The simple answer is, whatever you are measuring or trying to achieve, you can rest-assured that ultrasonic measurement will achieve what you want it to. However, for the small 5% of the applications outlined above, radar will solve your problem.
Doppler and Transit Time are two very popular types of flow meter for non-invasive measurement of flow in full pipes.
Pulsar & Greyline product placement guide for Wastewater treatment plants.
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