1. Pedersen, A. FOA Report 607, (Research Institute of National Defense, Sweden, 1964).
2. Mitchel, J. D., Hale, L. C., Olsen, R. O., Randawa, J. S. & Rubio, R. Univ. Ill. Aeron. Rep. 48 (1972).
3. Rose, G., Widdel, H. U., Azcarraga, A. & Sanchez, J. Planet. Space Sci. 20, 871 (1972).
4. Bragin, Y. A., Tulinov, V. F., Smirnykh, L. N. & Yakovlev Kosm. issledovaniya isseldovaniya 11, 448–489 (1973).
5. Widdel, H. U., Rose, G. & Borchers, R. Pure appl. Geophys. 84, 154 (1971)