Transcript Lab C 2007 Tidal Analysis Lab

Lab C 2007
Tidal Analysis Lab
Ian Church
[email protected]
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Purpose
• Perform Harmonic Analysis on 7 Tide
Stations (Each Person Assigned 1 Station)
– Run T_Tide to extract the Harmonic
Constituents
– Compare the Predicted Tides to Original
Tides
– Extract and Explain the Residuals
– Compare the Residuals from each Station
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SW Bay of Fundy
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Station Selection
Station
Name
St. John, NB
Rui
Eastport, ME
Lei
Cutler, ME
Paul
Yarmouth, NS
Tyson
North Head, NB
Clark
Digby, NS
Auke
Brier Island, NS
Faisal
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T_Tide
• T_Tide Harmonic Analysis Toolbox
– http://www.eos.ubc.ca/~rich/#T_Tide
• Set of Matlab routines that can be used
to perform classical harmonic analysis
• Read the reference:
R. Pawlowicz, B. Beardsley, and S. Lentz, "Classical tidal harmonic
analysis including error estimates in MATLAB using T_TIDE",
Computers and Geosciences 28 (2002), 929-937.
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Steps:
1. Download T_Tide
– See Lab Webpage for Link
2. Open Matlab and Change your
“Current Directory” to T_Tide Directory
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Using T_Tide
Explanation of each subroutine
Demo of
t_tide
program
Same as
Example
from Class
How to Run t_tide
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Using T_Tide
• Save Tide Time Series Data from Lab
Webpage
– For input: Only Need One
Column of Tide Data
– Need to know Sampling Interval
– Hours? Minutes?
2.247
2.456
2.678
2.885
…
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Using T_Tide
Input
• Tide Data
• Flags
– Interval
– Start Time
– Latitude
Output
• Structure
– Constituent Names
– Frequency
– Amplitude, Amp Error,
Phase, Phase Error
• Predicted Time Series
from Constituents
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Run T_Tide
[Tide_Struct, Pred_Out] =
t_tide(TideData,'interval',1/6, 'start
time', StartTime,'latitude',44+38/60);
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Run T_Tide
[Tide_Struct, Pred_Out] =
t_tide(TideData,'interval',1/6, 'start
time', StartTime,'latitude',44+38/60);
• Tide_Struct
– Structure (Constituent Names, Frequency, Amplitude, Amp Error,
Phase, Phase Error)
• Pred_Out
– Predicted Tide Time Series
– Same interval as input tide time series
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Run T_Tide
[Tide_Struct, Pred_Out] =
t_tide(TideData,'interval',1/6, 'start
time', StartTime,'latitude',44+38/60);
• TideData
– One Column of Water Level Observations
loaded into Matlab
– >> TideData =
load('North_Head15min.txt');
– Must know the time between observations
for next step
2.247
2.456
2.678
2.885
…
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Run T_Tide
[Tide_Struct, Pred_Out] =
t_tide(TideData,'interval',1/6, 'start
time', StartTime,'latitude',44+38/60);
• ‘interval’ is a fixed option in t_tide
– See >>help t_tide for explanation
– 1/6 is the interval between observations (units = hours)
• 15 minutes = 1/4
• 10 minutes = 1/6
• 6 minutes = 1/10
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Run T_Tide
[Tide_Struct, Pred_Out] =
t_tide(TideData,'interval',1/6,
'start time',StartTime,'latitude‘,44+38/60);
• ‘start time’ is a fixed option in t_tide
– See >>help t_tide for explanation
• StartTime is the start time of the tidal data series
• StartTime  Matlab Serial Date Number
– Ex: StartTime = datenum(2006,6,22,0,0,0)
• help datenum
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Start Time
• Need to be working in correct time zone
• Ensure that the time zone associated
with the observations is the same as the
one associated with the published
harmonic constituents (Bluefile of NOAA
website)
• Bluefile: +4 hours
• NOAA: GMT
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Run T_Tide
[Tide_Struct, Pred_Out] =
t_tide(TideData,'interval',1/6, 'start
time', StartTime,'latitude',44+38/60);
• For Nodal Corrections
– Helps resolve satellite constituents
– See Slide 34 from Nov 2nd lecture
– See T_Tide reference from lab webpage
• Latitude in Decimal Degrees for Station
Location
• Ex: 44 degrees 38 minutes  44+38/60 degrees
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Deliverables
(See Lab Webpage)
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