National Aeronautics and Space Administration

Stage 2 validation has been achieved for the MYD21 Collection 6 LST&E products.

The MYD21 (MODIS-Aqua) Collection 6 (C6) LST&E products have been validated to Stage 2 status using a combination of Temperature and Radiance-based methods over a global set of sites in the USA, China, Spain, Portugal, and Southern Africa.

The results summarized in Table 1 and Figure 1 show that the MYD21 C6 LST products have an average root mean square error (RMSE) of 1.33 K with negligible bias and accuracies independent of land cover type. The heritage MYD11 C6 LST products have an average RMSE of 2.32 K and show large biases (3-5 K) over dryland regions due to an overestimation of emissivity in the longwave bands documented in several studies [Malakar et al., 2016; Li et al., 2020; Hulley and Cook, 2020]. The MYD21 C6 emissivity spectra had an average accuracy of 1.31% for all TIR bands (29, 31, 32) when compared to lab measured spectra at six pseudo-invariant sites shown in Figure 2.

The MOD21 (MODIS-Terra) LST&E products have yet be fully validated since they were affected by the band 29 crosstalk calibration issue apparent in C6, and were only produced up to 2005 as a result. This issue has been addressed in C6.1 with updated calibration coefficients and all MOD21 products are currently in reprocessing with expected release in Spring 2021.

Table 1. A summary of MODIS MYD21 and MYD11 LST validation results of studies where the validation was performed
for both products simultaneously, i.e. one to one validation comparison with in-situ data

Figure 1. Summary of LST validation of the MYD21 and MYD11 C6 products from 2002-2018 using a combination of
Temperature-based and Radiance-based validation methods at two water, two vegetated, and six pseudo-invariant sand dunes sites in the U.SA [1, 6].

Figure 2. Emissivity spectra comparisons between the MOD21 and MOD11 products and lab measurements of sand
samples collected at six pseudo-invariant sand dune sites in the USA.

Details of MxD21 C6 LST&E validation practices can be found in the MxD21 ATBD here https://modis.gsfc.nasa.gov/data/dataprod/mod21.php and in Malakar et al. 2016.