186SL0923150035501 202B 19830623 19840130 0545S 03512W 2 00000X 0000 MM 186SL0923250035501 Natal-B Brazil ORSTOM 186SL092330001 186SL092330002 QUALITY ASSESSMENT OF SEA LEVEL DATA 186SL092330003 by the 186SL092330004 TOGA SEA LEVEL CENTER/NATIONAL OCEANOGRAPHIC DATA CENTER 186SL092330005 JOINT ARCHIVE FOR SEA LEVEL 186SL092330006 186SL092330007Station : Natal-B Latitude: 05 45.1S 186SL092330008Country : Brazil Longitude: 035 11.7W 186SL092330009JASL # : 202B Time Meridian: 030W (GMT + 2) 186SL092330010GLOSS # : 197 TOGA #: A016 NODC #: 50035501 186SL092330011Contributor : ORSTOM 186SL092330012 LOP Museum 186SL092330013 43-45 rue Cuvier 186SL092330014 75231 Paris Cedex 05 186SL092330015 FRANCE 186SL092330016Originator : same 186SL092330017Original Data: digital 186SL092330018Instrmnt Type: Aanderaa WLR5 (bottom-mounted pressure gauge) 186SL092330019Digitzd Intvl: one hour 186SL092330020Present Data : Hourly, daily, and monthly values obtained by: 186SL092330021 Hourly : direct digitization, no filter 186SL092330022 Daily : 119-point convolution filter (Bloomfield, 1976) 186SL092330023 centered on noon applied to the hourly data 186SL092330024 with respective periods of the 95, 50, and 5% 186SL092330025 amplitude points at 124.0, 60.2, and 40.2 hours 186SL092330026 Monthly: Simple average of all daily values; calculated if 186SL092330027 7 or fewer days are missing 186SL092330028Span of data : 23 Jun 1983 - 30 Jan 1984 186SL092330029Gaps > 1 mon : none 186SL092330030Time Refernce: GMT (00-23 hours) Space-filler Flag :-9999 186SL092330031Units : millimeters Missing Data Flag :99999 186SL092330032Refernce Levl: Due to the nature of the bottom-mounted pressure 186SL092330033 gauges, no link could be established between the 186SL092330034 zero of the gauge values and fixed points on land. 186SL092330035 Also, tide staff observations or the like were 186SL092330036 unavailable. This series has no long-term 186SL092330037 reference level. 186SL092330038Comment : The depth of the instrument in the water was 186SL092330039 about 5m. Techniques of data processing 186SL092330040 by the originator are discussed in the second 186SL092330041 reference below. 186SL092330042 186SL092330043 The Natal pressure gauge records consist of 186SL092330044 three separate segments: 186SL092330045 Natal-A: 28 Oct 1982 - 29 Mar 1983 186SL092330046 Natal-B: 23 Jun 1983 - 30 Jan 1984 186SL092330047 Natal-C: 01 Feb 1984 - 05 Nov 1985 186SL092330048 The series was broken into segments because 186SL092330049 level jumps could be identified at the time 186SL092330050 of instrument replacements. 186SL092330051 186SL092330052 Due to the tendency for pressure gauge sensors 186SL092330053 to drift, it is beneficial for investigators 186SL092330054 to know the time span of each instrument 186SL092330055 deployment (time/date as yyyy/mm/dd/hh(GMT)): 186SL092330056 Series start stop 186SL092330057 Natal-A 1982/10/28/09 - 1983/03/29/23 186SL092330058 Natal-B 1983/06/23/14 - 1984/01/30/12 186SL092330059 Natal-C 1984/01/30/13 - 1984/04/20/19 186SL092330060 Natal-C 1984/04/20/20 - 1984/08/07/14 186SL092330061 Natal-C 1984/08/07/15 - 1985/11/05/19 186SL092330062 186SL092330063 For more information: 186SL092330064 186SL092330065 Verstraete, J.M., 1988. Sea level variations in 186SL092330066 the tropical Atlantic. Time series of ocean 186SL092330067 measurements, Technical series, UNESCO,4,33-47. 186SL092330068 186SL092330069 Verstraete, J.M., 1992. Accuracy of shallow 186SL092330070 pressure gauges. Joint IAPSO-IOC Workshop on 186SL092330071 Sea Level Measurements and Quality Control, 186SL092330072 Paris, 12-13 October, 1992. IOC Workshop 186SL092330073 Report No. 81, UNESCO. pp. 70-76. 186SL092330074 186SL092330075 CI MISSING REPLACED GAPS QUESTIONABLE 186SL092330076YEAR (%) DATA OR BAD DATA FLUCTUATIONS 186SL092330077---- --- -------------------- --------------- -------------------- 186SL0923300781983 52 none none none 186SL0923300791984 8 none none none 186SL092330080 186SL092330081 QUALITY ASSESSMENT POLICY 186SL092330082 186SL092330083 The quality assessment is mostly based on the residuals 186SL092330084 (observed data minus predicted tides) of the hourly data. This 186SL092330085 assessment also applies to the daily and monthly data since 186SL092330086 they were derived from the quality-controlled hourly data. 186SL092330087 186SL092330088 The following abbreviations are used in the assessment: 186SL092330089 JASL - Joint Archive for Sea Level; GLOSS - Global Sea Level 186SL092330090 Observing System; TOGA - Tropical Ocean Global Atmosphere 186SL092330091 research program; NODC - National Oceanographic Data Center; 186SL092330092 Instrmnt - instrument; Digitzd Intvl - digitized interval; 186SL092330093 Gaps > 1 mon - missing data in a span greater than one month; 186SL092330094 Refernce - reference. 