Differential GPS Surveys Research Articles

Evaluating the effectiveness and robustness of machine learning models with varied geo-environmental factors for determining vulnerability to water flow-induced gully erosion

Assessing and mapping the vulnerability of gully erosion in mountainous and semi-arid areas is a crucial field of research due to the significant environmental degradation observed in such regions. In order to tackle this problem, the present study aims to evaluate the effectiveness of three commonly used machine learning models: Random Forest, Support Vector Machine, and Logistic Regression. Several geographic and environmental factors including topographic, geomorphological, environmental, and hydrologic factors that can contribute to gully erosion were considered as predictor variables of gully erosion susceptibility. Based on an existing differential GPS survey inventory of gully erosion, a total of 191 eroded gullies were spatially randomly split in a 70:30 ratio for use in model calibration and validation, respectively. The models’ performance was assessed by calculating the area under the ROC curve (AUC). The findings indicate that the RF model exhibited the highest performance (AUC = 89%), followed by the SVM (AUC = 87%) and LR (AUC = 87%) models. Furthermore, the results highlight those factors such as NDVI, lithology, drainage, and density were the most influential, as determined by the RF, SVM, and LR methods. This study provides a valuable tool for enhancing the mapping of soil erosion and identifying the most important influencing factors that primarily cause soil deterioration in mountainous and semi-arid regions.

Seasonal morphodynamics of multiple intertidal bars (MITBs) on a meso‐ to macrotidal beach

AbstractMultiple intertidal bar (MITB) beach systems comprise a succession of subdued, shore‐parallel sandbars, developed under low‐energy conditions in meso‐ to macrotidal settings. Their relatively stable morphologies over long timescales are commonly attributed to a dynamic equilibrium, driven primarily by seasonal morphodynamics. The seasonal behaviour is, however, poorly understood. The relationship between temporal and spatial hydrodynamic forcing and morphological changes was investigated through monthly differential GPS surveys in Dundrum Bay (Northern Ireland) from April 2019 to March 2020, associated with variations in nearshore wave conditions, simulated using the SWAN wave model. During low‐energy summer conditions, southeast waves helped promote MITB stability and a slight increase in bar crest elevation, with the seaward‐most bar buffering and preserving the inner bar system through wave dissipation. In the winter, a progressive increase in wave energy, and a switch in wave direction (southwest to south), initiated the highest rates of cross‐shore bar migration and a lowering of bar crests. While the seaward‐most bar remained largely submerged, the shoreward‐most bar played a key role in protecting the upper‐beach and/or foredune. Winter conditions also forced a newly observed mesoscale longshore drift involving offshore sediment transport in the southwest and onshore transport in the northeast. Cross‐shore variability in MITB behaviour at seasonal timescales was, however, primarily driven by local hydrodynamic conditions, including variations in wave energy and direction. Conversely, alongshore variability was largely influenced by the complex nearshore bathymetry, headlands and an active ebb delta, all interacting with changing hydrodynamic forcing. These results challenge the seasonal equilibrium model for MITB systems and highlight longer‐term patterns of sediment movement.

A Preliminary Assessment of a Newly-Defined Multispectral Hue Space for Retrieving River Depth with Optical Imagery and In Situ Calibration Data

Bathymetry is a key element in the modeling of river systems for flood mapping, geomorphology, or stream habitat characterization. Standard practices rely on the interpolation of in situ depth measurements obtained with differential GPS or total station surveys, while more advanced techniques involve bathymetric LiDAR or acoustic soundings. However, these high-resolution active techniques are not so easily applied over large areas. Alternative methods using passive optical imagery present an interesting trade-off: they rely on the fact that wavelengths composing solar radiation are not attenuated at the same rates in water. Under certain assumptions, the logarithm of the ratio of radiances in two spectral bands is linearly correlated with depth. In this study, we go beyond these ratio methods in defining a multispectral hue that retains all spectral information. Given n coregistered bands, this spectral invariant lies on the (n−2)-sphere embedded in Rn−1, denoted Sn−2 and tagged ‘hue hypersphere’. It can be seen as a generalization of the RGB ‘color wheel’ (S1) in higher dimensions. We use this mapping to identify a hue-depth relation in a 35 km reach of the Garonne River, using high resolution (0.50 m) airborne imagery in four bands and data from 120 surveyed cross-sections. The distribution of multispectral hue over river pixels is modeled as a mixture of two components: one component represents the distribution of substrate hue, while the other represents the distribution of ‘deep water’ hue; parameters are fitted such that membership probability for the ‘deep’ component correlates with depth.

