186SL0932171014701 223B 19831212 19850109 1440N 01726W 2 00000X 0000 MM 186SL0932271014701 Dakar-B Senegal ORSTOM 186SL093230001 186SL093230002 QUALITY ASSESSMENT OF SEA LEVEL DATA 186SL093230003 by the 186SL093230004 TOGA SEA LEVEL CENTER/NATIONAL OCEANOGRAPHIC DATA CENTER 186SL093230005 JOINT ARCHIVE FOR SEA LEVEL 186SL093230006 186SL093230007Station : Dakar-B Latitude: 14 40.0N 186SL093230008Country : Senegal Longitude: 017 25.8W 186SL093230009JASL # : 223B Time Meridian: 015W (GMT + 1) 186SL093230010GLOSS # : 253 TOGA #: A026 NODC #: 71014701 186SL093230011Contributor : ORSTOM 186SL093230012 LOP Museum 186SL093230013 43-45 rue Cuvier 186SL093230014 75231 Paris Cedex 05 186SL093230015 FRANCE 186SL093230016Originator : same 186SL093230017Original Data: digital 186SL093230018Instrmnt Type: Aanderaa WLR5 (bottom-mounted pressure gauge) 186SL093230019Digitzd Intvl: one hour 186SL093230020Present Data : Hourly, daily, and monthly values obtained by: 186SL093230021 Hourly : direct digitization, no filter 186SL093230022 Daily : 119-point convolution filter (Bloomfield, 1976) 186SL093230023 centered on noon applied to the hourly data 186SL093230024 with respective periods of the 95, 50, and 5% 186SL093230025 amplitude points at 124.0, 60.2, and 40.2 hours 186SL093230026 Monthly: Simple average of all daily values; calculated if 186SL093230027 7 or fewer days are missing 186SL093230028Span of data : 12 Dec 1983 - 09 Jan 1985 186SL093230029Gaps > 1 mon : none 186SL093230030Time Refernce: GMT (00-23 hours) Space-filler Flag :-9999 186SL093230031Units : millimeters Missing Data Flag :99999 186SL093230032Refernce Levl: Due to the nature of the bottom-mounted pressure 186SL093230033 gauges, no link could be established between the 186SL093230034 zero of the gauge values and fixed points on land. 186SL093230035 Also, tide staff observations or the like were 186SL093230036 unavailable. This series has no long-term 186SL093230037 reference level. 186SL093230038Comment : The depth of the instrument in the water was about 186SL093230039 8 meters. Techniques of data processing 186SL093230040 by the originator are discussed in the second 186SL093230041 reference below. 186SL093230042 186SL093230043 The Dakar pressure gauge records consist of 186SL093230044 four separate segments: 186SL093230045 Dakar-A: 24 Dec 1982 - 12 Dec 1983 186SL093230046 Dakar-B: 12 Dec 1983 - 09 Jan 1985 186SL093230047 Dakar-C: 30 May 1986 - 16 Dec 1986 186SL093230048 Dakar-D: 16 Dec 1986 - 24 May 1989 186SL093230049 The series was broken into segments because 186SL093230050 level jumps could be identified at the time 186SL093230051 of instrument replacements. 186SL093230052 186SL093230053 Due to the tendency for pressure gauge sensors 186SL093230054 to drift, it is beneficial for investigators 186SL093230055 to know the time span of each instrument 186SL093230056 deployment (time/date as yyyy/mm/dd/hh(GMT)): 186SL093230057 Series start stop 186SL093230058 Dakar-A 1982/12/24/13 - 1983/01/25/10 186SL093230059 Dakar-A 1983/01/25/12 - 1983/03/17/15 186SL093230060 Dakar-A 1983/03/17/17 - 1983/05/16/10 186SL093230061 Dakar-A 1983/05/16/11 - 1983/07/20/10 186SL093230062 Dakar-A 1983/07/20/11 - 1983/12/12/10 186SL093230063 Dakar-B 1983/12/12/11 - 1984/04/30/11 186SL093230064 Dakar-B 1984/04/30/12 - 1984/10/04/11 186SL093230065 Dakar-B 1984/10/04/12 - 1985/01/09/12 186SL093230066 Dakar-C 1986/05/30/15 - 1986/12/16/15 186SL093230067 Dakar-D 1986/12/16/23 - 1988/09/21/01 186SL093230068 Dakar-D 1988/11/11/10 - 1989/05/24/10 186SL093230069 186SL093230070 For more information: 186SL093230071 186SL093230072 Verstraete, J.M., 1988. Sea level variations in 186SL093230073 the tropical Atlantic. Time series of ocean 186SL093230074 measurements, Technical series, UNESCO,4,33-47. 186SL093230075 186SL093230076 Verstraete, J.M., 1992. Accuracy of shallow 186SL093230077 pressure gauges. Joint IAPSO-IOC Workshop on 186SL093230078 Sea Level Measurements and Quality Control, 186SL093230079 Paris, 12-13 October, 1992. IOC Workshop 186SL093230080 Report No. 81, UNESCO. pp. 70-76. 186SL093230081 186SL093230082 CI MISSING REPLACED GAPS QUESTIONABLE 186SL093230083YEAR (%) DATA OR BAD DATA FLUCTUATIONS 186SL093230084---- --- -------------------- --------------- -------------------- 186SL0932300851983 6 none none none 186SL0932300861984 100 none none none 186SL0932300871985 3 none none none 186SL093230088 186SL093230089 QUALITY ASSESSMENT POLICY 186SL093230090 186SL093230091 The quality assessment is mostly based on the residuals 186SL093230092 (observed data minus predicted tides) of the hourly data. This 186SL093230093 assessment also applies to the daily and monthly data since 186SL093230094 they were derived from the quality-controlled hourly data. 186SL093230095 186SL093230096 The following abbreviations are used in the assessment: 186SL093230097 JASL - Joint Archive for Sea Level; GLOSS - Global Sea Level 186SL093230098 Observing System; TOGA - Tropical Ocean Global Atmosphere 186SL093230099 research program; NODC - National Oceanographic Data Center; 186SL093230100 Instrmnt - instrument; Digitzd Intvl - digitized interval; 186SL093230101 Gaps > 1 mon - missing data in a span greater than one month; 186SL093230102 Refernce - reference. 