www.sea-technology.com February 2016 / st 47
Argo foat CTDs returned from the feld indicate very low
drift (< -0.003 psu and -0.002° C) and sustained calibration
accuracy for deployment periods spanning two to six years.
If this pattern holds in other foats, two very important im-
plications for the Argo program emerge. First is a high level
of initial accuracy in Argo TS data sets, with tight bounds
for sustained accuracy in the feld. Second is a bimodal
sensor behavior, acceptable as is (accurate, negligible drift)
and compromised (broken or sensor performance leading
to drift). QA/QC of Argo data may best be able to exploit
this bi-modal behavior, rather than assigning a continuum of
drift/error on all sensors. This implies that for most purposes,
Argo data are usable as delivered to the
data servers without requiring QA/QC
beyond simple screening for outliers
exhibiting unreasonable temperature
and salinity measurements. The Argo
program was established with the goal
of providing real-time oceanographic
data to the public; this demonstration of
sustained accuracy supports the fulfll-
ment of that goal.
Latest Development
Sea-Bird Electronics recently updat-
ed the architecture of the SBE 41 and
SBE 41cp CTDs. This revised CTD uses an improved proces-
sor that can allow the 41/41cp to act as a science hub for
parameters increasingly gaining importance in autonomous
observations, such as oxygen, pH and chlorophyll. The SBE
41N, which implements this hub architecture, was recently
used by scientists to capture high-frequency (cp mode) oxy-
gen, pH, biological and radiometric data in new profling
foat missions.
Acknowledgments
Use of calibration data from recovered Argo foats are
courtesy of the University of Washington (SBE 41-0933,
Pre- and post-deployment calibration re-
sults for six Argo CTD conductivity sen-
sors. Initial calibrations all lie on the 0
line.