compositional gradients surrounding spherulites in obsidian and their relationship to spherulite growth and lava cooling spherical masses of crystal fibers spherulites crystalize from rhyolitic melt glass mainly in response to significant undercooling while lava cools spherulite growth should induce compositional gradients in the surrounding glass from expulsion of incompatible constituents and diffusion of those constituents away from the spherulite finite difference numerical modeling of one dimensional diffusion in which diffusivities are allowed to vary with temperature is used to investigate how compositional gradients reflect spherulite growth and lava cooling overall three forms of gradients are identified elements that diffuse quickly are expelled from the spherulite but then migrate away too quickly to become enriched at the boundary of the spherulite elements that diffuse slowly are trapped within the growing spherulite between those endmembers are elements that are not trapped yet diffuse slow enough that they become enriched at the contact their slow diffusion away then elevates their concentrations in the surrounding glass how enriched those elements are at the spherulite matrix interface and how far their enrichments extend outwards into the glass reflect how spherulites grow and thermal conditions during growth concentrations of h2o rb f li cl na k sr cs ba and be were measured in and around spherulites in obsidian from a 4 7 1 km3 rhyolite lava dome erupted from tequila volcano mexico measurable concentration gradients are found for h2o rb and f attributes of those gradients and the behaviors of the other elements are in accord with their experimentally constrained diffusivities spherulites appear to have grown following radial rather than volumetric growth the observed gradients and lack of others are more consistent with growth mainly below the glass transition which would necessitate the dome cooling at ca 10 5 to 10 7 c s 1 such slow cooling is consistent with the relatively large volume of the dome

a comparison of measured and wind derived ekman transport at 11 n in the atlantic ocean abstract a comparison of measured and wind derived ageostrophic transport is presented from a zonal transect spanning the atlantic ocean along 11 n the transport per unit depth shows a striking surface maximum that decays to nearly zero at a depth of approximately 100 m we identify this flow in the upper 100 m as the ekman transport the sustained values of wind stress and the penetration depth of the ekman transport reported here are considerably greater than in previous observations which were made in conditions of light winds the transport of 12 0 5 5 106 m3 s 1 calculated from the difference of geostrophic shear and shear measured by an acoustic doppler current profiler is in good agreement with that estimated from the shipboard winds 8 8 1 9 106 m3 s 1 and from climatology 13 5 0 3 106 m3 s 1 qualitatively the horizontal distribution of the wind driven flow was best predicted by the shipboard winds the cumulative transport increased linearly over the western three fourths of t

a wind forced ekman spiral as a good statistical fit to low frequency currents in a coastal strait ekman s classical analysis of wind driven currents is a fundamental component of the modern circulation theory of the oceans but there have been few good observations of the predicted ekman spiral where the velocity vector rotates clockwise in direction in the northern hemisphere and decays exponentially in magnitude with increasing depth an analysis of recent cyclesonde velocity measurements based on the use of empirical orthogonal functions however suggests that a classical ekman spiral was a good statistical fit to a significant portion of the low frequency current fluctuations in the strait of georgia british columbia for fluctuation periods of about 5 to 10 days

direct evidence for an ekman balance in the california current moored acoustic doppler current profiler velocity estimates and buoy wind observations made during a period of moderate southward winds were used to test the ekman balance at a site in the california current as in prior studies the wind driven flow was separated from the total flow by subtraction of a deep reference current the wind driven flow was shown to be in an ekman balance on daily timescales over a period of several months the mean observed transport was to the right of the wind and agreed to within 3 in magnitude and 4 in phase with the predicted ekman transport although the error bar was about 20 the mean velocity profile was a smooth spiral qualitatively similar although flatter than the theoretical ekman spiral prom the observed mean momentum balance profiles of the turbulent stress and eddy viscosity were inferred eddy viscosity estimates within the wind mixed layer were o 100 cm2 s 1

assessment of radiometric correction techniques in analyzing vegetation variability and change using time series of landsat images abstract the homogeneity of time series of satellite images is crucial when studying abrupt or gradual changes in vegetation cover via remote sensing data various sources of noise affect the information received by satellites making it difficult to differentiate the surface signal from noise and complicates attempts to obtain homogeneous time series we compare different procedures developed to create homogeneous time series of landsat images including sensor calibration atmospheric and topographic correction and radiometric normalization two seasonal time series of landsat images were created for the middle ebro valley ne spain covering the period 1984 2007 different processing steps were tested and the best option selected according to quantitative statistics obtained from invariant areas simultaneous medium resolution images and field measurements the optimum procedure includes cross calibration between landsat sensors atmospheric correction using complex radiative transfer models a non lambertian topographic correction and a relative radiometric normalization using an automatic procedure finally three case studies are presented to illustrate the role of the different radiometric correction procedures when analyzing and explaining gradual and abrupt temporal changes in vegetation cover as well as temporal variability we have shown that to analyze different vegetation processes with landsat data it is necessary to accurately ensure the homogeneity of the multitemporal datasets by means of complex radiometric correction procedures failure to follow such a procedure may mean that the analyzed processes are non recognizable and that the obtained results are invalid

diffusion of dissolved co2 and cl in hydrous silicic to intermediate magmas the bulk diffusivity of dissolved co sub 2 in obsidian and dacite melts containing 0 11 wt dissolved water at 800 1 100c and 1 gpa was characterized using a sup 14 c radiotracer technique five values were also obtained for cl in melts containing 8 h sub 2 o carbon dioxide diffusivity d sub co sub 2 in nominally dry molten obsidian is similar to previously reported values for a simple melt in the na sub 2 o al sub 2 o sub 3 sio sub 2 system and for dry basalt indicating little effect of melt composition on bulk co sub 2 diffusion three d sub co sub 2 values for hydrous dacite melt are consistent with this lack of a melt composition effect dissolved water however causes an increase of d sub co sub 2 in molten obsidian by about an order of magnitude for each 5 of added water the activation energy of approximately 18 kcal mol is lower by a factor of approximately 3 than that for diffusion in dry basalt in comparison with existing data for diffusion of water in silicic melts at their typical liquidus temperatures d sub co sub 2 is generally lower unless the melt contains more than about 6 dissolved h sub 2 o in which case d sub co sub 2 approximately d sub h sub 2 0 the few data obtained frommore chlorine diffusion reveal the d sub cl is lower by a factor of 5 10 than d sub co sub 2 in the same melt the overall systematics of the new data on dissolved volatile diffusion indicate that diffusional fractionation effects are likely to be most significant in silicic to intermediate magmas having water contents in the 0 4 range less

mapping the buraburi granite in the himalaya of western nepal remote sensing analysis in a collisional belt with vegetation cover and extreme variation of topography abstract the aim of the present study is to define the most suitable methodologies for aster data pre processing and analysis in order to enhance peraluminous granitoid rocks in rugged and vegetated areas the research started with raw image data pre processing and continued with a comparison of satellite field and laboratory data the masking technique adopted to isolate rocky pixels was of fundamental importance to perform further analysis an integration of density sliced images and false colour composite images of band ratio relative absorption band depth and principal component analysis allowed us to generate a geological map that highlights a new granitoid body buraburi granite and the surrounding host rocks in the dolpo region western nepal the buraburi granite was mapped and sampled integrating remotely sensed aster data with analysis of rocks and minerals spectral signatures the innovative approach that we have adopted considers the absorption features of particular lichen species acidophilic the results highlight the importance of considering acidophilic lichen means of detecting granitoid rocks furthermore since peraluminous granitoids i e buraburi granite have a considerable al2o3 bulk rock content the muscovite al oh absorption peaks centred in the 6th aster band were also considered an important parameter for their detection field observations confirm the results of remote sensing analysis showing the intrusive relationship between the newly discovered 110 km 2 granitoid body and the wall rocks of the higher himalayan crystalline and the tibetan sedimentary sequence in conclusion the proposed methods have great potential for granitoid mapping in vegetated and rough terrains particularly those with climatic and geological conditions similar to the ones of the southern himalayan belt

diffusion of ca and f in haplogranitic melt from dissolving fluorite crystals at 900 1000 c and 100 mpa 1 the diffusion rates of ca and f into haplogranitic melt were determined by concentration profiles in glasses produced by dissolving fluorite crystals into haplogranitic melt at 900 1000 c and 75 100 mpa starting products were synthesized from oxides of haplogranitic composition at two aluminosities na2o k2o al2o3 1 05 and 1 68 fluorite crystals or crystal powders were coupled with powders or solid cylinders of haplogranitic glass water was added to the runs resulting in two runs at h2o 1 20 and 1 40 wt and three runs thought to be water saturated the materials were then subjected to the conditions of interest in either a stellite cold seal apparatus or an internally heated pressure vessel electron microprobe traverses of the quenched glasses produced in these experiments revealed negative concentration gradients in ca and f away from the fluorite glass boundary these gradients are comparable to an error function solution in the first approximation for specific ca and f diffusivities dca and df respectively the ca diffusion coefficient increased from 3 36 0 19 10 9 to 2 16 0 28 10 8 cm2 s and f diffusivity increased from 1 16 0 09 10 8 to 6 59 0 62 10 8 cm2 s as temperature increased from 900 to 1000 c these diffusivities are comparable to other published melt diffusion data for the dissolution of multicomponent minerals where the diffusants move independently calcium and fluorine diffusivities increase from 2 77 0 09 10 9 to 2 16 0 28 10 8 cm2 s and from 2 27 0 10 10 8 to 6 59 0 62 10 8 cm2 s respectively with increasing water content at 1000 c likely due to melt depolimerization the large difference in the concentrations of ca c0ca and f c0f at the fluorite glass interface suggests that these two elements diffuse independently in the melt in contrast the concentration gradient for na parallels that of f suggesting complexing between these two elements

