First of all I beg you pardon for my bad English but I'm Italian and I do a lot of mistakes....
As far as I know the theoretical explanation of the poor PI's air tests compared to soil ones is mainly related to PI intrinsic way to reveal metal objects.
As you may know Pulse Induction detectors work by analyzing the residual magnetization time-constants of metal targets.
The transmitted pulse train will create an induced magnetic field on the metal target that will be captured by the RX coil (or by the monocoil in the RX timings). The intensity and duration of this residual magnetization time-constants is strongly related to the conductive properties of medium where the target's buried. The more the medium (soil, water, sand, wood) is conductive the longer the residual magnetization will last. Air is not as conductive as soil, sand etc so signals will be weaker.
Have a nice day!
Leonardo
As far as I know the theoretical explanation of the poor PI's air tests compared to soil ones is mainly related to PI intrinsic way to reveal metal objects.
As you may know Pulse Induction detectors work by analyzing the residual magnetization time-constants of metal targets.
The transmitted pulse train will create an induced magnetic field on the metal target that will be captured by the RX coil (or by the monocoil in the RX timings). The intensity and duration of this residual magnetization time-constants is strongly related to the conductive properties of medium where the target's buried. The more the medium (soil, water, sand, wood) is conductive the longer the residual magnetization will last. Air is not as conductive as soil, sand etc so signals will be weaker.
Have a nice day!
Leonardo