{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,28]],"date-time":"2026-03-28T18:58:28Z","timestamp":1774724308545,"version":"3.50.1"},"reference-count":45,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2018,5,4]],"date-time":"2018-05-04T00:00:00Z","timestamp":1525392000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["41574030"],"award-info":[{"award-number":["41574030"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["41574027"],"award-info":[{"award-number":["41574027"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["41325015"],"award-info":[{"award-number":["41325015"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Ionosphere research using the Global Navigation Satellite Systems (GNSS) techniques is a hot topic, with their unprecedented high temporal and spatial sampling rate. We introduced a new GNSS Ionosphere Monitoring and Analysis Software (GIMAS) in order to model the global ionosphere vertical total electron content (VTEC) maps and to estimate the GPS and GLObalnaya NAvigatsionnaya Sputnikovaya Sistema (GLONASS) satellite and receiver differential code biases (DCBs). The GIMAS-based Global Ionosphere Map (GIM) products during low (day of year from 202 to 231, in 2008) and high (day of year from 050 to 079, in 2014) solar activity periods were investigated and assessed. The results showed that the biases of the GIMAS-based VTEC maps relative to the International GNSS Service (IGS) Ionosphere Associate Analysis Centers (IAACs) VTEC maps ranged from \u22123.0 to 1.0 TECU (TEC unit) (1 TECU = 1 \u00d7 1016 electrons\/m2). The standard deviations (STDs) ranged from 0.7 to 1.9 TECU in 2008, and from 2.0 to 8.0 TECU in 2014. The STDs at a low latitude were significantly larger than those at middle and high latitudes, as a result of the ionospheric latitudinal gradients. When compared with the Jason-2 VTEC measurements, the GIMAS-based VTEC maps showed a negative systematic bias of about \u22121.8 TECU in 2008, and a positive systematic bias of about +2.2 TECU in 2014. The STDs were about 2.0 TECU in 2008, and ranged from 2.2 to 8.5 TECU in 2014. Furthermore, the aforementioned characteristics were strongly related to the conditions of the ionosphere variation and the geographic latitude. The GPS and GLONASS satellite and receiver P1-P2 DCBs were compared with the IAACs DCBs. The root mean squares (RMSs) were 0.16\u20130.20 ns in 2008 and 0.13\u20130.25 ns in 2014 for the GPS satellites and 0.26\u20130.31 ns in 2014 for the GLONASS satellites. The RMSs of receiver DCBs were 0.21\u20130.42 ns in 2008 and 0.33\u20131.47 ns in 2014 for GPS and 0.67\u20130.96 ns in 2014 for GLONASS. The monthly stability of the GPS satellite DCBs was about 0.04 ns (0.07 ns) in 2008 (2014) and that for the GLONASS satellite DCBs was about 0.09 ns in 2014. The receiver DCBs were less stable than the satellite DCBs, with a mean value of about 0.16 ns (0.47 ns) in 2008 (2014) for GPS, and 0.48 ns in 2014 for GLONASS. It can be demonstrated that the GIMAS software had a high accuracy and reliability for the global ionosphere monitoring and analysis.<\/jats:p>","DOI":"10.3390\/rs10050705","type":"journal-article","created":{"date-parts":[[2018,5,7]],"date-time":"2018-05-07T03:12:21Z","timestamp":1525662741000},"page":"705","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":43,"title":["Global Ionosphere Mapping and Differential Code Bias Estimation during Low and High Solar Activity Periods with GIMAS Software"],"prefix":"10.3390","volume":"10","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-8683-4230","authenticated-orcid":false,"given":"Qiang","family":"Zhang","sequence":"first","affiliation":[{"name":"GNSS Research Center, Wuhan University, No. 129 Luoyu Road, Wuhan 430079, China"}]},{"given":"Qile","family":"Zhao","sequence":"additional","affiliation":[{"name":"GNSS Research Center, Wuhan University, No. 129 Luoyu Road, Wuhan 430079, China"},{"name":"Collaborative Innovation Center of Earth and Space Science, Wuhan University, No. 129 Luoyu Road, Wuhan 430079, China"}]}],"member":"1968","published-online":{"date-parts":[[2018,5,4]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1405","DOI":"10.1007\/s00190-017-1032-z","article-title":"Methodology and consistency of slant and vertical assessments for ionospheric electron content models","volume":"91","author":"Krankowski","year":"2017","journal-title":"J. Geodesy"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"565","DOI":"10.1029\/97RS02707","article-title":"A global mapping technique for GPS-derived ionospheric total electron content measurements","volume":"33","author":"Mannucci","year":"1998","journal-title":"Radio Sci."