It is a well known fact that ionospheric delay error is a predominant factor which influences the positioning accuarcy of GNSS.Although the main part of the first-order ionospheric delay error can be removed by the fr...It is a well known fact that ionospheric delay error is a predominant factor which influences the positioning accuarcy of GNSS.Although the main part of the first-order ionospheric delay error can be removed by the frequency-dependent behaviors of the ionosphere,the second-order ionospheric delay error must be eliminated to achieve millimetre-scale positioning accuracy.Due to COSMIC occultation providing electron density profiles on the global scale,the paper presents the first-order and the second-order ionospheric delay error analysis on the global scale using the inversion of electron density profiles from COSMIC occultation data during 2009–2011.Firstly,because of the special geographical location of three ISR(incoherent scatter radar),the first-order and the second-order ionospheric delay errors are calculated and discussed;the paper also shows and analyzes the diurnal,seasonal,semi-annual variation of ionospheric delay error with respect to signal direction.Results show that for the L1 signal path,the first-order ionospheric delay error is the largest near the equator,which is circa 7 m;the maximum second-order ionospheric delay error are circa 0.6 cm,0.8 cm and 0.6 cm respectively for L1 signals coming from the zenith,the north and the south at 10 degree elevation angles.The second-order ionospheric delay error on the L1 signal path from zenith are the symmetry between 15°and 15°with respect to magnetic equator,and are nearly zero at the magnetic equator.For the first time,the second-order ionospheric delay error on the global scale is presented,so this research will greatly contribute to analysing the higher-order ionospheric delay error characteristics on the global scale.展开更多
The patterns of soil nitrogen （N） isotope composition at large spatial and temporal scales and their relationships to environmental factors illustrate N cycle and sources of N, and are integrative indicators of the ...The patterns of soil nitrogen （N） isotope composition at large spatial and temporal scales and their relationships to environmental factors illustrate N cycle and sources of N, and are integrative indicators of the terrestrial N cycle and its response to global change. The objectives of this study were： i） to investigate the patterns of soil N content and natural abundance of 15N （δ15N） values in different ecosystem types and soil profiles on the Qinghai-Tibetan Plateau; ii） to examine the effects of climatic factors and soil characteristics on the patterns of soil N content and soil δ15N values; and iii） to test the relationship between soil δ15N values and soil C/N ratios across ecosystems and soil profiles. Soil profiles were sampled at 51 sites along two transects 1 875 km in length and 200 km apart and distributed in forest, meadow and steppe on the Qinghai-Tibetan Plateau. Each site was sampled every 10 cm from a soil depth of 0 to 40 cm and each sample was analyzed for soil N content and δ15N values. Our results indicated that soil N and 515N values （0-40 cm） in meadows were much higher than in desert steppe. Soil N decreased with soil depth for each ecosystem, while variations of soil ~15N values along soil profiles were not statistically significant among most ecosystems but for mountain meadow, lowland meadow, and temperate steppe where soil δ15N values tended to increase with soil depth. The parabolic relationship between soil δ15N values and mean annual precipitation indicated that soil δ15N values increased with increasing precipitation in desert steppe up to 500 mm, and then decreased with increasing precipitation across all other ecosystems. Moreover, the parabolic relationship between δ15N values and mean annual temperature existed in all individual ecosystem types. Soil N and δ15N values （0-0 cm） increased with an increase in soil silt and clay contents. Furthermore, a threshold of C/N ratio of about 11 divided the parabolic relationship between soil δ15N values and soil C/N ratios into positive （C/N 〈 11） and negative （C/N 〉 11） parts, which was valid across all ecosystems and soil profiles. The large explanatory power of soil C/N ratios for soil δ15N values suggested that C and N concentrations, being strongly controlled by precipitation and temperature, were the primary factors determining patterns of soil δ15N on the Qinghai-Tibetan Plateau.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.41174023,41374014 and 41304030)the National High Technology Research and Development Program of China(Grant No.2013AA122501)the Data analysis center(Grant No.GFZX0301040308-06)
