are the viking lander sites representative of the surface of mars abstract global remote sensing observations of mars are compared with remote sensing observations of the two viking lander site regions and with orbiter and lander imaging of the sites the lander sites do not fit most of the global trends of remote sensing data the presence of a duricrust in the top meter of the surface is inferred for most regions of high thermal inertia although the duricrust is thinner at the lander sites than elsewhere regions of low thermal inertia are covered by greater than several centimeters of unconsolidated dust a thin microns thick layer of bright dust appears at the surface at the lander sites and these locations may be regions of incipient formation of low thermal inertia the lander sites are intermediate in structure between classical bright and dark regions and are distinctive from most of the rest of the planet

present day tilting of the great lakes region based on water level gauges by using monthly mean water levels at 55 sites around the great lakes a regional model of vertical crustal motion was computed for the region in comparison with previous similar studies over the great lakes 15 additional gauge sites data from all seasons instead of the 4 summer months and 8 additional years of data were used all monthly water levels available between 1860 and 2000 as published by the u s national ocean survey and the canadian hydrographic service were used for each lake basin the vertical velocities of the gauge sites relative to each other were simultaneously computed using the least squares adjustment technique our algorithm solves for and removes a monthly bias common to all sites as well as site specific biases it also properly weighs the input water levels resulting in a realistic estimation of the uncertainties in tilting parameters the relative velocities obtained for each lake were then combined to obtain relative velocities over the entire great lakes region finally the gradient of the relative rates for the regional model was found to agree best with the ice 3g global isostatic model of tushingham and peltier whereas the ice 4g gradients were too small around the great lakes

an analysis of the late glacial lake levels within the western lake superior basin based on digital elevation models abstract this study establishes a detailed lake level history for the lake superior basin by mapping strandlines from 10 m and 3 m digital elevation models there are 24 levels above the mid holocene nipissing level and elevations increase along a direction of 23 1 due to post glacial rebound the highest level the epi duluth is steeper than subsequent levels and may pre date the lake view ice advance into the western lake superior basin at the end of the younger dryas stade the most prominent level is the duluth ca 10 800 cal yr bp ice retreat exposed successively lower outlets routing overflow to the lake michigan and huron basins by 10 600 cal yr bp lake levels in the western superior basin had dropped almost 200 m this transformative period is complicated by multiple basin wide events the influx of glacial lake agassiz overflow the creation of three sub aqueous moraines and a red to gray color transition in basin sediments a later drawdown event has been hypothesized to have initiated the 9300 cal yr bp cooling event but this flood was much smaller than estimated previously if freshwater triggered the 9300 cal yr bp event the source of the water must have been lake agassiz not lake superior

lava flow topographic measurements for radar data interpretation surface topography is of great importance in radar backscattering but the quantitative interpretation of data collected in the field is still a difficult problem we present topographic profiles at 25 cm and 5 cm horizontal resolution for three sites along a lava flow on kilauea volcano and use these data to illustrate techniques for surface roughness analysis height and slope distributions and the height autocorrelation function are evaluated as a function of varying lowpass filter wavelength for the 25 cm data rms slopes are found to increase rapidly with decreasing topographic scale and are typically much higher than those found by modeling of magellan altimeter data for venus a more robust description of the surface roughness appears to be the ratio of rms height to surface height correlation length for all three sites this parameter falls within the range of values typically found from model fits to magellan altimeter waveforms the 5 cm profile data are used to estimate the effect of small scale roughness on quasi specular scattering

