Dear Colleagues,

The last several decades have seen digital elevation modelling become a standard tool in science (especially in environmental and geoscience), engineering, and everyday life. All types of objects are modeled, ranging from the ground surface (including that of other celestial bodies), subsurface objects like caves, submarine features (reefs, seamount, submarine canyons) natural and man-made objects, various structures like power lines, forests, 3D cities, etc. Petabytes of digital elevation data are being created daily via airborne or terrestrial laser scanning, UAVs, stereophotogrammetry (e.g., SfM), etc. Moreover, these data are in a wide range of scales from microtopography at the cm or dm scale to global planetary coverages.

Many of the users are now satisfied if they can afford or can have access to a digital elevation model at the scale, resolution, and accuracy that suits their needs. However, what is new in the last decade that many users have now more than one dataset covering the same features. The multitemporal character of these data is advantageous as it makes possible a very important application: change detection. On the other hand, two or more datasets might have been gathered using different technologies, resolution, and accuracies. Many users (and often processing systems) are not aware of these technological details that makes change detection a challenge: do we see a real change or are these just artefacts, due to the differing technology or accuracy?

The target of this Special Issue is twofold. On one hand, it will focus on case histories showing how digital elevation data can be used to detect changes (on various scales) or how digital elevation models can be kept up-to-date for everyday use, including on-going changes in the modeled space. The other focus is a methodological issue: how the various (often archive) elevation datasets characterized by different properties can be integrated to make them suitable for detecting changes, filtering out the artefacts.

Some topics that this Special Issue intends to cover using multitemporal elevation data are as follows:

• changes in low relief areas like floodplains
• evolution of small-scale features like gravel beds, terraces, postglacial valleys
• proofs of base level drop (stream long profiles, abandoned channels, wind gaps)
• indication of erosion, sedimentation, weathering
• incipient or on-going mass movements (scarps, toe of the landslide, volumetry)
• indication of tectonic geomorphic activity: recent or in the past
• proving the historic sequence of acting surface processes (e.g., erosion predates/postdates impact) on Earth or on other celestial bodies
• volumetric calculations like estimation of the volume of recent volcanic activity or lava flow, or calculation of "missing volume"
• changes in cryosphere and surroundings
• methodological considerations and user data requirements of digital elevation data to detect certain surface processes
• modelling of subaqueous surfaces like river beds, sinter terraces, coral reefs, seamounts, submarine canyons
• effects (e.g., subsidence, collapse) due to subsurface human activity like mining, tunnel building, or subsurface fires
• evolution of natural and human-influenced peatlands
• effects and detection of animal activities on surface like beaver dams, termites, badger's setts, foxholes
• separation of data acquisition errors, processing artefact from real observable changes, considerations on detection limits
• problems of change detection and modelling of special surfaces like karst, overhanging cliffs, caves, stalactites, and stalagmites

Dr. Balázs Székely
Guest Editor

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