mesoscale oceanographic processes beneath the ice of fram strait a major component of the fram strait marginal ice zone experiment was the investigation of air sea ice interactions processes and circulation patterns found behind the local ice edge and on scales greater than 10 kilometers mesoscale and large scale neutrally buoyant floats ice tethered cyclesondes and helicopter based measurements were used to obtain uniquely integrated and consistent views of the mesoscale ocean features beneath the ice cover of fram strait within the vicinity of the yermak plateau three distinct regions of mesoscale motion were observed that coincided with the shallow topography of the plateau the northward flowing atlantic water over the western flank of the plateau and the strong current shear zone of the east greenland polar front a subice meander of the front was also observed which was probably occluded subsequently

coupled ice ocean dynamics in the marginal ice zones upwelling downwelling and eddy generation this study is aimed at modeling mesoscale processes such as upwelling downwelling and ice edge eddies in the marginal ice zones a two dimensional coupled ice ocean model is used for the study the ice model is coupled to the reduced gravity ocean model through interfacial stresses the parameters of the ocean model were chosen so that the dynamics would be nonlinear the model was tested by studying the dynamics of upwelling winds parallel to the ice edge with the ice on the right produce upwelling because the air ice momentum flux is much greater than air ocean momentum flux thus the ekman transport is greater under the ice than in the open water the stability of the upwelling and downwelling jets is discussed the downwelling jet is found to be far more unstable than the upwelling jet because the upwelling jet is stabilized by the divergence a constant wind field exerted on a varying ice cover will generate vorticity leading to enhanced upwelling downwelling regions i e wind forced vortices steepening and strengthening of vortices are provided by the nonlinear terms when forcing is time varying the advection terms will also redistribute the vorticity the wind reversals will separate the vortices from the ice edge so that the upwelling enhancements are pushed to the open ocean and the downwelling enhancements are pushed underneath the ice

detection and classification of surface roughness in an arctic marginal sea ice zone sea ice dynamic and thermodynamic processes are important and highly variable elements of the marginal ice zone miz this study examines the detection and classification of statistically separable sea ice classes in the miz through a range of temporal and spatial scales a helicopter based laser system was used to obtain large scale and a ship based laser profiler to identify small scale roughness types respectively the analysis of variance of surface height data from helicopter and ship based laser systems active microwave amw c band backscattering data and passive microwave pmw 37 and 89 ghz brightness temperature data reveal different classes that statistically differ from one another we found significant statistical difference in variances in amw data with six classes that differ in vv polarization three classes in vh polarization and five classes in hh polarization in the miz e g snow covered first year ice ice rubble pancake ice frost flowers melt pond flooded ice and ice edge of southeastern beaufort sea the pmw emission was not as effective at discrimination yielding only one statistically separable class the results can potentially be extended to satellite based investigations of the miz at regional scales copyright 2012 john wiley sons ltd

sar image statistics related to atmospheric drag over sea ice the possibility of using synthetic aperture radar sar data to distinguish sea ice regions with different atmospheric drag is explored both the amplitude of the radar return and statistics derived from sar image data are examined roughness statistics data from several pack ice areas are used in a backscatter model to predict the return from surfaces with measured drag coefficients the results suggest that the scattering coefficient for typical radar wavelengths is insensitive to the roughness elements responsible for the observed drag coefficient variations over pack ice free of major ridges for marginal ice zones where ice concentration and floe deformation contribute to atmospheric drag a simple model for the atmospheric boundary layer is used to provide qualitative relationships between drag coefficient and regional ice properties ice concentration floe size distribution floe edge density derivable from sar data simple algorithms to produce maps of ice concentration and edge density are outlined and applied to 23 5 cm sar digital image data

variations of mesoscale and large scale sea ice morphology in the 1984 marginal ice zone experiment as observed by microwave remote sensing during the summer 1984 marginal ice zone experiment in the fram strait and greenland sea mizex 84 passive and active microwave sensors on five aircraft and the nimbus 7 scanning multichannel microwave radiometer smmr acquired synoptic sequential observations which when combined give a comprehensive sequential description of the mesoscale and large scale ice morphology variations during the period june 9 through july 16 1984 the high resolution ice concentration distributions in these images agree well with the low resolution smmr distributions for diffuse ice edges the 30 smmr ice concentration isopleth corresponds to the ice edge while for compact conditions the ice edge falls within the 40 to 50 smmr isopleths throughout the experiment ice edge meanders and eddies repeatedly formed moved and disappeared but the ice edge remained within a 100 km wide zone the ice pack behind this alternately diffuse and compact edge underwent rapid and pronounced variations in ice concentration over a 200 km wide zone the aircraft microwave images show the complex structures and ephemeral nature of the mesoscale sea ice morphology the difference in oceanographic forcing between the eastern and western sectors of the experiment area generated pronounced ice morphology differences on the yermak plateau from 3 e to 10 e the weak ocean circulation allowed the wind to be the dominant force in determining the ice morphology to the southwest of this region over the molloy deep and the greenland continental shelf break from 3 e to 8 w the ice morphology was dominated by the energetic east greenland current with its associated eddies and meanders

dependence of boundary layer structure near an ice edge coastal front upon geostrophic wind direction the dependence of boundary layer bl features within a coastal front created by temperature and roughness differences across a surface interface upon the direction of a large scale geostrophic wind is examined with idealized simulations using parameters appropriate to an ice edge maximum vertical velocities and strongest horizontal gradients occur when the vertically averaged bl velocity near the ice edge parallels the ice edge this occurs at the on ice geostrophic angle for which frictional modification of the geostrophic wind optimally counters thermally induced cross interface flow at the ice edge this optimal angle is greater for ice on right when looking downwind assuming northern hemisphere rotation flow than for ice on left flow due to asymmetry introduced by surface friction the associated vertical velocity maxima also vary asymmetrically with geostrophic wind direction the optimal angle depends upon the average surface roughness at the interface whereas the vertical velocity maxima depend upon the differential surface roughness across the interface for a prototype ice edge the optimal on ice angle is 20 larger and its vertical velocity maximum 3 times larger for ice on right flow with differential surface roughness accounting for nearly half of the magnitude asymmetry along ice velocity jets develop only when the large scale geostrophic wind nearly parallels the ice edge the curl of the surface stress is sensitive to changes in geostrophic wind direction changing sign over the water when the large scale geostrophic wind approximately parallels the ice edge because of frontal collapse the width of the surface transition region has a relatively minor influence on these results

