186SL0926150033201 203B 19840417 19851123 0350S 03224W 2 00000X 0000 MM 186SL0926250033201 Fer. de Nor.-B Brazil ORSTOM 186SL092630001 186SL092630002 QUALITY ASSESSMENT OF SEA LEVEL DATA 186SL092630003 by the 186SL092630004 TOGA SEA LEVEL CENTER/NATIONAL OCEANOGRAPHIC DATA CENTER 186SL092630005 JOINT ARCHIVE FOR SEA LEVEL 186SL092630006 186SL092630007Station : Fernando de Noronha-B Latitude: 03 49.7S 186SL092630008Country : Brazil Longitude: 032 24.2W 186SL092630009JASL # : 203B Time Meridian: 030W (GMT + 2) 186SL092630010GLOSS # : 198 TOGA #: A021 NODC #: 50033201 186SL092630011Contributor : ORSTOM 186SL092630012 LOP Museum 186SL092630013 43-45 rue Cuvier 186SL092630014 75231 Paris Cedex 05 186SL092630015 FRANCE 186SL092630016Originator : same 186SL092630017Original Data: digital 186SL092630018Instrmnt Type: Aanderaa WLR5 (bottom-mounted pressure gauge) 186SL092630019Digitzd Intvl: one hour 186SL092630020Present Data : Hourly, daily, and monthly values obtained by: 186SL092630021 Hourly : direct digitization, no filter 186SL092630022 Daily : 119-point convolution filter (Bloomfield, 1976) 186SL092630023 centered on noon applied to the hourly data 186SL092630024 with respective periods of the 95, 50, and 5% 186SL092630025 amplitude points at 124.0, 60.2, and 40.2 hours 186SL092630026 Monthly: Simple average of all daily values; calculated if 186SL092630027 7 or fewer days are missing 186SL092630028Span of data : 17 Apr 1984 - 23 Nov 1985 186SL092630029Gaps > 1 mon : none 186SL092630030Time Refernce: GMT (00-23 hours) Space-filler Flag :-9999 186SL092630031Units : millimeters Missing Data Flag :99999 186SL092630032Refernce Levl: Due to the nature of the bottom-mounted pressure 186SL092630033 gauges, no link could be established between the 186SL092630034 zero of the gauge values and fixed points on land. 186SL092630035 Also, tide staff observations or the like were 186SL092630036 unavailable. This series has no long-term 186SL092630037 reference level. 186SL092630038Comment : The depth of the instrument in the water was 186SL092630039 about 7.9 m. Techniques of data processing 186SL092630040 by the originator are discussed in the second 186SL092630041 reference below. 186SL092630042 186SL092630043 The original gauge was destroyed in June 1983 and 186SL092630044 a new gauge was installed in 1984 about a mile 186SL092630045 away. The original series is called Fernando de 186SL092630046 Noronha-A. 186SL092630047 186SL092630048 Due to the tendency for pressure gauge sensors 186SL092630049 to drift, it is beneficial for investigators 186SL092630050 to know the time span of each instrument 186SL092630051 deployment (time/date as yyyy/mm/dd/hh(GMT)): 186SL092630052 Series start stop 186SL092630053 203A 1982/11/07/19 - 1983/06/28/12 186SL092630054 203B 1984/04/17/15 - 1985/11/13/12 186SL092630055 186SL092630056 For more information: 186SL092630057 186SL092630058 Verstraete, J.M., 1988. Sea level variations in 186SL092630059 the tropical Atlantic. Time series of ocean 186SL092630060 measurements, Technical series, UNESCO,4,33-47. 186SL092630061 186SL092630062 Verstraete, J.M., 1992. Accuracy of shallow 186SL092630063 pressure gauges. Joint IAPSO-IOC Workshop on 186SL092630064 Sea Level Measurements and Quality Control, 186SL092630065 Paris, 12-13 October, 1992. IOC Workshop 186SL092630066 Report No. 81, UNESCO. pp. 70-76. 186SL092630067 186SL092630068 CI MISSING REPLACED GAPS QUESTIONABLE 186SL092630069YEAR (%) DATA OR BAD DATA FLUCTUATIONS 186SL092630070---- --- -------------------- --------------- -------------------- 186SL0926300711984 71 none none none 186SL0926300721985 87 none none none 186SL092630073 186SL092630074 QUALITY ASSESSMENT POLICY 186SL092630075 186SL092630076 The quality assessment is mostly based on the residuals 186SL092630077 (observed data minus predicted tides) of the hourly data. This 186SL092630078 assessment also applies to the daily and monthly data since 186SL092630079 they were derived from the quality-controlled hourly data. 186SL092630080 186SL092630081 The following abbreviations are used in the assessment: 186SL092630082 JASL - Joint Archive for Sea Level; GLOSS - Global Sea Level 186SL092630083 Observing System; TOGA - Tropical Ocean Global Atmosphere 186SL092630084 research program; NODC - National Oceanographic Data Center; 186SL092630085 Instrmnt - instrument; Digitzd Intvl - digitized interval; 186SL092630086 Gaps > 1 mon - missing data in a span greater than one month; 186SL092630087 Refernce - reference. 