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HF Backscatter Echoes from White Sands Spread F Experiment

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A series of experiments were run during the period 5-16 October 1970 in which HF radars at the White Sands Missile Range WSMR were used to search for direct backscatter from ionospheric irregularities produced by the Boulder heater. The observations were made from White Sands because radars at this location view the heated volume normal to the earths magnetic field. If the irregularities are field aligned as might be expected from the similarity between the range spreading seen on Boulder ionograms and that due to the field- aligned irregularities responsible for natural spread-F then they will be aspect sensitive and the radar cross-section will be greatest looking normal to the field. Direct echoes from the heated volume were unquestionably observed. Returns were found at radar frequencies up to 30 MHz the highest frequency available at times when the local plasma frequency over Boulder was as low as 5 MHz at the layer peak. These echoes occurred at the expected range and were well correlated in time with the turn-on and turn-off of the heating transmitter. The results varied greatly from day to day for reasons that are not yet understood. When a direct echo was observed it grew continuously while the heater was on and died rapidly when it was turned off lasting about 10 seconds at 30 MHz and 100 seconds at 13 MHz. Typically the direct returns exhibited doppler spectra a few Hertz wide with a net doppler offset of a few Hertz at 30 MHz, implying a relative velocity between scatterers of a few tens of meters per second and a net southward drift of comparable magnitude.

Subject Categories:

  • Atmospheric Physics
  • Active and Passive Radar Detection and Equipment
  • Electromagnetic Pulses

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