low level detection radar

I work on PC simulation of the F/A-18 and I’m currently working on the low level detection radar modelisation .

For ground radar generally associated with SAM it is easy to get the low level of its radar by extrapolating its missile minimum altitude capacity .

But I’m particulary interesting by the ship air search radar ( SPY / SPS series / russian series ) : as we have seen during the russian buzzing of this autumn ship radar coverage is maybe perfectible ( I don’t know if they have using very low level flying approach ) . I would like to know what is approximately the order of grandeur of their minimum altitude detection : 60 feets , 50 , 10 ???

If anyone could help me Thanks !