venus the nature of the surface from venera panoramas images of the surface of venus obtained by the soviet venera 9 10 13 and 14 landers have been analyzed to provide a basis for understanding the nature of geologic processes operating there the four spacecraft landed in the beta phoebe region at median elevations in the upland rolling plains province the landing points are each separated by distances of more than a thousand kilometers the venera panoramas were digitized and transformed into various perspectives in order to facilitate analysis and comparison with other planetary surfaces bedrock is exposed at the venera 10 13 and 14 sites and is characterized by semicontinuous flat polygonal to subrounded patches up to several meters in width the bedrock surface is often dominated by subhorizontal to horizontal layered plates with thicknesses of several centimeters and abundant linear and polygonal vertical fractures angular to subangular layered to platy blocks in the 5 to 70 cm range dominate the venera 9 site and occur much less frequently at the other sites blocks appear to share many characteristics with the exposed bedrock and are interpreted to be largely derived from it soils particles 1 cm are abundant at the venera 9 10 and 13 sites but are uncommon at venera 14 features indicative of a strong eolian influence moats dunes wind tails are not observed a striking aspect of the venera landing sites is their extreme similarity despite separation distances of thousands of kilometers several hypotheses are considered for the origin of the bedrock surfaces and we investigate in detail the hypothesis that bedrock originated from surface lava flows in this interpretation the broadly platy nature of the surface is analogous to the rolling and undulating nature of terrestrial pahoehoe flows caused by the formation and deformation of a semisolid crust the layering is interpreted to be formed by a combination of upper thermal boundary layer formation and horizontal sheets formed by cooling and shearing during flow emplacement vertical fractures are attributed largely to joint patterns formed during cooling this interpretation made on the basis of surface morphology is consistent with venera 13 and 14 geochemical results which reported high potassium basalt and tholeiitic basalt compositions respectively if this interpretation is correct large regions of the beta phoebe area are likely to be characterized by lava flows the relative freshness of features observed by venera 14 suggests that some bedrock surfaces are geologically young or that erosion rates are low

reports venus identification of banded terrain in the mountains of ishtar terra high resolution images obtained with the arecibo radar system at a wavelength of 12 6 centimeters reveal numerous parallel 10 to 20 kilometer wide bands of high radar backscatter situated on and oriented parallel to the major mountain ranges of the ishtar terra region of venus geometric and morphological characteristics suggest that the bands represent earth like tectonic deformational features such as folds and faults

physical conditions at the base of a fast moving antarctic ice stream boreholes drilled to the bottom of ice stream b in the west antarctic ice sheet reveal that the base of the ice stream is at the melting point and the basal water pressure is within about 1 6 bars of the ice overburden pressure these conditions allow the rapid ice streaming motion to occur by basal sliding or by shear deformation of unconsolidated sediments that underlie the ice in a layer at least 2 meters thick the mechanics of ice streaming plays a role in the response of the ice sheet to climatic change

venus gravity anomalies and their correlations with topography this report provides a summary of the high resolution gravity data obtained from the pioneer venus orbiter radio tracking data gravity maps covering a 70 latitude band through 360 of longitude are displayed as line of sight and vertical gravity topography converted to gravity and bouguer gravity maps are also shown in both systems topography to gravity ratios are made over several regions of the planet there are markedly different ratios for the aphrodite area as compared to the beta and atla areas

remote sensing of the fram strait marginal ice zone sequential remote sensing images of the fram strait marginal ice zone played a key role in elucidating the complex interactions of the atmosphere ocean and sea ice analysis of a subset of these images covering a 1 week period provided quantitative data on the mesoscale ice morphology including ice edge positions ice concentrations floe size distribution and ice kinematics the analysis showed that under light to moderate wind conditions the morphology of the marginal ice zone reflects the underlying ocean circulation high resolution radar observations showed the location and size of ocean eddies near the ice edge ice kinematics from sequential radar images revealed an ocean eddy beneath the interior pack ice that was verified by in situ oceanographic measurements

use of synthetic aperture radar derived kinematics in mapping mesoscale ocean structure within the interior marginal ice zone synthetic aperture radar sar imagery of the marginal ice zone over the western sector of the yermak plateau defined a region of anomalous ice motion that could not be accounted for by simple free drift movement of the sea ice based on daily averaged winds over the same time period from june 29 to july 6 1984 sea ice trajectories within this anomalous region are however consistent with oceanic forcing of the pack ice by a mesoscale eddy that had recently formed off the polar front although the use of such imagery has already been shown to be a diagnostic tool in mapping ocean features at the ice edge the observed correlation 50 to 70 km behind the local ice edge indicates that sar imagery has the potential to define energetic mesoscale and larger oceanic features well within the polar pack ice

global color and albedo variations on io abstract three multispectral mosaics of io have been produced from voyager imaging data a global mosaic from each of the voyager 1 and voyager 2 data sets and a high resolution mosaic of the region surrounding the volcano ra patera the mosaics are maps of normal albedo and color in accurate geometric map formats io s photometric behavior mapped with a two image technique is spatially variable especially in the bright white areas the disk integrated color and albedo of the satellite have been remarkably constant over recent decades despite the volcanic activity and the many differences between voyager 1 and 2 images acquired just 4 months apart this constancy is most likely due to the consistent occurrence of large pele type plumes with relatively dark red deposits in the region from long 240 to 360 a transient brightening southeast of pele during the voyager 1 encounter was probably due to real changes in surface and or atmospheric materials rather than to photometric behavior the intrinsic spectral variability of io as seen in a series of two dimensional histograms of the multispectral mosaics consists of continuous variation among three major spectral end members the data were mapped into five spectral units to compare them with laboratory measurements of candidate surface materials and to show the planimetric distributions unit 1 is best fit by the spectral reflectance of ordinary elemental sulfur and it is closely associated with the peletype plume deposits unit 2 is strongly confined to the polar caps above about latitude 50 but its composition is unknown unit 5 is probably so 2 with relatively minor contamination it is concentrated in the equatorial region and near the long lived prometheus type plumes units 3 and 4 are gradational between units 1 and 5 in addition to so 2 and elemental sulfur other plausible components of the surface are polysulfur oxides fecl 2 na 2 s and nahs

tectonics and evolution of venus the global tectonics of venus differs significantly from that of earth most markedly in that the surface is covered predominately by gently rolling terrain there apparently are no features like ocean rises the gravity is positively correlated with topography at all wavelengths and the few highlands are estimated to be supported or compensated at a depth of approximately 100 kilometers the surface of venus appears to be covered mainly by an ancient crust the high surface temperature making subduction difficult it seems likely that well over 1 billion years ago water was destabilized at the surface and soon after plate tectonics ceased the highlands appear to be actively supported presumably as manifestations of long enduring hot spots

