186SL0876112091101 136A 19830101 19901231 2127N 09150E 2 00000R 0000 MM 186SL0876212091101 Cox's Bazaar Bangladesh BIWTA 186SL087630001 186SL087630002 QUALITY ASSESSMENT OF SEA LEVEL DATA 186SL087630003 by the 186SL087630004 TOGA SEA LEVEL CENTER/NATIONAL OCEANOGRAPHIC DATA CENTER 186SL087630005 JOINT ARCHIVE FOR SEA LEVEL 186SL087630006 186SL087630007Station : Cox's Bazaar Latitude: 21 27.0N 186SL087630008Country : Bangladesh Longitude: 091 50.0E 186SL087630009JASL # : 136A Time Meridian: 090E (GMT + 6 hr) 186SL087630010GLOSS # : none TOGA #: none NODC #: 12091101 186SL087630011Contributor : Bangladesh Inland Water Transport Authority (BIWTA) 186SL087630012 Dept. of Hydrography 186SL087630013 141-143, Motijheel C/A 186SL087630014 Dhaka - 1000 186SL087630015 BANGLADESH 186SL087630016Originator : same 186SL087630017Original Data: analog 186SL087630018Instrmnt Type: float and well type gauge (Munro) 186SL087630019Digitzd Intvl: hourly 186SL087630020Present Data : Hourly, daily, and monthly values obtained by: 186SL087630021 Hourly : original data are hourly 186SL087630022 Daily : 119-point convolution filter (Bloomfield, 1976) 186SL087630023 centered on noon applied to the hourly data 186SL087630024 with respective periods of the 95, 50, and 5% 186SL087630025 amplitude points at 124.0, 60.2, and 40.2 hours 186SL087630026 Monthly: Simple average of all daily values; calculated if 186SL087630027 7 or fewer days are missing 186SL087630028Span of data : 01 Jan 1977 - 31 Dec 1990 186SL087630029Gaps > 1 mon : 22 Nov 1979 - 31 Dec 1979 186SL087630030Time Refernce: GMT (hours 00-23) Space-filler Flag :-9999 186SL087630031Units : millimeters Missing Data Flag :99999 186SL087630032Refernce Levl: The sea level heights are referred to the zero 186SL087630033 point assigned to the tide staff. Bench mark 186SL087630034 information is available upon request from BIWTA. 186SL087630035 Level shifts were identified in the series and 186SL087630036 adjusted as follows for a short time segment: 186SL087630037 value added 186SL087630038 period (hour)day/month/year to original(mm) 186SL087630039 ----------------------------- --------------- 186SL087630040 (18)22/10/1984-(16)31/12/1984 -250 186SL087630041 This adjustment is uncertain to a few cm. 186SL087630042Comment : The hourly residuals suggest a level shift on 186SL087630043 24 Sep 1979 of about +20 cm. The daily difference 186SL087630044 plot with Hiron Point also shows this suspicious 186SL087630045 feature. Other level jumps appear on 22 July 1980 186SL087630046 (about -40 cm), 1 Dec 1980 (about +20 cm), and 186SL087630047 2 Oct 1982 (-20 cm). These features are under 186SL087630048 investigation by the originators. The following 186SL087630049 periods contain a substantial amount of interpol- 186SL087630050 ation of 2-5 hour gaps occurring in succession 186SL087630051 (day/month/year): 04/06/1980-27/06/1980; 186SL087630052 01/12/1981-10/07/1983; 19/09/1985-24/09/1985; 186SL087630053 10/03/1986-06/04/1986; 01/05/1987-31/12/1990. 186SL087630054 The interpolated short gaps do not appear to 186SL087630055 contaminate the low-frequency information. 186SL087630056 The hourly residuals contain large periodic 186SL087630057 fluctuations. It is not clear whether this is 186SL087630058 due to phase shifts in the timing of the gauge or 186SL087630059 due to the inability of the tidal analysis to 186SL087630060 completely resolve all the tidal constituents at 186SL087630061 this shallow water site. 186SL087630062 186SL087630063 CI MISSING REPLACED GAPS QUESTIONABLE 186SL087630064YEAR (%) DATA OR BAD DATA FLUCTUATIONS 186SL087630065---- --- -------------------- --------------- -------------------- 186SL0876300661977 98 55-63 none see comment above 186SL0876300671978 98 175-181 none see comment above 186SL0876300681979 89 326-365 none see comment above 186SL0876300691980 100 none none see comment above 186SL0876300701981 100 none none see comment above 186SL0876300711982 100 none none see comment above 186SL0876300721983 100 none (18)364-(17)365 see comment above 186SL0876300731984 100 none none see comment above 186SL0876300741985 100 none none see comment above 186SL0876300751986 87 29-34,58-62,85-90, none see comment above 186SL087630076 120-125,148-153,176- 186SL087630077 181,211-216,239-244, 186SL087630078 302-307,330-335 186SL0876300791987 100 none none see comment above 186SL0876300801988 100 none none see comment above 186SL0876300811989 98 133-141 none see comment above 186SL0876300821990 96 98-112,365 none see comment above 186SL087630083 186SL087630084 QUALITY ASSESSMENT POLICY 186SL087630085 186SL087630086 The quality assessment is mostly based on the residuals 186SL087630087 (observed data minus predicted tides) of the hourly data. This 186SL087630088 assessment also applies to the daily and monthly data since 186SL087630089 they were derived from the quality-controlled hourly data. 186SL087630090 186SL087630091 The following abbreviations are used in the assessment: 186SL087630092 JASL - Joint Archive for Sea Level; GLOSS - Global Sea Level 186SL087630093 Observing System; TOGA - Tropical Ocean Global Atmosphere 186SL087630094 research program; NODC - National Oceanographic Data Center; 186SL087630095 Instrmnt - instrument; Digitzd Intvl - digitized interval; 186SL087630096 Gaps > 1 mon - missing data in a span greater than one month; 186SL087630097 Refernce - reference. 