Areas Of High Relief Research Articles

Higher genetic diversity is associated with stable water refugia for a gecko with a wide distribution in aridAustralia

AbstractAimThose locations and features providing refugia for species during unfavourable climatic phases may be important to identify and conserve to help protect biodiversity in the near future. During the Pleistocene, climates oscillated between glacial and interglacial periods. In the Northern Hemisphere, the impact from glacial ice sheets caused species to disperse to warmer southern refugia, but less is known about changes to species' distributions during these periods in the Southern Hemisphere.LocationIn Australia, the climate alternated between highly arid and wetter periods during the Pleistocene. It has been proposed that arid refugia may be associated with the inland ranges (areas of higher relief), the mesic east, or areas that maintained favourable species‐specific ecological conditions. We tested these hypotheses with a phylogeographical analysis of a widely distributed tree‐dwelling gecko,Gehyra variegata(2n = 40a chromosomal race) throughout the central and eastern regions of arid Australia.MethodsWe generated a mtDNAsequence and microsatellite dataset by sampling 740G. variegata40athroughout its known distribution. We also use species distribution modelling to predict the species' likely past, present and future distribution.ResultsThe majority ofG. variegata40alineages diverged during the Pleistocene, and those located in regions of arid Australia where mean annual water run‐off is highest, displayed higher levels of genetic diversity in comparison locations with lower run‐off. We also show that genetic diversity increased with proximity to water sources.Main conclusionsIt is likely thatG. variegata40acontracted to refugia associated with stable water sources during Pleistocene arid phases. However, modelling suggests that unfavourable climate conditions will be present in this region by 2070. Therefore, Pleistocene refugia forG. variegata40aare unlikely to be refugia in the future. More generally, our results suggest that water run‐off could be a useful predictor to identify favourable conditions for some arid species.

Ecomorphodynamic feedbacks and barrier island response to disturbance: Insights from the Virginia Barrier Islands, Mid-Atlantic Bight, USA

Ecomorphodynamic feedbacks play an important role in the susceptibility and response of barrier islands to disturbance by overwash. Dune-building grasses, like Ammophila breviligulata, can help to restore areas of high relief after overwash events (i.e., resist disturbance). If overwash recurs before dunes have reestablished, however, overwash-adapted “maintainer” species, like Spartina patens (upright variety), may preferentially survive. Maintainer species help to preserve low, flat topography, thereby increasing the likelihood of future overwash (i.e., reinforcing disturbance). Under frequent disturbance conditions, this positive feedback may lead to overwash persistence. We explore the potential influence of the maintainer feedback on two morphologically distinct barrier islands in the Virginia Coast Reserve (VCR), located in the Mid-Atlantic Bight of the U.S. East Coast.Combined topographic and vegetation surveys show that on Hog Island (high-relief, rotating), where dunes dominated by A. breviligulata are ubiquitous, overwash zones are currently limited in extent and related to beach width rather than dominance by S. patens. Historical aerial photos and stratigraphic evidence (ground-penetrating radar, cores) indicate that gradual recovery has taken place following overwash events on Hog Island, except where the beach is narrow and eroding. Conversely, on Metompkin Island (low-relief, transgressing), overwash is widespread and dominated by S. patens, particularly along the rapidly migrating northern half of the island, where shell armoring is also common. Overwash has generally been more prevalent and persistent here than on Hog Island. We present a new conceptual model of the response of barrier islands to disturbance incorporating ecological and physical processes. Our findings suggest that in barrier systems where both dune-building grasses and overwash-adapted maintainer species are common (like the VCR), the maintainer feedback is likely to be a more important dynamic on islands already susceptible to frequent disturbance because of physical factors. The maintainer feedback, therefore, has the potential to accelerate large-scale shifts from dune-dominated to overwash-dominated barrier morphologies as the effects of climate change (increased storm intensity, sea level rise) cause overwash to become more frequent.