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"635","DOI":"10.1016\/S0273-1177(03)00029-2","article-title":"The International GPS Service (IGS) Ionosphere Working Group","volume":"31","author":"Feltens","year":"2003","journal-title":"Adv. Space Res."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"263","DOI":"10.1007\/s00190-008-0266-1","article-title":"The IGS VTEC maps: A reliable source of ionospheric information since 1998","volume":"83","author":"Juan","year":"2009","journal-title":"J. Geodesy"},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Roma-Dollase, D., Hern\u00e1ndez-Pajares, M., Krankowski, A., Kotulak, K., Ghoddousi-Fard, R., Yuan, Y., Li, Z., Zhang, H., Shi, C., and Wang, C. (2017). Consistency of seven different GNSS global ionospheric mapping techniques during one solar cycle. J. Geodesy, in press.","DOI":"10.1007\/s00190-017-1088-9"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"483","DOI":"10.1029\/RS023i004p00483","article-title":"A comparison of mapped and measured total ionospheric electron content using global positioning system and beacon satellite observations","volume":"23","author":"Lanyi","year":"1988","journal-title":"Radio Sci."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1695","DOI":"10.1029\/97RS00451","article-title":"Studying the ionosphere with the Global Positioning System","volume":"32","author":"Davies","year":"1997","journal-title":"Radio Sci."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"887","DOI":"10.1007\/s00190-011-0508-5","article-title":"The ionosphere: Effects, GPS modeling and the benefits for space geodetic techniques","volume":"85","author":"Juan","year":"2011","journal-title":"J. Geodesy"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"485","DOI":"10.1007\/s00190-016-0977-7","article-title":"Temporal and spatial variations of global ionospheric total electron content under various solar conditions","volume":"91","author":"Liu","year":"2017","journal-title":"J. Geodesy"},{"key":"ref_10","unstructured":"Schaer, S., Beutler, G., Rothacher, M., and Springer, T.A. (1996, January 19\u201321). Daily global ionosphere maps based on GPS carrier phase data routinely produced by the CODE Analysis Center. Proceedings of the IGS AC Workshop, Silver Spring, MD, USA."},{"key":"ref_11","unstructured":"Schaer, S., Gurtner, W., and Feltens, J. (1998, January 9\u201311). IONEX: The ionosphere map exchange format version 1. Proceedings of the IGS AC Workshop, Darmstadt, Germany."},{"key":"ref_12","unstructured":"Schaer, S. (1999). Mapping and Predicting the Earth\u2019s Ionosphere Using the Global Positioning System, Astronomical Institute, University of Berne."},{"key":"ref_13","unstructured":"Mannucci, A.J., Wilson, B.D., and Edwards, C.D. (1993, January 22\u201324). A new method for monitoring the Earth\u2019s ionospheric total electron content using the GPS global network. Proceedings of the Institute of Navigation GPS-93, Salt Lake City, UT, USA."},{"key":"ref_14","unstructured":"Komjathy, A., Wilson, B.D., Runge, T.F., Boulat, B.M., Maimucci, A.J., Reyes, M.J., and Sparks, L.C. (2002, January 28\u201330). A new ionospheric model for wide area differential GPS: The multiple shell approach. Proceedings of the National Technical Meeting of the Institute of Navigation, San Diego, CA, USA."},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Feltens, J. (2007). Development of a new three-dimensional mathematical ionosphere model at European Space Agency\/European Space Operations Centre. Space Weather, 5.","DOI":"10.1029\/2006SW000294"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"393","DOI":"10.1029\/97GL00092","article-title":"A two-layer model of the ionosphere using Global Positioning System data","volume":"24","author":"Juan","year":"1997","journal-title":"Geophys. Res. Lett."