Aqua MODIS surface reflectance band 1-2-1 data from the MYD09GQ product over western United States, March 14, 2017.View full-size image
The MYD09GQ Version 6 product provides an estimate of the surface spectral reflectance of Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) 250 meter (m) bands 1 and 2, corrected for atmospheric conditions such as gasses, aerosols, and Rayleigh scattering. Along with the 250 m bands are the Quality Assurance (QA) layer and five observation layers. This product is intended to be used in conjunction with the quality and viewing geometry information of the 500 m product (MYD09GA).
|File Size||95 MB|
|Temporal Extent||2002-07-04 to Present|
|Geographic Dimensions||1200 km x 1200 km|
|Number of Science Dataset (SDS) Layers||8|
|Columns/Rows||4800 x 4800|
|Pixel Size||250 m|
|SDS Name||Description||Units||Data Type||Fill Value||No Data Value||Valid Range||Scale Factor|
|num_observations||Number of observations per 250m pixel||N/A||8-bit signed integer||-1||N/A||0 to 127||N/A|
|sur_refl_b01_1||Surface Reflectance Band 1||N/A||16-bit signed integer||-28672||N/A||-100 to 16000||0.0001|
|sur_refl_b02_1||Surface Reflectance Band 2||N/A||16-bit signed integer||-28672||N/A||-100 to 16000||0.0001|
|QC_250m_1||Surface Reflectance 250m Quality Assurance||Bit Field||16-bit unsigned integer||2995||N/A||0 to 4096||N/A|
|obscov_1||Observation coverage||Percent||8-bit signed integer||-1||N/A||0 to 100||0.01|
|iobs_res_1||Observation number||N/A||8-bit unsigned integer||255||N/A||0 to 254||N/A|
|orbit_pnt_1||Orbit pointer||N/A||8-bit signed integer||-1||N/A||0 to 15||N/A|
|granule_pnt _1||Granule pointer||N/A||8-bit unsigned integer||255||N/A||0 to 254||N/A|
The Number of Science Dataset Layers is a minimum of 8. If the "L2G Storage Format" metadata value is "full" additional data layers are present with the suffix _f. If the "L2GStorageFormat" metadata value is "compact" additional data layers are present with the suffix _c.
The QC_250m_1 layer is stored in an efficient bit-encoded manner. The unpack_sds_bits executable from the LDOPE Tools is available to the user community to help parse and interpret this layer.
The QA bit flags for the QC_250m_1 layer is provided in Table 8 of the User Guide on page 19.
Quality assurance information should be considered when determining the usability of data for a particular science application. The ArcGIS MODIS-VIIRS Python Toolbox contains tools capable of decoding quality data layers while producing thematic quality raster files for each quality attribute.
In addition to data access and transformation processes, AppEEARS also has the capability to unpack and interpret the quality layers.
The Collection 6 MODIS Land Surface Reflectance product (MYD09) may incorrectly flag retrievals as ‘High Aerosol’ over brighter surfaces and at higher view angles. This will impact the downstream MODIS BRDF/Albedo (MCD43) and Vegetation Index (MOD13 and MYD13) data products which use the aerosol quantity flag to screen out high aerosol values.
Corrections will be implemented in Collection 6.1 reprocessing in 2020.
For complete information about the MYD09GQ known issues please refer to the MODIS Land Quality Assessment website.