Evaluation of the geometric stability and the accuracy potential of digital cameras — Comparing mechanical stabilisation versus parameterisation

Recent tests on the geometric stability of several digital cameras that were not designed for photogrammetric applications have shown that the accomplished accuracies in object space are either limited or that the accuracy potential is not exploited to the fullest extent. A total of 72 calibrations were calculated with four different software products for eleven digital camera models with different hardware setups, some with mechanical fixation of one or more parts. The calibration procedure was chosen in accord to a German guideline for evaluation of optical 3D measuring systems [VDI/VDE, VDI/VDE 2634 Part 1, 2002. Optical 3D Measuring Systems–Imaging Systems with Point-by-point Probing. Beuth Verlag, Berlin]. All images were taken with ringflashes which was considered a standard method for close-range photogrammetry. In cases where the flash was mounted to the lens, the force exerted on the lens tube and the camera mount greatly reduced the accomplished accuracy. Mounting the ringflash to the camera instead resulted in a large improvement of accuracy in object space. For standard calibration best accuracies in object space were accomplished with a Canon EOS 5D and a 35 mm Canon lens where the focusing tube was fixed with epoxy (47  μm maximum absolute length measurement error in object space). The fixation of the Canon lens was fairly easy and inexpensive resulting in a sevenfold increase in accuracy compared with the same lens type without modification. A similar accuracy was accomplished with a Nikon D3 when mounting the ringflash to the camera instead of the lens (52  μm maximum absolute length measurement error in object space). Parameterisation of geometric instabilities by introduction of an image variant interior orientation in the calibration process improved results for most cameras. In this case, a modified Alpa 12 WA yielded the best results (29  μm maximum absolute length measurement error in object space). Extending the parameter model with FiBun software to model not only an image variant interior orientation, but also deformations in the sensor domain of the cameras, showed significant improvements only for a small group of cameras. The Nikon D3 camera yielded the best overall accuracy (25  μm maximum absolute length measurement error in object space) with this calibration procedure indicating at the same time the presence of image invariant error in the sensor domain. Overall, calibration results showed that digital cameras can be applied for an accurate photogrammetric survey and that only a little effort was sufficient to greatly improve the accuracy potential of digital cameras.     

Assessment of drought over the past two millennia using near-shore sediment cores from a Canadian boreal lake

Lack of long-term studies on drought in the boreal region of northwest Ontario limits our ability to assess the vulnerability of this region to climate change. We investigated changes in diatoms, scaled chrysophytes, and sedimentary pigments in two near-shore cores from Gall Lake to infer limnological and water-level changes over the last two millennia. The two coring locations, at modern water depths of 7.5 and 11.5 m, were selected to contrast inferences for past lake level based on distance from the modern water-depth boundary between predominantly benthic and planktonic diatom assemblages in surface sediments (6.0 m). Diatom-inferred depth inferences were more variable in the core from 7.5-m water depth, consistent with the hypothesis that the greatest changes occurred at water depths closest to the benthic:planktonic boundary. Both sites revealed a pronounced drought from ~AD 950 to 1300, synchronous with the medieval climate anomaly (MCA). This finding suggests a northeast expansion of the arid MCA into northwest Ontario, extending the known spatial extent of this megadrought. Scaled chrysophytes and sedimentary pigments suggest a recent increase in thermal stratification. Our findings indicate this region is more susceptible to changes in moisture than was previously suspected based on the instrumental record for the past century.     

Re-evaluation of the Cablac Limestone at its type area, East Timor: Revision of the Miocene stratigraphy of Timor

