Resurvey Interval

The resurvey interval is the period after which a charted area should be surveyed again, set by how fast the seabed changes and how heavily the area is used. Mobile sediment zones, dredged channels, river bars, and approaches to busy ports need short intervals, sometimes annual or after each storm season, while stable deep water can hold for decades. IHO S-44 and national hydrographic offices rank areas by traffic and seabed mobility to schedule resurveys; the goal is to keep the charted depth inside the relevant survey order before shoaling makes it unsafe. Repeated surveys are compared by difference modeling to detect change.