Life exists in the universe and therefore the astrophysical properties of the universe must be such that they allow the origin of life. We connect astrobiology and astrophysics via one astrobiological quantity—the pr...Life exists in the universe and therefore the astrophysical properties of the universe must be such that they allow the origin of life. We connect astrobiology and astrophysics via one astrobiological quantity—the probability of the origin of life. We show how this probability, if it is very low, will allow us to answer profound astrophysical questions such as the type of universe we live in, the fate of our universe, whether neutron stars, white and brown dwarfs evaporate and whether protons decay.展开更多
Using the FengYun-3C(FY-3C)onboard BeiDou Navigation Satellite System(BDS)and Global Positioning System(GPS)data from 2013 to 2017,this study investigates the performance and contribution of BDS to precise orbit deter...Using the FengYun-3C(FY-3C)onboard BeiDou Navigation Satellite System(BDS)and Global Positioning System(GPS)data from 2013 to 2017,this study investigates the performance and contribution of BDS to precise orbit determination(POD)for a low-Earth orbit(LEO).The overlap comparison result indicates that code bias correction of BDS can improve the POD accuracy by 12.4%.The multi-year averaged one-dimensional(1D)root mean square(RMS)of the overlapping orbit differences(OODs)for the GPS-only solution is 2.0,1.7,and 1.5 cm,respectively,during the 2013,2015,and 2017 periods.The 1D RMS for the BDS-only solution is 150.9,115.0,and 47.4 cm,respectively,during the 2013,2015,and 2017 periods,which is much worse than the GPS-only solution due to the regional system of BDS and the few BDS channels of the FY-3C receiver.For the BDS and GPS combined solution(also known as the GC combined solution),the averaged 1D RMS is 2.5,2.3,and 1.6 cm,respectively,in 2013,2015,and 2017,while the GC combined POD presents a significant accuracy improvement after the exclusion of geostationary Earth orbit(GEO)satellites.The main reason for the improvement seen after this exclusion is the unfavorable satellite tracking geometry and poor orbit accuracy of GEO satellites.The accuracy of BDS-only and GC combined solutions have gradually improved from 2013 to 2017,thanks to improvements in the accuracy of International GNSS Service(IGS)orbit and clock products in recent years,especially the availability of a high-frequency satellite clock product(30 s sampling interval)since 2015.Moreover,the GC POD(without GEO)was able to achieve slightly better accuracy than the GPS-only POD in 2017,indicating that the fusion of BDS and GPS observations can improve the accuracy of LEO POD.GC combined POD can significantly improve the reliability of LEO POD,simply due to system redundancy.An increased contribution of BDS to LEO POD can be expected with the launch of more BDS satellites and with further improvements in the accuracy of BDS satellite products in the near future.展开更多
In this work,an approach is developed to study the seismicity associated with the impoundment and level changes of a water reservoir(reservoir induced seismicity e RIS).The proposed methodology features a combination ...In this work,an approach is developed to study the seismicity associated with the impoundment and level changes of a water reservoir(reservoir induced seismicity e RIS).The proposed methodology features a combination of a semi-analytical poroelastic model with an earthquake nucleation approach based on rate-and-state frictional law.The combined approach was applied to the case of the Pertusillo Lake,located in the Val d’Agri area(Italy),whose large seasonal water level changes are believed to induce protracted micro-seismicity(local magnitude ML<3).Results show that the lake impoundment in 1962 could have produced up to 0.5 bar(1 bar=100 kPa)changes in Coulomb failure stress(DCFS),while the seasonal water level variation is responsible for variation up to 0.05 bar.Modeling results of the seismicity rates in 20012014 show that the observed earthquakes are well correlated with the modeled DCFS.Finally,the reason that the seismicity is only observed at southwest of the Pertusillo Lake is provided,which is likely attributed to different rock lithologies and depletion caused by significant hydrocarbon exploitation in the northeastern sector of the lake.展开更多
