Björn Riedel - Academia.edu (original) (raw)

Papers by Björn Riedel

Science of remote sensing, May 1, 2024

Journal of photogrammetry, remote sensing and geoinformation science, May 29, 2024

Permafrost is an important component of sub-Arctic environments and is extremely vulnerable to th... more Permafrost is an important component of sub-Arctic environments and is extremely vulnerable to the impact of climate change. During the last decades, permafrost regions in northern high latitudes have been exposed to greater temperature changes than other regions worldwide. Increased temperatures cause rapid thawing of permafrost which can lead to changes in hydrological processes. Therefore, capturing dynamics of land surface temperature (LST) as one of the key factors affecting the thermal regime of permafrost landscapes at high spatial resolution is crucial for better monitoring these areas under drastic warming projected due to climate change. Landsat imagery at 30 m resolution offers the potential to obtain a consistent coverage of near-surface temperature values. In this study LST values from Landsat were compared with in-situ based soil freeze/thaw (F/T) index, air and soil temperature measurements obtained at the Abisko peatland site in the permafrost areas of northern Sweden. The soil F/T index is an important proxy that describes the relationship between the unfrozen soil water content and the soil temperature in freezing soils. From 2017 to 2022, comparisons between Landsat LST and soil F/T index show high similarity between them in identifying frozen state, thawed state, and transition periods. In addition, Landsat LST values were found to be better correlated with air temperature (R2 > 90%) than with soil temperature (R2 > 80%) measurements. Overall, it is concluded that Landsat LST offers great potential for monitoring surface temperature changes in high-latitude permafrost regions and provides a promising source of input data for developing models to determine the spatial heterogeneity of freezing and thawing cycles.

EGU General Assembly Conference Abstracts, Apr 1, 2019

These datasets display seasonal and multiannual surface displacement models based on microwave da... more These datasets display seasonal and multiannual surface displacement models based on microwave data of ESA's Sentinel-1 satellite system. The data was processed via Interferometric Aperture Radar (InSAR) time series techniques, using an adapted version of the Small BAseline Subset (SBAS) algorithm. The purpose of this study is to understand sediment flux mechanics, especially those related to permafrost and periglacial landforms, and how the changing climate may affect these processes in the NamCo area in the future. To that end we developped three surface displacement models. The freeze-thaw model describes seasonal surface displacement caused by freezing and thawing of the active layer in autumn and spring respectively. We observe vertical amplitudes of up to 20 mm in areas, where the water content of the soil is high. The multiannual velocity model shows the mean surface velocity over the entire time period of approximetly 3-4 years. Time series results of regions with a small slopes were decomposed from ascending and descending data to show the surface velocity component in vertical and east-west direction. Time series results of regions with a larger slope were projected in the downslope direction, with the assumption that creep and sliding processes are dominant, which transport sediment along the direction of the steepest slope. Most flat areas are relatively stable but we observe material accumulation near parts of the rivers and subsidence in some permafrost areas, which could be related to permafrost degradation. The fastest landforms are rockglaciers, which move with velocities of up to 24 cm/yr. The third model is the seasonal velocity model, where we compare the line-of-sight velocities of sloped areas in the summer months to the winter months. Most slopes slide signifcantly faster in summer, driven by the thawing ground due to higher air temperature and monsoonal rainfall, while most of the fastest moving landforms move with a constant velocity throughout the year.

Isprs Journal of Photogrammetry and Remote Sensing, Nov 1, 2000

The multi-epoch deformation monitoring of a series of super-hot steel beams by digital closerange... more The multi-epoch deformation monitoring of a series of super-hot steel beams by digital closerange photogrammetry is reported. An on-line configuration of three CCD cameras was established to measure both stable reference points and targets subject to positional displacement. Measurements for each beam were conducted at 70-80 epochs over two hours as the steel cooled from 1100 C to near room temperature. Special targeting was required to accommodate the changing colour of the beams from white-hot to brown as they cooled and ensure target survival through a large temperature range. A computational approach was employed whereby the photogrammetric triangulation process for any given recording epoch utilised all images obtained up until that time. The paper discusses all aspects of the project in which seven beams were monitored to a dimensional tolerance of close to 1 mm (RMS 1sigma).

ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences, May 17, 2022

Tropospheric delay variability remains a significant source of error in the InSAR-derived measure... more Tropospheric delay variability remains a significant source of error in the InSAR-derived measurements. Numerical weather models have been proposed as an alternative technique to mitigate tropospheric delays in InSAR and have become a standard procedure for some multi-temporal InSAR processing workflows. This study evaluates the viability of three numerical weather models for mitigating tropospheric delay in InSAR for a tropical region. We assess their performance in correcting tropospheric delay in Sentinel-1 interferograms at different spatial wavelengths using variograms. Their performance is validated using GNSS tropospheric delay and our proposed SAR-derived tropospheric delay estimates. The results indicate that numerical weather model estimates do not mitigate short-wavelength turbulent delays, but can mitigate long-wavelength stratified delays to some extent, which may also introduce additional errors in interferograms. At a spatial wavelength of 40 km, 36% of the interferograms showed increased spatial autocorrelation after correction with GACOS, 55% with ERA-5, and 51% with MERRA-2. In contrast the InSAR-derived tropospheric delays resulted in a significant reduction in variance at all wavelengths indicating the ability to mitigate both turbulent and stratified delays. Our study demonstrates the limited potential of numerical weather model estimates to satisfactorily mitigate trophospheric noise in InSAR and the capability of InSAR-derived trophospheric delay to significantly correct tropospheric noise in InSAR.

Geophysical Journal International, May 1, 2007

Due to the impact of ocean tide the Ekstroemisen (Ekstroem Ice Shelf, Antarctica) still shows ver... more Due to the impact of ocean tide the Ekstroemisen (Ekstroem Ice Shelf, Antarctica) still shows vertical displacements at its assumed grounding line. These can reach amplitudes of 5 cm. The low tide amplitudes are smaller than the corresponding high tide amplitudes. This indicates that the ice body touches the bedrock during the low tides. An elastic feedback of the ice body can be observed as little as 1 km behind the assumed grounding line. The maximum vertical displacements can still reach 1 cm. These results are based on data collected in the grounding zone of the Ekstroemisen during the austral summer of 1997. This region has been studied by using a combined sensor field that makes continuous records using Global Positioning System (GPS), gravimeter and tiltmeter instruments to derive the elastic response of the ice body to the ocean tides. The resulting time-series which has to be analysed is biased by outliers, incomplete data or complex trend functions. It is nearly impossible to analyse the very short time periods without assuming hypotheses. It turns out that standard algorithms like correlation functions, various Fourier transforms or functional regressions are not suitable to solve the parametrization of time-series in the region of the grounding zone, where several kinematic and gravimetric processes overlap. After a thorough analysis of these time-series with an average length of 8 d we managed to homogenize the results of the hybrid and non-simultaneous observations. We were able to create a set of robust parameters to describe the ice shelf motion in the grounding zone, based on non-linear programming.

Annals of Glaciology, 1999

During the austral summer 1996^97 an extensive field program with geophysical and geodetic observ... more During the austral summer 1996^97 an extensive field program with geophysical and geodetic observations was carried out in the vicinity of the grounding line of Ekstro« misen, Dronning Maud Land, Antarctica. The main emphasis of the joint program was placed on continuous observations of the horizontal as well as the vertical component of the ice displacement across the grounding zone. Data-processing methods for the in parts discontinuous time series and the vertical displacements in the area of the grounding zone are described, and first results presented, with the focus on the influence of the ocean tides on grounded ice. Tidal-induced deflections with amplitudes of up to 0.15 m were recorded at a station on grounded ice 1km from the grounding line.

Climate change and the associated rise in air temperature have affected the Tibetan Plateau to a ... more Climate change and the associated rise in air temperature have affected the Tibetan Plateau to a significantly stronger degree than the global average over the past decades. This has 15 caused deglaciation, permafrost degradation and increased precipitation, heavily changing the water balance of this region. Surface displacement processes are likely to change as the ground continues to warm up and as such it is vital to understand both seasonal and interannual processes dynamics. The Nam Co area is well suited to studying these processes via Interferometric Synthetic Aperture Radar (InSAR) time series analysis, due to its lack of higher vegetation and relatively thin snow cover. 20 The short revisit time of the Sentinel-1 system further reduces the risk of temporal decorrelation, making it possible to produce surface displacement models with good spatial coverage. We created three different surface displacement models to study freeze-thaw processes, seasonal sliding and linear creep. Most slopes of the area are unstable, with velocities of 8 to 17 mm yr-1 , and some landforms reach velocities of up to 18 cm yr-1. The monsoonal climate accelerates those movements 25 during the summer months through high temperatures and heavy rainfall. The fastest moving landforms, some of which have been identified as rock glaciers, do not follow this seasonal pattern of accelerated velocity in summer, instead they follow a linear sliding pattern. It is unclear if this linearity is connected to the ice content in those landforms. Flat regions at Nam Co are mostly stable on a multiannual scale but some experience subsidence, which could be caused by permafrost 30 degradation. We observe a very clear seasonal freeze-thaw cycle in the valleys, where thawing and subsequent freezing of the active layer cause a vertical oscillation of the ground of up to a few centimeters, especially near streams and other water bodies.