The Cablac Limestone, widely recorded in Timor, has its type area on Cablac Mountain where it was regarded as a Lower Miocene shallow-marine carbonate-platform succession. The Bahaman-like facies placed in the Cablac Limestone are now known to belong to the Upper Triassic–Lower Jurassic rather than the Lower Miocene. On the northern slopes of Cablac Mountain, a crush breccia, formerly regarded as the basal conglomerate of the formation, is now considered to have developed along a high-angle fault separating Banda Terrane units of Asian affinity from an overthrust limestone stack containing units belonging to the Gondwana and Australian-Margin Megasequences. The Cablac breccia includes rock fragments that were probably derived locally from these tectonostratigraphic units after terrane emplacement and overthrusting. Clasts include peloid and oolitic limestones of the Upper Triassic–Lower Jurassic derived from the Gondwana Megasequence, deep-water carbonate pelagites of the Cretaceous and Paleogene derived from the Australian-Margin Megasequence, Upper Oligocene–Lower Miocene (Te Letter Stage) shallow-water limestone derived from the Banda Terrane, and a younger Neogene calcarenite containing clasts of mixed tectonostratigraphic affinity. There is no evidence for significant sedimentary or tectonic transport of clasts that form the breccia. The clast types and the present understanding of the geological history of Timor suggest that the crush breccia formed late in the Plio-Pleistocene uplift history of Timor. It is not the basal conglomerate of the Cablac Limestone. However, the clasts of an Upper Oligocene–Lower Miocene limestone found in the breccia suggest that a shallow-marine limestone unit of this age either outcrops in the region and has not been detected in the field, or has been eroded completely during late Neogene uplift. The clasts are similar in age and lithology to an Upper Oligocene–Lower Miocene formation that unconformably overlies a metamorphic complex in the Booi region of West Timor, similar to the Lolotoi Metamorphic Complex (Banda Terrane) that is juxtaposed against the crush breccia of Cablac Mountain. The Cablac Limestone at its type area includes a mixed assemblage of carbonate rock units ranging in age from Triassic to Plio-Pleistocene and representing diverse facies. As a formation, the name “Cablac Limestone” should be discarded for a Cenozoic unit. The Upper Oligocene–Lower Miocene shallow-water limestone unit that is typified by outcrops in the Booi region of West Timor, and that has contributed to clasts in the Cablac breccia, is informally named the Booi limestone. It is considered part of the allochthonous Banda Terrane of Asian affinity and represents the only shallow-marine Lower Miocene unit known from Timor. The only other Miocene sedimentary unit known from Timor includes carbonate pelagites – designated the Kolbano beds – probably deposited on an Australian continental terrace at water depths between 1000 and 3000 m. On the northeastern edge of Cablac Mountain, oolitic limestone and associated units of the Gondwana Megasequence, the Kolbano beds of the Australian-Margin Megasequence, and the Booi limestone and associated metasediments of the Banda Terrane were juxtaposed by a Plio-Pleistocene high-angle fault along which the Cablac crush breccia formed.     

Tertiary foraminiferal rock samples from the western Solomon Sea

Rock fragments dredged from four R/VNatsushima stations contain Tertiary foraminifera. The oldest sample is an upper bathyal biomicrite of Early Eocene age (52 to 53.5 Ma) from the the Trobriand Platform. Upper Oligocene-Lower Miocene neritic limestones were located off the Trobriand Platform and on the inner wall of the New Britain Trench. Miocene bathyal sediments come from the Trobriand Platform; similar Pliocene rocks were recovered here as well as from the inner wall of the New Britain Trench and the central part of the Solomon Sea Basin. No reworked pre-Tertiary foraminifera are present in any sample.     

Sedimentary and foraminiferal facies in Exmouth Gulf,in arid tropical northwestern Australia

Exmouth Gulf is a major U‐shaped embayment on the northwestern coast of Western Australia, at a latitude of 22°S. Water temperatures are 18–31°C and normal oceanic salinity is maintained by strong tidal currents despite the hot, arid climate. A series of sediment grab samples were collected and analysed for particle‐size and foraminiferal diversity. Samples contained mud, quartzose fine sand and coarse carbonate sand fractions. The muddiest facies are located in the most sheltered areas of the gulf: mangrove channels, tidal flats, southwestern flanks and the deeper axial region. Quartzose fine sands probably have mixed origins which might include: southern aeolian dunes; cyclone‐related reworking of beach and near‐shore deposits; and reworked relict shelf alluvium. The shallow‐water fair‐weather wave climate may play a significant role in localised sediment dispersal and sorting along the eastern margin of the gulf. Sediment distributions within the gulf are complicated by low sedimentation rates through much of the central and western areas of the gulf, significant mixing, and possible inheritance of pre‐Holocene alluvium. The Holocene foraminiferal assemblage recorded from Exmouth Gulf is overwhelmingly dominated by benthic species: agglutinated, calcitic‐porcellaneous, and calcitic‐hyaline groups. The distribution of individual foraminiferal species shows relatively simple patterns, governed by environmental parameters. Live individuals are rare.     