a ring shear device for the study of till deformation tests on tills with contrasting clay contents abstract deformation of subglacial sediment may have had a profound influence on the geomorphic effects and dynamics of pleistocene ice sheets but data that bear on the rheology of such sediment are few and contradictory a means of studying systematically the mechanical properties of glacial tills is provided by a ring shear device that shears a large annular specimen to high strains at variable rates special features of the device allow continuous observation of the distribution of shear strain measurement of local stresses normal to the direction of shear and isolation of wall effects thus far a linear viscous putty and two tills with different clay contents 4 and 32 by weight have been tested the experiments with till indicate as expected that the presence of dispersed clay minerals reduces markedly both the residual strength and hydraulic diffusivity of till clay also reduces spatial variations in normal stress associated with grain bridges the walls bounding the specimen support only 9 17 of the total resistance to shearing strain was localized in both tills but not in the linear viscous putty strain localization in the tills indicates that their theology departs significantly from linear and bingham viscous models

radar evidence for cratering on venus to date many craterlike features have been detected in earth based radar and pioneer venus imagery of the surface of venus but whether they are of impact or endogenic origin is still in question the morphologic and polarization characteristics of these features as observed from earth based radar data obtained at the arecibo observatory provide additional information that may be useful in their identification this paper examines the extent to which this information can be used in conjunction with our knowledge of the morphologic and polarization properties of impact craters and volcanic calderas on other terrestrial bodies to constrain inferences about the origin of the craterlike features on venus results indicate that only two features exhibit unambiguous characteristics that could tentatively distinguish them as volcanic or impact in origin however the observed trends imply that any age of the surface derived from observed crater densities must represent an upper bound on the actual age

the effect of observed ice conditions on the drag coefficient in the summer east greenland sea marginal ice zone the summer east greenland sea marginal ice zone is a region characterized by extreme horizontal variations of surface roughness characteristics the surface drag coefficient is found to be correlated with these roughness characteristics in particular ice concentration and ice floe roughness and size the estimates of wind stress and wind speed yield neutral drag coefficients cdn with standard deviations of 2 3 0 8 10 3 for areas with less than 40 ice concentration and 4 0 1 1 10 3 for ice concentrations greater than 70 much of the variation in cdn for a given ice concentration is explained by differences in ice floe size and roughness very small concentrated rough floes that have been affected by wave action produce twice as much wind stress cdn 4 2 0 7 10 3 as relatively large flat floes cdn 2 1 0 6 10 3 and 4 times as much as typical open ocean for a given wind speed and stability the drag coefficients in this region are higher than other marginal ice zones probably a result of the presence of large amounts of multiyear ice floes that extend higher above the ocean surface and create more drag than first year floes

mesoscale eddies in the fram strait marginal ice zone during the 1983 and 1984 marginal ice zone experiments during the summer marginal ice zone experiment in fram strait in 1983 and 1984 fourteen mesoscale eddies in both deep and shallow water were studied between 78 o and 81on sampling combined satellite and aircraft remote sensing observations conductivity temperature depth observations drift of surface and subsurface floats and current meter measurements typical scales of these eddies were 20 40 km rotation was mainly cyclonic with a maximum speed in several cases subsurface of up to 40 cm s observations further suggest that the eddy lifetime was at least 20 to 30 days five generation sources are suggested for these eddies several of the eddies were topographically trapped while others primarily formed by combined baroclinic and barotropic instability moved as much as 10 15 km d with the mean current the vorticity balance in the nontrapped eddies is dominated by the stretching of isopycnals accompanied by a change in the radial shear in the most completely observed eddy south of 79on the available potential energy exceeded the kinetic energy by a factor of 2 quantitative estimates suggest that the abundance of these eddies enhances the ice edge melt up to 1 2 km d

greenland sea odden sea ice feature intra annual and interannual variability the odden is a large sea ice feature that forms in the east greenland sea that may protrude eastward to 5 e from the main sea ice pack at about 8 w between 73 and 77 n it generally forms at the beginning of the winter season and can cover 300 000 km2 throughout the winter the outer edge of the odden may advance and retreat by several hundred kilometers on timescales of a few days to weeks satellite passive microwave observations from 1978 through 1995 provide a continuous record of the spatial and temporal variations of this extremely dynamic phenomenon aircraft synthetic aperture radar satellite passive microwave and ship observations in the odden show that the odden consists of new ice types rather than older ice types advected eastward from the main pack the 17 year record shows both strong interannual and intra annual variations in odden extent and temporal behavior for example in 1983 the odden was weak in 1984 the odden did not occur and in 1985 the odden returned late in the season an analysis of the ice area and extent time series derived from the satellite passive microwave observations along with meteorological data from the international arctic buoy program iabp determined the meteorological forcing associated with odden growth maintenance and decay the key meteorological parameters that are related to the rapid ice formation and decay associated with the odden are in order of importance air temperature wind speed and wind direction oceanographic parameters must play an important role in controlling odden formation but it is not yet possible to quantify this role because of a lack of long term oceanographic observations

arctic sea ice signatures for passive microwave algorithms passive microwave satellite data can be used to estimate the concentrations of three surface types open water first year ice and multiyear ice these estimates are made with an algorithm that requires knowing the microwave signatures of each of these three surface types for the scanning multichannel microwave radiometer the algorithm proposed by cavalieri et al 1984 known as the smmr team algorithm is widely used two unsatisfying properties of this algorithm are 1 its estimates of multiyear ice concentrations are much lower than its estimates of summer ice concentrations and are also significantly lower than independent estimates of arctic ocean multiyear ice and 2 it produces variations in estimated concentration that appear to be caused by spatial and temporal variations in the signatures we examine two alternative sets of signatures one set varies temporally but not spatially and is defined by the modes of major peaks in histograms of brightness temperature the other set is defined as the overall means of the temporally varying signatures we call these new constant signatures an estimate of the average bias of the winter multiyear ice is derived and a corresponding correction applied to the new constant signatures both sets of new signatures have essentially the same precision 0 05 fractional area for winter ice concentration 0 10 for summer ice concentration and 0 15 to 0 3 for winter multiyear ice concentration these error estimates are upper bounds to the true precision especially for multiyear ice for which some true concentration changes are included in the variability the precision estimates include all spatial and temporal signature variability and are compatible with estimates of sea ice emissivity variability given in the literature because the temporally varying signatures provide only a slightly better precision we prefer the new constant signatures both sets of new signatures result in about 0 6 to 0 7 winter multiyear ice for the arctic ocean substantially more than the 0 3 to 0 4 computed using the original team algorithm signatures and in the same range as several independent estimates of the multiyear ice 0 54 to 0 75

