Data Quality Assessment for ARM Radiation Data (QCRAD) VAP Now Operational

 
Published: 31 July 2016
An example plot shows diffuse shortwave data at the Azores for the year 2015. The red curve represents physically possible limits, the green and blue curves represent empirically determined limits for indeterminate and bad data respectively. Points identified by a misaligned solar tracker are shown in cyan.
An example plot shows diffuse shortwave data at the Azores for the year 2015. The red curve represents physically possible limits; the green and blue curves represent empirically determined limits for indeterminate and bad data respectively. Points identified by a misaligned solar tracker are shown in cyan.

The Data Quality Assessment for ARM Radiation Data (QCRAD) value-added product (VAP) is now running operationally for the ARM Mobile Facility deployment at Oliktok Point, Alaska, and Eastern North Atlantic site in the Azores. QCRAD has long been the recommended ARM datastream for broadband surface irradiance measurements.

This VAP applies multiple data quality checks, applies a correction for errors due to infrared loss in shortwave radiometric measurements, and calculates a best-estimate total downwelling shortwave irradiance value.

The QCRAD methodology uses climatological analyses of the surface radiation measurements to define reasonable limits for testing the data for unusual data values. The main assumption is that the majority of the measurements are “good” data, which for field sites operated with care—such as those of the ARM Facility—is a reasonable assumption.

Data that fall outside the normal range of occurrences are labeled either “indeterminate” or “bad,” depending on how far outside the normal range the particular datum resides. The methodology not only sets fairly standard maximum and minimum value limits, but includes many cross-comparisons based on what has been learned about how these instruments behave in the field in developing other VAPs.

The QCRAD VAP routinely produces two daily files containing one-minute radiation measurement fields and their QC values. The *.c1-level file includes auxiliary information and detailed qc flags. The *.s1-level summary file includes a simplified version of the qc flags and fewer auxiliary data values.

During operational processing, the QCRAD VAP applies a generic correction to the shortwave (SW) downwelling hemispheric flux to correct for infrared loss within the radiometer. On a yearly basis, a more detailed correction that uses infrared loss corrections derived for the specific instruments (rather than the generic correction) is applied. This correction will affect the output of the downwelling SW values for those occasions where the sum of the direct plus diffuse SW is not available as the “best estimate” for downwelling SW. When the *.c2 and *.s2 files are available, they should be used.

Feedback and use of the data are welcomed and encouraged. For questions or to report data problems, please contact Yan Shi or Laura Riihimaki. To access the data set, please browse the ARM Data Archive. (Go here to create an account to download the data.)

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The ARM Climate Research Facility is a national scientific user facility funded through the U.S. Department of Energy’s Office of Science. The ARM Facility is operated by nine Department of Energy national laboratories.