GM2.11

EDI
From historical images to modern high resolution topography: methods and applications in geosciences

Recent advances in image collection, e.g. using uncrewed aerial vehicles (UAVs), and topographic measurements, e.g. using terrestrial or airborne LiDAR, are providing an unprecedented insight into landscape and process characterization in geosciences. In parallel, historical data including terrestrial, aerial, and satellite photos as well as historical digital elevation models (DEMs), can extend high-resolution time series and offer exciting potential to distinguish anthropogenic from natural causes of environmental change and to reconstruct the long-term evolution of the surface from local to landscape scale.

For both historic and contemporary scenarios, the rise of techniques with ‘structure from motion’ (SfM) processing has democratized data access and offers a new measurement paradigm to geoscientists. Photogrammetric and remote sensing data are now available on spatial scales from millimetres to kilometres and over durations of single events to lasting time series (e.g. from sub-second to decadal-duration time-lapse), allowing the evaluation of event magnitude and frequency interrelationships.

The session welcomes contributions from a broad range of geoscience disciplines such as geomorphology, cryosphere, volcanology, hydrology, bio-geosciences, and geology, addressing methodological and applied studies. Our goal is to create a diversified and interdisciplinary session to explore the potential, limitations, and challenges of topographic datasets for the reconstruction and interpretation of past and present 2D and 3D changes in different environments and processes. We further encourage contributions describing workflows that optimize data acquisition and processing to guarantee acceptable accuracies and to automate data application (e.g. geomorphic feature detection and tracking), and field-based experimental studies using novel multi-instrument and multi-scale methodologies. This session invites contributions on the state of the art and the latest developments in i) modern photogrammetric and topographic measurements, ii) remote sensing techniques as well as applications, iii) modelling technologies, and iv) data processing tools, for instance, using machine learning approaches.

Co-organized by GI1/HS1.1/NH6/SSS11
Convener: Livia PiermatteiECSECS | Co-conveners: Anette EltnerECSECS, Penelope HowECSECS, Mike James, Mark Smith
vPICO presentations
| Wed, 28 Apr, 16:15–17:00 (CEST)

vPICO presentations: Wed, 28 Apr

Chairpersons: Livia Piermattei, Anette Eltner
16:15–16:17
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EGU21-13196
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ECS
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solicited
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Highlight
Friedrich Knuth, David Shean, and Shashank Bhushan

Mountain glaciers have lost significant mass over the past century in response to a globally warming climate. However, on interannual to decadal time scales, many glaciers in Western North America show periods of both advance and retreat. To better understand these systems and their sensitivity to climate forcing, we are generating regional records of glacier surface elevation change from scanned historical film photographs acquired between the 1950s to 1990s. Our results will help constrain projections of future glacier change under different climate scenarios, as well as impacts on downstream water resources and geohazard risk.

Historical image pre-processing and manual ground control point (GCP) selection are time-intensive bottlenecks during traditional SfM processing workflows. We developed an automated photogrammetry processing pipeline (HSfM) to systematically process large archives of vertical aerial film photographs and generate sub-meter resolution digital elevation models (DEMs), without manual GCP selection. We present several case studies for glaciers in the Western North America using photos from the USGS North American Glacier Aerial Photography (NAGAP) and Earth Explorer Aerial Photography Single Frame archives, which differ in terms of available image overlap, survey area extent, and terrain characteristics. Absolute vertical accuracy of <0.5-1.0 m is achieved through iterative closest point (ICP) co-registration over stable bare-ground surfaces between the historical DEMs and modern high-resolution satellite or lidar reference DEMs. We demonstrate the potential for these new DEM records to quantify geodetic glacier mass balance and geomorphological change including moraine deposition, moraine degradation, and sediment redistribution in proglacial areas.

How to cite: Knuth, F., Shean, D., and Bhushan, S.: Historical Structure From Motion (HSfM): Automated production of high-resolution DEMs from historical aerial photography for long-term geodetic change analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13196, https://doi.org/10.5194/egusphere-egu21-13196, 2021.

