186SL0931171014701 223A 19821224 19831212 1440N 01726W 2 00000X 0000 MM 186SL0931271014701 Dakar-A Senegal ORSTOM 186SL093130001 186SL093130002 QUALITY ASSESSMENT OF SEA LEVEL DATA 186SL093130003 by the 186SL093130004 TOGA SEA LEVEL CENTER/NATIONAL OCEANOGRAPHIC DATA CENTER 186SL093130005 JOINT ARCHIVE FOR SEA LEVEL 186SL093130006 186SL093130007Station : Dakar-A Latitude: 14 40.0N 186SL093130008Country : Senegal Longitude: 017 25.8W 186SL093130009JASL # : 223A Time Meridian: 015W (GMT + 1) 186SL093130010GLOSS # : 253 TOGA #: A026 NODC #: 71014701 186SL093130011Contributor : ORSTOM 186SL093130012 LOP Museum 186SL093130013 43-45 rue Cuvier 186SL093130014 75231 Paris Cedex 05 186SL093130015 FRANCE 186SL093130016Originator : same 186SL093130017Original Data: digital 186SL093130018Instrmnt Type: Aanderaa WLR5 (bottom-mounted pressure gauge) 186SL093130019Digitzd Intvl: one hour 186SL093130020Present Data : Hourly, daily, and monthly values obtained by: 186SL093130021 Hourly : direct digitization, no filter 186SL093130022 Daily : 119-point convolution filter (Bloomfield, 1976) 186SL093130023 centered on noon applied to the hourly data 186SL093130024 with respective periods of the 95, 50, and 5% 186SL093130025 amplitude points at 124.0, 60.2, and 40.2 hours 186SL093130026 Monthly: Simple average of all daily values; calculated if 186SL093130027 7 or fewer days are missing 186SL093130028Span of data : 24 Dec 1982 - 12 Dec 1983 186SL093130029Gaps > 1 mon : none 186SL093130030Time Refernce: GMT (00-23 hours) Space-filler Flag :-9999 186SL093130031Units : millimeters Missing Data Flag :99999 186SL093130032Refernce Levl: Due to the nature of the bottom-mounted pressure 186SL093130033 gauges, no link could be established between the 186SL093130034 zero of the gauge values and fixed points on land. 186SL093130035 Also, tide staff observations or the like were 186SL093130036 unavailable. This series has no long-term 186SL093130037 reference level. 186SL093130038Comment : The depth of the instrument in the water was about 186SL093130039 8 meters. Techniques of data processing 186SL093130040 by the originator are discussed in the second 186SL093130041 reference below. 186SL093130042 186SL093130043 The Dakar pressure gauge records consist of 186SL093130044 four separate segments: 186SL093130045 Dakar-A: 24 Dec 1982 - 12 Dec 1983 186SL093130046 Dakar-B: 12 Dec 1983 - 09 Jan 1985 186SL093130047 Dakar-C: 30 May 1986 - 16 Dec 1986 186SL093130048 Dakar-D: 16 Dec 1986 - 24 May 1989 186SL093130049 The series was broken into segments because 186SL093130050 level jumps could be identified at the time 186SL093130051 of instrument replacements. 186SL093130052 186SL093130053 Due to the tendency for pressure gauge sensors 186SL093130054 to drift, it is beneficial for investigators 186SL093130055 to know the time span of each instrument 186SL093130056 deployment (time/date as yyyy/mm/dd/hh(GMT)): 186SL093130057 Series start stop 186SL093130058 Dakar-A 1982/12/24/13 - 1983/01/25/10 186SL093130059 Dakar-A 1983/01/25/12 - 1983/03/17/15 186SL093130060 Dakar-A 1983/03/17/17 - 1983/05/16/10 186SL093130061 Dakar-A 1983/05/16/11 - 1983/07/20/10 186SL093130062 Dakar-A 1983/07/20/11 - 1983/12/12/10 186SL093130063 Dakar-B 1983/12/12/11 - 1984/04/30/11 186SL093130064 Dakar-B 1984/04/30/12 - 1984/10/04/11 186SL093130065 Dakar-B 1984/10/04/12 - 1985/01/09/12 186SL093130066 Dakar-C 1986/05/30/15 - 1986/12/16/15 186SL093130067 Dakar-D 1986/12/16/23 - 1988/09/21/01 186SL093130068 Dakar-D 1988/11/11/10 - 1989/05/24/10 186SL093130069 186SL093130070 For more information: 186SL093130071 186SL093130072 Verstraete, J.M., 1988. Sea level variations in 186SL093130073 the tropical Atlantic. Time series of ocean 186SL093130074 measurements, Technical series, UNESCO,4,33-47. 186SL093130075 186SL093130076 Verstraete, J.M., 1992. Accuracy of shallow 186SL093130077 pressure gauges. Joint IAPSO-IOC Workshop on 186SL093130078 Sea Level Measurements and Quality Control, 186SL093130079 Paris, 12-13 October, 1992. IOC Workshop 186SL093130080 Report No. 81, UNESCO. pp. 70-76. 186SL093130081 186SL093130082 CI MISSING REPLACED GAPS QUESTIONABLE 186SL093130083YEAR (%) DATA OR BAD DATA FLUCTUATIONS 186SL093130084---- --- -------------------- --------------- -------------------- 186SL0931300851982 2 none none none 186SL0931300861983 95 none (16)076-(05)077 26-33 186SL093130087 186SL093130088 QUALITY ASSESSMENT POLICY 186SL093130089 186SL093130090 The quality assessment is mostly based on the residuals 186SL093130091 (observed data minus predicted tides) of the hourly data. This 186SL093130092 assessment also applies to the daily and monthly data since 186SL093130093 they were derived from the quality-controlled hourly data. 186SL093130094 186SL093130095 The following abbreviations are used in the assessment: 186SL093130096 JASL - Joint Archive for Sea Level; GLOSS - Global Sea Level 186SL093130097 Observing System; TOGA - Tropical Ocean Global Atmosphere 186SL093130098 research program; NODC - National Oceanographic Data Center; 186SL093130099 Instrmnt - instrument; Digitzd Intvl - digitized interval; 186SL093130100 Gaps > 1 mon - missing data in a span greater than one month; 186SL093130101 Refernce - reference. 