Slope Failure Hazard in the Atlantic Provinces: A Review

Slope failures present a common hazard throughout the world and have considerable impact on transportation, forestry, coastal and urban development, and other human activities. Although little recognized in much of Atlantic Canada, mass movements have resulted in as many as 71 fatalities in Newfoundland. Due to the high relief of Newfoundland, rockfalls have caused several fatalities and damage to property is frequent. In the Ferryland disaster of ca. 1823, 42 fishermen were reportedly killed when a cave roof collapsed onto them. Debris torrents and flows are widespread particularly in areas of higher relief in Newfoundland and Cape Breton Island, and tend to be most hazardous for highway engineering and community development. Typically, a thin cover of till or colluvium overlies a steeply sloping and polished bedrock substrate. Failure is generally triggered by rainfall events. Rotational slumps of glaciomarine clays are particularly evident along the major river valleys of Labrador and are an important consideration for hydroelectric development such as along the lower Churchill River. Numerous sackungs have been identified, notably in the ultramafic rocks of western Newfoundland. In other areas of Atlantic Canada, earthflows frequently affect transportation routes and commonly involve movement of saturated sediment during spring thaw. Along the Gulf of St. Lawrence and Northumberland Strait and the Bay of Fundy coastlines, the combination of friable Carboniferous and Permian sediments, glaciotectonic activity, frost wedging, and coastal erosion has resulted in numerous small failures, along with incremental retreat of coastal cliffs. Ongoing climate change will have an impact on slope failure activity. The pattern of increasing summer frequency and intensity of thunderstorms and hurricane events, increased winter precipitation in some locations, and more erratic freeze-thaw events during late winter and spring, will result in an increase in debris torrents triggered by precipitation, and rockfalls triggered by freeze-thaw. Human utilization of coastal areas for recreation and residential construction is also increasing both the frequency and hazard of slope failures across Atlantic Canada.

Proximate environmental forcing in fine-scale geochemical records of calcareous couplets (Upper Cretaceous and Palaeocene of the Basque-Cantabrian Basin, eastern North Atlantic)

Calcareous couplets are key elements in reconstructing the evolution of a sedimentary basin due to the influence of forcing mechanisms such as climate, sea level and tectonism on their depositional patterns. Proposed forcing mechanisms, however, are often not mutually exclusive and even constraining the relative importance of different processes is problematic. Added to the question of discriminating forcing mechanisms, a major challenge is to produce high-sampling density so that observations lie within temporal resolutions equal to or finer than the timescales on which different forcing operates. Here, we show fine-scale (1 sample/~2cm) CaCO3, δ18O and δ13C records and sedimentological observations from three different sites (Isla de Castro, Sopelana-Ma, and Sopelana-Da) with calcareous couplets in the Basque Cantabrian Basin (eastern North Atlantic) to illustrate the potential of fine-sampling strategies to help distinguish proximate environmental forcing. Partial redistribution of carbonate during burial diagenesis has been proposed for these sediments. Our CaCO3, δ18O and δ13C data could thus be dismissed as diagenetic signals if only one sample was collected from each bed. Detailed observations of the fine-scale geochemical records, however, challenge purely diagenetic explanations. Combined with sedimentology, the CaCO3, δ18O and δ13C values, partially altered by diagenesis, are interpreted to have resulted from alternating climates. The proximate forcing through which alternating climates caused the geochemical patterns, though, was different in each section, due to their specific palaeogeographic positions in the basin and the properties of the seawater masses. The proximity of continental areas of high relief to the Isla de Castro section supported a high continental influence during its deposition. The Sopelana-Ma sediments are assigned to a transgressive system tract, a condition that is interpreted to have promoted a high influence of oceanic processes in its depositional setting. Finally, a relatively cool, oxygen-rich water mass with high oxidation potential influenced the geochemical and depositional patterns of Sopelana-Da. Beyond the climatic and oceanographic dynamics inferred for a basin that linked the western Tethys with Boreal domains during major marine transgressions of the Late Cretaceous to Palaeocene, an implication of our work is that if similar fine-scale geochemical records were applied to calcareous couplets spanning major events in Earth's history (e.g., ocean anoxic events), alternative forcing scenarios leading to and out of these events could be discriminated.