16:17–16:19
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EGU21-139
Ulrich Kamp, Karina Yager, Elise Arnett, Krysten Bowen, Kate Truitt, Anton Seimon, Tracie Seimon, and Alvaro Ivanoff

Terrestrial and aerial image analysis has proven to be a valuable survey method for documenting terrestrial landscape change related to, for example, biodiversity, urbanization, and environmental services such as land vegetation or forest cover and use, glacier extent, and water resources. Historical oblique aerial photographs offer exceptional opportunities to extend the observational record beyond the period covered by traditional nadir aerial surveys and satellite imagery. Here we apply these methods in the Cordillera Vilcanota of Southern Peru, home to the largest high alpine lake, Sibinacocha, in the Andes, a primary source of the Amazon River. The Shippee-Johnson aerial expedition of 1931 produced oblique photographs of glaciated peaks of the Cordillera Vilcanota. To determine the extent of glacial loss, we compared the 1931 glacier extents with more recent ones derived from satellite imagery analyses using Agisoft Metashape and Pixcavator. The identification of the flight camera positions from 1931 proved to be challenging, since the original photographs come with only rudimentary information. For three test glaciers, the Metashape analysis showed a glacier recession of between 50% and 95% from 1931 to 2018. Preliminary Pixcavator analysis results demonstrated a area decrease of 62% at two glacier termini between 1931 and 2020. Future studies will include repeating the oblique aerial photographs across the Vilcanota and other Andean mountain ranges, and also include ground truth and UAS imagery analysis.

How to cite: Kamp, U., Yager, K., Arnett, E., Bowen, K., Truitt, K., Seimon, A., Seimon, T., and Ivanoff, A.: Using repeat oblique aerial photography and satellite imagery to detect glacial change in the Cordillera Vilcanota, Peru, since 1931, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-139, https://doi.org/10.5194/egusphere-egu21-139, 2020.

16:19–16:21
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EGU21-1476
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ECS
Jakob Rom, Florian Haas, Tobias Heckmann, Moritz Altmann, Fabian Fleischer, Camillo Ressl, and Michael Becht

The future development of debris flow processes regarding frequency and magnitude in terms of climate change is currently the subject of intensive research. One reason for this is that datasets that extend over decades are often incomplete and biased towards high magnitude events based on the poor data availability in text records, for example.

Within this study, we investigate the development of slope-type debris flows in Horlachtal, a small catchment (~ 55 km²) within the Stubai Alps, Austria. Here, aerial images are available from 2018 back to 1947, which enables the creation of orthoimages. These allow a detailed mapping of debris flow processes even with smaller magnitudes. The resulting large dataset of debris flow process zones from 1947 to 2018 (10 time steps) can give some hints about the development of the frequencies of slope-type debris flows for the last 71 years. Due to their high spatial resolution and accuracy, two LiDAR datasets from 2006 and 2017 were used to calculate the volumes of debris flow deposits and thus the magnitude of debris flows within this time. Using a volume-area relationship on the base of the LiDAR data, we are able to estimate the volumes of debris flow deposits even for the older time steps, which can give an idea of changes in the magnitude of debris flow deposits for the last 71 years.

The results show a highly active time period between 1990 and 2010 as well as a high number of debris flows between 1953 and 1974. An increasing trend in numbers per year and volume per year is recognizable, but some uncertainties remain due to mapping issues, which include resolution of aerial images, shadow effects, snow cover etc.

How to cite: Rom, J., Haas, F., Heckmann, T., Altmann, M., Fleischer, F., Ressl, C., and Becht, M.: Development of slope-type debris flows regarding frequencies and magnitudes based on aerial images since 1947 in Horlachtal, Austria, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1476, https://doi.org/10.5194/egusphere-egu21-1476, 2021.

