Effects of 450-kg surface explosions on HF radio reflection from the E layer


  • T. Joseph Fitzgerald,

  • Robert C. Carlos


We describe ionospheric disturbances caused by the passage of acoustic shock waves at the E layer generated by the surface detonation of ordinance with effective yields of 450 kg of high explosive during an exercise conducted by the U.S. Air Force at a bombing range near the Nevada Test Site. We deployed a network of HF bistatic ionospheric sounders consisting of two transmitter and two receiver stations at the Nevada Test Site on April 4, 1991. The frequencies of the transmissions were chosen so that the HF radio waves were totally reflected in the E layer of the ionosphere at an altitude of approximately 100 km. The transmissions were highly stable continuous wave (CW) tones at two frequencies separated by 100 kHz so that two altitudes separated by approximately 0.5 km could be probed. The network sampled four geographic locations in the ionosphere in a line covering a horizontal range of 60 km. At two time periods during the day (1930 and 2400 UT), we detected a series of disturbances in the sounder data that continued for 10 min and consisted of Doppler-shifted peaks that chirped rapidly from positive to negative Doppler. We describe the effects produced by the surface explosions and interpret the disturbance in terms of diffraction induced by electron density changes accompanying the passage of the acoustic waves from the explosions through the reflection altitudes of the HF transmissions.