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1081","DOI":"10.1029\/97RS00431","article-title":"Neural network modeling of the ionospheric electron content at global scale using GPS data","volume":"32","author":"Juan","year":"1997","journal-title":"Radio Sci."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"1237","DOI":"10.1016\/S1364-6826(99)00054-1","article-title":"New approaches in global ionospheric determination using ground GPS data","volume":"61","author":"Juan","year":"1999","journal-title":"J. Atmos. Sol.-Terr. Phys."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"20789","DOI":"10.1029\/98JA01272","article-title":"Global observation of the ionospheric electronic response to solar events using ground and LEO GPS data","volume":"103","author":"Juan","year":"1998","journal-title":"J. Geophys. Res. Space Phys."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"2473","DOI":"10.1029\/2000GL000032","article-title":"Improving the Abel inversion by adding ground GPS data to LEO radio occultations in ionospheric sounding","volume":"27","author":"Juan","year":"2000","journal-title":"Geophys. Res Lett."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"331","DOI":"10.1007\/s00190-014-0778-9","article-title":"SHPTS: Towards a new method for generating precise global ionospheric TEC map based on spherical harmonic and generalized trigonometric series functions","volume":"89","author":"Li","year":"2015","journal-title":"J. Geodesy"},{"key":"ref_22","first-page":"1186","article-title":"Modeling global ionospheric delay with IGS ground-based GNSS observations","volume":"37","author":"Zhang","year":"2012","journal-title":"Geomat. Inf. Sci. Wuhan Univ."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"988","DOI":"10.1016\/j.asr.2012.06.026","article-title":"Eliminating negative VTEC in global ionosphere maps using inequality-constrained least squares","volume":"51","author":"Zhang","year":"2013","journal-title":"Adv. Space Res."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"46","DOI":"10.1109\/99.660313","article-title":"OpenMP: An industry-standard API for shared-memory programming","volume":"5","author":"Dagum","year":"1998","journal-title":"IEEE Comput. Sci. Eng."},{"key":"ref_25","first-page":"227","article-title":"Application of parallel computing with OpenMP in global ionosphere mapping","volume":"43","author":"Zhang","year":"2018","journal-title":"Geomat. Inf. Sci. Wuhan Univ."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"199","DOI":"10.1029\/GL017i003p00199","article-title":"An automatic editing algorithm for GPS data","volume":"17","author":"Blewitt","year":"1990","journal-title":"Geophys. Res. Lett."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"9420","DOI":"10.1002\/2017JB014750","article-title":"Impact and implementation of higher-order ionospheric effects on precise GNSS applications","volume":"122","author":"Hadas","year":"2017","journal-title":"J. Geophys. Res. Solid Earth"},{"key":"ref_28","unstructured":"Schaer, S., Beutler, G., Mervart, L., Rothacher, M., and Wild, U. (1995, January 15\u201317). Global and regional ionosphere models using the GPS double difference phase observable. Proceedings of the IGS Workshop, Potsdam, Germany."},{"key":"ref_29","doi-asserted-by":"crossref","unstructured":"Davies, K. (1990). Ionospheric Radio, The Institution of Engineering and Technology.","DOI":"10.1049\/PBEW031E"},{"key":"ref_30","unstructured":"Mannucci, A.J., Wilson, B.D., Yuan, D.N., Lindqwister, U.J., and Runge, T.F. (1995, January 15\u201317). Global monitoring of ionospheric total electron content using the IGS network. Proceedings of the IGS Workshop, Potsdam, Germany."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"2424","DOI":"10.1002\/2016JA023680","article-title":"Attribution of interminimum changes in global and hemispheric total electron content","volume":"122","author":"Emmert","year":"2017","journal-title":"J. Geophys. Res. Space Phys."