turbulent mixing under drifting pack ice in the weddell sea by providing cold dense water that sinks and mixes to fill the abyssal world ocean high latitude air sea ice interaction is the main conduit through which the deep ocean communicates with the rest of the climate system a key element in modeling and predicting oceanic impact on climate is understanding the processes that control the near surface exchange of heat salt and momentum in 1992 the united states russian ice station weddell 1 traversed the western weddell sea during the onset of winter providing a platform for direct measurement of turbulent heat flux and reynolds stress in the upper ocean data from a storm early in the drift indicated i well formed ekman spirals in both velocity and turbulent stress ii high correlation between mixed layer heat flux and temperature gradients iii that eddy viscosity and eddy thermal diffusivity were similar about 0 02 square meters per second and iv that the significant turbulent length scale 2 to 3 meters through most of the boundary layer was proportional to the wavelength at the peak in the weighted vertical velocity spectrum the measurements were consistent with a simple model in which the bulk eddy viscosity in the neutrally buoyant mixed layer is proportional to kinematic boundary stress divided by the coriolis parameter

on the response of the ocean to a moving storm the nonlinear dynamics abstract a novel and efficient numerical method is used to investigate the nonlinear equations of motion for the upper layer of a two layer ocean in which the lower layer is infinitely deep and at rest the efficiency is achieved by seeking solutions that are in a steady state translating in equilibrium with the storm oscillations are found in the wake of the storm two features of the response are attributed to the nonlinear terms in the equation of motion 1 a rapid transition from a maximum in the downwelling phase to a maximum in the upwelling phase of each oscillation followed by a gradual relaxation to the next downwelling maximum and 2 a displacement of the maximum response usually to the right of the storm track by 40 km it is shown that the horizontal pressure gradient terms can be neglected from the momentum equations for fast large storms in which case a lagrangian integration can be performed following fluid particles this enables feature 1 to be attributed to the along tra

near inertial ocean current response to hurricane frederic abstract hurricane frederic passed with 80 to 130 km of the u s naval oceanographic office current meter arrays in water depths ranging from 100 to 470 m near the desoto canyon region and within 150 km of an ocean thermal energy conversion otec mooring in 1050 m of water excitation of near inertial waves by the moving hurricane was observed throughout the water column along the canyon walls and at the otec site the frequencies of the waves were blue shifted between 1 to 6 above the local inertial frequency the horizontal wavelength of 250 km is consistent with an energetic first baroclinic mode response but is considerably below the linear theory prediction of 550 km the inferred vertical wavelengths of the immediate response exceeded 1000 m along the northern and eastern sides of the canyon since the currents throughout the water column increased within hours of the hurricane passage later the vertical wavelengths were about equal to the water depth the vertical group velocities associated

radiometric scene normalization using pseudoinvariant features abstract a scene to scene radiometric normalization technique has been developed which corrects for atmospheric degradations illumination effects and sensor response differences in multitemporal multispectral imagery the technique is based on the statistical invariance of the reflectance of man made in scene elements such as concrete asphalt and rooftops differences in the grey level distributions of these invariant objects is assumed to be a linear function and is corrected statistically to perform the normalization the technique exhibits errors in reflectance of approximately 1 for landsat tm and high resolution air photo imagery in all spectral regions studied

wind driven ocean currents and ekman transport oceanographic engineering of the woods hole oceanographic institution and the massachusetts institute of technology woods hole ma 02543 oceanographers have long sought to verify the theoretical ekman transport relation which predicts that a steady wind stress acting together with the coriolis force will produce a transport of water to the right of the wind in situ measurements of wind and ocean currents provide a detailed view of this phenomenon by separating the wind driven current from the measured total current and by averaging over a long record it is found that the observed transport is consistent with theoretical ekman transport to within about 10 percent in this case the wind driven transport is strongly surface trapped with 95 percent occurring in the upper 25 meters as a result of fair summer weather

the subinertial momentum balance of the north atlantic subtropical convergence zone abstract the upper ocean to forcing by pressure gradients and wind stress is examined using observations from the frontal air sea interaction experiment a moored way acquired time series of winds upper ocean currents temperatures and salinities between winter and late spring in a region of the sargasso sea known for the presence of upper ocean fronts these fronts have timescales of 10 days and dominate current variance while winds varied with the 4 day timescale of passing weather systems employing a frequency domain regression model it is found that gestrophy accounts for most of the low frequency 100 h current variance in the seasonal pycnoclino but wind forced shear becomes important nearer the surface in particular currents oriented in the typical ne sw alonfront direction display geostrophic balance while those perpendicular to them do not wind forcing can produce geostrophic currents indirectly through ekman pumping and knowledge of the geostrophic shear is required to distinguish be

forced stage response to a moving hurricane abstract the upper ocean s response to three hurricanes norbert 1984 josephine 1984 and gloria 1985 is examined using field observations and a numerical ocean model our goal is to describe the physical processes that determine the structure and amplitude of hurricane driven upper ocean currents all three of these northern hemisphere hurricanes produced a rightward biased response of the mixed layer current and transport this asymmetry arises because the wind stress vector rotates clockwise on the right side of the track and remains nearly parallel with the inertially rotating mixed layer current during most of the hurricane passage the maximum observed mixed layer current varied from 0 8 m s 1 in response to josephine which was a large but comparatively weak hurricane to 1 7 m s 1 in response to gloria which was very large and also intense these cases have been simulated with a three dimensional numerical model that includes a treatment of wind driven vertical mixing within the primitive

image based mapping of surface fissures for the investigation of landslide dynamics abstract the development of surface fissures is an important indicator for understanding and forecasting slope movements landslide investigations therefore frequently include the elaboration and interpretation of maps representing their spatial distribution typically comprising intensive field work and instrumentation it is only recently that aerial photography with sub decimetre spatial resolution is becoming more commonly available and opens a window to analyse such features from a remote sensing perspective while these data are in principle helpful to elaborate maps from image interpretation techniques there is still no image processing technique available to extract efficiently these geomorphological features this work proposes a largely automated technique for the mapping of landslide surface fissures from very high resolution aerial images the processing chain includes the use of filtering algorithms and post processing of the filtered images using object oriented analysis the accuracy of the resulting maps is assessed by comparisons with several expert maps in terms of affected area fissure density and fissure orientation under homogenous illumination conditions true positive rates up to 65 and false positive rates generally below 10 are achieved the resulting fissure maps provide sufficient detail to infer mechanical processes at the slope scale and to prioritize areas for more detailed ground investigations or monitoring

the probable occurrence of interstitial al in hydrous f bearing and f free aluminosilicate melts experiments carried out on the system sio2 naalsi3o8 kalsi3o8 qz ab or at 1 kbar in the presence of h2o and f show that the quartz alkali feldspar field boundary is progressively displaced towards the feldspar join as f contents increase from 0 to 4 wt f increasing p h 2 o in the absence of f has already been shown to have a similar effect tuttle and bowen 1958 luth jahns and tuttle 1964 the increased size of the quartz field in the f bearing system compared to the hydrous system is believed to be caused by progressive removal of al from the tetrahedral network of the melt by complexing with f the residual network in the melt is thus enriched in si and this stabilizes precipitation of quartz rather than feldspar for certain bulk compositions the common presence of quench cryolite na3alf6 in certain experiments carried out with 4 wt f supports this interpretation and indicates that some al in the melt may be present in six fold coordination with f the effect of h2o in the absence of f may be similar with al being progressively removed from four fold coordination as more h2o is dissolved in the melt although a proportion of al in hydrous melts may occur in six fold coordination dry melts predominantly contain al in four fold coordination this major difference in al complexing may be one of the main causes for differences in the high pressure phase relations of wet and dry albearing silicate systems

radiometric normalization of multitemporal high resolution satellite images with quality control for land cover change detection the radiometric normalization of multitemporal satellite optical images of the same terrain is often necessary for land cover change detection e g relative differences in previous studies ground reference data or pseudo invariant features pifs were used in the radiometric rectification of multitemporal images ground reference data are costly and difficult to acquire for most satellite remotely sensed images and the selection of pifs is generally subjective in addition previous research has been focused on radiometric normalization of two images acquired on different dates the problem of conservation of radiometric resolution in the case of radiometric normalization between more than two images has not been addressed this article reports on a new procedure for radiometric normalization between multitemporal images of the same area the selection of pifs is done statistically with quality control principal component analysis pca is used to find linear relationships between multitemporal images of the same area the satellite images are normalized radiometrically to a common scale tied to the reference radiometric levels the procedure ensures the conservation of radiometric resolution for the multitemporal images involved the new procedure is applied to three landsat 5 thematic mapper tm images from three different years august 1986 1987 and 1991 and of the same area quality control measures show that the error in radiometric consistency between the multitemporal images is reduced effectively the normalized difference vegetation index ndvi is calculated using the radiometrically normalized multitemporal imagery and assessed in the context of land cover change analysis

