Outline of Quality Control Flags

Shawn R. Smith
COARE Data Processing Center for Surface Meteorology
Center for Ocean Atmospheric Prediction Studies
Florida State University

3 January 1996

The quality control flags are single alphabetic characters for each data value indicating 
the quality of that specific value.  Only those variables with a qcindex have flag values
(the qcindex is an integer pointer to the flag for a selected variable).  The flags are:

A  -  Original data had unknown units.  The units shown were determined using a
      climatology or some other method.
      
B  -  Original data were out of the range bounds outlined (Table 1).

C  -  Time data are not sequential or date/time not valid.

D  -  Data failed the Air Temperature is always greater than or equal to the Wet-bulb Temperature
      is always greater than or equal to the Dew Point Temperature test.
      
E  -  Data failed resultant wind recomputation check.  When the data set includes the
      platform's speed and direction along with the platform relative wind speed and
      direction, the prescreen program recomputes the earth relative wind speed and
      direction and compares the computed values to the reported earth relative wind
      speed and direction.  A failed test occurs when the wind direction difference is 
      >10 deg.C or the wind speed difference is >5 m/s.
      
F  -  Platform velocity unrealistic.  Determined by platform position and speed data.

G  -  Data are greater than 4 standard deviations from the means in the da Silva et al.
      (1994) COADS climatology.  The test is only applied to pressure, temperature, sea
      temperature, relative humidity, and wind speed data.
      
H  -  Discontinuity found in data.

I  -  Interesting feature found in data.  More specific information on the feature is
      contained in the data reports.  Examples include: hurricanes passing station, sharp
      sea water temperature gradients, strong convective events, etc.
      
J  -  Data are of poor quality by visual inspection, DO NOT USE.

K  -  Data suspect/use with caution - this flag applies when the data look to have obvious
      errors, but no specific reason for the error can be determined.
	
L  -  Oceanographic platform passes over land or fixed platform moves dramatically.

M  -  Known instrument malfunction.

P  -  Position of platform or its movement are uncertain.  Data should be used with
      caution.
      
Q  -  Data questionable.  Similar to the K flag, however the original data arrived flagged
      for use with caution so the Q flag is assigned.
      
S  -  Spike in the data.  Usually one or two sequential data values (sometimes up to 4
      values) that are drastically out of the current data trend.  Spikes occur for many
      reasons including power surges, typos, data logging problems, lightning strikes,
      etc.
      
T  -  Time duplicate in data.

Z  -  Data passed evaluation.

Table 1: Prescreening Program Range Bounds

Variable               Lower Bound   Upper Bound     Units      Comments
------------------------------------------------------------------------------
time                   1-1-1980      12-31-1999		
latitude                    -90              90      degrees	
longitude                     0             359      degrees	
platform heading              0             359      degrees	
platform speed                0              15      m/s        research vessels
                              0               0      m/s        stationary buoys
                              0               2      m/s        drifters
plat. wind direction          0             360      degrees	
plat. wind speed              0              40      m/s	
wind direction                0             360      degrees	
wind speed                    0              40      m/s	
atmospheric pressure        950            1050      mb         sea level
air temperature             -10              40      deg. C	
wet bulb temperature        -10              40      deg. C	
dew point temperature       -10              40      deg. C	
sea temperature               0              35      deg. C	
relative humidity             0             100      percent	
radiation                     0            1400      W/m2	
specific humidity             0              48      g/kg
rain rate                     0             150      mm/hr


Reference:

da Silva, A. M., C. C. Young, and S. Levitus, 1994:  Atlas of Surface Marine Data, Volumes 1:
Algorithms and Procedures.  NOAA Atlas Series.  In preparation.