A bad sounding that stands out from the surrounding surface, either above it (a shoal flier) or below it (a deep flier). Fish, bubbles, wake, multipath and edge-of-swath noise are common causes. Fliers that survive cleaning bend the gridded surface, and a shoal flier on a chart can invent a hazard. Quality control tools scan finished grids for them, and a processor reviews every hit, because some turn out to be real objects.
Flier finder pulled 40 hits on the outer edge, all junk except the piling stub off the pier.
A flier on top of a known wreck may be a mast; on a flat mud bottom it is almost always a fish.
Also heard as
- flyer
- spike
- edge flier
Related terms
Cleaning
Reviewing survey data to reject spikes, noise and false bottoms before building final products.
Bottom detection
The method a multibeam uses to pick the instant the seabed echo arrives in each beam and turn it into a depth.
Holiday
A gap in survey coverage where no data was collected, which must be filled before the survey is complete.
Gridding
Turning millions of scattered soundings into a regular grid of depth values at a chosen cell size.