topographic normalization of landsat tm images of forest based on subpixel sun canopy sensor geometry abstract because trees are geotropic perpendicular to the geoid topography has no control over the sun crown geometry what topography does influence is the relative positioning of trees and thus the amount of shadowing cast by them within the canopy as satellite sensors in general measure the collective radiance of many trees inside their instantaneous field of view the overall canopy brightness at the pixel scale is strongly controlled by canopy shadowing and hence by the topography the removal of or compensation for topographic effects on forest images should be based on the normalization of mutual shadowing at the subpixel scale rather than on the normalization of sun terrain sensor geometry at the pixel scale the sun canopy sensor scs topographic correction model was developed to characterize and hence correct the topographic effects on forest images testing with simulated image data showed the scs model to be accurate root mean squared residual error

combination of digital elevation models with spot 1 hrv multispectral imagery for reflectance factor mapping abstract digital numbers in spot 1 hrv multispectral imagery were transformed to reflectance factor values this approach is based on a simplified scene radiance equation that is developed in this paper the values of some parameters needed in the equation such as path radiance total normal optical thickness and diffuse spectral irradiance were estimated by using multiple linear regression in a small test site of homogeneous ground cover located within the study area the calculated values of reflectance factors were presented by dimensionless digital numbers ranging from 0 to 255 which corresponds respectively to the values of reflectance factors from 0 to 1 the feasibility of this approach has been tested against the spot 1 hrv multispectral imagery above a canopy of picaussel forest of the quillan region in the eastern pyrenean mountain in france

influence of the geostrophic wind direction on the atmospheric boundary layer flow proper simulation and modelling of geophysical flows is crucial to the study of numerical weather prediction wind energy and many other applications when simulating the atmospheric boundary layer coriolis forces act as a result of earth s rotation the horizontal component of earth s rotation which is often neglected influences the balance of vertical momentum the horizontal component results in systematic differences in the structure and statistics of stratified atmospheric boundary layers as a function of the direction of the geostrophic velocity these differences are particularly relevant to atmospheric flows which include inhomogeneous roughness elements such as drag disks or wind turbines since the presence of these drag elements alters the balance between turbulent stresses and the coriolis contributions in reynolds stress budgets even at latitudes as high as 45 circ changing the geostrophic wind velocity vector direction alone changes the magnitude of shear stress and therefore vertical transport of kinetic energy in the conventionally neutral atmospheric boundary layer up to 15 as such the boundary layer height shear and veer profiles surface friction velocity and other key features are affected by the direction of the geostrophic wind the influence of the horizontal component of earth s rotation in stable nocturnal boundary layers depends on the strength of the stratification as there is a strong influence in the present study and a weak influence in the gewex atmospheric boundary layer study gabls case a model of the effect of the horizontal component on the boundary layer shear stress is also proposed and verified with the present simulations while not studied here the present observations are also relevant to the oceanic ekman boundary layer

ekman drift in homogeneous water measurements made with satellite tracked buoys drogued in different layers between the sea surface and 30 m depth under homogeneous winter conditions in the north sea allow analysis of the ekman currents under a large variety of wind conditions the experiment lasted from november 20 1991 until february 29 1992 the first 4 weeks of this period during which the buoys stayed close together are used to determine the ekman stresses the total current field is a superposition of barotropic currents due to sea level variations and ekman currents the classical ekman theory is not able to describe properly the observed deflection of the currents to the right of the wind direction and their decay with depth this deflection is 10 near the sea surface and increases to approximately 50 in 25 m depth the relation between wind stress and the stress field in the interior of the water is given by a tensor which describes the rotation and the variation of the stress with increasing depth the concept of eddy viscosity is applicable if a viscosity tensor is used to relate stress and vertical shear the viscosity tensor is a function of the vertical coordinate only and is independent from the wind stress it shows maximum values in 15 to 20 m depth and may be due to langmuir circulation cells further studies are needed to determine the physics of this tensor its magnitude in the interior of the mixed layer exceeds 1000 cgs units consequently ekman currents are weak and may not be the dominant currents within the mixed layer

direct observations of the ekman balance at 10 n in the pacific abstract the wind driven transport and velocity structure are estimated from direct current measurements and geostrophic shears along a transpacific section at 10 n the total velocity field is dominated by the north equatorial current and its eddies while the shear features near inertial oscillations and a wind driven current spiral the section averaged cross track ageostrophic shear can be approximated as a slab layer 30 40 m thick with a velocity of 0 05 m s 1 overlying a sheared layer in which the velocity goes to zero below 80 m the resulting zonally integrated ageostrophic mass transport is 62 10 109 kg s 1 northward similar to the estimate of 52 10 109 kg s 1 predicted by the ekman balance using winds measured from the ship climatological winds yield similar transport the zonally averaged velocity relative to the top of the thermocline forms a clockwise spiral decaying with depth as has been found at higher latitudes this mean wind driven spiral results from the diurnal cycling o

observations of the velocity response to wind forcing in the upper ocean the response of the horizontal velocity field to forcing by the local wind was observed in the upper 150 m of the ocean by profiling with vector measuring current meters from the research platform flip as it drifted off the coast of california in january 1977 in the mixed layer approximately 50 m deep motion at frequencies lower than 0 1 cph was coherent with the wind stress rotary cross spectral analysis showed that the shear in the surface layer was related to the local wind stress and that the structure of the response at low frequencies was similar to but did not agree completely with the predictions of simple linear eddy viscosity models

experimental constraints on the mobility of rhenium in silicate liquids abstract the volatization of rhenium re from melts of natural basalt dacite and a synthetic composition in the cao mgo al2o3 sio2 system has been investigated at 0 1 mpa and 1250 1350 c over a range of fo2 conditions from log fo2 10 to 0 68 experiments were conducted using open top pt crucibles doped with re and yb analysis of quenched glasses by laser ablation inductively coupled plasma mass spectrometry la icp ms normal to the melt gas interface showed concentration profiles for re to which a semi infinite one dimensional diffusion model could be applied to extract diffusion coefficients d the results show re diffusivity in basalt at 1300 c in air is log dre 7 2 0 3 cm2 s and increases to log dre 6 6 0 3 cm2 s when trace amounts of cl were added to the starting material at fo2 conditions below the nickel nickel oxide nno buffer re diffusivity decreases to log d re reducing 7 6 0 2 cm 2 s and to log d re dacite 8 4 0 2 cm 2 s in dacitic melt in the cmas composition log d re cmas 7 5 0 1 the diffusivity of re is comparable to ar and co2 in basalt at 500 mpa favoring its release as a volatile our results support the contention that subaerial degassing is the cause of lower re concentrations in arc type and ocean island basalts compared to mid ocean ridge basalts

evaluation of topographic effects in remotely sensed data abstract remotely sensed data are generally analyzed assuming flat terrain as the spectral signature of the ground depends upon the orientation of the surface slope the topography has to be considered for efficient radiometric corrections in mountainous regions in this paper we present a modelization of the atmospheric downward radiance at the ground level which gives us the relative contributions of the direct solar beam and of the diffused radiation for different atmospheric turbidities and different solar incidence angles lastly we estimate the influence of the topography on these contributions to show up which effects can be neglected

wind energy input to the ekman layer wind stress energy input through the surface ageostrophic currents is studied the surface ageostrophic velocity is calculated using the classical formula of the ekman spiral with the ekman depth determined from an empirical formula the total amount of energy input over the global oceans for subinertial frequency is estimated as 2 4 tw averaged over a period from 1997 to 2002 or 2 3 tw averaged over a period from 1948 to 2002 based on daily wind stress data from ncep ncar thus in addition to the energy input to the near inertial waves of 0 5 0 7 tw reported by alford and by watanabe and hibiya the total energy input to the ekman layer is estimated as 3 tw this input is concentrated primarily over the southern ocean and the storm track in both the north pacific and north atlantic oceans

turbulence intensity measurements in a wind driven mixed layer neutrally buoyant high drag floats were used to measure vertical velocity in the upper ocean mixed layer during a period of rapid mixed layer deepening resulting from a storm salinity and temperature profiles air sea fluxes and surface wave spectra were also measured the location georgia strait british columbia is coastal with strong horizontal variability and may not be representative of the open ocean the floats moved freely within the deepening mixed layer the envelope of their motion corresponded closely to the extent of the mixed layer the maximum vertical velocity was 0 12 m s21 the rms vertical velocity was about 0 02 m s21 2 the mean square vertical velocity excluding surface waves was 1 5 3 0 clearly higher than the upper bound 2 u of found in solid wall turbulent boundary layers the authors speculate that these anomalously high vertical 2 u velocities were due to langmuir circulations generated by surface waves these cannot occur in solid wall boundary layers