Inspired by recent significant agricultural yield losses in the eastern China and a missing operational monitoring system,we developed a comprehensive drought monitoring model to better understand the impact of indivi...Inspired by recent significant agricultural yield losses in the eastern China and a missing operational monitoring system,we developed a comprehensive drought monitoring model to better understand the impact of individual key factors contributing to this issue.The resulting model,the‘Humidity calibrated Drought Condition Index’(HcDCI)was applied for the years 2001 to 2019 in form of a case study to Weihai County,Shandong Province in East China.Design and development are based on a linear combination of the Vegetation Condition Index(VCI),the Temperature Condition Index(TCI),and the Rainfall Condition Index(RCI)using multi-source satellite data to create a basic Drought Condition Index(DCI).VCI and TCI were derived from MODIS(Moderate Resolution Imaging Spectroradiometer)data,while precipitation is taken from CHIRPS(Climate Hazards Group InfraRed Precipitation with Station data)data.For reasons of accuracy,the decisive coefficients were determined by the relative humidity of soils at depth of 10-20 cm of particular areas collected by an agrometeorological ground station.The correlation between DCI and soil humidity was optimized with the factors of 0.53,0.33,and 0.14 for VCI,TCI,and RCI,respectively.The model revealed,light agricultural droughts from 2003 to 2013 and in 2018,while more severe droughts occurred in 2001 and 2002,2014-2017,and 2019.The droughts were most severe in January,March,and December,and our findings coincide with historical records.The average temperature during 2012-2019 is 1℃ higher than that during the period 2001-2011 and the average precipitation during 2014-2019 is 192.77 mm less than that during 2008-2013.The spatio-temporal accuracy of the HcDCI model was positively validated by correlation with agricultural crop yield quantities.The model thus,demonstrates its capability to reveal drought periods in detail,its transferability to other regions and its usefulness to take future measures.展开更多
The Real-Time Global Navigation Satellite System(GNSS)Precise Positioning Service(RTPPS)is recognized as the most promising system by providing precise satellite orbit and clock correc-tions for users to achieve centi...The Real-Time Global Navigation Satellite System(GNSS)Precise Positioning Service(RTPPS)is recognized as the most promising system by providing precise satellite orbit and clock correc-tions for users to achieve centimeter-level positioning with a stand-alone receiver in real-time.Although the products are available with high accuracy almost all the time,they may occasionally suffer from unexpected significant biases,which consequently degrades the positioning perfor-mance.Therefore,quality monitoring at the system-level has become more and more crucial for providing a reliable GNSS service.In this paper,we propose a method for the monitoring of realtime satellite orbit and clock products using a monitoring station network based on the Quality Control(QC)theory.The satellites with possible biases are first detected based on the outliers identified by Precise Point Positioning(PPP)in the monitoring station network.Then,the corresponding orbit and clock parameters with temporal constraints are introduced and esti-mated through the sequential Least Square(LS)estimator and the corresponding Instantaneous User Range Errors(IUREs)can be determined.A quality indicator is calculated based on the IUREs in the monitoring network and compared with a pre-defined threshold.The quality monitoring method is experimentally evaluated by monitoring the real-time orbit and clock products generated by GeoForschungsZentrum(GFZ),Potsdam.The results confirm that the problematic satellites can be detected accurately and effectively with missed detection rate 4×10^(-6) and false alarm rate 1:2×10^(-5).Considering the quality alarms,the PPP results in terms of RMS of positioning differences with respect to the International GNSS Service(IGS)weekly solution in the north,east and up directions can be improved by 12%,10%and 27%,respectively.展开更多
