The use of the US Navy Navigation Satellite System (NNSS) for the determination of the ionospheric electron content up to the height of 1100 km

Abstract

The importance of low orbiting satellites for the determination of the ionospheric electron content up to heights of 1100 km has a new significance due to the recent use of geostationary satellites which now enable the determination of the total electron content up to heights of 36 000 km. Due to technical problems aboard the spacecraft Explorer 22 (S-66) the beacons which transmitted continuously for 4 years were switched off in 1969 [SCHMIDT, 1966; SCHMIDT, TAURIAINEN 1970]. At the MPI discussions were started on whether the equipment should be and could be modified for receiving the beacons of other low orbiting satellites in order to determine the total electron content of the ionosphere with sufficient accuracy. The application of the group delay method, which will be in operation for the first time aboard the geostationary satellite ATS-F (launch date Max 1973), yields the total electron content up to the height of the satellite (36 000 km) with an accuracy 5 % [SCHMIDT, 1970a]. If by means of actual simultaneous measurements, e.g. using beacons of low orbiting satellites, one can determine the total electron content up to 1100 km height with roughly the same accuracy, one can expect to measure for the first time the exospheric electron content by means of beacons. It has to be assumed however that the content up to 36 000 km exceeds that up to 1100 km by more than 5 %. Therefore the MPI tried to get information about the beacon system of the US-NNSS satellites [ANDERLE, 1970]. Since last summer the beacon observations are to international participation. Since spring 1970 the modified S-66 receiving equipment was used for test recordings of the Dispersive-Doppler. effect, receiving the 150 MHz and 400 MHz beacons of the 5 US-NNSS satellites.