Development of an Underwater Acousitic Profiler Equipped with Digital Recorder for Survey of Brackish Water Lakes

众所周知，在半咸水湖泊中，海水被淡水覆盖。它们的共同边界，即被认为是晕线的边界，有时出现在回声测深记录上。这种现象是由于盐水和淡水交界处声阻抗的急剧变化而引起的，被称为深散射层。已经执行了使用更灵敏的回声探测设备分析这一边界的项目。该部件通过修改200 kHz精密回声探测器（Model 101，Senbon Denki Co.，Ltd.）。接收电路被修改为使用直接放大器，以保持信号的线性和准确性。此外，接收电路还配有数字记录信号输出。该记录器由12位1 MHz采样的高速A/D转换器和使用8 mm磁带（最大2.2GByte）的EXABYTE磁带机组成。在中海湖，在水深约6 m处可观察到清晰的反射体，并有附加反射体，与水质变化，特别是盐度变化相对应。新研制的配有数字记录器的水声剖面仪，对了解咸水湖的许多现象有很大的帮助。

In brackish lakes it is well known that sea water is overlain by fresh water. Their mutual boundary, which is recognized as the boundary of the haloline, sometimes appears on echo-sounding records. These phenomena are caused by the rapid change of acoustic impedance at the boundary of saline and fresh water, and has been termed the deep scattering layr (D.S.L.). The project to analyze this boundary using more sensitive echo-sounding equipment has been performed. This component was made by modification of a 200 kHz precision echo-sounder (Model 101, Senbon Denki Co., Ltd.). The receiving circuit was modified to use straight amplifiers to maintain the linearity and accuracy of signals. In addition, the recieving circuit was equipped with signal output for digital recording. The recorder consists of a 12 bit higt-speed A/D converter at 1MHz sampling and an EXABYTE tape drive using 8 mm tape (max.2.2GByte). Clear reflector in Lake Nakaumi could be observed in water about 6 m in depth with additinal refletors, correspoudig to changes in water quality, particularly changes in salinity. The newly developed underwater acoustic profiler equipped with a digital recorder can contribute much in understanding many phenomena of brackish lakes.