow in and around slabs microplate motion and trench rollback are intimately linked to the amount of yielding in the subducting slab hinge slab morphology and the presence of high viscosity structures in the lower mantle beneath the slab

computing ocean surface currents over the coastal california current system using 30 min lag sequential sar images as compared with conventional methods for measuring ocean surface currents spaceborne synthetic aperture radar sar offers cloud penetrating ocean current observation capability at high spatial resolution while some studies have shown the potential of sar for studying ocean surface currents through feature tracking they have only analyzed a few images to demonstrate the basic measurement technique and no concise general technique has been developed this paper shows the application of the maximum cross correlation mcc method to generate ocean surface currents from nearly two years of available sequential spaceborne c band sar imagery from the envisat asar and ers 2 advanced microwave instrument sar sensors over the coastal california current system the data processing strategies are discussed in detail and results are compared with hf radar measured currents one dimensional wavenumber spectra of the sar derived surface currents agree with the k 2 power law as predicted by submesoscale resolution models comparisons with hf radar currents show encouraging results with mcc sar vectors oriented slightly counterclockwise relative to hf radar vectors mcc sar surface currents are found to have larger magnitudes than hf radar currents approx 11 cm s which may be due to the fact that sar penetrates only a few centimeters into the ocean surface whereas hf radar currents are averaged over the top 1 m of the ocean surface the larger part of this magnitude difference is contained in the along shore component which can be attributed to higher hf radar accuracy in the direct radial cross shore measurements as compared with along shore components derived from multiple cross shore radial measurements

measurement of surface currents using sequential synthetic aperture radar images of slick patterns near the edge of the gulf stream two dimensional surface currents are estimated over an area of 100 km2 near the inshore edge of the gulf stream by correlating the surface slick patterns observed on two synthetic aperture radar sar images collected about 20 min apart the currents obtained from this analysis are found to agree well with shipboard acoustic doppler current profiler adcp measurements at 10 to 20 m depths the orientations of the long linear slicks observed in this region differ from the mean current direction by about 16 but coincide with the direction of maximum radial deformation or strain as calculated from the observed current field the calculated current gradients indicate a mean surface convergence of about 2 10 5 s 1 and a cyclonic vorticity of about 1 10 4 s 1 values which fall within the range of previous estimates in the study area these results suggest that slick patterns may be used to infer surface current magnitude and direction from a time sequence of sar images but that care must be exercised in inferring current directions from the orientations of slick patterns within a single image

sea surface velocities in shallow seas extracted from sequential coastal zone color scanner satellite data sequential images of visible wavelength reflectance from channel 3 540 560 nm of the coastal zone color scanner czcs have been used for computing advective velocities in the eastern english channel using the maximum cross correlation technique the computation method known as matched filtering is widely used by meteorologists and has recently been applied by oceanographers to detect sea surface motion from satellite infrared images provided accurate coregistration of images is achieved by matching ground control points significant correlation is obtained when the technique is applied to czcs data and coherent velocity distributions are obtained for united kingdom shelf waters the residual circulation patterns for the english channel are found to be consistent with previous studies and recent observations

first analysis of terrasar x along track insar derived current fields we present the first analysis of surface current fields derived from terrasar x along track interferometric synthetic aperture radar along track insar ati data the images were acquired over the mouth of the elbe river germany during six satellite overpasses in spring and summer 2008 using the experimental aperture switching mode of terrasar x in this mode the phased array synthetic aperture radar sar antenna is split into two halves for receiving but in contrast to the dual receive antenna mode which uses two independent receivers in parallel a single receiver is multiplexed to process signals from the two antenna halves in an alternating manner at a doubled pulse repetition frequency the effective ati baseline is on the order of 0 8 m the sar ati raw data processing is described in another paper in this issue this paper focuses on the conversion of the basic interferograms into line of sight surface current fields which includes an elimination of ship signatures identification and correction as far as possible of imaging artifacts additional filtering and smoothing and a subtraction of contributions of wave motions to detected velocities according to a theoretical model we evaluate the quality of the results by comparison with current fields from a numerical flow model and with available in situ data the ati performance of terrasar x is found to be basically consistent with theoretical expectations after applying the same data processing algorithms to all six images mean differences between terrasar x derived currents and reference currents in our main test area range from 0 11 to 0 08 m s in five of the six cases with one outlier at 0 42 m s the spatial current variations within the terrasar x derived current fields are consistent with the model in three cases but unrealistically strong variations across the images are found in the other three cases we attribute this to shortcomings of our preliminary raw data processing algorithms which can probably be fixed after some more detailed analysis and testing the results obtained so far encourage us to believe that our internal performance goal of a typical current measuring accuracy of 0 1 m s at an effective spatial resolution better than 1 km can be met

