User`s manual

Appendix IV: Derived Parameter Formulas
102
average sound velocity = [m/s]
Average sound velocity is the harmonic mean (average) from the surface to
the current CTD depth. The average is calculated on the downcast only. The
first window begins when pressure is greater than a minimum specified
pressure and salinity is greater than a minimum specified salinity.
• In SEASAVE and in SBE Data Processing’s Data Conversion module, the
algorithm also requires user input of a pressure window size and time window
size. It then calculates:
d
i
= depth at end of window – depth at start of window [meters]
v
i
= (sound velocity at start of window + sound velocity at end of window) / 2 [m/sec]
• In SBE Data Processing’s Derive module, the algorithm is based on the
assumption that the data has been bin averaged already. Average sound
velocity is computed scan-by-scan:
d
i
= depth of current scan – depth of previous scan [meters]
v
i
= sound velocity of this scan (bin) [m/sec]
(Notes:
1. To calculate gravity for the depth algorithm (used in calculating average
sound velocity), SEASAVE uses the latitude from a NMEA navigation device,
if NMEA is enabled in the .con file. If your system does not have NMEA,
enter the desired latitude on the Miscellaneous tab in Configure Inputs.
2. Enter the minimum pressure, minimum salinity, pressure window size, and
time window size on the Miscellaneous tab in Configure Inputs.)
Surface
> Minimum specified pressure and salinity
d
i
and v
i
Average
sound velocity
Average
sound velocity
d
i
and v
i
Σ
d
i
Δ
p,p=min
p=p
Σ
d
i
/ v
i
Δ
p,p=min
p=p