wind driven motions in the northeast pacific as measured by lagrangian drifters abstract analysis is presented of the time dependent motion of 47 surface drifters in the northeast pacific during fall 1987 and 16 drifters in fall and winter 1989 90 the drifters were designed at 15 m depth and were designed to have wind produced slips less than 2 cm s 1 for wind speeds up to 20 m s 1 the coherence of velocity and local wind is presented for motions with periods between 1 day and 40 days for periods between 5 and 20 days drogue motion at 15 m depth is found to be highly coherent with local wind with an average phase of 70 to the right of the rotating wind vector these results differ from analyses of fgge type drifters as reported by mcnally et al and niiler in the same area a model of wind produced slip as a function of drifter design is used to provide a possible explanation of the differences a linear regression which accounts for 20 40 of the current variance gives water motion al 0 5 of wind speed and 68 to the right of the wind vector assuming an ekman type balance

ion microprobe studies of water in silicate melts concentration dependent water diffusion in obsidian abstract the temperature dependence of water diffusivity in rhyolite melts over the range 650 950 c and pt h2o 700 bars is evaluated from water concentration distance profiles measured in glass with an ion microprobe diffusivities are exponentially dependent on concentration over this temperature range and vary from about 10 8 cm2 s at 650 c to about 10 7 cm2 s at 950 c at 2 wt water water solubility also varies with temperature at a rate of 0 14 wt per 100 c increase the avtivation energy ea appears to be constant at 19 1kal mole for 1 2 and 3 wt h2o comparison of these data with results for cation diffusion indicates that this value is a minimum ea for diffusion of any species in a rhyolite melt compensation plots of log10d0 the frequency factor versus ea indicate that hydrous rhyolite melts follow the same trend as anhydrous basalts d0 increases for h2o and ca2 1 as ea decreases this suggests that these molecules may diffuse by different mechanisms than do monovalent cations and that hydration of the melt affects diffusion of ca2 and h2o differently than it does monovalent cation diffusion the results imply that dramatic increases in cation diffusivities by hydration 1 may occur with additions of less than 1 wt h2o

improving fmask cloud and cloud shadow detection in mountainous area for landsats 4 8 images abstract we developed a new algorithm called mfmask mountainous fmask for automated cloud and cloud shadow detection for landsats 4 8 images acquired in mountainous areas the mfmask algorithm built upon the success of the fmask algorithm zhu and woodcock 2012 zhu et al 2015 is designed for cloud and cloud shadow detection in mountainous areas where the fmask algorithm is not performing well the inputs of the mfmask algorithm include landsat top of atmosphere toa reflectance brightness temperature bt and digital elevation models dems compared to fmask mfmask can separate water and land pixels better in mountainous areas with the aid of dems moreover mfmask produces better cloud detection results than fmask in mountainous areas after bt is linearly normalized by dems to provide more accurate cloud shadow detection in mountainous areas mfmask uses a double projection approach to better predict cloud shadow shape on slope side additionally mfmask applies a topographic correction to remove terrain shadows and estimates cloud base height with neighboring clouds both will reduce the possibility of cloud and cloud shadow mismatch and increase cloud shadow detection accuracy for places with large topographic gradient to test the performance of the proposed mfmask algorithm a total of 67 landsat images acquired in mountainous areas from different parts of the world were selected for assessing the accuracy of cloud detection in which 15 of them were used for assessing the accuracy of cloud shadow detection compared with fmask mfmask can provide substantial improvements in cloud and cloud shadow detection accuracies for places with large topographic gradient and also work well for relatively flat terrain

modeling discrete forest anisotropic reflectance over a sloped surface with an extended goms and sail model topographic effects on canopy reflectance play a pivotal role in the retrieval of surface biophysical variables over rugged terrain in this paper we proposed a new canopy anisotropic reflectance model for discrete forests geometric optical and mutual shadowing and scattering from arbitrarily inclined leaves model coupled with topography gosailt which considers the effects of slope aspect geotropic nature of tree growth multiple scattering and diffuse skylight gosailt simulated areal proportions of four scene components i e sunlit crown shaded crown sunlit background and shaded background were evaluated using the geometric optical model for sloping terrains gost model the canopy reflectances simulated by gosailt were validated against two reflectance data sets discrete anisotropic radiative transfer dart simulations and wide angle infrared dual model line area array scanner widas observations compared with a horizontal surface the forest canopy reflectance over a steep slope 60 is significantly distorted with absolute relative bias values of 0 048 79 60 and 0 056 12 02 for the red and near infrared nir bands respectively the gosailt simulated component areal proportions show close agreements with gost moreover gosailt simulations have high overall accuracy red band coefficient of determination r 2 0 96 root mean square error rmse 0 003 and mean absolute percentage error mape 3 91 and nir band r 2 0 78 rmse 0 019 mape 3 94 when compared with the dart simulations these extensive validations indicate good performances of gosailt in canopy reflectance simulations over sloped surfaces

halogens in volcanic systems the transport degassing and atmospheric release of halogens from active volcanism on earth have been the focus of increasing interest over the last few decades and have recently been the subject of the 1st workshop on halogens in volcanic systems and their environmental impacts that was held in december of 2007 at yosemite lodge in yosemite national park california as an introduction to this chemical geology special issue collecting contributions from many of the participants at the workshop we review here recent advances in this field including experimental and theoretical investigations of halogen behaviour in volcanic and related magmatic systems we discuss previous research on several aspects of halogen geochemistry including halogen abundances in the mantle and magmas on earth the effects of halogens on phase equilibria and melt viscosities their partitioning between melt and fluid phase s upon decompression cooling and crystallisation of magmas in the earth s crust and their final atmospheric release as volcanic gases the role of halogens in the genesis of hydrothermal systems and in the transport of ore forming metals is also reviewed and we discuss our current understanding of atmospheric processing of volcanic halogens in both the troposphere and stratosphere and their consequent impacts in spite of these recent advancements our current understanding of halogen geochemistry at active volcanoes is still far too fragmentary and the key questions that require answers from future research are summarised in our conclusions

on the response of the ocean to a moving storm parameters and scales abstract this paper has two purposes one is to present a new and efficient multilevel numerical model for calculating the response of the ocean to a moving storm the second is to show how on a time scale of a few inertial periods following the arrival of the storm the maximum horizontal and vertical velocities found in the wake can be calculated using a linear ekman model and a knowledge of that part of the change in the depth of the wind mixed layer due to entrainment this is demonstrated over a range of experiments with the multilevel numerical model these integrate the full nonlinear equations of motion with realistic ocean stratification and involve substantial entrainment of water into the wind mixed layer it is also shown that on this time scale the horizontal currents are confined near the surface but that the vertical velocity field extends throughout the depth of the ocean it is shown in appendix b that the wind forcing need only be large or fast for the forced response not to feel t

the three dimensional steady circulation in a homogenous ocean induced by a stationary hurricane based on the classical ekman layer theory a simple analytical solution of the steady flow induced by a stationary hurricane in a homogenous ocean is discussed the model consists of flow converging in an inward spiral in the deeper layer and diverging in the upper layer the simple analytical model indicates that both the upwelling flux and the horizontal transport increase linearly with increasing radius of maximum winds furthermore they both have a parabolic relationship with the maximum wind speed the coriolis parameter also affects the upwelling flux the response to a hurricane is stronger at low latitudes than that at middle latitudes numerical solutions based on a regional version of an ocean general circulation model are similar to the primary results obtained through the analytical solution thus the simplifications made in formulating the analytical solution are reasonable although the analytical solution in this paper is sought for a rather idealized ocean it can help to make results from the more complicated numerical model understandable these conceptual models provide a theoretical limit structure of the oceanic response to a moving hurricane over a stratified ocean

scs c a modified sun canopy sensor topographic correction in forested terrain topographic correction based on sun canopy sensor scs geometry is more appropriate than terrain based corrections in forested areas since scs preserves the geotropic nature of trees vertical growth regardless of terrain view and illumination angles however in some terrain orientations scs experiences an overcorrection problem similar to other simple photometric functions to address this problem we propose a new scs c correction that accounts for diffuse atmospheric irradiance based on the c correction a rigorous comprehensive and flexible method for independent validation based on canopy geometric optical reflectance models is also introduced as an improvement over previous validation approaches and forms a secondary contribution of this paper results for a full range of slopes aspects and crown closures showed scs c provided improved corrections compared to the scs and four other photometric approaches cosine c minnaert statistical empirical for a rocky mountain forest setting in western canada it was concluded that scs c should be considered for topographic correction of remote sensing imagery in forested terrain