a sault outlet referenced mid to late holocene paleohydrograph for lake superior constructed from strandplains of beach ridges the most detailed lake superior paleohydrograph relative to the current outlet near sault ste marie ontario michigan was constructed from four strandplains of beach ridges this provides a history of water level glacial isostatic adjustment gia and the active outlet prior to monitoring and regulation four relative paleohydrographs that are offset and subparallel owing to differences in gia were produced from 321 basal foreshore elevations and 56 optically stimulated luminescence ages subtracting modeled elevations in defined millennial lake phases between relative paleohydrographs and similarity between an inferred sault ste marie hereinafter sault paleohydrograph and data near the zero isobase corroborates rates of gia derived from water level gauges a change in trend in the sault paleohydrograph is related to the final separation of lake superior from lakes michigan and huron and is the youngest age reported at 1060 100 years a near horizontal trend in the sault paleohydrograph for the past millennium has an intercept that is close to the historical average for lake superior a consistently linear trend from about 2 to 1 ka suggests a relatively stable outlet similar to the past millennium but a decreasing trend from 3 to 1 ka suggests an outlet other than the sault although intercept data beyond the last millennium are similar in elevation to the reported bedrock sill near chicago hansel et al 1985 we argue that the port huron outlet was the active outlet during this time and the inferred paleohydrograph of baedke and thompson 2000 requires reevaluation resume le paleo hydrogramme le plus detaille pour le lac superieur par rapport a l exutoire actuel pres de sault ste marie ontario michigan a ete construit apartir de quatre anciennes plaines intertidales de cretes de plage ces donnees fournissent un historique du niveau de l eau de l ajustement isostatique glaciaire et d un exutoire actif avant le suivi et la regularisation quatre paleo hydrogrammes relatifs decales et subparalleles en raison de differences d ajustement isostatique glaciaire ont ete produits a partir de 321 elevations de base de l estran et 56 ges determinees par luminescence optique stimulee la soustraction des elevations modelisees dans des phases de lac millenaires definies entre des paleo hydrogrammes relatifs et la similitude entre un paleo hydrogramme infere pour le sault ste marie sault ainsi que les donnees aproximite de l isobase zero corroborent les taux d ajustement isostatique glaciaire derives de jauges de niveau d eau un changement de tendance dans le paleo hydrogramme du sault est reliee a la separation finale du lac superieur du lac michigan huron et constitue le plus jeune ge rapporte soit 1060 100 ans une tendance presque horizontale dans le paleo hydrogramme du sault pour le dernier millenium a un intercepte qui est pres de la moyenne historique pour le lac superieur une tendance lineaire constante depuis 2 a 1 ka suggere un exutoire relativement stable semblable acelui du dernier millenaire mais une tendance decroissante depuis 3 a 1 ka suggere un exutoire autre que celui du sault bien que les donnees d intercepte au deladu dernier millenaire aient une elevation semblable a celle rapportee pour le seuil de socle rocheux a proximite de chicago hansel et al 1985 nous proposons que l exutoire port huron constituait l exutoire actif acette epoque et que le paleo hydrogramme infere de baedke et thompson 2002 demande a etre reevalue traduit par la redaction

radiocarbon dating of basal peats supports separation of lake superior from lakes michigan huron about 1250 years ago abstract lake superior represents an important component of the aquatic ecosystem in north america along its south shore ongoing lake level rise accelerated erosion and wetland loss are major environmental concerns to coastal communities a better prediction of the future of this shore requires placing the instrumental lake level records in a geological context however our knowledge of the late holocene history of the world s largest freshwater body remains fragmentary here we present a sedimentary record of late holocene relative lake level changes by dating transgressive basal peats resting directly on a sandy substrate along a bathymetric gradient in bark bay slough wisconsin our record shows a moderate lake level rise at 1 4 0 2 mm yr from about 2200 to 1250 cal yr bp as a result of relatively slow differential uplift of bark bay relative to the controlling outlet at port huron the rise accelerated to 2 3 0 2 mm yr at about 1250 cal yr bp when sault ste marie emerged as the controlling outlet thereby separating superior from lakes michigan huron and giving rise to the modern hydrographic regime of the upper great lakes the timing of this event in our record is about 1000 yr later than that estimated in most previous studies but our data complement and confirm the younger age of lake separation inferred using a different methodology our results not only provide pertinent information for hydrological regulation navigation operation and infrastructural design in the upper great lakes but also provide insight into freshwater wetland succession on flooded coasts

