1. Introduction

MODIS-Aqua Reprocessing 2013.1 is a partial mission reprocessing to mitigate mirror-side striping artifacts detected in ocean color products over the last year of the mission (August 2012-September 2013). Data collected prior to 1 August 2012 is unchanged.

2. Changes

2.1. Instrument Calibration

The basis of this reprocessing is the MODIS Calibration Support Teams (MCST) look-up table (LUT) V6.1.17.7_OC6. From start of mission through end of 2012, this LUT is identical to V6.1.17.7_OC2, which is the LUT applied for R2013.0. This LUT includes time-varying corrections for changes in response versus scan angle (RVS) for bands 8 and 9, which were derived using observations of desert sites. Uncertainty in this method resulted in a growing discrepancy between the two mirror sides that varied across the scan and resulted in mirror-side striping in the derived ocean color products. The revised calibration from MCST significantly reduces these artifacts. The OBPG cross-calibration corrections, similar to Meister et al. 2011 but using global MODIS-Aqua Level-3 water-leaving radiance retrievals as the vicarious calibration source, have been updated to further improve mirror-side, detector, and cross-scan stability. The updated cross-calibration corrections, in combination with the new MCST LUT, are merged into the processing starting in August 2012, to minimize any discontinuity.

2.2. Processing Algorithms

Processing algorithms are identical with the previous reprocessing (R2010.0, R2012.0, R2013.0).

3. Results

The impact to large-scale regional means in the ocean color time-series is minimal. The plot below shows the averages of the MODIS Aqua Rrs in global deep water as a function of time both for R2013.0 (AT101, solid lines) and R2013.1 (AT103, dashed lines).

The plots below show the chlorophyll trend across-scan for day 130 of 2013. The red and blue colors indicate the different mirror sides, and the lines indicate individual detectors of the 10 MODIS along-track detectors per band. These plots were derived by accumulating all clear-water pixels over a global day, normalizing them to their co-located 15-day mean value (averaged over many scan geometries), stratifying the data by mirror-side, detector, and scan pixel, and averaging. The plot on the left shows the result before the R2013.1 calibration update, where severe mirror-side differences and significant detector striping is evident. The plot on the left is after R2013.1 reprocessing, showing that these artifacts have been significantly reduced.

4. Update R2013.1.1

On 8 November 2013 a partial reprocessing back to mission date 1 September 2013 was performed. This change just incorporated improved instrument calibration knowledge. Again, the impact to large-scale regional means in the ocean color time-series is minimal. The plot below shows the averages of the MODIS Aqua Rrs in global deep water as a function of time before and after the change.

The plots below show the chlorophyll trend across-scan for day 289 of 2013. The plot on the left shows the result before the R2013.1.1 calibration update, and the plot on the left is after R2013.1.1 reprocessing. Results just demonstrate that cross-scan, mirror-side, and detector striping artifacts have been significantly reduced.