Holocene lake-level fluctuations of Selin Co on the central Tibetan plateau: Regulated by monsoonal precipitation or meltwater?

Over the Tibetan Plateau (TP), lakes as paleoenvironmental archives have been the most extensively investigated for their sensitivities to climate change on different timescales. Well-preserved shoreline and terrace remains surrounding these lakes provide critical geomorphological and sedimentary evidence that can be used to infer past lake levels over geological timescales. These features can offer an analogue for understanding how future lake-levels respond to global warming. In this study, we investigated a series of water level-related depositional profiles around the Selin Co basin from the central TP, by dating 28 samples using K-feldspar luminescence techniques. Combining the obtained chronological data with sedimentological, stratigraphic evidence and differential GPS survey observations, the Holocene history of lake-level fluctuations in Selin Co was inferred. The results show a stable highstand between 10 ka and 7 ka but a striking subsequent lake-level decline. This pattern appears to follow the solar insolation-forced changes in the intensity of the Indian summer monsoon (ISM), particularly during the early Holocene. However, such gradual weakening of ISM intensity after the early Holocene may not interpret the dramatically rapid shrinking of Selin Co, implying other components are largely underrecognized driving factors accounting for the effective moisture of lakes in the early Holocene. Here, we argue that the increased meltwater input from glaciers and permafrost, together with increased precipitation, might have resulted in the high lake level at 10–7 ka, as the high summer temperature during the early Holocene induced massive melting water flow into the lake. By 7 ka, the abrupt lake-level drop is likely related to the decreased meltwater owing to decreasing regional temperatures documented from glacier landforms, ice cores and lacustrine sediments. Therefore, we highlight that meltwater from glaciers and permafrost poured into lakes on the central TP, particularly during warm periods on the millennial timescales, might also dominate the Holocene high lake levels.

Evaluation of Cartosat-2E Data for Large-Scale Urban Mapping

Large-scale maps are a prerequisite for sustainable management of urban areas for which very high-resolution satellite (VHRS) imagery can be effectively utilized. PAN sharpened (merged) orthorectified product of Cartosat–2E satellite launched by ISRO (0.6 m spatial resolution) has been evaluated for 1:4000 scale mapping in Dehradun and Rishikesh, India. Root mean square error (RMSE) of Cartosat-2E data is found to be 29.03 m in Dehradun and 28.15 m in Rishikesh. However, after the induction of GCPs collected from the Differential GPS (DGPS) survey, RMSE error reduced to less than 1 m, which is acceptable for urban mapping as per atal mission for rejuvenation and urban transformation (AMRUT) design and standards. It is observed that system-level improvements in data acquisition and the use of high accuracy GCPs can assist in harnessing the potential of Cartosat-2E for large-scale urban mapping at 1:4000 scale. It is also found that Cartosat 2E data can be utilized for identification of a large number of subclasses (~ 39) of urban land use land cover and building footprints as per the AMRUT design standards which have a great potential to reduce project cost and volume of human resources for large-scale urban mapping as compared to conventional ground-based methods.