TERRAIN CORRECTION OF POLARIMETRIC SAR DATA AND ITS APPLICATION IN MAPPING MOUNTAIN GLACIER FACIES WITH RADARSAT-2 SAR

Abstract. Synthetic Aperture Radar (SAR) data can be difficult to interpret over glacierized terrain, especially in areas of high relief where most of the smaller glaciers of the world are found. The two primary objectives of this paper are to correct the topographically induce distortions inherent in SAR image of rugged terrain and to map glacier facies in the corrected polarimetric (PolSAR) image. Methods for terrain correction of PolSAR developed in this paper, which base on the coherency matrix data, utilize polarimetric signature to refine the location accuracy and perform the pixel size normalization on each element of the coherency matrix using the backward integration method. Moreover, azimuth-slope correction is immediately following after radiometric correction. A supervised classification is performed on the orthorectified image to map the spatial distribution of snow and ice. The visual boundary between wet snow and bare ice surface is delineated on the orthorectified image too. These results show that glacier facies and the wet snow line can be mapped reasonably well using Radarsat-2 PolSAR in a mountainous environment.

A physics-based atmospheric and BRDF correction for Landsat data over mountainous terrain

Steep terrain affects optical satellite images through variations it creates in both irradiance and bidirectional reflectance distribution function (BRDF) effects. To obtain the corrected land surface reflectance and detect land surface change through time series analysis over rugged surfaces, it is necessary to remove or reduce the topographic effects. In this paper a physics-based BRDF and atmospheric correction model that handles both flat and inclined surfaces in conjunction with a 1-second SRTM (Shuttle Radar Topographic Mission) derived Digital Surface Model (DSM) product was applied to 8 Landsat scenes covering different seasons and terrain types in eastern Australia. Visual assessment showed that the algorithm removed much of the topographic effect and detected deep shadows in all 8 images. An indirect validation based on the change in correlation between the data and terrain slope showed that the correlation coefficient between the surface reflectance factor and the cosine of the incident (sun) angle reduced dramatically after the topographic correction algorithm was applied. The correlation coefficient typically reduced from 0.80–0.70 to 0.05 in areas of significant relief. It was also shown how the terrain corrected surface reflectance can provide suitable input data for multi-temporal land cover classification in areas of high relief based on spectral signatures and spectral albedo, while the products based only on BRDF and atmospheric correction cannot. To provide comparison with previous work and to validate the proposed algorithm, two empirical methods based on the C-correction were used as well as the established SCS-method to provide benchmarks. The proposed method was found to achieve the same measures of shade reduction without empirical regression.

Foraging distribution of Pacific harbor seals (Phoca vitulina richardii) in a highly impacted estuary

Assessing the relative importance of environmental and anthropogenic influences on the distribution of wild populations is an important step in designing spatially explicit plans for their management and protection. We examined environmental variables correlated with the spatial distribution of eastern Pacific harbor seals (Phoca vitulina richardii), a marine mammal common to coastal waters, in a large, highly urbanized estuary. We assessed the relationship between prey abundance, depth, bottom relief, proximity to terrestrial haul-out sites and 3 potential sources of anthropogenic influence, and the in-water spatial distribution of seals. We identified locations of seals using satellite-linked telemetry, and used partial Mantel tests to assess which environmental variables were most strongly linked to seal foraging distribution, given spatial autocorrelation within variables. Mann-Whitney tests were used to compare environmental characteristics of locations of seals with a random distribution of locations. Because harbor seals are central-place foragers, we incorporated spatial distribution of seals relative to the central place into our analyses. High prey abundance and proximity to the haul-out site were strongly associated with the spatial distribution of seals. Harbor seals also tended to use deeper waters and areas of high bottom relief within the estuary. There was no consistent spatial relationship between the 3 anthropogenic factors and the distribution of seals, although seals tended to be found closer than expected to sites of high human activity. In highly impacted coastal areas where limited alternate suitable habitat exists, foraging seals may need to rely on disturbed (suboptimal) areas, and as a result may habituate to human presence in areas rich in food resources.

