About analysis domains

An analysis domain defines the initial set of data points (samples or single targets) that are available for analysis. Analysis domains can take the form of:

Analysis domains can be defined on single beam echograms, single target echograms and scenes.

Note: Analysis is affected by the settings defined on the Analysis page of the Variable Properties dialog box.

The topics discussed on this page include:

What is included in an analysis domain?

Single beam and single target echograms

Data points with time/distance or depth coordinates that are inside the boundary of the analysis domain are included in the analysis domain.

Data points with time/distance or depth coordinates that place them on a boundary of the analysis domain are treated as follows:

If the data point is on the...

Then...

Upper boundary

it is included in the analysis domain

Lower boundary

it is not included in the analysis domain

Left boundary

it is included in the analysis domain

Right boundary

it is not included in the analysis domain

Notes:

Multibeam echograms

Created, detected or virtual surfaces may be used as boundaries to include data points for detections and analysis. Data points inside the boundary are included. Data points outside and on the boundary are excluded.

Scenes (for multibeam data)

Analysis domains on scenes take the form of 3D regions.

Data points are included in an analysis domain if:

Data points with latitude, longitude and depth coordinates that place them on the boundaries of the analysis domain are highly unlikely to occur and inclusion is undefined in this circumstance.

Data points can be excluded from analysis domains on scenes with the usage of Exclude above and Exclude below surfaces.

Analysis settings

Data points (samples or single targets) that are included in an analysis domain are then retained or discarded for further analysis based on the settings defined on the Analysis page. The content of this section may benefit from the topics and background covered by About samples and echo integration.

Exclusions based on lines

Data points are excluded from further analysis if they are:

Analysis based on regions and samples

Data points (samples or single targets) are treated as no data if they are:

These samples are assigned a value of no data and they have no sample thickness. In effect, such samples are not counted in the calculations of Thickness_mean and Height_mean. See also the special case below.

Selecting Apply bad data regions also affects:

Special case

Samples within a Bad data (no data) region or with a value of no data in concert with the selection of the Analysis page settings Apply bad data regions and Include the volume of no-data samples.

These samples are assigned a value of no data and have a sample thickness. The sample thickness is included in calculations of the Thickness_mean and Height_mean. The settings can affect both entire pings and parts of pings. The key intent of this special case is the robust assumption (in the absence of any further information) about samples in Bad data (no data) regions. You are assuming, in effect, that these samples have a backscatter value equal to the mean of the good samples in the domain.

Prior to Echoview 5.4 it has always been possible to make this (commonly-desired) assumption by scaling the reported Thickness_mean of the domain (and hence the NASC) using the various analysis domain analysis variables (no_data_samples etc.).

Integration cues and outcomes - examples

 

Use Apply bad data regions

Use Apply bad data regions

Use Include volume of no data samples

Hatching cue, Outcomes, Assumptions

Hatching cue, Outcomes, Assumptions

Bad data (no data)

 

Purple border, grey hatch.
Does not use no-data sample intervals in Thickness mean.

This data effectively reduces Thickness mean and reduces reported volume for NASC.

Purple border, grey hatch.
Use no-data sample intervals in Thickness mean.

This data effectively is converted to the mean of the analysis domain. This gives you greater flexibility in calculating your NASC based results.

Bad data (empty water)

 

Green hatch.
Uses empty water samples in Sv mean count and Thickness calculations.

This data is deemed to have no acoustic return.

Green hatch.
Uses empty water samples in Sv mean count and Thickness calculations.

This data is deemed to have no acoustic return.

Analysis

 

Red hatch.

Good samples used in analysis calculations.

Red hatch.

Good samples used in analysis calculations.

Intersections

Data points in intersections of regions or other designated areas may change in nature, for calculation purposes, according to an order of precedence:

  1. Good
  2. Bad data (empty water)
  3. Bad data (no data)
  4. Above Exclude above line
  5. Below Exclude below line

With the Good category being dominated by any of the following categories, and the Below Exclude below line category dominating any of the preceeding categories.

The Processed data operator can often make clear how samples are affected by Analysis page settings.

The screeshot to the right shows region types, integration cues and intersections.

Regions include:

  • Bad data (empty water) region
  • Analysis region with integration hatching
  • Bad data (no data) region
Analysis hatching

Exclusions based on surfaces

Data points that are included in an analysis domain are then retained or discarded for further analysis based on the settings defined on the Analysis page.

Data points are excluded from further analysis if they are:

Excluded data points

Excluded data points are ignored for these primary calculations:

In turn, these quantities variously affect the calculation of:

Notes:

Good data points

The data points that are included in an analysis domain and not subsequently excluded are known as good data points.

When you perform an on-screen integration or an on-screen analysis of an analysis domain, all good data points will be overlayed with analysis-hatching (providing that the Show Analysis option on the Echogram page of the EV File Properties dialog is selected).

Tip

You can view the good data points for an entire echogram using the Processed Data operator. This operator assigns a value of no data to excluded data points.

You can view information about a data point as follows:

See also

About analysis
About analysis variables

Samples

About integration
About samples and integration
About no data
Thickness mean and Height mean
ABC and NASC
About biomass estimation
About single targets
About no data
Sv_mean
Analysis page
Bad data regions
Special data values