Handbook of Quality Control Procedures and Methods for Surface Meteorology Data - COAPS
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Abstract
The Data Assembly Center (DAC) for Surface Meteorology at Florida State University is charged with collecting, quality controlling, archiving, and distributing all underway surface meteorological data from WOCE vessels worldwide. The scope of the DAC 's collection efforts also includes all surface meteorological data from WOCE-sponsored experiments (i.e. Subduction Experiment). Types of data collected include standard ship bridge observations, advanced automated systems (e.g. Improved METeorology (IMET) measurements system), and all other practically obtainable surface meteorological data from WOCE research vessels and buoys.
Once the data are collected, the DAC verifies the accuracy of the measurements using a series of data quality evaluation procedures. The focus of the DAC Handbook of Quality Control Procedures and Methods is to describe the methodology and detail these quality control (QC) procedures. The DAC intends for this document to be used by the WOCE scientific community as well as other interested researchers. The flagging procedures contained in this report may also be of general interest to data evaluators from the international data centers (NCDC, NCAR, BODC, etc.).
The overall goal of the DAC's QC is to provide a well-documented, reliable, and consistent data set to the scientific community. The DAC evaluates the data to the best level possible with the QC results depending primarily on the level of knowledge of the incoming data as well as examination and analysis of the data. Information provided about how the data were collected, i.e. metadata, is an essential component of any data set, particularly in light of the historical context of climate variability. Metadata will be included with all DAC quality controlled data sets either as additions to the data or as a part of the QC reports. Ideally, the metadata contains information on the instrument setup, calibrations, and formats for the meteorological data.
Data quality flagging, not value replacement, is the method used to denote suspect or erroneous data. The choice to flag questionable data at the DAC, as opposed to data correction, was made to insure the data remain in the original form that was sent to the DAC. For scientific reasons, the end user must determine appropriate utilization of the flags provided. This will allow additional processing/decisions to be made at later times.
The QC procedure for all WOCE data sets is a four-step process schematically outlined in Fig. 1. The process begins with the acquisition of a WOCE meteorological data set and accompanying metadata (e.g. README file). The first step of the QC is converting the meteorological data to a standard format for internal use at the DAC. The format includes metadata and is described in Section 2. Once converted, the data are sent through an automated preprocessing program that checks for values outside of a realistic range, statistical outliers, unrealistic ship movements, etc. The preprocessing procedures are outlined in Section 3. During the third step of the QC, the preprocessed meteorological data are visually inspected by a trained Data Quality Evaluator (DQE) using the VIsual Data Assessment Tool (VIDAT). VIDAT is an interactive, graphically-based tool developed at the FSU DAC, that allows the DQE to add or remove QC flags from the meteorological data. VIDAT is described in detail in Section 4. When the meteorological data have passed all final inspections, the data are converted to a standard format suitable for public distribution and further analysis. At this time a QC report is written combining flag information from the preprocessor and the DQE 's VIDAT evaluation. More information, i.e. calibrations done prior to the data's arrival at the DAC, may be extracted from the metadata and added to the QC report. The resulting quality controlled data and report are then made available for the WOCE community.