For 2D Sonic Anemometers, they can divided into two types as well:
1. Two ultrasound paths: with 4 arms; easier to develop compared to the three ultrasounds paths; low accuracy when the wind comes in one ultrasound path causing aerodynamic turbulence.
2. Three ultrasound paths: with 3 arms; one path redundancy; relatively high accuracy and less aerodynamic turbulence.