186SL093130102 186SL093130103 The following corrections are made to the hourly data 186SL093130104 prior to this assessment: 186SL093130105 1) Gaps or obviously wrong data points in a span less than 186SL093130106 25 hours are filled by the predicted tide method*. 186SL093130107 2) Timing errors of exact increments of an hour are corrected 186SL093130108 by shifting the data. 186SL093130109 3) Reference level shifts are only corrected after information 186SL093130110 from tide staff readings or comparative readings with a fixed 186SL093130111 bench mark are checked to verify that the shift was not a 186SL093130112 natural event. If comparative readings are missing or 186SL093130113 incomplete, comparisons of the data with nearby stations 186SL093130114 may warrant the adjustment of some obvious shifts. 186SL093130115 4) Data with unresolved datum shifts are not disseminated. 186SL093130116 However, if sufficient time spans of data are available before 186SL093130117 or after the year(s) with the unresolved shift(s), a subset of 186SL093130118 quality assured data is made available. Thus, the Span field 186SL093130119 in the Quality Assessment may not match the span of the 186SL093130120 distribution data set. As the questionable datum shifts are 186SL093130121 resolved, the data set will be updated. Although this policy 186SL093130122 adds some complexity, it allows more rapid dissemination of 186SL093130123 at least the quality assured years. 186SL093130124 186SL093130125 For each year, the following information is documented from 186SL093130126 the quality-controlled hourly data with dates given as the nth 186SL093130127 day of the year starting from 1 January: 186SL093130128 1) a Completeness Index (CI) based on the percentage of hours 186SL093130129 with available data, 186SL093130130 2) a list of gaps longer than a day, 186SL093130131 3) a summary of days with consecutive missing or obviously 186SL093130132 wrong data in a time span longer than 6 but less than 25 186SL093130133 hours that have been replaced, with hours in parentheses, and 186SL093130134 4) a summary of days with questionable fluctuations in the 186SL093130135 residual series. Fluctuations within the residuals are 186SL093130136 considered significant and are noted if they are greater than 186SL093130137 25 cm. This policy has changed slightly as of October 1992: 186SL093130138 only suspicious fluctuations due to obvious instrumentation 186SL093130139 problems are noted. Minor timing drifts are no longer 186SL093130140 included in the list of questionable days. 186SL093130141 186SL093130142 Note : If the predicted tides poorly model the observed heights 186SL093130143 due to the inability of the tidal analysis to completely resolv 186SL093130144 the non-linear shallow water effects, the residuals are not 186SL093130145 suitable for assessing the data quality. Instead, a subjective 186SL093130146 comment on the quality of the data is provided. 186SL093130147 186SL093130148 *The predicted tides are obtained with the use of a harmonic 186SL093130149 analysis program (Foreman, 1977) which is executed on a year 186SL093130150 of apparently good data for a given station. The Predicted 186SL093130151 Tide Method for filling gaps consists of statistically 186SL093130152 comparing the predicted tides to the observed data and 186SL093130153 shifting the predicted tides in time to correct for timing 186SL093130154 differences. Then the linear interpolation between hourly 186SL093130155 values at the end points of the gap in the residual series is 186SL093130156 added to the corresponding corrected predicted tide data to 186SL093130157 obtain interpolated values over the span of the gap. 186SL093130158 186SL093130159 Bloomfield, P., 1976. Fourier Analysis of Time Series: An 186SL093130160 Introduction. New York: John Wiley and Sons. pp 129-137. 186SL093130161 186SL093130162 Foreman, M., 1977. Manual For Tidal Height Analysis and 186SL093130163 Prediction. Institute of Ocean Sciences, Patricia Bay, 186SL093130164 Victoria B.C. Pacific Marine Science Report 77-10. 186SL093130165 186SL09316 19821 999999999999999999999999999999999999999999999999 186SL09316 19822 999999999999999999999999999999999999999999999999 186SL09316 19831 8410000 8391000 8380000 8330000 8383000 8492000 186SL09316 19832 8467000 8459000 8427000 8460000 845300099999999