Over the past 500 million years in Earth's history,five mass extinctions("Big Five")have been identified,each with an extinction rate of exceeding 75%of marine species[1].Abrupt climatic and environmenta...Over the past 500 million years in Earth's history,five mass extinctions("Big Five")have been identified,each with an extinction rate of exceeding 75%of marine species[1].Abrupt climatic and environmental changes attributed to intra-or extraterrestrial events were proposed to cause these mass extinctions.Today the world is likely facing an ongoing biotic crisis,the socalled sixth mass extinction[2],due to the accelerated climate and environmental changes resulting from various anthropogenic activities.It is estimated that the average rate of vertebrate species loss in the last century is 100 times greater than the background rate[2].Deciphering the causes and mechanisms of past mass extinctions therefore is of great importance,as it provides critical knowledge for understanding the pattern and underlying mechanism of current biodiversity loss.展开更多
The Earth orientation parameters play a crucial role in positioning and navigation.Very-long-baseline interferometry(VLBI)stands as the sole technology that offers a comprehensive set of Earth orientation parameters.T...The Earth orientation parameters play a crucial role in positioning and navigation.Very-long-baseline interferometry(VLBI)stands as the sole technology that offers a comprehensive set of Earth orientation parameters.The technology offers a highly precise measurement of dUT1.In order to facilitate diverse space activities,it is imperative for China to establish an independent capability for high-precision dUT1 support.To this end,China Next-Generation VLBI Network(CNVN)has been constructed.In this paper,VieSched++is employed to identify the optimal single baseline for dUT1 estimation among 11 potential VLBI Global Observing System antenna locations in China,followed by the determination of an optimized 3-station network.We integrated CNVN with a space-tracking vessel to enhance the precision of dUT1 estimation.The results demonstrate that the optimal single baseline between Jiamusi and Kashi in China yields dUT1 estimates with a mean formal error of less than 13μs and a repeatability better than 33μs during observations lasting for both 1 and 1.5 h.The optimal 3-station network comprising Jiamusi,Kashi,and Shanghai demonstrates the capability to provide dUT1 estimates with an mean formal error of less than 8μs and a repeatability of less than 31μs.The North Atlantic Ocean is identified as the optimal location for the space-tracking vessel when combined with the 4-antenna CNVN,enabling an estimation of dUT1 with an mean formal error of less than 5μs and a repeatability of less than 15μs after 1 h of observation.展开更多
基金supported by the National Natural Science Foundation of China(42025703,42325202,and 42277072)。
文摘Over the past 500 million years in Earth's history,five mass extinctions("Big Five")have been identified,each with an extinction rate of exceeding 75%of marine species[1].Abrupt climatic and environmental changes attributed to intra-or extraterrestrial events were proposed to cause these mass extinctions.Today the world is likely facing an ongoing biotic crisis,the socalled sixth mass extinction[2],due to the accelerated climate and environmental changes resulting from various anthropogenic activities.It is estimated that the average rate of vertebrate species loss in the last century is 100 times greater than the background rate[2].Deciphering the causes and mechanisms of past mass extinctions therefore is of great importance,as it provides critical knowledge for understanding the pattern and underlying mechanism of current biodiversity loss.
基金supported by the National Natural Science Foundation of China(NSFC)under Grant Number 42304044the Natural Science Foundation of Henan,China,under Grant Number 222300420385。
文摘The Earth orientation parameters play a crucial role in positioning and navigation.Very-long-baseline interferometry(VLBI)stands as the sole technology that offers a comprehensive set of Earth orientation parameters.The technology offers a highly precise measurement of dUT1.In order to facilitate diverse space activities,it is imperative for China to establish an independent capability for high-precision dUT1 support.To this end,China Next-Generation VLBI Network(CNVN)has been constructed.In this paper,VieSched++is employed to identify the optimal single baseline for dUT1 estimation among 11 potential VLBI Global Observing System antenna locations in China,followed by the determination of an optimized 3-station network.We integrated CNVN with a space-tracking vessel to enhance the precision of dUT1 estimation.The results demonstrate that the optimal single baseline between Jiamusi and Kashi in China yields dUT1 estimates with a mean formal error of less than 13μs and a repeatability better than 33μs during observations lasting for both 1 and 1.5 h.The optimal 3-station network comprising Jiamusi,Kashi,and Shanghai demonstrates the capability to provide dUT1 estimates with an mean formal error of less than 8μs and a repeatability of less than 31μs.The North Atlantic Ocean is identified as the optimal location for the space-tracking vessel when combined with the 4-antenna CNVN,enabling an estimation of dUT1 with an mean formal error of less than 5μs and a repeatability of less than 15μs after 1 h of observation.