an objective method for computing advective surface velocities from sequential infrared satellite images using cross correlations between sequential infrared satellite images an objective technique is developed to compute advective sea surface velocities cross correlations are computed in 32 x 32 pixel search second image and 22 x 22 template first image windows from gradients of sea surface temperature computed from the satellite images velocity vectors computed from sequential images of the british columbia coastal ocean generally appear coherent and consistent with the seasonal surface current in the region during periods of strong wind forcing as indicated by maps of sea level pressure the image advective velocities are stronger and more coherent spatially and appear to cross surface temperature gradients when winds are weaker the advective velocities correspond better with the infrared temperature patterns suggesting the increased contribution of the geostrophic current to the surface flow velocities determined from coincident near surface drogued 5 10 m buoys positioned every half hour by internal loran c units in mid june show excellent agreement with the image advective velocities in addition conductivity temperature and depth ctd measurements taken during the buoy tracking confirm the homogeneity of the upper 10 m and ctd derived geostrophic currents are consistent with

state of stress in slabs as a function of large scale plate kinematics the state of stress of slabs subducting worldwide as revealed by seismicity is extremely variable both with depth and between different subduction zones although in principle slab pull should enhance downdip extension in the slab the reconstructed stress fields for intermediate depths between 100 and 300 km range from downdip compression to downdip extension using 2 d viscoelastic plane strain models we investigate the dependency of the stress field of slabs on geometry dip of the slab and kinematics velocity of convergence between upper and lower plates and their absolute velocity with respect to the underlying mantle of subduction zones we conclude that although the state of stress in slabs is also controlled by other processes downdip compression in the subducting slab is enhanced by mantle flow opposing the direction of the dip of the slab whereas downdip extension is favored by mantle flow in the same direction of the slab dip i e sustaining it these predictions are in agreement with available geophysical observations although exceptions to this simple pattern are observed worldwide in addition if the slab is decoupled from the upper plate convergence between upper and lower plates induces a downdip compressional component of stress within the slab decreasing the magnitude of extension in models characterized by mantle flow sustaining the slab and increasing compression in models with mantle flow opposing subduction however these are second order variations when compared to the control exerted by absolute plate kinematics and by the magnitude of slab pull sensitivity analysis of rheological parameters allows us to conclude that these results are generally consistent although low values of viscosity of the lithospheric mantle render this prediction less stable

interferometric radar measurement of ocean surface currents we describe a new method of measuring surface currents using an interferometric synthetic aperture radar an airborne implementation has been tested over the san francisco bay near the time of maximum tidal flow resulting in a map of the east west component of the current only the line of sight component of velocity is measured by this technique where the signal to noise ratio was strongest statistical fluctuations of less than 4 cm s 1 were observed for ocean patches of 60 60 m

mapping the agulhas current from space an assessment of asar surface current velocities 1 over 2 years of surface current information collected in the agulhas current region and derived from the doppler centroid anomalies of envisat s advanced synthetic aperture radar asar are examined the sources of errors and potential use of asar surface current velocities for oceanographic research are assessed asar surface current velocities are compared to surface drifter data and merged altimetry observations maps of sea surface temperature are used to establish the asar s capacity to capture the synoptic circulation discrepancies between observed and predicted asar velocities result predominantly from inadequate wind corrections combined with radar incidence angles below 30 occasionally observed wind induced outliers cause a bias in the estimated asar velocities but do not affect the ability of the asar to systematically image regions of strong surface current flow and shear time averaged maps of asar derived surface current velocity seem able to accurately capture the position as well as the intensity of the agulhas current the ability of the asar to pick up the smaller features of the circulation along the shelf break also shows that variability along the agulhas bank is of the same order of magnitude as that observed in the agulhas retroflection asar surface current velocities offer a very good complement to altimetry in regions where the mean dynamic topography is poorly resolved the quasi synoptic nature of asar acquisitions combined with the relatively high resolution of asar surface current velocities also make it attractive for studies of submesoscale processes and western boundary current dynamics

