Research on Dem Construction Methods With Effective Integration of Topographic Feature Lines

In cities and other human activity areas, the implementation of various ground projects has resulted in significant changes in natural surface morphology, a prominent feature of which is the formation of a variety of discontinuous terrains, such as roads and building basements. In the process of DEM modeling of these landforms, traditional modeling methods produce obvious topographic distortions at topographic prominences, which limits the application depth of DEMs in these areas. To solve these problems, this paper proposes a DEM modeling method to enhance the expression of discontinuous terrain from the perspective of simplicity and convenience for application. The method is based on terrain data such as topographic feature lines, altimetric points, and contour lines. First, parallel feature lines are generated according to a certain distance. Then, vertices are inserted into the topographic feature line and the parallel feature line according to the specified step length, and the known altimetric points are selected from both sides of the original topographic feature line to estimate the height value of the vertices. Finally, by combining the topographic feature line, parallel feature line and other available topographic data for TIN construction, the result can effectively express the special topography of discontinuous terrain. In this study, a region in Nanjing City, Jiangsu Province, China, was selected as the study area to conduct a DEM construction experiment. The experimental results showed that the DEM constructed by this method could well express the morphological characteristics of discontinuous terrain, and the height accuracy of the construction results was also significantly improved compared with that of the conventional method.

Lithospheric structure of the Iberian Central System (Iberian Massif) imaged by the wide-angle seismic reflection/refraction CIMDEF experiment

<p>The Iberian Central System represents an outstanding topographic feature in the central Iberian Peninsula. It is an intraplate mountain range formed by igneous and metasedimentary rocks of the Variscan Iberian Massif that has been exhumed since the Eocene in the context of the Alpine orogeny. The Iberian Central System has been conventionally interpreted as a thick-skinned pop-up mountain range thrust over the Duero and Tajo foreland basins. However, its lithospheric structure and the P-wave velocity distribution are not yet fully resolved. In order to place geophysical constraints on this relevant topographic feature, to identify lithospheric discontinuities, and to unravel the crustal deformation mechanisms, a wide-angle seismic reflection and refraction experiment, CIMDEF (Central Iberian Mechanism of DEFormation), was acquired in 2017 and 2019. It is a NNW-SSE oriented 360-km long profile that runs through the Duero basin, the Iberian Central System and the Tajo basin. First results based on forward modeling by raytracing show an irregularly layered lithosphere and allow to infer the depth extent of the northern Iberian Central System batholith. The crust is ~ 31 km thick under the Duero and Tajo basins and thickens to ~ 39 km under the Iberian Central System. A conspicuous thinning of the lower crust towards the south of the Iberian Central System is also modeled. Along this transect, a continuous and high amplitude upper mantle feature is observed and modeled as the reflection of an interface dipping from 58 to 62 km depth featuring a P-wave velocity contrast of 8.2 to 8.3 km/s. Our preliminary results complement previous models based on global-phase seismic and noise interferometry and gravity data, provide new constraints to validate the accuracy of passive seismic methods at lithospheric scale, and contribute with a resolute P-wave velocity model of the study area to unravel the effect of the Alpine reactivation on the central Iberian Massif.<br>This project has been funded by the EIT-RawMaterials 17024 (SIT4ME) and the MINECO projects: CGL2016-81964-REDE, CGL2014-56548-P.</p>

Active subglacial lakes and channelized water flow beneath the Kamb Ice Stream

We identify two previously unknown subglacial lakes beneath the stagnated trunk of the Kamb Ice Stream (KIS). Rapid fill-drain hydrologic events over several months are inferred from surface height changes measured by CryoSat-2 altimetry and indicate that the lakes are probably connected by a subglacial drainage network, whose structure is inferred from the regional hydraulic potential and probably links the lakes. The sequential fill-drain behavior of the subglacial lakes and concurrent rapid thinning in a channel-like topographic feature near the grounding line implies that the subglacial water repeatedly flows from the region above the trunk to the KIS grounding line and out beneath the Ross Ice Shelf. Ice shelf elevation near the hypothesized outlet is observed to decrease slowly during the study period. Our finding supports a previously published conceptual model of the KIS shutdown stemming from a transition from distributed flow to well-drained channelized flow of subglacial water. However, a water-piracy hypothesis in which the KIS subglacial water system is being starved by drainage in adjacent ice streams is also supported by the fact that the degree of KIS trunk subglacial lake activity is relatively weaker than those of the upstream lakes.