beach ridge development in lake michigan shoreline behavior in response to quasi periodic lake level events abstract strandplains of arcuate beach ridges are common in coastal embayments in parts of the great lakes similarities in beach ridge development and geomorphology are recognizable in many of the embayments in the lake michigan basin despite differences in size and shape available sediment type and supply predepositional slope and topography and hydrographic regime between the embayments these similarities are primarily a product of three scales of quasiperiodic lake level variation ranging in time from 30 to 600 years and in water level change from 0 5 to 3 7 m the interaction of these three lake level variations can be represented on a curray 1964 diagram rate of water level change versus rate of sediment supply the position of any shoreline on the diagram and the type of behavior the shoreline is experiencing is a product of the interaction of the three variations two large strandplains of late holocene beach ridges occur at opposite ends of lake michigan toleston beach and thompson embayment the two areas exhibit similar patterns of beach ridge development for the past 2600 calendar years that is both areas form beach ridges about every 30 years groups of 4 to 6 beach ridges reflect a longer term lake level variation of about 150 years only during the largest variation of about 600 years in duration do the two areas differ the rise to the 1700 cal yr b p high caused the erosion of beach ridges back to 2800 cal yrs b p in northern lake michigan in southern lake michigan no erosion occurred during this lake level high differences in shoreline development between the two areas are related to the rate of sediment supply to the shorelines as the sediment sink for the southern half of lake michigan the southern strandplain received a greater sediment flux than the northern strandplain during the latter part of the late holocene and produced a continuous record of beach ridge development

bell regio venus integration of remote sensing data and terrestrial analogs for geologic analysis the geology and surface morphology of bell regio 18 42 n 32 58 e are investigated using a combination of magellan venera and analogous terrestrial data the properties of surface units are compared to either direct terrestrial analog measurements or to the behaviors predicted by theoretical models five major volcanic sources are identified from geologic mapping tepev mons nefertiti corona a large shield volcano east of tepev and two small edifices southeast of tepev the volcano api mons lies northeast of the main bell uplift the oldest volcanic units are associated with an extensive low shield volcano east of tepev mons and a small edifice southeast of tepev the annular flow apron of tepev mons formed next with volcanism at a second small edifice on the southeast flank of tepev mons producing the youngest flow units comparisons between magellan data terrrestrial radar images and field topography profiles suggest that only three units resemble terrestrial a a flows the remainder are consistent with smoother pahoehoe type surfaces this suggests that most of the flow units were erupted at relatively low volume effusion rates 100 m3 s over long periods of time or had very low viscosities one flow unit has a knobby texture which resembles large tumuli or ridge structures much of the tectonic deformation in the area is in the form of fractures circumferential to the edifices and isolated blocks of tessera terrain there are no rift zones such as those which occur at beta regio atla regio or western eistla regio tepev mons is characterized by very steep slopes up to 40 along the east flank a relatively flat summit and two large 11 and 31 km calderas though covered in places by high dielectric material the tepev mons summit area is relatively smooth with the exception of annular rough deposits which ring the two calderas these calderas are quite shallow on the order of a few hundred meters at most with no discernible difference in radius between individual altimeter footprints inside and outside the larger eastern feature magellan and venera data suggest that the eastern caldera is covered by a layer of unconsolidated material ejecta from miriam crater has produced a halo with a dielectric constant of 6 7 surrounding nefertiti corona and potanina crater ejecta is the likely source material for radar dark wind streaks south of tepev mons a low dielectric e 2 3 triangular region on the south flank of tepev mons may be a pyroclastic or crater ejecta deposit which has been spread westward by the wind this region has undergone a wide variety of volcanic processes with a major shift in eruptive style from the older low relief eastern volcanic center to the steep slopes and large summit calderas characteristic of tepev mons and the two smaller edifices