Opencast lignite mining in the Lusatia region of Germany has resulted in large scale landscape disturbances, which require suitable recultivation techniques in order to promote plant growth and establishment in the re...Opencast lignite mining in the Lusatia region of Germany has resulted in large scale landscape disturbances, which require suitable recultivation techniques in order to promote plant growth and establishment in the remaining nutrient-poor substrates with low water-holding capacity. Thus, the effects of two commercial soil additives （CSA）, a hydrophilic polymer mixed with volcanic rock flour and bentonite （a-CSA）, and digester solids from biogas plants enriched with humic acids and bentonite （b-CSA）, on soil organic carbon （SOC） storage, plant yields and root biomass were assessed after cultivating perennial crops （Dactylis 9lornerata L.） in monoculture and Helianthus annuus L.-Brassica napus L. in crop rotation systems. The CSA were incorporated into the top 20 cm soil depth using a rotary spader. The results indicated that a-CSA led to a significant increase in plant yield during the first year, and improved root biomass in the following year. As a result, SOC stocks increased, especially in the 0 10 cm soil layer. No significant sequestration of additional SOC was observed on b-CSA-amended plots at the end of both years. Bulk density values decreased in all treatments under the monoculture system. It can be concluded that application of a-CSA enhanced soil water availability for plant uptake and consequently promoted plant growth and organic carbon sequestration. The relative enrichment of organic matter without effects on water-holding capacities of b-CSA treatments suggested that it was not suitable for rapid land reclamation.展开更多
When formation flying spacecrafts are used as platform to gain earth oriented observation, precise baselines between these spacecrafts are always essential. Gravity recovery and climate experiment （GRACE） mission is...When formation flying spacecrafts are used as platform to gain earth oriented observation, precise baselines between these spacecrafts are always essential. Gravity recovery and climate experiment （GRACE） mission is aimed at mapping the global gravity field and its variation. Accurate baseline of GRACE satellites is necessary for the gravity field modeling. The determination of kinematic and reduced dynamic relative orbits of twin satellites has been studied in this paper, and an accuracy of 2 mm for dynamic relative orbits and 5 mm for kinematic ones can be obtained, whereby most of the double difference onboard GPS ambiguities are resolved.展开更多
THE Barra do Itapirapua carbonatite belongs to a Cretaceous province related to the opening of the SouthAtlantic, and is emplaced in a Proterozoic granite. The carbonatite is mainly composed of plutonic magnesio-and f...THE Barra do Itapirapua carbonatite belongs to a Cretaceous province related to the opening of the SouthAtlantic, and is emplaced in a Proterozoic granite. The carbonatite is mainly composed of plutonic magnesio-and ferrocarbonatite and is mineralizing host of a REE mineralization related to late-to post-magmatic hydrothermal processes. The non-overprinted carbonatite has low bulk REE contents, andmagmatic pyrochlore is the major carrier of REE. In the altered mineralized carbonatite, corrosion cavitiesin primary ankerite are filled with a hydrothermal mineral assemblage of quartz, apatite, fluorite, RE-fluorocarbonates, barite, sulfides and Fe-oxides in variable proportions. Two types of hydrothermally overprinted carbonatites can be distinguished: type Ⅰ containing quartz and RE-fluorocarbonates, enriched inLREE and with ∑REE of up to 3% (weight percent), which is two orders of magnitude higher than thenon-overprinted carbonatite; and type Ⅱ containing apatite as the major hydrothermal mineral, and enriched in HREE. The END of the mineralized carbonatite reveals a nonradiogenic isotopic signature andsuggests a carbonatite-related source for the REE展开更多
