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The first full-mission AVHRR FRAC SST dataset with nominal 1.1km resolution at nadir was created from three Metop First Generation (FG) satellites: A (2006-present), B (2012-present) and C (2018-present), using the NOAA Advanced Clear-Sky Processor for Ocean (ACSPO) enterprise system. Historical reprocessing (Reanalysis-1, RAN1) starts at the beginning of each mission and continues into near-real time (NRT) processing. ACSPO generates two SST products: Global Regression (GR) SST, highly sensitive to the skin SST, and Piecewise Regression (PWR) SST, a proxy for the depth SST. The effect of orbital and sensor drift on the stability of the SST time series is mitigated by retraining the regression coefficients daily against matchups with the drifting and tropical moored buoys. Those matchups are collected within moving windows: 91-day for GR and 361-day for PWR, with the offsets adjusted within a 31 day window. In RAN1, all training and offset correction windows are centered at the processed day. In NRT processing, the training and offset delayed windows of the same sizes and ending in 4-10 days prior to the processed day are used. This mitigates longterm calibration trends on scales from 1-2 months in both RAN1 and NRT. Short-term variations in SST biases in NRT are higher than in RAN1 but do not exceed ~0.05 K. Delayed-mode RAN processing follows the NRT with a lag of ~2 months, resulting in higher quality, more consistent Metop-FG SST record. The presentation evaluates the performance of the ACSPO AVHRR FRAC dataset and compares it with the EUMETSAT OSISAF Metop-A and -B FRAC SSTs available in PO.DAAC.
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