Status for: Downwelling Surface Radiation/Photosynthetically Active Radiation (MCD18)

General Accuracy Statement

MODIS downward shortwave radiation (DSR) and photosynthetically active radiation (PAR) products (MCD18) are currently considered to be Validated Stage 1.

The MCD18 data products were assessed with field measurements of DSR and PAR collected at BSRN, AmeriFlux, European Flux and OzFlux stations across the world. The instantaneous DSR has a bias of -15.4 W/m2 and root mean square error (RMSE) of 101.0 W/m2, while the instantaneous PAR has a bias of -0.6 W/m2 and RMSE of 45.7 W/m2. RMSE of daily DSR is 32.3 W/m2, and that of the daily PAR is 13.1 W/m2.

DSR/PAR comparisons with in situ data
Figure 1. Comparison results of the MCD18A1 and MCD18A2 C6 instantaneous products with in situ data measured
in 2018.

Further analysis showed the accuracy of MODIS DSR and PAR retrievals are dependent on the availability of surface reflectance input. The data quality is compromised when no actual surface reflectance product is available and climatological values are used instead. It was also revealed that the number of daily MODIS overpass counts affects the accuracy of estimating daily DSR and PAR. The RMSE of daily results drops significantly with the increase of daily overpass numbers.

A programming error in the early version of the MCD18 software code caused an overestimation issue. The software code has been updated to fix this problem. The updated code was used to generate MODIS DSR and PAR C6 products from 2018 onwards. Please note that the MCD18 C6 dataset from year 2000 to 2010 has not been reprocessed and is still considered not to be appropriate for use in quantitative scientific publications.

Product status updated:  November 2019
Product version:  Collection 6
Supporting Studies:

Title: Estimation of all-sky instantaneous surface incident shortwave radiation from Moderate Resolution Imaging Spectroradiometer data using optimization method
Author: Zhang, Y., He, T., Liang, S., Wang, D., & Yu, Y.
Source: Remote Sensing of Environment, 209, 468-479, doi:10.1016/j.rse.2018.02.052
View Abstract and Access Publication
Title: A new set of MODIS land products (MCD18): downward shortwave radiation and photosynthetically active radiation
Author: Wang, D., Liang, S., Zhang, Y., Gao, X., Brown, M., & Jia, A.
Source: Science of Remote Sensing (submitted)
View Abstract and Access Publication