186SL0937171053901 249B 19930120 19940405 1306N 05937W 2 00000R 0000 MM 186SL0937271053901 Bridgetown-B Barbados Gov. of Barbados 186SL093730001 186SL093730002 QUALITY ASSESSMENT OF SEA LEVEL DATA 186SL093730003 by the 186SL093730004 TOGA SEA LEVEL CENTER/NATIONAL OCEANOGRAPHIC DATA CENTER 186SL093730005 JOINT ARCHIVE FOR SEA LEVEL 186SL093730006 186SL093730007Station : Bridgetown-B Latitude: 13 06.0N 186SL093730008Country : Barbados Longitude: 059 37.0W 186SL093730009JASL # : 249B Time Meridian: 060W (GMT - 4 hr) 186SL093730010GLOSS # : none TOGA #: none NODC #: 71053901 186SL093730011Contributor : Government of Barbados 186SL093730012 Coastal Conservation Project Unit 186SL093730013 Oistins Government Complex, Oistins 186SL093730014 Christchurch 186SL093730015 BARBADOS 186SL093730016Originator : same 186SL093730017Original Data: digital 186SL093730018Instrmnt Type: Endeco YSI 1029SSM pressure transducer 186SL093730019Digitzd Intvl: variable 186SL093730020Present Data : Hourly, daily, and monthly values obtained by: 186SL093730021 Hourly : unconfirmed 186SL093730022 Daily : 119-point convolution filter (Bloomfield, 1976) 186SL093730023 centered on noon applied to the hourly data 186SL093730024 with respective periods of the 95, 50, and 5% 186SL093730025 amplitude points at 124.0, 60.2, and 40.2 hours 186SL093730026 Monthly: Simple average of all daily values; calculated if 186SL093730027 7 or fewer days are missing 186SL093730028Span of data : 20 Jan 1993 - 05 Apr 1994 186SL093730029Gaps > 1 mon : 01 Aug 1993 - 04 Feb 1994 186SL093730030Time Refernce: GMT (hours 00-23) Space-filler Flag :-9999 186SL093730031Units : millimeters Missing Data Flag :99999 186SL093730032Refernce Levl: The sea level heights are referred to the recorder 186SL093730033 zero datum. This zero datum is located 1.62 m 186SL093730034 below the Lamont datum which is the reference 186SL093730035 datum used for all local bench mark surveys, which 186SL093730036 are available upon request from the originators. 186SL093730037 This series is separate from Bridgetown-A because 186SL093730038 of an apparent level shift of about 60 cm during 186SL093730039 the 1992 data gap. 186SL093730040Comment : The daily and monthly means do not reveal any 186SL093730041 obvious reference level shifts. 186SL093730042 186SL093730043 CI MISSING REPLACED GAPS QUESTIONABLE 186SL093730044YEAR (%) DATA OR BAD DATA FLUCTUATIONS 186SL093730045---- --- -------------------- --------------- -------------------- 186SL0937300461993 53 213-365 none 197-203 186SL0937300471994 16 1-35 none none 186SL093730048 186SL093730049 QUALITY ASSESSMENT POLICY 186SL093730050 186SL093730051 The quality assessment is mostly based on the residuals 186SL093730052 (observed data minus predicted tides) of the hourly data. This 186SL093730053 assessment also applies to the daily and monthly data since 186SL093730054 they were derived from the quality-controlled hourly data. 186SL093730055 186SL093730056 The following abbreviations are used in the assessment: 186SL093730057 JASL - Joint Archive for Sea Level; GLOSS - Global Sea Level 186SL093730058 Observing System; TOGA - Tropical Ocean Global Atmosphere 186SL093730059 research program; NODC - National Oceanographic Data Center; 186SL093730060 Instrmnt - instrument; Digitzd Intvl - digitized interval; 186SL093730061 Gaps > 1 mon - missing data in a span greater than one month; 186SL093730062 Refernce - reference. 186SL093730063 186SL093730064 The following corrections are made to the hourly data 186SL093730065 prior to this assessment: 186SL093730066 1) Gaps or obviously wrong data points in a span less than 186SL093730067 25 hours are filled by the predicted tide method*. 