dart radiative transfer modelling for sloping landscapes abstract topography is one of the key factors that impact remotely sensed data and their interpretation indeed combined with the viewing geometry and neighbour effects it strongly affects the direct diffuse and multi scattered scene irradiance which in turn impacts the radiative budget and remote sensing signals of the landscapes the increased availability of digital elevation models dem and the advancement of 3d radiative transfer rt models allow us to better address these topographic effects dart discrete anisotropic radiative transfer is one of the most accurate and comprehensive 3d rt models that simulate remote sensing observations of natural and urban landscapes with topography and atmosphere it simulates environmental effects i e impact of adjacent landscape on the observed landscape using a so called infinite slope mode that infinitely duplicates the observed landscape while ensuring the continuity of slope and altitude at the dem edges up to dart version 5 7 4 this mode was slightly inaccurate and computer intensive depending on the topography this paper presents an innovative modelling strategy that greatly improves it in terms of accuracy image quality and computer efficiency for that a fictive auxiliary oblique plane adapted to the landscape topography is introduced for managing the scene illumination the earth atmosphere coupling and the storage of the radiation that exits the scene before being projected onto the sensor plane improvements and validations are illustrated both visually and quantitatively by dart images radiometric products and radiative budget for example the observed reflectance of a lambertian slope is equal to the expected analytical value in addition the solar plane reflectance of a forest on a mountain slope experimental scene has an average error of about 0 01 relative to the reflectance of the same forest stand in the reference scene i e nine duplications of the experimental scene this new modelling is already integrated in the official dart version https dart omp eu

deep ocean response to hurricanes as revealed by an ocean model with free surface part i axisymmetric case abstract an axisymmetric hydrostatic ocean model containing a rigid bottom and a free surface is constructed to study the barotropic and baroclinic response in the upper and deep ocean to a wind stress corresponding to a stationary tropical cyclone the numerical model covers a domain of 800 km and 1475 m in r and z directions respectively with a uniform radial resolution of 20 km and a stretched vertical resolution from 5 to 54 m the vertical mixing is parameterized based on a local richardson number and a mixing length the model ocean is spun up with the wind stress of hurricane eloise a strong tangential circulation develops that extends to the ocean floor with a maximum speed of 1 2 m s 1 at the surface the circulation on the r z plane which also extends to the ocean floor oscillates with time with a maximum upwelling of 0 1 cm s 1 at the center surface height has a maximum depression of 57 cm the deep overturning causes density changes deep in the ocean a maximum temperature decrease of

geometric optical bidirectional reflectance modeling of the discrete crown vegetation canopy effect of crown shape and mutual shadowing in the case where a vegetation cover can be regarded as a collection of individual discrete plant crowns the geometric optical effects of the shadows that the crowns cast on the background and on one another strongly condition the brightness of the vegetation cover as seen from a given viewpoint in the hemisphere an asymmetric hotspot in which the shape of the hotspot is related to the shape of the plant crowns in the scene is created at large zenith angles illumination shadows will preferentially shadow the lower portions of adjacent crowns further these shadows will be preferentially obscured since adjacent crowns will also tend to obscure the lower portions of other crowns this effect produces a bowl shaped bidirectional reflectance distribution function brdf in which the scene brightness increases at the function s edges formulas describing the hotspot and mutual shadowing effects are derived and examples that show how the shape of the brdf is dependent on the shape of the crowns their density their brightness relative to the background and the thickness of the layer throughout which the crown centers are distributed are presented

assessment of different topographic corrections in landsat tm data for mapping vegetation types 2003 different methods for topographic correction of landsat thematic mapper images have been assessed in the context of mapping vegetation types the best results were obtained with a variation of the c method which takes into account the overcorrection of low illuminated slopes by the original c method the performance of this method was tested using two criteria the changes in the spectral characteristics of the image and the reduction in standard deviation of each vegetation type after the correction

chemical diffusion of fluorine in melts in the system na2oal2o3sio2 the volatilization of fluorine from three melts in the system na2oal2o3sio2 has been investigated at 1 atm pressure and 1200 1400 c the melts chosen have base compositions corresponding to albite jadeite and a peraluminous melt with 75 mole sio2 melt spheres were suspended from platinum loops in a vertical tube furnace in a flow of oxygen gas then quenched sectioned and analysed by electron microprobe the microprobe scans indicate that transport of fluorine to the melt vapor interface is by binary concentration independent interdiffusion of fluorine and oxygen fo interdiffusivity increases in the order albite peraluminous jadeite there is no simple reciprocal relationship between fo interdiffusivity and melt viscosity comparison with data on high pressure interdiffusivity of fluorine and oxygen in jadeite melt indicates that fo interdiffusivity increases with pressure from 0 001 to 10 kbar while the activation energy remains unchanged fluorine chemical diffusivity in albite melt is substantially lower than h2o chemical diffusivity in obsidian melts suggesting that different diffusive mechanisms are responsible for the transport of f and h2o in igneous melts fluorine diffuses in albite melt via an anionic exchange with oxygen whereas water probably diffuses in obsidian melt via an alkali exchange mechanism

a simple analytical model of the diurnal ekman layer abstractthe effects of time varying turbulent viscosity on horizontal currents in the ocean surface boundary layer are considered using a simple theoretical model that can be solved analytically this model reproduces major aspects of the near surface ocean diurnal cycle in velocity and shear while retaining direct parallels to the steady state ekman solution the parameter dependence of the solution is explored and quantitative measures of the low frequency rectification of velocity and shear are derived results demonstrate that time variability in eddy viscosity leads to significant changes to the time averaged velocity and shear fields with important implications for the interpretation of observations and modeling of the near surface ocean these findings mirror those of more complete numerical modeling studies suggesting that some of the rectification mechanisms active in those studies may be independent of the details of the boundary layer turbulence

stratified ekman layers under fair weather conditions the time averaged wind driven current forms a spiral in which the current vector decays and turns clockwise with increasing depth these spirals resemble classical ekman spirals they differ in that their rotation depth scale exceeds the e folding depth of the speed by a factor of 2 to 4 and they are compressed in the downwind direction a related property is that the time averaged stress is evidently not parallel to the time averaged vertical shear we develop the hypothesis that the flat spiral structure may be a consequence of the temporal variability of stratification within the upper 10 20 m of the water column this variability is associated primarily with the diurnal cycle and can be treated by a time dependent diffusion model or a mixed layer model the latter can be simplified to yield a closed solution that gives an explicit account of stratified spirals and reasonable hindcasts of midlatitude cases at middle and higher latitudes the wind driven transport is found to be trapped mainly within the upper part of the ekman layer the diurnal warm layer at tropical latitudes the effects of diurnal cycling are in some ways less important and ekman layer currents are likely to be significant to much greater depths in that event the lower part of the ekman layer is likely to be affected by stratification variability that may be nonlocal

roughness reflectance relationship of bare desert terrain an empirical study a study of the bidirectional reflectance distribution function brdf in relation to surface roughness properties was conducted in arid land near fowlers gap research station new south wales australia such empirical study is necessary for investigating the possibility of determining terrain geomorphological parameters from bidirectional reflectance data a new apparatus was developed to take accurate hemispherical directions radiance measurements hdrm a digitizer for three dimensional in situ roughness measurements was also developed more than 70 hemispherical data sets were collected for various illumination conditions and surface types of desert stony pavements and rocky terrain slopes in general it was found that most of the surfaces exhibited an anisotropic reflection combining a major component of backscattering the brdf of different surface types in relation to their roughness properties as determined by the field digitizer were then examined results showed that sites that are considered to differ significantly from a geomorphological point of view would not necessarily form a different brdf

the topographic normalization of hyperspectral data implications for the selection of spectral end members and lithologic mapping abstract compact airborne spectrographic imager casi hyperspectral data is used to investigate the effects of topography on the selection of spectral end members and to assess whether the topographic correction improves the discrimination of rock units for lithologic mapping a publicly available digital elevation model dem at a scale of 1 50 000 is used to model the radiance variation of the scene as a function of topography assuming a lambertian surface skylight is estimated and removed from the airborne data using a dark object correction the casi data is corrected on a pixel by pixel basis to normalize the scene to a uniform solar illumination and viewing geometry the results show that topography has the effect of expanding end member clusters at times resulting in the overlap of clusters and that the correction process can effectively reduce the variation in detected radiance due to changes in local illumination when topographic effects are embedded in the hyperspectral data methods typically used for the selection of end members such as the convex hull method can miss end members or result in the selection of nonrepresentative pixels as end members thus end members selected by some conventional methods are very likely incomplete or nonrepresentative if the topographic effect is embedded in the data as shown in this study the topographic correction can reveal hidden end members and achieve a better representation of end members via the statistical center of isolated clusters

dynamical roles of mixed layer in regulating the meridional mass heat fluxes 1 the mixed layer is an important component of the oceanic circulation system recent progress in energetics of the oceanic circulation suggests that the amount of external mechanical energy available for mixing is directly linked to the strength of the meridional overturning circulation using an analytical two dimensional model and a three dimensional numerical model it is shown that the meridional distribution of mixed layer depth plays an important role in regulating the meridional overturning circulation and poleward heat flux in fact if the mixed layer at low and middle latitudes is deeper because of increase in mechanical energy input to the turbulence in the upper ocean the meridional overturning circulation and poleward heat flux are enhanced in a steady circulation system and at the same time it may take less mechanical energy to support the subsurface diapycnal mixing