Topography correlated atmospheric delay correction in radar interferometry using wavelet transforms

Atmospheric delay is one of the major sources of error in repeat pass interferometry. We propose a new approach for correcting the topography‐correlated components of this artifact. To this aim we use multiresolution wavelet analysis to identify the components of the unwrapped interferogram that correlate with topography. By using a forward wavelet transform we break down the digital elevation model and the unwrapped interferogram into their building blocks based on their frequency properties. We apply a cross‐correlation analysis to identify correlated coefficients that represent the effect of the atmospheric delay. Thus, the correction to the unwrapped interferogram is obtained by down‐weighting the correlated coefficients during inverse wavelet transform. We test this approach on real and synthetic data sets that are generated over the San Francisco Bay Area. We find that even in the presence of tectonic signals, this method is able to reduce the correlated component of the atmospheric delay by up to 75% and improves the signal in areas of high relief. The remaining part is most likely due to 3D heterogeneities of the atmosphere and can be reduced by integrating temporal information or using complementary observations or models of atmospheric delay.

GIS modelling of earthquake damage zones using satellite remote sensing and DEM data

The devastating earthquake that occurred in Wenchuan County, Sichuan Province, China, on the 12th May 2008, caused widespread damage and devastation to rural communities and economy. The terrain of the entire region has been weakened and is now highly susceptible to long-term slope instability that will trouble this region for many years to come. Before the earthquake, the maximum seismic intensity expected in the region was VI–VIII in the 12-degree Liedu scale (the intensity measure adopted in China). However, the actual intensity caused by the earthquake ranged between VIII and XI. The seismic intensity map is practical for regional guidance but lacks the detail to provide an adequate representation of the true damage level, in terms of current status and future potential in such a seismically active and populated region, especially when the hazards and risks are likely to be multiple and cascading in high relief areas. This paper presents a GIS based novel approach to earthquake damage zone modelling using satellite remote sensing and DEM data. The novelty is to take into account the co-seismic ground deformation (measured using differential SAR interferometry) as an important modulating factor in modelling the susceptibility of earthquake related geohazards, together with conventional multi-criteria factors which draw on geological and topographical variables such as rock competence, slope, proximity to drainage, and fracture density. The modulating effect of the earthquake greatly enhances the susceptibility in the areas where the majority of the ensuing landslides and debris-flows actually took place. When this susceptibility model is further modulated by the mapped surface disruption caused by the earthquake (which encompasses all forms of mass movement and urban destruction), it is directly linked to seismic intensity and we call it “ earthquake damage ”. The output earthquake damage map represents both the current damage status as well as the future damage (hazard) potential. The resulting earthquake damage map for the Beichuan region clearly defines a series of zones of increasing seismic intensity, approximately corresponding to Liedu values VIII–XI but with great details.

A comparison of Landsat TM and MODIS vegetation indices for estimating forage phenology in desert bighorn sheep (Ovis canadensis nelsoni) habitat in the Sonoran Desert, USA

Sonoran Desert bighorn sheep (Ovis canadensis mexicana) occupy rugged upland areas that experience irregular periods of vegetation growth associated with precipitation events. These episodic and often spatially limited events provide important forage and preformed water resources that may be important drivers of animal movement and habitat use. Habitat-use models that incorporate forage phenology would broaden our understanding of desert bighorn ecology and have considerable potential to inform conservation efforts for the species. Field-based methods are of limited utility to characterize vegetation phenology across large areas. Vegetation indices (VI) derived from satellite imagery are a viable alternative, but may be confounded by areas of high relief and shadow effects that can degrade VI values. The varying spatial and temporal resolutions of readily available satellite sensors, such as the Landsat thematic mapper (TM) and moderate-resolution imaging spectrometer (MODIS), present additional challenges. In this study, we sought to minimize degrading effects of terrain on TM- and MODIS-based estimates of vegetation phenology. We compared effects of high topographic relief on time series MODIS- and TM-based VI such as the normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI) using VI departures from average (DA) in shaded and unshaded areas. Sun elevation angle negatively impacted TM-derived NDVI and EVI values in areas of steep terrain. In contrast, MODIS-derived NDVI values were insensitive to sun elevation and terrain effects, whereas MODIS-derived EVI was degraded in areas of steep terrain. Time series MODIS NDVI and EVI DA values differed significantly during months of low sun elevation angle. Average MODIS EVI departure values were ≥20% lower than NDVI under these conditions, confounding time series estimates of plant phenology. Our best results were obtained from MODIS 16-day composited NDVI. These remote-sensing-based VI estimates of seasonal plant phenology and productivity can be used to inform models of habitat use and movements of desert bighorn over large areas.

