What is the difference between guided wave radar and non-contact radar level measurement?

Non-contact (through-air) radar transmits microwave pulses that reflect off the liquid surface; suitable for large tanks but affected by foam, vapor, and turbulence. Guided wave radar (GWR) sends pulses along a probe/cable submerged in the tank, providing better signal strength, accuracy in difficult conditions (foam, low dielectric), and ability to measure interface levels. GWR requires contact with process but is less affected by tank internals and atmospheric conditions.