186SL093230103 186SL093230104 The following corrections are made to the hourly data 186SL093230105 prior to this assessment: 186SL093230106 1) Gaps or obviously wrong data points in a span less than 186SL093230107 25 hours are filled by the predicted tide method*. 186SL093230108 2) Timing errors of exact increments of an hour are corrected 186SL093230109 by shifting the data. 186SL093230110 3) Reference level shifts are only corrected after information 186SL093230111 from tide staff readings or comparative readings with a fixed 186SL093230112 bench mark are checked to verify that the shift was not a 186SL093230113 natural event. If comparative readings are missing or 186SL093230114 incomplete, comparisons of the data with nearby stations 186SL093230115 may warrant the adjustment of some obvious shifts. 186SL093230116 4) Data with unresolved datum shifts are not disseminated. 186SL093230117 However, if sufficient time spans of data are available before 186SL093230118 or after the year(s) with the unresolved shift(s), a subset of 186SL093230119 quality assured data is made available. Thus, the Span field 186SL093230120 in the Quality Assessment may not match the span of the 186SL093230121 distribution data set. As the questionable datum shifts are 186SL093230122 resolved, the data set will be updated. Although this policy 186SL093230123 adds some complexity, it allows more rapid dissemination of 186SL093230124 at least the quality assured years. 186SL093230125 186SL093230126 For each year, the following information is documented from 186SL093230127 the quality-controlled hourly data with dates given as the nth 186SL093230128 day of the year starting from 1 January: 186SL093230129 1) a Completeness Index (CI) based on the percentage of hours 186SL093230130 with available data, 186SL093230131 2) a list of gaps longer than a day, 186SL093230132 3) a summary of days with consecutive missing or obviously 186SL093230133 wrong data in a time span longer than 6 but less than 25 186SL093230134 hours that have been replaced, with hours in parentheses, and 186SL093230135 4) a summary of days with questionable fluctuations in the 186SL093230136 residual series. Fluctuations within the residuals are 186SL093230137 considered significant and are noted if they are greater than 186SL093230138 25 cm. This policy has changed slightly as of October 1992: 186SL093230139 only suspicious fluctuations due to obvious instrumentation 186SL093230140 problems are noted. Minor timing drifts are no longer 186SL093230141 included in the list of questionable days. 186SL093230142 186SL093230143 Note : If the predicted tides poorly model the observed heights 186SL093230144 due to the inability of the tidal analysis to completely resolv 186SL093230145 the non-linear shallow water effects, the residuals are not 186SL093230146 suitable for assessing the data quality. Instead, a subjective 186SL093230147 comment on the quality of the data is provided. 186SL093230148 186SL093230149 *The predicted tides are obtained with the use of a harmonic 186SL093230150 analysis program (Foreman, 1977) which is executed on a year 186SL093230151 of apparently good data for a given station. The Predicted 186SL093230152 Tide Method for filling gaps consists of statistically 186SL093230153 comparing the predicted tides to the observed data and 186SL093230154 shifting the predicted tides in time to correct for timing 186SL093230155 differences. Then the linear interpolation between hourly 186SL093230156 values at the end points of the gap in the residual series is 186SL093230157 added to the corresponding corrected predicted tide data to 186SL093230158 obtain interpolated values over the span of the gap. 186SL093230159 186SL093230160 Bloomfield, P., 1976. Fourier Analysis of Time Series: An 186SL093230161 Introduction. New York: John Wiley and Sons. pp 129-137. 186SL093230162 186SL093230163 Foreman, M., 1977. Manual For Tidal Height Analysis and 186SL093230164 Prediction. Institute of Ocean Sciences, Patricia Bay, 186SL093230165 Victoria B.C. Pacific Marine Science Report 77-10. 186SL093230166 186SL09326 19831 999999999999999999999999999999999999999999999999 186SL09326 19832 999999999999999999999999999999999999999999999999 186SL09326 19841 8295000 8345000 8301000 8329000 8380000 8394000 186SL09326 19842 8391000 8369000 8403000 8356000 8326000 8280000 186SL09326 19851 999999999999999999999999999999999999999999999999 186SL09326 19852 999999999999999999999999999999999999999999999999