186SL092330095 186SL092330096 The following corrections are made to the hourly data 186SL092330097 prior to this assessment: 186SL092330098 1) Gaps or obviously wrong data points in a span less than 186SL092330099 25 hours are filled by the predicted tide method*. 186SL092330100 2) Timing errors of exact increments of an hour are corrected 186SL092330101 by shifting the data. 186SL092330102 3) Reference level shifts are only corrected after information 186SL092330103 from tide staff readings or comparative readings with a fixed 186SL092330104 bench mark are checked to verify that the shift was not a 186SL092330105 natural event. If comparative readings are missing or 186SL092330106 incomplete, comparisons of the data with nearby stations 186SL092330107 may warrant the adjustment of some obvious shifts. 186SL092330108 4) Data with unresolved datum shifts are not disseminated. 186SL092330109 However, if sufficient time spans of data are available before 186SL092330110 or after the year(s) with the unresolved shift(s), a subset of 186SL092330111 quality assured data is made available. Thus, the Span field 186SL092330112 in the Quality Assessment may not match the span of the 186SL092330113 distribution data set. As the questionable datum shifts are 186SL092330114 resolved, the data set will be updated. Although this policy 186SL092330115 adds some complexity, it allows more rapid dissemination of 186SL092330116 at least the quality assured years. 186SL092330117 186SL092330118 For each year, the following information is documented from 186SL092330119 the quality-controlled hourly data with dates given as the nth 186SL092330120 day of the year starting from 1 January: 186SL092330121 1) a Completeness Index (CI) based on the percentage of hours 186SL092330122 with available data, 186SL092330123 2) a list of gaps longer than a day, 186SL092330124 3) a summary of days with consecutive missing or obviously 186SL092330125 wrong data in a time span longer than 6 but less than 25 186SL092330126 hours that have been replaced, with hours in parentheses, and 186SL092330127 4) a summary of days with questionable fluctuations in the 186SL092330128 residual series. Fluctuations within the residuals are 186SL092330129 considered significant and are noted if they are greater than 186SL092330130 25 cm. This policy has changed slightly as of October 1992: 186SL092330131 only suspicious fluctuations due to obvious instrumentation 186SL092330132 problems are noted. Minor timing drifts are no longer 186SL092330133 included in the list of questionable days. 186SL092330134 186SL092330135 Note : If the predicted tides poorly model the observed heights 186SL092330136 due to the inability of the tidal analysis to completely resolv 186SL092330137 the non-linear shallow water effects, the residuals are not 186SL092330138 suitable for assessing the data quality. Instead, a subjective 186SL092330139 comment on the quality of the data is provided. 186SL092330140 186SL092330141 *The predicted tides are obtained with the use of a harmonic 186SL092330142 analysis program (Foreman, 1977) which is executed on a year 186SL092330143 of apparently good data for a given station. The Predicted 186SL092330144 Tide Method for filling gaps consists of statistically 186SL092330145 comparing the predicted tides to the observed data and 186SL092330146 shifting the predicted tides in time to correct for timing 186SL092330147 differences. Then the linear interpolation between hourly 186SL092330148 values at the end points of the gap in the residual series is 186SL092330149 added to the corresponding corrected predicted tide data to 186SL092330150 obtain interpolated values over the span of the gap. 186SL092330151 186SL092330152 Bloomfield, P., 1976. Fourier Analysis of Time Series: An 186SL092330153 Introduction. New York: John Wiley and Sons. pp 129-137. 186SL092330154 186SL092330155 Foreman, M., 1977. Manual For Tidal Height Analysis and 186SL092330156 Prediction. Institute of Ocean Sciences, Patricia Bay, 186SL092330157 Victoria B.C. Pacific Marine Science Report 77-10. 186SL092330158 186SL09236 19831 999999999999999999999999999999999999999999999999 186SL09236 19832 5946000 5962000 5924000 5910000 5911000 5898000 186SL09236 19841 58800209999999999999999999999999999999999999999 186SL09236 19842 999999999999999999999999999999999999999999999999