Satellite Vegetation Health Products and their Applications: From AVHRR to VIIRS

The satellite-derived vegetation health (VH) products, developed from former Advanced Very High-Resolution Radiometer (AVHRR) and current Visible Infrared Imager Radiometer Suite (VIIRS), have been applied successfully for drought monitoring and assessment of the vegetation condition worldwide. In particular, compared to AVHRR, the follow-on sensor VIIRS onboard the latest generation of operational polar orbiting satellites, called the Joint Polar Satellite System (JPSS) series provides radiance measurements with much finer spatial resolution and exceptional data quality. Benefited from advances in VIIRS observations better quality and higher resolution Normalized Difference Vegetation Index (NDVI), brightness temperature (BT), and their derived vegetation health indices are achieved. With early launch of Suomi National Polar-orbiting Partnership (S-NPP) in 2011, middle launch of NOAA-20 in 2017 and later launch of NOAA-21 in 2022, the VIIRS-based weekly VH time series have been produced more than ten years since 2012. To account for possible differences in VIIRS sensor performance including sampling and calibration in real satellite operations, even though the sensors are designed very similar, it is critical to understand the continuity and consistency of the VIIRS-based VH products between S-NPP, NOAA-20 and NOAA-21. An inter-comparison study was conducted based on available products during their overlap periods. The results presented here 1) assess the differences of VH products and whether continuity and consistency are confirmed as expected; 2) investigate how the differences at the NDVI/BT level would affect the corresponding vegetation health indices. The inter-comparison is demonstrated on not only global scale, but also over 34 selected targets to consider ecosystem difference.