leaf area index estimation of boreal and subarctic forests using vv hh envisat asar data of various swaths this paper demonstrates the potential of dual polarization synthetic aperture radar sar images in the estimation of the leaf area index lai of boreal forests the sar data do not suffer from the low sun elevation and frequent cloud cover which often complicate the use of optical wavelengths for lai retrieval in the area the analysis was based on a large number of environmental satellite envisat advanced synthetic aperture radar asar alternating polarization vertical polarization vv horizontal polarization hh single look complex images covering several test sites boreal and subarctic during summers 2003 2006 the swath range from is1 to is7 was studied in all test sites a linear regression with the vv hh backscattering ratio as the independent variable could typically be used for the estimation of lai all swaths could be used for the estimation but larger incidence angles generally performed better the best results were obtained for swath is6 the swaths could be used also together but better results were obtained using the diverse swaths individually the lai estimation error decreased essentially exponentially with the number of pixels averaged to give one backscattering value the lai estimation accuracy for a set of average quality asar images of swath is6 reached 0 1 when the averaging number of pixels was 33 150 which would correspond to an area of about 2 2 km2 for images with no overlap the spatial lai estimation error decreased with the number of images covering the same area

the history of the major rivers of southern britain during the tertiary the evolution of the drainage system of lowland britain is discussed on the basis of available geological evidence including that from terrestrial sites and that which has more recently become available from offshore exploration of the north sea the english and bristol channels and the irish sea tertiary stratigraphy throws considerable light on landform and river development paleocene destruction of a chalk cover which seems to have been incomplete in western britain was accompanied by basin sedimentation under a tropical climate the major elements the thames solent hampshire proto avon river irish sea river and possibly an early trent river existed almost throughout the cenozoic the influence of atlantic rifting and thermal doming in nw britain appears to have been stronger and more temporally focused than the persistent flexuring that determined and maintained tertiary drainage lines in the se here also the folded mesozoic terrains on the surface contrast with the more dominant block faulted relief of the palaeozoic oldlands the rivers of the se can be shown to have extended or reduced their lengths in response to relative sea level change and gentle warping drainage antecedence the destruction of the solent system and the breaching of the english channel are also evident by contrast the major river systems of the west are now entirely submerged long term stability of the drainage pattern reflects a persistent tectonic regime in the south with a subdued low relief landscape having a weathered regolith and dense vegetation cover meandering river channels and alluvial styles predominated although channel forms varied according to sediment load slope and discharge variability coarse gravel dominated accumulations are rare and localized chemically stable lithologies dominate the clastic component throughout it is apparent that the deeply incised river valleys seen today are related to high predominantly coarse sediment yields encouraged by substantial rapid climate changes in the pleistocene this emphasizes the significance of mechanical compared with chemical weathering for the rate and nature of landscape dissection and the modifications that have arisen as a result of glaciation frost climate weathering rapidly changing climates and sea levels the stratigraphical evidence here reviewed is at variance with older largely geomorphologically based landform evolution models denudational chronology but gives considerable support to the recent proposals emphasizing the significance of paleocene erosion and enduring low relief landscapes and drainage systems evolving alongside fold development during the paleogene given the depobasin evidence now available postulated fluvially active episodes can and must be linked to contemporaneous deposition some at least of the many controversies involving the identity of erosion surfaces the dating of them using only residual deposits and weathering mantles and the selection of particular tertiary episodes as ones of landscape development can now be resolved

a three dimensional radar backscatter model of forest canopies three dimensional forest backscatter model which takes full account of spatial position of trees in a forest stand is described a forest stand was divided into cells according to arbitrary spatial resolution the cells may include crown trunk and gap components determined by the shape size and position of the trees the forest floor is represented by a layer of ground cells a ray tracing method was used to calculate backscattering components of 1 direct crown backscatter 2 direct backscattering from ground 3 direct backscattering from trunk 4 crown ground scattering and 5 trunk ground scattering both the attenuation and time delay of microwave signals within cells other than gap were also calculated from ray tracing the backscattering mueller matrices of these components within the same range intervals were incoherently added to yield the total backscattering of an image pixel by assuming a zero mean multiplicative gaussian noise for image speckle the high resolution images were aggregated to simulate a sar image with a given spatial resolution and number of independent samples looks a well characterized 150 m x 200 m forest stand in maine usa was used to parameterize the model the simulated radar backscatter coefficients were compared with actual jpl sar data the model gives reasonable prediction of backscattering coefficients averaged over the entire stand with agreement between model and data within 1 35 db for all channels the correlations between simulated images and sar data 10 by 15 pixels were positive and significant at the 0 001 level for all frequencies p l and c bands and polarizations hh hv and vv

