We need to determine the level of the ‘bunker’. Doesn’t need to be super specific, steps of 20% would be sufficient.
Any ideas what sensor I could use? Was thinking of multiple HRXL Ultrasonic sensors placed on the iron beam:
But capacitive sensors mounted on the side? Could that be a solution as well? Range should be +/- 4cm then
Perhaps any of you has a bright idea 
Just a thought, maybe you could use multiple TCRT5000 sensors?
They cost a couple of £’s each, or less if buying multiple units. There are two outputs on the sensor, 1 is a digital high/low, the other is an analog voltage, and the voltage level varies according to how close an object is to the IR Tx/Rx LED. I use one for analog gas meter monitoring paired up with an ESP 32, and it is housed in a 3D-printed casing for protection.
If you have access to the outside of ‘the bunker’ you could easily drill a small hole in the steel for the IR Tx/Rx LED’s to shine through, and if correctly placed several of these offer you a % full reading. I’d experiment with 1 first so you can work out the code and fine-tune the setup to recognize when the sensor is obscured by carrots or onions.
I hope that helps.
Cheers,
Mike.
Hoi Marco
In the industry we used this brand:
https://www.sick.com/de/de/distanzsensoren
Far from cheap, but reliable.
