Frequently Asked Questions

Why does Collection 3 ARD have a higher latency than Collection 2 ARD?

Collection 3 ARD appears to lag about a week behind Collection 2 ARD. When will this be fixed?

Collection 2 ARD uses Collection 5 MODIS Bidirectional Reflectance Distribution Function data (BRDF) which was decommissioned and replaced by Collection 6 BRDF as of 2018. Since no real BRDF is available, Collection 2 ARD uses seasonal MODIS BRDF. In contrast, Collection 3 ARD uses the “real” Collection 6 MODIS BRDF for new acquisitions, so needs to “wait” until this are available. BRDF is derived from 16 days of MODIS observations over the area (to ensure 16 different view/solar angles can be used to simulate the model), hence the delay. To conclude, Collection 3 ARD has a higher latency than Collection 2 ARD, but uses more reliable and up-to-date calibration.