13 September 2023
Individual aerosol optical depth (AOD) products vary in continuity, data quality, and temporal resolution, because of differences in instrument design and data processing. The Aerosol Optical Depth Best Estimate value-added product (AODBE VAP), previously known as Quality Control Aerosol Optical Depth (QCAOD), merges individual products to generate combined AOD with high-quality, enhanced continuity and fine (1-minute) temporal resolution. Two AODBE data products are available: the first (AODBE2CH) at two wavelengths—500 and 870 nanometers—and the second (AODBE5CH) at five wavelengths—415, 500, 615, 673, and 870 nm. In addition, AODBE provides uncertainty assessment of the individual and combined AODs.
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The AODBE VAP 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 wavelength 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 each wavelength with 1-minute temporal resolution using individual AODs identified during the first step. For the AODBE2CH product, 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 AODBE5CH product provides combined AODs calculated as a third-degree, least-squares polynomial best fit of the identified AODs, in addition to the combined AODs calculated as the mean.