MYD21A1N v006

MODIS/Aqua Land Surface Temperature/3-Band Emissivity Daily L3 Global 1 km SIN Grid Night

PI: Glynn C. Hulley


A new suite of Moderate Resolution Imaging Spectroradiometer (MODIS) Land Surface Temperature and Emissivity (LST&E) products are available in Collection 6. The MYD21 Land Surface Temperature (LST) algorithm differs from the algorithm of the MYD11 LST products, in that the MYD21 algorithm is based on the ASTER Temperature/Emissivity Separation (TES) technique, whereas the MYD11 uses the split-window technique. The MYD21 TES algorithm uses a physics-based algorithm to dynamically retrieve both the LST and spectral emissivity simultaneously from the MODIS thermal infrared bands 29, 31, and 32. The TES algorithm is combined with an improved Water Vapor Scaling (WVS) atmospheric correction scheme to stabilize the retrieval during very warm and humid conditions.

The MYD21A1N dataset is produced daily from nighttime Level 2 Gridded (L2G) intermediate LST products. The L2G process maps the daily MYD21 swath granules onto a sinusoidal MODIS grid and stores all observations falling over a gridded cell for a given day. The MOD21A1 algorithm sorts through all these observations for each cell and estimates the final LST value as an average from all observations that are cloud free and have good LST&E accuracies. The nighttime average is weighted by the observation coverage for that cell. Only observations having an observation coverage greater than a 15% threshold are considered. The MYD21A1N product contains seven Science Datasets (SDS), which include the calculated LST as well as quality control, the three emissivity bands, view zenith angle, and time of observation. MYD21A1N products are available two months after acquisition due to latency of data inputs. Additional details regarding the methodology used to create this Level 3 (L3) product are available in the Algorithm Theoretical Basis Document (ATBD).


Product Maturity

Aqua MODIS LST&E products are validated to stage 1 maturity level.

Collection and Granule


Characteristic Description
CollectionAqua MODIS
File Size~1.4 MB
Temporal ResolutionDaily
Temporal Extent2002-07-04 to Present
Spatial ExtentGlobal
Coordinate SystemSinusoidal
File FormatHDF-EOS
Geographic Dimensions1200 km x 1200 km


Characteristic Description
Number of Science Dataset (SDS) Layers7
Columns/Rows1200 x 1200
Pixel Size1000 m


SDS Name Description Units Data Type Fill Value No Data Value Valid Range Scale Factor Additional Offset
LST_1KM Land surface temperature Kelvin 16-bit unsigned integer 0 N/A 7500 to 65535 0.02 N/A
QC Quality Control (QC) N/A 16-bit unsigned integer N/A N/A 0 to 65535 N/A N/A
Emis_29 Band 29 emissivity N/A 8-bit unsigned integer 0 N/A 1 to 255 0.002 0.49
Emis_31 Band 31 emissivity N/A 8-bit unsigned integer 0 N/A 1 to 255 0.002 0.49
Emis_32 Band 32 emissivity N/A 8-bit unsigned integer 0 N/A 1 to 255 0.002 0.49
View_Angle MODIS view zenith angle Degree 8-bit unsigned integer 255 N/A 0 to 130 N/A -65
View_Time Time of MODIS observation Hours 8-bit unsigned integer 255 N/A 0 to 240 0.1 N/A

Product Quality

The Quality Control (QC) 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 the quality layer.

The final quality bit for the output product reflects the lowest quality values from all observations that went into the final average. The bit definition index for the QC layer is available in the User Guide on page 23.

Known Issues

For complete information about the MYD21A1N known issues please refer to the MODIS Land Quality Assessment website.


Using the Data



DOI: 10.5067/MODIS/MYD21A1N.006

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