ABC and NASC

ABC and NASC are measures of area scattering rather than volume scattering. They are calculated when integrating a region, cell or selection and available for export as analysis variables when integrating by regions, or by cells.  NASC or nautical area scattering coefficient is identical to sA as used by Simrad and is the area backscattering coefficient (ABC) scaled by 4ϖ and 1 nautical mile squared. This terminology follows MacLennan et al (2002).

ABC (Area Backscattering Coefficient - m2m-2)

ABC is also known as sa.

ABC is calculated as:

Where

Sv         = mean volume backscattering strength of the domain being integrated (dB re 1 m2m-3).

T          = mean thickness of the domain being integrated (m).

NASC (Nautical Area Scattering Coefficient - m2nmi-2)

NASC is also known as sA.

NASC is calculated as:

  

Where

4ϖ        = Steradians in a sphere - converting "backscattering" cross-section to "scattering" cross-section.
1852     = meters per nautical mile (m/nmi)
S
v         = mean volume backscattering strength of the domain being integrated (dB re 1 m2m-3).
T
        = mean thickness of the domain being integrated.
ABC
    = Area Backscattering Coefficient (m2m-2)

Notes:

See also

Area backscattering strength
Mean_height

Sv mean

Thickness mean and Height mean