RIOS : Radar Inlet Observing System
Assessing navigability of tidal inlets
The Radar Inlet Observing System (RIOS) has been developed to measure the position of inlet channels and shoals continuously (hourly) through all conditions, and to make results available in near real-time.

The Corps from both its civil works and military support obligations need to know the navigability of tidal inlets. Considerable resources are spent annually surveying inlet channels but these efforts are limited by stretched funds and personnel, dynamic channels that may change substantially during storms, and reduced access by traditional surveying either due to treacherous sea conditions or denied regions. Traditional remote sensing techniques are not always viable options in coastal and brown-water settings where bubbles and turbidity levels are high. Existing bathymetric inversion algorithms (calculating depth from measured wave speed) may also be highly erroneous in these environments where linear wave theory does not accurately reflect wave speed.

RIOS utilizes X-band radar to measure wave conditions, including wave breaking, speed, period, and angle, from which depths on the shoals and channels are determined. These inferred depths are estimated from a combination of wave breaking intensity and measured depths from prior surveys and radar-derived wave speed. The system is fully automated, and provides updated results every hour via wireless internet. RIOS is self-sufficient with respect to power, utilizing roof-mounted solar panels and an internal diesel generator.

All referenced times are in UTC (Universal or Greenwich Time)

Present location:
Oregon Inlet, NC

Satellite image

Snapshot of Present Conditions

One radar rotation showing conditions at the start of hourly collection

Mean Radar Intensity

12-minute average of radar intensity showing regions of breaking waves and strong currents
Shoal Position
25-hour average (de-tided) shoal positions, updated every hour, as defined by the magnitude of slope gradients (highlights shoal edges). 'Daily' image represents highest skill(r2) over past 24 hours.
RIOS Bathymetry
Depth estimates determined from scaled radar intensity model that uses previously measured bathymetry and depths calculated from inversion of RIOS-measured wave speed. 'Daily' image represents highest skill(r2) over past 24 hours.
Navigation Support

Navigation Route

Most frequently navigated route within the past 24 hours.

Hourly Wave Conditions at Bar

Wave breaking conditions across the seaward bar in the navigation channel.

Shoal and Beach Change Map Overlays




Comparisons of shoal and beach position between results with the highest skill of a given day. Time difference on plots shown in units of decimal days. Color scale on plts: light=accretion, dark=loss
Documentation and References
McNinch, J. E.; Brodie, K. L.; Slocum, R. K., RADAR INLET OBSERVING SYSTEM (RIOS): CONTINUOUS REMOTE SENSING OF WAVES, CURRENTS, AND BATHYMETRY AT TIDAL INETS, Proceedings of the 2012 Oceans Conference in IEEE Xplore, Norfolk, VA.

Point of Contact
Dr. Jesse McNinch
Field Research Facility, Coastal Observation and Analysis Branch, CHL 252-261-6840 x243