Triton Bathymetry - Manual (Page 38)

Page 34
8.3.2 DTM – Standard Deviation Layer
This layer gives the standard deviation of the sounding values
within each grid cell. Note that when selecting which QC
layers to produce in the BathyOne Wizard the user can
specify how many soundings are needed in a grid cell in order
to make this calculation. Mathematically, there needs to be
at least 2 values in order to calculate a standard deviation.
For hydrography, to have enough confidence in the determined grid cell depth, there
should be at least 5 soundings in that grid cell to be sure a low standard deviation is not
due to too small a population of soundings. Often for chart production at least 10
soundings per grid cell are required before the depth value is accepted and used.
Shown below are two examples of standard deviation layers. On the left is the standard
deviation was derived from a 0.5m grid, while the image to the right comes from a 1m grid.
The density values from the previous section came from the 0.5m grid shown left. Note
there is no standard deviation where the sounding density was less than 5 soundings per
grid cell.
The image shown right comes from the 1m grid which has a higher sounding density. From
this image the user can see that most of the grid has a low standard deviation, with the
larger values coming from the center of the grid where there is a known wreck. Note that
calculating the standard deviation is required in order to determine IHO compliance.
0.5m grid 1m grid