16:21–16:23
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EGU21-2791
Thomas JB Dewez, Claire Rault, and Bertrand Aunay

Geographical Surveys now distribute online their historical aerial photographs. The batches of digital images, holding the appearance and relief of the forever gone landscape, can be processed with automated Structure-from-Motion (SFM) photogrammetric pipelines. Are the results trustworthy? In this communication, we report the results of exploratory tests performed with Agisoft Metashape on sets of 1978, ~1/27.000, vertical aerial photographs from IGN-France over la Réunion volcanic island in the Indian Ocean. Georeferencing deliberately used ground control points and check points collected on IGN's web mapping portal. Validation was obtained from lidar and photogrammetric acquisition of 2015.

First, our results show that scanned photographs do not strictly map camera coordinates to image coordinates from one file to the next. Photos are slightly shifted and rotated on each scan. The photogrammetric assumption of a single camera per batch of images is thus violated. A preprocessing step, automated with Python, locates fiducials, computes camera principal point, rotates and crops the image file to a unique image reference frame. This feature is absent from Agisoft Metashape when fiducial coordinates are unknown.

Second, in the photogrammetric pipeline, camera calibration parameters are deduced from matched sparse points. The sensitivity of the "align" function was explored. The smallest RMS errors were ±7.03m for 11 ground-control points and ±5.45m for 9 independent check points when setting Align quality to "high" and a 4-parameters camera model using focal length (f), eccentricity (cx, cy), one radial distortion parameter (K1). A higher number of parameters delivered no accuracy improvement and correlated parameters. Intensive random sampling of sparse points subsets conducted to stable estimates of focal length and eccentricity. Improving the robustness of focal length determination would require additional, oblique photographs, which was not the spirit of historical survey design and were never acquired in past surveys.

Third, collecting ground control points on https://geoportail.gouv.fr resulted in digital surface model elevation accuracy within +/- 3.34m (Median Absolute Deviation). Validation was computed on a 2015 lidar digital terrain model at 5m resolution on stable grounds. Scanning artefacts, probably due to variable scanning velocity of the digitizing head, introduced elevation variation stripes in Difference of DEM (DoD), parallel to the scanner direction. This pattern limits the detection of geomorphologically meaningful differences.

Fourth, a DoD between 2015-1978 for the Cirque de Salazie, in the north-east of La Réunion Island, highlighted landsliding masses active some time during the last 37 years and 13 cyclones. Beyond this proof of concept, archive aerial photographs in La Réunion go back until 1949 and covered the island twenty times. This time scale offers a welcome hindsight when producing landslide risk mitigation maps.

This work was published in open-access in

Rault, C., Dewez, T. J. B., and Aunay, B., 2020, Structure-from-Motion processing of aerial archive photographs: sensitivity analyses pave the way for quantifying geomorphological changes since 1978 in la Réunion island, ISPRS Ann. Photogramm. Remote Sens. Spatial Inf. Sci., V-2-2020, 773–780, https://doi.org/10.5194/isprs-annals-V-2-2020-773-2020, 2020.

How to cite: Dewez, T. J., Rault, C., and Aunay, B.: Structure-from-Motion applied to historical aerial photographs: parameter variability and application on landslide cyclonic evolution on France's La Réunion Island, Indian Ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2791, https://doi.org/10.5194/egusphere-egu21-2791, 2021.

16:23–16:25
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EGU21-2952
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ECS
Luca Forti, Andrea Pezzotta, Eleonora Regattieri, Guido Stefano Mariani, Filippo Brandolini, and Andrea Zerboni

