Echo Sounding of Frozen Lake from Surface of Ice and Performance of Transistorized Compact Echo Sounder at Low Temperature

When sounding a lake or an artificial lake of electric power plant by an echo sounder installed on a boat, the error due to inaccuracy of positions, is large because of difficulty of determination of accurate positions, and moreover, great efforts are needed. On a frozen lake it is easy to determine positions with accuracy. Besides, echo sounding from the surface of ice is possible. Therefore, sounding from it is more speedy and accurate than that by a boat. The pond-smelt can be detected from the surface of ice, too. The se are new methods of sounding of lake and detection of fish school on the frozen lake, which have never been published. It is pointed out that easier sounding is possible by using the latest transistorized compact fish finder.