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STAR / SMCD / VIIRS Aerosol Calibration and Validation

VIIRS Aerosol Algorithm Changes

The table below lists major algorithm changes to date (December 31, 2015).

*Algorithm changes*
Description of change	Date (month/day/year)	Time (UTC) (hour:minute)	Impact
Revised ingest of NAAPS aerosol data to fill AOT where no VIIRS retrievals are made.	08/10/2012	16:18	Minor. Before the change NAAPS aerosol data were "upside down"; the algorithm change corrected this. Note that NAAPS-filled data are not used in the EDR. Users also have the option of disregarding NAAPS-filled pixels in the IP.
Corrected calculation of molecular spherical albedo.	08/10/2012	16:18	Minor; This change fixes an error in calculating the molecular spherical albedo. Analysis of the error showed that it had only a minor impact on the retrieved AOT.
Logic in counting the land/water pixels in the AOT EDR aggregation algorithm was corrected.	10/15/2012	15:19	Minor. No more incorrect AOT fill values near granule edges.
Tests for identifying volcanic ash were tuned out in the VIIRS Cloud Mask (VCM) algorithm.	11/02/2012		Significant. No volcanic ash in Suspended Matter (SM) product after this update.
Erroneous change in reading VCM input.	10/15/2012		Significant. AOT retrievals were performed for cloudy pixels as well, rendering AOT values invalid.
Reading VCM input was corrected.	11/27/2012	14:58	Significant. Retrievals are no longer performed for cloudy pixels; invalid AOT values are eliminated.
New spectral surface reflectance ratios over land were implemented.	01/22/2013		Significant. Previously observed overall high AOT bias (compared to MODIS and AERONET) was significantly reduced.
Fixed a minor bug that caused missing granules under certain circumstances when retrieval for a pixel failed.	07/10/2013	16:37	Minor. Failure of retrieval of single pixel no longer results in an entire missing granule.
VIIRS M6 (746 nm) band is no longer used in over-ocean inversion when quality flag indicates "Out of Range" (due to saturation over bright dust plumes).	11/14/2013	20:25	Minor. AOT retrieval in bright dust plumes scenes should be improved, but due to the infrequent occrance of the event no noticbale impact on AOT retrieval is observed.
Calculation of residual for band M7 is skipped in over-ocean aerosol retrieval	02/20/2014	14:41	Minor. In the calculation of residual over ocean the contribution of band M7 is meant to be ignored since the observed and calculated M7 reflectances are the same. The impact on AOT retrieval is negligible.
Fixed a coding Error in the VIIRS Aerosol Algorithm Land Residual Calculation	02/20/2014	14:41	Minor. A coding error causes incorrect surface reflectance in band M5 to be used in the first three iterations of the residual calculation. This can result in a significant error in AOT when an incorrect aerosol model is selected as a result of the error in the residual calculation. But due to the infrequent occurrence of the event, no significant impact on AOT retrieval is observed.
Consistency check on the Angstrom Exponent and Suspended Matter QFs; AOT Quality at Bowtie deleted pixels is corrected as 'Not Produced'	08/13/2014	15:25	Minor. Angstrom Exponent and Suspended Matter QFs are in better consistency with AOT QFs. No significant impact on AOT retrieval is observed. Some impact on the Suspended Matter product.
Update internal snow/snowmelt test and implement internal spatial homogeneity test	06/22/2015	19:43	Significant for snow covered regions during springthaw seasons. High AOT biases over high latitudes during spring thaw seasons are corrected with better snow and snowmelt screening; high AOT biases over unfavorable heterogeneous retrieving conditions, such as popcorn cloud scences and snowmelt regions, are also corrected with better snowmelts tests and homogeneity test. Changes are over land only.
Remove the internal ephemeral water test; update the internal bright surface test (Mx8.11)	12/17/2015	20:08	Significant over desert and some very heavy smoke events. Excessive ephemeral water screening over desert regions is removed; Regain more AOT retrievals for very heavy smoke plumes that were previously screend by the internal ephemeral water test; Improve the performance of the internal bright surface test, particularly over desert regions
Add AOT and residuals from all five land aerosol models in the IVAOT outputs	Mx8.12 TTO	TBD	No impact on the VIIRS aerosol retrievals. More diagnostic evaluation on the performance of all five land aerosol models can be conducted; Downstream products such as surface reflectance have wider selection of AOT retrievals as their inputs in terms of their perference of land aerosol models.