In recent years,the large Low Earth Orbit(LEO)constellations have become a hot topic due to their great potential to improve the Global Navigation Satellite Systems(GNSS)positioning performance.One of the important fo...In recent years,the large Low Earth Orbit(LEO)constellations have become a hot topic due to their great potential to improve the Global Navigation Satellite Systems(GNSS)positioning performance.One of the important focus is how to obtain the accurate and reliable orbits for these constellations with dozens of LEO satellites.The GNSS-based Precise Orbit Determination(POD)will be exclusively performed to achieve this goal,where the Integer Ambiguity Resolution(IAR)plays a key role in acquiring high-quality orbits.In this study,we present a comprehensive analysis of the benefit of the single-receiver IAR in LEO POD and discuss its implication for the future LEO constellations.We perform ambiguity-fixed LEO POD for four typical missions,including Gravity Recovery and Climate Experiment(GRACE)Follow-On(GRACE-FO),Swarm,Jason-3 and Sentinel-3,using the Uncalibrated Phase Delay(UPD)products generated by our GREAT(GNSS+REsearch,Application and Teaching)software.The results show that the ambiguity fixing processing can significantly improve the accuracy of LEO orbits.There are negligible differences between our UPD-based ambiguity-fixed orbits and those based on the Observable Signal Bias(OSB)and Integer Recovery Clock(IRC)products,indicating the good-quality of UPD products we generated.Compared to the float solution,the fixed solution presents a better consistency with the external precise science orbits and the largest accuracy improvement of 5 mm is achieved for GRACE-FO satellites.Meanwhile,the benefit can be observed in laser ranging residuals as well,with a Standard Deviation(STD)reduction of 3–4 mm on average for the fixed solutions.Apart from the absolute orbits,the relative accuracy of the space baseline is also improved by 20–30%in the fixed solutions.The result demonstrates the superior performance of the ambiguity-fixed LEO POD,which appears as a particularly promising technique for POD of future LEO constellations.展开更多
In this opinion paper,we,a group of scientists from environmental-,geo-,ocean-and information science,argue visual data exploration should become a common analytics approach in Earth system science due to its potentia...In this opinion paper,we,a group of scientists from environmental-,geo-,ocean-and information science,argue visual data exploration should become a common analytics approach in Earth system science due to its potential for analysis and interpretation of large and complex spatio-temporal data.We discuss the challenges that appear such as synthesis of heterogeneous data from various sources,reducing the amount of information and facilitating multidisciplinary,collaborative research.We argue that to fully exploit the potential of visual data exploration,several bottlenecks and challenges have to be addressed:providing an efficient data management and an integrated modular workflow,developing and applying suitable visual exploration concepts and methods with the help of effective and tailored tools as well as generating and raising the awareness of visual data exploration and education.We are convinced visual data exploration is worth the effort since it significantly facilitates insight into environmental data and derivation of knowledge from it.展开更多
文摘Life exists in the universe and therefore the astrophysical properties of the universe must be such that they allow the origin of life. We connect astrobiology and astrophysics via one astrobiological quantity—the probability of the origin of life. We show how this probability, if it is very low, will allow us to answer profound astrophysical questions such as the type of universe we live in, the fate of our universe, whether neutron stars, white and brown dwarfs evaporate and whether protons decay.
基金We are very grateful to the IGS,GFZ,and WHU for providing the precise orbit and clock products of GPS and BDS.Thanks also go to the EPOS-RT/PANDA software from GFZ.This study is financially supported by the National Natural Science Foundation of China(41774030,41974027,41974029,and 41505030)the Hubei Province Natural Science Foundation of China(2018CFA081)The numerical calculations in this paper were done on the supercomputing system at the Supercomputing Center of Wuhan University.