slab stress and strain rate as constraints on global mantle flow dynamically consistent global models of mantle convection with plates are developed that are consistent with detailed constraints on the state of stress and strain rate from deep focus earthquakes models that best fit plateness criteria and plate motion data have strong slabs that have high stresses the regions containing the m w 8 3 bolivia and m w 7 6 tonga 1994 events are considered in detail modeled stress orientations match stress patterns from earthquake focal mechanisms a yield stress of at least 100 mpa is required to fit plate motions and matches the minimum stress requirement obtained from the stress drop for the bolivia 1994 deep focus event the minimum strain rate determined from seismic moment release in the tonga slab provides an upper limit of 200 mpa on the strength in the slab

evolving force balance during incipient subduction nearly half of all active subduction zones initiated during the cenozoic all subduction zones associated with active back arc extension have initiated since the eocene hinting that back arc extension may be intimately associated with an interval several tens of myr following subduction initiation that such a large proportion of subduction zones are young indicates that subduction initiation is a continuous process in which the net resisting force associated with forming a new subduction zone can be overcome during the normal evolution of plates subduction initiation is known to have occurred in a variety of tectonic settings old fracture zones transform faults and extinct spreading centers and through polarity reversal behind active subduction zones although occurring within different tectonic settings four known subduction initiation events izu bonin mariana ibm along a fracture zone tonga kermadec along an extinct subduction boundary new hebrides within a back arc and puysegur fiordland along a spreading center were typified by rapid uplift within the forearc followed by sudden subsidence other constraints corroborate the compressive nature of ibm and tonga kermadec during initiation using an explicit finite element method within a two dimensional domain we explore the evolving force balance during initiation in which elastic flexure viscous flow plastic failure and heat transport are all considered in order to tie theory with observation known tectonic settings of subduction initiation are used as initial and boundary conditions we systematically explore incipient compression of a homogeneous plate a former spreading center and a fracture zone the force balance is typified by a rapid growth in resisting force as the plate begins bending reaching a maximum value dependent on plate thickness but typically ranging from 2 to 3 1012 n m for cases that become self sustaining this is followed by a drop in stress once a shear zone extends through the plate the formation of a throughgoing fault is associated with rapid uplift on the hanging wall and subsidence on the footwall cumulative convergence not the rate of convergence is the dominant control on the force balance viscous tractions influence the force balance only if the viscosity of the asthenosphere is 1020 pa s and then only after plate failure following plate failure buoyancy of the oceanic crust leads to a linear increase with crustal thickness in the work required to initiate subduction the total work done is also influenced by the rate of lithospheric failure a self sustaining subduction zone does not form from a homogeneous plate a ridge placed under compression localizes subduction initiation but the resisting ridge push force is not nearly as large as the force required to bend the subducting plate the large initial bending resistance can be entirely eliminated in ridge models explaining the propensity for new subduction zones to form through polarity reversals a fracture zone fz placed in compression leads to subduction initiation with rapid extension of the overriding plate a fz must be underthrust by the older plate for 100 150 km before a transition from forced to self sustaining states is reached in fz models the change in force during transition is reflected by a shift from forearc uplift to subsidence subduction initiation is followed by trench retreat and back arc extension moderate resisting forces associated with modeled subduction initiation are consistent with the observed youth of pacific subduction zones the models provide an explanation for the compressive state of western pacific margins before and during subduction initiation including ibm and tonga kermadec in the eocene and the association of active back arcs with young subduction zones on the basis of our dynamic models and the relative poles of rotation between pacific and australia during the eocene we predict that the northern segment of the tonga kermadec convergent margin would have initiated earlier with a progressive southern migration of the transition between forced and self sustaining states

