Acknowledgements

Thanks to the following organizations who provide publicly available base station data:

[CDDIS]   http://cddis.gsfc.nasa.gov

[CORS]   http://www.ngs.noaa.gov

[ALTCORS]   http://alt.ngs.noaa.gov

[EPN]   http://www.pecny.cz

[FLEPOS]   https://www.agiv.be/producten/flepos

[IGE]   http://www.ign.es/ign/main/index.do

[IGNI]   http://ign.fr

[SOPAC]   http://garner.ucsd.edu

[AUSLIG]   http://www.ga.gov.au

[GSI]   http://terras.gsi.go.jp

[ASI]   http://geodaf.mt.asi.it

[OLG]   http://www.oeaw.ac.at

[BKGE]   http://igs.bkg.bund.de

[BKGI]   http://igs.bkg.bund.de

[DUT]   http://gnss1.tudelft.nl

[ROB]   http://gnss.be

[UNAVCO]   http://www.unavco.org

[SPICC]   http://icc.cat

[TRIGNET]   http://trignet.co.za

[LINZ]   http://www.linz.govt.nz

[RBMC]   http://ibge.gov.br/home/