Kenneth Emil Austin¹, Doerte Mann², Adam C Woolace³, Christian P Walls⁴, Karl Feaux³, Glen S Mattioli⁵, Stephen T Dittmann⁶, James Downing⁷, Kathleen Marian Hodgkinson⁸ and Warren W Gallaher¹, (1)UNAVCO, Inc., Boulder, CO, United States, (2)UNAVCO, Inc. Boulder, Boulder, CA, United States, (3)UNAVCO, Inc. Boulder, Boulder, CO, United States, (4)UNAVCO, Inc. Forestville, Forestville, CA, United States, (5)Universidad Nacional, Autónoma de México, Departamento de Geomagnetismo y Exploración, Instituto de Geofísica, Mexico, DF, Mexico, (6)UNAVCO, Boulder, CO, United States, (7)UNAVCO, Inc. Boulder, Boulder, United States, (8)UNAVCO, Socorro, NM, United States