Because of differences in instrument design and data processing, individual aerosol optical depth (AOD) products vary in continuity, data quality, and temporal resolution. The new Quality Control Aerosol Optical Depth (QCAOD) value-added product (VAP) merges individual products to generate a combined AOD at two wavelengths—500 and 870 nanometers—with high-quality, enhanced continuity and fine (1-minute) temporal resolution. In addition, QCAOD provides uncertainty assessment of the individual and combined AODs.
Currently an evaluation VAP, QCAOD covers a 21-year period (1997–2018) at the Atmospheric Radiation Measurement (ARM) user facility’s Southern Great Plains (SGP) atmospheric observatory. The VAP merges four individual AOD products from four co-located, ground-based instruments.
Here is a list of the instruments with the corresponding datastreams in parentheses:
- two multifilter rotating shadowband radiometers, one at the SGP Central Facility, or C1 (mfrsraod1michC1.c1), and the other at extended facility E13, which is co-located with SGP C1 (mfrsraod1michE13.c1)
- the normal incidence multifilter radiometer at SGP C1 (nimfraod1michC1.c1)
- the Cimel sunphotometer at SGP C1 (sgpcsphotaodfiltqav3C1.a1).
QCAOD involves two main steps regarding the uncertainty assessment.
First, it identifies the individual AODs with good quality and harmonized 1-minute temporal resolution. The subsequent pairwise intercomparison of the identified AODs at 500 nm provides basic statistics: mean bias together with slope and square of correlation coefficient.
Second, it calculates the combined AOD and its variability (or uncertainty) at 500 and 870 nm with 1-minute temporal resolution using individual AODs identified during the first step. The combined AOD is calculated as the mean of the identified AODs at a given time step, while its variability is specified by both range and standard deviation.
The QCAOD evaluation VAP is available now and is the preferred AOD data product for the January 16, 1997–December 6, 2018, time span.
NOTE: For the period before January 16, 1997, this product contains AODs from a single datastream (sgpcsphotaodfiltqav3C1.a1) and should not be used.
More information about QCAOD can be found on the VAP web page.
To share your experience—such as how you use the data and how well they work for you—or to ask a question, contact Erol Cromwell, the VAP’s lead developer, or Evgueni Kassianov.
Access the data set in the ARM Data Center. (Go here to create an account to download the data.)
To cite the QCAOD data, please use doi:10.5439/1435403.