Slip rates and paleoearthquakes along the east segment of the Guanggaishan–Dieshan fault zone, West Qinling Range, NW China

The WNW-trending Guanggaishan–Dieshan fault (GDF) is located in the West Qinling Range at a site of tectonic junction between the Tibetan plateau, the Sichuan basin and the Ordos block. Tectonically, this region is bounded by the East Kunlun fault to the southwest, the West Qinling fault to the north, and the Longmenshan fault to the southeast. The activity of the GDF is essentially related with the northeastward expansion of the Tibetan Plateau and associated strain partition between the East Kunlun fault and the West Qinling fault. This study reported the sense of fault movement, rate of fault slip, and the timing of three paleoseismic events on the east segment of the Guanggaishan–Dieshan fault (EGDF) with which no historical earthquake has been documented before. We focused our investigation on three branch faults in the central part of the EGDF using a range of study methods, e.g. structural mapping, paleoseismological trenching, unmanned aircraft vehicle photogrammetry, differential GPS survey, as well as radiocarbon and optically stimulated luminescence dating. Our new results highlighted: (1) the EGDF is dominated by the left-lateral sense of movement with a minor component of dip slip, (2) the range-bounding branch is characterized by a maximum left-lateral slip rate of 0.72 ± 0.34 mm/year and a maximum vertical-slip rate of 0.13 ± 0.03 mm/year, respectively. Kinematics of the EGDF is similar to many other active faults in the West Qinling Range, together they play a joint role in accommodating and transferring the residual left-lateral slip of the East Kunlun Fault. Three paleoseismic events were identified on the range-bounding fault based on two types of event markers: cut-cover relation and colluvial deposition. The ages of the most recent two events are estimated to be 2765–3320 cal. year BP and 12,775–13,005 cal. year BP and the age of the oldest event is as early as 18,495–32,950 cal. year BP. In contrast, there is no compelling evidence to show paleoseismic event along the rest two branches, and further work is needed to demonstrate this.

Rate of active shortening across the southern thrust front of the Greater Caucasus in western Georgia from kinematic modeling of folded river terraces above a listric thrust

Although the Greater Caucasus (GC) Mountains accommodate a significant fraction of orogen-perpendicular Arabia-Eurasia convergence at their longitude, the locations and slip rates of the active structures absorbing this shortening are poorly known. Here we report the first late Quaternary shortening rate for an active thrust in the GC determined from dating and reconstructing a deformed landform. In the Rioni basin along the southwestern flank of the GC, terraces along the Enguri River have been folded by the south-vergent Tsaishi anticline and record Quaternary shortening along the southernmost exposed frontal structure. Terrace surfaces are well preserved and together with underlying Mesozoic-to-Neogene strata clearly record folding. We use high-resolution topographic data from differential GPS surveys and bedding attitudes across the fold to construct a kinematic model that describes both the terrace deformation and finite shortening across the anticline recorded by the folded strata. We calculate that a deformed terrace records 106.1 +38.7/-36.4 m of slip since abandonment. Optically stimulated luminescence dating of quartz in a loess cap on this terrace indicates it was abandoned before 94.1 ± 12.8 ka, implying a geologic shortening rate of 1.09 +0.62/-0.43 mm/yr since ∼100 ka. This work confirms that the frontal structure of the Rioni fold-thrust belt is Quaternary-active, but has a rate that falls short of the regional geodetic shortening rate of 3-5 mm/yr. We infer that the missing late Quaternary shortening is accommodated by additional structures within the GC to the north. Folding of late Quaternary terraces and a possible coseismic scarp along the frontal structure of the GC together imply that structures in the western GC may be capable of coseismic rupture within and beneath the adjacent basin, in addition to blind ruptures within the main range such as the 1991 Racha earthquake. Thus, the GC system appears to be broadly analogous to the Himalaya, where the foreland fold-thrust belt connects by a shallow seismogenic detachment to structures beneath the main range. The geometry of this detachment may influence earthquake rupture initiation and propagation, potentially playing a significant role in the seismic hazard of the GC.

Structure from motion photogrammetry in ecology: Does the choice of software matter?

