SOUTH AFRICAN NAVY HYDROGRAPHIC OFFICE

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SOUTH AFRICAN NAVYHYDROGRAPHIC OFFICE

• CREATED BY RUTH FARRE

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SOUTH AFRICAN NAVYHYDROGRAPHIC OFFICE

• HISTORICAL SUMMARY
• PRESENT SITUATION
• SRD TIDE GAUGE
• KALESTO RADAR TIDE GAUGE
• FUTURE PROSPECTS

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HISTORICAL SUMMARY

• SAN HO began installing own float- actuated
  KENT gauges in 1958.
• By the mid 1980s the tide gauge (TG) network was
  aging and spares were becoming difficult to come
  by. Replacement of the network was urgently
  needed on a significant scale.
• A project with CSIR resulted in the development
  of a modern Acoustic Water Level Recorder.
• Came into service in 1990
• Total of 8 installed throughout RSA and Namibia
• These gauges were a total failure. They were
  erratic, difficult to tune and grossly
  inaccurate.
• Virtually no usable data was obtained
• These gauges were abandoned between 1996 and 1998

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HISTORICAL SUMMARY

• Replacement gauges were tendered for, with SRD
  Acoustic Gauges meeting SAN HO and IMTs
  (Institute of Maritime Technology)
  specifications.
• Somewhat hurriedly installed in 1996, in tubes as
  per manufacturers recommendations.
• SRD data was unsatisfactory, independent study
  done
• Recalibration of SRD gauges and check calibration
  in situ devised.
• Performance has subsequently been just acceptable
  but not to the standard required.
• OTT KALESTO Radar Tide Gauge put on trial in
  2002 by the SAN HO and IMT.
• Performs with a high degree of accuracy and
  stability than encountered in the past.

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SOUTH AFRICAN NAVYHYDROGRAPHIC OFFICE

• HISTORICAL SUMMARY
• PRESENT SITUATION
• SRD TIDE GAUGE
• KALESTO RADAR TIDE GAUGE
• FUTURE PROSPECTS

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TIDAL STATIONS IN RSA
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PRESENT SITUATION

• There are 10 tidal stations throughout South
  Africa covering the West, East and Southern
  coast.
• PORT NOLLOTH ? SRD Acoustic Gauge
• SALDANHA ? SRD Acoustic Gauge
• CAPE TOWN ? SRD Acoustic Gauge
• SIMONS TOWN ? SRD Acoustic Gauge, KALESTO
  Radar, GPS
• MOSSEL BAY ? SRD Acoustic Gauge
• KNYSNA ? SRD Acoustic Gauge
• PORT ELIZABETH ? SRD Acoustic Gauge
• EAST LONDON ? SRD Acoustic Gauge
• DURBAN ? SRD Acoustic Gauge
• RICHARDS BAY ? KALESTO Radar, GPS
• (GPS IS OWNED AND OPPERATED BY HARTRAO -
  HARTEBEESHOEK RADIO ASTRONOMICAL OBSERVATORY)

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SOUTH AFRICAN NAVYHYDROGRAPHIC OFFICE

• HISTORICAL SUMMARY
• PRESENT SITUATION
• SRD TIDE GAUGE
• KALESTO RADAR TIDE GAUGE
• FUTURE PROSPECTS

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SRD TIDE GAUGE

• TECHNICAL DATA, The system is as follows
• Data logger, transducer, control box, junction
  box, modem telephone line. (Rather bulky)
• Measuring range ? 15 meters
• Measuring range ? selectable up to 30 min
• Averaging period ? between 1 and 32 measurements
• Acoustic frequency ? 50 kHz
• Powered by ? electricity, back-up lead battery
• Data dumped once a week via modem to office PC.

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SRD TIDE GAUGE

• Independent study with IMT showed
• Data errors due to temperature gradients formed
  in tubes
• Solution remove or modify existing tubes to
  maintain a well mixed air column around the
  transducer.
• Claimed accuracy of 0.05 by the manufacturers
  was not achieved
• no response to this by manufacturers.
• Solution post data processing after calibration
  in situ to establish each gauges individual
  calibration factors.
• In Situ calibration process devised
• Allows the following to be reliably established
  on site
• ABSOLUTE ACCURACY
• MEASUREMENT REPEATABILITY
• INSTRUMENT DATUM OFFSET
• RSA network calibrated and levelled to TG
  benchmark every 6 months.

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CALIBRATION OF SRD GAUGES
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SRD TIDE GAUGE

• Data has high spike density that has to be edited
  out by hand annually
• This is very unscientific, time consuming and
  human error comes into play.
• (Graphics to follow indicate this spike density.)