Advances in Geosciences, Jan 2, 2008

Synthetic Aperture Radar Interferometry (InSAR) is an established method for the detection and mo... more Synthetic Aperture Radar Interferometry (InSAR) is an established method for the detection and monitoring of earth surface processes. This approach has been most successful where the observed area fulfills specific requirements, such as sufficient backscattering, flat slope gradients or very slow changes of vegetation. We investigated the capability of two different InSAR techniques and achieved good results for the recognition of landslides in China and Greece that compared well with geodetic derived movement rates. This demonstrates the strong potential of SAR Interferometry for the detection of landslides and earth surface movements.

Introduction elastic beam approach The influence of ocean tides on an ice shelf was first describ... more Introduction elastic beam approach The influence of ocean tides on an ice shelf was first described by Robin (1958). He observed the vertical movement of the Maudheimisen (today: Quarisen) during the Norwegian-BritishSwedish Antarctic expedition from 1949 to 1952. A simplified model for the description of the tidal influenced behaviour of ice shelves was introduced in Glaciology through Holdsworth (1969, 1977). His approach was based on the work from Hetenyi (1946). This standard elastic beam approach deals with small displacements of a thin elastic beam (s. fig. 1). The acting forces are caused from ocean tides. The input data for this model are mean ice thickness h, tidal signal for one site wa and the assumption of a fixed grounding line (hinge line). A detailed application of this approach is published in Holdsworth (1974) for Erebus glacier tongue.

The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Jun 5, 2019

The project 'Determinations on the absolute sea-level rise on the German North Sea and Baltic Sea... more The project 'Determinations on the absolute sea-level rise on the German North Sea and Baltic Sea coasts', funded by the Federal Ministry of Education and Research (BMBF) , has the overall goal to estimate the absolute sea level change in those coastal areas. A major issue associated with detecting absolute sea level changes is the relative character of tidal records. To calibrate the tidal records, a spatial vertical land movement model for northern Germany has been set up. To this end we combined a network from German Height Reference Systems (Deutsches Haupthöhennetz, DHHN 95 and DHHN 2016), reprocessed data from 180 permanent GNSS stations and results from Persistent Scatterer (PS) Interferometry. PS processing covers an approximately 50 km wide strip along the 1200 km long German coast. We processed two tracks from Sentinel-1A and-1B from October 2014 to September 2018 and generated a combined spatial solution for the estimation of vertical land movement. In general, vertical velocities from PS Interferometry range between ±2 mm/a and show a homogeneous distribution for coastal areas. Therefore we consider them as stable. We observe subsidence in the area around Groningen and Emden through hydrocarbon extraction. In Wilhelmshaven and Etzel subsidence associated with cavern storage is visible. Processed GNSS data and PSI results overlap in time from 2014 to 2016. The integration of the spatial multi-temporal PS results with point-wise GNSS time series data are required, as they form the main input data for the further development of our vertical displacement model of northern Germany.

Permafrost and Periglacial Processes, May 13, 2021

The western Nyainqêntanglha Range on the Tibetan Plateau reaches an elevation of 7,162 m and is c... more The western Nyainqêntanglha Range on the Tibetan Plateau reaches an elevation of 7,162 m and is characterized by an extensive periglacial environment under semi-arid climatic conditions. Rock glaciers play an important part of the water budget in high mountain areas and recent studies suggest that they may even act as climate-resistant water storages. In this study we present the first rock glacier inventory of this region containing 1,433 rock glaciers over an area of 4,622 km. To create the most reliable inventory we combine manually created rock glacier outlines with an automated classification approach. The manual outlines were generated based on surface elevation data, optical satellite imagery and a surface velocity estimation. This estimation was generated via InSAR time series analysis with Sentinel-1 data from 2016 to 2019. Our pixel-based automated classification was able to correctly identify 87.8% of all rock glaciers in the study area at a true positive rate of 69.5%. In total, 65.9% of rock glaciers are classified as transitional with surface velocities of 1-10 cm/yr. In total, 18.5% are classified as active with higher velocities of up to 87 cm/yr. The southern windward side of the mountain range contains more numerous and more active rock glaciers. We attribute this to higher moisture availability supplied by the Indian Monsoon.

