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Data Processing Notes
Acoustic Surface Reverberation Experiment, 1993
07 Nov 2000, AJP
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General
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    Five surface moorings were deployed during ASREX 93. The Upper Ocean
    Processes Group was responsible for two of the moorings, one 
    supporting a Seatex Wavescan wave rider buoy and the other a 3 m 
    discus buoy. The other three moorings were deployed by investigators
    from the Rosenstiel School of Marine and Atmospheric Science, 
    Scripps Institution of Oceanography, and the Canadian Institute for
    Ocean Sciences. An overview of the complete array is provided by
    Galbraith et al. (1996).

    Only the meteorological and oceanographic data from the UOP discus
    mooring are documented here. The discus mooring was outfitted with
    two independent meteorological sensor systems, a VAWR and an IMET
    system. The VAWR was used as the primary meteorological system, 
    supplemented by data from the IMET system as described below.


Meteorology
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  Wind Speed

    The VAWR was used as the primary wind speed record. The VAWR wind 
    speeds (cup anemometer) were about 10% higher than the IMET speeds 
    (propeller). 

  Wind Direction:

    The VAWR was was used as the primary wind direction record up until
    the wind vane broke on 15 January 1994. The IMET wind sensor 
    suffered from RF interference which contaminated about 20% of the
    records. Thus, from 15 January to the end of the experiment the wind
    direction was estimated using a combination of the the VAWR compass 
    and the IMET wind data. Galbraith et al. (1996) give a more complete
    description.

    A magnetic variation (also referred to as magnetic declination) of
    -15.9 degrees was applied as a rotation to the east and north wind
    components. Speed and direction were computed from the components. 

    Wind directions are in oceanographic convention (direction
    towards), opposite to the meteorological convention (direction
    from).

   Air Temperature:

    The IMET was used as the primary air temperature record, based on a
    smaller amplitude diurnal heating signal than the VAWR. The larger 
    diurnal cycle was presumed to be a result of radiative heating.

  Sea Surface Temperature

    The VAWR was used as the primary sea temperature record. 

  Barometric Pressure

    The VAWR was used as the primary barometric pressure record.

  Relative Humidity

    The VAWR was used as the primary relative humidity record. 

  Longwave Radiation

    The VAWR was used as the primary longwave radiation record (the 
    IMET did not measure shortwave during ASREX 93). The record showed
    a diurnal cycle with an amplitude of about 13 W/m^2, which was
    presumed to be due to radiative heating. This error was reduced
    significantly by subtracting 3.6% of the incoming shortwave signal
    from the longwave record.

  Shortwave Radiation

    The VAWR was used as the primary shortwave radiation record. 
    
  Precipitation

    Precipitation was not measured during ASREX 93.


Temperature 
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  Sampling:

    The sampling interval for the VMCMs was 2 min, whereas the T-pods
    sampled at 7.5 min and Seacat on the buoy bridle at 3.75 min. All
    data were averaged and interpolated as necesary to produce records
    with a common 7.5 min time base.

  Performance:

    Three temperature sensors (two T-pods and one Seacat) were deployed
    at 1 m on the buoy bridle. The Seacat was chosen for 1 m record due 
    to greater measurement precision. 

    The Seacat at 450 m had a short record. Missing data are indicated 
    by a fill value.

    The VMCM records ended approximately ten days before the mooring 
    recovery. The temperature data file was truncated to include only 
    the period when all of the VMCMs were operating.

  Calibration and Adjustments:

    In most cases temperature sensors were pre- and post- calibrated to
    within 0.02 C accuracy. No information is available about biases or
    adjustments that may have been applied to the ASREX 93 temperature
    data.


Velocity
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  Sampling:

    All VMCMs sampled at 2 min.

  Performance:

    All of the VMCMs returned complete velocity records, although the 
    records ended approximately ten days before the mooring recovery. 
    The velocity data file includes only the time period when all of 
    the VMCMs were operating.

  Magnetic Variation: 

    A magnetic variation (also referred to as magnetic declination) of
    -15.9 degrees was applied as a rotation to the east and north
    velocity components. Speed and direction were computed from the
    components.