# Aggregation_index

The Aggregation_index is an analysis export variable available in exported integration analyses.

It reports the aggregation index (m-1)of the domain. It is calculated by evaluating the reciprocal of the Equivalent area for the samples of the domain which was analyzed. The exported Aggregation_index is equivalent to the 'Index of aggregation' as used by Urmy et al (2012). Urmy et al noted that Index of aggregation values are "high when small areas are much denser than the rest of the distribution".

## Algorithm

Where:

IA is the Aggregation_index (m-1). z is the depth (m) of a sample in the analysis domain. sv(z) is the sample volume-backscattering coefficient at z.

Sv (dB re 1m-1) is the (mean) Volume backscattering strength of the sample at z.

Notes:Thresholded Sv (dB) values are handled as 0 in the linear domain.