Yes worked with it in the past and GPR only works under certain conditions and its penetration is limited. Being a fluid has nothing to do with it !
"Metallic objects and water have a higher dielectric constant and are more reflective, however since they are smooth with respect to the system wavelength, and usually flat, the radar beam is specularly reflected, away from the sensor."
Interface problem...
I stand corrected.
Thank you.
TXnMA