186SL0934171014701 223D 19861216 19890524 1440N 01726W 2 00000X 0000 MM 186SL0934271014701 Dakar-D Senegal ORSTOM 186SL093430001 186SL093430002 QUALITY ASSESSMENT OF SEA LEVEL DATA 186SL093430003 by the 186SL093430004 TOGA SEA LEVEL CENTER/NATIONAL OCEANOGRAPHIC DATA CENTER 186SL093430005 JOINT ARCHIVE FOR SEA LEVEL 186SL093430006 186SL093430007Station : Dakar-D Latitude: 14 40.0N 186SL093430008Country : Senegal Longitude: 017 25.8W 186SL093430009JASL # : 223D Time Meridian: 015W (GMT + 1) 186SL093430010GLOSS # : 253 TOGA #: A026 NODC #: 71014701 186SL093430011Contributor : ORSTOM 186SL093430012 LOP Museum 186SL093430013 43-45 rue Cuvier 186SL093430014 75231 Paris Cedex 05 186SL093430015 FRANCE 186SL093430016Originator : same 186SL093430017Original Data: digital 186SL093430018Instrmnt Type: Aanderaa WLR5 (bottom-mounted pressure gauge) 186SL093430019Digitzd Intvl: one hour 186SL093430020Present Data : Hourly, daily, and monthly values obtained by: 186SL093430021 Hourly : direct digitization, no filter 186SL093430022 Daily : 119-point convolution filter (Bloomfield, 1976) 186SL093430023 centered on noon applied to the hourly data 186SL093430024 with respective periods of the 95, 50, and 5% 186SL093430025 amplitude points at 124.0, 60.2, and 40.2 hours 186SL093430026 Monthly: Simple average of all daily values; calculated if 186SL093430027 7 or fewer days are missing 186SL093430028Span of data : 16 Dec 1986 - 24 May 1989 186SL093430029Gaps > 1 mon : none 186SL093430030Time Refernce: GMT (00-23 hours) Space-filler Flag :-9999 186SL093430031Units : millimeters Missing Data Flag :99999 186SL093430032Refernce Levl: Due to the nature of the bottom-mounted pressure 186SL093430033 gauges, no link could be established between the 186SL093430034 zero of the gauge values and fixed points on land. 186SL093430035 Also, tide staff observations or the like were 186SL093430036 unavailable. This series has no long-term 186SL093430037 reference level. 186SL093430038Comment : The depth of the instrument in the water was about 186SL093430039 8 meters. Techniques of data processing 186SL093430040 by the originator are discussed in the second 186SL093430041 reference below. 186SL093430042 186SL093430043 The Dakar pressure gauge records consist of 186SL093430044 four separate segments: 186SL093430045 Dakar-A: 24 Dec 1982 - 12 Dec 1983 186SL093430046 Dakar-B: 12 Dec 1983 - 09 Jan 1985 186SL093430047 Dakar-C: 30 May 1986 - 16 Dec 1986 186SL093430048 Dakar-D: 16 Dec 1986 - 24 May 1989 186SL093430049 The series was broken into segments because 186SL093430050 level jumps could be identified at the time 186SL093430051 of instrument replacements. 186SL093430052 186SL093430053 Due to the tendency for pressure gauge sensors 186SL093430054 to drift, it is beneficial for investigators 186SL093430055 to know the time span of each instrument 186SL093430056 deployment (time/date as yyyy/mm/dd/hh(GMT)): 186SL093430057 Series start stop 186SL093430058 Dakar-A 1982/12/24/13 - 1983/01/25/10 186SL093430059 Dakar-A 1983/01/25/12 - 1983/03/17/15 186SL093430060 Dakar-A 1983/03/17/17 - 1983/05/16/10 186SL093430061 Dakar-A 1983/05/16/11 - 1983/07/20/10 186SL093430062 Dakar-A 1983/07/20/11 - 1983/12/12/10 186SL093430063 Dakar-B 1983/12/12/11 - 1984/04/30/11 186SL093430064 Dakar-B 1984/04/30/12 - 1984/10/04/11 186SL093430065 Dakar-B 1984/10/04/12 - 1985/01/09/12 186SL093430066 Dakar-C 1986/05/30/15 - 1986/12/16/15 186SL093430067 Dakar-D 1986/12/16/23 - 1988/09/21/01 186SL093430068 Dakar-D 1988/11/11/10 - 1989/05/24/10 186SL093430069 186SL093430070 For more information: 186SL093430071 186SL093430072 Verstraete, J.M., 1988. Sea level variations in 186SL093430073 the tropical Atlantic. Time series of ocean 186SL093430074 measurements, Technical series, UNESCO,4,33-47. 186SL093430075 186SL093430076 Verstraete, J.M., 1992. Accuracy of shallow 186SL093430077 pressure gauges. Joint IAPSO-IOC Workshop on 186SL093430078 Sea Level Measurements and Quality Control, 186SL093430079 Paris, 12-13 October, 1992. IOC Workshop 186SL093430080 Report No. 81, UNESCO. pp. 70-76. 186SL093430081 186SL093430082 CI MISSING REPLACED GAPS QUESTIONABLE 186SL093430083YEAR (%) DATA OR BAD DATA FLUCTUATIONS 186SL093430084---- --- -------------------- --------------- -------------------- 186SL0934300851986 4 none none none 186SL0934300861987 100 none none none 186SL0934300871988 86 265-316 (18)129-(06)130 none 186SL093430088 (15)188-(01)189 186SL093430089 (20)235-(19)236 186SL0934300901989 39 none none none 186SL093430091 186SL093430092 QUALITY ASSESSMENT POLICY 186SL093430093 186SL093430094 The quality assessment is mostly based on the residuals 186SL093430095 (observed data minus predicted tides) of the hourly data. This 186SL093430096 assessment also applies to the daily and monthly data since 186SL093430097 they were derived from the quality-controlled hourly data. 186SL093430098 186SL093430099 The following abbreviations are used in the assessment: 186SL093430100 JASL - Joint Archive for Sea Level; GLOSS - Global Sea Level 186SL093430101 Observing System; TOGA - Tropical Ocean Global Atmosphere 186SL093430102 research program; NODC - National Oceanographic Data Center; 186SL093430103 Instrmnt - instrument; Digitzd Intvl - digitized interval; 186SL093430104 Gaps > 1 mon - missing data in a span greater than one month; 186SL093430105 Refernce - reference. 