S. Schaer, G. Beutler, L. Mervart, and M. Rothacher, “Global and regional ionosphere models using the GPS double difference phase observable,” I and Proceedings (1995) The IGS workshop on special topics and new directions, pages 77-92, Potsdam German, May.
S. Schaer, G. Beutler, L. Mervart, and M. Rothacher, “Global and regional ionosphere models using the GPS double difference phase observable,” in Proceedings of the IGS Workshop on Special Topics and New Directions, pp. 77–92, Potsdam, Germany, May 1995.