A source `S` and a detector `D` high frequency waves are a distance `d` apart on the ground. The direct wave from `S` is found to be in phase at `D` with the wave from `S` that is reflected from horizontal layer at an altitude `H`. The incident and reflected rayes make the same angle with the reflecting layer. When the layer rises a distance `h`, no signal is detected at `D` . Negle ct absorption in the atmosphere and find the relation between d,h, `H` and the wavelength `lambda` of the waves.

Explanation

`(SA + AD) - SD = n lambda` for reinforcement at `D`
Against `(SB + BD) = n lambda + ( lambda)/( 2)` for total annulment at `D`
Subtracting , `(SB + BD) - (SA + AD) = (lambda)/(2)`
` 2( SB - SA) = (lambda)/( 2)`
or ` lambda = 2 sqrt( 4(H + h)^(2) + d^(2)) - 2 sqrt( 4H^(2) + d^(2))`