mars dual polarization radar observations with extended coverage abstract thirteen centimeter wavelength radar observations of mars made in 1982 at arecibo observatory yield accurate measurements of the full backscatter spectrum in two orthogonal polarizations the data which were obtained for several widely separated subradar longitudes at 24 n latitude provide the first global view of the distribution of small scale surface roughness on mars the diffuse component of the echo exhibits strong spatial variations areas of maximum depolarization correlate well with volcanic regions tharsis and elysium while the heavily cratered upland terrain yields relatively low depolarization parts of tharsis give near complete depolarization polaziation ratio c 1 when viewed at oblique angles of incidence northern martian plains regions tharsis elysium and amazonis may comprise the most extensive area of severe decimeter scale surface roughness in the inner solar system on the average the northern martian tropics yield higher diffuse radar cross sections d 0 05 0 12 and a higher of degree disk integrated depolarization c 0 1 0 4 than is found for the moon mercury and venus comparisons between the moon and mars using radar data ground truth and simple scattering models suggest that mars possesses a relatively high average coverage by decimeter scale rocks also discussed are several of the more interesting quasispecular scattering results the most unsual of which were obtained over the olympus mons aureole region

interpretation of planetary radar observations the relationship between actual and inferred slope distributions we examined the distribution of surface slopes of a variety of terrestrial surfaces by field measurement representing surfaces formed by a wide range of processes and compared the results to planetary radar data slope distributions of the measured surfaces differed considerably from the distributions assumed by accepted models of radar scattering the rms slope values for the terrestrial surfaces ranged from 0 to 16 5 compared to a range of rms slope values of 1 to about 10 for planetary surfaces as inferred from radar observations while the great majority of planetary surfaces observed by radar have rms slope estimates in the lower end of this range 5 nearly all of the terrestrial surfaces we measured have rms slope values greater than 5 we also used hagfors model of radar scattering to predict the return that would be expected from surfaces where two discrete surface types were present within the radar field of view and found that the shapes of the resulting slope distributions differed from those predicted by the hagfors model for homogeneous surfaces additionally the resulting best fit rms slope was a nonlinear combination of those of the pure surfaces emphasizing the smoother surface together these results suggest that current methods of determining surface roughness from radar may significantly underestimate the roughness of planetary surfaces and that the derived rms slope can best be used as a qualitative guide to the physical interpretation of actual surface properties

beach ridge development and lake level variation in southern lake michigan abstract the most accurate source of information on lake level fluctuations in the great lakes is the historical record from lake level gauges although it can be semiquantitatively extended back into the late 1700 s the historical record is too short to recognize long term patterns of lake level behavior to extend the historical record information must be obtained from the great lakes geologic record such information includes the elevation and age of geomorphic features and stratigraphic sequences one of the longest geologic records of late holocene lake level variation is preserved in a beach ridge complex along the southern shore of lake michigan called the toleston beach this strandplain contains over 150 beach ridges that arc across northwestern indiana and fan out into northeastern illinois each ridge was formed during the fall from a high lake level and the elevation of the foreshore deposits in each ridge provides information on the upper physical limit of lake level over the past 4000 years three scales of quasi periodic lake level variation were determined by radiocarbon dating basal peats of wetlands between the ridges and by measuring the elevation of foreshore swash deposits within ridges these three scales are 1 a short term and small scale fluctuation of 25 to 35 years with a range of about 0 5 to 0 6 m 2 an intermediate term and meso scale fluctuation of 140 to 160 years and a range of about 0 8 to 0 9 m and 3 a long term and large scale fluctuation of 500 to 600 years and a range of 1 8 to 3 7 m the short term and intermediate term fluctuations are reflected in the historical record an increase in the rate of shoreline progradation from east to west across indiana s shoreline causes differential preservation of the lake level fluctuations that is groups of four to six ridges in the western part of the strandplain that formed in response to the small scale fluctuations combine eastward into single ridges and groups of ridges representing the meso scale fluctuations the large scale fluctuations produced the most dramatic response in the western part of the toleston beach here following each high stand individual spits prograded southward off of a bedrock headland the successive spit extensions created several small lakes landward of the spits and started the 20 km eastward stream mouth deflection of the grand calumet river across indiana s western lakeshore