Located along the Tigris River in the Kurdistan Region of Iraq (KRI), the Mosul Dam reservoir is the second biggest dam of the Near East, and represents an important water storage for local human activities. The Dam was built between 1981 and 1988 north of the village of Eski Mosul; along this part of the Tigris River several archaeological sites were inundated. Analysis of historical images derived from Declassified Corona satellite acquired between December 1967 and August 1968 reveals seasonal changes of the Tigris riverbed, shifting across the hydrological year from meandering to anastomosing. The geomorphological mapping was carried out on the December 1967 and. in August 1968, Corona images were taken, in order to estimate the modification of several fluvial geomorphological elements such as floodplain and point, middle and longitudinal bars. Here, such evidence is compared with Landsat data collected between the 1990ies and today, in order to detect the first phases of filling of the basin and the control of inherited Tigris channel belt over the reservoir. Moreover, we also noticed an influence of the ancient Tigris course on is recent insertion into the lake. Our work permitted to reconstruct the ancient fluvial landscape below the Mosul Dam Lake, and its evolution in response to seasonal variation of the discharge.

How to cite: Forti, L., Pezzotta, A., Regattieri, E., Mariani, G. S., Brandolini, F., and Zerboni, A.: Below the Mosul Dam Lake. Geomorphological reconstruction of historical fluvial pattern of the Tigris River , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2952, https://doi.org/10.5194/egusphere-egu21-2952, 2021.

16:25–16:27
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EGU21-16371
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ECS
Diego Cusicanqui, Antoine Rabatel, Xavier Bodin, Christian Vincent, Emmanuel Thibert, Pierre Allain Duvillard, and André Revil

Glacial and periglacial environments are highly sensitive to climate change, even more in mountain areas where warming is faster and, as a consequence, perennial features of the cryosphere like glaciers and permafrost have been fast evolving in the last decades. In the European Alps, glaciers retreat and permafrost thawing have led to the destabilization of mountain slopes, threatening human infrastructures and inhabitants. The observation of such changes at decadal scales is often limited to sparse in situ observations.

Here, we present three study cases of mountain permafrost sites based on a multidisciplinary approach over almost seven decades. The goal is to investigate and quantify morphodynamic changes and understand the causes of these evolutions. We used stereo-photogrammetry techniques to generate orthophotos and (DEMs) from historical aerial images (available, in France since 1940s). From this, we produced diachronic comparison of DEMs to quantify vertical surface changes, as well as feature tracking techniques of multi-temporal digital orthophotos for estimating horizontal displacement rates. Locally, high-resolution datasets (i.e. LiDAR surveys, UAV acquisitions and Pléiades stereo imagery) were also exploited to improve the quality of photogrammetric products. In addition, we combine these results with geophysics (ERT and GPR) to estimate the ice content, geomorphological surveys to describe the complex environments and the relationship with climatic forcing.

The first study case is the Laurichard rock glacier, where we were able to quantify changes of emergence velocities, fluxes, and volume. Together with an acceleration of surface velocity, important surface lowering have been found over the period 1952-2019, with a striking spatiotemporal reversal of volume balance.

The second study site is the Tignes glacial and periglacial complex, where the changes of thermokarstic lakes surface were quantified. The results suggest that drainage probably affects the presence and the evolution of the largest thermorkarst. Here too, a significant ice loss was found on the central channel concomitant to an increase in surface velocities.

The third study site is the Chauvet glacial and periglacial complex where several historical outburst floods are recorded during the 20th century, likely related to the permafrost degradation, the presence of thermokarstic lakes, and an intra-glacial channel. The lateral convergence of ice flow, due to the terrain subsidence caused by the intense melting, may cause the closure of the channel with a subsequent refill of the thermokarstic depression and finally a new catastrophic event.

Our results highlight the important value of historical aerial photography for having a longer perspective on the evolution of the high mountain cryosphere, thanks to accurate quantification of pluri-annual changes of volume and surface velocity. For instance, we could evidence : (1) a speed-up of the horizontal displacements since the 1990s in comparison with the previous decades; (2) an important surface lowering related to various melting processes (ice-core, thermokarst) for the three study sites; (3) relationships between the observed evolution and the contemporaneous climate warming, with a long-term evolution controlled by the warming of the ground and short-term changes that may relate to snow or precipitation or to the activity of the glacial-periglacial landforms.