lightning measurements from the pioneer venus orbiter the plasma wave instrument on the pioneer venus orbiter frequently detects strong and impulsive low frequency signals when the spacecraft traverses the nightside ionosphere near periapsis these particular noise bursts appear only when the local magnetic field is strong and steady and when the field is oriented to point down to the ionosphere thus the signals have all characteristics of lightning whistlers we have tried to identify lightning sources between the cloud layers and the planet itself by tracing rays along the b field from the orbiter down toward the surface an extensive data set consisting of measurements through orbit 1185 strongly indicates a clustering of lightning sources near the beta and phoebe regios with an additional significant cluster near the atla regio at the eastern edge of aphrodite terra these results suggest that there are localized lightning sources at or near the planetary surface

venus volcanism and rift formation in beta regio a new high resolution radar image of beta regio a venus highland area confirms the presence of a major tectonic rift system and associated volcanic activity the lack of identifiable impact craters together with the apparent superposition of the theia mons volcanic structure on the rift system suggest that at least some of the volcanic activity occurred in relatively recent geologic time the presence of topographically similar highland areas elsewhere on venus aphrodite terra dali chasma and diana chasma suggests that rifting and volcanism are significant processes on venus

bottom ablation and heat transfer coefficients from the 1983 marginal ice zone experiments bottom ablation in the marginal ice zone miz is a fundamental process that controls the ice edge position in both the winter and the summer during the east and west marginal ice zone experiments mizex west and mizex east in 1983 periodic sonic distance measurements between the overlying ice and transducers fixed on masts below ice floes determined the bottom ablation the melt rates for floes within 15 km of the ice edge ranged from near zero when the ice was in water at the freezing point to 0 5 m d 1 when the ice entered warm water greater than 3 k to the south simultaneous velocity and temperature measurements at 2 m below the ice in mizex west and at 2 m and 10 m below the ice in mizex east show the response of the melt rate to changing oceanographic conditions for the first time the combined oceanographic and ablation measurements allow the direct calculation of the bulk heat transfer coefficient ch between the ice and the ocean at 2 m and 10 m below the ice for the bering sea experiment ch was 8 10 4 while for the fram strait experiment ch varied from 2 10 4 to 4 10 4 within each set of experiments ch remained nearly constant over a wide range of melt rates relative ice water speeds and seawater temperatures

on venus impact basins viscous relaxation of topographic relief the question of whether impact basins dating from the time of heavy bombardment of the inner solar system are preserved on the surface of venus is of paramount importance for an understanding of the geological processes that have shaped that planet two types of features have been suggested as candidates for impact basins on venus 1 large quasi circular topographic depressions and 2 large quasi circular regions of low radar backscatter surrounded by terrain of greater radar backscatter and generally displaying little topographic relief as a guide to the expected character of an impact basin on venus we have calculated the viscous relaxation with time of the topographic relief of such a basin under the assumption that the surface temperature of the planet has been at or near its presently high value since the time of basin formation the viscous relaxation model includes the effects of a decrease in effective viscosity with depth and the partial to complete isostatic compensation of initial topography we conclude that an impact basin several hundred kilometers or greater in diameter and 3 b y old or greater in age should have negligible topographic relief at present this conclusion does not exclude the hypothesis that quasi circular features of low radar backscatter but little topographic relief may be relaxed remnants of ancient impact basins large quasi circular depressions on venus such as atalanta planitia however cannot exceed a few hundred million years in age otherwise their initial topographic relief would be excessive such large depressions are thus likely to be geologically young and to have resulted from processes other than impact an additional process must therefore have operated on venus to create large roughly circular areas of lowland terrain one possibility is that these topographic features are analogs on venus to terrestrial platform basins produced by lithospheric extension and thermal subsidence

venus summary and review of science research activities 1983 87 in the past four years the first high resolution synoptic images of the surface of venus have been obtained and we have learned more about the nature of its surface and atmosphere the major accomplishments of the u s s r in venus exploration have been observed with great interest by u s investigators some of whom have begun joint research efforts with soviet scientists venera 15 and 16 radar imaging experiments and new data obtained at the arecibo observatory have provided answers to some important questions conjectured volcanic features have been resolved into unmistakable calderas or distinct lava flow morphologies the question of whether venus like the earth may have high erosion rates is answered and from the observed number of presumed impact craters it appears that resurfacing rates on venus are much smaller than on earth no evidence of water or wind activity has been seen

instruments and methods direct measurement of sliding at the glacier bed sliding at the base of trapridge glacier yukon territory canada was measured using a drag spool we describe this simple and inexpensive instrument as well as its installation and operation from 1990 to 1992 seven sites were instrumented with drag spools at six of the sites basal sliding during the period of observation accounted for 50 70 of the total flow observed at the glacier surface the contribution from ice creep is known to be small so most of the remaining surface motion must be attributed to subglacial sediment deformation for the seventh site the observed sliding rate was 90 of the total flow an indication that the sliding contribution varies spatially across the bed diurnal variations in the response of one of our instruments appear to be correlated to subglacial water pressure fluctuations and are interpreted in terms of changes in sliding velocity rather than the opening and closing of basal cavities

investigation of the effects of summer melt on the calculation of sea ice concentration using active and passive microwave data active and passive microwave data sets acquired during the 1984 marginal ice zone miz experiment aircraft flights in the fram strait region are used to examine the effects of ice surface melt on microwave signatures and their resulting error in the calculation of sea ice concentration conditions examined with the active passive data set include ice floes with moist and dry snow cover and both heavily ponded and ridged surfaces passive sensors on the nasa cv 990 aircraft included the aircraft electrically scanning microwave radiometer esmr operating at 19 4 ghz and aircraft multichannel microwave radiometer ammr operating at 10 7 18 0 21 0 and 37 0 ghz active microwave sensors flown on the canadian centre for remote sensing cv 580 aircraft included the environmental research institute of michigan synthetic aperture radar sar operating at 1 2 and 9 4 ghz coincident ammr and sar measurements of individual floes identified in aerial photography are used to describe the effects of surface melt on the calculation of sea ice concentration and in particular the response of the passive microwave polarization and spectral gradient characteristics to different stages of surface melt although the onset and progression of summer melt are not uniform throughout the arctic the stages of summer melt observed in the miz are also observed on a large scale in the central arctic this is demonstrated using nimbus 7 smmr data and arctic ocean buoy temperature data over one annual cycle finally the potential of optimally combining both active and passive microwave data in an effort to ameliorate these surface melt effects during the summer months is also explored

