1. Introduction
Wind measurement is an important factor for detecting
natural phenomena in various industrial fields. Wind
measurement can be applied not only to industrial fields
but also to environmental monitoring and controlling
systems, indoor air conditioning systems, the weather
forecasting systems and so on. To improve problems with
the previous mechanical sensors, methods that use MEMStype
sensors or ultrasonic sensors [1–3] have been studied.
A MEMS-type sensor is a contact type so that the abrasion
property is high. It is sensitive to dust, and it is difficult to
use for a 2D anemometer in the atmosphere [4]. A method
to use ultrasonic sensors is being studied and developed
because this method has a distinguished advantage over the
non-contact type [1]. For measuring wind velocity using an
ultrasonic sensor, there are two methods: transit-time
measurement and vortex measurement [5–7]. With vortex
measurement it is difficult to measure wind direction. So
the method of transit-time measurement is used to measure
wind velocity and direction [8].