How to cite: Cusicanqui, D., Rabatel, A., Bodin, X., Vincent, C., Thibert, E., Duvillard, P. A., and Revil, A.: Using historical aerial imagery to assess multidecadal kinematics and elevation changes. Application to mountain permafrost in the French Alps., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16371, https://doi.org/10.5194/egusphere-egu21-16371, 2021.

16:27–16:29
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EGU21-5046
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ECS
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solicited
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Highlight
Sebastian Mikolka-Flöry, Tobias Heckmann, Michael Becht, and Norbert Pfeifer

Historical terrestrial images for identification, documentation, and especially the quantification of change in the alpine landscape are a largely unused source. Metric exploitation requires estimating the unknown camera parameters (camera location, angular attitude, and focal length) by photogrammetric resection. This is a challenging task, especially the identification of ground control points in mountainous terrain is time consuming and requires experience. Furthermore, due to the limited field of view of single images only small areas are captured. Hence, despite their possibility to provide quantitative information from more than one hundred years ago, integrating information from these historical images into subsequent analysis is often avoided.

Enabling their usage requires suitable software as well as users willing to engage in the challenge of image orientation. To facilitate this, a virtual Mapathon was organized, inviting participants to collaboratively orient historical images of the Val Martell (Italy) in the Ortler Alps. The participants from varying geoscience backgrounds (e.g. Botany, Climatology, Geomorphology, Glaciology, Hydrology) had little experience in photogrammetry prior to the Mapathon. Nevertheless, within one day nearly 100 images were oriented by 20 participants. The Mapathon was organized as a video conference using a web-based 3D image orientation software linked to an image database. Sessions with the whole group and in small teams alternated. Working in small teams stimulated internal discussions, promoting the understanding and success of each participant. Feedback received from the participants shows that the Mapathon helped overcoming the initial problem of getting started. Furthermore, the gained knowledge allows the participants to work with historical terrestrial images on their own in the future. 

The set of oriented historical images created within the Mapathon further underlines the potential of historical terrestrial images. Due to  the availability of numerous oriented images, the limited fields of view of individual images can be combined, allowing the documentation of changes for larger areas. With the calculation of the viewshed for each image, the image database can not only be queried by metadata, but more importantly by location and spatial coverage. Especially the possibility to search for images capturing a certain region of interest will encourage scientists to include historical terrestrial images into their analysis.

How to cite: Mikolka-Flöry, S., Heckmann, T., Becht, M., and Pfeifer, N.: Experiences from a Virtual Mapathon for collaborative Georeferencing of historical terrestrial Images in Alpine regions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5046, https://doi.org/10.5194/egusphere-egu21-5046, 2021.

16:29–16:31
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EGU21-11925
Ryusei Ishii, Patrice Carbonneau, and Hitoshi Miyamoto

Archival imagery dating back to the mid-twentieth century holds information that pre-dates urban expansion and the worst impacts of climate change.  In this research, we examine deep learning colorisation methods applied to historical aerial images in Japan.  Specifically, we attempt to colorize monochrome images of river basins by applying the method of Neural Style Transfer (NST).    First, we created RGB orthomosaics (1m) for reaches of 3 Japanese rivers, the Kurobe, Ishikari, and Kinu rivers.  From the orthomosaics, we extract 60 thousand image tiles of `100 x100` pixels in order to train the CNN used in NST.  The Image tiles were classified into 6 classes: urban, river, forest, tree, grass, and paddy field.  Second, we use the VGG16 model pre-trained on ImageNet data in a transfer learning approach where we freeze a variable number of layers.  We fine-tuned the training epochs, learning rate, and frozen layers in VGG16 in order to derive the optimal CNN used in NST.  The fine tuning resulted in the F-measure accuracy of 0.961, 0.947, and 0.917 for the freeze layer in 7,11,15, respectively.  Third, we colorize monochrome aerial images by the NST with the retrained model weights.  Here used RGB images for 7 Japanese rivers and the corresponding grayscale versions to evaluate the present NST colorization performance.  The RMSE between the RGB and resultant colorized images showed the best performance with the model parameters of lower content layer (6), shallower freeze layer (7), and larger style/content weighting ratio (1.0 x10⁵).  The NST hyperparameter analysis indicated that the colorized images became rougher when the content layer selected deeper in the VGG model.  This is because the deeper the layer, the more features were extracted from the original image.  It was also confirmed that the Kurobe and Ishikari rivers indicated higher accuracy in colorisation.  It might come from the fact that the training dataset of the fine tuning was extracted from these river images.  Finally, we colorized historical monochrome images of Kurobe river with the best NST parameters, resulting in quality high enough compared with the RGB images.  The result indicated that the fine tuning of the NST model could achieve high performance to proceed further land cover classification in future research work.

