Echograms can contain areas which contain no data. These areas are termed "no data areas", and they contribute nothing to analyses. They commonly arise, for example, when the range over which data are collected changes during a survey (such as when the water depth changes). A no data area is a part of the echogram in which no samples are found.
There are also situations in which valid samples are associated with no value. These are termed "no data samples", and they also contribute nothing to analyses. This situation arises, for example, where data are masked in a virtual echogram or if thresholded values are set to "no data" on the Data page of the Variable Properties dialog box. A no data sample is a sample that has the value "no data".
Samples with the value "no data" are exported with a special export value.
The color with which no data areas and no data samples are displayed depends upon the color scheme in use. It is typically black.
Notes:
Special export values
Sample point inclusion
About Echocolor
Palette properties dialog box
About Integration