ocean surface currents from avhrr imagery comparison with land based hf radar measurements we focus on inverting the surface temperature or heat equation to obtain the surface velocity field in the coastal ocean and compare the results with those from the maximum cross correlation mcc technique and with the in situ velocity fields measured by the rutgers university coastal ocean dynamics radar codar when compared with codar fields velocities from the heat equation and mcc have comparable accuracies but the heat equation technique better resolves the finer scale flow features we use the results to directly calculate the surface divergence and vorticity this is possible because we convert the traditionally underdetermined heat inversion problem to an overdetermined one without constraining the velocity field with divergence vorticity or energy statements because no a priori assumptions are made about the vorticity it can be calculated directly from the velocity results the derived vorticity field has typical open ocean magnitudes 5 times 10 5 s and exhibits several structures a warm core ring gulf stream filament and a diverging flow consistent with the types of flows required to kinematically deform the sea surface temperature patterns into the observed configurations

environmental correlations of landslide frequency along new highways in the himalaya preliminary results abstract variables which correlate with accelerated landslide activity are identifed in a study of two new hill roads at almora and nainital u p india cumulatively 32 of the roadcut is affected by rockfall and 27 by the slumping of rock and or regolith correlation and discriminant analyses suggest that rockfalling may be predictable from measures of the frequency of enlarged joints in the roadcut supported by members of an inter related complex of variables including slope angle roadcut height apparent dip rock strength and upslope vegetation cover direct measures of environmental instability such as the undermining of the roadbed by erosion were also shown to have value however the study found few useful environmental indicators of slumping a positive relation between slumping and tree cover upslope may reflect the fact that forest survives as a relict landuse in locations which are undeveloped because of their instability

computing advective velocities from satellite images of sea surface temperature a method of employing sequential satellite images of sea surface temperature sst patterns to estimate surface advective current velocities is described sst images are obtained by processing data received twice daily from the advanced very high resolution radiometer the current velocities are estimated by applying a maximum cross correlation mcc technique on two time lapsed images the mcc technique involves computing matrices of cross correlation coefficients and identifying correlation peaks a two stage multilevel statistical test over two dimensional correlations is developed for determining the relative significance levels of velocity estimates the test also identifies areas where the mcc technique cannot be effective aspects of implementation and limitations of the mcc technique for computing current velocity are also discussed advective velocity fields computed through mcc for the chatham rise area in new zealand extending from 40 5 degrees s 173 5 degrees e to 49 degrees s 178 degrees w show good agreement with the known geostrophic flow patterns in this area

remote sensing of ocean currents a method of remotely measuring near surface ocean currents with a synthetic aperture radar sar is described the apparatus consists of a single sar transmitter and two receiving antennas the phase difference between sar image scenes obtained from the antennas forms an interferogram that is directly proportional to the surface current the first field test of this technique against conventional measurements gives estimates of mean currents accurate to order 20 percent that is root mean square errors of 5 to 10 centimeters per second in mean flows of 27 to 56 centimeters per second if the full potential of the method could be realized with spacecraft then it might be possible to routinely monitor the surface currents of the world s oceans

direct ocean surface velocity measurements from space improved quantitative interpretation of envisat asar observations previous analysis of advanced synthetic aperture radar asar signals collected by esa s envisat has demonstrated a very valuable source of high resolution information namely the line of sight velocity of the moving ocean surface this velocity is estimated from a doppler frequency shift consistently extracted within the asar scenes the doppler shift results from the combined action of near surface wind on shorter waves longer wave motion wave breaking and surface current both kinematic and dynamic properties of the moving ocean surface roughness can therefore be derived from the asar observations the observations are compared to simulations using a radar imaging model extended to include a doppler shift module the results are promising comparisons to coincident altimetry data suggest that regular account of this combined information would advance the use of sar in quantitative studies of ocean currents

comparison of velocity estimates from advanced very high resolution radiometer in the coastal transition zone two methods of estimating surface velocity vectors from advanced very high resolution radiometer avhrr data were applied to the same set of images and the results were compared with in situ and altimeter measurements the first method used an automated feature tracking algorithm and the second method used an inversion of the heat equation the 11 images were from 3 days in july 1988 during the coastal transition zone field program and the in situ data included acoustic doppler current profiler adcp vectors and velocities from near surface drifters the two methods were comparable in their degree of agreement with the in situ data yielding velocity magnitudes that were 30 50 less than drifter and adcp velocities measured at 15 20 m depth with rms directional differences of about 60 these differences compared favorably with a baseline difference estimate between adcp vectors interpolated to drifter locations within a well sampled region high correlations between the avhrr estimates and the coincident geosat geostrophic velocity profiles suggested that the avhrr methods adequately resolved the important flow features the flow field was determined to consist primarily of a meandering southward flowing current interacting with several eddies including a strong anticyclonic eddy to the north of the jet incorporation of sparse altimeter data into the avhrr estimates gave a modest improvement in comparisons with in situ data