Late Neogene and active orogenic uplift in the Central Pontides associated with the North Anatolian Fault: Implications for the northern margin of the Central Anatolian Plateau, Turkey

Surface uplift at the northern margin of the Central Anatolian Plateau (CAP) is integrally tied to the evolution of the Central Pontides (CP), between the North Anatolian Fault (NAF) and the Black Sea. Our regional morphometric and plate kinematic analyses reveal topographic anomalies, steep channel gradients, and local high relief areas as indicators of ongoing differential surface uplift, which is higher in the western CP compared to the eastern CP and fault‐normal components of geodetic slip vectors and the character of tectonic activity of the NAF suggest that stress is accumulated in its broad restraining bend. Seismic reflection and structural field data show evidence for a deep structural detachment horizon responsible for the formation of an actively northward growing orogenic wedge with a positive flower‐structure geometry across the CP and the NAF. Taken together, the tectonic, plate kinematic, and geomorphic observations imply that the NAF is the main driving mechanism for wedge tectonics and uplift in the CP. In addition, the NAF Zone defines the boundary between the extensional CAP and the contractional CP. The syntectonic deposits within inverted intermontane basins and deeply incised gorges suggest that the formation of relief, changes in sedimentary dynamics, and >1 km fluvial incision resulted from accelerated uplift starting in the early Pliocene. The Central Pontides thus provide an example of an accretionary wedge with surface‐breaking faults that play a critical role in mountain building processes, sedimentary basin development, and ensuing lateral growth of a continental plateau since the end of the Miocene.

Systematic InSAR tropospheric phase delay corrections from global meteorological reanalysis data

[1] Despite remarkable successes achieved by Differential InSAR, estimations of low tectonic strain rates remain challenging in areas where deformation and topography are correlated, mainly because of the topography-related atmospheric phase screen (APS). In areas of high relief, empirical removal of the stratified component of the APS may lead to biased estimations of tectonic deformation rates. Here we describe a method to correct interferograms from the effects of the spatial and temporal variations in tropospheric stratification by computing tropospheric delay maps coincident with SAR acquisitions using the ERA-Interim global meteorological model. The modeled phase delay is integrated along vertical profiles at the ERA-I grid nodes and interpolated at the spatial sampling of the interferograms above the elevation of each image pixel. This approach is validated on unwrapped interferograms. We show that the removal of the atmospheric signal before phase unwrapping reduces the risk of unwrapping errors in areas of rough topography.

Intraspecific and Interspecific Spatial Distribution of Three Eastern North Pacific Catshark Species and Their Egg Cases (Chondrichthyes: Scyliorhinidae)

Information on the distribution of three species of eastern North Pacific (ENP) catsharks (Apristurus brunneus, Apristurus kampae, and Parmaturus xaniurus) and their egg cases was previously unavailable despite being a species of interest for fisheries management evaluation and policy regulation. Data were generated from specimens collected by survey cruises from June 2001 through October 2004 between northern Washington to San Diego, California, U.S.A. and from known catch locations of specimens in museum collections. Longline catches consisted mainly of P. xaniurus, with occasional catch of gravid female A. brunneus. Conversely, trawl catches consisted mainly of Apristurus species. The three catshark species exhibited distinct differences in latitudinal and bathymetric range, albeit with partial overlap. Apristurus brunneus was typically found between 300 and 942 m along the entire area surveyed, while A. kampae always occurred .1,000-m depth and was not found north of 426N. Parmaturus xaniurus was caught between 300- and 550-m depth between 406N and 326N. Egg cases of A. brunneus and P. xaniurus were collected in trawl surveys and observed in video footage taken by remotely operated vehicle. These egg cases were located in specific sites on areas of high vertical relief at 300- to 500-m depth. Nursery grounds, which were previously unknown for these catshark species, were described within the Monterey Bay Canyon and along the California coastline were identified on the basis of recurrence and specificity of oviposition. This paper describes the range of A. brunneus, A. kampae, and P. xaniurus in the ENP, detailing latitudinal, bathymetric, sexual, and ontogenetic intra- and interspecific segregation patterns.

