QCAOD

Because of differences in instrument design and data processing, individual aerosol optical depth (AOD) products vary in continuity, data quality, and temporal resolution. The Quality Control Aerosol Optical Depth (QCAOD) value-added product (VAP) generates 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.

QCAOD covers a 21-year period (1997–2018) at ARM’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 these instruments with the corresponding datastreams in parentheses:

• two multifilter rotating shadowband radiometers, one at the SGP Central Facility, or C1 (mfrsraod1michC1.c1), and the second at extended facility E13, which is co-located with C1 (mfrsraod1michE13.c1)
• the normal incidence multifilter radiometer at C1 (nimfraod1michC1.c1)
• the Cimel sunphotometer at 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 defined AODs at 500 nm provides the basic statistics: mean bias together with slope and square of correlation coefficient from linear regression. 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.

PURPOSE

The QCAOD VAP generates a combined AOD at two wavelengths (500 and 870 nanometers) with high-quality, enhanced continuity and fine (1-minute) temporal resolution.