PURPOSE: To readily and reliably measure the direction to the location of a thunderbolt by performing a specific computation on the basis of the two largest voltages of the microphone output voltages from three or more ultrasonic receiving microphones.
CONSTITUTION: Ultrasonic waves accompanied by a thunderbolt are detected by four or more microphones 1'W4' which are almost the same in directivity. Then, two pairs of microphones 1'W4', which are correspondent to the largest and second largest output in a level comparison selecting part 7. The outputs of the selected two pairs of microphones 1W4 are substracted in a computating part 8, and a horizontal degree on the basis of a holizontal degree - (maximum value ÷ second largest value) table, which has been prepared by precounting them as corresponding values of the directions to thunderbolts, is displayed as the direction to a thunderbolt in a displaying part 9. Therefore, the direction to a thunderbolt can be measured readily and reliably.
KAIZU RIYOUSUKE
KOGA KUNIAKI
