Development of small ADCP with a memory for off-line data processing

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In 1994, the basic plan for developing the equipment was firstly studied. A trial equipment was improvised and tested. However, the product was lost when the building and the factory of Aleck Electronics Ltd fell down because of the earthquake in the area of South Hyogo in January, 1995.In 1995, a trial production and a test was started again after the company was reconstructed. Then the basic plan was revised with a consideration of the easiness of obtaining parts and the period of research as well as the performance of the equipment : One pulse type with a frequency of 800kHz is adopted. In the estimation of Doppler shift, the variation of wave period is directly measured, ie, the period of gate signal whose frequency is reduced from the original echo signal by mixing a wave of constant frequency and by a low pass filter is measured by a digital clock of 20 MHz.A field experiment was carried out in the Lake Kasumigaura in order to investigate the appropriate method for off-line data processing which was the major subject of this research. An ordinal ADCP makes an on-line data processing during measurement in order to make the output signal more stable, which is "simple averaging" because of the restriction of time. However, most of information contained in the original data is lost through this process. On the other hand, because the new ADCP stores the original time series, we can adopt any sophisticated mathematics for data processing after the measurement. A combination of "moving AR model" and "moving average" got the best result among 6 methods of data processing which authors investigated. This method generates a time series of velocity which has the most stability and the finest time resolution.ADCP data obtained from a moving boat has a kind of error which is generated by rolling and pitching of the boat. The characteristics of the error is investigated and a method for data correction was developed.