airborne synthetic aperture radar observations of spiral eddy slick patterns in the southern california bight 1 repeat sampling on hourly time scales using an airborne synthetic aperture radar sar is used to investigate the occurrence and evolving characteristics of spiral shaped slick patterns commonly presumed to be indicators of submesoscale ocean eddies in the area around santa catalina island california 33 4 n 118 4 w simultaneous sar imagery and boat survey data are examined over two 5 h long periods spaced 3 days apart in april 2003 the sar imagery reveals several spiral like patterns roughly 5 km in diameter occurring downstream of the western end of catalina we believe that the most likely formation mechanism for these patterns is current wake instability related to the flow of the southern california countercurrent along the north shore of catalina in one case there is an observed cold core eddy and vortex sheet attached to the tip of the island similar to island wake simulations done by dong and mcwilliams 2007 in another case the sar imagery shows a series of slick patterns that at least initially resemble spiral eddies but the data show no clear evidence of actual ocean eddies being present either at depth or through a rotating surface expression a speculation is that such features signify island wake eddies that are relatively weak and dissipate quickly an unexpected finding was how quickly a spiral slick pattern could deteriorate suggesting a time scale for the surface feature of the order of only several hours an implication of this result is that care is needed when interpreting a single satellite sar imagery for evidence of active submesoscale eddies recommendations are made for future field studies

rheologic controls on slab dynamics several models have been proposed to relate slab geometry to parameters such as plate velocity or plate age however studies on the observed relationships between slab geometry and a wide range of subduction parameters show that there is not a simple global relationship between slab geometry and any one of these other subduction parameters for all subduction zones numerical and laboratory models of subduction provide a method to explore the relative importance of different physical processes in determining subduction dynamics employing 2 d numerical models with a viscosity structure constrained by laboratory experiments for the deformation of olivine we show that the observed range in slab dip and the observed trends between slab dip and convergence velocity subducting plate age and subduction duration can be reproduced without trench motion i e slab roll back for locations away from slab edges successful models include a stiff slab that is 100 1000 times more viscous than previous estimates from models of plate bending the geoid and global plate motions we find that slab dip in the upper mantle depends primarily on slab strength and plate boundary coupling with a small dependence on subducting plate age once the slab sinks into the lower mantle the primary processes controlling slab evolution are 1 the ability of the stiff slab to transmit stresses up dip 2 resistance to slab descent into the higher viscosity lower mantle and 3 subduction induced flow in the mantle wedge corner

retrieval of sea surface range velocities from envisat asar doppler centroid measurements the processing steps and error corrections needed to retrieve estimates of sea surface range doppler velocities from envisat advanced synthetic aperture radar wide swath medium resolution image products are presented retrieval accuracies based on examination of the corrected doppler shift measurements are assessed the root mean square errors of the doppler shift after bias corrections are found to be 4 7 and 3 9 hz in vv and hh polarizations respectively at 35 incidence angle this corresponds to horizontal doppler velocities of 23 and 19 cm s

on the relationships between slab dip back arc stress upper plate absolute motion and crustal nature in subduction zones 1 statistical analysis of modern oceanic subduction zone parameters such as the age of a downgoing plate or the absolute plate motions is performed in order to investigate which parameter controls the dip of a slab and conversely what the influence of slab geometry is on upper plate behavior for that purpose parameters have been determined from global databases along 159 transects from all subduction zones that are not perturbed by nearby collision or ridge plateau seamount subduction on the basis of tomographic images slabs that penetrate through or lie on the 670 km discontinuity are also identified the results of the statistical analysis are as follows 1 back arc stress correlates with slab dip i e back arc spreading is observed for deep dips deeper than 125 km larger than 50 whereas back arc shortening occurs only for deep dips less than 30 2 slab dip correlates with absolute motion of the overriding plate the correlation is even better when the slab lies on or even more penetrates through the 670 km discontinuity 3 slabs dip more steeply by about 20 on average beneath oceanic overriding plates than beneath continental ones 4 slabs dip more steeply on average by about 10 near edges 5 slab dip does not correlate with the magnitude of slab pull the age of subducting lithosphere at the trench the thermal regime of the subducting lithosphere the convergence rate or the subduction polarity east versus west the present study provides evidence that the upper plate absolute motion plays an important role on slab dip as well as on upper plate strain retreating overriding plates are often oceanic ones and thus may partially explain the steeper slab dips beneath oceanic upper plates one can infer that low slab dips correlate well with compression in continental advancing upper plates whereas steep dips are often associated with extension in oceanic retreating upper plates excess weight of old slabs is often counterbalanced by other forces probably asthenospheric in origin such as lateral mantle flow near slab edges or anchor forces to determine slab dip

