Development of Ultra-Sonic Current Meter for Long Term Nearshore Current Observation in Surf Zones and Its Application

1.用于海浪海流长期观测的超声波型流速仪的研制：在超声波海流计的基础上，对现有的海浪流速仪进行了改进和发展。针对海浪带内气泡侵入和波浪破碎产生的流沙噪声干扰，研制了一种新的海流计噪声处理电路。由于入射波及其诱导的近岸流，海浪带内的流是三维的。电流计探头也得到了改进，能够测量电流的三维分量。进行了大约两年的长期观测，以检查新开发的海流计的适用性，并调查绪方海岸海浪带的海流。冲浪带海流特征：利用流速仪采集了绪方海岸海流的大量现场数据。对观测资料进行了分析，部分是为了研究近岸长期流的特征。1)没有明显的潮汐影响，有显著的风浪影响。冬季有5次强流，夏季有弱流，但持续时间较短。2)当沙丘通过时，在风浪的早期存在显著的沿岸流，但在海况充分发展时，近岸存在强流，其最大流速可达几十厘米/S，这一近岸流的发现可能对解决滩涂过程有很大的帮助。

1. Decelopment of ultra-sonic-type current meter for long term observation of currents in surf zone: Based on ultra-sonic current meters available in surf zones were developed and improved. for noise disturbance by bubble intrusion and drifting sand by wave breaking in surf zones, a noise disposing circuit of the current meter was newly developed. The currents in the surf zone are three dimensional due to incoming waves and their induced nearshore currents. The current meter probe was also improved being able to measure three dimensional components of the currents. Long term observations of about two years were carried out for examining the applicability of the newly developed current meters and investigating currents in the surf zone at ogata coast.2. Characteristics of the currents in surf zones: A lot of field data of the currents at ogata coast were collected by use of the current meter. The pbserved data were analysed partly to investigate characteristics of long term nearshore currents. 1) No remarkable influence of tides exists and remarkable ones exist due to winds and waves. In winter period, styong currents exist five times a month and in summar period weak currents exist, but their duration are usually very short. 2) When a mosoon passes, at the earier stage of wind waves longshore currents exist remarkablly, but in the fully developed sea state strong offshore currents exist and their maximum velocities reach several tens cm/s. This findings of the nearshore currents may contribute greatly to solve the beach processes.