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1 A Dove nanosatellite with its telescope, camera, solar panels, and communication antenna in operational mode. Courtesy of Planet Labs. (https://www. satimagingcorp.com/satellite-sensors/other-satellitesensors/dove-3m/.) et al. (2020), Roelfsema et al. (2021) and Kennedy (2021). The Atlas primarily uses data from Planet Labs, which has developed constellations of about 130 nanosatellites called Doves (1) that have been launched with continual improvement from the International Space Station (Planet Labs, 2017). Each Dove is solar powered, weighs 5 kg (11 lbs), and collectively, they can take multispectral images with a resolution of less than 4 m 2 /pixel for an area of ~200 million km 2 every day. Each image in the Allen Atlas is a single image or a mosaic selected for sparse cloud cover and the highest levels of water clarity. Images also are subjected to a number of analytical adjustments including orthorectification, in which they are corrected for distortions from the sensors and from the angle between the satellite and the imaged position on Earth, to accurately position features. Algorithms are also applied to mask clouds and correct for atmospheric distortion, surface reflection, and sun glint. Corrections for water conditions include those for light attenuation due to absorption with increasing depth, light scattering, and reflection from the bottom. The optical images presented here use the visible spectrum (red, green, and blue wavelengths), which corresponds with human perception. More information on this technology can be found in Sayfin (2020) and Kopacz et al. (2020). The Atlas has mapped nearly all coral reef areas within 30° north and south of the equator. In addition to providing optical satellite images (2a), the Atlas provides classified geomorphic attributes (thematic maps) of each reef. Using all four spectral bands (blue, green, red, and near infrared) of the Dove satellite system, spectral reflectance properties of land and marine areas can document atoll benthic (bottom) properties objectively and over large areas. Thus, changes in concentrations of photosynthetic pigments in coral, algae, and seagrass, as well as light scattering by inorganic materials and sand or rubble derived from
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... can be partially exposed depending on the amplitude of the tide, storm conditions, and angle into deeper water. It may develop sediment bars, dunes or ripples in response to wave and current forcing ( Figure 1.11a). ...
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... with sufficiently protected areas including the lee side of shorelines, islands, or lagoons may develop seagrass meadows like in several of the northern Gilbert Islands (Figure 1.11b). Extensive seagrass areas have also been reported from inner lagoons or behind vegetated islets of Kwajalein and several other atolls in the Marshall Islands (McKenzie et al., 2021). ...
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... mangroves occur on the islands of Tuvalu and are particularly extensive in the protection of reeftop islands or in and around some of the almost land-locked lagoons (Woodroffe, 1987). On Beru Atoll in the southern Gilbert Islands, a well-developed mangrove community occurs in the shallows of the lagoon as it does elsewhere in Kiribati (Figure 1.11c). Mangroves provide significant benefits for atoll environments that include shoreline and sediment stabilization by their extensive root systems, which in turn provide resistance to the erosive effects of wind, waves, and currents. ...
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... can be partially exposed depending on the amplitude of the tide, storm conditions, and angle into deeper water. It may develop sediment bars, dunes or ripples in response to wave and current forcing ( Figure 1.11a). ...
Context 5
... with sufficiently protected areas including the lee side of shorelines, islands, or lagoons may develop seagrass meadows like in several of the northern Gilbert Islands (Figure 1.11b). Extensive seagrass areas have also been reported from inner lagoons or behind vegetated islets of Kwajalein and several other atolls in the Marshall Islands (McKenzie et al., 2021). ...
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... mangroves occur on the islands of Tuvalu and are particularly extensive in the protection of reeftop islands or in and around some of the almost land-locked lagoons (Woodroffe, 1987). On Beru Atoll in the southern Gilbert Islands, a well-developed mangrove community occurs in the shallows of the lagoon as it does elsewhere in Kiribati (Figure 1.11c). Mangroves provide significant benefits for atoll environments that include shoreline and sediment stabilization by their extensive root systems, which in turn provide resistance to the erosive effects of wind, waves, and currents. ...
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Kebumen terletak di Provinsi Jawa Tengah yang telah ditetapkan sebagai Geopark Nasional pada tahun 2018. Geopark Kebumen, yang kemudian diajukan sebagai UNESCO Global Geopark pada tahun 2023, diharapkan akan meningkatkan jumlah kunjungan wisatawan dan peneliti ke kabupaten ini. Peningkatan ini memiliki konsekuensi penting dalam menjamin ketersediaa...
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... As an equatorial nation, Kiribati does not experience marked seasonal changes in temperature, although squalls and rains are more common in the austral summer season ("Aumeang") from November to March than the dry austral winter ("Aumaiaki"). Tides in Kiribati are dominantly semidiurnal, with spring range of over 2 m and neap range of less than 0.6 m (Goldberg and Rankey, 2023). Traditional knowledge suggests that the spring tides during the "Aumeang" season are higher, and this factor could impact wave energy that reaches shorelines. ...
... In the austral winter, the more gentle trade winds are most common. Tides in Tokelau are semidiurnal with spring tide range of roughly 1.3 m, and neap tide range of less than 0.4 m (Goldberg and Rankey, 2023). Tokelau is in the Pacific cyclone belt; direct hits by cyclonic storms are infrequent, but when they do strike, they can have major impact on the atolls. ...
Although there is general agreement that global change will influence low-lying atoll islands, considerable uncertainty remains concerning the nature, rates, and causes of morphological change (or, conversely, the stability) of islands. As the net geomorphical product of sediment erosion, transport, and accumulation, islands are intimately tied to reef flat sedimentological processes. Recognizing the morphodynamical linkages between reef flats and islands, the purpose of this study is to examine the nature and controls on spatial and temporal variations in sediment transport pathways on reef flats and their relation to island planform changes or stability on atolls of Tokelau and Kiribati. GIS analysis of historical aerial images and high-resolution remote-sensing data capture patterns of reef flat change up to 72 years in duration with up to weekly temporal resolution. Data reveal how granular materials that make up bars and islands on reef flats respond to physical oceanographic processes via sedimentary-geomorphical change across temporal scales, from “instantaneous” impacts of cyclones or swell events to seasonal to multi-decadal shifts. Each of these shifts is manifest as migration of sediment of island beaches and bar forms, but the character varies markedly—bars form new islands, others erode and disappear; some changes are cyclic, others are directional, still others are hybrid; sediment can be transported lagoonward, oceanward, along the reef flat, or in combinations thereof; and migration rates reach up to 10 s of m/month. Although sea-level change likely plays a modulating role, much of the considerable spatial and temporal variability relates to differences in energy controlled by seasonal change in swell direction and climate shifts. Nonetheless, sedimentary response to these external forcings at any specific location also is shaped by local factors, such as trade wind-generated lagoonal waves and currents, atoll lagoon size and depth, margin width and orientation relative to waves, and autogenic processes such as attachment of migrating bars. Collectively, these influences shape the spatially and temporally heterogeneous sediment flux to and from islands, and thus the variable response of islands to ongoing sea-level change. Understanding such local influences is requisite to predictive understanding of how global change might impact these sensitive seascapes.