the structural development of the wessex basin the mesozoic and cenozoic structures of southern england form part of a system of disturbances which extends across the channel into northern france they are reviewed in the light of published data from south dorset basin development started with permo triassic rifting and is believed to have continued through the jurassic and early cretaceous with intermittent growth on deep seated listric normal faults probably associated with roll over anticlines this regime had ceased by the aptian and the basin passed through a period of relative stability in the late cretaceous followed by tectonic inversion and in the miocene by northwards compressive movement along the former normal faults this partially restored the earlier separative displacement at depth and probably accentuated pre existing roll over anticlines it was expressed in the surficial upper cretaceous palaeogene sequence as monoclinal flexuring the early rifting and the change from overall n s crustal stretching to compression may reflect plate tectonic events in the north atlantic region

a re examination of the evidence for a plio pleistocene marine transgression on the chiltern hills iii deposits a petrological re examination of the deposits that wooldridge and linton used as evidence for a plio pleistocene marine transgression on the chiltern hills indicates that many are fluvial and some have been reworked in a periglacial climate however those from little heath and rothamsted hertfordshire and lane end buckinghamshire are confirmed as marine and plio pleistocene subsidence during the pleistocene is suggested by the northeasterly decline in height of the few truly marine deposits

extension tectonics in the wessex basin southern england the permian to cretaceous tectonic evolution of the wessex basin was controlled by horizontal tensional and vertical isostatic forces within the lithosphere the gross morphologies of its constituent structures were governed by the location of variscan thrust and wrench faults in the upper and middle crust which suffered extensional reactivation in tensional stress fields oriented approximately nw se several episodes of crustal extension can be resolved in early permian early triassic early jurassic and late jurassic early cretaceous times these were characterized by the rapid subsidence of fault bounded basins and commonly by erosion of adjacent upfaulted blocks superimposed upon the fault controlled subsidence dominant during periods of fault quiescence and becoming increasingly important with time a component of regional subsidence is considered to have a thermal origin this suggests that crustal extension was accompanied by some form of not necessarily uniform lithospheric thinning subsidence analyses assuming local airey isostasy give cumulative crustal extension factors of 20 28 beneath the grabens a more reasonable assumption of regional airey compensation indicates basinwide crustal extension of 13 17 which is consistent with birps offshore deep seismic reflection data

the structure and evolution of the wessex basin southern england an example of inversion tectonics abstract the wessex basin of southern england consists of four main sub basins each sub basin is thought to be fundamentally controlled by the normal reactivation of hercynian basement thrust and wrench or transfer faults post hercynian polyphase reactivation of both east west thrust and northwest southeast transfer faults tended to compartmentalise the basement thereby leading to the initiation of discrete permian cretaceous depocentres while rifting was confined to the western portions of the area during the permo triassic easterly migration in the mesozoic allowed the initiation of the weald and channel basins the sub basins represent therefore simple sinistral pull apart basins opening along northwest southeast faults this same fault direction is postulated to have also played a major role in controlling and or modifying the development of european basins in general major pre aptian uplift and erosion is largely attributed to the thermal effects and hence the isostatic uplift of the basin associated with continental rifting of the bay of biscay and the north atlantic margins major inversion and hence basin destruction began in the late cretaceous early tertiary with the uplift of the channel weald and vale of pewsey basins and culminated in the oligocene miocene synchronous with the helvetic phase of alpine deformation wessex basin inversion was facilitated by the thrust reactivation of variscan faults above an intracrustal detachment surface the same surface which allowed upper crustal extension and hence basin initiation in the permo triassic the structural development of the wessex basin both during extension basin formation phase and compression inversion phase was ultimately controlled by the plate motion of africa relative to europe such plate motions successfully predict the observed nw se sinistral motion from the stephanian to the aptian e w sinistral motion during the aptian cenomanian and largely nw se dextral motion from the cenomanian to the present day

aspects of basin inversion in southern britain the wessex basin of southern england a permian to cretaceous extensional basin can be structurally divided into a set of constituent asymmetrical graben bounded by major e w trending zones of en echelon syn depositional normal faults the graben were inverted in late cretaceous and tertiary times by compressive stresses oriented roughly north south inversion structures fall into two related categories regional upwarps overlie earlier graben depocentres and were formed by bulk shortening of the graben fill superimposed upon and geographically delimiting the regional upwarps are roughly east west trending linear zones of en echelon inversion structures these coincide with the earlier graben bounding faults and typically have the form of monoclinal or periclinal flexures each underlain by a partially reversed normal fault the linear reverse fault monocline inversion structures were a relatively inefficient method of basin shortening because upper crustal faults in the region steepen upward markedly reversal of these faults under compression resulted in a shortening discrepancy at shallow depths locally particularly in south dorset this was overcome by bucklefolding and low angle reverse faulting which increased the amount of shortening attainable across the linear inversion structures elsewhere however the shortening discrepancy was accommodated by bulk shortening and regional upwarp of the graben sedimentary fill this occurred preferentially in those graben containing young poorly lithified and therefore weak sediments thus the early cretaceous depocentres of the weald and channel basins were strongly upwarped with axial uplifts of over 1000 m conversely graben having older more lithified sequences suffered little regional upwarp shortening primarily by fault reversal along the linear inversion structures the amount of crustal shortening which accompanied inversion was considerably less than the earlier crustal extension

