Although a slightly different situation....the concept of marrying up data from different sources is the same. During periods of foggy weather producing visibility not much greater than the length of my 41 foot sailboat ... overlaying the Radar display onto the Chart plotter (moving map driven by the GPS) was very effective in navigating in the waters I called home.
The auto pilot was in Heading mode ...the chart plotter told me where the Markers, Buoys, and known obstructions were supposed to be ... and the Radar showed where they actually were along with other Vessels that were in my area. Add in AIS data being tagged to the Vessel Returns and getting around was easy and safe.
Buoys have a habit of being moved by storms or by the Coast a Guard as the channel shifts due to storms and erosion so GPS alone cannot be relied upon ...thus making the use of Radar so important. Determining the reason for the Variance is the problem as you might not know the cause of the Return not being where at the Map depicted location ...and there is nothing showing on the Radar at the GPS designated location.
Even Oil Rigs move about with delayed notice to air crews sometimes!
Resolving ambiguity can be an issue while using this new hi-tech equipment.
The Nav system could carry out a pre-planned Route with up to 99 Waypoints in the Nav Mode.
Point being ... technology properly used can very much enhance Situational awareness!
Even the Fog Horn on the boat was automated.....leaving a hand free that otherwise would have been ringing a Bell!
The Radar had to be properly adjusted to obtain the most accurate Returns as it had multiple modes that included both surface Returns and Weather modes just as Aviation Radars do.
Originally Posted by
Scattercat
My comments above are more concerned with IMC / VMC conditions & the "how to" rather than the rules governing such. Yes, the correct use of the radar, should form a very important part of the picture, but it should be cross-checked with all other available data sources. The advent of reliable, GPS based navigation systems, allows for RNAV only IMC letdowns, which should then complement radar return information. I would be concerned if, during an ARA, the rig GPS location was not where the radar was painting a target, & visa versa.