Ultrasonic distance measurement is nothing new, it relies on time of flight measurements of ultrasonic pulses. This is commonly seen in cars for parking aid or in industrial applications for part detection, etcetera.
While getting the distance to the nearest object is nice for this, why not go a step further? There are projects which create volumetric data by scanning with a single sensor an stepper motors. This works but is slow. It should be possible to create volumetric data of a large room without the need to move the sensor mechanically: What I'm thinking of is ultrasonic interferometry.
What's needed is not a single sensor but a sensor array, some analogue acquisition and maths.
The project log will begin will be some entries about the theoretical background, while I'll be working on hardware and software, which I'll describe later.