radar modeling of a boreal forest the authors report on the use of microwave modeling ground truth and synthetic aperture radar sar data to investigate the characteristics of forest stands a mixed coniferous forest stand has been modeled at sar frequencies p l and c bands the extensive measurements of ground truth and canopy geometry parameters were performed in a 200 m square hemlock dominated plot inside a forest hemlock trees in the forest are modeled by characterizing tree trunks branches and needles leaves with randomly oriented lossy dielectric cylinders whose area and orientation distributions are prescribed the distorted born approximation is used to compute the backscatter at p l and c sar frequencies

assessment of scattering mechanism of polarimetric sar signal from mountainous forest areas this study aims to understand the effects of the topographic slope variation on the vegetation backscattering characteristics of polarimetric imaging radar most of the previous studies in modeling microwave backscattering signatures of vegetated area have been carried out over relatively flat areas in order to model vegetation scattering mechanisms of mountainous forests this paper presents an improvement of the radiative transfer model that accounts for the tilted scattering surface beneath a forest canopy an l band polarimetric synthetic aperture radar sar data set acquired by the nasa jet propulsion laboratory airborne sar system was used to test and to assess the vegetation scattering model for a sloping forest area experimental result shows the proposed model to be adequate for evaluating slope induced changes in microwave scattering mechanisms

modeling and observation of the radar polarization signature of forested areas to understand radar measurements of forested areas the authors have developed a model of l band 25 cm microwave scattering from a forest the forest floor is layer of nearly vertical dielectric cylinders representing tree trunks above this layer is a second layer consisting of randomly oriented cylinders which represent branches the authors identify several scattering mechanisms and calculate the corresponding stokes matrices which combine to give the total stokes matrix and resulting polarization signature it is found that this simple model permits accurate prediction of the polarization of the scattered waves and that additional mechanisms including the effects of leaves and twigs are not required for the 25 cm observation of the forests studied the authors present measurements of the polarization signature acquired over a forested area and show comparisons with model calculations

kaolins in gravels and saprolites in north east scotland evidence from stable h and o isotopes for palaeocene miocene deep weathering stable isotope ratios can provide important evidence for estimating groundwater temperatures during the formation of clay minerals in response to chemical weathering of rocks at the landsurface in this paper we investigate weathering kaolins found in buchan ne scotland stable oxygen and hydrogen isotopes for kaolins from weathered clasts in post cretaceous fluvial gravels and from clay rich saprolites developed in dalradian metamorphic and caledonian igneous rocks indicate weathering under warm groundwater temperatures of 23 5 c comparisons with cenozoic palaeotemperatures derived from north sea sediments indicate that weathering took place under humid tropical climates of the palaeocene eocene the 25 m deep weathering profiles in the buchan gravels indicate that these coarse quartzite and flint bearing gravels are older than previously thought and were likely deposited by rivers which also fed thick palaeocene early eocene deep water sand fans in the western north sea basin a later phase of kaolin weathering at lower temperatures of 15 5 c took place in the middle miocene kaolinitic weathering remnants are largely confined to elevations of 100 m in eastern buchan and define a well preserved deeply weathered cenozoic landscape in north east scotland

the effect of topography on radar scattering from vegetated areas the ways in which radar scattering from vegetated areas is affected by the topography of the surface underneath the vegetation are discussed it is shown using a discrete scatterer model that the dominant scattering mechanism may change drastically when the ground surface is tilted relative to the horizontal for a horizontal ground surface for example the total scattering may be dominated by scattering off the tree trunks followed by a reflection off the ground surface for a relatively small tilt in the ground surface the ground trunk interaction term may be replaced by scattering from the branches alone as the dominant scattering mechanism the effect of the topography is more pronounced for scattering by longer wavelengths and the implications on algorithms designed to infer forest woody biomass and soil and vegetation moisture using polarimetric sar data are discussed the effect of the topography on the scattering behavior from forested areas is illustrated with images acquired by the nasa jpl three frequency polarimetric sar over the black forest in germany

