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Processing Flags and Masks

As the data is processed, checks are made for different defined conditions (shown in the table below). When certain tests and conditions are met for a given pixel, then a flag is applied to that pixel for that condition. This is done in the processing by setting the bit number assigned to that condition. A pixel can have more than one flag applied to it.

If a certain flag exists for a pixel, it can be specified that a mask should be applied to it. During processing of Level 2 or Level 3 (or both), if a conditon is set as a mask, then the flagged pixel will be set to zero and not valid. The pixel is removed from the valid data values and will not affect your analysis.

The table below shows the flags and masks that are operational in the Level 2 and Level 3 Ocean Color Processing.
(Flags in RED are masked at Level 3 - ocean color processing)

Level-2 Flags

BitNameDescription
01ATMFAILAtmospheric correction failure
02LANDPixel is over land
03sparespare
04HIGLINTHigh sun glint
05HILTObserved radiance very high or saturated
06HISATZENHigh sensor view zenith angle
07COASTZPixel is in shallow water
08NEGLWNegative water-leaving radiance retrieved
09STRAYLIGHTStraylight contamination is likely
10CLDICEProbable cloud or ice contamination
11COCCOLITHCoccolithofores detected
12TURBIDWTurbid water detected
13HISOLZENHigh solar zenith
14HITAUHigh aerosol optical thickness
15LOWLWVery low water-leaving radiance (cloud shadow)
16CHLFAILDerived product algorithm failure
17NAVWARNNavigation quality is reduced
18ABSAERpossible absorbing aerosol (disabled)
19sparespare
20MAXAERITERAerosol iterations exceeded max
21MODGLINTModerate sun glint contamination
22CHLWARNDerived product quality is reduced
23ATMWARNAtmospheric correction is suspect
24DARKPIXELRayleigh-subtraced radiances is negative
25SEAICEPossible sea ice contamination
26NAVFAILBad navigation
27FILTERPixel rejected by user-defined filter
28SSTWARNSST quality is reduced
29SSTFAILSST quality is bad
30HIPOLHigh degree of polarization
31PRODFAILDerived product failure
32OCEANnot cloud or land

  • HIGLINT:This bit is set if glint reflectance exceeds 0.005

  • HILT:This bit is set if digital count value in bands 7 and 8 is above knee

  • HISATZEN:This bit is set if 60 degree satellite zenith threshold is reached

  • STRAYLIGHT: MODIS, SeaWiFS

  • SSTWARN: If the sst (or sst4) product is requested for output, this bit will be set in l2_flags if qual_sst (or qual_sst4) is 1.

  • SSTFAIL: If the sst (or sst4) product is requested for output, this bit will be set in l2_flags if qual_sst (or qual_sst4) is greater than or equal to 2.



    • To read more about the masks and flags used in the processing,
    download the following pdf: Algorithm Updates for the Fourth SeaWiFS Data Reprocessing.


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    Updated: Wednesday, 01-Jul-2009 17:04:20 EDT