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MODIS Daily Surface Reflectance 1km and 500m QA Science Data Sets
The QA information below is excerpted from an HDF-EOS file of the MODIS Surface Reflectance product MYD09GA, and is also available in the V005 file specifications found at ftp://modular.nascom.nasa.gov/pub/LatestFilespecs/collection5/.
The MYD09GA product includes two data groups, one for the 1-km state data and one for the 500-m reflectance data. Between both, there are four bit fields subject to interpretation. Table 1 describes the 1-km QA State. Table 2 is the bit legend for the 1-km geolocation flags. Table 3 describes the 500-m QA values. Table 4 interprets the q_scan values relating 250-m to 500-m data.
Table 1: 1-kilometer State QA Descriptions (16-bit)
Note that all bit flags in this SDS can be applied to the respective 500m and 250m reflectance data.
| Bit No. | Parameter Name | Bit Comb. | state_1km |
| 0-1 | cloud state | 00 | clear |
| 01 | cloudy | ||
| 10 | mixed | ||
| 11 | not set, assumed clear | ||
| 2 | cloud shadow | 1 | yes |
| 0 | no | ||
| 3-5 | land/water flag | 000 | shallow ocean |
| 001 | land | ||
| 010 | ocean coastlines and lake shorelines | ||
| 011 | shallow inland water | ||
| 100 | ephemeral water | ||
| 101 | deep inland water | ||
| 110 | continental/moderate ocean | ||
| 111 | deep ocean | ||
| 6-7 | aerosol quantity | 00 | climatology |
| 01 | low | ||
| 10 | average | ||
| 11 | high | ||
| 8-9 | cirrus detected | 00 | none |
| 01 | small | ||
| 10 | average | ||
| 11 | high | ||
| 10 | internal cloud algorithm flag | 1 | cloud |
| 0 | no cloud | ||
| 11 | internal fire algorithm flag | 1 | fire |
| 0 | no fire | ||
| 12 | MOD35 snow/ice flag | 1 | yes |
| 0 | no | ||
| 13 | Pixel is adjacent to cloud | 1 | yes |
| 0 | no | ||
| 14 | BRDF correction performed | 1 | yes |
| 0 | no | ||
| 15 | internal snow algorithm flag | 1 | yes |
| 0 | no |
Table 2: 1-kilometer Geolocation Flags (16-bit)
| Bit No. | Description | Bit Comb. | state_1km |
| 0-2 | fill | 00 | Fill |
| 3 | Sensor range validity flag | 0 | Valid |
| 1 | Invalid | ||
| 4 | Digital elevation model quality flag | 0 | Valid |
| 1 | Missing/inferior | ||
| 5 | Terrain data validity | 0 | Valid |
| 1 | Invalid | ||
| 6 | Ellipsoid intersection flag | 0 | Valid intersection |
| 1 | No intersection | ||
| 7 | Input data flag | 0 | Valid |
| 1 | Invalid |
Table 3: 500-meter QA Descriptions (32-bit)
| Bit No. | Parameter Name | Bit Comb. | QC_500m |
| 0-1 | MODLAND QA bits | 00 | corrected product produced at ideal quality all bands |
| 01 | corrected product produced at less than ideal quality some or all bands | ||
| 10 | corrected product not produced due to cloud effects all bands | ||
| 11 | corrected product not produced due to other reasons some or all bands may be fill value [Note that a value of (11) overrides a value of (01)]. | ||
| 2-5 | band 1 data quality four bit range | 0000 | highest quality |
| 0111 | noisy detector | ||
| 1000 | dead detector; data interpolated in L1B | ||
| 1001 | solar zenith >= 86 degrees | ||
| 1010 | solar zenith >= 85 and < 86 degrees | ||
| 1011 | missing input | ||
| 1100 | internal constant used in place of climatological data for at least one atmospheric constant | ||
| 1101 | correction out of bounds pixel constrained to extreme allowable value | ||
| 1110 | L1B data faulty | ||
| 1111 | not processed due to deep ocean or clouds | ||
| 6-9 | band 2 data quality four bit range | SAME AS BAND ABOVE | |
| 10-13 | band 3 data quality four bit range | SAME AS BAND ABOVE | |
| 14-17 | band 4 data quality four bit range | SAME AS BANDABOVE | |
| 18-21 | band 5 data quality four bit range | SAME AS BAND ABOVE | |
| 22-25 | band 6 data quality four bit range | SAME AS BAND ABOVE | |
| 26-29 | band 7 data quality four bit range | SAME AS BAND ABOVE | |
| 30 | atmospheric correction performed | 1 | yes |
| 0 | no | ||
| 31 | adjacency correction performed | 1 | yes |
| 0 | no |
The 250-m samples are for each of four quadrants within a 500-m cell. The first line/sample is in the upper left (north-west) corner of the image.
0 -- first 250m line (row), first 250m sample (column)
1 -- first 250m line, second 250m sample
2 -- second 250m line, first 250m sample
3 -- second 250m line, second 250m sample.
Table 4: 250-meter Scan Value Information Description (8-bit)
| Bit No. | Parameter Name | Bit Comb. | q_scan |
| 0 | missing observation in quadrant 4 [+0.5 row, +0.5 column]; | 1 | yes |
| 0 | no | ||
| 1 | missing observation in quadrant 3 [+0.5 row, -0.5 column]; | 1 | yes |
| 0 | no | ||
| 2 | missing observation in quadrant 2 [-0.5 row, +0.5 column] | 1 | yes |
| 0 | no | ||
| 3 | missing observation in quadrant 1 [-0.5 row, -0.5 column] | 1 | yes |
| 0 | no | ||
| 4 | scan of observation in quadrant 4 [+0.5 row, +0.5 column] | 1 | same |
| 0 | different | ||
| 5 | scan of observation in quadrant 3 [+0.5 row, +0.5 column] | 1 | same |
| 0 | different | ||
| 6 | scan of observation in quadrant 2 [+0.5 row, +0.5 column] | 1 | same |
| 0 | different | ||
| 7 | scan of observation in quadrant 1 [+0.5 row, +0.5 column] | 1 | same |
| 0 | different |
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