Beton- Und Stahlbetonbau, 2008

Der Bericht stellt ein praxistaugliches, digitales System zur Erfassung und Auswertung von Rissen... more Der Bericht stellt ein praxistaugliches, digitales System zur Erfassung und Auswertung von Rissen in Massivbauwerken vor. Das unter dem Namen "Digitales Rissmesssystem (DRS)" bekannt gewordene System dient der objektiven Bestimmung von Rissbreiten einschliesslich der Erfassung vor Ort sowie der Auswertung und Speicherung der Ergebnisse. Zur Bestimmung der Rissbreite werden ein spezielles Kamerasystem sowie eine entsprechende Auswertesoftware verwendet, die im Bericht naeher beschrieben werden. Das System wurde am Amt fuer Verkehrsmanagement der Landeshauptstadt Duesseldorf entwickelt. Grundlage der Rissbestimmung mit konventioneller Digitalfotographie ist die optische Erkennung unterschiedlicher Grautoene von Umgebung (hell) und Riss (dunkel), wobei die Rissbreiten zwischen erkannten Risskanten (Helligkeitsspruenge) ermittelt werden. Anhand von mehreren Dutzend Auswertestellen je Zentimeter Risslaenge werden die Risse mit einem Programm ausgewertet und die Kenndaten, dies sind mittlere Rissbreite, Streubreite und Rauigkeitsprofil, angegeben. Fuer die Anwendung bei der Zustandspruefung von Bauwerken wird mit dieser Entwicklung dem Anwender ein einfach handhabbares System zur Verfuegung gestellt, das Risse praezise aufmisst. Die Rissposition wird mittels Georeferenzierung bestimmt, sodass bei Wiederholungsmessungen immer zuverlaessig am selben Ort gemessen werden kann. ABSTRACT IN ENGLISH: A digital system - ready for its practical use - is presented to precisely record and analyse cracks at concrete or masonry structures. It uses a standard digital camera and a specific cylindrical attachment to photographically record crack pattern at surfaces. Crack parameters like medium widths, width variations or width profiles are analysed from several dozen measurement points per centimetre of a crack using a developed software tool. Applications on site - like bridge evaluations according to DIN 1076 - and in the lab - like monitoring of shear crack developments - illustrate handling, precision and data extent of the system in comparison to standard methods. (A)

ZfV - Zeitschrift für Geodäsie, Geoinformation und Landmanagement, Oct 1, 2010

Zusammenfassung Die Support Vector Machines (SVM) bieten eine Vielzahl von praktischen Einsatzmög... more Zusammenfassung Die Support Vector Machines (SVM) bieten eine Vielzahl von praktischen Einsatzmöglichkeiten für die Modellierung von Ergebnissen geodätischer Messungen. Im ersten Teil dieses Artikels ist in einem theoretischen Überblick die Herleitung der SVM erfolgt. Hier wurden die linearen und nichtlinearen Algorithmen zur Mustererkennung und Regression eingeführt. Der zweite Teil dieses Artikels präsentiert einerseits anhand von kleineren Rechenbeispielen die Funktionsweise dieser Algorithmen. Andererseits demonstrieren bereits erfolgte praktische Anwendungen im Bereich der Überwachung tektonisch aktiver Gebiete und rutschungsgefährdeter Hänge den Umfang der Anwendungsmöglichkeiten. Summary The support vector machines (SVM) offer a lot of possibilities to model the results of geodetic observations. The theoretical overview of SVM including their derivation has already been presented within the first part of this publication. Herein, the linear and nonlinear algorithms for pattern recognition and regression purposes have been explained. This available second part is focussed on the practice of SVM computations. Accordingly, small computational examples will show, on the one hand, how these algorithms work. On the other hand, the adaptation of SVM on the monitoring of recently active tectonics or of dangerous landslides will demonstrate their scope of use.