Combination of Aerial, Satellite, and UAV Photogrammetry for Quantifying Rock Glacier Kinematics in the Dry Andes of Chile (30°S) Since the 1950s

The diachronic analysis of aerial and satellite imagery, uncrewed aerial vehicle (UAV) and in situ surveys obtained between 1956 and 2019 are employed to analyse landform surface kinematics for the Tapado site located in the Dry Andes of Chile. A feature tracking procedure was used between series of orthorectified and co-registered images to calculate surface velocities on several ice-debris landforms, including rock glaciers and debris-covered glaciers. For the active rock glaciers, the results exhibit typical viscous flow, though local destabilisation process seems to occur, increased velocities since 2000 (>1 m/yr) and terminus advance. Nevertheless, the debris-covered glaciers displays heterogeneous spatial patterns of surface velocities, together with collapse (downwasting) associated with the development of thermokarst depressions and supraglacial ponds. Our findings show that surface kinematics and multitemporal observations derived from different sensors are valuable tools for differentiating between glacial and periglacial features. The pluri-decadal time series since 1956 constitute a unique dataset for documenting the surface kinematics of creeping mountain permafrost in the Southern Hemisphere. The approach developed in this work offers a way forward to reconstruct the recent behaviour of glacial and periglacial features in the Andes, where archival aerial photographs are available but have not previously been processed rigorously to obtain an accurate assessment of landform kinematics.

The Global Geodetic Observing System (GGOS) – infrastructure underpinning Earth science

<p>The Global Geodetic Observing System (GGOS) is the contribution of Geodesy to the observation and monitoring of the Earth System. Geodesy is the science of determining and representing the shape of the Earth, its gravity field and its rotation as a function of time. A core element to reach this goal are stable and consistent geodetic reference frames, which provide the fundamental layer for the determination of time-dependent coordinates of points or objects, and for describing the motion of the Earth in space. Traditionally, geodetic reference frames have been used for surveying, mapping, and space-based positioning and navigation. With modern instrumentation and analytical techniques, Geodesy is now capable of detecting time variations ranging from large and secular scales to very small and transient deformations with increasing spatial and temporal resolution, high accuracy, and decreasing latency. GGOS has been working closely with components of International Association of Geodesy (IAG) to provide consistent and openly available observations of the spatial and temporal changes of the shape and gravity field of the Earth, as well as the temporal variations of the Earth’s rotation. These efforts make available a global picture of the surface kinematics of our planet, including the ocean, ice cover, continental water, and land surfaces, as well as estimates of mass anomalies, mass transport, and mass exchange in the System Earth. Surface kinematics and mass transport together are the key to global mass balance determination, and are an important contribution to understanding the energy budget of our planet. In order to play its vital role, GGOS has following missions; a) to provide the observations needed to monitor, map, and understand changes in the Earth’s shape, rotation, and mass distribution, b) to provide the global geodetic frame of reference that is the fundamental backbone for measuring and consistently interpreting key global change processes and for many other scientific and societal applications, c) to benefit science and society by providing the foundation upon which advances in Earth and planetary system science and applications are built. For the mission, GGOS works tighter with components of the IAG, more specifically, IAG Services, IAG Commissions and IAG Inter-Commission Committees. The IAG Services provide the infrastructure and products on which all contributions of GGOS are based, and the IAG Commissions and IAG Inter-Commission Committees provide expertise and support to address key scientific issues within GGOS. Together with the IAG components, GGOS provides the fundamental infrastructure underpinning Earth sciences and their applications.</p>

Classification and kinematics of the Planpincieux Glacier break-offs using photographic time-lapse analysis

Herein, we present results obtained from time-lapse imagery acquired by a digital single-lens reflex camera during 2014–18 used to monitor the Planpincieux Glacier on the Italian side of the Grandes Jorasses (Mont Blanc massif). We processed the images using image cross-correlation to measure the surface kinematics of the most active lobe of the glacier that presents a high velocity and frequent ice detachments. During the monitoring, we observed two or three periods of sharp acceleration per year that culminated with large break-offs followed by analogous decelerations. Overall, we registered more than 350 failures with a volume >100 m3, of which, 14 events had volumes larger than 10 000 m3. The study identified a monotonic positive relationship between the velocity and failure volume that may be used to estimate the volume of the collapses before an event. We identified the thresholds of velocity and acceleration that characterise the activation of the speed-up periods. The study allowed the characterisation of three different instability processes that lead to the break-off of ice chunks from the glacier terminus: (i) disaggregation, (ii) slab fracture and (iii) water tunnelling failure which can be differentiated based on the rheology, the volume involved and the trigger process.

A surface kinematics buoy (SKIB) for wave–current interaction studies

Global navigation satellite systems (GNSSs) and modern motion-sensor packages allow the measurement of ocean surface waves with low-cost drifters. Drifting along or across current gradients provides unique measurements of wave–current interactions. In this study, we investigate the response of several combinations of GNSS receiver, motion-sensor package and hull design in order to define a prototype “surface kinematics buoy” (SKIB) that is particularly optimized for measuring wave–current interactions, including relatively short wave components that are important for air–sea interactions and remote-sensing applications. The comparison with existing Datawell Directional Waverider and Surface Wave Instrument Float with Tracking (SWIFT) buoys, as well as stereo-video imagery, demonstrates the performance of SKIB. The use of low-cost accelerometers and a spherical ribbed and skirted hull design provides acceptable heave spectra E(f) from 0.09 to 1 Hz with an acceleration noise level (2πf)4E(f) close to 0.023 m2 s−3. Velocity estimates from GNSS receivers yield a mean direction and directional spread. Using a low-power acquisition board allows autonomous deployments over several months with data transmitted by satellite. The capability to measure current-induced wave variations is illustrated with data acquired in a macro-tidal coastal environment.

Nonlinear Wave Kinematics near the Ocean Surface

Estimation of second-order, near-surface wave kinematics is important for interpretation of ocean surface remote sensing and surface-following instruments, determining loading on offshore structures, and understanding of upper-ocean transport processes. Unfortunately, conventional wave theories based on Stokes-type expansions do not consider fluid motions at levels above the unperturbed fluid level. The usual practice of extrapolating the fluid kinematics from the unperturbed free surface to higher points in the fluid is generally reasonable for narrowband waves, but for broadband ocean waves this results in dramatic (and nonphysical) overestimation of surface velocities. Consequently, practical approximations for random waves are at best empirical and are often only loosely constrained by physical principles. In the present work, the authors formulate the governing equations for water waves in an incompressible and inviscid fluid, using a boundary-fitted coordinate system (i.e., sigma or s coordinates) to derive expressions for near-surface kinematics in nonlinear random waves from first principles. Comparison to a numerical model valid for highly nonlinear waves shows that the new results 1) are consistent with second-order Stokes theory, 2) are similar to extrapolation methods in narrowband waves, and 3) greatly improve estimates of surface kinematics in random seas.