Assessing rockfish abundance in complex habitats using acoustics and cameras.

Many species of rockfishes (Sebastes spp.) are difficult to assess using trawl surveys due to their propensity to aggregate near the seafloor in rocky high relief areas. A feasibility study was conducted during October 2009 in such an area south of Kodiak Island, AK, to evaluate the use of standard fisheries acoustic survey methods in conjunction with stereo‐video cameras for estimating the distribution and abundance of dusky and northern rockfishes. Uniformly spaced parallel transects were repeatedly surveyed using single beam echosounders over several days. A multibeam echosounder was used to characterize the seafloor as trawlable or untrawlable and these designations were corroborated by camera. Rockfish abundance was estimated using a combination of acoustic and camera measurements. At least 80% of the rockfish detections were observed in untrawlable habitat areas, and within 2.0 m of the seafloor. Over half of the rockfish seen by the camera were within the acoustic dead zone. Repeat passes exhibited high precision and there was no significant difference in fish abundance or height off bottom between night and day. Future work is planned during summer 2011 to evaluate the feasibility of using these methods in broader areas and for other rockfishes in the Gulf of Alaska.

Sequence-stratigraphic interpretation of structurally controlled deposition: Middle Miocene Kareem Formation, southwestern Gulf of Suez, Egypt

ABSTRACT The structural evolution and sequence-stratigraphic architecture of the syn-rift Middle Miocene (Langhian) Kareem Formation were studied in the Western Sub-Basin (WSB) of the Gulf of Suez, Egypt. Biostratigraphic data, facies interpretations, and log data from thirteen wells were used to construct six tectono-sedimentary scenarios and lithofacies-distribution maps, which illustrate the paleogeography during six systems tracts. Abrupt thickness and facies changes reflect deep basins and adjacent high-relief areas created by differential fault-block movements. Within the WSB seven individual fault blocks record complex, tectonically controlled deposition of the Kareem Formation, which we subdivide into two third-order sequences. Earlier tectonic interpretations, facies analysis, and stratigraphic correlations from individual fault blocks were used to interpret the varying depositional settings during six systems tracts and, as a consequence, to discern the structural evolution of the WSB during the Middle Miocene.

Delayed accumulation of placers during exhumation of orogenic gold in southern New Zealand

The giant gold placer system on the Otago Schist of southern New Zealand was derived from Mesozoic orogenic gold deposits in the underlying schist basement. The core of the schist basement was exhumed in the middle Cretaceous, coeval with the accumulation of the oldest preserved nonmarine sedimentary rocks in the area (ca 112 Ma). Those sedimentary rocks contain quartz clasts, with distinctive ductile deformation textures, that were derived from structural zones in, or adjacent to, major orogenic gold deposits. Quartz textures in these structural zones are readily distinguishable from the rest of the schist belt, and hence provide a fingerprint for erosion of gold. The earliest sedimentary rocks on the margins of the gold-bearing schist belt are immature, and were derived from unoxidised outcrops in areas of high relief. Gold was not liberated from unoxidised basement rocks during erosion, and was removed from the system without placer concentration. Placer concentration did not begin until about 20 million years later, when oxidative alteration of gold deposits had facilitated gold grain size enhancement from micron scale (primary) to millimetre scale (secondary). Subsequent erosion and recycling of gold in the early Cenozoic, and again in the late Cenozoic, caused additional concentration of gold in progressively younger deposits. The Klondike giant placer goldfield of Canada had a similar geological history to the Otago placer field, and Klondike placer accumulation occurred in the late Cenozoic, at least 70 million years after Mesozoic exhumation of orogenic gold. The giant placer deposit on the western slopes of the Sierra Nevada in California occurs in Eocene and younger sedimentary rocks, at least 40 million years younger than the timing of major exhumation of the source rocks. Circum-Pacific giant gold placers formed under entirely different tectonic regimes from the emplacement of their source orogenic deposits, and these giant placer deposits do not form in foreland basins associated with convergent orogens. Formation of giant placers requires less active erosion and more subdued topography than the collisional orogenic activity that accompanied emplacement of source gold deposits in basement rocks, as well as oxidative alteration of the primary deposits to liberate gold from sulfide minerals and enhance secondary gold grain size.