forest textural properties from simulated microwave backscatter the influence of spatial resolution abstract to explore the effects of radar scene degradation on the interpretation of forest pattern we used a model to simulate l band 23 cm backscatter vv hv and hh polarizations for a range of resolutions 5 m 10 m 12 1 m 15 m and 24 2 m simulated pixels were parameterized with tree density and height for each tree 3 cm dbh covering a 200 m 150 m area from an immature conifer dominated stand in the northern experimental forest located near howland maine airborne synthetic aperture radar airsar imagery from the stand was used to evaluate the ability of the model to predict single pixel and textural patterns at 12 1 m resolution although the model was unable to accurately predict pixel by pixel responses probably due to registration error textural patterns from the hh polarized image were correlated to the simulated patterns the model s assumption of randomly distributed stems within each pixel was another probable source of error as trees in this stand were aggregated at scales from 1 m to 50 m despite model inadequacies significant pattern was found at all simulated backscatter resolutions for all polarizations for most quadrat sizes 2 but only for smaller quadrat sizes 2 for within pixel structural properties i e stem branch and leaf biomasses stem density and average height this suggests that radar textural information resulting from forest heterogeneity should be available at scales coarser than 24 2 m for forests of similar structure

cenozoic uplift and subsidence in the north atlantic region geological evidence revisited abstract the topographic evolution of the passive margins of the north atlantic during the last 65 myr is the subject of extensive debate due to inherent limitations of the geological geomorphological and geophysical methods used for studies of uplift and subsidence we have compiled a database of sign time and amplitude where possible of topographic changes in the north atlantic region during the cenozoic 65 0 ma our compilation is based on published results from reflection seismic studies aft apatite fission track studies vr vitrinite reflectance trends maximum burial sediment supply studies mass balance calculations and extrapolation of seismic profiles to onshore geomorphological features the integration of about 200 published results reveal a clear pattern of topographic changes in the north atlantic region during the cenozoic 1 the first major phase of cenozoic regional uplift occurred in the late palaeocene early eocene ca 60 50 ma probably related to the break up of the north atlantic between europe and greenland as indicated by the northward propagation of uplift it was preceded by middle palaeocene uplift and over deepening of some basins of the north sea and the surrounding areas 2 a regional increase in subsidence in the offshore marginal areas of norway the northern north sea the northern british isles and west greenland took place in the eocene ca 57 35 ma 3 the oligocene and miocene 35 5 ma were characterized by regional tectonic quiescence with only localised uplift probably related to changes in plate dynamics 4 the second major phase of regional uplift that affected all marginal areas of the north atlantic occurred in the plio pleistocene 5 0 ma its amplitude was enhanced by erosion driven glacio isostatic compensation despite inconclusive evidence this phase is likely to be ongoing at present

upper cretaceous tectonic disruptions in a placid chalk sequence in the anglo paris basin syn upper cretaceous tectonic movements are recognized along tectonic axes including the portsdown south downs axis sandown pericline kingston anticline the fecamp st valery fault blocks and at the bresle valley axis a spatial relationship is described between surface structures chalk sedimentation and deeper level fault systems identified on seismic sections the ouse valley between lewes and newhaven sussex provides the strongest evidence for this relationship in the chalk of the anglo paris basin the sedimentary features that can be related to tectonic lines are local thickness changes anomalous sequences including scour surfaces such as strahan9s hardground rowe9s flintless belt isle of wight the downend slump sequence portsdown these discordant surfaces and slumps relate to particular tectonic 9hinge lines9 whilst other sedimentary features such as the tilleul hardgrounds appear to have formed flat ramps over blocks these two types of tectono sedimentary feature are used to delineate horst like structures from tilted surfaces or half grabens which underlie the surface periclinal fold belts rejuvenation movements along tectonic axes during the cenomanian to campanian are discussed in relation to the currently recognized sequence stratigraphy and sea level curves for the period

an analysis of cotswold topography insights into the landscape response to denudational isostasy we have used the nextmap britain digital terrain model dtm to determine the lithospheric response to erosional unloading and the contribution of tectonics in the form of elastic plate flexure to the cotswold scarp and vale landscape the calculations take into account lithology variations and along strike changes in escarpment retreat we show that flexural rock uplift as a result of erosional unloading varies spatially and may contribute up to 50 of the relief in the cotswold region this is supported by morphometric analysis of concavity and steepness for 66 longitudinal river profiles that drain the scarp and dip slope of the escarpment viscoelastic plate models suggest that the uplift is initially rapid up to 8 m ka 1 and essentially complete within 50 ka these initial rates are compatible with an early post anglian incision rate inferred from the thames terraces the staircase terrace pattern suggests however that there have been a number of denudational isostatic events each associated with a climate cycle finally the analysis reveals an inherited proto landscape that has a subdued relief when compared with the modern dtm such a relief is consistent with an early extension of the river thames through the vale of moreton to the north of the present day cotswold hills

