What sensor, using what physical principle, can penetrate a closed rectangular object like the trailer of a truck and tell if the space is empty or loaded?
Why is this question relevant? One of the biggest problems of maintaining & building roads is to understand how much load is transported over that road per time increment. A loaded truck can bring much more damage to a road than many cars can (a 18 wheeler can have the impact of over nine thousand cars). Current in-road, at-speed weighing technology can cost millions. The reason for this questions is trying to find a way to use existing low cost sensors (or a combination of multiple sensors) at the roadside to assist with estimating the weight of a truck. If we know the truck/ trailer combination is empty or full, we typically know the lowest and maximum load weight. And then can estimate the average load on this road per time increment. This is much better than current vehicle counts and is commercially very interesting.
Many thanks for staying on topic and trying to point me in the right direction.
Initial thoughts: It is easy if you can visually see the load (like on a logging truck). It is hard if it is a closed curtainsider, bulk load or container truck from a stationary roadside measurement unit.
Computer vision could be used to compare the bounce of the cab, analyze the suspension; use thermal camera to detect higher temperature of tyres or axis; acoustics of empty vs loaded. What other sensors/ physical principles should be tried like measure on an uphill stretch: slower truck of same vehicle class will be loaded truck.
Again, many thanks for sharing your thoughts on what physical principle could be tried to tackle the problem to detect if a confined space is empty or filled, from the outside without weighing it. An approximation with an acceptable error rate is fine.