How far can a ping be heard by say an electrostatic mic?
If the ping went out concurrent with an IR led flash, the thing with the mic might see that, know the air temperature and calculate closely how far the flash/ping generator is away. On close to standard days sound may travel 343M/1056ft plus or minus some for warmer or colder air. Get it right and you can be within 2cm maybe less using Arduino.
It's not as neat as point at something and know but if your mic can hear the ping at 1000ft, you can measure land.