fracture corridors and fault reactivation example from the chalk isle of thanet kent england abstract fracture corridors elongated zones of narrowly spaced highly connected fractures can generate the main fluid flow pathways in natural reservoirs and can be responsible for an early water break through in hydrocarbon reservoirs understanding this fracturing is necessary for reservoir behaviour prediction an outcrop analogue of a chalk fractured reservoir from the isle of thanet in se england is used to understand the development of fracture corridors and to characterize their relationship with faulting and folding we show that fracture corridors are associated with strike slip reactivation on sub seismic faults in a context of polyphase deformation they nucleate on slip patch tips or on areas of stress concentration due to fault plane dip strike irregularities steps or fault intersections fracture corridors generated are oblique to the fault which they initiate on with increasing deformation fractures composing the corridor are sheared and a fault can develop within the fracture corridor the relationship between folding and fracture corridor development in this area is indirect both are localized by a pre existing basement fault that allows stress concentration and reorientation and promotes fault reactivation in the chalk cover this work emphases the importance of the distribution of sub seismic faults in fractured reservoirs as they can control the development of fracture corridors

lithospheric flexure uplift and landscape evolution in south central england the high level river gravels in oxfordshire the northern drift group which range in age from early pleistocene to around 450 ka contain pebbles that were derived from a source area to the north near birmingham the pebbles could not have been transported across the upper triassic and lower jurassic clay outcrops of the midlands unless the region was at or close to sea level the present day cotswold escarpment ranges from 70 to 215 m this uplift must therefore have occurred after deposition of the northern drift group when the drainage of the midlands appears to have shifted from towards the thames basin to the bristol channel area it is concluded that lithospheric flexure due to the removal of 500 km 3 of soft late triassic and early jurassic clays and marls from large areas of the midlands and their re deposition in the celtic deep might account for this late pleistocene uplift uplift in the midlands is the likely explanation for both the tilted approximately 0 3 plateau surface in north oxfordshire and the change in strike of the jurassic beds sw of northamptonshire although some uplift occurred in se england during the early cenozoic and miocene we demonstrate here that there has been significant uplift of the region in the late pleistocene the tilted plateau surface in north oxfordshire may therefore be a relatively young i e post 450 ka feature related to tectonic uplift in the midlands

sir c x sar observations of rain storms abstract the spaceborne imaging radar c x band synthetic aperture radar observations of rain storms are the first multipolarization and multifrequency observations of precipitation from space in addition to numerous often dramatic images of severe weather systems obtained by forming a synthetic aperture in the usual side looking attitude several data takes were performed while the radar antennas were parallel to the ground and the radar beams were pointing at nadir these opportunities coincided with the passage of the shuttle over tropical cyclone odille in the southern indian ocean during the first flight and over typhoon seth in the western pacific during the second flight the resulting observations or more appropriately the resulting measurements demonstrate for the first time the capability of a spaceborne multifrequency multipolarization microwave radar system to quantify precipitation rates to detect hydrometeor phase and to classify rain type

investigation of multifrequency multipolarization radar signatures of rain cells over the ocean using sir c x sar data radar signatures of rain cells are investigated using multifrequency multipolarization synthetic aperture radar sar images acquired from the space shuttle endeavour during the spaceborne imaging radar c x band sar sir c x sar missions in april and october 1994 in sir c x sar images radar signatures of rain cells over the ocean usually consist of irregularly shaped bright and dark patches that strongly depend on radar frequency and polarization the radar signatures of rain cells observed in sir c x sar imagery of the ocean originate from 1 the scattering and attenuation of the microwaves by raindrops and ice particles in the atmosphere and 2 the modification of the sea surface roughness induced by the impact of raindrops and by wind gusts associated with rain cells raindrops impinging on the sea surface generate ring waves which enhance the sea surface roughness but they also generate turbulence in the upper water layer which reduces the sea surface roughness depending on the radar wavelength ocean areas struck by rain can have higher or lower normalized radar cross section nrcs than the surrounding rain free area in ocean areas where heavy rain is impinging on the sea surface the x and c band nrcs is usually enhanced and the l band nrcs is reduced from the phase difference between the horizontally and vertically copolarized signals estimates of the rain rate are obtained the present analysis shows further that the presently used wind speed retrieval algorithms for the scatterometers aboard the ers and adeos satellites may yield biased wind fields if several rain cells lie within a scatterometer resolution cell

