186SL0861171026401 216A 19900710 19901113 1652N 02459W 2 00000R 0000 MM 186SL0861271026401 Porto Grande Portugal Inst. Hidro. Marinha 186SL086130001 186SL086130002 QUALITY ASSESSMENT OF SEA LEVEL DATA 186SL086130003 by the 186SL086130004 TOGA SEA LEVEL CENTER/NATIONAL OCEANOGRAPHIC DATA CENTER 186SL086130005 JOINT ARCHIVE FOR SEA LEVEL 186SL086130006 186SL086130007Station : Porto Grande,Cape Verde Latitude: 16 52.0N 186SL086130008Country : Portugal Longitude: 024 59.0W 186SL086130009JASL # : 216A Time Meridian: 015W (GMT - 1 hr) 186SL086130010GLOSS # : 254 TOGA #: A023 NODC #: 71026401 186SL086130011Contributor : Instituto Hidrografico de Marinha 186SL086130012 Rua das Trinas, 49 186SL086130013 P-1296 186SL086130014 Lisboa Codex 186SL086130015 PORTUGAL 186SL086130016Originator : same 186SL086130017Original Data: analog 186SL086130018Instrmnt Type: A.OTT R20T, float and stilling well 186SL086130019Digitzd Intvl: one hour 186SL086130020Present Data : Hourly, daily, and monthly values obtained by: 186SL086130021 Hourly : direct digitization, no filter 186SL086130022 Daily : 119-point convolution filter (Bloomfield, 1976) 186SL086130023 centered on noon applied to the hourly data 186SL086130024 with respective periods of the 95, 50, and 5% 186SL086130025 amplitude points at 124.0, 60.2, and 40.2 hours 186SL086130026 Monthly: Simple average of all daily values; calculated if 186SL086130027 7 or fewer days are missing 186SL086130028Span of data : 10 Jul 1990 - 13 Nov 1990 186SL086130029Gaps > 1 mon : none 186SL086130030Time Refernce: GMT (00-23 hours) Space-filler Flag :-9999 186SL086130031Units : millimeters Missing Data Flag :99999 186SL086130032Refernce Levl: The data have been linked to tide staff zero 186SL086130033 and fixed bench marks by the originators. 186SL086130034Comment : No obvious problems were noted in the hourly 186SL086130035 or daily data. However, due to the short span, 186SL086130036 the data are not in the final archive. 186SL086130037 186SL086130038 CI MISSING REPLACED GAPS QUESTIONABLE 186SL086130039YEAR (%) DATA OR BAD DATA FLUCTUATIONS 186SL086130040---- --- -------------------- --------------- -------------------- 186SL0861300411990 34 none none none 186SL086130042 186SL086130043 QUALITY ASSESSMENT POLICY 186SL086130044 186SL086130045 The quality assessment is mostly based on the residuals 186SL086130046 (observed data minus predicted tides) of the hourly data. This 186SL086130047 assessment also applies to the daily and monthly data since 186SL086130048 they were derived from the quality-controlled hourly data. 186SL086130049 186SL086130050 The following abbreviations are used in the assessment: 186SL086130051 JASL - Joint Archive for Sea Level; GLOSS - Global Sea Level 186SL086130052 Observing System; TOGA - Tropical Ocean Global Atmosphere 186SL086130053 research program; NODC - National Oceanographic Data Center; 186SL086130054 Instrmnt - instrument; Digitzd Intvl - digitized interval; 186SL086130055 Gaps > 1 mon - missing data in a span greater than one month; 186SL086130056 Refernce - reference. 186SL086130057 186SL086130058 The following corrections are made to the hourly data 186SL086130059 prior to this assessment: 186SL086130060 1) Gaps or obviously wrong data points in a span less than 186SL086130061 25 hours are filled by the predicted tide method*. 186SL086130062 2) Timing errors of exact increments of an hour are corrected 186SL086130063 by shifting the data. 186SL086130064 3) Reference level shifts are only corrected after information 186SL086130065 from tide staff readings or comparative readings with a fixed 186SL086130066 bench mark are checked to verify that the shift was not a 186SL086130067 natural event. If comparative readings are missing or 186SL086130068 incomplete, comparisons of the data with nearby stations 186SL086130069 may warrant the adjustment of some obvious shifts. 186SL086130070 4) Data with unresolved datum shifts are not disseminated. 186SL086130071 However, if sufficient time spans of data are available before 186SL086130072 or after the year(s) with the unresolved shift(s), a subset of 186SL086130073 quality assured data is made available. Thus, the Span field 186SL086130074 in the Quality Assessment may not match the span of the 186SL086130075 distribution data set. As the questionable datum shifts are 186SL086130076 resolved, the data set will be updated. Although this policy 186SL086130077 adds some complexity, it allows more rapid dissemination of 186SL086130078 at least the quality assured years. 186SL086130079 186SL086130080 For each year, the following information is documented from 186SL086130081 the quality-controlled hourly data with dates given as the nth 186SL086130082 day of the year starting from 1 January: 186SL086130083 1) a Completeness Index (CI) based on the percentage of hours 186SL086130084 with available data, 186SL086130085 2) a list of gaps longer than a day, 186SL086130086 3) a summary of days with consecutive missing or obviously 186SL086130087 wrong data in a time span longer than 6 but less than 25 186SL086130088 hours that have been replaced, with hours in parentheses, and 186SL086130089 4) a summary of days with questionable fluctuations in the 186SL086130090 residual series. Fluctuations within the residuals are 186SL086130091 considered significant and are noted if they are greater than 186SL086130092 25 cm. This policy has changed slightly as of October 1992: 186SL086130093 only suspicious fluctuations due to obvious instrumentation 186SL086130094 problems are noted. Minor timing drifts are no longer 186SL086130095 included in the list of questionable days. 186SL086130096 186SL086130097 Note : If the predicted tides poorly model the observed heights 186SL086130098 due to the inability of the tidal analysis to completely resolv 186SL086130099 the non-linear shallow water effects, the residuals are not 186SL086130100 suitable for assessing the data quality. Instead, a subjective 186SL086130101 comment on the quality of the data is provided. 186SL086130102 186SL086130103 *The predicted tides are obtained with the use of a harmonic 186SL086130104 analysis program (Foreman, 1977) which is executed on a year 186SL086130105 of apparently good data for a given station. The Predicted 186SL086130106 Tide Method for filling gaps consists of statistically 186SL086130107 comparing the predicted tides to the observed data and 186SL086130108 shifting the predicted tides in time to correct for timing 186SL086130109 differences. Then the linear interpolation between hourly 186SL086130110 values at the end points of the gap in the residual series is 186SL086130111 added to the corresponding corrected predicted tide data to 186SL086130112 obtain interpolated values over the span of the gap. 186SL086130113 186SL086130114 Bloomfield, P., 1976. Fourier Analysis of Time Series: An 186SL086130115 Introduction. New York: John Wiley and Sons. pp 129-137. 186SL086130116 186SL086130117 Foreman, M., 1977. Manual For Tidal Height Analysis and 186SL086130118 Prediction. Institute of Ocean Sciences, Patricia Bay, 186SL086130119 Victoria B.C. Pacific Marine Science Report 77-10. 186SL086130120 186SL08616 19901 999999999999999999999999999999999999999999999999 186SL08616 19902 99999999 856000 847000 8730009999999999999999