strand plain evidence for late holocene lake level variations in lake michigan lake level is a primary control on shoreline behavior in lake michigan the historical record from lake level gauges is the most accurate source of information on past lake levels but the short duration of the record does not permit the recognition of long term patterns of lake level change longer than a decade or two to extend the record of lake level change the internal architecture and timing of development of five strand plains of late holocene beach ridges along the lake michigan coastline were studied relative lake level curves for each site were constructed by determining the elevation of foreshore swash zone sediments in the beach ridges and by dating basal wetland sediments in the swales between ridges these curves detect long term 30 yr lake level variations and differential isostatic adjustments over the past 4700 yr at a greater resolution than achieved by other studies the average timing of beach ridge development for all sites is between 29 and 38 yr ridge this correspondence occurs in spite of the embayments containing the strand plains being different in size orientation hydrographic regime and available sediment type and caliber if not coincidental all sites responded to a lake level fluctuation of a little more than three decades in duration and a range of 0 5 to 0 6 m most pronounced in the relative lake level curves is a fluctuation of 120 180 yr in duration this 150 yr variation is defined by groups of four to six ridges that show a rise and fall in foreshore elevations of 0 5 to 1 5 m within the group the 150 yr variation can be correlated between sites in the lake michigan basin the 30 and 150 yr fluctuations are superimposed on a long term loss of water to the lake michigan basin and differential rates of isostatic adjustment

radar images of mars full disk images of mars have been obtained with the use of the very large array vla to map the radar reflected flux density the transmitter system was the 70 m antenna of the deep space network at goldstone california the surface of mars was illuminated with continuous wave radiation at a wavelength of 3 5 cm the reflected energy was mapped in individual 12 minute snapshots with the vla in its largest configuration fringe spacings as small as 67 km were obtained the images reveal near surface features including a region in the tharsis volcano area over 2000 km in east west extent that displayed no echo to the very low level of the radar system noise the feature called stealth is interpreted as a deposit of dust or ash with a density less than about 0 5 gram per cubic centimeter and free of rocks larger than 1 cm across the deposit must be several meters thick and may be much deeper the strongest reflecting geological feature was the south polar ice cap which was reduced in size to the residual south polar ice cap at the season of observation the cap image is interpreted as arising from nearly pure co 2 or h 2o ice with a small amount of martian dust less than 2 percent by volume and a depth greater than 2 to 5 m only one anomalous reflecting feature was identified outside of the tharsis region although the elysium region was poorly sampled in this experiment and the north pole was not visible from earth

global methane emission through mud volcanoes and its past and present impact on the earth s climate a comment the role of mud volcanoes mvs as a source of methane ch4 flux to the atmosphere and the ocean has been increasingly recognised in the last several years milkov 2000 dimitrov 2002 2003 etiope and klusman 2002 kopf 2002 2003 milkov et al 2003 etiope and milkov 2004 in one of the most recent papers kopf 2003 claims to report a reliable estimate of the global ch4 emission from mvs however the significance and usefulness of the estimate presented by kopf 2003 are rather poor the used dataset is smaller than in previous studies although the author makes a reverse claim and some previously published works are misquoted and misinterpreted numerous arithmetic mistakes made during simple calculations and data manipulations lead to confusing results and conclusions in this comment we highlight some of the most significant problems with the estimates published by kopf 2003

selection of the mars pathfinder landing site the mars pathfinder spacecraft will land on a depositional fan near the mouth of the catastrophic outflow channel ares vallis 19 5 n 32 8 w this site offers the prospect of analyzing a variety of rock types from the ancient cratered highlands intermediate age ridged plains and reworked channel deposits analyses of these rocks by pathfinder instruments will enable first order scientific questions to be addressed such as differentiation of the crust the development of weathering products and the nature of the early environment as well as their subsequent evolution on mars constraints imposed by 1 spacecraft and rover designs which are robust 2 entry descent and landing 3 scientific potential at various sites and 4 safety were important considerations in site selection engineering constraints require a 70 km by 200 km smooth flat low slopes area located between 10 and 20 n that is below 0 km elevation with average radar reflectivity little dust and moderate rock abundance three regions on mars are between 10 and 20 n and below 0 km elevation chryse amazonis and isidis elysium science considerations favor sites at the mouths of outflow channels grab bag sites offer an assay of rock types on mars highland sites early crustal differentiation and climate and sites covered with dark unoxidized material sites are considered safe if they are clearly below 0 km elevation appear acceptably free of hazards in high resolution 50 m pixel viking orbiter images and have acceptable reflectivity and roughness at radar wavelengths thermal inertia rock abundance red to violet ratio and albedo recent 3 5 cm wavelength radar observations were used to verify elevation reflectivity and roughness within the landing ellipses three sites meet all of these criteria ares vallis tritonis lacus and isidis although isidis appears to be safer than tritonis and ares the greater scientific potential at ares vallis resulted in its selection comparisons of the grand coulee channel and the depositional ephrata fan of the channeled scabland in eastern washington with ares vallis and its depositional fan also suggest the ares vallis landing site is safe and scientifically interesting

