186SL0771112064601 147A 19850101 19871231 2448N 06658E 2 00000R 0000 MM 186SL0771212064601 Karachi Pakistan Nat. Inst. of Ocean. 186SL077130001 186SL077130002 QUALITY ASSESSMENT OF SEA LEVEL DATA 186SL077130003 by the 186SL077130004 TOGA SEA LEVEL CENTER/NATIONAL OCEANOGRAPHIC DATA CENTER 186SL077130005 JOINT ARCHIVE FOR SEA LEVEL 186SL077130006 186SL077130007Station : Karachi Latitude: 24 48.0N 186SL077130008Country : Pakistan Longitude: 066 58.0E 186SL077130009JASL # : 147A Time Meridian: 075E (GMT + 5.0 hr) 186SL077130010GLOSS # : 030 TOGA #: I018 NODC #: 12064601 186SL077130011Contributor : Pakistan National Institute of Oceanography 186SL077130012 37 K. Block 6 P.E.C.H.S. 186SL077130013 Karachi, 29 PAKISTAN 186SL077130014Originator : same 186SL077130015Original Data: unconfirmed 186SL077130016Instrmnt Type: unconfirmed 186SL077130017Digitzd Intvl: unconfirmed 186SL077130018Present Data : Hourly, daily, and monthly values obtained by: 186SL077130019 Hourly : unconfirmed 186SL077130020 Daily : 119-point convolution filter (Bloomfield, 1976) 186SL077130021 centered on noon applied to the hourly data 186SL077130022 with respective periods of the 95, 50, and 5% 186SL077130023 amplitude points at 124.0, 60.2, and 40.2 hours 186SL077130024 Monthly: Simple average of all daily values; calculated if 186SL077130025 7 or fewer days are missing 186SL077130026Span of data : 01 Jan 1985 - 31 Dec 1987 186SL077130027Gaps > 1 mon : 02 Sep - 01 Oct 1985; 01 Nov - 04 Dec 1985 186SL077130028Time Refernce: GMT (hours 00-23) Space-filler Flag :-9999 186SL077130029Units : millimeters Missing Data Flag :99999 186SL077130030Refernce Levl: The sea level heights are referred to the zero 186SL077130031 point assigned to the tide staff. Bench mark 186SL077130032 information is available upon request from the 186SL077130033 contributors. 186SL077130034Comment : The daily and monthly means do not show any 186SL077130035 signs of reference level shifts or trends. 186SL077130036 Significant timing errors occur 01-15 Nov 1985 and 186SL077130037 01 Jul - 31 Dec 1987. These errors were not 186SL077130038 correctable because the shifts in the timing were 186SL077130039 not integer increments of an hour. The remaining 186SL077130040 periods contain questionable fluctuations in the 186SL077130041 residuals (hourly data minus predicted tides) due 186SL077130042 to either timing errors or the tidal analysis not 186SL077130043 being able to resolve all the harmonics components. 186SL077130044 186SL077130045 CI MISSING REPLACED GAPS QUESTIONABLE 186SL077130046YEAR (%) DATA OR BAD DATA FLUCTUATIONS 186SL077130047---- --- -------------------- --------------- -------------------- 186SL0771300481985 82 244-274,305-338 (03)042-(21)042 see comment above 186SL077130049 (04)128-(19)128 186SL077130050 (07)230-(23)230 186SL0771300511986 95 244-263 (01)070-(23)070 see comment above 186SL0771300521987 95 244-263 (01)118-(17)118 see comment above 186SL077130053 186SL077130054 QUALITY ASSESSMENT POLICY 186SL077130055 186SL077130056 The quality assessment is mostly based on the residuals 186SL077130057 (observed data minus predicted tides) of the hourly data. This 186SL077130058 assessment also applies to the daily and monthly data since 186SL077130059 they were derived from the quality-controlled hourly data. 186SL077130060 186SL077130061 The following abbreviations are used in the assessment: 186SL077130062 JASL - Joint Archive for Sea Level; GLOSS - Global Sea Level 186SL077130063 Observing System; TOGA - Tropical Ocean Global Atmosphere 186SL077130064 research program; NODC - National Oceanographic Data Center; 186SL077130065 Instrmnt - instrument; Digitzd Intvl - digitized interval; 186SL077130066 Gaps > 1 mon - missing data in a span greater than one month; 186SL077130067 Refernce - reference. 186SL077130068 186SL077130069 The following corrections are made to the hourly data 186SL077130070 prior to this assessment: 186SL077130071 1) Gaps or obviously wrong data points in a span less than 186SL077130072 25 hours are filled by the predicted tide method*. 