186SL093430106 186SL093430107 The following corrections are made to the hourly data 186SL093430108 prior to this assessment: 186SL093430109 1) Gaps or obviously wrong data points in a span less than 186SL093430110 25 hours are filled by the predicted tide method*. 186SL093430111 2) Timing errors of exact increments of an hour are corrected 186SL093430112 by shifting the data. 186SL093430113 3) Reference level shifts are only corrected after information 186SL093430114 from tide staff readings or comparative readings with a fixed 186SL093430115 bench mark are checked to verify that the shift was not a 186SL093430116 natural event. If comparative readings are missing or 186SL093430117 incomplete, comparisons of the data with nearby stations 186SL093430118 may warrant the adjustment of some obvious shifts. 186SL093430119 4) Data with unresolved datum shifts are not disseminated. 186SL093430120 However, if sufficient time spans of data are available before 186SL093430121 or after the year(s) with the unresolved shift(s), a subset of 186SL093430122 quality assured data is made available. Thus, the Span field 186SL093430123 in the Quality Assessment may not match the span of the 186SL093430124 distribution data set. As the questionable datum shifts are 186SL093430125 resolved, the data set will be updated. Although this policy 186SL093430126 adds some complexity, it allows more rapid dissemination of 186SL093430127 at least the quality assured years. 186SL093430128 186SL093430129 For each year, the following information is documented from 186SL093430130 the quality-controlled hourly data with dates given as the nth 186SL093430131 day of the year starting from 1 January: 186SL093430132 1) a Completeness Index (CI) based on the percentage of hours 186SL093430133 with available data, 186SL093430134 2) a list of gaps longer than a day, 186SL093430135 3) a summary of days with consecutive missing or obviously 186SL093430136 wrong data in a time span longer than 6 but less than 25 186SL093430137 hours that have been replaced, with hours in parentheses, and 186SL093430138 4) a summary of days with questionable fluctuations in the 186SL093430139 residual series. Fluctuations within the residuals are 186SL093430140 considered significant and are noted if they are greater than 186SL093430141 25 cm. This policy has changed slightly as of October 1992: 186SL093430142 only suspicious fluctuations due to obvious instrumentation 186SL093430143 problems are noted. Minor timing drifts are no longer 186SL093430144 included in the list of questionable days. 186SL093430145 186SL093430146 Note : If the predicted tides poorly model the observed heights 186SL093430147 due to the inability of the tidal analysis to completely resolv 186SL093430148 the non-linear shallow water effects, the residuals are not 186SL093430149 suitable for assessing the data quality. Instead, a subjective 186SL093430150 comment on the quality of the data is provided. 186SL093430151 186SL093430152 *The predicted tides are obtained with the use of a harmonic 186SL093430153 analysis program (Foreman, 1977) which is executed on a year 186SL093430154 of apparently good data for a given station. The Predicted 186SL093430155 Tide Method for filling gaps consists of statistically 186SL093430156 comparing the predicted tides to the observed data and 186SL093430157 shifting the predicted tides in time to correct for timing 186SL093430158 differences. Then the linear interpolation between hourly 186SL093430159 values at the end points of the gap in the residual series is 186SL093430160 added to the corresponding corrected predicted tide data to 186SL093430161 obtain interpolated values over the span of the gap. 186SL093430162 186SL093430163 Bloomfield, P., 1976. Fourier Analysis of Time Series: An 186SL093430164 Introduction. New York: John Wiley and Sons. pp 129-137. 186SL093430165 186SL093430166 Foreman, M., 1977. Manual For Tidal Height Analysis and 186SL093430167 Prediction. Institute of Ocean Sciences, Patricia Bay, 186SL093430168 Victoria B.C. Pacific Marine Science Report 77-10. 186SL093430169 186SL09346 19861 999999999999999999999999999999999999999999999999 186SL09346 19862 999999999999999999999999999999999999999999999999 186SL09346 19871 8222000 8223000 8228000 8289000 8306000 8319000 186SL09346 19872 8333000 8329000 8303000 8334000 8338000 8283000 186SL09346 19881 8201000 8243000 8227000 8249000 8265000 8269000 186SL09346 19882 8322000 8330000999999999999999999999999 8348000 186SL09346 19891 8305000 8298000 8269000 82690009999999999999999 186SL09346 19892 999999999999999999999999999999999999999999999999