Phases from Sea Echo! Why Should I Care??Phases from Sea Echo! Why Should I Care??

Nearly ALL Current Map Velocity Errors Come from Inaccurate Bearing Estimates

Three failures or sources in antennas/cabling produceerrors if not accounted for in software:

Amplitude changes/drifts through antennas/cablingAmplitude changes/drifts through antennas/cabling Most common occurrence; amplitudes adjusted "on the fly"Most common occurrence; amplitudes adjusted "on the fly"

Phase changes usually are abrupt, not driftingPhase changes usually are abrupt, not drifting Occur rarely; we do not adjust phases "on the fly"Occur rarely; we do not adjust phases "on the fly"

Distortions to the shape of the element patterns from idealDistortions to the shape of the element patterns from ideal Due to local environmental near-field obstructionsDue to local environmental near-field obstructions Rarely change after installation unless local environment changesRarely change after installation unless local environment changes

Using Phase from Sea Echo as a DiagnosticUsing Phase from Sea Echo as a Diagnostic

Logs of Sea-Echo Normalized Phases Calculated Every 10 min Are Stored in Every Site's 'Stat_SITE_2004_08_01.rdt' Files, Viewed with 'DiagDisplay'

Loop signal's phases are normalized with respect to monopoleLoop signal's phases are normalized with respect to monopole

1st-order Bragg peaks used to calculate phase estimates1st-order Bragg peaks used to calculate phase estimates

Makes use of fact that phases in two lobes of given loop shouldMakes use of fact that phases in two lobes of given loop shoulddiffer by ~180°differ by ~180°

Two causes for changes with time in loop phase histories:Two causes for changes with time in loop phase histories:

Natural changes in sea state/wind direction -- not hardware relatedNatural changes in sea state/wind direction -- not hardware related Change or failure in system/hardwareChange or failure in system/hardware

Must Be Able to Tell the DifferenceMust Be Able to Tell the Difference

Don Barrick

What Does Phase Mean: Single Signal in Positive LobeWhat Does Phase Mean: Single Signal in Positive Lobe

Positive lobe max (blue) at 45°

Negative lobe max (red) at 225°

Coast cuts off at 20°

Sum all signals into both lobes

What is signal phase?What is signal phase? Signal is positiveSignal is positive So phase is 0°So phase is 0°

LandLandSeaSea

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What Does Phase Mean: Single Signal in Negative LobeWhat Does Phase Mean: Single Signal in Negative Lobe

Positive lobe max (blue) at 45°

Negative lobe (red) max at 225°

Signal enters negative lobe

Sum all signals into both lobes

What is signal phase?What is signal phase? Signal is negativeSignal is negative So phase is 180°So phase is 180°

LandLandSeaSea

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What Does Phase Mean: Equal Amp Sea Echo over 180° What Does Phase Mean: Equal Amp Sea Echo over 180°

Arrows show amp of receivedsignal

Positive voltages: blue arrows

Negative voltage: red arrows

Sum all signals into both lobes

What is signal phase, What is signal phase, VVtt?? Signal is positiveSignal is positive So phase is 0°So phase is 0°LandLand

SeaSea

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What Does Phase Mean: Wind Waves from South What Does Phase Mean: Wind Waves from South

Sn distribution strongest from

South

Positive voltages: blue arrows

Negative voltage: red arrows

Sum all signals into both lobes

What is signal phase, What is signal phase, VVtt?? Signal is negativeSignal is negative So phase is 180°So phase is 180°LandLand

SeaSea

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What Does Phase Mean: Wind Waves Decaying What Does Phase Mean: Wind Waves Decaying

Sn distribution from South are

beginning to weaken

Positive voltages: blue arrows

Negative voltage: red arrows

Sum all signals into both lobes

What is signal phase, What is signal phase, VVtt?? Signal amplitude is zeroSignal amplitude is zero So phase is indeterminateSo phase is indeterminate Like weather vane whenLike weather vane when

wind dies to zero, flops inwind dies to zero, flops inany directionany direction

LandLandSeaSea

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What 'Phase Stability' Due to Sea State Depends on:What 'Phase Stability' Due to Sea State Depends on:

Both Bragg peaksBoth Bragg peaks Where advancing is stronger, receding is weakerWhere advancing is stronger, receding is weaker Either can dominate in phase determination depending on wind waveEither can dominate in phase determination depending on wind wave

direction with respect to that loop lobesdirection with respect to that loop lobes

Angle subtended by coastlineAngle subtended by coastline As sea view approaches 360°, phase becomes indeterminateAs sea view approaches 360°, phase becomes indeterminate For coastline angles < 180°, phase is usually stable at least forFor coastline angles < 180°, phase is usually stable at least for

one of the loopsone of the loops

One of loops will normally show stable phasesOne of loops will normally show stable phases Dominant wind/wave direction will be along that loop's seaward lobeDominant wind/wave direction will be along that loop's seaward lobe Other lobe's phase will often vary when sea state changes directionOther lobe's phase will often vary when sea state changes direction

In practice, phases will almost never be 0° or 180° because ofIn practice, phases will almost never be 0° or 180° because of Differential phase shifts in monopole and loop channelsDifferential phase shifts in monopole and loop channels Phase 'Phase 'jumpsjumps' should, however, be ~180° unless very distorted pattern' should, however, be ~180° unless very distorted pattern

When Are Phases Unstable or Jump Due to HardwareWhen Are Phases Unstable or Jump Due to Hardware

When antenna has been replacedWhen antenna has been replaced New obstacles near siteNew obstacles near site Significant frequency change: > 7%Significant frequency change: > 7% Rx cables with differential lengths introduced/replacedRx cables with differential lengths introduced/replaced Monopole antenna, cable, or Rx channel fails (more common)Monopole antenna, cable, or Rx channel fails (more common)

If both loops jump at same time, must be due to monopole failureIf both loops jump at same time, must be due to monopole failure Check amplitude history, S/N with 'DiagDisplay' to confirmCheck amplitude history, S/N with 'DiagDisplay' to confirm

One loop antenna, cable, or Rx channel fails (less common)One loop antenna, cable, or Rx channel fails (less common) If one loop jumps to new state and stays there, may be due to loopIf one loop jumps to new state and stays there, may be due to loop

channel failurechannel failure Check amplitude history, S/N with 'DiagDisplay' to confirmCheck amplitude history, S/N with 'DiagDisplay' to confirm

Antennas/cables leave CODAR equalized when new or repairedAntennas/cables leave CODAR equalized when new or repaired If in doubt for one loop, useIf in doubt for one loop, use

Transponder measurementsTransponder measurements Stable loop phase for unstable oneStable loop phase for unstable one

Phases must be 'set' in 'Phases.txt' only for ideal pattern opsPhases must be 'set' in 'Phases.txt' only for ideal pattern ops When hardware fails or deteriorates, amplitudes are much moreWhen hardware fails or deteriorates, amplitudes are much more

likely to change state than phaseslikely to change state than phases