Using the Faraday rotation technique, the Deep Space Network of the Jet Propulsion Laboratory (JPL) monitors ionospheric total electron content (TEC) at its three complexes at Goldstone, California, Canberra, Australia, and Madrid, Spain, to correct data used in the orbit determination process for ionospheric effects. With the number of earth satellites suitable for Faraday rotation measurements steadily decreasing, JPL is investigating other ways to determine ionospheric TEC. One promising method has been developed by MacDoran and Spitzmesser. This method exploits the coherent P code modulation of the two L band signals (1575.42 and 1227.60 MHz) transmitted by satellites of the NAVSTAR Global Positioning System (GPS), but does not require knowledge of the code. It has been named SLIC, for satellite L band ionospheric calibration. With the full complement of 18 GPS satellites in operation in 1987, continuous ionospheric sampling in at least four directions will be feasible with SLIC. In this paper, TEC data measured at Goldstone using SLIC are compared with the results of mapping Goldstone Faraday TEC to the five GPS satellite lines of sight. The results of the two methods are in reasonable agreement.