lava flow surface roughness and depolarized radar scattering surface roughness has a strong controlling influence on radar scattering and other types of remote sensing observations we compare field measurements of surface topography and dielectric constant for a range of lava flow textures to aircraft multipolarization radar observations at 5 7 24 and 68 cm c l and p band wavelengths the roughness is found to vary with scale in a self affine fractal manner for scale lengths between 25 cm the smallest horizontal step size and 3 5 m this result is used to demonstrate that a two component surface description consisting of the fractal dimension and rms height or slope at some reference scale can resolve some of the ambiguities in previous efforts to quantify roughness at all three radar wavelengths the hv backscatter cross section is found to vary in an approximately exponential fashion with the rms height or allan deviation at some reference scale up to a saturation point where the surface appears entirely diffusely scattering to the radar based on these observations we use a parameter defined as the ratio of rms height to the particular scale of measurement backscatter values at 24 cm wavelength and the topographic profile data were used to derive expressions which link the hv radar cross section to or to the analogous wavelength scale rms slope these equations provide a reasonable fit to 24 and 68 cm echoes and for rough surfaces at 5 7 cm but yield poor results for 5 7 cm echoes on smooth terrain we conclude that the roughness at the two larger scales is well described by a single fractal dimension and rms height but that texture at very small scales is characterized by different statistics this inference is supported by analysis of 5 cm horizontal spacing topographic profiles the relationships defined here allow determination of the surface rms height or slope at the scale of the radar wavelength given radar data at additional wavelengths a more complete view of the statistical properties of the surface can be developed such techniques may be useful in analyses of synthetic aperture radar images for terrestrial volcanic areas magellan data for venus and other planetary radar observations

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

widespread drought episodes in the western great lakes region during the past 2000 years geographic extent and potential mechanisms we compared high resolution reconstructions of peatland water table depth at two raised bogs in the western great lakes region separated by 1000 km the sites included minden bog in southeastern michigan and hole in the bog in north central minnesota our objectives were to 1 determine whether large decadal to multidecadal droughts of the past 2000 yrs were spatially and temporally coherent across the region and 2 assess the underlying mechanisms of widespread droughts in the region we found a strong correlation between bog inferred records of moisture variability in the two regions r 0 53 between 2100 and 600 bp extreme drought events centered on 1850 1800 1650 1000 800 and 700 bp are recorded in both regions many of these drought events were contemporaneous with large droughts already documented at sites far to the west in the great plains and rocky mountains to identify potential modern climate analogues we used empirical orthogonal function eof analysis to reveal spatial modes of variability in drought and precipitation records of north america for the past century the first eofs of annual precipitation and palmer drought severity index pdsi were similar to each other and consistent with a pattern of widespread continental drought correlations between these eofs and annual sea surface temperatures ssts indicate strong relationships to ssts in both the atlantic and pacific basins we hypothesize that widespread droughts between 1000 and 700 bp were related to amplification of a spatial mode of moisture variability associated with an anomalously warm north atlantic a warm mid latitude north pacific and an anomalously cold tropical pacific a more extensive network of hydroclimate records developed using a consistent set of methods and proxies could be used in conjunction with high resolution records of past ssts to test this hypothesis