Image‐based modeling, and more precisely, Structure from Motion (SfM) and Multi‐View Stereo (MVS), is emerging as a flexible, self‐service, remote sensing tool for generating fine‐grained digital surface models (DSMs) in the Earth sciences and ecology. However, drone‐based SfM + MVS applications have developed at a rapid pace over the past decade and there are now many software options available for data processing. Consequently, understanding of reproducibility issues caused by variations in software choice and their influence on data quality is relatively poorly understood. This understanding is crucial for the development of SfM + MVS if it is to fulfill a role as a new quantitative remote sensing tool to inform management frameworks and species conservation schemes. To address this knowledge gap, a lightweight multirotor drone carrying a Ricoh GR II consumer‐grade camera was used to capture replicate, centimeter‐resolution image datasets of a temperate, intensively managed grassland ecosystem. These data allowed the exploration of method reproducibility and the impact of SfM + MVS software choice on derived vegetation canopy height measurement accuracy. The quality of DSM height measurements derived from four different, yet widely used SfM‐MVS software—Photoscan, Pix4D, 3DFlow Zephyr, and MICMAC, was compared with in situ data captured on the same day as image capture. We used both traditional agronomic techniques for measuring sward height, and a high accuracy and precision differential GPS survey to generate independent measurements of the underlying ground surface elevation. Using the same replicate image dataset (n = 3) as input, we demonstrate that there are 1.7, 2.0, and 2.5 cm differences in RMSE (excluding one outlier) between the outputs from different SfM + MVS software using High, Medium, and Low quality settings, respectively. Furthermore, we show that there can be a significant difference, although of small overall magnitude between replicate image datasets (n = 3) processed using the same SfM + MVS software, following the same workflow, with a variance in RMSE of up to 1.3, 1.5, and 2.7 cm (excluding one outlier) for “High,” “Medium,” and “Low” quality settings, respectively. We conclude that SfM + MVS software choice does matter, although the differences between products processed using “High” and “Medium” quality settings are of small overall magnitude.

Influence of Topographic Resolution and Accuracy on Hydraulic Channel Flow Simulations: Case Study of the Versilia River (Italy)

The Versilia plain, a well-known and populated tourist area in northwestern Tuscany, is historically subject to floods. The last hydrogeological disaster of 1996 resulted in 13 deaths and in loss worth hundreds of millions of euros. A valid management of the hydraulic and flooding risks of this territory is therefore mandatory. A 7.5 km-long stretch of the Versilia River was simulated in one-dimension using river cross-sections with the FLO-2D Basic model. Simulations of the channel flow and of its maximum flow rate under different input conditions highlight the key role of topography: uncertainties in the topography introduce much larger errors than the uncertainties in roughness. The best digital elevation model (DEM) available for the area, a 1-m light detection and ranging (LiDAR) DEM dating back to 2008–2010, does not reveal all the hydraulic structures (e.g., the 40 cm thick embankment walls), lowering the maximum flow rate to only 150 m3/s, much lower than the expected value of 400 m3/s. In order to improve the already existing input topography, three different possibilities were considered: (1) to add the embankment walls to the LiDAR data with a targeted Differential GPS (DGPS) survey, (2) to acquire the cross section profiles necessary for simulation with a targeted DGPS survey, and (3) to achieve a very high resolution topography using structure from motion techniques (SfM) from images acquired using an unmanned aerial vehicle (UAV). The simulations based on all these options deliver maximum flow rates in agreement with estimated values. Resampling of the 10 cm cell size SfM-DSM allowed us to investigate the influence of topographic resolution on hydraulic channel flow, demonstrating that a change in the resolution from 30 to 50 cm alone introduced a 10% loss in the maximum flow rate. UAV-SfM-derived DEMs are low cost, relatively fast, very accurate, and they allow for the monitoring of the channel morphology variations in real time and to keep the hydraulic models updated, thus providing an excellent tool for managing hydraulic and flooding risks.