flow in the lower continental crust as a mechanism for the quaternary uplift of south east england constraints from the thames terrace record abstract the sequence of terraces of the river thames in south east england has been shown to date from the early pleistocene onwards and to provide an indication of the quaternary uplift history of the region using this evidence supplemented by altitudes of pliocene and early pleistocene marine sediments we have determined the pliocene and quaternary uplift histories of five representative localities clacton colchester and dartford for the lower thames and cookham and reading for the middle thames these uplift histories have been modelled using a physics based technique which calculates the isostatic response involving flow in the lower continental crust induced by cyclic loading at the earth s surface our results suggest that the late pliocene and early pleistocene part of the uplift history of our study region was initiated following the deterioration in climate starting at 3 1 ma which marked the start of upland glaciation elsewhere in europe the later increase in uplift rates in the middle pleistocene followed the start of intensified cyclic loading by very large continental ice sheets during and after oxygen isotope stage ois 22 at 0 87 ma dartford cookham and reading in the interior of south east england are all shown to have begun to uplift quite rapidly at rates of up to 0 1 mm a 1 following the start of forcing at 3 1 ma they have since uplifted by distances which increase gradually westward from 200 to 250 m of which a uniform 70 m has occurred since ois 22 at 0 87 ma in contrast clacton and colchester near the present north sea coastline experienced slow subsidence until the late early pleistocene but have nonetheless uplifted since ois 22 by similar distances to the other sites

a microwave scattering model for layered vegetation a microwave scattering model was developed for layered vegetation based on an iterative solution of the radiative transfer equation up to the second order to account for multiple scattering within the canopy and between the ground and the canopy the model is designed to operate over a wide frequency range for both deciduous and coniferous forest and to account for the branch size distribution leaf orientation distribution and branch orientation distribution for each size the canopy is modeled as a two layered medium above a rough interface the upper layer is the crown containing leaves stems and branches the lower layer is the trunk region modeled as randomly positioned cylinders with a preferred orientation distribution above an irregular soil surface comparisons of results obtained using this model with measurements from deciduous and coniferous forests show good agreement at several frequencies for both like and cross polarizations

tertiary structures and hydrocarbon entrapment in the weald basin of southern england abstract the weald basin of southeast england was formed by rapid subsidence associated with thermal relaxation following early mesozoic extensional block faulting the basin appears initially to have taken the form of an easterly extension of the wessex basin but became the major depocentre during the upper jurassic and lower cretaceous with associated active faulting these movements appear to have ceased prior to albian times and a full upper cretaceous cover is believed to have been deposited in a gentle downwarp which extended far beyond the confines of the weald and wessex basins major inversion of the weald basin took place in the tertiary with both gentle regional uplift which in the eastern part of the basin is estimated to have exceeded 5000 feet 1525 metres and intense local uplift along pre existing zones of weakness which led to the formation of compressional features such as tight folds and reverse faults zones of tertiary deformation appear to have been strongly influenced by underlying particularly hercynian structural trends lower jurassic source rocks reached maturity in the early cretaceous and initial migration occurred at this time often over long distances into traps closed by pre aptian faults tertiary tilting and uplift led to the breaching of many of these pre existing traps and the formation of large folded closures a second phase of hydrocarbon migration particularly of gas took place at this time with significant vertical migration along fault zones major reservoirs located to date occur in middle jurassic carbonates and upper jurassic sandstones but deep burial in the basin has caused considerable destruction of primary reservoir characteristics changes in the temperature and pressure regimes and the mobilization of fluids within the basin resulting from the tertiary uplift caused further diagenetic changes particularly in the carbonate reservoirs exploration of the weald basin remains at a very early stage with a low drilling density to date the more recent drilling has focussed on earlier structures but traps formed or modified during the tertiary movements represent important exploration objectives although general deterioration in reservoir quality towards the centre and east of the basin makes large fold closures in these areas less attractive

derivation of the chalk superficial deposits of the north downs england an application of discriminant analysis abstract stepwise discriminant analysis was used on particle size and heavy mineral data from 276 sediment samples including 39 from published sources to distinguish between palaeocene and plio pleistocene deposits found above the cretaceous chalk in southeast england and to determine parent materials of the soils and superficial deposits of the central north downs of 71 known cases in situ deposits 85 9 were correctly classified using textural data sig 99 9 and 89 7 of 29 known cases sig 99 9 using heavy mineral data the best textural discriminating variables were sand graphic mean clay and graphic skewness and the best heavy mineral discriminants were kyanite plus staurolite andalusite and garnet discriminant analysis has achieved good differentiation between marine plio pleistocene sands clay with flints loess and palaeocene groups and allowed objective classification of sediments of unknown origin the distribution of parent materials revealed strongly upholds the earlier interpretation z geomorphol 39 1995 433 that in the central north downs except where palaeocene residuals survive the superficial cover above the chalk consists of in situ clay with flints sensu stricto beneath plateau drift and loess clay with flints is seen as residual and plateau drift as a pleistocene soliflucted deposit textural affinities of reading beds clay and clay with flints elicited by a third discriminant analysis using additional published data from 22 samples suggest their common derivation from chalk residua

