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"Boulders"
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Improving YOLOv5 with Attention Mechanism for Detecting Boulders from Planetary Images
It is of great significance to apply the object detection methods to automatically detect boulders from planetary images and analyze their distribution. This contributes to the selection of candidate landing sites and the understanding of the geological processes. This paper improves the state-of-the-art object detection method of YOLOv5 with attention mechanism and designs a pyramid based approach to detect boulders from planetary images. A new feature fusion layer has been designed to capture more shallow features of the small boulders. The attention modules implemented by combining the convolutional block attention module (CBAM) and efficient channel attention network (ECA-Net) are also added into YOLOv5 to highlight the information that contribute to boulder detection. Based on the Pascal Visual Object Classes 2007 (VOC2007) dataset which is widely used for object detection evaluations and the boulder dataset that we constructed from the images of Bennu asteroid, the evaluation results have shown that the improvements have increased the performance of YOLOv5 by 3.4% in precision. With the improved YOLOv5 detection method, the pyramid based approach extracts several layers of images with different resolutions from the large planetary images and detects boulders of different scales from different layers. We have also applied the proposed approach to detect the boulders on Bennu asteroid. The distribution of the boulders on Bennu asteroid has been analyzed and presented.
Journal Article
Animal tracks and human footprints in prehistoric hunter-gatherer rock art of the Doro! nawas mountains
Namibia is rich in hunter-gatherer rock art from the Later Stone Age (LSA); this is a tradition of which well-executed engravings of animal tracks in large numbers are characteristic. Research into rock art usually groups these motifs together with geometric signs; at best, therefore, it may provide summary lists of them. To date, the field has completely disregarded the fact that tracks and trackways are a rich medium of information for hunter-gatherers, alongside their deeper, culture-specific connotations. A recent research project, from which this article has emerged, has attempted to fill this research gap; it entailed indigenous tracking experts from the Kalahari analysing engraved animal tracks and human footprints in a rock art region in central Western Namibia, the Doro! nawas Mountains, which is the site of recently discovered rock art. The experts were able to define the species, sex, age group and exact leg of the specific animal or human depicted in more than 90% of the engravings they analysed (N = 513). Their work further demonstrates that the variety of fauna is much richer in engraved tracks than in depictions of animals in the same engraving tradition. The analyses reveal patterns that evidently arise from culturally determined preferences. The study represents further confirmation that indigenous knowledge, with its profound insights into a range of particular fields, has the capacity to considerably advance archaeological research.
Journal Article
Disturbance-mediated facilitation by an intertidal ecosystem engineer
Ecosystem engineers facilitate communities by providing a structural habitat that reduces abiotic stress or predation pressure for associated species. However, disturbance may damage or move the engineer to a more stressful environment, possibly increasing the importance of facilitation for associated communities. In this study, we determined how disturbance to intertidal boulders (i.e., flipping) and the subsequent movement of a structural ecosystem engineer, the tube-forming serpulid worm Galeolaria caespitosa, from the bottom (natural state, low abiotic stress) to the top (disturbed state, high abiotic stress) surface of boulders influenced the importance of facilitation for intertidal communities across two intertidal zones. Theory predicts stronger relative facilitation should occur in the harsher environments of the top of boulders and the high intertidal zone. To test this prediction, we experimentally positioned boulders with the serpulids either face up or face down for 12 months in low and high zones in an intertidal boulder field. There were very different communities associated with the different boulders and serpulids had the strongest facilitative effects on the more stressful top surface of boulders with approximately double the species richness compared to boulders lacking serpulids. Moreover, within the serpulid matrix itself there was also approximately double the species richness (both zones) and abundance (high zone only) of small invertebrates on the top of boulders compared to the bottom. The high relative facilitation on the top of boulders reflected a large reduction in temperature by the serpulid matrix on that surface (up to 10°C) highlighting a key role for modification of the abiotic environment in determining the community-wide facilitation. This study has demonstrated that disturbance and subsequent movement of an ecosystem engineer to a more stressful environment increased the importance of facilitation and allowed species to persist that would otherwise be unable to survive in that environment.
Journal Article
Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu—A spinning top–shaped rubble pile
The Hayabusa2 spacecraft arrived at the near-Earth carbonaceous asteroid 162173 Ryugu in 2018. We present Hayabusa2 observations of Ryugu’s shape, mass, and geomorphology. Ryugu has an oblate “spinning top” shape, with a prominent circular equatorial ridge. Its bulk density, 1.19 ± 0.02 grams per cubic centimeter, indicates a high-porosity (>50%) interior. Large surface boulders suggest a rubble-pile structure. Surface slope analysis shows Ryugu’s shape may have been produced from having once spun at twice the current rate. Coupled with the observed global material homogeneity, this suggests that Ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation. From these remote-sensing investigations, we identified a suitable sample collection site on the equatorial ridge.