文摘Using the FengYun-3C(FY-3C)onboard BeiDou Navigation Satellite System(BDS)and Global Positioning System(GPS)data from 2013 to 2017,this study investigates the performance and contribution of BDS to precise orbit determination(POD)for a low-Earth orbit(LEO).The overlap comparison result indicates that code bias correction of BDS can improve the POD accuracy by 12.4%.The multi-year averaged one-dimensional(1D)root mean square(RMS)of the overlapping orbit differences(OODs)for the GPS-only solution is 2.0,1.7,and 1.5 cm,respectively,during the 2013,2015,and 2017 periods.The 1D RMS for the BDS-only solution is 150.9,115.0,and 47.4 cm,respectively,during the 2013,2015,and 2017 periods,which is much worse than the GPS-only solution due to the regional system of BDS and the few BDS channels of the FY-3C receiver.For the BDS and GPS combined solution(also known as the GC combined solution),the averaged 1D RMS is 2.5,2.3,and 1.6 cm,respectively,in 2013,2015,and 2017,while the GC combined POD presents a significant accuracy improvement after the exclusion of geostationary Earth orbit(GEO)satellites.The main reason for the improvement seen after this exclusion is the unfavorable satellite tracking geometry and poor orbit accuracy of GEO satellites.The accuracy of BDS-only and GC combined solutions have gradually improved from 2013 to 2017,thanks to improvements in the accuracy of International GNSS Service(IGS)orbit and clock products in recent years,especially the availability of a high-frequency satellite clock product(30 s sampling interval)since 2015.Moreover,the GC POD(without GEO)was able to achieve slightly better accuracy than the GPS-only POD in 2017,indicating that the fusion of BDS and GPS observations can improve the accuracy of LEO POD.GC combined POD can significantly improve the reliability of LEO POD,simply due to system redundancy.An increased contribution of BDS to LEO POD can be expected with the launch of more BDS satellites and with further improvements in the accuracy of BDS satellite products in the near future.
基金funded by a research agreement between the Swiss Seismological Service(SED)and the Istituto Nazionale di Geofisica e Vulcanologiathe RISE project under the European Union’s Horizon 2020 research and innovation programme(Grant No.821115)financed by a SNSF Ambizione Energy grant(PZENP2160555)。
文摘In this work,an approach is developed to study the seismicity associated with the impoundment and level changes of a water reservoir(reservoir induced seismicity e RIS).The proposed methodology features a combination of a semi-analytical poroelastic model with an earthquake nucleation approach based on rate-and-state frictional law.The combined approach was applied to the case of the Pertusillo Lake,located in the Val d’Agri area(Italy),whose large seasonal water level changes are believed to induce protracted micro-seismicity(local magnitude ML<3).Results show that the lake impoundment in 1962 could have produced up to 0.5 bar(1 bar=100 kPa)changes in Coulomb failure stress(DCFS),while the seasonal water level variation is responsible for variation up to 0.05 bar.Modeling results of the seismicity rates in 20012014 show that the observed earthquakes are well correlated with the modeled DCFS.Finally,the reason that the seismicity is only observed at southwest of the Pertusillo Lake is provided,which is likely attributed to different rock lithologies and depletion caused by significant hydrocarbon exploitation in the northeastern sector of the lake.
基金Under the auspices of Shenzhen Science and Technology Program(No.KQTD20180410161218820)Guangdong Basic and Applied Basic Research Foundation(No.2021A1515012600)。
文摘Inspired by recent significant agricultural yield losses in the eastern China and a missing operational monitoring system,we developed a comprehensive drought monitoring model to better understand the impact of individual key factors contributing to this issue.The resulting model,the‘Humidity calibrated Drought Condition Index’(HcDCI)was applied for the years 2001 to 2019 in form of a case study to Weihai County,Shandong Province in East China.Design and development are based on a linear combination of the Vegetation Condition Index(VCI),the Temperature Condition Index(TCI),and the Rainfall Condition Index(RCI)using multi-source satellite data to create a basic Drought Condition Index(DCI).VCI and TCI were derived from MODIS(Moderate Resolution Imaging Spectroradiometer)data,while precipitation is taken from CHIRPS(Climate Hazards Group InfraRed Precipitation with Station data)data.For reasons of accuracy,the decisive coefficients were determined by the relative humidity of soils at depth of 10-20 cm of particular areas collected by an agrometeorological ground station.The correlation between DCI and soil humidity was optimized with the factors of 0.53,0.33,and 0.14 for VCI,TCI,and RCI,respectively.The model revealed,light agricultural droughts from 2003 to 2013 and in 2018,while more severe droughts occurred in 2001 and 2002,2014-2017,and 2019.The droughts were most severe in January,March,and December,and our findings coincide with historical records.The average temperature during 2012-2019 is 1℃ higher than that during the period 2001-2011 and the average precipitation during 2014-2019 is 192.77 mm less than that during 2008-2013.The spatio-temporal accuracy of the HcDCI model was positively validated by correlation with agricultural crop yield quantities.The model thus,demonstrates its capability to reveal drought periods in detail,its transferability to other regions and its usefulness to take future measures.