Quality Assessment and Glaciological Applications of Digital Elevation Models Derived from Space-Borne and Aerial Images over Two Tidewater Glaciers of Southern Spitsbergen

In this study, we assess the accuracy and precision of digital elevation models (DEM) retrieved from aerial photographs taken in 2011 and from Very High Resolution satellite images (WorldView-2 and Pléiades) from the period 2012–2017. Additionally, the accuracy of the freely available Strip product of ArcticDEM was verified. We use the DEMs to characterize geometry changes over Hansbreen and Hornbreen, two tidewater glaciers in southern Spitsbergen, Svalbard. The satellite-based DEMs from WorldView-2 and Pléiades stereo pairs were processed using the Rational Function Model (RFM) without and with one ground control point. The elevation quality of the DEMs over glacierized areas was validated with in situ data: static differential GPS survey of mass balance stakes and GPS kinematic data acquired during ground penetrating radar survey. Results demonstrate the usefulness of the analyzed sources of DEMs for estimation of the total geodetic mass balance of the Svalbard glaciers. DEM accuracy is sufficient to investigate glacier surface elevation changes above 1 m. Strips from the ArcticDEM are generally precise, but some of them showed gross errors and need to be handled with caution. The surface of Hansbreen and Hornbreen has been lowering in recent years. The average annual elevation changes for Hansbreen were more negative in the period 2015–2017 (−2.4 m a−1) than in the period 2011–2015 (−1.7 m a−1). The average annual elevation changes over the studied area of Hornbreen for the period 2012–2017 amounted to −1.6 m a−1. The geodetic mass balance for Hansbreen was more negative than the climatic mass balance estimated using the mass budget method, probably due to underestimation of the ice discharge. From 2011 to 2017, Hansbreen lost on average over 1% of its volume each year. Such a high rate of relative loss illustrates how fast these glaciers are responding to climate change.

DEM generation from Worldview-2 stereo imagery and vertical accuracy assessment for its application in active tectonics

The DEM-generation technology from high-resolution satellite imagery enables us to generate a wide range of high-resolution topographic data rapidly, improving the efficiency of data acquisition greatly. This method is more efficient than airborne Light Detection And Ranging (LiDAR) in terrain reconstruction, since satellite imagery covers a larger area without difficulties in field deployment. Previous researches evaluated the accuracy of DEMs generated from stereo imagery of different satellite sensors, however there is not enough quantitative analysis concerning the capability of satellite-based DEM in active tectonic studies. Therefore, in this paper, we presented a study to investigate the accuracy to measure heights of fault scarps using the DEM obtained from Worldview-2 stereo imagery and chose the Kumysh fault in the southern margin of Kumysh Basin (Eastern Tian Shan, China) as our test site. Point cloud data were obtained from stereo satellite imagery, both with and without GCPs respectively. Prior to the generation of the DEM, we compared the overall elevation differences of the point clouds and the fault scarp swaths. The overall elevation difference ranges from −1.2 to 0.4 m, with the mean value of −0.57 m, while the elevation difference of fault scarp swaths range from −1.1 to 0 m, with the mean value of −0.4 m. Afterwards, we generated a 0.5 m resolution DEM of 5-km swath along the Kumysh fault, measured the heights of fault scarps on different levels of alluvial fans, and compared the topographic profiles obtained from DEM and post-processed differential GPS (ppGPS) survey. Our results show that: (1) the elevation difference between the topographic profiles ranges from −2.82–4.47 m, the shape of the fault scarp can be accurately reconstructed by satellite-based DEM with the deviation of 0.29 m after elevation correction; (2) the accuracy of the height measurement of fault scarps can reach 0.25 m. These findings indicate that the DEM generated from Worldview-2 stereo imagery is capable of measuring relative deformed topographic features, which could be of great interest to professionals exploring the use and accuracy of satellite stereo imagery for active tectonic applications.

