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Sea Level Measurement and InterpretationAPPENDIX I.GLOSS Requirements for Tide Gauges(update from the third edition of the manual)The aim of any tide gauge recording should be to operatea gauge which is accurate to better than 1 cm atall times; i.e. in all conditions of tide, waves, currents,weather etc. This requires dedicated attention to gaugemaintenance and data quality control. In brief, the majorrequirements for GLOSS stations are (IOC, 1997):• A sampling of sea level, averaged over a period longenough to avoid aliasing from waves, at intervals oftypically 6 or 15 minutes, or even 1 minute or less ifthe instrument is to be used also for tsunami warning(IOC 1997 states: ‘but in all circumstances theminimum sampling interval should be one hour’,which these days is an insufficient sampling formost agencies);• Gauge timing be compatible with level accuracy,which means a timing accuracy better than oneminute (and in practice, to seconds or better, withelectronic gauges);• Measurements must be made relative to a fixed andpermanent local tide gauge bench mark (TGBM).This should be connected to a number of auxiliarymarks to guard against its movement or destruction.Connections between the TGBM and thegauge zero should be made to an accuracy of a fewmillimetres at regular intervals (e.g. annually);• GLOSS gauges to be used for studies of long termtrends, ocean circulation and altimeter calibrationneed to be equipped with GPS receivers (andmonitored possible by other geodetic techniques)located as close to the gauge as possible;• The readings of individual sea levels should bemade with a target accuracy of 10 mm;• Gauge sites should, if possible, be equipped forrecording tsunami signals, implying that the site beequipped with a pressure sensor capable of 15-secondsor 1-minute sampling frequency, and possiblyfor recording wave conditions, implying 1-secondsampling frequency;• Gauge sites should be also equipped for automaticdata transmission to data centres by means of satellite,Internet etc., in addition to recording datalocally on site;• Sea level measurements should be accompanied byobservations of atmospheric pressure, and if possiblewinds and other environmental parameters,which are of direct relevance to the sea level dataanalysis.Regular (e.g. daily) inspection of data will informoperators when a gauge is malfunctioning, andlead to overall better long-term data sets. Datafrom gauges in polar or other remote locations willinevitably be inspected less frequently, unless satellitedata transmission can be installed. Similarly, datafrom the relatively few gauges recording only onpaper charts will be slow to reach centres for qualitycontrol; these must be considered priorities forupgrading to meet modern standards.Operators of gauges must always be aware of possiblesystematic jumps in sea level time-series whenone form of recording is replaced by a ‘better’one. All gauges have systematic errors, but thoseerrors will be irrelevant for time-series work if thesame technique is used throughout. New-technologygauges are, by definition, less well understoodthan old ones, and they must always be operatedalongside the older ones until sufficient experiencehas been acquired.52IOC <strong>Manual</strong>s and Guides No 14 vol IV
Sea Level Measurement and InterpretationAPPENDIX II.Previous volumes of the IOC <strong>Manual</strong>on Sea Level Measurement and InterpretationAny reader of the present Volume of the IOC <strong>Manual</strong> would do well to also read Volumes 1, 2 and 3. They werepublished some years ago (in 1985, 1994 and 2000, respectively), but do contain sections that are still of interest.The contents of Volume 3 are shown below. Copies of the three earlier volumes can be downloaded from www.pol.ac.uk/psmsl/manualsTable of Contents of <strong>Manual</strong> on Sea Level Measurement and Interpretation, v. III: Reappraisals and recommendationsas of the year 2000, IOC. <strong>Manual</strong>s and guides; 141. Introduction1.1 Historical Background1.2 Tide Gauges1.3 GLOSS Requirements1.4 Layout of Volume 32. Tide Gauge Technologies2.1 Acoustic Tide Gauges2.1.1 Acoustic Gauges with Sounding Tubes2.1.1.1 The NOAA NGWLMS System2.1.1.2 The Australian SEAFRAME System2.1.1.3 Other Users of Acoustic Sounding Tube Gauges and Calibration Comments2.1.1.4 Similar Hardware Available2.1.2 Acoustic Gauges in the Open Air2.1.2.1 Experience in Spain2.1.2.2 Experience in South Africa2.2 Pressure Sensor Tide Gauges2.2.1 Single Transducer Systems2.2.1.1 The Datum of a Single Transducer Pressure System2.2.2 Multiple Pressure Transducer Systems (‘B’ Gauges)2.2.3 Pressure Transducers in Stilling Wells2.2.4 Bubbler Pressure Gauges2.2.5 Bottom Mounted Pressure Gauges2.3 Float Gauges in Stilling Wells2.4 Radar Tide Gauges and Other New Technologies2.5 General Principles of Choice of a Tide Gauge Site2.6 Comments on Desirable Recording Frequency2.7 Synthesis of the Merits of Different Technologies and Recommendations3. Data Transmission Methods3.1 Introduction3.2 Satellite and Global Mobile Phone Data Links3.3 Packages Available within GLOSSIOC <strong>Manual</strong>s and Guides No 14 vol IV53
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