holocene evolution of the great barrier reef insights from 3d numerical modelling abstract the holocene reef in the outer great barrier reef gbr represents an archetypal reef system forming a thin veneer 10 30 m built upon an older pleistocene reef surface the morphology stratigraphy and maturity degree of lagoonal sediment infilling of the modern reef results from the complex interplay between biologic and abiologic processes reef accretion sediment erosion transport and deposition basement substrate and holocene sea level rise combining 3d forward stratigraphic modelling carbonate 3d with a re analysis of published observational data we quantitatively simulate the holocene evolution of one tree reef southern gbr as a well constrained model system and explore the main processes affecting reef growth in the gbr and elsewhere we test the influence of different basement substrate surfaces sea level curves reef accretion rates sediment erosion and transport parameters and assess their relative importance in controlling reef evolution particularly growth histories 3d internal structure and stratigraphy and reef maturity quantitative comparisons between our best estimate model output and the observed data confirm that we are able to simulate a 75 match of the main morphologic and growth characteristics of one tree reef the range of parameters tested produced the full spectrum of reef maturities from unfilled juvenile buckets to planar senile reefs with completely sediment infilled lagoons we conclude that the shape and depth of the basement substrate has the strongest influence significantly impacting reef evolution and final maturity including the shape of the bucket the size of the reef margins and internal reef structure in contrast variations in sea level sediment production erosion and transport mainly controlled the degree of lagoonal sediment filling this study has implications for better understanding the past evolution of the gbr and other reefs but also lays the foundation for improved predictions of possible trajectories of modern reefs in general in the face of future environmental changes

multipolarization sar data for surface feature delineation and forest vegetation characterization this paper presents the utility of multipolarization synthetic aperture radar sar data for surface feature delineation and forest vegetation characterization three channels of ratioed data vv hh vh hh and vh vv are generated from the hh vv and vh polarization data v vertical h horizontal the ratioed data are linearly stretched to yield a digital number within a range of 0 to 255 the techniques for reducing sar speckle noise and for measuring the degree of separation are discussed for surface feature delineation the results indicate that cross polarization as well as cross polarization ratioed data better delineate those surface features that are difficult to separate by like polarization data the results suggest using a median value filtering technique to reduce within plot data fluctuation to increase the separability measure for forest vegetation characterization the results indicate that multipolarization sar data may be used to estimate forest properties such as total tree biomass basal area and tree height

rain footprints on c band synthetic aperture radar images of the ocean revisited abstract it is well known that rain leaves footprints on the sea surface that sometimes become visible on synthetic aperture radar sar images rain cells can easily be detected on sar images at all radar frequencies when they are associated with a downdraft pattern but rain cells are not always associated with downdraft and rain can also occur in other forms as stratified rain rain bands and squall lines it turns out that radar signatures of rain at c band are much more complex than at l or x band radar and that it is particularly difficult to identify unambiguously rain events on c band sar images acquired over the ocean this is because c band lies in the transition region where raindrops impinging onto the sea surface can increase usually or decrease the backscattered radar power and where volume scattering and attenuation by rain drops in the atmosphere are not always negligible at very high rain rates in order to get an insight into the physical mechanisms causing the c band radar signatures of rain we first revisit results obtained from historic laboratory and field experiments and multi frequency multi polarization sar data acquired during the sir c x sar spaceshuttle mission in 1994 then we analyze several c band sar images acquired by the european satellites envisat and sentinel 1a and the canadian satellite radarsat 2 and compare them whenever possible with quasi coincident and collocated weather radar images the observational data show that at low to medium rain rates the main physical mechanism causing c band radar signatures of rain is bragg scattering at ring waves generated by the rain drops impinging onto the sea surface which increase the radar backscatter however areas of increased radar backscatter are often accompanied by adjacent areas of decreased radar backscatter which is due to attenuation of the bragg waves by turbulence also generated by the impinging rain drops furthermore we present a full polarimetric radarsat 2 sar image of a rain cell together with a polarimetric decomposition analysis which shows that the c band radar signature of a rain cell is caused by surface scattering the observation show that radar signatures of rain cells often contain segments where the co polarized as well the cross polarized radar backscatter are strongly enhanced which indicates non bragg scattering contributions to the scattering process furthermore the polarimetric decomposition analysis shows that the c band radar signature of a rain cell is dominated by surface scattering possible mechanisms like scattering at splash products are discussed whether the normalized radar cross section nrcs due to rain is increased or decreased depends on rain rate wind speed incidence angle and history of the rain event at low to moderate wind speeds 10 m s 1 and low to high rain rates but