How to cite: Ishii, R., Carbonneau, P., and Miyamoto, H.: Colorisation of archival aerial imagery using deep learning, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11925, https://doi.org/10.5194/egusphere-egu21-11925, 2021.

16:31–16:33
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EGU21-11843
Béla Kovács, Márton Pál, and Fanni Vörös

The use of aerial photography in topography has started in the first decades of the 20th century. Remote sensed data have become indispensable for cartographers and GIS staff when doing large-scale mapping: especially topographic, orienteering and thematic maps. The use of UAVs (unmanned aerial vehicles) for this purpose has also become widespread for some years. Various drones and sensors (RGB, multispectral and hyperspectral) with many specifications are used to capture and process the physical properties of an examined area. In parallel with the development of the hardware, new software solutions are emerging to visualize and analyse photogrammetric material: a large set of algorithms with different approaches are available for image processing.

Our study focuses on the large-scale topographic mapping of vegetation and land cover. Most traditional analogue and digital maps use these layers either for background or highlighted thematic purposes. We propose to use the theory of OBIA – Object-based Image Analysis to differentiate cover types. This method involves pixels to be grouped into larger polygon units based on either spectral or other variables (e.g. elevation, aspect, curvature in case of DEMs). The neighbours of initial seed points are examined whether they should be added to the region according to the similarity of their attributes. Using OBIA, different land cover types (trees, grass, soils, bare rock surfaces) can be distinguished either with supervised or unsupervised classification – depending on the purposes of the analyst. Our base data were high-resolution RGB and multispectral images (with 5 bands).

Following this methodology, not only elevation data (e.g. shaded relief or vector contour lines) can be derived from UAV imagery but vector land cover data are available for cartographers and GIS analysts. As the number of distinct land cover groups is free to choose, even quite complex thematic layers can be produced. These layers can serve as subjects of further analyses or for cartographic visualization.

 

BK is supported by Application Domain Specific Highly Reliable IT Solutions” project  has been implemented with the support provided from the National Research, Development and Innovation Fund of Hungary, financed under the Thematic Excellence Programme TKP2020-NKA-06 (National Challenges Subprogramme) funding scheme.

MP and FV are supported by EFOP-3.6.3-VEKOP-16-2017-00001: Talent Management in Autonomous Vehicle Control Technologies – The Project is financed by the Hungarian Government and co-financed by the European Social Fund.

How to cite: Kovács, B., Pál, M., and Vörös, F.: Object-based image segmentation in photogrammetry for cartographic use, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11843, https://doi.org/10.5194/egusphere-egu21-11843, 2021.

16:33–16:35
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EGU21-6012
Askoa Ibisate, Alfredo Ollero, J. Horacio García, Josu Ortiz Martínez de Lahidalga, Ana Sáenz de Olazagoitia, Yilena Hermoso, Carmelo Conesa-García, and Alvaro Gómez-Gutiérrez

Ephemeral rivers hydromorphological processes are intermittent and many times of fast response. Therefore they remain still quite unknown. The geomorphological mapping of river forms and geomorphological units is a useful tool to recognize the evolution, changes and the response of river adjustments of hydrological events.

