Quality Control Procedures

Every day, the instruments voltage in the dataloggers are downloaded to the UVMRP database servers at Colorado State University. This process typically takes four hours. Any sites which experience connectivity issues are addressed by UVMRP staff on the next business day. After the download processes are completed, numerous automated scripts begin the tasks of applying quality control and calibration factors to ensure that the data is of the highest standard.

The Quality Control (QC) procedures for the UVMRP database consist of a combination of daily automated detection and manual visual inspection of the raw data files. The visual inspection of segments of the raw and calibrated data is based upon known problems with specific instruments, error codes found during the capturing of the data, and errors due to weather-related problems, which can cause aberrant positive or negative spikes in the data. The QC codes for this type of data are either manually entered for short duration problems or via automatic batch programming for longer duration problems. QC codes are divided into three levels which indicate how serious the problem is, in order to provide automated caution statements for file transfers and web users.

Mauna Loa Observatory

Another critical issue for continued operation of the monitoring program is the accurate and frequent characterization of the radiometric, spectral, and angular responses of the instruments in a manner that is traceable to the National Institute of Standards and Technology (NIST). The Central UV Calibration Facility (CUCF), established in 1994 at the NOAA Earth System Research Laboratory in Boulder, CO, is recognized as the premier UV calibration lab by the World Meteorological Organization. To maintain scientifically-credible calibration of the instruments, UVMRP primarily uses in-situ Langley calibration techniques with an improved cloud screening module and a stable total optical depth selection module for the daily data, augmented by cycling the instruments through an intercomparison platform at the world-renown Mauna Loa Observatory (MLO), and supplemented on an as-needed basis with laboratory NIST-traceable lamp calibrations from CUCF. MLO, HI and CUCF, Boulder, CO are used by several other atmospheric monitoring organizations for similar calibration purposes. The original project instrumentation deployed at MLO in November 1997 as part of the climatological network has now become part of a suite of reference instruments. In December 2009 mounting pads and associated dataloggers were installed for additional reference instruments and for field instruments that are cycling through for periodic re-calibration.

New Langley Process

An analysis program has been implemented for UV-MFRSR and UVB-1 broadband instruments that have recently been calibrated at MLO. The purpose is to confirm the quality of the Langley calibration process which is used to calibrate UV-MFRSR heads at MLO, and the calibration program that is used to calibrate UVB broadband instruments deployed concurrently with the MFRSRs. The technique uses the synthetic spectrum algorithm applied to the UV MFRSR measurements to obtain erythemal irradiances averaged over the calibration deployment period (usually about a month) and compares these averages with the UVB broadband instruments’ measurements averaged over the same period. In an ideal world all the mean values should agree. The extent to which the means show disagreement serves as an additional quality control measure for our data collection network and avoids complications that arise in the rare case of a nonconforming instrument being deployed to a field site.