186SL092630088 186SL092630089 The following corrections are made to the hourly data 186SL092630090 prior to this assessment: 186SL092630091 1) Gaps or obviously wrong data points in a span less than 186SL092630092 25 hours are filled by the predicted tide method*. 186SL092630093 2) Timing errors of exact increments of an hour are corrected 186SL092630094 by shifting the data. 186SL092630095 3) Reference level shifts are only corrected after information 186SL092630096 from tide staff readings or comparative readings with a fixed 186SL092630097 bench mark are checked to verify that the shift was not a 186SL092630098 natural event. If comparative readings are missing or 186SL092630099 incomplete, comparisons of the data with nearby stations 186SL092630100 may warrant the adjustment of some obvious shifts. 186SL092630101 4) Data with unresolved datum shifts are not disseminated. 186SL092630102 However, if sufficient time spans of data are available before 186SL092630103 or after the year(s) with the unresolved shift(s), a subset of 186SL092630104 quality assured data is made available. Thus, the Span field 186SL092630105 in the Quality Assessment may not match the span of the 186SL092630106 distribution data set. As the questionable datum shifts are 186SL092630107 resolved, the data set will be updated. Although this policy 186SL092630108 adds some complexity, it allows more rapid dissemination of 186SL092630109 at least the quality assured years. 186SL092630110 186SL092630111 For each year, the following information is documented from 186SL092630112 the quality-controlled hourly data with dates given as the nth 186SL092630113 day of the year starting from 1 January: 186SL092630114 1) a Completeness Index (CI) based on the percentage of hours 186SL092630115 with available data, 186SL092630116 2) a list of gaps longer than a day, 186SL092630117 3) a summary of days with consecutive missing or obviously 186SL092630118 wrong data in a time span longer than 6 but less than 25 186SL092630119 hours that have been replaced, with hours in parentheses, and 186SL092630120 4) a summary of days with questionable fluctuations in the 186SL092630121 residual series. Fluctuations within the residuals are 186SL092630122 considered significant and are noted if they are greater than 186SL092630123 25 cm. This policy has changed slightly as of October 1992: 186SL092630124 only suspicious fluctuations due to obvious instrumentation 186SL092630125 problems are noted. Minor timing drifts are no longer 186SL092630126 included in the list of questionable days. 186SL092630127 186SL092630128 Note : If the predicted tides poorly model the observed heights 186SL092630129 due to the inability of the tidal analysis to completely resolv 186SL092630130 the non-linear shallow water effects, the residuals are not 186SL092630131 suitable for assessing the data quality. Instead, a subjective 186SL092630132 comment on the quality of the data is provided. 186SL092630133 186SL092630134 *The predicted tides are obtained with the use of a harmonic 186SL092630135 analysis program (Foreman, 1977) which is executed on a year 186SL092630136 of apparently good data for a given station. The Predicted 186SL092630137 Tide Method for filling gaps consists of statistically 186SL092630138 comparing the predicted tides to the observed data and 186SL092630139 shifting the predicted tides in time to correct for timing 186SL092630140 differences. Then the linear interpolation between hourly 186SL092630141 values at the end points of the gap in the residual series is 186SL092630142 added to the corresponding corrected predicted tide data to 186SL092630143 obtain interpolated values over the span of the gap. 186SL092630144 186SL092630145 Bloomfield, P., 1976. Fourier Analysis of Time Series: An 186SL092630146 Introduction. New York: John Wiley and Sons. pp 129-137. 186SL092630147 186SL092630148 Foreman, M., 1977. Manual For Tidal Height Analysis and 186SL092630149 Prediction. Institute of Ocean Sciences, Patricia Bay, 186SL092630150 Victoria B.C. Pacific Marine Science Report 77-10. 186SL092630151 186SL09266 19841 99999999999999999999999999999999 7867000 7897000 186SL09266 19842 7923000 7923000 7910000 7924000 7914000 7897000 186SL09266 19851 7893000 7879000 7893000 7862000 7865000 7854000 186SL09266 19852 7857000 7908000 7896000 78760009999999999999999