Measuring change means comparing two surveys, and the comparison inherits the uncertainty of both. Anything smaller than the combined detection limit is not erosion, it is noise, and we mark it as such rather than reporting it as change.
Every repeat survey reuses the same marks, the same setup and the same flight lines. Consistency between visits is worth more here than absolute accuracy in any single one of them.
Working the tide
Coastal flights are planned against the tide table, not the calendar. The waterline moves further in an hour than a year of erosion does, so surveys are matched to the same tidal state or the comparison is meaningless.
Reporting
Change maps, volumes of loss and gain, retreat distance along a fixed baseline, and a clear statement of what the survey pair can and cannot detect.