identification of eroded areas using remote sensing in a badlands landscape on marls in the central spanish pyrenees abstract identification of erosion areas on a regional scale can be very useful for environmental planning and can help reduce land degradation and sediment yield to streams and reservoirs remote sensing techniques were used to determine erosion and erosion risk areas in a badlands landscape in the esera river catchment spanish pyrenees the size sparse vegetation cover and high erosion level in the badlands enabled good visual and digital discrimination relative to other land covers and surfaces the maximum likelihood algorithm was used for obtaining a spectral distance map to the bare soil signature characteristic of badlands on marls the roc receiver operating characteristic curve analysis was applied to this map for obtaining an optimum classification of the badlands two alternative classification thresholds were set to determine erosion areas and areas at risk of erosion two classification performance statistics the model s sensitivity and specificity were calculated as a means of expressing the uncertainty omission and commission errors associated to both maps most erosion risk areas coincided with low vegetation cover surrounding the badland areas

geometric and radiometric correction of tm data of mountainous forested areas methodologies to improve landsat tm thematic mapper forest classifications of alpine regions through the removal of some radiometric and geometric distortions are tested besides correcting for sensor and system induced errors geometric errors are corrected using a digital elevation model then scene related effects such as differences in illumination as well as the height dependent atmospheric influence and adjacency effects are corrected the improvement of the accuracy of a forest classification is demonstrated by comparison with ground truth data

halogen diffusion in magmatic systems our current state of knowledge diffusion of halogens has the potential to influence petrogenetic processes in magma chambers and conduit degassing processes this contribution reviews our current state of knowledge concerning halogen diffusion and the influence of halogens on the diffusion of major elements in silicate melts the addition of halogens to silicate melts at common natural concentration levels will have little effect on the diffusion of major elements however the differences between the diffusivity of water the diffusivities of halogens and the diffusivity of sulfur are significant enough that during melt inclusion entrapment or during rapid bubble or crystal growth diffusive fractionation between water and the halogens and between halogens and sulfur are expected to occur and can influence the compositions of melt inclusions crystals and volcanic gases

detecting and characterizing ekman currents in the southern ocean abstractthis study presents a unique array of velocity profiles from electromagnetic autonomous profiling explorer em apex profiling floats in the antarctic circumpolar current acc north of kerguelen the authors use these profiles to examine the nature of ekman spirals formed by the action of the wind on the ocean s surface in light of ekman s classical linear theory and more recent enhancements vertical decay scales of the ekman spirals were estimated independently from current amplitude and rotation assuming a vertically uniform geostrophic current decay scales from the ekman current heading were twice as large as those from the current speed decay indicating a compressed spiral consistent with prior observations and violating the classical theory however if geostrophic shear is accurately removed the observed ekman spiral is as predicted by classical theory and decay scales estimated from amplitude decay and rotation converge toward a common value no statistically robust relationship is

on the slippage of deep drogued drifters deep drogued drifters are in use to measure the near surface geostrophic currents an attempt is made to study the slippage of these drifters due to wind and ekman currents the results are based on a data set from the unstratified north sea obtained in winter 1991 1992 where the currents were decomposed into ekman currents and barotropic currents the influence of these ekman currents on the drift performance of drifters drogued below the mixed layer in the barotropic current is determined by using quadratic drag laws in 90 of all cases 1540 data points the combined effect of wind drag and ekman currents on buoy and 100 m tether produces a slippage of less than 2 cm s drifters drogued within the mixed layer show less slippage due to the reduced drag on the tether but they are primarily designed to measure the actual near surface currents which are strongly dependent on the wind conditions it is concluded that deep drogued drifters are a reliable device to study weakly baroclinic geostrophic currents

directional reflectance factor distributions for two forest canopies abstract directional reflectance factor distributions were measured over one pine pinus silvestris and one spruce stand picea abies with sun elevations in the range 30 50 measurements were made from a helicopter at 200 m altitude using a handheld radiometer with wavelength bands centered at 0 68 0 85 and 1 6 m assuming bilateral symmetry only one half of the hemisphere was measured with 45 azimuthal and 15 zenithal increments up to 60 off nadir both stands showed a highly anisotropic reflectance especially in the red band and less pronounced differences in the 0 85 m band the effect in the 1 6 m band was intermediate between the two other bands in the red band the reflectance of the spruce stand varied with a factor of 7 within the measured cone but markedly less for the pine stand the data were also analyzed along a transect corresponding to the spot off nadir geometry as typical for summer registrations in scandinavia it was found that at 27 off nadir in a wnw direction the reflectance increased by a factor of up to 1 6 as compared to nadir measurement systematic reflectance variation within the spot field of view was up to 10 for the spruce canopy in the maximum westerly off nadir direction since spruce forest is among the most anisotropically reflecting vegetation types due to its geometrical structure and dense canopy the stated values probably represent maximum values for the angular dependence that will be met in applications

gost a geometric optical model for sloping terrains gost is a geometric optical go model for sloping terrains developed in this study based on the four scale go model which simulates the bidirectional reflectance distribution function brdf of forest canopies on flat surfaces the four scale go model considers four scales of canopy architecture tree groups tree crowns branches and shoots in order to make this model suitable for sloping terrains the mathematical description for the projection of tree crowns on the ground has been modified to consider the fact that trees grow vertically rather than perpendicularly to sloping grounds the simulated canopy gap fraction and the area ratios of the four scene components sunlit foliage sunlit background shaded foliage and shaded background by gost compare well with those simulated by 3 d virtual canopy computer modeling techniques for a hypothetical forest gost simulations show that the differences in area ratios of the four scene components between flat and sloping terrains can reach up to 50 60 in the principal plane and about 30 in the perpendicular plane two case studies are conducted to compare modeled canopy reflectance with observations one comparison is made against landsat 5 thematic mapper tm reflectance demonstrating the ability of gost to model canopy reflectance variations with slope and aspect of the terrain another comparison is made against modis surface reflectance showing that gost with topographic consideration outperforms that without topographic consideration these comparisons confirm the ability of gost to model canopy reflectance on sloping terrains over a large range of view angles

volatile heavy metal mobility in silicate liquids implications for volcanic degassing and eruption prediction abstract the volatilization of cd re tl pb sb and te from melts in the system cao mgo al 2 o 3 sio 2 cmas and na 2 o mgo al 2 o 3 sio 2 nmas has been investigated at 0 1 mpa and 1200 1350 c experiments were conducted in air using metal doped melts in pt crucibles analysis of quenched glasses by laser ablation inductively coupled plasma mass spectrometry la icp ms normal to the melt gas interface produced concentration profiles for cd re tl pb sb and te to which a semi infinite one dimensional diffusion model could be applied to extract diffusion coefficients d the melt was also doped with cu zn in mo sn and w but concentration profiles for these metals did not develop in the cmas composition at 1300 c the fastest diffusing element was cd having a log d cd 6 5 0 2 the slowest element was re with log d re 7 5 0 3 diffusivities of sb te pb and tl have intermediate values where log d sb 7 1 0 1 log d te 7 2 0 3 log d pb 7 1 0 2 log d tl 7 0 0 2 cm 2 s in the nmas composition log d re 6 5 0 2 log d sb 6 0 0 2 log d pb 6 1 0 1 log d tl 5 8 0 2 cm 2 s values for cd and te were not determined differences in diffusivity of volatile heavy metal ions to a melt gas interface lead to significant fractionation between these metals in magmas during degassing given the observed differences in cd and re diffusivities in the cmas composition we predict an increase in the normalized cd re ratio in the gas phase with increasing bubble growth rate monitoring of the cd re ratios in aerosols from degassing volcanoes may provide a tool for predicting volcanic eruption

spectral correction for the effect of crown shape at the single tree level an approach using a lidar derived digital surface model for broad leaved canopy the spectral response of a single tree on remotely sensed images may be affected by the crown shape yielding brighter sun facing sides and darker sides facing away from the sun to correct this crown shape effect we assumed that the roughness of the canopy surface within a single crown resembles the topography of the land surface in the case of a closed upper canopy layer i e canopy surface of broad leaved deciduous trees previous topographic normalizations have proved to be useful in correcting the effect of rugged terrain at a large landscape scale however are they also useful in correcting the rough canopy surface at the scale of a single crown we applied conventional topographic corrections cosine minnaert and c to a canopy surface model csm of 66 trees which was derived from airborne small footprint lidar data the 12 band spectral data of each tree were acquired from the aircraft with 0 5 m spatial resolution and analyzed to validate the corrections among the tested methods the c correction was the most successful in applying to the csm whereas the minnaert and cosine corrections yielded errors in the reflectance of some steep canopy surfaces we assessed the spectral feature of each tree in terms of tree vigor by using the vegetation index employing the red edge 700 nm and green 541 nm bands following the correction the overall accuracy was improved from 75 5 to 84 5 thus we suggest that the effect of crown shape be carefully considered and corrected in single crown level analyses of remotely sensed spectra