Modelling gully-erosion susceptibility in a semi-arid region, Iran: Investigation of applicability of certainty factor and maximum entropy models

Gully erosion susceptibility mapping is a fundamental tool for land-use planning aimed at mitigating land degradation. However, the capabilities of some state-of-the-art data-mining models for developing accurate maps of gully erosion susceptibility have not yet been fully investigated. This study assessed and compared the performance of two different types of data-mining models for accurately mapping gully erosion susceptibility at a regional scale in Chavar, Ilam, Iran. The two methods evaluated were: Certainty Factor (CF), a bivariate statistical model; and Maximum Entropy (ME), an advanced machine learning model. Several geographic and environmental factors that can contribute to gully erosion were considered as predictor variables of gully erosion susceptibility. Based on an existing differential GPS survey inventory of gully erosion, a total of 63 eroded gullies were spatially randomly split in a 70:30 ratio for use in model calibration and validation, respectively. Accuracy assessments completed with the receiver operating characteristic curve method showed that the ME-based regional gully susceptibility map has an area under the curve (AUC) value of 88.6% whereas the CF-based map has an AUC of 81.8%. According to jackknife tests that were used to investigate the relative importance of predictor variables, aspect, distance to river, lithology and land use are the most influential factors for the spatial distribution of gully erosion susceptibility in this region of Iran. The gully erosion susceptibility maps produced in this study could be useful tools for land managers and engineers tasked with road development, urbanization and other future development.

Quaternary tectonic evolution of the Pamir‐Tian Shan convergence zone, Northwest China

AbstractThe Pamir‐Tian Shan collision zone in the western Tarim Basin, northwest China, formed from rapid and ongoing convergence in response to the Indo‐Eurasian collision. The arid landscape preserves suites of fluvial terraces crossing structures active since the late Neogene that create fault and fold scarps recording Quaternary deformation. Using geologic and geomorphic mapping, differential GPS surveys of deformed terraces, and optically stimulated luminescence dating, we create a synthesis of the active structures that delineate the timing, rate, and migration of Quaternary deformation during ongoing convergence. New deformation rates on eight faults and folds, when combined with previous studies, highlight the spatial and temporal patterns of deformation within the Pamir‐Tian Shan convergence zone during the Quaternary. Terraces spanning ~130 to ~8 ka record deformation rates between ~0.1 and 5.6 mm/yr on individual structures. In the westernmost Tarim Basin, where the Pamir and Tian Shan are already juxtaposed, the fastest rates occur on actively deforming structures at the interface of the Pamir‐Tian Shan orogens. Farther east, as the separation between the Pamir‐Tian Shan orogens increases, the deformation has not been concentrated on a single structure, but rather has been concurrently distributed across a zone of faults and folds in the Kashi‐Atushi fold‐and‐thrust belt and along the NE Pamir margin, where shortening rates vary on individual structures during the Quaternary. Although numerous structures accommodate the shortening and the locus of deformation shifts during the Quaternary, the total shortening across the western Tarim Basin has remained steady and approximately matches the current geodetic rate of 6–9 mm/yr.

First in situ record of decadal glacier mass balance (2003–2014) from the Bhutan Himalaya

AbstractThis study presents the first decadal mass-balance record of a small debris-free glacier in the Bhutan Himalaya, where few in situ measurements have been reported to date. Since 2003 we have measured the mass balance of Gangju La glacier, which covers an area of 0.3km2 and extends from 4900 to 5200ma.s.l., using both differential GPS surveys (geodetic method) and stake measurements (direct method). The observed mass balance ranged from –1.12 to –2.04mw.e. a–1 between 2003 and 2014. The glacier exhibited much greater mass loss than neighbouring glaciers in the eastern Himalaya and southeastern Tibet, which are expected to be sensitive to climate change due to the monsooninfluenced humid climate. Observed mass-balance profiles suggest that the equilibrium-line altitude has been higher than Gangju La glacier since 2003, implying that the entire glacier has experienced net ablation for at least the past decade.