dual polarization radar observations of mars tharsis and environs abstract observations of the tharsis region of mars with the 12 6 cm radar at arecibo observatory have yielded radar echoes which are highly depolarizes and which are in terms of total echo power dominated by diffuse rather than quasi specular backscattering the observations were made on february 7 8 and 9 1980 and the subradar track extended from 77 to 126 w longitude at 22 n latitude dual polarized reception was employed i e the echo was received in the same sense of circular polarization as transmitted depolarized sense as well as in the opposite polarized sense the disk integrated ratio of depolarized power to polarized power averages 0 37 and the ratio of diffuse power to quasi specular power averages 3 2 the depolarized spectra are dominated by a broad enhancement identified primarily with echoes from the tharsis ridge implying that extensive areas of tharsis are rough on decimeter scales the major tharsis shield volcanoes are candidates for sources of strong depolarization although they alone cannot account for the entire depolarization enhancement

optically stimulated luminescence dating of late holocene raised strandplain sequences adjacent to lakes michigan and superior upper peninsula michigan usa this study evaluates the accuracy of optically stimulated luminescence to date well preserved strandline sequences at manistique thompson bay lake michigan and tahquamenon and grand traverse bays lake superior that span the past 4500 yr the single aliquot regeneration sar method is applied to produce absolute ages for littoral and eolian sediments sar ages are compared against ams and conventional 14 c ages on swale organics modern littoral and eolian sediments yield sar ages b100 yr indicating near if not complete solar resetting of luminescence prior to deposition beach ridges that yield sar ages b2000 yr show general agreement with corresponding 14 c ages on swale organics significant variability in 14 c ages n2000 cal yr b p complicates comparison to sar ages at all sites however a sar age of 4280 f 390 yr uic913 on ridge77 at tahquamenon bay is consistent with regional regression from the high lake level of the nipissing ii phase ca 4500 cal yr b p sar ages indicate a decrease in ridge formation rate after 1500 yr ago likely reflecting separation of lake superior from lakes huron and michigan this study shows that sar is a credible alternative to 14 c methods for dating littoral and eolian landforms in great lakes and other coastal strandplains where 14 c methods prove problematic

mars pathfinder landing site assessment with goldstone delay doppler and cw radar experiments we present the results of 3 5 cm delay doppler and doppler only continuous wave or cw radar experiments to assess three potential mars pathfinder landing sites ares vallis tritonis lacus and northwest nw isidis the regional relief at all of the landing sites is appropriate for a pathfinder landing sequence east west slopes do not exceed 3 at any of the sites we find that ares vallis has a hagfors rms slope of rms 4 8 1 1 as measured by delay doppler radar and rms 6 4 0 6 measured by cw radar these values are similar to or less than the previous measurements of the viking lander 1 region the tritonis lacus landing site is rougher with delay doppler rms 5 6 0 6 while the nw isidis landing site is very smooth both in a regional sense slopes 0 7 and in a hagfors rms slope sense rms 1 8 0 2 reflectivities at all of the sites should be sufficient to allow the radar altimeter on pathfinder to function properly

local time and altitude variation of equatorial thermosphere midnight density maximum mdm san marco drag balance measurements we present the first study of the local time and altitude variation of the mdm the density component of the equatorial midnight pressure bulge an important feature in the nighttime motions of the ionosphere thermosphere system in the equatorial region the neutral density data of the san marco 3 sm3 and san marco 5 sm5 satellites were averaged to obtain 24 hr density variations from april to december in 1971 and 1988 from these variations the mdm amplitude as a function of altitude and local time was obtained at altitudes from 220 to 400 km at the geographic equator we show the first evidence of downward phase propagation of the mdm together with a vertical structure not observed before which may suggest an ionospheric interaction or perhaps a viscous dissipation effect in 1971 the mdm propagates rather gradually from about 350 to 220 km in about two hours in 1988 there appear two regions in which the mdm time shows little change with height with a discontinuous jump in between the two regions the net effect is still a downward displacement of the mdm with local time the results show significant seasonal and solar activity effects during low solar activity periods 1971 the mdm occurs earlier in equinox than in solstice for all altitudes consistent with the seasonal variation of the midnight temperature maximum mtm however with higher solar activity 1988 and at altitudes below 340 km the mdm occurs earlier in solstice than in equinox raising new questions on solar activity effects on the relative phases of the tidal oscillations of the neutral density and the neutral temperature

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