A diachronic geomorphological mapping has been done in some ephemeral rivers located in Ebro basin, Segura basin and Calabrian ephemeral rivers. We are presenting the specific results of six reaches distributed by the Ebro basin (Tudela, Reajo, Alpartir, Cariñena, Valcodo, Sosa and Seco). The first historical aerial image is that of the American Flight B of 1956-57, another of the mid 80’s, the last official ortophotography available (around 2017), and a specific flight with an unmanned aerial vehicle (UAV) done during the winter of 2019. An altimetry correction has been performed on the first two images.

Different categories have been identified within the channel (active channel, principal channel and secondary channel), the sediment bars (vegetated, scant vegetated and non-active paleo-bars), the deposits coming from bank failures or tributaries, rocky areas, exhumed old sediment areas, consolidated or unconsolidated granular bed. The categories were mapped at different scales depending on the image quality (for example, from ≤ 1/300 scale of the UAV to ≤ 1/1,000 scale of the American flight).

This evolutionary cartography allows comparing the geomorphology of each river reach among different dates, considering the different resolution of the images and its limitations (i.e. previously, the results were unified to compare among them), and relating to the fluvial processes and changes on the river and basin.

This research was funded by ERDF/Spanish Ministry of Science, Innovation and Universities—State Research Agency (AEI) /Project CGL2017-84625-C2-1-R; State Program for Research, Development and Innovation Focused on the Challenges of Society. 

How to cite: Ibisate, A., Ollero, A., García, J. H., Ortiz Martínez de Lahidalga, J., Sáenz de Olazagoitia, A., Hermoso, Y., Conesa-García, C., and Gómez-Gutiérrez, A.: Geomorphological evolution of ephemeral rivers through historical and UAVs images, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6012, https://doi.org/10.5194/egusphere-egu21-6012, 2021.

16:35–16:37
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EGU21-12007
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ECS
Shuyang Xu and Ping Fu

Glacier mechanical ablation, such as ice calving, collapsing and flaking, plays a significant role in amplifying glacier recession. Mechanical ablation, as a non-linear response to climatic changes, caused by structural instabilities are mainly attributed to interactions of water-ice/glacier, which could be strengthened by the enhanced meltwater runoffs when rain season meets with ablation season. Similar to water-terminating glaciers, ice calving (or large-scale ice collapsing) events have happened in land-terminating glaciers in the southeastern Tibetan Plateau such as Hailuogou (HLG) glacier. However, other than ice calving events with water involved and dry calving events, ice calving of HLG glacier is roughly in the middle state between them. Previous studies have shown that HLG glacier have maintained negative mass balance in recent years with sustaining retreat, accompanied by mechanical ice loss events. Seven field trips to HLG glacier were conducted from 2017 to 2020 (concentrated from June to November). A cost-effective Unmanned Aerial Vehicle (UAV; DJI Mavic Pro) was used to capture images from ice fall to glacier terminus. Agisoft Metashape Pro was used to produce dense point cloud, digital surface model and ortho-images, etc. Results indicate that, under the intense interactions of water-ice/glacier, glacier terminus has been retreating continually, the terminal ice cliffs have gone through a succession of structural changes, the proglacial river have diverted several times, and the position of subglacial channel outlet had multi-times shifts accompanied with the periodic occurrences of terminal ice cave. The surrounding glacial landscapes have been altered accordingly such as the increasing runoffs from glacier river, the narrowing glacier ice fall, upward invasions by periglacial vegetation, and etc. The combination of repeated UAV mapping and rapidly streamlined terrain reconstruction technique provides a cost-effective option for short-term monitoring of glacier dynamics, especially for more precise detection on mechanical ablation, compared with datasets from commercial satellites.

How to cite: Xu, S. and Fu, P.: Short-term Glacial Dynamics Detection of a Maritime Glacier in Southeastern Tibetan Plateau using Cost-effective UAV and Rapid Photogrammetry Techniques, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12007, https://doi.org/10.5194/egusphere-egu21-12007, 2021.