venus limited extension and volcanism along zones of lithospheric weakness three global scale zones of possible tectonic origin are described as occurring along broad low rises within the equatorial highlands on venus lat 50 n to 50 s long 60 to 310 the two longest of these tectonic zones the aphrodite beta and themis atla zones extend for 21 000 and 14 000 km respectively several lines of evidence indicate that beta and atla regiones located at the only two intersections of the three major tectonic zones are dynamically supported volcanic terranes associated with currently active volcanism rift valleys south of aphrodite terra and between beta and phoebe regiones are characterized by 75 to 100 km widths raised rims and extensions of only a few tens of kilometers about the same magnitudes as in continental rifts on the earth horizontal extension on venus was probably restricted by an early choking off of plate motion by high crustal and upper mantle temperatures and the subsequent loss of water and an asthenosphere

venus global surface radar reflectivity observations of the surface of venus carried out by the pioneer venus radar mapper at a wavelength of 17 centimeters reveal a global mean reflectivity at normal incidence of 0 13 0 03 over the surface variations from a low of 0 03 0 01 to a high of 0 4 0 1 are found with theia mons previously identified as possibly volcanic showing a value of 0 28 0 07 regions of high reflectivity may consist of rocks with substantial inclusions of highly conductive sulfides

hot spot heat transfer its application to venus and implications to venus and earth gross similarities between earth and venus suggest that both planets might be expected to lose heat by the same mechanism available data do not resolve plate tectonics on venus however and other heat loss mechanisms such as hot spot heat loss have been suggested using a model which gives a relationship among surface elevation lithospheric thickness and heat flux we test the hot spot heat loss mechanism for venus and determine that it can easily explain the predicted heat loss of the planet with a modest number of hot spots of the order of 35 approximately 93 of the mapped topography of venus can be explained solely on the basis of lithospheric thickness variations additional compensation is required for topography above a radius of 6053 km and this can be effected by incorporating a variable thickness crust into the model if crust is assumed to be generated on the crests of the hot spots probably by processes associated with volcanism the model is consistent with almost 99 of the mapped venus topography the model is also basically consistent with available gravity data and interpretations which indicate compensated topography and great depths of compensation 100 1000 km for the mid latitudes of the planet the remaining approximately 1 of the topography not explained by hot spot crustal generation is thought to be compensated at a shallower depth primarily by variations in crustal thickness which are not directly related to hot spot volcanism the models relating surface elevation to lithospheric thickness and heat flow are grossly consistent with either a plate tectonic or hot spot heat loss mechanism for venus the range of lithospheric thicknesses implied by the range of elevations on venus implies that if plate tectonics is the dominant heat loss mechanism on venus the mean plate velocities are slower than on earth slow spreading ridges should be resolvable by the available venus topographic data but are not apparent comparison and analysis of the hypsometric curves for earth and venus suggest basic differences between the curves the skewed terrestrial ocean floor curve being consistent with plate tectonics but the relatively symmetrical venusian curve indicates that either plate tectonics differs on venus from the terrestrial analogue or that plate tectonics does not dominate the topographic expression of venus tectonism the venusian curve is consistent with a hot spot heat loss mechanism a hot spot crustal genesis mechanism is proposed which would probably result in crust very similar to the granite greenstone terranes of many terrestrial archaean cratons we speculate that hot spot heat loss may have preceded plate tectonics as the dominant terrestrial heat loss mechanism

characterization of venera 15 16 geologic units from pioneer venus reflectivity and roughness data abstract geologic units have been defined for the surface of venus from venera 15 16 image data a characterization of these geologic units is carried out using information on surface properties derived from pioneer venus pv reflectivity and rms slope data the geologic context provided by venera 15 16 units allows additional more specific interpretations of surface radar properties to be made characterization of venera units results in the definition of four groups of venera units i smooth rocky units ii rough rocky units iii rough high dielectric units and iv diffusely scattering units on the basis of correlations of surface morphology to spatial and statistical distributions in rms slope and reflectivity data we test models for the origin of the surface properties of some units we conclude that plains and tectonic units can be contrasted in terms of the average roughness of the surface and that tectonic deformation appears to roughen the surface at 0 5 to 10 m and 5 to 50 cm scales this tectonic weathering process appears to dominate the erosional regime of venus unlike earth or mars production and transport of soils dominates only a small portion 5 of the surface some of the venera units display distinctive spatial and statistical distributions of pv radar data in particular apparent low reflectivity in the tesserae appears to be caused by small 5 50 cm rock fragments on the surface which cause diffuse scattering at pioneer venus wavelenghts analysis of models for the formation of these fragments suggests that they are due to the pervasive deformation undergone by the tesserae finally aspects of this study have been used to extend results of venera image data analysis southward of 30 n lat resulting in a prediction of the distribution of tessera such results can aid in magellan investigations

continental rifting and the origin of beta regio venus topographic maps based on pioneer venus altimetry suggest that beta regio an elevated feature centered at 27 n 282 e is analogous to domes associated with continental rift systems on earth this interpretation is consistent with the commonly quoted analogy between the east african rift system and the topography of the region from beta regio southward to phoebe regio if beta regio is a dome major structural uplift of the crust of venus is implied suggesting a more dynamic upper mantle than would be the case if beta regio were simply a large volcanic construct

vega landing sites venera 15 16 unit analogs from pioneer venus reflectivity and rms slope data pioneer venus radar data on surface properties have been used to compare the vega spacecraft landing sites with the northern 1 4 of venus mapped by the orbiters venera 15 and 16 the regions surrounding both landing sites possess surface reflectivity and small scale roughness properties most similar to those of mapped volcanoes and volcanic plains regions and different surface properties than those of mapped tectonic units regions analogous to the vega 1 site are relatively rare covering 2 8 percent of the mapped surface vega 2 analogs are much more common and cover 22 6 percent of the surface neither landing site is representative of the nearby highlands of aphrodite but the vega 2 landing site is similar to much of the northern plains of venus

feedback between ice flow barotropic flow and baroclinic flow in the presence of bottom topography coupling between externally driven barotropic flow and locally driven baroclinic flow in the presence of an ice cover and topography is studied the topography is a necessary ingredient in this coupling this study shows that the observed mesoscale activity of the ice edge seen in satellite imagery does not necessarily reflect the mesoscale baroclinic activity in the ocean besides oceanic eddies the ice cover can trace the topographic changes via the coupling to the barotropic flow a two layer ocean model coupled to an ice model is constructed to simulate an ice ocean system with a varying bottom topography in the absence of wind forcing the ice cover reflects the externally driven barotropic ocean response especially topographically forced taylor columns by forming ice streamers or meanders some of these features propagate advected with the ocean currents as a whole downstream creating an image of eddy propagation even though there is no baroclinic structure underneath when downwelling favorable winds ice on the left from the wind direction are turned on in addition to this background barotropic flow the ekman flow in the ocean toward the open ocean will enhance the meandering of the ice edge due to the barotropic flow during upwelling favorable winds the ice edge stays rather compact including the case when a strong baroclinic cyclonic vortex is developing beneath an ice meander supported by the taylor column in the ocean

