Sonic Anemometer-Thermometer for General Use

Abstract

The recently developed sonic anemometer-thermometer has many excellent characteristics which cannot be attained by traditional anemometers, and we can measure air temperature as well as wind velocity with the same sensor at the same time. But most of the examples developed in the past were aimed for the application to the study of micrometeorology in light winds. The present author has aimed to develop the sonic anemometer-thermometer for general purposes including storm observations. The system adopted is of the pulse-time difference method. It is decided to adopt this method because the instrument in this method is less affected by noises and has wide observational ranges. But the past instruments in this method had the fault that the timing of the receiving pulse becomes erroneous in case of decreasing of receiving power of the signal. This fault is covered in this case by adopting high efficient barium titaniate sound transducers and high gain amplifiers to get sharp rising of the receiving pulse wave forms. A new votlage analogue output circuit was developed for this instrument that enables to use various kinds of recorders. The shape of the sound head has great importance to attain good signal to noise ratio when wind direction coincides with sound path orientation in high winds. The shape of the head has been developed through wind tunnel experiments and the present one is not the final one but a temporary choise. It is found by the wind tunnel experiment that it does not work well if wind is stronger than 30m/sec along the sound path. But except such case the instrument has proved to work satisfactory well and to be easy to handle with. The sound frequency of the pulse is 100kc and pulse frequency is about 300 pulses per second. The attenuation of short period changes on the records caused by the line averaged character of the sensor is also discussed in this paper.