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"335","DOI":"10.5194\/angeo-26-335-2008","article-title":"Global electron content: A new conception to track solar activity","volume":"26","author":"Afraimovich","year":"2008","journal-title":"Ann. Geophys."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"191","DOI":"10.1007\/s00190-008-0300-3","article-title":"The international GNSS service in a changing landscape of global navigation satellite systems","volume":"83","author":"Dow","year":"2009","journal-title":"J. Geodesy"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"121","DOI":"10.1007\/s00190-008-0244-7","article-title":"Analysis of the bias between TOPEX and GPS vTEC determinations","volume":"83","author":"Azpilicueta","year":"2009","journal-title":"J. Geodesy"},{"key":"ref_35","unstructured":"CNES (2016). Jason-3 Products Handbook, CNES. SALP-MU-M-OP-16118-CN."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"1103","DOI":"10.1186\/BF03352960","article-title":"Scale factor mitigating non-compliance of double-frequency altimeter measurements of the ionospheric electron content over the oceans with GPS-TEC maps","volume":"61","author":"Gulyaeva","year":"2009","journal-title":"Earth Planets Space"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"A01301","DOI":"10.1029\/2003JA010058","article-title":"Analysis of TEC data from the TOPEX\/Poseidon mission","volume":"109","author":"Jee","year":"2004","journal-title":"J. Geophys. Res. Atmos."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"161","DOI":"10.1029\/2010JA015432","article-title":"Assessment of GPS global ionosphere maps (GIM) by comparison between CODE GIM and TOPEX\/Jason TEC data: Ionospheric perspective","volume":"115","author":"Jee","year":"2010","journal-title":"J. Geophys. Res. Space Phys."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"2055","DOI":"10.1016\/S1364-6826(02)00224-9","article-title":"Performance of different TEC models to provide GPS ionospheric corrections","volume":"64","author":"Juan","year":"2002","journal-title":"J. Atmos. Sol.-Terr. Phys."},{"key":"ref_40","unstructured":"Wilson, B.D., and Mannucci, A.J. (1993, January 22\u201324). Instrumental biases in ionospheric measurements derived from GPS data. Proceedings of the 6th International Technical Meeting of the Satellite Division of the Institute of Navigation (ION GPS 1993), Salt Lake City, UT, USA."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"209","DOI":"10.1007\/s00190-015-0867-4","article-title":"Determination of differential code biases with multi-GNSS observations","volume":"90","author":"Wang","year":"2016","journal-title":"J. Geodesy"},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"159","DOI":"10.1007\/s10291-014-0426-0","article-title":"A study on the dependency of GNSS pseudorange biases on correlator spacing","volume":"20","author":"Hauschild","year":"2016","journal-title":"GPS Solut."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"191","DOI":"10.1002\/navi.64","article-title":"Differential code bias estimation using multi-GNSS observations and global ionosphere maps","volume":"61","author":"Montenbruck","year":"2014","journal-title":"Navigation"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"1059","DOI":"10.1007\/s00190-012-0565-4","article-title":"Two-step method for the determination of the differential code biases of COMPASS satellites","volume":"86","author":"Li","year":"2012","journal-title":"J. Geodesy"},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"353","DOI":"10.1007\/s00190-008-0281-2","article-title":"GNSS processing at CODE: Status report","volume":"83","author":"Dach","year":"2009","journal-title":"J. Geodesy"}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/10\/5\/705\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T15:03:17Z","timestamp":1760194997000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/10\/5\/705"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2018,5,4]]},"references-count":45,"journal-issue":{"issue":"5","published-online":{"date-parts":[[2018,5]]}},"alternative-id":["rs10050705"],"URL":"https:\/\/doi.org\/10.3390\/rs10050705","relation":{},"ISSN":["2072-4292"],"issn-type":[{"value":"2072-4292","type":"electronic"}],"subject":[],"published":{"date-parts":[[2018,5,4]]}}}