文摘It is a well known fact that ionospheric delay error is a predominant factor which influences the positioning accuarcy of GNSS.Although the main part of the first-order ionospheric delay error can be removed by the frequency-dependent behaviors of the ionosphere,the second-order ionospheric delay error must be eliminated to achieve millimetre-scale positioning accuracy.Due to COSMIC occultation providing electron density profiles on the global scale,the paper presents the first-order and the second-order ionospheric delay error analysis on the global scale using the inversion of electron density profiles from COSMIC occultation data during 2009–2011.Firstly,because of the special geographical location of three ISR(incoherent scatter radar),the first-order and the second-order ionospheric delay errors are calculated and discussed;the paper also shows and analyzes the diurnal,seasonal,semi-annual variation of ionospheric delay error with respect to signal direction.Results show that for the L1 signal path,the first-order ionospheric delay error is the largest near the equator,which is circa 7 m;the maximum second-order ionospheric delay error are circa 0.6 cm,0.8 cm and 0.6 cm respectively for L1 signals coming from the zenith,the north and the south at 10 degree elevation angles.The second-order ionospheric delay error on the L1 signal path from zenith are the symmetry between 15°and 15°with respect to magnetic equator,and are nearly zero at the magnetic equator.For the first time,the second-order ionospheric delay error on the global scale is presented,so this research will greatly contribute to analysing the higher-order ionospheric delay error characteristics on the global scale.
基金Supported by the National Basic Research Program(973 Program)of China(No.2010CB833503)the Chinese Academy of Sciences for Strategic Priority Research Program(No.XDA05050602)+1 种基金the Key Projects in the National Science and Technology Pillar Program(No.2013BAC03B03)the Open Research Fund of Chinese Academy of Sciences(No.O8R8B161PA)
文摘The patterns of soil nitrogen （N） isotope composition at large spatial and temporal scales and their relationships to environmental factors illustrate N cycle and sources of N, and are integrative indicators of the terrestrial N cycle and its response to global change. The objectives of this study were： i） to investigate the patterns of soil N content and natural abundance of 15N （δ15N） values in different ecosystem types and soil profiles on the Qinghai-Tibetan Plateau; ii） to examine the effects of climatic factors and soil characteristics on the patterns of soil N content and soil δ15N values; and iii） to test the relationship between soil δ15N values and soil C/N ratios across ecosystems and soil profiles. Soil profiles were sampled at 51 sites along two transects 1 875 km in length and 200 km apart and distributed in forest, meadow and steppe on the Qinghai-Tibetan Plateau. Each site was sampled every 10 cm from a soil depth of 0 to 40 cm and each sample was analyzed for soil N content and δ15N values. Our results indicated that soil N and 515N values （0-40 cm） in meadows were much higher than in desert steppe. Soil N decreased with soil depth for each ecosystem, while variations of soil ~15N values along soil profiles were not statistically significant among most ecosystems but for mountain meadow, lowland meadow, and temperate steppe where soil δ15N values tended to increase with soil depth. The parabolic relationship between soil δ15N values and mean annual precipitation indicated that soil δ15N values increased with increasing precipitation in desert steppe up to 500 mm, and then decreased with increasing precipitation across all other ecosystems. Moreover, the parabolic relationship between δ15N values and mean annual temperature existed in all individual ecosystem types. Soil N and δ15N values （0-0 cm） increased with an increase in soil silt and clay contents. Furthermore, a threshold of C/N ratio of about 11 divided the parabolic relationship between soil δ15N values and soil C/N ratios into positive （C/N 〈 11） and negative （C/N 〉 11） parts, which was valid across all ecosystems and soil profiles. The large explanatory power of soil C/N ratios for soil δ15N values suggested that C and N concentrations, being strongly controlled by precipitation and temperature, were the primary factors determining patterns of soil δ15N on the Qinghai-Tibetan Plateau.
