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

Bit	Name	Description
01	ATMFAIL	Atmospheric correction failure
02	LAND	Pixel is over land
03	BADANC	Reduced quality of ancillary data
04	HIGLINT	High sun glint
05	HILT	Observed radiance very high or saturated
06	HISATZEN	High sensor view zenith angle
07	COASTZ	Pixel is in shallow water
08	NEGLW	Negative water-leaving radiance retrieved
09	STRAYLIGHT	Straylight contamination is likely
10	CLDICE	Probable cloud or ice contamination
11	COCCOLITH	Coccolithofores detected
12	TURBIDW	Turbid water detected
13	HISOLZEN	High solar zenith
14	HITAU	High aerosol optical thickness
15	LOWLW	Very low water-leaving radiance (cloud shadow)
16	CHLFAIL	Derived product algorithm failure
17	NAVWARN	Navigation quality is reduced
18	ABSAER	possible absorbing aerosol (disabled)
19	TRICHO	Possible trichodesmium contamination
20	MAXAERITER	Aerosol iterations exceeded max
21	MODGLINT	Moderate sun glint contamination
22	CHLWARN	Derived product quality is reduced
23	ATMWARN	Atmospheric correction is suspect
24	DARKPIXEL	Rayleigh-subtraced radiances is negative
25	SEAICE	Possible sea ice contamination
26	NAVFAIL	Bad navigation
27	FILTER	Pixel rejected by user-defined filter
28	SSTWARN	SST quality is reduced
29	SSTFAIL	SST quality is bad
30	HIPOL	High degree of polarization
31	spare	spare
32	OCEAN	not 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.

Curator: OceanColor Webmaster

Authorized by: gene carl feldman