186SL087630098 186SL087630099 The following corrections are made to the hourly data 186SL087630100 prior to this assessment: 186SL087630101 1) Gaps or obviously wrong data points in a span less than 186SL087630102 25 hours are filled by the predicted tide method*. 186SL087630103 2) Timing errors of exact increments of an hour are corrected 186SL087630104 by shifting the data. 186SL087630105 3) Reference level shifts are only corrected after information 186SL087630106 from tide staff readings or comparative readings with a fixed 186SL087630107 bench mark are checked to verify that the shift was not a 186SL087630108 natural event. If comparative readings are missing or 186SL087630109 incomplete, comparisons of the data with nearby stations 186SL087630110 may warrant the adjustment of some obvious shifts. 186SL087630111 4) Data with unresolved datum shifts are not disseminated. 186SL087630112 However, if sufficient time spans of data are available before 186SL087630113 or after the year(s) with the unresolved shift(s), a subset of 186SL087630114 quality assured data is made available. Thus, the Span field 186SL087630115 in the Quality Assessment may not match the span of the 186SL087630116 distribution data set. As the questionable datum shifts are 186SL087630117 resolved, the data set will be updated. Although this policy 186SL087630118 adds some complexity, it allows more rapid dissemination of 186SL087630119 at least the quality assured years. 186SL087630120 186SL087630121 For each year, the following information is documented from 186SL087630122 the quality-controlled hourly data with dates given as the nth 186SL087630123 day of the year starting from 1 January: 186SL087630124 1) a Completeness Index (CI) based on the percentage of hours 186SL087630125 with available data, 186SL087630126 2) a list of gaps longer than a day, 186SL087630127 3) a summary of days with consecutive missing or obviously 186SL087630128 wrong data in a time span longer than 6 but less than 25 186SL087630129 hours that have been replaced, with hours in parentheses, and 186SL087630130 4) a summary of days with questionable fluctuations in the 186SL087630131 residual series. Fluctuations within the residuals are 186SL087630132 considered significant and are noted if they are greater than 186SL087630133 25 cm. This policy has changed slightly as of October 1992: 186SL087630134 only suspicious fluctuations due to obvious instrumentation 186SL087630135 problems are noted. Minor timing drifts are no longer 186SL087630136 included in the list of questionable days. 186SL087630137 186SL087630138 Note : If the predicted tides poorly model the observed heights 186SL087630139 due to the inability of the tidal analysis to completely resolv 186SL087630140 the non-linear shallow water effects, the residuals are not 186SL087630141 suitable for assessing the data quality. Instead, a subjective 186SL087630142 comment on the quality of the data is provided. 186SL087630143 186SL087630144 *The predicted tides are obtained with the use of a harmonic 186SL087630145 analysis program (Foreman, 1977) which is executed on a year 186SL087630146 of apparently good data for a given station. The Predicted 186SL087630147 Tide Method for filling gaps consists of statistically 186SL087630148 comparing the predicted tides to the observed data and 186SL087630149 shifting the predicted tides in time to correct for timing 186SL087630150 differences. Then the linear interpolation between hourly 186SL087630151 values at the end points of the gap in the residual series is 186SL087630152 added to the corresponding corrected predicted tide data to 186SL087630153 obtain interpolated values over the span of the gap. 186SL087630154 186SL087630155 Bloomfield, P., 1976. Fourier Analysis of Time Series: An 186SL087630156 Introduction. New York: John Wiley and Sons. pp 129-137. 186SL087630157 186SL087630158 Foreman, M., 1977. Manual For Tidal Height Analysis and 186SL087630159 Prediction. Institute of Ocean Sciences, Patricia Bay, 186SL087630160 Victoria B.C. Pacific Marine Science Report 77-10. 186SL087630161 186SL08766 19831 1470000 1445000 1635000 1781000 1919000 2133000 186SL08766 19832 2157000 2302000 2111000 2070000 2256000 1827000 186SL08766 19841 1744000 1640000 1734000 1866000 2155000 2471000 186SL08766 19842 2336000 2383000 2213000 2199000 1836000 1790000 186SL08766 19851 1468000 1497000 1722000 1770000 2039000 2361000 186SL08766 19852 2339000 2287000 2136000 2171000 2029000 1827000 186SL08766 19861 1577030 147305099999999 17860109999999999999999 186SL08766 19862 238402099999999 2152010 206803099999999 1741010 186SL08766 19871 1624000 1658000 1644000 1833000 2028000 2316000 186SL08766 19872 2733000 2591000 2412000 2199000 2304000 2163000 186SL08766 19881 1922000 1863000 1820000 2029000 2295000 2521000 186SL08766 19882 2361000 2369000 2218000 2122000 2144000 1973000 186SL08766 19891 1794000 1823000 1802000 192500099999999 2335000 186SL08766 19892 2392000 2336000 2310000 2225000 2099000 1903000 186SL08766 19901 1811000 1783000 189700099999999 2178000 2554000 186SL08766 19902 2655000 2514000 2327000 2236000 2120000 1941010