基金funded by the National Natural Science Foundation of China(42030109).
文摘The Real-Time Global Navigation Satellite System(GNSS)Precise Positioning Service(RTPPS)is recognized as the most promising system by providing precise satellite orbit and clock correc-tions for users to achieve centimeter-level positioning with a stand-alone receiver in real-time.Although the products are available with high accuracy almost all the time,they may occasionally suffer from unexpected significant biases,which consequently degrades the positioning perfor-mance.Therefore,quality monitoring at the system-level has become more and more crucial for providing a reliable GNSS service.In this paper,we propose a method for the monitoring of realtime satellite orbit and clock products using a monitoring station network based on the Quality Control(QC)theory.The satellites with possible biases are first detected based on the outliers identified by Precise Point Positioning(PPP)in the monitoring station network.Then,the corresponding orbit and clock parameters with temporal constraints are introduced and esti-mated through the sequential Least Square(LS)estimator and the corresponding Instantaneous User Range Errors(IUREs)can be determined.A quality indicator is calculated based on the IUREs in the monitoring network and compared with a pre-defined threshold.The quality monitoring method is experimentally evaluated by monitoring the real-time orbit and clock products generated by GeoForschungsZentrum(GFZ),Potsdam.The results confirm that the problematic satellites can be detected accurately and effectively with missed detection rate 4×10^(-6) and false alarm rate 1:2×10^(-5).Considering the quality alarms,the PPP results in terms of RMS of positioning differences with respect to the International GNSS Service(IGS)weekly solution in the north,east and up directions can be improved by 12%,10%and 27%,respectively.
基金Supported by the German Federal Ministry of Education and Research (BMBF)
文摘Opencast lignite mining in the Lusatia region of Germany has resulted in large scale landscape disturbances, which require suitable recultivation techniques in order to promote plant growth and establishment in the remaining nutrient-poor substrates with low water-holding capacity. Thus, the effects of two commercial soil additives （CSA）, a hydrophilic polymer mixed with volcanic rock flour and bentonite （a-CSA）, and digester solids from biogas plants enriched with humic acids and bentonite （b-CSA）, on soil organic carbon （SOC） storage, plant yields and root biomass were assessed after cultivating perennial crops （Dactylis 9lornerata L.） in monoculture and Helianthus annuus L.-Brassica napus L. in crop rotation systems. The CSA were incorporated into the top 20 cm soil depth using a rotary spader. The results indicated that a-CSA led to a significant increase in plant yield during the first year, and improved root biomass in the following year. As a result, SOC stocks increased, especially in the 0 10 cm soil layer. No significant sequestration of additional SOC was observed on b-CSA-amended plots at the end of both years. Bulk density values decreased in all treatments under the monoculture system. It can be concluded that application of a-CSA enhanced soil water availability for plant uptake and consequently promoted plant growth and organic carbon sequestration. The relative enrichment of organic matter without effects on water-holding capacities of b-CSA treatments suggested that it was not suitable for rapid land reclamation.
基金Supported by the National Natural Science Foundation of China (No. 40874004, No.40504002)the National 973 Program of China (No.2006CB701301)+1 种基金the National 863 Program of China (No. 2006AA12Z326, No. 2007AA12Z345)the 111 Project(No. B07037)
文摘When formation flying spacecrafts are used as platform to gain earth oriented observation, precise baselines between these spacecrafts are always essential. Gravity recovery and climate experiment （GRACE） mission is aimed at mapping the global gravity field and its variation. Accurate baseline of GRACE satellites is necessary for the gravity field modeling. The determination of kinematic and reduced dynamic relative orbits of twin satellites has been studied in this paper, and an accuracy of 2 mm for dynamic relative orbits and 5 mm for kinematic ones can be obtained, whereby most of the double difference onboard GPS ambiguities are resolved.
