Continuity of global MODIS terrestrial primary productivity estimates in
the VIIRS era using model-data fusion
Abstract
The NASA Terra and Aqua satellites have been successfully operating for
over two decades, exceeding their original 5-year design life. However,
the era of NASA’s Earth Observing System (EOS) may be coming to a close
as early as 2023. Similarities between the Moderate Resolution Imaging
Spectroradiometer (MODIS), aboard Aqua and Terra, and the Visible
Infrared Imaging Radiometer Suite (VIIRS) sensors aboard the Suomi NPP,
NOAA-20 and NOAA-21 satellites enable potential continuity of long-term
earth observational records in the VIIRS era. We conducted a
comprehensive calibration and validation of the MODIS MOD17 product,
which provided the first global, continuous, weekly estimates of
ecosystem gross primary productivity (GPP) and annual estimates of net
primary productivity (NPP). Using Bayesian model-data fusion, we
combined an 18-year record of tower fluxes with prior data on plant
traits and hundreds of field measurements of NPP to benchmark MOD17 and
to develop the first terrestrial productivity estimates from VIIRS. The
updated mean global GPP (NPP) flux from MOD17 and the new VNP17 for
2012-2018 is 127 ±2.8 Pg C year-1 (58 ±1.1 Pg C year-1), which compares
well with independent top-down and bottom-up estimates. Both MOD17 and
VNP17 depict upward productivity trends over recent decades, with
2000-2018 MOD17 GPP (NPP) rising by 0.47 (0.25) Pg C year-2 but slowing
to 0.35-0.44 (0.11-0.13) Pg C year-2 over 2012-2021, with a greater
reduction in the NPP growth rate. The new VIIRS VNP17 product has the
potential to extend these continuous estimates of global, terrestrial
primary productivity beyond 2030.