Elevation changes measured during 1966–2010 on the monsoonal temperate glaciers' ablation region, Gongga Mountains, China

Temperate glaciers are more sensitive to climate change than are polar or continental glaciers, and can drive remarkable runoff variation in local water catchments. Changes in the glacier area and surface elevation of the three monsoonal temperate glaciers in the Gongga Mountains, China, were analyzed using series of remote sensing images and digital elevation model (DEM) data. All possible sources of uncertainty were considered in detail. The results showed that the total glacier area decreased by 4.3 km2 (6.7%) between 1966 and 2010. A comparison of glacier surface elevations using DEMs derived from dual-frequency differential GPS (DGPS) surveys in 2010, and from 1966 to 1989 from topographic maps. The three glaciers underwent significant mass loss from 1966 to 2010 and the mean surface elevation changes were −0.90 ± 0.45 m/y, −1.06 ± 0.45 m/y, and −1.12 ± 0.45 m/y for Hailuogou (HLG), Dagongba (DGB) and Yanzigou (YZG) Glaciers, respectively, from 1966 to 2010. Analysis of the meteorological data showed that the mean annual air temperature increase was the main reason for the thinning and volume loss. Thinning of the glacier tongue and volume loss was more intense in the period 1989–2010 than in 1966–89. Debris thickness and other factors are also believed to play important roles in differential thinning among different areas and periods.

A case study integrating remote sensing and distinct element analysis to quarry slope stability assessment in the Monte Altissimo area, Italy

Over last decade geomatic techniques have been increasingly used for the geometrical characterization of rock slopes. Terrestrial laser scanning and digital terrestrial photogrammetry in particular are now frequently used in the characterization of joint surfaces and slope geometry. Although the use of these techniques for the structural characterization of slopes is widely documented, limited research has been undertaken to improve our understanding of the importance of the derived data quality in the construction of slope geometry imported into 3D numerical models. One of the most common problems encountered in the use of these techniques, especially in case of slopes with complex geometry, is the presence of occlusions. In this context, the aims of this paper are to describe how the integrated use of terrestrial laser scanning, digital terrestrial photogrammetry and topographic surveys can mitigate the influence of occlusions and how the slope geometry gained from these surveys can be important in slope stability analyses. For this purpose a case study in the Monte Altissimo area (Apuan Alps, Italy) will be presented. Several geomatic techniques were used for studying a slope overhanging the Granolesa quarry. Special emphasis will be given to the importance of using Total Station and Differential GPS surveys as tools for data fusion. Moreover, in order to validate this procedure, the accuracy and precision of the output were determined through comparison of 3D models derived from laser scanning and digital terrestrial photogrammetry.Furthermore, two different analyses with the three-dimensional distinct element code, 3DEC, were carried out in order to highlight the advantages and limitations of using data obtained from terrestrial remote sensing techniques as opposed to models based on topographic maps.

Recent deep-seated coastal landsliding at San Onofre State Beach, California

Airborne LiDAR collected during the period 1998–2010 and differential GPS surveys conducted over 2008–2013 show recent reactivation and movement of a large deep-seated coastal landslide at San Onofre State Beach, San Diego County, California. The overall slide complex extends about 700m alongshore, 150m inland, and an unknown distance offshore. Differencing digital elevation models and tracking field monuments (benchmarks) provide time series of quantitative topographic landslide changes and new insight in to the slide motion sequences and mechanics. The slide contains several distinct primary and secondary regions moving and deforming at different rates. Primary slide motion includes slow seaward translational motion, rotational slipping, and upward offshore movement. Secondary processes of basal wave erosion and new inland cliffline failures contribute to primary landslide destabilization. The landslide exhibits lithologic and structural controls, is driven by a combination of marine and subaerial processes, influences local beach morphology, and deviates from typical southern California coastal cliff processes which mostly involve shallow landslides and topples. Large-scale, cross-shore slide rotation has recently created new nearshore reefs. Eroded cliff sediments provide a local beach sand source and probably influence local nearshore ecosystems. All known time periods of major historical landslide activity were preceded by elevated seasonal rainfall and analysis suggests elevated rainfall generated primary slide motion as opposed to wave action. As of spring 2013, landslide activity has slowed, but continued positive feedbacks including toe removal by wave activity suggest that future landsliding will probably threaten coastal infrastructure.

