AATSR Level 2 Flags

Flags are raised at different stages during measurement and processing, and the final level 2 flags are a result of this. The purpose of these flags is to provide

  1. information about the validity of pixel content with respect to algorithms used,
  2. surface type information (land/water/cloud),
  3. information about the presence of cloud, and the algorithm used to detect it
  4. information that may have a bearing on data quality.

The flags are stored in 2 bytes, with bits 14 and 15 left blank.

Flag code Value Bit* Binary Explanation
NADIR_SST ONLY_ VALID 1 0 000000 00000001 True when temperatures could be retrieved from nadir measurements, whether SST, cloud top BT at 11um, or land BT at 11um.
NADIR_SST_ONLY_ 37_ MY_VALID 2 1 000000 00000010 Night time; pixel with valid SST calculated using a 3 channel algorithm (11, 12 and 3.7 from nadir view).
DUAL_SST_ VALID 4 2 000000 00000100 Sea, ice or land temperature has been retrieved using both nadir and forward view, using either a 4 or a 6 channel algorithm, using both look angles.
DUAL_SST_ VALID_37_MY 8 3 000000 00001000 Night time pixel with valid SST calculated using a 6 channel algorithm (11, 12 and 3.7 from both look-angles).
LAND 16 4 000000 00010000 Land pixel. sst_nadir image shows BT at 11um as an estimate of land temperature (may change when algorithms for land temperature developed).
NADIR_CLOUD 32 5 000000 00100000 Cloud identified as a result of cloud clearing tests performed on nadir view (AATSR handbook 2.5.1.1.10).
NADIR_BLANKING 64 6 000000 01000000 RA-2 or ASAR was transmitting when the nadir measurement was made, possible cause of interference.
NADIR_COSMETIC 128 7 000000 10000000 Nadir look pixel with missing data has been filled in by interpolation from neighbouring sample
FWARD_CLOUD 256 8 000001 00000000 Cloud identified as a result of cloud clearing tests performed on forward view (AATSR handbook 2.5.1.1.10).
FWARD_BLANKING 512 9 000010 00000000 RA-2 or ASAR was transmitting when the forward measurement was made, possible cause of interference.
FWARD_COSMETIC 1024 10 000100 00000000 Forward look pixel filled in with data from neighbouring sample
CLOUDY_16_MY 2048 11 001000 00000000 Cloud identified by the1.6 um histogram test (AATSR handbook 2.6.1.1.10.6) , which detects cloud over sea pixels only based on a histogram from a window of 32x32 pixels.
CLOUDY_ 11_ 12_MY 4096 12 010000 00000000 Clouds identified with the 11/12 or 11/3.7 nadir/forward test (AATSR handbook 2.6.1.1.10.7 ), capable of detecting small, vertical clouds.
CLOUDY_ HISTO 8192 13 100000 00000000 Cloud identified by the IR histogram test (see AATSR handbook 2.6.1.1.10.8)

*   Binary position containing 1 when the flag is set.