文摘THE Barra do Itapirapua carbonatite belongs to a Cretaceous province related to the opening of the SouthAtlantic, and is emplaced in a Proterozoic granite. The carbonatite is mainly composed of plutonic magnesio-and ferrocarbonatite and is mineralizing host of a REE mineralization related to late-to post-magmatic hydrothermal processes. The non-overprinted carbonatite has low bulk REE contents, andmagmatic pyrochlore is the major carrier of REE. In the altered mineralized carbonatite, corrosion cavitiesin primary ankerite are filled with a hydrothermal mineral assemblage of quartz, apatite, fluorite, RE-fluorocarbonates, barite, sulfides and Fe-oxides in variable proportions. Two types of hydrothermally overprinted carbonatites can be distinguished: type Ⅰ containing quartz and RE-fluorocarbonates, enriched inLREE and with ∑REE of up to 3% (weight percent), which is two orders of magnitude higher than thenon-overprinted carbonatite; and type Ⅱ containing apatite as the major hydrothermal mineral, and enriched in HREE. The END of the mineralized carbonatite reveals a nonradiogenic isotopic signature andsuggests a carbonatite-related source for the REE
基金National Natural Science Foundation of China[41974027]Sino-German mobility programme[M-0054].
文摘In recent years,the large Low Earth Orbit(LEO)constellations have become a hot topic due to their great potential to improve the Global Navigation Satellite Systems(GNSS)positioning performance.One of the important focus is how to obtain the accurate and reliable orbits for these constellations with dozens of LEO satellites.The GNSS-based Precise Orbit Determination(POD)will be exclusively performed to achieve this goal,where the Integer Ambiguity Resolution(IAR)plays a key role in acquiring high-quality orbits.In this study,we present a comprehensive analysis of the benefit of the single-receiver IAR in LEO POD and discuss its implication for the future LEO constellations.We perform ambiguity-fixed LEO POD for four typical missions,including Gravity Recovery and Climate Experiment(GRACE)Follow-On(GRACE-FO),Swarm,Jason-3 and Sentinel-3,using the Uncalibrated Phase Delay(UPD)products generated by our GREAT(GNSS+REsearch,Application and Teaching)software.The results show that the ambiguity fixing processing can significantly improve the accuracy of LEO orbits.There are negligible differences between our UPD-based ambiguity-fixed orbits and those based on the Observable Signal Bias(OSB)and Integer Recovery Clock(IRC)products,indicating the good-quality of UPD products we generated.Compared to the float solution,the fixed solution presents a better consistency with the external precise science orbits and the largest accuracy improvement of 5 mm is achieved for GRACE-FO satellites.Meanwhile,the benefit can be observed in laser ranging residuals as well,with a Standard Deviation(STD)reduction of 3–4 mm on average for the fixed solutions.Apart from the absolute orbits,the relative accuracy of the space baseline is also improved by 20–30%in the fixed solutions.The result demonstrates the superior performance of the ambiguity-fixed LEO POD,which appears as a particularly promising technique for POD of future LEO constellations.
文摘In this opinion paper,we,a group of scientists from environmental-,geo-,ocean-and information science,argue visual data exploration should become a common analytics approach in Earth system science due to its potential for analysis and interpretation of large and complex spatio-temporal data.We discuss the challenges that appear such as synthesis of heterogeneous data from various sources,reducing the amount of information and facilitating multidisciplinary,collaborative research.We argue that to fully exploit the potential of visual data exploration,several bottlenecks and challenges have to be addressed:providing an efficient data management and an integrated modular workflow,developing and applying suitable visual exploration concepts and methods with the help of effective and tailored tools as well as generating and raising the awareness of visual data exploration and education.We are convinced visual data exploration is worth the effort since it significantly facilitates insight into environmental data and derivation of knowledge from it.
