Frozen volatiles like drinking water ice are far more reflective to S-band radio waves than lunar rocks. Radio waves even have various qualities when mirrored off ice than off silicate rock. An Assessment on the signals returned from orbit 234 showed reflection qualities suggestive of water ice for that forever https://icecapsmoonrock98901.jts-blog.com/26062005/the-smart-trick-of-ice-caps-moonrock-that-no-one-is-discussing