derivation of sea surface tidal current from spaceborne sar constellation data in this paper we demonstrate an application of spaceborne synthetic aperture radar sar constellation data to derive sea surface tidal current at high spatial resolution the maximum cross correlation mcc method which has been widely applied to optical remote sensing data to derive sea surface velocities is applied to x band sar data from terrasar x tsx and tandem x tdx which were operating in pursuit monostatic mode because of the short temporal interval of tsx and tdx s pursuit acquisitions temporal de correlation is minimized to derive tidal current fields that exhibit significant temporal and spatial variations in addition we combined data from tdx and another x band sar cosmo skymed to obtain a virtual sar constellation data pair which was also analyzed using the mcc method to derive the tidal current field case studies of hangzhou bay in the east china sea and amrum island in the north sea are presented the sar derived tidal current fields were compared to the results of numerical model simulations high frequency hf radar measurements and in situ measurements mcc coefficients that are greater than 0 8 are an appropriate threshold for the further derivation of tidal currents comparisons to finite volume community ocean model hf radar and general estuarine transport model results yield root mean square errors of 0 13 0 06 and 0 05 m s respectively measurements from three field stations were also compared to the mcc sar retrievals yielding differences of 0 3 0 07 and 0 09 m s

an improved composite surface model for the radar backscattering cross section of the ocean surface 2 model response to surface roughness variations and the radar imaging of underwater bottom topography in the companion paper we have presented an improved composite surface model for the calculation of normalized radar backscattering cross sections nrcs of the ocean surface the proposed model accounts for the impact of the full two dimensional ocean wave spectrum on the radar backscatter and was shown to reproduce measured absolute nrcs values for a variety of radar configurations and wind speeds satisfactorily after some reasonable tuning of the input ocean wave spectrum this paper focuses on the modulation of the nrcs in the presence of spatially varying surface currents first the sensitivity of the nrcs to intensity variations of different ocean wave spectral components is investigated then the hydrodynamic modulation of the wave spectrum over underwater bottom topography in tidal waters is computed in different ways and the resulting radar signatures are discussed the composite surface model yields comparable radar signatures at high 10 ghz x band and low 1 ghz l band radar frequencies which is in much better agreement with experimental results than the predictions of a first order bragg scattering model on the other hand measured variations of the nrcs at high radar frequencies appear to be still underestimated in some cases which may be due to shortcomings of our description of the wave current interaction by conventional weak hydrodynamic interaction theory possible improvements of the theory are discussed and requirements for future experiments are formulated

velocity observations of the california current derived from satellite imagery 1 this research examines the potential of ocean velocity observations generated from the maximum cross correlation technique mcc applied to thermal infrared imagery to capture the total current at a high sampling rate especially in the nearshore region allowing for a novel view of the california current comparison of 12 years of weekly ocean velocity fields derived from the mcc method with velocity observations from drifting buoys reveals strong correspondence between the data sets the mcc method however is able to produce over 10 times the number of observations comparison of mcc velocities with geostrophic velocities from altimetry demonstrates differences that suggest ageostrophic currents in the mcc observations that are likely wind driven the time averaged mean velocity field from mcc observations reveals strong offshore jet like features that extend off of coastline promontories eddy statistics from the mcc velocity observations indicate dramatically different dynamics in the nearshore and offshore regions differences in spatial statistics derived from the mcc observations compared to previous studies of the region are attributed to wind driven currents in the observations that can dominate the variability of the current in the nearshore region