k u band airborne radar altimeter observations of marginal sea ice during the 1984 marginal ice zone experiment pulse limited airborne radar data taken in june and july 1984 with a 13 8 ghz altimeter over the fram strait marginal ice zone are analyzed with the aid of large format aerial photography airborne synthetic aperture radar data and surface observations variations in the radar return pulse waveforms are quantified and correlated with ice properties recorded during the marginal ice zone experiment results indicate that the wide beam altimeter is a flexible instrument capable of identifying the ice edge with a high degree of accuracy calculating the ice concentration and discriminating a number of different ice classes this suggests that microwave radar altimeters have a sensitivity to sea ice which has not yet been fully exploited when fused with ssm i avhrr and ers 1 synthetic aperture radar imagery future ers 1 altimeter data are expected to provide some missing pieces to the sea ice geophysics puzzle

spatial patterns of increases and decreases in the length of the sea ice season in the north polar region 1979 1986 recently it was reported that sea ice extents in the northern hemisphere showed a very slight but statistically significant decrease over the 8 8 year period of the nimbus 7 scanning multichannel microwave radiometer smmr data set in this paper the same smmr data are used to reveal spatial patterns in increasing and decreasing sea ice coverage specifically the length of the ice season is mapped for each full year of the smmr data set 1979 1986 and the trends over the 8 years in these ice season lengths are also mapped these trends show considerable spatial coherence with a shortening in the sea ice season apparent in much of the eastern hemisphere of the north polar ice cover particularly in the sea of okhotsk the barents sea and the kara sea and a lengthening of the sea ice season apparent in much of the western hemisphere of the north polar ice cover particularly in davis strait the labrador sea and the beaufort sea

surface characteristics of venus derived from pioneer venus altimetry roughness and reflectivity measurements the three primary data sets for the pioneer venus orbiter radar experiment topography roughness and reflectivity contain important information about the geological and textural characteristics of the surface of venus we have subdivided the range of roughness and reflectivity values into three categories as follows roughness in degrees rms slope relatively smooth 1 2 5 transitional from smooth to rough 2 5 5 and relatively rough 5 and fresnel reflectivity surfaces dominated by soil or porous material 0 2 we have analyzed each of these data sets and their relationships to each other in order to define areas of the surface that are characterized by distinctive properties e g rough rocky surfaces smooth soil surfaces we then describe the abundance and areal distribution of such areas and locally calibrate the geological significance of some of the surface types by examining high resolution images from spacecraft and earth based observatories we find that the majority of venus is covered by regionally contiguous rock and bedrock surfaces many of the smooth surfaces we interpret to be of volcanic origin most likely lava flows while rougher surfaces are locally characterized by tectonic deformation of several types soil surfaces cover less than about 27 of the planet and are generally patchy in their distribution on the basis of the distribution of these surfaces we see no evidence for the extensive preservation of an ancient global regolith or for widespread topographically controlled erosion lateral transport and sedimentation the small percentage of the surface of venus characterized by high dielectric material appears to originate from several processes including primary lava flows probably containing enrichments of high dielectric materials such as metal or metal oxides e g theia mons in beta regio and exposure of high dielectric materials by tectonic deformation e g maxwell montes in ishtar terra these global data set correlations provide a fundamental frame work for understanding the nature of the surface of venus and will permit extrapolation of local and regional findings from future geochemical and imaging experiments to a global context

earth based radar studies of planetary surfaces and atmospheres radar has been used as a remote sensing tool since 1946 when the first echoes from the moon were detected by ground based radar systems since then the sensitivity of our most powerful radar systems has increased by a factor of about 1012 and radar studies of mercury venus earth s moon mars the galilean moons of jupiter the rings of saturn and a dozen asteroids have been made specific studies range from simple measurements of distance or reflectivity to detailed maps or images of reflectivity altimetry and various other model parameters this paper presents a short review of the more recent observations and summarizes current research activities associated with each body an attempt is made to anticipate the observational data set that should be available during the next decade such data will be useful for remote sensing applications either directly or combined with data from other programs the usefulness of the radar data is also dependent upon theoretical models that explain the observed scattering such models often are dependent upon parameters that are not measurable by radar likewise models that predict other physical measurements may be influenced by parameters that are easily measured by radar thus many more exciting applications of radar data should become apparent as further observations are made by other techniques and as models are developed to explain the observed quantities

aircraft and satellite passive microwave observations of the bering sea ice cover during mizex west passive microwave measurements of the bering sea ice cover were made with the nasa cv 990 airborne laboratory and with the nimbus 7 scanning multichannel microwave radiometer smmr during february 1983 as part of the bering sea marginal zone experiment mizex west microwave data obtained with the cv 990 include radiances from both imaging and dual polarized fixed beam radiometers spanning a range of frequencies from 10 to 183 ghz the imagery at 19 and 92 ghz provide a description of the marginal ice zone delineating regions of open water ice compactness and ice edge structure comparison of these images with ice concentration maps derived from the smmr data shows that the maps provide an accurate description of the ice edge and interior pack polynyas analysis of the fixed beam data shows that spectral differences increase with a decrease in ice thickness and the polarization at both 18 and 37 ghz distinguishes among new young and first year sea ice types finally these results are shown to agree with surface based radiometric measurements

a coupled ice ocean model of upwelling in the marginal ice zone a dynamical coupled ice ocean numerical model for the marginal ice zone miz is suggested and used to study upwelling dynamics in the miz the nonlinear sea ice model has a variable ice concentration and includes internal ice stress the model is forced by stresses on the air ocean and air ice surfaces the main coupling between the ice and the ocean is in the form of an interfacial stress on the ice ocean interface the ocean model is a linear reduced gravity model the wind stress exerted by the atmosphere on the ocean is proportional to the fraction of open water while the interfacial stress ice ocean is proportional to the concentration of ice a new mechanism for ice edge upwelling is suggested based on a geostrophic equilibrium solution for the sea ice medium the upwelling reported in previous models invoking a stationary ice cover is shown to be replaced by a weak downwelling due to the ice motion most of the upwelling dynamics can be understood by analysis of the divergence of the across ice edge upper ocean transport on the basis of numerical model an analytical model is suggested that reproduces most of the upwelling dynamics of the more complex numerical model

