23
arrangements are robust in regions of small tidal amplitude and temperature
gradients, very long stilling wells in areas of extreme tides such as the east coast of
North America, and regions where near-surface atmospheric temperature gradients
can be significant, report large errors.
Microwave Radar Water Level Sensors
The shortcomings discussed above, added to the need for significant infrastructure
and maintenance for the acoustic tide gauges, have recently driven the development
of free-standing microwave radar water level sensors (Park et al. 2014). These
instruments require little more infrastructure than a vertical support periodically
referenced to a geodetic benchmark network and dispense with the stilling well
although they are still mounted in relatively protected waters where wave action is
moderate. The instrument, mounted at a height of a few meters, emits a conical
radar pulse at 26 GHz and calculates time of flight of the return pulse. Resulting
seawater level is calculated from multiple readings averaging out the wave-induced
oscillations.
Implementation of a global ocean observing system, coordinated by the World
Meteorological Organization and the Intergovernmental Oceanographic Commission
of UNESCO (IOC), has been spearheaded by the development of a Global Sea
Level Observing System (GLOSS). In general, technological improvements have
mirrored those followed by the NOAA NWLON, but many regions, lagging far
behind, still operate float gauges with analog graph paper readout.
2.2.5 Ocean Waves
Surface Waves
The ocean surface wave spectrum spans amplitudes of millimeters to tens of meters.
A wave field measured by a research vessel in Rockall Trough west of Scotland
(Holliday et al. 2006) exhibited a significant wave height of 18.5 m and one individual rogue wave was measured at a height of 29.1 m. Wave properties of interest
are the height or amplitude of the waves, the direction of propagation, and the wave
period, the latter being the time recorded between passages of successive wave
crests. Real-world wave fields, however, are chaotic with superimposed wave trains
of varying height, direction, and period.
Wave Observation from Surface Platforms
Waves are today most commonly measured using gyroscopically stabilized platforms or chip-mounted microelectromechanical accelerometer devices measuring
heave, pitch, and roll together with associated 3D fluxgate compasses for the
2.2 Electronic Sensors and Instruments for Ocean Observing
arrangements are robust in regions of small tidal amplitude and temperature
gradients, very long stilling wells in areas of extreme tides such as the east coast of
North America, and regions where near-surface atmospheric temperature gradients
can be significant, report large errors.
Microwave Radar Water Level Sensors
The shortcomings discussed above, added to the need for significant infrastructure
and maintenance for the acoustic tide gauges, have recently driven the development
of free-standing microwave radar water level sensors (Park et al. 2014). These
instruments require little more infrastructure than a vertical support periodically
referenced to a geodetic benchmark network and dispense with the stilling well
although they are still mounted in relatively protected waters where wave action is
moderate. The instrument, mounted at a height of a few meters, emits a conical
radar pulse at 26 GHz and calculates time of flight of the return pulse. Resulting
seawater level is calculated from multiple readings averaging out the wave-induced
oscillations.
Implementation of a global ocean observing system, coordinated by the World
Meteorological Organization and the Intergovernmental Oceanographic Commission
of UNESCO (IOC), has been spearheaded by the development of a Global Sea
Level Observing System (GLOSS). In general, technological improvements have
mirrored those followed by the NOAA NWLON, but many regions, lagging far
behind, still operate float gauges with analog graph paper readout.
2.2.5 Ocean Waves
Surface Waves
The ocean surface wave spectrum spans amplitudes of millimeters to tens of meters.
A wave field measured by a research vessel in Rockall Trough west of Scotland
(Holliday et al. 2006) exhibited a significant wave height of 18.5 m and one individual rogue wave was measured at a height of 29.1 m. Wave properties of interest
are the height or amplitude of the waves, the direction of propagation, and the wave
period, the latter being the time recorded between passages of successive wave
crests. Real-world wave fields, however, are chaotic with superimposed wave trains
of varying height, direction, and period.
Wave Observation from Surface Platforms
Waves are today most commonly measured using gyroscopically stabilized platforms or chip-mounted microelectromechanical accelerometer devices measuring
heave, pitch, and roll together with associated 3D fluxgate compasses for the
2.2 Electronic Sensors and Instruments for Ocean Observing