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In collecting any type of meteorological data, it is generally a good practice to subject the data to quality control (QC) checks. Sometimes this is done in real time, and sometimes it is done during post-processing of the data. In the Model VT-1, primary checks on the data validity are performed in real time as the data are collected, and a Reliability value of either 0 or 9 is assigned, with 9 indicating reliable data and 0 indicating unreliable data. These primary checks involve testing the data signal-to-noise ratio, the signal amplitude (strength), and the number of valid samples for the averaging period. If the user desires, secondary QC tests can be enabled to test data that have passed the primary acceptance criteria. When enabled, the secondary QC checks are performed at each data averaging interval, and intermediate Reliability values are assigned to data that do not meet these secondary tests. The graphic shown below displays the menu for the Secondary Quality Control Options in the Model VT-1 software (which is called PCSodar):
The various QC tests include rate-of-change of component and vector speeds, maximum component standard deviation, standard deviation ratio of the horizontal components, noise tests, echo checks and tests for precipitation interference. When the data do not meet these secondary QC tests, the data Reliability value is lowered to an intermediate value (5 or less). Typically, the user will want to exclude any data from the final validated data base when the Reliability value is less than 9.
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