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Handbook No. 1
Do NDBC's meteorological and oceanographic sensors measure data for the entire hour?
Sensors that are installed on board moored buoys and at C-MAN sites generally do not measure and record data for the entire hour. Continuously recording data drastically increases power consumption. Therefore, for most NDBC-measured environmental data, with spectral wave measurements and continuous winds being exceptions, an eight-minute period is used for data collected by sensors on board moored buoys and a two-minute acquisition period is used for data collected by sensors at C-MAN sites.
Starting in July 2004, the end-of-acquisition time is reported as the official observation time, to the hour and minute resolution. Before July 2004, the observation time is simply the rounded hour nearest to the acquisition period, not displaying minutes. July's change makes the observation times more consistent with the data provided to the archive centers. Starting in August 1993, the end-of-acquisition time is reported as the official observation time for data provided to the national archive centers. Before August 1993, the observation time is the rounded hour nearest to the acquisition period.
Note: Wave data normally have acquisition periods that do not overlap meteorological data acquisition. Currently, wave data times are rounded to the nearest hour for 40 minute acquisition systems or nearest half hour for 20 minute acquisition systems. Reporting the actual end-of-acquisition time for wave data is under consideration. However, on some pages, wave information is displayed on the same lines as meteorological data, and will always appear to have the meteorological data time for those displays.
For ocean current measurements, Acoustic Doppler Current Profiler (ADCP) times are rounded to the nearest hour. For oceanographic data measurements, times are rounded to the nearest hour. Reporting the actual end-of-acquisition times for these data will be taken under consideration.
For Continuous Wind stations, the end-of-acquisition time is given in the record. For other stations, the actual acquisition period may be determined by knowing the station type and payload. The end-of- acquisition minute is reported for DACT and VEEP payloads, and is minute 50 for those payloads installed on moored buoys. This means that 1200 UTC data was recorded from 1142-1150 UTC. The start of acquisition is reported for all GSBP payloads, and is minute 40 for GSBP's installed on moored buoys. This means that 1200 UTC data was recorded from 1140-1148 UTC. The end-of- acquisition minute for C-MAN sites is the top of the hour. Prior to January 1992, the end-of-acquisition time was minute 25 for Gulf of Mexico C-MAN stations. During the period from September 1993 to August 1994, the end-of-acquisition times on West Coast C-MAN sites were changed from minute 25 to the top of the hour.
However, some stations do not follow the above timing convention and have non-standard acquisition times.
Wave acquisition times are also listed on this WWW server.