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GRAPHIC OF SRD ACTUAL VALUES18 FEBRUARY 2003 - 1
MARCH 2003
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GRAPHIC OF SRD ACTUAL VALUES11 MARCH 2003 - 17
MARCH 2003
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GRAPHIC OF SRD ACTUAL VALUES vs PREDICTED
VALUES11 MARCH 2003 - 17 MARCH 2003
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GRAPHIC OF SRD ACTUAL VALUES vs SRD PREDICTED
VALUES11 FEBRUARY 2003 - 31 MARCH 2003
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EFFECT OF LIGHTNING STRIKE ON SRD HARDWARE.
(LIGHTENING PROTECTION IS INADEQUATE FOR SOUTH
AFRICAN WEATHER SYSTEMS)
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SRD TIDE GAUGE

• Technical assistance is unsatisfactory
• Periodically the power supply has to be
  disconnected from the gauge for 30 seconds and
  then restored.
• This is the solution to the periodic
  unwillingness to download via modem
• This is becoming more and more frequent, and is
  creating considerable down time.
• The transducers are beginning to rust
• This is becoming worse and could be a reason for
  poor data quality.

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SOUTH AFRICAN NAVYHYDROGRAPHIC OFFICE

• HISTORICAL SUMMARY
• PRESENT SITUATION
• SRD TIDE GAUGE
• KALESTO RADAR TIDE GAUGE
• FUTURE PROSPECTS

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KALESTO RADAR GAUGE IN SITU
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KALESTO RADAR TIDE GAUGE

• On trial, under calibration ? Analysis of 1443
  readings (mean of 2.496)
• 81 of readings were within 2mm of the above mean
• 93 of readings were within 3mm of the above mean
• 97 of readings were within 5mm of the above mean
• TECHNICAL DATA, The system is as follows
• Data logger, sensor, modem telephone line.
• Measuring range ? 1.5 - 30 meters
• Averaging period ? 17 seconds (40 values,
  creating mean values)
• Sensor technology ? 24, 125 GHz, 5mW
• Powered by ? electricity, small battery
• Data dumped twice a week via modem to office PC.

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KALESTO RADAR GAUGEPLATFORM FOR EASY ACCESS TO
GAUGE DURING LEVELING AND CALIBRATION.
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KALESTO CABINET CONTENTS
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KALESTO RADAR TIDE GAUGE

• Independent study with IMT showed
• KALESTO performed consistently within the
  manufactures claimed accuracy parameters.
• Confirmed results achieved by SAN HO
• In Situ calibration process devised
• Allows the following to be reliably established
  on site
• ABSOLUTE ACCURACY
• MEASUREMENT REPEATABILITY
• INSTRUMENT DATUM OFFSET
• RSA network calibrated and levelled to TG
  benchmark every 6 months.

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CALIBRATION OF KALESTOAT LONG STAY.
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MEASUREMENTS OF THE KALESTO RADAR GAUGE

• FROM TOP OF BLACK BOX TO THE TRANSDUCER FACE
  (Tx) IS 0.400m

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CALIBRATING THE KALESTO RADAR GAUGE

• Example of a calculation for check calibration of
  radar gauge, if A 3.422m (known value)
• Av. A above CD Av B
• Av A MSL 3.422
• ? (D-B) 1.063
• less E to Tx - 0.400
• ? Ref Face MSL 4.085
• CD MSL - 1.015
• 5.100
• ? Ht of Tx 5.100m above CD
• ? readings _at_ short stay
• 5.100 - (2.750 - 0.400) 2.750m
• ? readings _at_ long stay
• 5.100 - (3.750 - 0.400) 1.750m

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KALESTO RADAR TIDE GAUGE

• Data has an extremely low spike density that has
  to be edited out by hand annually
• This is now a lot less time consuming and there
  is now less chance for human error comes into
  play.
• (Graphics to follow indicate this spike density.)
• Adequate lightening protection.
• Technical assistance is satisfactory.

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GRAPHIC OF SRD ACTUAL VALUES vs KALESTO ACTUAL
VALUES11 MARCH 2003 - 17 MARCH 2003
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GRAPHIC OF SRD ACTUAL VALUES vs KALESTO ACTUAL
VALUES18 FEBRUARY 2003 - 1 MARCH 2003
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GRAPHIC OF KALESTO ACTUAL VALUES vs SRD
PREDICTED VALUES.31 JULY 2003 - 10 AUGUST 2003
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KALESTO RADAR TIDE GAUGE

• Technical assistance is satisfactory
• Periodically the power supply has to be
  disconnected from the gauge for 30 seconds and
  then restored.
• This is the solution to the periodic
  unwillingness to download via modem
• This is becoming more and more frequent, and is
  creating considerable down time.
• The transducers are beginning to rust
• This is becoming worse and could be a reason for
  poor data quality.

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SOUTH AFRICAN NAVYHYDROGRAPHIC OFFICE

• HISTORICAL SUMMARY
• PRESENT SITUATION
• SRD TIDE GAUGE
• KALESTO RADAR TIDE GAUGE
• FUTURE PROSPECTS

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FUTURE PROSPECTS

• SAN HO intends to upgrade entire RSA network with
  the KALESTO Radar Tide Gauge
• upgrade will take place as budget permits
• Have two new gauges awaiting installation
• Port Nolloth (to get GPS as well)
• Port Elizabeth
• Will keep bast of SRD gauges installed for
  back-up and data quality checks.
• Proposal to install a gauge and GPS at Marion
  Island
• Fast Data to continue being sent to PSMSL and
  GLOSS.