186SL093730068 2) Timing errors of exact increments of an hour are corrected 186SL093730069 by shifting the data. 186SL093730070 3) Reference level shifts are only corrected after information 186SL093730071 from tide staff readings or comparative readings with a fixed 186SL093730072 bench mark are checked to verify that the shift was not a 186SL093730073 natural event. If comparative readings are missing or 186SL093730074 incomplete, comparisons of the data with nearby stations 186SL093730075 may warrant the adjustment of some obvious shifts. 186SL093730076 4) Data with unresolved datum shifts are not disseminated. 186SL093730077 However, if sufficient time spans of data are available before 186SL093730078 or after the year(s) with the unresolved shift(s), a subset of 186SL093730079 quality assured data is made available. Thus, the Span field 186SL093730080 in the Quality Assessment may not match the span of the 186SL093730081 distribution data set. As the questionable datum shifts are 186SL093730082 resolved, the data set will be updated. Although this policy 186SL093730083 adds some complexity, it allows more rapid dissemination of 186SL093730084 at least the quality assured years. 186SL093730085 186SL093730086 For each year, the following information is documented from 186SL093730087 the quality-controlled hourly data with dates given as the nth 186SL093730088 day of the year starting from 1 January: 186SL093730089 1) a Completeness Index (CI) based on the percentage of hours 186SL093730090 with available data, 186SL093730091 2) a list of gaps longer than a day, 186SL093730092 3) a summary of days with consecutive missing or obviously 186SL093730093 wrong data in a time span longer than 6 but less than 25 186SL093730094 hours that have been replaced, with hours in parentheses, and 186SL093730095 4) a summary of days with questionable fluctuations in the 186SL093730096 residual series. Fluctuations within the residuals are 186SL093730097 considered significant and are noted if they are greater than 186SL093730098 25 cm. This policy has changed slightly as of October 1992: 186SL093730099 only suspicious fluctuations due to obvious instrumentation 186SL093730100 problems are noted. Minor timing drifts are no longer 186SL093730101 included in the list of questionable days. 186SL093730102 186SL093730103 Note : If the predicted tides poorly model the observed heights 186SL093730104 due to the inability of the tidal analysis to completely resolv 186SL093730105 the non-linear shallow water effects, the residuals are not 186SL093730106 suitable for assessing the data quality. Instead, a subjective 186SL093730107 comment on the quality of the data is provided. 186SL093730108 186SL093730109 *The predicted tides are obtained with the use of a harmonic 186SL093730110 analysis program (Foreman, 1977) which is executed on a year 186SL093730111 of apparently good data for a given station. The Predicted 186SL093730112 Tide Method for filling gaps consists of statistically 186SL093730113 comparing the predicted tides to the observed data and 186SL093730114 shifting the predicted tides in time to correct for timing 186SL093730115 differences. Then the linear interpolation between hourly 186SL093730116 values at the end points of the gap in the residual series is 186SL093730117 added to the corresponding corrected predicted tide data to 186SL093730118 obtain interpolated values over the span of the gap. 186SL093730119 186SL093730120 Bloomfield, P., 1976. Fourier Analysis of Time Series: An 186SL093730121 Introduction. New York: John Wiley and Sons. pp 129-137. 186SL093730122 186SL093730123 Foreman, M., 1977. Manual For Tidal Height Analysis and 186SL093730124 Prediction. Institute of Ocean Sciences, Patricia Bay, 186SL093730125 Victoria B.C. Pacific Marine Science Report 77-10. 186SL093730126 186SL09376 19931 99999999 1256000 1255000 1282000 1363000 1358000 186SL09376 19932 13650009999999999999999999999999999999999999999 186SL09376 19941 99999999 1217040 1236000999999999999999999999999 186SL09376 19942 999999999999999999999999999999999999999999999999