QUALITY ASSESSMENT OF SEA LEVEL DATA by the UH SEA LEVEL CENTER/NATIONAL OCEANOGRAPHIC DATA CENTER JOINT ARCHIVE FOR SEA LEVEL updated: 20 May 2011 Station : Crozet-A Latitude: 46 25.5S Country : France Longitude: 051 52.2E JASL # : 178A Time Meridian: 045E (GMT + 3 hr) GLOSS # : 021 TOGA #: none NODC #: 34056101 Contributor : Service d'Observation ROSAME, LEGOS/OMP 14 Ave. Edouard Belin 31400 Toulouse FRANCE Originator : same Original Data: digital Instrmnt Type: MORS (bottom-mounted pressure gauge). The tide gauge is installed in the Baie du Navire, Possession Island, in the Crozet archipielago, nearby the Alfred Faure french scientific base. The gauge is a MORS automatic tide gauge station and consists of a ventilated ParoScientific pressure sensor at the base of a stilling well which is used to filter waves. The ventilation of the sensor results in a measurement of the total pressure (atmosphere + ocean) minus the atmosphere; hence, a direct measure of sea level, assuming water density is properly estimated. These data have not been corrected for the inverted barometer effect. Digitzd Intvl: 15 minutes Present Data : Hourly, daily, and monthly values obtained by: Hourly : Four minute integration time is used for the bottom pressure measurement. Data are recorded on the in-board memory every 15 minutes. Data are transmitted via ARGOSS every 30 minutes to Toulouse. The data are then processed to decrypt the messages and compute sea level based on i) relative bottom pressure, ii) water temperature, and iii) barometric pressure. From this set of data in combination with salinity, which is periodically measured but is assumed to be constant over extended periods, one computes water density based on the UNESCO formula for the sea-water equation; thus, the sea level is deduced and an hourly sub-sample is extracted. Daily : 119-point convolution filter (Bloomfield, 1976) centered on noon applied to the hourly data with respective periods of the 95, 50, and 5% amplitude points at 124.0, 60.2, and 40.2 hours Monthly: Simple average of all daily values; calculated if 7 or fewer days are missing Span of data : 18 Nov 1995 - 27 Jun 1999 Gaps > 1 mon : 18 Feb 1997 - 10 Dec 1998 Time Refernce: GMT (00-23 hours) Space-filler Flag :-9999 Units : millimeters Missing Data Flag : 9999 Existing : Yes Operational : Yes Sat. Trans. : Yes Distribution : 1995-1999 Refernce Levl: Presently no link is established between the tide gauge and fixed bench marks. Please refer to the originator for the up-to-date status. A GPS "pilar" has been established, but presently has not been linked to the tide station. Series 178A is separate from 178B because 1995-1999 gauge was installed lower in the stilling well and a correction constant to the 2000-2001 series is not available. Comment : Pressure transducers typically have long-term tendencies to drift. However, the originators have calibrated the instrument before deployment and due to the shallow resting level of about 2.3 m at high tide, the potential drift would be very small. Post-retrieval calibrations have not been performed. Please refer to the originators for the up-to-date status. For this data set, no explicit correction has been applied in this regards. The plot of the hourly data minus the predicted tides reveals data with excellent timing characteristics and no obviously erroneous data. CI MISSING REPLACED GAPS QUESTIONABLE YEAR (%) DATA OR BAD DATA FLUCTUATIONS ---- --- -------------------- --------------- -------------------- 1995 12 none none none 1996 77 71-74,121-127,130- (18)064-(02)065 none 132,137-140,144-148, (10)066-(06)067 152-177,180-191,193- (14)068-(22)068 233,315-317 (02)069-(10)069 (14)069-(06)070 (14)070-(02)071 (10)084-(02)085 (14)086-(02)087 (18)087-(02)088 (14)095-(02)096 (11)100-(18)100 (22)100-(18)101 (18)105-(06)106 (18)107-(14)108 (10)109-(06)110 (22)110-(06)111 (10)111-(18)111 (18)112-(02)113 (19)115-(06)116 (10)116-(06)117 (14)117-(06)118 (18)118-(10)119 (10)120-(22)120 (13)122-(02)123 (10)128-(18)128 (22)128-(06)129 (10)129-(18)129 (14)132-(06)133 (14)133-(22)133 (22)134-(06)135 (10)135-(06)136 (10)136-(06)137 (14)140-(06)141 (10)141-(22)141 (14)142-(22)142 (02)143-(10)143 (18)148-(06)149 (13)149-(02)150 (10)150-(22)150 (18)151-(06)152 (09)175-(06)176 (14)177-(06)178 (10)178-(22)178 (22)183-(06)184 (10)187-(06)188 (14)191-(10)192 (14)192-(04)193 (14)198-(06)199 (10)201-(02)202 (14)205-(02)206 (04)208-(14)208 (18)217-(02)218 (10)218-(18)218 (20)299-(04)300 (20)305-(16)306 (09)310-(16)310 (01)319-(17)319 1997 13 49-365 none none 1998 6 1-344 none none 1999 37 92-107,130-152,170- none none 172,173-177