List of Quality Control Tests Sorted by the Stage Numbers
The following table is a complete list of data quality control tests sorted by the stage numbers.
The complete list of data quality control tests sorted by the test numbers is available here.
|QUALITY CONTROL TEST||DESCRIPTION|
|Stage 1: Location and Identification Tests|
|Platform Identification||This test is the very first to be done. It checks the station identifiers in the incoming file to a list of known identifiers.|
|Impossible Date/Time||This test verifies that the date and time of the observation is sensible.|
|Impossible Location||This test verifies that the profile's position is possible; that is, that the latitude falls between -90 and 90 and the longitude between -180 and 180.|
|Position on Land||This tests if the location of the observation is on land or water. It does so by comparing the location with a file of known bathymetric values.|
|Impossible Speed||This tests if the speed of the platform conforms to the characteristics known of the platform. This test checks the ship speed between two consecutive profiles. The ship speed is calculated from the time–space position at the beginning of the profile and those from the end of the preceding profile. If the end position or date/time of the preceding profile is missing, the test uses the coordinates at the beginning of the preceding profile to determine ship speed. The calculated speed is compared with the ship's cruising speed.|
|Impossible Sounding||This tests if the sounding is sensible given a digital bathymetry.|
Stage 2: Profile TestsAll of Stage 1 tests should be performed. These rules are used to check if observed parameter values are within probable globally defined limits
|Global Impossible Parameter Values||checks if the pressure, temperature, and salinity data are globally possible based on the criteria in the table below. If a data value is judged impossible and thus erroneous, its QC flag is replaced by 4.
|Regional Impossible Parameter Values||checks if the pressure, temperature, and salinity are regionally possible based on the criteria in the table below. If a data value is judged impossible and thus erroneous, its QC flag is replaced by 4.|
|Increasing Depth||A given pressure (depth) is considered doubtful when it is shallower than the preceding record and its QC flag is set to 3. Erroneous or missing pressure values are not considered.|
|Global Profile Envelope||checks whether the temperature and salinity data are within the envelope of permitted limits by depth range (see the table below). The data value is judged doubtful if it does not fall within the permitted interval and its QC flag is set to 3. Erroneous or missing temperature or salinity values are not considered.
|Constant Profile||The test is applied in two forms to data received through the GTS. The first applies to those stations that have data digitized at inflection points. If not digitized at inflection points, the second form of the test is applied.|
|Freezing Point||The freezing point is calculated from the salinity and the pressure. A temperature value lower than the corresponding freezing point is judged erroneous and its flag is set to 4. Temperature data previously judged erroneous or missing are not considered. It is expressed as a relationship between temperature, salinity and pressure.|
|Spike||A spike is detected by comparing a data value (V2) with the previous (V1) and next (V3) values.
If ( | (V2 - (V3+V1))/2 | - | (V1-V3) /2 | ) is greater than the threshold value, then V2 fails the test. The threshold values for temperature and salinity are noted in the table below. The data that fail this test are doubtful and their QC flags are set to 3. The temperature and salinity data previously judged erroneous or missing are not considered.
|Top and Bottom Spike||A spike at the surface is detected by comparing the value of the tested data point (V1) to the value of the next point (V2) so that if | (V1 - V2 | is less than the threshold value no spike is detected.
A spike at the bottom is detected by comparing the value of the tested data point (V2) with the value of the preceding data point (V1) so that if | ( V2 – V1 ) | is less that the threshold value no spike is detected. If a spike is identified, then the QC flag 3 is assigned. Temperature or salinity records previously judged erroneous or missing are not considered.
|Gradient||Vertical gradients of temperature and salinity are calculated to determine if they exceed the limits specified in the table below.
If | V2 - (V1 + V3) / 2 | / (change in pressure) is greater than the gradient limit then V2 fails the test. V1, V2, and V3 are three successive values of temperature or salinity. A QC flag of 3 is then assigned to V2. Temperature or salinity records previously judged doubtful, erroneous, or missing are not considered.
|Density Inversion||This test compares the density of one data point (V2) with that of the preceding data point (V1).
If V2-V1 is less than -0.05, the test fails and the density is considered doubtful (QC flag 3). Density values previously judged doubtful, erroneous, or missing are not considered.
|Bottom||The test begins with the bathymetry file in the location of the station being examined to find the maximum permitted depth at the station.|
|Temperature Inversion||This test operates by searching for both a local minimum and a local maximum occurring in a temperature profile within a layer not more than 50 m in thickness.|
Stage 3: Climatology Tests
|Levitus Seasonal Statistics||This test determines if the temperature and salinity observations lie within certain ranges of the mean value given by the Levitus Seasonal Statistics Atlas|
|Emery and Dewar Climatology||This test uses the Emery and Dewar climatology to test if the observed temperatures and salinities lie within 3 standard deviations of the climatological mean.|
|Asheville SST Climatology||This test determines if the observed sea surface temperature lies within 3 standard deviations of the Asheville climatological mean for the given location and month.|
|Levitus Monthly Climatology||This test compares the mean and standard deviations of an observed profile to that of the Monthly Levitus climatology of temperature and salinity.|
|Levitus Annual Climatology||This test compares the mean and standard deviations of an observed profile to that of the Annual Levitus climatology of temperature and salinity.|
Stage 4: Profile Consistency Tests
|Waterfall||This test examines adjacent profiles in an incoming file to determine if they are similar in form.|
Stage 5: Visual Inspection
|Cruise Track||This test involves the visual inspection of the data as received at the processing centre. The stations of observations should be arranged in what constitute "cruises". This test plots the cruise track, allowing the identification of gross position errors.|
|Profiles||This step is of the utmost importance. It allows one to see and compare the original STD profile with the one resulting from the quality control procedure (in which the data marked as doubtful, erroneous, or missing are not shown). The validity of the data set is determined at this step in the quality control. The profiles of the observations should be viewed at each station. This review will identify any questionable variations in the parameters and set quality flags as appropriate.|
- 1. How to acknowledge GTSPP data?
- 2. How to encode the GTSPP quality tests?
- 3. How to find the XBT information?
- 4. How to interpret the GTSPP ASCII files?
- 5. How to interpret the GTSPP quality test codes and results?
- 6. How to select only stations with temperature and salinity profiles
- 7. How to select only stations that have a quality flag of 'good' for the position and date/time
- 8. What are the GTSPP Best Copy files?
- 9. What are the GTSPP QC flags?
- 10. What are the GTSPP QC tests?