Ground retreat and slope evolution on regraded surface-mine dumps,waunafon, gwent

Ground retreat was monitored on two vegetated and two unvegetated profiles over a five-year period. The average annual retreat of the two unvegetated profiles was 5.84 mm and 3.62 mm; that of the two vegetated profiles 2.34 mm and 2.07 mm. Slope evolution was controlled by the mid-slope-ward migration of two zones of accelerated erosion and the resulting replacement of a central rectilinear slope segment by the upper and lower slope elements.     

Coupled rainfall and water vapour stable isotope time series reveal tropical atmospheric processes on multiple timescales

High-frequency stable isotope data are useful for validating atmospheric moisture circulation models and provide improved understanding of the mechanisms controlling isotopic compositions in tropical rainfall. Here, we present a near-continuous 6-month record of O- and H-isotope compositions in both water vapour and daily rainfall from Northeast Australia measured by laser spectroscopy. The data set spans both wet and dry seasons to help address a significant data and knowledge gap in the southern hemisphere tropics. We interpret the isotopic records for water vapour and rainfall in the context of contemporaneous meteorological observations. Surface air moisture provided near-continuous tracking of the links between isotopic variations and meteorological events on local to regional spatial scales. Power spectrum analysis of the isotopic variation showed a range of significant periodicities, from hourly to monthly scales, and cross-wavelet analysis identified significant regions of common power for hourly averaged water vapour isotopic composition and relative humidity, wind direction, and solar radiation. Relative humidity had the greatest subdiurnal influence on isotopic composition. On longer timescales (weeks to months), isotope variability was strongly correlated with both wind direction and relative humidity. The high-frequency records showed diurnal isotopic variations in O- and H-isotope compositions due to local dew formation and, for deuterium excess, as a result of evapotranspiration. Several significant negative isotope anomalies on a daily scale were associated with the activity of regional mesoscale convective systems and the occurrence of two tropical cyclones. Calculated air parcel back trajectories identified the predominant moisture transport paths from the Southwest Pacific Ocean, whereas moisture transport from northerly directions occurred mainly during the wet season monsoonal airflow. Water vapour isotope compositions reflected the same meteorological events as recorded in rainfall isotopes but provided much more detailed and continuous information on atmospheric moisture cycling than the intermittent isotopic record provided by rainfall. Improved global coverage of stable isotope data for atmospheric water vapour is likely to improve simulations of future changes to climate drivers of the hydrological cycle.     

Consensus among multiple trophic levels during high- and low-water stands over the last two millennia in a northwest Ontario lake

We investigated the modern distribution of fossil midges within a dimictic lake and explored downcore patterns of inferred lake depths over the last 2000 years from previously published proxies. Modern midge distribution within Gall Lake showed a consistent and predictable pattern related to the lake-depth gradient with recognizable assemblages characteristic of shallow-water, mid-depth and profundal environments. Interpretations of downcore changes in midge assemblages, in conjunction with quantitative lake-depth inferences across a priori defined (based on diatom data) ~ 500-yr wet and dry periods, demonstrated that both invertebrate and algal assemblages exhibited similar timing and nature of ecological responses. Midges were quantified by their relative abundance, concentrations and an index of Chaoborus to chironomids, and all showed the greatest differences between the wet and dry periods. During the low lake-level period of the Medieval Climate Anomaly (MCA: AD 900 to 1400), profundal chironomids declined, shallow-water and mid-depth chironomids increased, chironomid-inferred lake level declined and the Chaoborus-to-chironomid index decreased. The coherence between multiple trophic levels provides strong evidence of lower lake levels in Gall Lake during the MCA.     

Tertiary foraminiferal rock samples from the western Solomon Sea

Rock fragments dredged from four R/VNatsushima stations contain Tertiary foraminifera. The oldest sample is an upper bathyal biomicrite of Early Eocene age (52 to 53.5 Ma) from the the Trobriand Platform. Upper Oligocene-Lower Miocene neritic limestones were located off the Trobriand Platform and on the inner wall of the New Britain Trench. Miocene bathyal sediments come from the Trobriand Platform; similar Pliocene rocks were recovered here as well as from the inner wall of the New Britain Trench and the central part of the Solomon Sea Basin. No reworked pre-Tertiary foraminifera are present in any sample.