186SL0897171053901 249A 19900501 19910829 1306N 05937W 2 00000R 0000 MM 186SL0897271053901 Bridgetown-A Barbados Gov. of Barbados 186SL089730001 186SL089730002 QUALITY ASSESSMENT OF SEA LEVEL DATA 186SL089730003 by the 186SL089730004 TOGA SEA LEVEL CENTER/NATIONAL OCEANOGRAPHIC DATA CENTER 186SL089730005 JOINT ARCHIVE FOR SEA LEVEL 186SL089730006 186SL089730007Station : Bridgetown-A Latitude: 13 06.0N 186SL089730008Country : Barbados Longitude: 059 37.0W 186SL089730009JASL # : 249A Time Meridian: 060W (GMT - 4 hr) 186SL089730010GLOSS # : none TOGA #: none NODC #: 71053901 186SL089730011Contributor : Government of Barbados 186SL089730012 Coastal Conservation Project Unit 186SL089730013 Oistins Government Complex, Oistins 186SL089730014 Christchurch 186SL089730015 BARBADOS 186SL089730016Originator : same 186SL089730017Original Data: digital 186SL089730018Instrmnt Type: Endeco YSI 1029SSM pressure transducer 186SL089730019Digitzd Intvl: variable 186SL089730020Present Data : Hourly, daily, and monthly values obtained by: 186SL089730021 Hourly : unconfirmed 186SL089730022 Daily : 119-point convolution filter (Bloomfield, 1976) 186SL089730023 centered on noon applied to the hourly data 186SL089730024 with respective periods of the 95, 50, and 5% 186SL089730025 amplitude points at 124.0, 60.2, and 40.2 hours 186SL089730026 Monthly: Simple average of all daily values; calculated if 186SL089730027 7 or fewer days are missing 186SL089730028Span of data : 01 May 1990 - 29 Aug 1991 186SL089730029Gaps > 1 mon : 01 Jul 1990 - 02 Aug 1990 186SL089730030Time Refernce: GMT (hours 00-23) Space-filler Flag :-9999 186SL089730031Units : millimeters Missing Data Flag :99999 186SL089730032Refernce Levl: The sea level heights are referred to the recorder 186SL089730033 zero datum. This zero datum is located 1.62 m 186SL089730034 below the Lamont datum which is the reference 186SL089730035 datum used for all local bench mark surveys, which 186SL089730036 are available upon request from the originators. 186SL089730037Comment : The daily and monthly means do not reveal any 186SL089730038 obvious reference level shifts. However, there 186SL089730039 appears to be a drift in the sensor from roughly 186SL089730040 mid-August 1991 to the end of the record. The 186SL089730041 timing of the hourly values appears to be good. 186SL089730042 186SL089730043 CI MISSING REPLACED GAPS QUESTIONABLE 186SL089730044YEAR (%) DATA OR BAD DATA FLUCTUATIONS 186SL089730045---- --- -------------------- --------------- -------------------- 186SL0897300461990 57 129-131,182-214, (02)123-(13)123 none 186SL089730047 278-279 186SL0897300481991 65 57-60 none none 186SL089730049 186SL089730050 QUALITY ASSESSMENT POLICY 186SL089730051 186SL089730052 The quality assessment is mostly based on the residuals 186SL089730053 (observed data minus predicted tides) of the hourly data. This 186SL089730054 assessment also applies to the daily and monthly data since 186SL089730055 they were derived from the quality-controlled hourly data. 186SL089730056 186SL089730057 The following abbreviations are used in the assessment: 186SL089730058 JASL - Joint Archive for Sea Level; GLOSS - Global Sea Level 186SL089730059 Observing System; TOGA - Tropical Ocean Global Atmosphere 186SL089730060 research program; NODC - National Oceanographic Data Center; 186SL089730061 Instrmnt - instrument; Digitzd Intvl - digitized interval; 186SL089730062 Gaps > 1 mon - missing data in a span greater than one month; 186SL089730063 Refernce - reference. 186SL089730064 186SL089730065 The following corrections are made to the hourly data 186SL089730066 prior to this assessment: 186SL089730067 1) Gaps or obviously wrong data points in a span less than 186SL089730068 25 hours are filled by the predicted tide method*. 