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Virtual height of a layer

Short answer

The virtual height is the apparent reflection height obtained from echo delay measured by an ionosonde, assuming straight-line propagation at light speed. It is always greater than the actual reflection height because the wave slows and bends gradually, and is used to calculate skip distance and MUf.

Define virtual height of an ionospheric layer.

The virtual height of an ionospheric layer is the height at which a wave sent up from the earth would appear to be reflected if it travelled straight up and down at the speed of light and were reflected sharply like a mirror, instead of being gradually bent inside the layer.

              A  <- virtual reflection point
             / \       (h' = virtual height)
            /   \
   ~~~~~~~~/~~~~~\~~~~~~ actual reflection:
          (       )     gradual bending
   ------/---------\---- bottom of layer
        /           \
   ----T-------------R---- earth

It is measured with an ionosonde from the echo delay t: h' = c·t/2. The wave actually travels slower inside the layer and bends gradually, so the virtual height is always greater than the actual height of reflection. It is used to calculate skip distance and MUF.

✓ Answer checked by Claude Opus 5.5 (high effort)

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