In the murky depths where cameras fail and sonar fragments, a former Ecovacs engineer named Cao Jinlong has identified a quiet but consequential gap: underwater robots can move, but they cannot truly see. This summer, his startup Xinyang Micro secured $1.6 million to bring acoustic perception — long trusted in medicine — into the world of autonomous machines, beginning with the humble swimming pool. It is a small entry point into a vast question about how machines will come to understand environments that human senses were never built for.