11:00 AM - 11:15 AM
[AOS19-02] 17 year observation of bottom water current on deep seafloor offshore of Tokachi in Hokkaido: Recovery of acoustic Doppler current profiler (ADCP) data of cabled observatory
Keywords:acoustic Doppler current profiler (ADCP), long term observation on deep seafloor offshore of Tokachi in Hokkaido, benthic organisms
In order to observe earthquakes and tsunamis in Kuril Trench region, the cabled observatory attached with three ocean bottom seismometers (OBSs) and two pressure gauges (PGs) along a 240km long submarine was deployed offshore of Kushiro-Tokachi in Hokkaido in 1999. The observatory is equipped not only with the OBSs and the PGs but also with various types of sensors, such as hydrophones, an acoustic Doppler current profiler (ADCP), an electro-magnetic current meter, a CTD (conductivity, temperature and depth) sensor, and a video camera. The ADCP is mounted on the cable-end station which is located at a depth of 2540 m offshore of Tokachi. The observation with the ADCP was continued until 2016 after the deployment. However, much of the data are left unanalyzed and moreover some might be dissipated. This time, the recovery of the ADCP data is carried out.
The raw data of the ADCP are usually converted to the ASCII data by using the software “WinADCP” which is supplied by Teledyne RDI Instruments. There are some problems with the raw ADCP data. Some of the data contain bit errors due to the communication error during data transmission. The raw data contain check sum bytes at each record obtained at one ping. The WinADCP converts each raw record to ASCII only when the corresponding check sum bytes are normal. In other words, if there is a single bit error in a record, the corresponding whole record including the other part without error cannot be converted. This time, we refer to the documentations produced by Teledyne RDI Instruments and decode the raw binary data directly. As a result, we can convert some raw data that cannot be done with the WinADCP.
The ADCP measures the vertical profile of the current velocities in 48 layers. The thickness of each layer is 8 meters and the height of the bottom layer is 12 meters from the seafloor. The sampling rate is usually 30 minutes. The ADCP measures not only current velocities but also acoustic backscatter (echo) intensity from each layer and the bottom water temperature. The echo intensity indicates the concentration of the suspended materials in each layer. The echo intensity tends to have a peak in late spring or early summer. Meanwhile visual observation of the seafloor was carried out with the video camera of the cable-end station from June 2006 to June 2008. JPEG format still images were acquired approximately every 10 seconds. Although significant turbidity has not been observed, moderate increase in benthic organisms tends to be observed in May or June. Those phenomena may relate to the spring bloom in sea surface.
Including the above phenomena preliminary results obtained through the data recovery will be reported in the presentation.
The raw data of the ADCP are usually converted to the ASCII data by using the software “WinADCP” which is supplied by Teledyne RDI Instruments. There are some problems with the raw ADCP data. Some of the data contain bit errors due to the communication error during data transmission. The raw data contain check sum bytes at each record obtained at one ping. The WinADCP converts each raw record to ASCII only when the corresponding check sum bytes are normal. In other words, if there is a single bit error in a record, the corresponding whole record including the other part without error cannot be converted. This time, we refer to the documentations produced by Teledyne RDI Instruments and decode the raw binary data directly. As a result, we can convert some raw data that cannot be done with the WinADCP.
The ADCP measures the vertical profile of the current velocities in 48 layers. The thickness of each layer is 8 meters and the height of the bottom layer is 12 meters from the seafloor. The sampling rate is usually 30 minutes. The ADCP measures not only current velocities but also acoustic backscatter (echo) intensity from each layer and the bottom water temperature. The echo intensity indicates the concentration of the suspended materials in each layer. The echo intensity tends to have a peak in late spring or early summer. Meanwhile visual observation of the seafloor was carried out with the video camera of the cable-end station from June 2006 to June 2008. JPEG format still images were acquired approximately every 10 seconds. Although significant turbidity has not been observed, moderate increase in benthic organisms tends to be observed in May or June. Those phenomena may relate to the spring bloom in sea surface.
Including the above phenomena preliminary results obtained through the data recovery will be reported in the presentation.