186SL089730069 2) Timing errors of exact increments of an hour are corrected 186SL089730070 by shifting the data. 186SL089730071 3) Reference level shifts are only corrected after information 186SL089730072 from tide staff readings or comparative readings with a fixed 186SL089730073 bench mark are checked to verify that the shift was not a 186SL089730074 natural event. If comparative readings are missing or 186SL089730075 incomplete, comparisons of the data with nearby stations 186SL089730076 may warrant the adjustment of some obvious shifts. 186SL089730077 4) Data with unresolved datum shifts are not disseminated. 186SL089730078 However, if sufficient time spans of data are available before 186SL089730079 or after the year(s) with the unresolved shift(s), a subset of 186SL089730080 quality assured data is made available. Thus, the Span field 186SL089730081 in the Quality Assessment may not match the span of the 186SL089730082 distribution data set. As the questionable datum shifts are 186SL089730083 resolved, the data set will be updated. Although this policy 186SL089730084 adds some complexity, it allows more rapid dissemination of 186SL089730085 at least the quality assured years. 186SL089730086 186SL089730087 For each year, the following information is documented from 186SL089730088 the quality-controlled hourly data with dates given as the nth 186SL089730089 day of the year starting from 1 January: 186SL089730090 1) a Completeness Index (CI) based on the percentage of hours 186SL089730091 with available data, 186SL089730092 2) a list of gaps longer than a day, 186SL089730093 3) a summary of days with consecutive missing or obviously 186SL089730094 wrong data in a time span longer than 6 but less than 25 186SL089730095 hours that have been replaced, with hours in parentheses, and 186SL089730096 4) a summary of days with questionable fluctuations in the 186SL089730097 residual series. Fluctuations within the residuals are 186SL089730098 considered significant and are noted if they are greater than 186SL089730099 25 cm. This policy has changed slightly as of October 1992: 186SL089730100 only suspicious fluctuations due to obvious instrumentation 186SL089730101 problems are noted. Minor timing drifts are no longer 186SL089730102 included in the list of questionable days. 186SL089730103 186SL089730104 Note : If the predicted tides poorly model the observed heights 186SL089730105 due to the inability of the tidal analysis to completely resolv 186SL089730106 the non-linear shallow water effects, the residuals are not 186SL089730107 suitable for assessing the data quality. Instead, a subjective 186SL089730108 comment on the quality of the data is provided. 186SL089730109 186SL089730110 *The predicted tides are obtained with the use of a harmonic 186SL089730111 analysis program (Foreman, 1977) which is executed on a year 186SL089730112 of apparently good data for a given station. The Predicted 186SL089730113 Tide Method for filling gaps consists of statistically 186SL089730114 comparing the predicted tides to the observed data and 186SL089730115 shifting the predicted tides in time to correct for timing 186SL089730116 differences. Then the linear interpolation between hourly 186SL089730117 values at the end points of the gap in the residual series is 186SL089730118 added to the corresponding corrected predicted tide data to 186SL089730119 obtain interpolated values over the span of the gap. 186SL089730120 186SL089730121 Bloomfield, P., 1976. Fourier Analysis of Time Series: An 186SL089730122 Introduction. New York: John Wiley and Sons. pp 129-137. 186SL089730123 186SL089730124 Foreman, M., 1977. Manual For Tidal Height Analysis and 186SL089730125 Prediction. Institute of Ocean Sciences, Patricia Bay, 186SL089730126 Victoria B.C. Pacific Marine Science Report 77-10. 186SL089730127 186SL08976 19901 99999999999999999999999999999999 1991040 1949000 186SL08976 19902 99999999 1911020 1904000 1873020 1866000 1866000 186SL08976 19911 1782000 1819030 1957010 1944000 2046000 2106000 186SL08976 19912 2219000 237902099999999999999999999999999999999