Not quite. Light waves are so short you'll get some return from almost any surface. This isn't true of radar, and it's not just what substance the outbound radar hits but how flat it is, too. You may get no return. Or almost none. Even round posts give very little return IIRC. There's also an echo problem with long waves such as sound and radar, particularly in urban areas. In which case what you think is a firm direct return may be a very indirect return that happens to be in synch with the signal you were expecting.