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 produce errors if not accounted for in software: Amplitude 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 drifting Phase 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 ideal Distortions to the shape of the element patterns from ideal Due to local environmental near-field obstructions Due to local environmental near-field obstructions Rarely change after installation unless local environment changes Rarely change after installation unless local environment changes

Using 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 monopole 1st-order Bragg peaks used to calculate phase estimates 1st-order Bragg peaks used to calculate phase estimates Makes use of fact that phases in two lobes of given loop should Makes use of fact that phases in two lobes of given loop should 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 related Natural changes in sea state/wind direction -- not hardware related Change or failure in system/hardware Change or failure in system/hardware Must Be Able to Tell the Difference Must Be Able to Tell the Difference Don Barrick

What 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 positive Signal is positive So phase is 0° So phase is 0° Land Sea Coastline

What 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 negative Signal is negative So phase is 180° So phase is 180° Land Sea Coastline

What Does Phase Mean: Equal Amp Sea Echo over 180° Arrows show amp of received signal Positive voltages: blue arrows Negative voltage: red arrows Sum all signals into both lobes What is signal phase, V t ? What is signal phase, V t ? Signal is positive Signal is positive So phase is 0° So phase is 0° Land Sea Coastline

What Does Phase Mean: Wind Waves from South S n distribution strongest from South Positive voltages: blue arrows Negative voltage: red arrows Sum all signals into both lobes What is signal phase, V t ? What is signal phase, V t ? Signal is negative Signal is negative So phase is 180° So phase is 180° Land Sea Coastline

What Does Phase Mean: Wind Waves Decaying S n 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, V t ? What is signal phase, V t ? Signal amplitude is zero Signal amplitude is zero So phase is indeterminate So phase is indeterminate Like weather vane when Like weather vane when wind dies to zero, flops in any direction Land Sea Coastline

What 'Phase Stability' Due to Sea State Depends on: Both Bragg peaks Both Bragg peaks Where advancing is stronger, receding is weaker Where advancing is stronger, receding is weaker Either can dominate in phase determination depending on wind wave Either can dominate in phase determination depending on wind wave direction with respect to that loop lobes Angle subtended by coastline Angle subtended by coastline As sea view approaches 360°, phase becomes indeterminate As sea view approaches 360°, phase becomes indeterminate For coastline angles < 180°, phase is usually stable at least for For coastline angles < 180°, phase is usually stable at least for one of the loops One of loops will normally show stable phases One of loops will normally show stable phases Dominant wind/wave direction will be along that loop's seaward lobe Dominant wind/wave direction will be along that loop's seaward lobe Other lobe's phase will often vary when sea state changes direction Other lobe's phase will often vary when sea state changes direction In practice, phases will almost never be 0° or 180° because of In practice, phases will almost never be 0° or 180° because of Differential phase shifts in monopole and loop channels Differential phase shifts in monopole and loop channels Phase 'jumps' should, however, be ~180° unless very distorted pattern Phase 'jumps' should, however, be ~180° unless very distorted pattern

When Are Phases Unstable or Jump Due to Hardware When antenna has been replaced When antenna has been replaced New obstacles near site New obstacles near site Significant frequency change: > 7% Significant frequency change: > 7% Rx cables with differential lengths introduced/replaced Rx 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 failure If both loops jump at same time, must be due to monopole failure Check amplitude history, S/N with 'DiagDisplay' to confirm Check 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 loop If one loop jumps to new state and stays there, may be due to loop channel failure Check amplitude history, S/N with 'DiagDisplay' to confirm Check amplitude history, S/N with 'DiagDisplay' to confirm Antennas/cables leave CODAR equalized when new or repaired Antennas/cables leave CODAR equalized when new or repaired If in doubt for one loop, use If in doubt for one loop, use Transponder measurements Transponder measurements Stable loop phase for unstable one Stable loop phase for unstable one Phases must be 'set' in 'Phases.txt' only for ideal pattern ops Phases must be 'set' in 'Phases.txt' only for ideal pattern ops When hardware fails or deteriorates, amplitudes are much more When hardware fails or deteriorates, amplitudes are much more likely to change state than phases