186SL077130073 2) Timing errors of exact increments of an hour are corrected 186SL077130074 by shifting the data. 186SL077130075 3) Reference level shifts are only corrected after information 186SL077130076 from tide staff readings or comparative readings with a fixed 186SL077130077 bench mark are checked to verify that the shift was not a 186SL077130078 natural event. If comparative readings are missing or 186SL077130079 incomplete, comparisons of the data with nearby stations 186SL077130080 may warrant the adjustment of some obvious shifts. 186SL077130081 4) Data with unresolved datum shifts are not disseminated. 186SL077130082 However, if sufficient time spans of data are available before 186SL077130083 or after the year(s) with the unresolved shift(s), a subset of 186SL077130084 quality assured data is made available. Thus, the Span field 186SL077130085 in the Quality Assessment may not match the span of the 186SL077130086 distribution data set. As the questionable datum shifts are 186SL077130087 resolved, the data set will be updated. Although this policy 186SL077130088 adds some complexity, it allows more rapid dissemination of 186SL077130089 at least the quality assured years. 186SL077130090 186SL077130091 For each year, the following information is documented from 186SL077130092 the quality-controlled hourly data with dates given as the nth 186SL077130093 day of the year starting from 1 January: 186SL077130094 1) a Completeness Index (CI) based on the percentage of hours 186SL077130095 with available data, 186SL077130096 2) a list of gaps longer than a day, 186SL077130097 3) a summary of days with consecutive missing or obviously 186SL077130098 wrong data in a time span longer than 6 but less than 25 186SL077130099 hours that have been replaced, with hours in parentheses, and 186SL077130100 4) a summary of days with questionable fluctuations in the 186SL077130101 residual series. Fluctuations within the residuals are 186SL077130102 considered significant and are noted if they are greater than 186SL077130103 25 cm. This policy has changed slightly as of October 1992: 186SL077130104 only suspicious fluctuations due to obvious instrumentation 186SL077130105 problems are noted. Minor timing drifts are no longer 186SL077130106 included in the list of questionable days. 186SL077130107 186SL077130108 Note : If the predicted tides poorly model the observed heights 186SL077130109 due to the inability of the tidal analysis to completely resolv 186SL077130110 the non-linear shallow water effects, the residuals are not 186SL077130111 suitable for assessing the data quality. Instead, a subjective 186SL077130112 comment on the quality of the data is provided. 186SL077130113 186SL077130114 *The predicted tides are obtained with the use of a harmonic 186SL077130115 analysis program (Foreman, 1977) which is executed on a year 186SL077130116 of apparently good data for a given station. The Predicted 186SL077130117 Tide Method for filling gaps consists of statistically 186SL077130118 comparing the predicted tides to the observed data and 186SL077130119 shifting the predicted tides in time to correct for timing 186SL077130120 differences. Then the linear interpolation between hourly 186SL077130121 values at the end points of the gap in the residual series is 186SL077130122 added to the corresponding corrected predicted tide data to 186SL077130123 obtain interpolated values over the span of the gap. 186SL077130124 186SL077130125 Bloomfield, P., 1976. Fourier Analysis of Time Series: An 186SL077130126 Introduction. New York: John Wiley and Sons. pp 129-137. 186SL077130127 186SL077130128 Foreman, M., 1977. Manual For Tidal Height Analysis and 186SL077130129 Prediction. Institute of Ocean Sciences, Patricia Bay, 186SL077130130 Victoria B.C. Pacific Marine Science Report 77-10. 186SL077130131 186SL07716 19851 1516000 1537000 1598000 1660000 1732000 1696000 186SL07716 19852 1657000 163001099999999 151702099999999 1527040 186SL07716 19861 1442000 1470000 1574000 1617000 1585000 1701000 186SL07716 19862 1555000 154601099999999 1499000 1549000 1598000 186SL07716 19871 1576000 1741000 1736000 1741000 1834000 1872020 186SL07716 19872 1552000 154501099999999 1498000 1549000 1596010