A new suite of Moderate Resolution Imaging Spectroradiometer (MODIS) Land Surface Temperature and Emissivity (LST&E) products are available in Collection 6. The MOD21 Land Surface Temperatuer (LST) algorithm differs from the algorithm of the MOD11 LST products, in that the MOD21 algorithm is based on the ASTER Temperature/Emissivity Separation (TES) technique, whereas the MOD11 uses the split-window technique. The MOD21 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 MOD21A2 dataset is an 8-day composite LST product that uses an algorithm based on a simple averaging method. The algorithm calculates the average from all the cloud free MOD21A1D and MOD21A1N daily acquisitions from the 8-day period. Unlike the MOD21A1 data sets where the daytime and nighttime acquisitions are separate products, the MOD21A2 contains both daytime and nighttime acquisitions as separate Science Dataset (SDS) layers within a single Hierarchical Data Format (HDF) file. The LST, Quality Control (QC), view zenith angle, and viewing time have separate day and night SDS layers, while the values for the MODIS emissivity bands 29, 31, and 32 are the average of both the nighttime and daytime acquisitions. MOD21A2 products are available two months after acquisition due to latency of data inputs. Additional details regarding the method used to create this Level 3 (L3) product are available in the Algorithm Theoretical Basis Document (ATBD).
Terra MODIS LST&E products are provisional and have not been validated for their science quality. Further details regarding MODIS land product validation for the MOD21 data products are available from the MODIS Land Team Validation site.
|File Size||~5.3 MB|
|Temporal Extent||2000-02-18 to 2005-12-31|
|Geographic Dimensions||1200 km x 1200 km|
|Number of Science Dataset (SDS) Layers||11|
|Columns/Rows||1200 x 1200|
|Pixel Size||1000 m|
|SDS Name||Description||Units||Data Type||Fill Value||No Data Value||Valid Range||Scale Factor||Additional Offset|
|LST_Day_1KM||Day Land surface temperature||Kelvin||16-bit unsigned integer||0||N/A||7500 to 65535||0.02||N/A|
|QC_Day||Day Quality Control (QC)||N/A||8-bit unsigned integer||N/A||N/A||0 to 255||N/A||N/A|
|View_Angle_Day||Day MODIS view zenith angle||Degree||8-bit unsigned integer||255||N/A||0 to 130||N/A||-65|
|View_Time_Day||Time of MODIS observation for day||Hours||8-bit unsigned integer||255||N/A||0 to 240||0.1||N/A|
|LST_Night_1KM||Night Land Surface Temperature||Kelvin||16-bit unsigned integer||0||N/A||7500 to 65535||0.02||N/A|
|QC_Night||Night Quality Control (QC)||N/A||8-bit unsigned integer||N/A||N/A||0 to 255||N/A||N/A|
|View_Angle_Night||Night view zenith angle||Degree||8-bit unsigned integer||255||N/A||0 to 130||N/A||-65|
|View_Time_Night||Time of Observation for night||Hours||8-bit unsigned integer||255||N/A||0 to 240||0.1||N/A|
|Emis_29||Average Day/Night Band 29 emissivity||N/A||8-bit unsigned integer||0||N/A||1 to 255||0.002||0.49|
|Emis_31||Average Day/Night Band 31 emissivity||N/A||8-bit unsigned integer||0||N/A||1 to 255||0.002||0.49|
|Emis_32||Average Day/Night Band 32 emissivity||N/A||8-bit unsigned integer||0||N/A||1 to 255||0.002||0.49|
The 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 26.
For complete information about the MOD21A2 known issues please refer to the MODIS Land Quality Assessment website.