Journal Article
The application of UAV-derived SfM-MVS photogrammetry for the investigation of storm wave boulder deposits on a small rocky island in the semi-enclosed Northern Adriatic Sea
The inventory and categorization of an extensive coastal boulder assemblage originating from storm wave transport on the coastline of Fenoliga Island (Northern Adriatic Sea, southern Istria, Croatia) are presented and discussed herein. The study adopted the use of a commercial Uncrewed Aerial Vehicle (UAV) and Structure from Motion-MultiView Stereo (SfM-MVS) photogrammetry for the construction of a 3D model of the island. A Digital Elevation Model (DEM) and an orthomosaic were produced and employed for the mapping of the boulder assemblage in a GIS. In total, 592 boulders were identified and mapped. Using SfM-MVS-derived products allowed for the identified boulders to be categorized based on size classification. Amassed data relating to the boulder characteristics was inserted and stored in a GIS, including the results of a comparative assessment with historical Google Earth imagery which enabled the 'quantification of boulder transport over a 9-year timeframe'. Field evidence indicates that boulders were created in-situ via the quarrying of bedrock strata by breaking waves causing increased water pressure within preexisting surfaces of weakness such as bedding planes and sub-vertical fractures. Once detached, the boulders were transported and deposited during storm wave events. Repeated storm events can further displace previously detached clasts.
Journal Article
Glacial lake outburst floods as drivers of fluvial erosion in the Himalaya
Glacial lake outburst floods (GLOFs) are exactly what they sound like. The sudden emptying of a glacial lake in high-topography regions like the Himalaya can quickly destroy everything in its path. Cook et al. intercepted a GLOF in the Bhotekoshi and Sunkoshi river valleys in central Nepal as they were monitoring the region in the aftermath of the 2015 Gorkha earthquake. They found that a massive amount of erosion occurred during the outburst flood, which suggests that GLOFs may be the primary factor in landscape evolution for these regions. Science , this issue p. 53 A very well monitored Himalayan glacial lake outburst flood shows the power of these large events to drive erosion. Himalayan rivers are frequently hit by catastrophic floods that are caused by the failure of glacial lake and landslide dams; however, the dynamics and long-term impacts of such floods remain poorly understood. We present a comprehensive set of observations that capture the July 2016 glacial lake outburst flood (GLOF) in the Bhotekoshi/Sunkoshi River of Nepal. Seismic records of the flood provide new insights into GLOF mechanics and their ability to mobilize large boulders that otherwise prevent channel erosion. Because of this boulder mobilization, GLOF impacts far exceed those of the annual summer monsoon, and GLOFs may dominate fluvial erosion and channel-hillslope coupling many tens of kilometers downstream of glaciated areas. Long-term valley evolution in these regions may therefore be driven by GLOF frequency and magnitude, rather than by precipitation.
Journal Article
Shape of (101955) Bennu indicative of a rubble pile with internal stiffness
The shapes of asteroids reflect interplay between their interior properties and the processes responsible for their formation and evolution as they journey through the Solar System. Prior to the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission, Earth-based radar imaging gave an overview of (101955) Bennu’s shape. Here we construct a high-resolution shape model from OSIRIS-REx images. We find that Bennu’s top-like shape, considerable macroporosity and prominent surface boulders suggest that it is a rubble pile. High-standing, north–south ridges that extend from pole to pole, many long grooves and surface mass wasting indicate some low levels of internal friction and/or cohesion. Our shape model indicates that, similar to other top-shaped asteroids, Bennu formed by reaccumulation and underwent past periods of fast spin, which led to its current shape. Today, Bennu might follow a different evolutionary pathway, with an interior stiffness that permits surface cracking and mass wasting.Near-Earth asteroid Bennu has a top-like shape with longitudinal ridges, macroporosity, prominent boulders and surface mass wasting, suggesting that it is a stiff rubble pile, according to early observations by the OSIRIS-REx mission.
Journal Article
A new species of terrestrially-nesting fanged frog
Herein, we describe a new species of terrestrially-nesting fanged frog from Sulawesi Island, Indonesia. Though male nest attendance and terrestrial egg deposition is known in one other Sulawesi fanged frog (Limnonectes arathooni), the new species exhibits a derived reproductive mode unique to the Sulawesi assemblage; male frogs guard one or more clutches of eggs festooned to leaves or mossy boulders one to two meters above small slow-moving streams, trickles, or seeps. This island endemic has thus far been collected at three sites on Sulawesi: one in the Central Core of the island, and two on the Southwest Peninsula-south of the Tempe Depression (a major biogeographical boundary). The new Limnonectes has the smallest adult body size among its Sulawesi congeners-with a maximum snout-vent length of about 30 millimeters. Beyond its unique reproductive behavior and body size, the species is further diagnosed on the basis of advertisement call and genetic distance from sympatric fanged frogs. The discovery and description of the new species highlights the remarkable reproductive trait diversity that characterizes the Sulawesi fanged frog assemblage despite that most species in this radiation have yet to be formally described.
Journal Article