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%                    I N T R O / C M . T E X 
%                    doc: Tue Feb  8 11:37:44 2000
%                    dlm: Wed Jun  7 21:57:46 2000
%                    (c) 2000 A.M. Thurnherr
%                    uE-Info: 152 16 NIL 0 0 72 3 2 4 ofnI
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\begin{figure}[t]

\placeFig{intro/moorings}

\caption[Current-meter moorings]{Current-meter mooring
positions; shading is the same as in \rfigNP{AMAR-bridge}; contour
interval is \m{250}; mooring ``A'' was not recovered.}

\labelFig{CM-stations}

\end{figure}

\Subsection{CM-sensors}{Sensors and Data}

Between July 1997 and July 1998 25 \emph{Aanderaa RCM 8}\REM{RCM 7 is
rated to \m{2000} but otherwise identical} current meters were deployed
on 8 moorings \rfig{CM-stations}. Mooring ``A'' was not recovered
successfully, leaving 7 moorings with three current meters each,
nominally at \m{1800}, \m{2100} and \m{2300}. All instruments had
temperature sensors installed. The \m{2100} current meters were
additionally fitted with \emph{Sea Tech Light Scattering Sensors}
(LSS), and some also with pressure and/or conductivity sensors.
 %
\begin{table}[t]
\begin{center}
\begin{tabular}{|crc|ccc|}
\hline
%----------------------------------------------------------------------
Mooring & Depth & IID & LSS & Conductivity & Pressure \\ \hline\hline
%======================================================================
B			& \m{1770}	& B18 & n/i & ok	& ok \\
(\m{2450})	& \m{2070}	& B21 & bad & n/i	& bad \\
			& \m{2270}	& B23 & n/i & bad	& ok \\
%----------------------------------------------------------------------
\hline
C			& \m{1840}	& C18 & n/i & n/i	& ok \\
(\m{2400})	& \m{2140}	& C21 & bad & ok	& bad \\
			& \m{2340}	& C23 & n/i & ok	& ok \\
%----------------------------------------------------------------------
\hline
D			& \m{1805}	& D18 & n/i & n/i	& ok \\
(\m{2520})	& \m{2105}	& D21 & bad & n/i	& bad \\
			& \m{2305}	& D23 & n/i & n/i	& n/i \\
%----------------------------------------------------------------------
\hline
E			& \m{1755}	& E18 & n/i & n/i	& ok \\
(\m{2890})	& \m{2055}	& E21 & bad & ok	& bad \\
			& \m{2255}	& E23 & n/i & partially bad	& n/i \\
%----------------------------------------------------------------------
\hline
F			& \m{1720}	& F18 & n/i & bad	& ok \\
(\m{2650})	& \m{2020}	& F21 & bad & ok	& bad \\
			& \m{2220}	& F23 & n/i & ok	& n/i \\
%----------------------------------------------------------------------
\hline	
G			& \m{1830}	& G18 & n/i & n/i	& ok \\
(\m{2410})	& \m{2130}	& G21 & bad & ok	& bad \\
			& \m{2330}	& G23 & n/i & ok	& n/i \\
%----------------------------------------------------------------------
\hline
H			& \m{1830}	& H18 & n/i & n/i	& ok \\
(\m{2450})	& \m{2130}	& H21 & bad & ok	& bad \\
			& \m{2330}	& H23 & n/i & ok	& n/i \\
%----------------------------------------------------------------------
\hline
\end{tabular}
\end{center}

\caption[Current-meter sensors and data recovery]{Current-meter
instrument list; water depths as recorded during mooring deployment are
given in parenthesis beneath the mooring letters; ``IID'' denotes the
instrument identifiers used in \protect\rchapNP{CM}; ``LSS'',
``Conductivity'', and ``Pressure'' columns indicate whether such
sensors were fitted (``n/i'' meaning ``not installed'') and the quality
of the recovered data.}

\label{tab:CM-sensors}

\end{table}
 %
\rTabNP{CM-sensors} lists the instruments and information concerning
their installed sensors and data quality. Velocity and temperature
data from all instruments were recovered successfully. Flow speeds and
directions were sampled every \s{72}. Every hour the vector-averaged
mean velocities and spot measurements from the other sensors were
recorded. Total common record length is \d{372} (\w{53} and \d[]{1}).

