MOD44B (C61) Vegetation Continuous Fields (VCF) - Retrieval Differences Due to Java Runtime Update
Users of the MOD44B Collection 6.1 (C61) Vegetation Continuous Fields (VCF) product should be aware of a discontinuity within the C61 record introduced by an update to the Java runtime environment.
In May 2025, the operational processing environment adopted an updated Java runtime (Java 21) to meet NASA security compliance requirements, replacing the older version (Java 11). Data for 2024 onward uses the new Java version. The MOD44B production software (PGE61) is sensitive to Java version variation, meaning identical inputs can yield slightly different retrievals depending on the Java version used.
As a result, a discontinuity exists within the C61 record. Testing shows these differences are concentrated over mixed vegetation landscapes, where retrievals may show lower percent tree cover, while stable landscapes such as forests show no differences (see Figure 1). These differences reflect a runtime/environment sensitivity and are not a defect in the science algorithm or a change in product quality.
Users conducting time-series analyses should exercise caution, as this runtime-related shift may introduce apparent changes not driven by actual land-cover dynamics. Such differences should be interpreted as an expected consequence of the Java runtime update.
