Consider an instrument that transmits radio waves at different frequencies vertically into the ionosphere and measures the time it takes them to return. Using this technique, one can indirectly measure the electron density as a function of height. Assume a ground-based transmitter emits a vertical signal that sweeps over a range of 1 to 15 MHz. If the peak electron density in the ionosphere is 2×106 electrons/cm3, what range of frequencies will be reflected back to the instrument on the ground? Neglect any absorption effects. Frequencies from _____ MHz to ____ MHz will be reflected back. Report answers to 3 significant digits.
Consider an instrument that transmits radio waves at different frequencies vertically into the ionosphere and measures the time it takes them to return. Using this technique, one can indirectly measure the electron density as a function of height.
Assume a ground-based transmitter emits a vertical signal that sweeps over a range of 1 to 15 MHz. If the peak electron density in the ionosphere is 2×106 electrons/cm3, what range of frequencies will be reflected back to the instrument on the ground? Neglect any absorption effects.
Frequencies from _____ MHz to ____ MHz will be reflected back. Report answers to 3 significant digits.
The idea of the critical frequency in the ionosphere must be used to determine the range of frequencies that will be reflected back to the sensor on the ground. The critical frequency, which is determined by the ionosphere's electron density, is the maximum frequency that can be reflected back to Earth.
The frequency at which the ionosphere's refractive index is equal to one is known as the critical frequency.
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