a numerical study of mesoscale ocean eddy interaction with a marginal ice zone observations made during the marginal ice zone experiment mizex program indicated the presence of mesoscale eddies in a marginal ice edge ocean front in the east greenland current the eddies range in scale from 5 to 80 km physical mechanisms including barotropic and baroclinic instability may be responsible for their presence although the evolution of isolated eddies at low latitudes has been the focus of many studies the effect of ice cover on eddy evolution and vice versa has had less attention here an examination of the interaction of isolated mesoscale ocean eddies with a marginal ice zone is presented results are obtained with a two layer nonlinear primitive equation ocean model and a coupled free drift ice model in the absence of winds the ice equilibrates rapidly to the ocean eddy velocity resulting in radial ice motion the ocean sea surface slope is found to provide an important force in the ice momentum balance in no wind simulations with along ice edge 10 m s winds the ice responds largely to the wind and to a lesser extent to the ocean eddy under ice the ocean eddy can be rapidly eroded by wind driven ice motion cyclones anticyclones are rapidly destroyed by along ice edge winds with ice on the left right

global radar units on venus derived from statistical analysis of pioneer venus orbiter radar data unsupervised linear discriminant cluster analysis of pioneer venus reflectivity and rms slope data has produced a classification of 15 radar units examination of four hypsometric provinces previously established for venus has been used to show that although the highland 6053 to 6055 5 km and mountainous greater than 6055 5 km provinces are distinctly different in their radar unit compositions from each other and from the lowlands less than 6051 km and rolling plains 6051 to 6053 km provinces the lowlands and rolling plains provinces are very nearly the same in their radar properties this observation indicates that hypsometry alone is not a reliable criterion for quantitative examination of the surface geology on venus a classification unit encompassment scheme has been developed that shows the presence of three distinct trends two toward elevations higher than the planetary mean elevation and the other toward elevations lower than the mean venera lander data and earth based radar images have been used to infer that seven units within the two higher elevation unit encompassment trends represent materials of mostly basaltic composition that differ only in their surface morphologies the physical characteristics of these materials indicate that they form terrains ranging from banded through rift valley to relatively flat and that the materials are composed of bedrock and soil in variable ratios three other radar classification units appear to be morphologically transitional forms between units of these two higher elevation unit encompassment trends the five remaining units are associated with the lower elevation unit encompassment trend their geologic significance cannot be determined with any certainty with the existing pioneer venus radar data the radar units that correspond to those of an existing radar unit map produced by supervised analysis display similar areal distributions on venus however our radar unit map shows more detail and is relatively unbiased in terms of unit definition this global radar classification image of the venusian surface provides a working data base from which more exacting geologic interpretations can be made when higherresolution imagery becomes available

mechanisms for lithospheric heat transport on venus implications for tectonic style and volcanism the tectonic and volcanic characteristics of the surface of venus are poorly known but these characteristics must be closely related to the mechanism by which venus rids itself of internal heat on the other solid planets and satellites of the solar system lithospheric heat transport is dominated by one of three mechanisms 1 plate recycling 2 lithospheric conduction and 3 hot spot volcanism we evaluate each mechanism as a candidate for the dominant mode of lithospheric heat transfer on venus and we explore the implications of each mechanism for the interpretation of venus surface features despite claims made to the contrary in the literature plate recycling on venus cannot be excluded on the basis of either theoretical arguments or present observations on topography and radar backscatter landforms resulting from plate convergence and divergence on venus would differ substantially from those on the earth because of the high surface temperature and the absence of oceans on venus the lack of free or hydrated water in subducted material the possibility that subduction would more commonly be accompanied by lithospheric delamination and the rapid spreading rates that would be required if plate recycling removes a significant fraction of the internal heat if plate recycling occurs on venus the rolling plains and lowlands provinces would be approximate analogs to terrestrial ocean basins in terms of age igneous rock type and formative process highlands on venus would be roughly analogous to terrestrial continents the hypothesis that lithospheric conduction dominates shallow heat transfer on venus leads to the prediction that the lithosphere is thin if venus has a global heat loss per mass equal to that for earth then temperatures marking the base of the thermal lithosphere on earth would be reached on venus at an average depth of about 40 km unless the mantle convective planform can maintain lithospheric regions of persistently low heat flow or unless the present atmospheric greenhouse on venus is geologically recent then such a lithospheric thickness leads to the conclusion that the topographic features contributing to the 13 km of relief on the planet must be geologically young the hypothesis that hot spot volcanism dominates lithospheric heat transfer on venus leads to the prediction that the surface must be covered with numerous active volcanic sources in particular if a typical venus hot spot has a volcanic flux equal to the average flux for the hawaiian hot spot for the last 40 m y then 104 such hot spots are necessary to remove the venus internal heat by volcanism such a number would produce enough volcanic material to resurface the entire planet to a depth of 1 km every 2 m y few areas of the planet would escape resurfacing for geologically long periods of time we find that none of the mechanisms for lithospheric heat transfer on venus can be excluded as unimportant at present it is likely that as on earth a combination of mechanisms operates on venus the strongest conclusion to emerge from this evaluation is that most of the major topographic features and probably many of the surface geological units on venus are young by comparison with the surfaces of the smaller terrestrial planets

interannual variability of monthly southern ocean sea ice distributions the region of the southern ocean exhibiting interannual variability in monthly averaged sea ice distributions has been mapped and analyzed using data from the nimbus 5 electrically scanning microwave radiometer esmr and the nimbus 7 scanning multichannel microwave radiometer smmr over the 13 year record from the two instruments 1973 1976 and late 1978 through mid 1987 interannual variability is particularly high for the early summer month of december when 10 106 km2 of the ocean had ice covered conditions in some years and ice free conditions in other years this area of december variability is almost three times the ocean area consistently having ice covered conditions in the 13 esmr smmr decembers in contrast in mid winter the area of consistent ice coverage far exceeds the area of variability which in spite of the much greater ice coverage overall is not as large as the area of variability in december the mid winter variability is confined to 1 a ring of variable width around the edge of the ice pack and 2 the location of the 1974 1976 weddell polynya separation of the results to the esmr and smmr time periods shows that ice in the west indian ocean and the ross sea tended to be more expansive in the earlier esmr years than in the later smmr years but that ice in the weddell sea tended to be less expansive in the esmr years in the bellingshausen and amundsen seas the esmr years tended to have less summer ice than the smmr years but not less winter ice the images and plots provide a succinct summary of the range of spatial distributions of southern ocean sea ice during the esmr and smmr time periods they can hence be used as a convenient base for comparisons with future sea ice distributions in the effort to identify occurrences of climate change