an investigation of terrain effects on the inversion of a forest reflectance model abstract the effects of terrain on conifer stand reflectance were estimated using sensitivity analysis of the li and strahler bidirectional reflectance brdf model and model inversions with both simulated and real landsat thematic mapper tm reflectance data emphasis was placed on surface characteristics and atmospheric correction was assumed the results of sensitivity analysis indicated that strong interactive effects between nadir coverage of crowns stand structure and the slope and aspect of the stand occur in the reflectance data this was supported by the results of model inversions using simulated reflectance data of sloping stands it was found that by neglecting slope in the inversion process significant errors occurred in the retrieved values of forest coverage finally inversion was tested using real tm reflectance data from a mountainous site in british columbia with a digital terrain model dtm forest attribute data and the 6s atmospheric code the results indicate that the effects of sloping terrain would preclude the retrieval of forest coverage unless terrain effects were specifically included in the inversion process

drift and mixing under the ocean surface revisited stratified conditions and model data comparisons 1 a one dimensional model of the ocean near surface currents is presented it includes the enhanced near surface mixing due to the waves the wave induced stokes drift the stokes coriolis sc effect and the stratification near surface current shears from this model are compared with the shears of the quasi eulerian currents measured using a wave following platform during the shelf mixed layer experiment smile it is shown that the downwind current shears observed during smile are well modeled however the observed crosswind shears are in poor agreement with the model the stokes coriolis sc term could qualitatively explain this misfit but it is one order of magnitude too weak the ekman stokes spiral of the model is compared with the spiral observed during the long time series of measurements long term upper ocean study 3 the effects of stratification are taken into account the mean velocity profiles of the model closely agree with observations however there is no evidence of the sc effect on the shape of the observed current profile the observed profile is found to be a consequence of the current rectification due to the time varying stratification the sc effect calculated from a numerical wave hindcast is weak but should have been observed in fact it is estimated that the wave induced bias in the current measurements is larger than the sc effect finally it is shown that the variation of surface drift with wave age which was estimated to be small in unstratified conditions is important in the presence of shallow mixed layers

spectral signature of alpine snow cover from the landsat thematic mapper mapping of snow and estimation of snow characteristics from satellite remote sensing data require that we distinguish snow from other surface cover and from clouds and compensate for the effects of the atmosphere and rugged terrain the spectral signature of the snowpack is calculated from a radiative transfer model accounting for scattering and absorption by the ice grains water inclusions and particulates in interpreting the spectral reflectance measured from the thematic mapper or from any other satellite we need to account for topographic effects without requiring that satellite data be precisely registered to digital elevation data because the poor quality of most digital elevation data introduces considerable noise into calculations of slope and azimuth for a range of snow types atmospheric profiles and topographic illumination conditions i estimate typical spectral signatures for the landsat thematic mapper tm images of the southern sierra nevada are analyzed to distinguish several classes of snow from other surface covers snow can be reliably distinguished from other surfaces and from clouds at all sun angles encountered in the mid latitudes in tm band 1 or 2 snow is brighter than other natural surfaces and in band 5 clouds are usually much more reflective than snow therefore the intersection of the following criteria maps the snow cover planetary reflectance rp in tm band 1 is greater than about 0 16 rp tm5 is less than about 0 2 the normalized band 2 5 difference rp tm2 rp tm5 rp tm2 rp tm5 is greater than about 0 4 large surface grain sizes can be distinguished from areas where the grain size is finer at the snow surface using tm bands 2 4 and 5 because of saturation in tm band 1 estimation of the degree of contamination by absorbing aerosols is not feasible rp tm2 rp tm5 rp tm2 rp tm5 is

calculating change curves for multitemporal satellite imagery mount st helens 1980 1995 abstract we developed and tested a method for analyzing multitemporal satellite imagery using change curves the method is flexible and allows an analyst to extract specific change parameters from the curves depending on the research question of interest eight landsat tm images of the mount st helens washington blast zone from 1984 to 1995 were geometrically and radiometrically corrected they were then transformed to estimates of green vegetation cover unsupervised clustering was performed on the set of eight transformed images and polynomial curves were fit to the cluster means from these fitted curves parameters of interest were extracted and returned to gis layers including number of years to reach 10 cover the greatest rate of cover increase during the study period and time integrated cover statistical analysis indicated that the curves did a good job of representing the change trajectories of unclustered pixels we demonstrated the use of change curve analysis by analyzing the importance in the revegetation of mount st helens of the different types of disturbance resulting from the volcanic eruption the change curve analysis is useful in a variety of applications where the data are continuous more than two dates of data are available and the underlying question of interest relates to trends in the data

assessing the spatial spectral and temporal consistency of topographically corrected landsat time series composites across the mountainous forests of nepal abstract in mountainous regions slope and aspect result in variations in the illumination condition and the same land cover type can therefore show differences in the reflectance depending on the orientation of the terrain slope towards the sun and the sensor of the satellite different topographic illumination correction methods exist and their performance varies depending on e g sun zenith and land cover type similarly a variety of evaluation criteria exist to assess the performance of the topographic correction methods and each evaluation criteria usually only considers certain aspects of the ability of the topographic correction method in reducing signal to noise in this article we present a novel framework for the evaluation of topographically corrected image composites using cloud computing we evaluated six topographic correction methods bin tan c correction minnaert with slope sun canopy sensor plus c correction statistical empirical and variable empirical coefficient algorithm in forest areas of four landsat footprints in nepal for a time series of image composites from 1988 to 2016 our evaluation shows that the statistical empirical topographic correction method provides the best overall performance but in some years and footprints also other methods can show the best performance we discuss these differences and related reasons in detail and give recommendations on the best use and evaluation of topographic correction methods

observations of seasonal variation in the ekman layer abstract the seasonal variation in the ekman layer is examined using observations from the long term upper ocean study lotus including surface meteorology current and temperature the near surface current is found to be coherent with the wind at low frequencies periods greater than one day using a wind relative averaging method the authors find the observed near surface volume transport to be consistent with ekman transport the mean current profile has a spiral shape that is flat compared to the classic ekman spiral in that it rotates less with depth than does the ekman spiral the mean current e folds over 12 m in the summer and 25 m in the winter with a decay in amplitude that implies eddy viscosities of 60 10 4 and 250 10 4 m2 s 1 respectively diurnal cycling is the dominant mode of variability in the summer and it determines the vertical structure of the spiral in the winter diurnal cycling is almost nonexistent due to greatly reduced solar insolation and stronger winds a persisten

topographic effects on bidirectional and hemispherical reflectances calculated with a geometric optical canopy model the effects of topography on both the bidirectional reflectance distribution function brdf and the hemispherical reflectance surface albedo of a forested scene are investigated with the li strahler geometric optical model the li strahler geometric optical model treats a vegetation canopy as an assemblage of partially illuminated tree crowns of spheroidal shape and through geometric optics and boolean set theory models the proportion of sunlit or shadowed canopy and background as functions of view angle illumination angle and crown geometry the model has been modified to accommodate a sloping surface in its computation of bidirectional and hemispherical reflectance when the brdf of a flat vegetated surface is compared to the brdf of a sloping surface that is similarly vegetated the interaction of the illumination angle and the slope distort the shape of the brdf a hemispherical integration of this distorted brdf provides an albedo for the sloping surface

the definition of remotely sensed reflectance quantities suitable for rugged terrain abstract the anisotropic scattering behavior of land surface is characterized by its bidirectional reflectance distribution function brdf however a physically consistent brdf definition is still lacking for heterogeneous and rugged terrain that accounts for approximately 24 of earth s land surface in this study we revisited current brdf definitions and updated them for rugged terrain with few dependent parameters illumination and viewing geometries terrain shadows effective areas of illumination and observation and anisotropic reflectance properties of subpixel scale slopes furthermore the bidirectional reflectance factor brf hemispherical directional reflectance factor hdrf directional hemispheric reflectance dhr and bi hemispherical reflectance bhr were proposed within the current physical framework of reflectance quantities these reflectance quantities have been adopted by the 3 d discrete anisotropic radiative transfer dart model to provide the simulations of remote sensing images to highlight the importance of a proper usage of such reflectance terms we used dart simulations to present the topographic effects on these reflectance quantities finally the other issues with respect to surface brdf brf such as spatial scale of rugged terrain characterization of anisotropic reflectance of micro scale surfaces derivative reflectance quantities topographic parameters wavelength dependence and reciprocity and future perspective were discussed

wind waves and fronts frictional effects in a generalized ekman model abstractocean currents in the surface boundary layer are sensitive to a variety of parameters not included in classic ekman theory including the vertical structure of eddy viscosity finite boundary layer depth baroclinic pressure gradients and surface waves these parameters can modify the horizontal and vertical flow in the near surface ocean making them of first order significance to a wide range of phenomena of broad practical and scientific import in this work an approximate green s function solution is found for a model of the frictional ocean surface boundary layer termed the generalized ekman or turbulent thermal wind balance the solution admits consideration of general more physically realistic forms of parameters than previously possible offering improved physical insight into the underlying dynamics closed form solutions are given for the wind driven flow in the presence of coriolis stokes shear a result of the surface wave field and thermal wind shear arising from a baroclinic

