Wind is the horizontal movement of air. The instrument used to measure wind speed is called an anemometer.
This circuit combines ideas from two earlier IFD's to implement, linearized thermal Anemometer. An Ambient - Temperature compensated device, It is robust and power efficient.
Anemometers make use of the Relationship between Airspeed (AF) and the Thermal Impedance (ZT) of the heat sensor. Here is one example of the T0-92's Thermal Impedance.
Where ZJ = "Total Immersion", Junction to case Thermal Impedance = 44 Degree Centrigrate/W
SC = Still Air, , Case to Ambient Conductivity = 6.4 MW/degree cent