16:37–16:39
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EGU21-14844
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ECS
Sebastián Vivero and Christophe Lambiel

In high alpine geomorphological research, different technologies are increasingly used to describe and monitor mass movements such as rock glaciers. Among them, the combination of Unmanned Aerial Vehicle (UAV) systems and Structure from Motion (SfM) techniques is gaining continuous interest due to rapid technological developments. In this study, we test the capability of repeated UAV surveys to accurately survey rock glacier deformation in the Lac des Vaux area, Valais Alps. The studied landform is located on a typical anthropic alpine environment in the Swiss Alps, where ski facilities and alpine tracks are a commonplace. A DJI Phantom 4 RTK UAV was flown twice in September 2019 and September 2020 to cover an area of about 0.25 km2 with nearly 1000 images each time. Differential corrections using a Virtual Reference Station (VRS) provided image geotags with centimetre-level accurate 3-D coordinates, thereby allowing dispensing with ground control. High-resolution orthomosaics and high-density point clouds are derived from the UAV-RTK surveys using a standard SfM processing workflow. The corresponding point clouds' accuracy was evaluated and adjusted based on stable terrain, reducing the 3-D alignment errors to a mean of 0.02 m. Elevation changes and surface kinematics in the rock glacier complex and its margins were quantified using point cloud operations and image correlation techniques. The results indicate that the landform has at least eight different lobes with mean velocities ranging between 0.1 and 1.3 m yr-1. The high-resolution analysis also permitted identifying moving lobes without morphological expression and small thermokarst depressions on the ski slope structure that traverses the rock glacier's active zone. Without relying on ground control, our approach achieves horizontal and vertical accuracies nearly as good as monitoring techniques using more traditional differential GNSS devices.

How to cite: Vivero, S. and Lambiel, C.: Rock glacier deformation using an Unmanned Aerial Vehicle (UAV) with RTK GNSS capability, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14844, https://doi.org/10.5194/egusphere-egu21-14844, 2021.

16:39–16:41
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EGU21-7166
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ECS
Ebubekir Karakoca and Levent Uncu

River systems are areas that respond most rapidly to regional and / or local tectonic movements, with global climate changes and general basement fluctuations that occurred during the Quaternary period. The most important geomorphological units where these events can be observed are terrace systems, which are the result of deposition and erosion processes. In fluvial geomorphology research on terrace systems, modern technological innovations are used as well as conventional field methods. Especially low-cost Unmanned Aerial Vehicles (UAV) and modern photogrammetry methods are preferred because they both provide detailed and precise identification of terraces and high resolution topography outputs in spatial and temporal terms.
This study aims to put a comprehensive mapping of the terrace systems observed in an area of 1.27 km² around Gemiciköy (Bilecik Province), which is located in the middle part of the Sakarya River valley, the largest river in Northwest Anatolia. Accordingly, we used the Structure from Motion (SfM) method which is based on photogrammetric principles and UAV. During the study, 582 images taken from a height of 100 m and having 80% overlap in line with the flight plans by using the DJI Mavic Mini UAV model were evaluated in Agisoft Metashape Professional software. With the use of image processing algorithms, the dense point cloud was first obtained, and then the orthomosaic and digital surface model with 3.29 cm resolution was produced. Two terrace levels (+10 m and +19 m) detected with digital surface modeling, and these were verified by stratigraphic and sedimentological observations made in the field.
As a result, low-cost UAV technologies are quite useful in terms of providing more detailed monitoring, mapping and analysis of river environments, together with the production of sensitive and high resolution topography data required in modern fluvial geomorphology research.

How to cite: Karakoca, E. and Uncu, L.: Mapping of Quaternary river terrace landforms with Unmanned Aerial Vehicle (UAV): A case study in the Sakarya River, NW Turkey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7166, https://doi.org/10.5194/egusphere-egu21-7166, 2021.

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