atmospheric boundary layer structure and drag coefficients over sea ice this paper estimates the air sea drag coefficient for first year ice from recent aircraft measurements and reconciles the range of observed drag coefficients 103cd 1 2 3 7 referenced to 10 m for all sea ice types based on ice roughness and seasonal meteorology for the purpose of sea ice modeling it is necessary to define an effective drag coefficient which relates regional stress to regional wind because sea ice is heterogeneous on scales less than 20 km regional stress is influenced by the distribution of surface roughness the buoyancy flux from quasi periodic leads and external atmospheric conditions principally the inversion height 103cd is 1 3 1 5 for smooth ice but is much greater for nonflat surfaces for wind speeds greater than 5 m s and air temperatures below freezing the effective 103cd is 2 5 3 0 for nearly continuous pack ice such as first year ice in seasonal ice zones and central arctic basin the range of values of 103cd is 3 0 3 7 for unstable boundary layers typical of off ice winds in the marginal ice zone miz or even greater if the ice has been broken by a recent storm cd values at the lower end of these ranges are associated with low inversion heights these coefficients are confirmed by 103cd of 2 9 2 5 and 3 1 for first year sea ice calculated from gust probe data collected by the noaa p 3 aircraft interior to the inner miz in the bering sea during the marginal ice zone experiment mizex west in february 1983 and 103cd of 2 6 for the arctic calculated from arctic ice dynamics joint experiment aidjex aircraft data for february 1976 the effective drag coefficient with the presence of even a small concentration of sea ice is greater than the oceanic value as shown by a 103cd of 2 2 calculated from noaa p 3 gust probe data over a 40 km track of 0 4 ice concentration in the outer miz of the greenland sea in june 1984 during mizex 84 the relation of surface wind and stress to the geostrophic wind for shallow inversion heights typical of high latitudes is reviewed with a turbulent closure atmospheric boundary layer model the winter arctic is typified by low inversions 100 m low geostrophic drag coefficients and large geostrophic surface wind turning angles with low functional dependence on surface roughness seasonal ice zones are typified by a more modest influence of the inversion on boundary layer characteristics

environmental correlates of arctic ice edge noise temporal variations of low frequency broadband ambient noise measured in early summer under drifting ice floes of the marginal ice zone miz are cross correlated with local environmental forces and ice field descriptors surface gravity wave forcing is the primary correlate of the noise its interaction with ice floes generates sound most likely via flexural floe failure and unloading motion within a few kilometers of the ice edge ice concentration is also well correlated with the noise most likely parametrically that is as ice concentration increases so does the density of potential sound sources in the ice field ice stress ice moment and wind stress magnitude while highly correlated with low frequency noise in the fully ice covered arctic are poor correlates in the miz lateral melt rate as a surrogate for thermally induced ice stress is also poorly correlated with low frequency miz noise when surface wave forcing is weak about 1 2 the time in this experiment episodes of high noise a

synoptic and mesoscale atmospheric features over the ice covered portion of the fram strait in spring data obtained during the coordinated eastern arctic experiment cearex from march 31 to april 20 1989 from two ice camps in the pack ice region in the fram strait have been analyzed the data show that the total period can be divided into two periods or regimes divided by a transition period the first period was a radiative type characterized by very low surface temperatures and low wind speeds fairly regular oscillations between southerly and northerly winds were caused by small scale disturbances in the surface pressure field associated with upper level waves of large amplitude during a transition period toward an advective weather type on april 11 a sharp frontal zone passed both ice camps the front was associated with a small scale low which had formed over the ice on the shallow but intense baroclinic zone along the northeastern greenland coast mesoscale vortices of this type may if numerous enough affect the horizontal transfer of heat from lower latitudes toward arctic regions as well as the ice drift through the fram strait

venus global radar reflectivity and correlations with elevation the global distribution of the reflectivity of the surface of venus as determined by the pioneer venus orbital radar instrument has been analyzed in a geological context and statistically correlated with elevation in addition a comparison between the reflectivity and rms slope roughness correlations with elevation permits radar geologic topographic zones to be identified the radar reflectivity at normal incidence and at a wavelength of 17 cm 1 76 ghz is a model dependent measure of the bulk dielectric constant of surfaces dominated by dry rocks and soils and depends on surface material properties such as porosity and conductivity only the quasi specular component of the radar echo was used in determining the reflectivity values analyzed in this study and for very rough surfaces the absolute magnitude of may be underestimated by 10 15 empirically derived relationships between and bulk density are used to interpret geologically the distribution the global mean of 0 13 is significantly greater than the average lunar and typical martian values of 0 07 suggesting the absence of a continuous soil mantle on venus the distribution is well described by a two stage gaussian distribution with modes at 0 11 and 0 14 the close proximity of these modes suggests that there is no fundamental dichotomy of surfaces on venus insofar as their properties in contrast with roughness less than 15 of venus has values low enough to indicate a major soil component on the surface approximately 27 of the surface is dominated by low porosity materials such as bedrock and less than 15 is enriched in high dielectrics the rest of the surface 43 is most simply envisioned as partially mantled bedrock perhaps an extension of the types of terrain viewed by the venera 10 and 13 landers the most plausible model for the highest and thus highest materials requires enrichment in ti and fe e g minerals such as rutile ilmenite and magnetite high titanium basalts such as those found on the moon would produce the required enrichment as would pyrites since surface geochemical measurements demonstrate that there are basalts in the venusian plains a model in which high titanium basalts are exposed at the highest elevations maxwell theia atla ovda is favored possible weathering of ilmenite in such basalts to produce rutile could explain the high materials in less elevated regions when correlated with elevation exhibits a complex nonmonotonic trend in which both decreases and increases are observed a major decrease in of 0 02 km 1 in the upper plains contrasts with the almost 1 rms km 1 increase in surface roughness over the same interval and may be an expression of increased soil production perhaps due to enhanced breakdown of silicates into carbonates in the lower highlands alternately the decrease could be due to increased centimeter scale roughening perhaps caused by the increase in regional slope in the highlands a major increase in 0 05 km 1 in the middle highlands correlates with a rapid rise in rms slope unlike rms slope however there is no overall correlation of with either elevation or regional slope suggesting that it may be a more locally controlled parameter hierarchical clustering analysis of the roughness and regional slope properties of venus demonstrates that distinct subregions are best defined on the basis of topographic zones in which the radar parameters follow well defined trends the lowland plains are extremely smooth at scales from centimeters to 100 km in general no single radar parameter e g serves to subdivide the surface into distinct geologic regions but taken together the radar parameters can be statistically correlated to define meaningful radar geologic units such units appear to correlate with the kinds of surfaces that can be seen on venus at kilometer resolution