Radar-Coding and Geocoding Lookup Tables for the Fusion of GIS and SAR Data in Mountain Areas

Synthetic aperture radar (SAR) image orthorectification induces an important alteration of information due to the side-looking geometry of SAR acquisition. In high-relief areas, the difficulty is increased by the foldover effect: The images acquired with low incidence angles cannot be registered by a bijective transformation like polynomial transformations, as usually proposed by conventional software. In this letter, a simple and efficient method, fitted to geocoded data and SAR images, is introduced to propose a generic coregistration tool that takes SAR geometry into account without requiring the exact sensor model, specific parameters, and precise navigation data. This method is based on a simulated SAR image and on the computation of lookup tables (LUTs) that represent the coordinate transform from one geometry to the other. Results are presented on a high-relief area in the Alps, where satellite and airborne SAR images are used for glacier evolution monitoring. A comparison to other sensor-independent approaches has been performed, showing that the proposed approach performs better in mountain areas. The resulting LUTs allow merging SAR data with the georeferenced data, either in ground geometry by orthorectifying the SAR information or in radar geometry by the inverse transformation, namely, radar-coding data from a geographic information system, to improve the analysis of SAR images and the result interpretation.

Estimating aboveground forest biomass from canopy reflectance model inversion in mountainous terrain

The amount and spatial distribution of aboveground forest biomass (AGB) are required inputs to forest carbon budgets and ecosystem productivity models. Satellite remote sensing offers distinct advantages for large area and multi-temporal applications, however, conventional empirical methods for estimating forest canopy structure and AGB can be difficult in areas of high relief and variable terrain. This paper introduces a new method for obtaining AGB from forest structure estimates using a physically-based canopy reflectance (CR) model inversion approach. A geometric-optical CR model was run in multiple forward mode (MFM) using SPOT-5 imagery to derive forest structure and biomass at Kananaskis, Alberta in the Canadian Rocky Mountains. The approach first estimates tree crown dimensions and stem density for satellite image pixels which are then related to tree biomass and AGB using a crown spheroid surface area approach. MFM estimates of AGB were evaluated for 36 deciduous (trembling aspen) and conifer (lodgepole pine) field validation sites and compared against spectral mixture analysis (SMA) and normalised difference vegetation index (NDVI) biomass predictions from atmospherically and topographically corrected (SCS+C) imagery. MFM provided the lowest error for all validation plots of 31.7 tonnes/hectare (t/ha) versus SMA (32.6 t/ha error) and NDVI (34.7 t/ha) as well as for conifer plots (MFM: 23.0 t/ha; SMA 27.9 t/ha; NDVI 29.7 t/ha) but had higher error than SMA and NDVI for deciduous plots (by 4.5 t/ha and 2.1 t/ha, respectively). The MFM approach was considerably more stable over the full range of biomass values (67 to 243 t/ha) measured in the field. Field plots with biomass > 1 standard deviation from the field mean (over 30% of plots) had biomass estimation errors of 37.9 t/ha using MFM compared with 65.5 t/ha and 67.5 t/ha error from SMA and NDVI, respectively. In addition to providing more accurate overall results and greater stability over the range of biomass values, the MFM approach also provides a suite of other biophysical structural outputs such as density, crown dimensions, LAI, height and sub-pixel scale fractions. Its explicit physical-basis and minimal ground data requirements are also more appropriate for larger area, multi-scene, multi-date applications with variable scene geometry and in high relief terrain. MFM thus warrants consideration for applications in mountainous and other, less complex terrain for purposes such as forest inventory updates, ecological modeling and terrestrial biomass and carbon monitoring studies.