a generalized radar backscattering model based on wave theory for multilayer multispecies vegetation a generalized radar scattering model based on wave theory is described the model predicts polarimetric radar backscattering coefficients for structurally complex vegetation comprised of multiple species and layers compared to conventional two layer crown trunk models modeling of actual forests has been improved substantially allowing better understanding of microwave interaction with vegetation the model generalizes an existing single species discrete scatterer model and by including scattering and propagation effects through judiciously defined vegetation layers enables its application to an arbitrary number of species types the scatterers within each layer are modeled as finite cylinders or disks having arbitrary size density and orientation as in the predecessor model the distorted born approximation is used to represent the propagation through each layer while scattering from each is modeled as a linear superposition of scattering from its respective random collection of scatterers interactions of waves within and between each layer and direct scattering from the ground are accounted for validation of the model is presented based on its application to 23 wooded savanna sites located in queensland australia and comparison with advanced land observing satellite alos phased arrayed l band synthetic aperture radar palsar and national aeronautics and space administration nasa jet propulsion laboratory jpl airborne synthetic aperture radar airsar data results indicate good agreement between simulated and actual backscattering coefficients particularly at hh and vv polarizations more discrepancies are found at hv polarizations and can be explained by uncertainties in the knowledge of input parameters such as inaccuracies in the surface model surface roughness parameterization and soil moisture

mid late holocene sea level variability in eastern australia a re analysis of sea level data from eastern australia based on 115 calibrated c 14 ages is used to constrain the origin timing and magnitude of sea level change over the last 7000 years we demonstrate that the holocene sea level highstand of 1 0 1 5 m was reached 7000 cal yr bp and fell to its present position after 2000 yr bp these findings are in contrast to most previous studies that relied on smaller datasets and did not include the now common conversion of conventional c 14 ages to calendar years during this 5000 year period of high sea level growth hiatuses in oyster beds and tubeworms and lower elevations of coral microatolls are interpreted to represent short lived oscillations in sea level of up to 1 m during two intervals beginning c 4800 and 3000 cal yr bp the rates of sea level rise and fall 1 2 mm yr 1 during these centennial scale oscillations are comparable with current rates of sea level rise the origin of the oscillations is enigmatic but most likely the result of oceanographic and climatic changes including wind strengths ice ablation and melt water contributions of both greenland and antarctic ice sheets

distribution petrology and mode of development of silcretes sarsens and puddingstones on the eastern south downs uk this paper presents the first intensive integrated field and laboratory study of an area of typical silcrete occurrence in the uk and enables parallels to be drawn with in situ silcretes in the neighbouring paris basin and other parts of northern europe silcrete distribution in the eastern south downs is localized and discontinuous with occurrence principally as dislocated boulders on the chalk these boulders mainly occur between the cuckmere and goldstone valleys with greatest concentrations around stanmer falmer rottingdean and in the goldstone valley many occur at higher levels in the landscape on or near interfluves usually peripheral to outliers of palaeocene sediments and in close association with claywith flints at lower levels they occur on valley floors and on the coastal plain within quaternary sediments boulders commonly have a axis dimensions of 0 5 2 m and thicknesses of 0 3 0 6 m silcretes in higher positions typically exhibit angular tabular or prismatic shapes whilst those in derived settings are more rounded suggesting weathering and erosion during transport from a localized high level silcrete lens or lenses three varieties of silcrete have been identified pale grey saccharoid sarsens are most widespread and exhibit a simple grain supported gs fabric with predominantly sand sized quartzose sediment cemented by optically continuous quartz overgrowths and minor micro and cryptocrystalline silica brown hard sarsens occur as smaller blocks mainly in the seaford head area these also exhibit a gs fabric but with more fine sediment and a greater variety of cement types textural and geochemical evidence suggests there is gradation between the saccharoid and hard varieties of sarsen conglomeratic puddingstone is common in the goldstone valley but rare elsewhere and shows closest similarity to saccharoid sarsen in texture and cementation silcrete micromorphology is universally simple and uniform with fabrics suggestive of groundwater or drainage line silicification the uniformity of sediments within all three types of silcrete indicates a common host suggested to be the upnor formation of the lambeth group palaeocene deposition of the host sediment appears to have been followed by illuviation of clay rich material via the primary fabric and along cracks to form geopetal caps drapes and vein like structures during silicification this finer material has been replaced by less well ordered silica whilst optically continuous quartz overgrowths characterize purer areas the silcrete was also affected by late stage influxes of iron oxides clay minerals and occasionally calcite on the basis of distributional and other evidence it is suggested that silicification occurred during the neogene or quaternary in association with acid leaching of lambeth group sediments probably under temperate conditions the timing of silcrete formation in the eastern south downs is thus much later than proposed for other parts of the uk