User Guide
Algorithm Theoretical Basis Document (ATBD)
File Specification
The MOD21 Land Surface Temperature and Emissivity (LST&E) swath data product is produced daily in five minute temporal increments of satellite acquisition. The swath is approximately 2,030 pixels along track and 1,354 pixels per line, at a nadir resolution of 1,000 meters. The MOD21 Land Surface Temperature (LST) algorithm differs from the MOD11 algorithm in that the MOD21 LST 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 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. MOD21 products are available two months after acquisition due to latency of data inputs. Additional details regarding the method used to create this Level 2 (L2) product are available in the Algorithm Theoretical Basis Document (ATBD).
Validation at stage 1 has been achieved for the MODIS Land Surface Temperature and Emissivity data products. Further details regarding MODIS land product validation for the MOD21 data products are available from the MODIS Land Team Validation site.
| Characteristic | Description |
|---|---|
| Collection | Terra MODIS |
| DOI | 10.5067/MODIS/MOD21.061 |
| File Size | ~4 MB |
| Temporal Resolution | < Daily |
| Temporal Extent | 2000-02-24 to Present |
| Spatial Extent | Global |
| Coordinate System | None (Swath) |
| Datum | N/A |
| File Format | HDF-EOS |
| Geographic Dimensions | 2300 km x 2300 km |
| Characteristic | Description |
|---|---|
| Number of Science Dataset (SDS) Layers | 15 |
| Columns/Rows | Varies by scene |
| Pixel Size | 1000 m |
| SDS Name | Description | Units | Data Type | Fill Value | No Data Value | Valid Range | Scale Factor | Additional Offset |
|---|---|---|---|---|---|---|---|---|
| LST | Land surface temperature | Kelvin | 16-bit unsigned integer | 0 | N/A | 7500 to 65535 | 0.02 | N/A |
| QC | Quality Control (QC) for LST and emissivity | 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 |
| LST_err | Land surface temperature error | Kelvin | 8-bit unsigned integer | 0 | N/A | 1 to 255 | 0.04 | N/A |
| Emis_29_err | Band 29 emissivity error | N/A | 16-bit unsigned integer | 0 | N/A | 1 to 65535 | 0.0001 | N/A |
| Emis_31_err | Band 31 emissivity error | N/A | 16-bit unsigned integer | 0 | N/A | 1 to 65535 | 0.0001 | N/A |
| Emis_32_err | Band 32 emissivity error | N/A | 16-bit unsigned integer | 0 | N/A | 1 to 65535 | 0.0001 | N/A |
| View_angle | MODIS view angle for current pixel | Degree | 8-bit unsigned integer | N/A | N/A | 0 to 180 | 0.5 | N/A |
| Emis_ASTER | ASTER Global Emissivity Dataset (GED) emissivity | N/A | 8-bit unsigned integer | 0 | N/A | 1 to 255 | 0.002 | 0.49 |
| PWV | Precipitable water vapor | cm | 16-bit unsigned integer | N/A | N/A | 0 to 65535 | 0.001 | N/A |
| oceanpix | Ocean-land mask | N/A | 8-bit unsigned integer | N/A | N/A | 0 to 1 | N/A | N/A |
| Latitude | Pixel latitude | Degree | 32-bit floating point | -999.0 | N/A | -90 to 90 | N/A | N/A |
| Longitude | Pixel longitude | Degree | 32-bit floating point | -999.0 | N/A | -180 to 180 | N/A | N/A |
| Value | Description |
|---|---|
| 0 | Land |
| 1 | Water |
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 bit definition index for the quality layer is available in Table 7 of the User Guide.
For complete information about known issues please refer to the MODIS/VIIRS Land Quality Assessment website.