1) We already knew about this, or were pretty certain. This not a 'find" but a confirmation

2) It's ICE, not water.

As for your comments about finding oil, of course it would be great if you could fly over the ground, transmit some sort of EM energy, and receive a positive signal from oil deposits.

Unfortunately, it doesn't work like that. (and a good job too, for my personal career, since my job is to find oil by whatever means we can use). EM transmission and reflection depends on the electrical permittivity of the materials, which is largely driven by their electrical conductivity.

Oil is an insulator, Rock is an insulator, Ice is an insulator. Fresh water is an insulator Salt water is an excellent conductor. So all these radar (EM of a specific wavelength) techniques are great at finding deposits of salty water in dry deserts. THey are also good at profiling the frozen ice deposits at Earth's pole (amd Mars'). They are very poor at finding fresh water in deserts, or oil in rock. They are PARTICULARLY poor at finding ANYTHING under a conductive layer of salt water (the ocean).

In addition, the wavelengths that penetrate dry or frozen ground are relatively long and have poor resolving power.

That is why we use sound-based methods (seismic) to map the rock layers in detail.

It is one of the little-trumpeted but MAJOR results of the Mars Radars - watch my lips here - There is NO water on Mars. It is ALL frozen.

I've been saying this for a decade. Willful denial of reality become a psychotic state after a while. Be careful you do not join the madhouse that insists there IS* water on Mars, despite abundant evidence to the contrary.

* Not WAS, or "could be in some circumstances" but IS.