Large Distributive Fluvial Systems: Characteristics, Distribution, and Controls on Development

Abstract An analysis of remotely sensed imagery reveals that fluvial planform geometries within aggrading continental areas are dominated by distributive fluvial systems (DFSs). We documented the gradient, length, apex location, planform, termination type, and tectonic and climatic setting of 415 examples of fluvial systems which in planform display a radial, distributive channel pattern and have an apex–toe distance > 30 km (large DFSs). The longest of these DFSs is 704 km in length, with the majority (72%) ranging between 30 and 100 km in length. Gradients on individual systems range from 0.00003 (0.0018°) to 0.02656 (1.5°). Six planform types are recognized, those with: (1) a single braided channel that bifurcates downstream into braided and/or straight channels, (2) a single dominant braided channel, (3) a single dominant braided channel which becomes sinuous downstream often bifurcating, (4) a single dominant sinuous channel, (5) a single sinuous channel that bifurcates downstream into smaller sinuous channels, and (6) multiple sinuous channels. Of the studied examples 58% occur within exorheic basins and 42% in endorheic basins, with seven different termination types recognized. In many examples, channel planform changes downstream from a distributive pattern to a contributory pattern. In others, channels terminate at an axial fluvial system, at the coast, in eolian dune fields, playa lakes, permanent lakes, or wetlands. Large DFSs and their catchments are developed in all climatic regimes, including drylands, tropical, subtropical, continental, and polar climates. Large DFSs occur in all tectonic settings, including extensional, compressional, strike-slip, and cratonic tectonic regimes. General trends and relationships between the different studied parameters can be observed, leading to a broad understanding of the main controls on large DFS development. All of the planform types occur in all tectonic settings and all climate zones. Braided planforms dominate all tectonic settings, but particularly compressional regimes. High-gradient braided systems tend to be associated with areas of high relief and are well developed in dryland climates where discharge is inferred to be intermittent in comparison to tropical climates. Large DFSs with sinuous planforms do occur in dryland climates but tend to predominate in wetter, more tropical climates where discharge is more constant and the fluvial systems can distribute bedload more efficiently. Sinuous systems also tend to have significantly lower gradients than braided systems. Although these general observations can be made, there are significant variations from these trends, which are inferred to be controlled by variations in (1) discharge related to climate and (2) sediment supply, which is a function of climate, catchment size, catchment lithology, and catchment relief. Large DFS length is controlled by the available horizontal accommodation space, which in turn is strongly related to tectonic setting. The longest DFSs occur in peripheral foreland basins and cratonic settings where lateral systems can develop across an extensive basinwards slope. Extensional, strike-slip, and piggy-back basins are narrower and have much more limited horizontal accommodation space. Consequently DFSs developed in these settings are shorter, with radii often less than 30 km. DFSs dominate in aggradational settings such as actively subsiding sedimentary basins and therefore form a significant proportion of alluvial sedimentary successions preserved in the rock record.

A tenfold increase in the Orange River mean Holocene mud flux: implications for soil erosion in South Africa

Soil erosion poses a major threat to sustainable agriculture in southern Africa but is difficult to quantify. One measure of soil erosion is the sediment flux of rivers. The Orange River is the principal source of sediment to the western margin of South Africa with an estimated mean mud flux over the last 11 500 years (the Holocene epoch) of 5.1 (3.2—7.4) million metric tons/year (Mt/yr). A total of 43 gigatons (Gt; 1015 g) representing 72% of the Holocene mud flux has accumulated on the shelf in the Orange River prodelta and mudbelt, a clayey fine-silt deposit focused on the inner to middle shelf. Only 8% (5 Gt) of the mud flux occurs in Holocene calcareous ooze on the slope. Comparison of the clay to mud ratio of offshore deposits with Orange River suspended sediment and catchment soils indicates that 20% (11 Gt) of the Holocene mud flux has been lost as clay beyond the margin. The Orange River mud flux prior to the building of large dams (1930—1969) is ten times greater than the mean Holocene mud flux and is reconciled with estimates of soil erosion within the catchment. A tenfold increase in the Orange River mud flux implies up to a hundredfold increase in total soil erosion depending on the extent of mud storage over periods of decades to centuries within the catchment. Erosion has shifted from areas of high relief and rainfall of the Drakensberg escarpment during the Holocene to intensely cultivated lands of low relief having moderate to high rainfall in the eastern catchment and to a lesser extent, grazing areas of the southern Orange River catchment.