Land Surface Temperature/Emissivity (MOD21)

sample thumbnail of LST image

Since NASA currenlty has two Land Surface Temperature (LST) and Emissivity products from the MODIS sensor, we have prepared this report to help users determine the best product for their needs.

The MOD11 product is the heritage LST product and the MOD21 product is the new LST product generated beginning with the distribution of Collection 6. The two products emanate from two different methodologies and thus are two separate products.

The new MODIS LST and Emissivity product (MOD21) uses a physically-based algorithm to dynamically retrieve both the LST and Emissivity simultaneously for the three MODIS thermal infrared bands (29, 31 and 32) at a spatial resolution of 1 km. The MOD21 product addresses the cold bias of 3-5 K in the MOD11 heritage split-window products over arid and semi-arid regions.

The MOD21 algorithm is based on the Temperature Emissivity Separation (TES) algorithm developed for ASTER data, which uses full radiative transfer simulations for the atmospheric correction, and an emissivity model based on the variability in the surface radiance data to dynamically retrieve both LST and spectral emissivity. 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. Simulations and validation results available in the ATBD have shown consistent accuracies at the 1 K level over all land surface types including vegetation, water, and deserts.

Note to users: The C6 Terra L2 and L3 MODIS LST products (MOD21) for the 2000-2005 time period are being released to public with a provisional maturity status, as these products may have been negatively impacted by an optical crosstalk issue in the IR bands (B27-B30). Although the crosstalk issue was present from the beginning of the mission, the impact on the product is not significant until after 2005. Thus, the Terra LST products are not being produced beyond 2005. The Aqua MODIS data are not affected by this crosstalk issue and the MYD21 LST products are considered to be science quality data with a Stage 1 validation status. The crosstalk issue has been addressed in C6.1 reprocessing, which is currently underway.