%----------------------------------------------------------------------

After approximately 7 months of deployment all LSS records show an
increasing trend followed by an abrupt (order 1 day) drop to zero
followed approximately 10 days later by a sudden increase to
\V{\approx\!4} (total range is \V{0$--$5}). The most likely explanation
for this behavior is a power drop of the instrument batteries
\perscomm{Aanderaa representative}. Because it cannot be determined
accurately which portions of the LSS records are contaminated by the
instrument failures these data were not used at all.

All pressure records from the \m{2100} instruments show sudden
increases between \dbar{3} and \dbar{150} coinciding with the sudden
LSS voltage increases. Because there are no coincident pressure changes
in any of the other records, these signals are assumed to be
contamination effects of the LSS failures. The remaining data
(temperature, conductivity, speed and direction) do not show any clear
indication for similar contamination --- because of the variability of
the data small calibration shifts cannot be excluded, however.

%----------------------------------------------------------------------

\subsection{Calibrations}

\begin{description}

\item[Speed:] manufacturer-specified linear calibration.

\item[Direction:] first, a manufacturer-specified linear calibration
was applied to map the raw data to the compass range. The compasses
were calibrated before and after deployment at \deg{10} intervals;
because of the calibration procedure, differences between the two
calibrations (nowhere greater than \deg{10}) are more likely to be
errors than shifts in the compass calibrations \perscomm{P.G.\ Taylor}
--- therefore, the more self-consistent of the two calibrations (based
on the difference at neighboring calibration points) was applied. In a
third step, the calibrated data were corrected for magnetic declination
(\deg{-15}), calculated for \latN{36}{25}/\lonW{33}{50}, January 1st
1998 with the \emph{IGRF95} model \cite{misc/IGRF95}.

\item[Pressure/Depth:] in addition to the contamination of the \m{2100}
instruments caused by the LSS failures \rsec{CM-sensors}, many of the
remaining pressure records also show trends and jumps of various
magnitudes. Because these could nowhere be correlated between separate
instruments on the same mooring they are all assumed to be sensor
problems and the affected data were removed from the records. From the
remaining data a mean offset to the nominal depth was calculated using
both pre- and post-deployment calibrations. From these a common mean
offset was estimated for each mooring and added to the nominal values
to yield the depths listed in \rtabNP{CM-sensors}. For the analysis
\rchap{CM} the nominal depths (\m{1800}, \m{2100}, \m{2300}) are used
exclusively.

\item[Temperature:] the sensors were calibrated both before and after
the deployment; a number of the post-deployment calibrations were
erroneous and were therefore re-done; the pre- and the repeated
post-deployment calibrations differ by up to \degC{0.5} without any
indication for similar sensor calibration shifts in the data but most
are of order \degC{0.03} or less. Because the quality of the
calibrations is somewhat doubtful and because the temperature records
do not show any recognizable trends or shifts which could be corrected
by taking the pre- to post-deployment calibration differences into
account, it was decided to individually apply the calibrations which
minimize the differences between the mean hydrography sampled during
the \F cruise \rsec{F-methods} and the mean temperatures calculated
from the first week of each current-meter record. (Because of the
variability of the hydrography on short time scales \rsec{intwaves} no
attempt was made to relate the temperature records to individual CTD
profiles.) Both nominal and calibrated depths were used, with the
calibrated depths resulting in smaller mean differences. The calibrated
temperatures are all low-biased between \degC{0.05} and \degC{0.08}.

\item[Salinity:] In a first step, the raw conductivity data were
plotted against time and the data sets marked ``bad'' \rtab{CM-sensors}
where the conductivity sensors were not working. One instrument (E23)
initially returned bad data --- based on a visual assessment the data
before deployment day 132 were removed. The remaining conductivity data
were calibrated in the same way as the temperature records. \REM{Based
on T/S plots, only B18 can be concluded to be good data albeit with a
shift of approximately \psu{-0.3}. The deep T/S plots all are ``blobs''
and assessment is not possible except to note that F23 has a weird
``spike'' at \degC{3.8}.}

\end{description}