Some comments on the flow velocity and thinning of Svenbreen, Dickson Land, Svalbard

In this study a differential GPS survey of flow velocity and surface elevation change of a small glacier Svenbreen, central Svalbard, is presented and discussed. The maximum measured velocity was 3.21 m a-1 at 463 m a.s.l., close the theoretical steady-state equilibrium line altitude. After decades of thinning known from earlier research, the glacier surface has been continuing to lower over the analysed time span 2010-2012 by 1.82 m a-1 at the front at 185 m a.s.l. and 0.08 m a-1 at 541 m a.s.l. Since the glacier dynamics is very low, the study concludes that negative mass balance is the main driver of negative geometry changes and that no new distinct landforms will be formed in the near-future in the glacier forefield.

CALIBRATION OF LOW COST DIGITAL CAMERA USING DATA FROM SIMULTANEOUS LIDAR AND PHOTOGRAMMETRIC SURVEYS

Abstract. Digital photogrammetric products from the integration of imagery and lidar datasets are a reality nowadays. When the imagery and lidar surveys are performed together and the camera is connected to the lidar system, a direct georeferencing can be applied to compute the exterior orientation parameters of the images. Direct georeferencing of the images requires accurate interior orientation parameters to perform photogrammetric application. Camera calibration is a procedure applied to compute the interior orientation parameters (IOPs). Calibration researches have established that to obtain accurate IOPs, the calibration must be performed with same or equal condition that the photogrammetric survey is done. This paper shows the methodology and experiments results from in situ self-calibration using a simultaneous images block and lidar dataset. The calibration results are analyzed and discussed. To perform this research a test field was fixed in an urban area. A set of signalized points was implanted on the test field to use as the check points or control points. The photogrammetric images and lidar dataset of the test field were taken simultaneously. Four strips of flight were used to obtain a cross layout. The strips were taken with opposite directions of flight (W-E, E-W, N-S and S-N). The Kodak DSC Pro SLR/c digital camera was connected to the lidar system. The coordinates of the exposition station were computed from the lidar trajectory. Different layouts of vertical control points were used in the calibration experiments. The experiments use vertical coordinates from precise differential GPS survey or computed by an interpolation procedure using the lidar dataset. The positions of the exposition stations are used as control points in the calibration procedure to eliminate the linear dependency of the group of interior and exterior orientation parameters. This linear dependency happens, in the calibration procedure, when the vertical images and flat test field are used. The mathematic correlation of the interior and exterior orientation parameters are analyzed and discussed. The accuracies of the calibration experiments are, as well, analyzed and discussed.

Topographic and geological mapping in the prehistoric area of Melka Kunture (Ethiopia)

This paper describes the results of topographical and geological surveys carried out at the prehistoric area of Melka Kunture (Ethiopia) in order to produce new detailed maps at a scale of 1:10,000 for supporting archaeological investigations and providing good reference cartography during fieldwork. The topographic support was created from the stereorestitution of two pairs of Standard Stereo IKONOS-2, 1m pan-sharpened satellite imageries covering an area of about 100km2. The topographic map was utilized both for the geological survey and for the interpretation of the palaeo-environmental evolution of the site based on present geomorphological features. The aerial triangulation of satellite images, performed using ground control points measured using differential GPS surveys, allowed the stereoscopic visualization of the area and the creation of a digital elevation model and orthophotos. These results were a useful cartographic aid during the geological survey when all the outcrops along gullies, streams, roads and rivers were inspected and documented through additional in-depth field checks. The geological map was created and refined using the digital elevation model and photointerpretation of stereo and orthoimageries, making it possible to fully identify the geological boundaries between formations and recognize geomorphological features.