The velocity of an air-coupled ultrasonic echo is influenced by external environmental parameters, such as temperature, humidity, and in-band ambient noise. The sensing range decreases as either temperature increases. Although the sensing rate also decreases as humidity increases, this can often be neglected, as the effects are minimal. The rate of attenuation across temperature and humidity is non-linear.

Equation 8.

Airborne debris such as dust, rain, or snow can weaken the ultrasonic energy and alter the field-of-view of the sensor. The performance of a closed-face transducer is not affected by minor dust or dirt deposits. However, if the sensor is partially submerged in water, or covered in mud, snow, or ice, ranging performance will diminish.