multitemporal evaluation of topographic normalization methods on deciduous forest tm data five empirical and nonempirical parametric topographic normalization methods the cosine scs minnaert b correction and c correction methods were applied to multitemporal landsat thematic mapper data bands 1 5 and 7 collected in different periods of the growing season april june and july of a mixed deciduous forest area 340 ha in the northern apennines the effectiveness of the models at removing topographic control preserving internal data variability and consistently normalizing radiance for flat pixels from band to band and image to image was evaluated the entirely empirical b correction outperformed the other considered methods without relying on any photometric function

impact of mesoscale eddies on kuroshio intrusion variability northeast of taiwan abundant mesoscale eddies propagate to the east of taiwan and affect the kuroshio current and its onshore intrusion northeast of taiwan but the dynamical process of how eddy activities modulate the kuroshio intrusion is still unclear in this study in situ ocean velocity observations drifter trajectories tide gauge measurements satellite sea surface height data and assimilative hybrid coordinate ocean model hycom reanalysis outputs were used to analyze a cyclonic eddy induced large kuroshio onshore intrusion during late autumn 2008 along with nine anticyclonic eddy events and seven cyclonic eddy events extracted from long term hycom reanalysis outputs the variability of the eddy induced intrusion were quantified the impacts of the cyclonic eddy and the anticyclonic eddy were opposite under the impact of cyclonic anticyclonic eddy the total onshore intrusion between 122 e and 124 e across the 200 m isobaths was decreased increased by 15 7 7 3 while the onshore intrusion west of 122 6 e and the northeastward current on the outer shelf was increased decreased by 30 6 4 7 and 31 10 1 respectively the arrival of cyclonic anticyclonic eddy brought positive negative potential vorticity pv flux and modulated the local ocean vertical stratification which weakened enhanced the cross slope pv gradient and the shelf slope constraint on the upper layer current therefore favored inhibited the kuroshio onshore intrusion this article is protected by copyright all rights reserved

modeling anisotropic reflectance over composite sloping terrain heterogeneous terrain significantly complicates signals received by airborne or satellite sensors it has been demonstrated that both solar direct beam and diffuse skylight illumination conditions are significant factors influencing the anisotropy of reflectance over mountainous areas several models and methods have been developed to account for topographic effects on surface reflectance at the pixel level in remote sensing however subtopographic effects are generally neglected for low spatial resolution pixels due to the complex law of radiative transfer and the limitations of higher spatial resolution digital elevation models which can lead to deviations in reflectance estimation accurately estimating the subtopographic effects on anisotropic reflectance over composite sloping terrain under different illumination conditions presents a challenge for remote sensing models and applications in this paper the diffused equivalent slope model desm was developed which is an anisotropic reflectance simulation model coupled with diffuse skylight over composite sloping terrain the corresponding subtopographic impact factor was also proposed to exhibit how microslope topography affects reflectance over composite sloping terrain under different illumination conditions simulated reflectance data sets simulated by the radiosity method and moderate resolution imaging spectroradiometer reflectance data were used to evaluate the performance of the desm model the results reveal that the desm model can accurately capture the reflectance anisotropy over composite sloping terrain under different illumination conditions and the subtopographic impact factor can account for the effects of microslope topography shadow and illumination conditions

large eddy simulation of the ekman transport in a stratified coastal sea a case study of the persian gulf abstract ekman transport is a key factor in the coastal upwelling regimes in the northern coastal region of the persian gulf in this paper the ocean module of parallelized large eddy simulation model palm was utilized so as to investigate the ekman layer and estimate the water mass transport in the persian gulf for the first time in order to take into account the effect of the topography on the ekman transport three experiments with the same initial and boundary conditions and different topographies were carried out the results indicated that in the vicinity of the shoreline and in shallow waters turbulent kinetic energy tke is 10 times stronger than in the offshore area it was concluded that in the presence of the shoreline the vertical velocity increases and in the onshore area the upwelling speed is 3 4 times larger than in the offshore area it was revealed that the ekman transport reached a steady state at the end of the simulation and reached a constant value of about 250 kg ms

cpbac a quick atmospheric correction method using the topographic information abstract topography is one of the most important factors that can affect the radiative transfer process in remote sensing earth observation by making the ground objects of the same type but in different topographical locations present different radiative characteristics which increases the complexity of spectral radiation information and violates the radiometric consistency among those type identical objects utilizing the topographic information we proposed a coupling parameter based atmospheric correction method or cpbac for short this method firstly establishes the radiative transfer equations using the data of objects with good lambertian properties under various topographical positions and then calculates the coupling parameters of atmosphere and topography and finally accomplishes both the atmospheric and topographic correction simultaneously using those parameters to validate it the landsat 7 multispectral data about one region in cody town of wyoming usa which was acquired in different seasons was used to do a comparison with the commonly used flaash and quac methods the comparison revealed that the cpbac method can effectively achieve atmospheric correction with its result similar to that produced by either flaash or quac and the topography caused spectral radiation difference among the objects of the same type was eliminated by showing an increased spectral consistency and a decreased relevance between radiometric information and topography although the assumptions which the cpbac method is based upon impose restrictions on its widespread use it can achieve the best effect when it is applied to handle the data containing objects of good lambertian properties located in different terrains and the selected pixels for the parameters calculation are various combinations of those with small slope and small sun zenith angle

hurricane generated depth averaged currents and sea surface elevation abstract a theory of the depth averaged currents and sea surface elevation generated by a moving hurricane in a stratified ocean with flat bottom is presented using a scale analysis of the depth integrated momentum and continuity equations it is found that the depth averaged currents are nearly nondivergent and determined entirely by the wind stress curl earth s rotation and ocean stratification have negligible effects the sea surface elevation is decomposed into four physically different parts caused by geostrophic adjustment to the depth averaged currents wind stress divergence inverted barometer offset and baroclinic effects when a hurricane moves with a uniform speed it generates quasi stationary alongtrack elongated depth averaged currents the sea surface elevation remaining after the hurricane passage is a combination of a trough geostrophically adjusted with the depth averaged currents and a sea surface elevation associated with baroclinic effects the barotropic response is analysed fo

vertical structure of the ocean current response to a hurricane abstract during the passage of hurricane norbert in 1984 the hurricane research division of noaa conducted a planetary boundary layer experiment that included the deployment of airborne expendable current profilers axcp a total of 16 axcps provided for the fist time high resolution vertical profiles of currents and temperatures in hurricane wind conditions this study focuses on the vertical structure of the near inertial baroclinic current excited by the passage of this hurricane the transient hurricane induced currents are isolated from the axcp profiles in norbert by subtracting a spatially averaged current near the center of hurricane norbert the wkbj scaled vertical wavenumber spectra are a decade greater than the garrett munk spectra gm75 the fist ten linear baroclinic free modes are calculated from the spatially averaged brunt vaisala frequency to allow a more direct comparison with the axcp observations in the current wind regime the near inertial response for the three dimensional v

building a forward mode three dimensional reflectance model for topographic normalization of high resolution 1 5 m imagery validation phase in a forested environment the aim of the topographic normalization of remotely sensed imagery tnrsi is to reduce reflectance variability caused by steep terrain and subsequently to improve land cover classification recently multiple forward mode fm mfm reflectance models for topographic normalizations of medium resolution 20 30 m satellite imagery have improved the classification of forested covers with respect to more conventional topographic corrections we propose an fm 3 d reflectance fm3dr model based on the discrete anisotropic radiative transfer simulator for the topographic normalization of high resolution 1 5 m imagery the feasibility of this approach was first verified on real ikonos imagery for three forest types within major biomes oak pine and high tropical forest in mexico next we formalized the topographic normalization performance index and variability as relevant criteria to test tnrsi across incident angles in terms of maximum likelihood classification effectiveness the fm3dr model outperformed five previously published topographic corrections cosine minnaert sun canopy sensor scs civco two stage and slope matching corrections and image based statistical strategies civco two stage and slope matching corrections tended to perform better than more analytical strategies cosine minnaert and scs corrections an asset of this approach versus former models is the realistic account of terrain related variation of understory and crown cover within a cover type on top of that once validated across forest types the model is sufficient for the application of a full mfm 3 d reflectance based topographic normalization without additional field measurement

variational estimation of the wind stress drag coefficient and the oceanic eddy viscosity profile abstract a variational optimal control technique is used to assimilate both meteorological and oceanographic observations into an oceanic ekman layer model an identical twin experiment is discussed first in which the observations are created by the dynamic model the field measurements from the lotus 3 long term upper ocean study 3 buoy are then analysed by fitting the model results to the data the unknown boundary condition the wind stress drag coefficient and the unknown vertical eddy viscosity distribution are deduced simultaneously from the data and an optimal estimate of the current field is obtained though the model is simple the results show that the variational assimilation technique is capable of extracting from the available observations a reasonable wind stress drag coefficient and vertical eddy viscosity distribution