MODIS To VIIRS Transition

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This document outlines key information related to the decommissioning plan for the Terra MODIS (Moderate Resolution Imaging Spectroradiometer) and Aqua MODIS missions and NASA's efforts to provide continuity between the MODIS and VIIRS (Visible Infrared Imaging Radiometer Suite) atmospheric data records. This information will better prepare our atmospheric science user community to plan and adapt to the forthcoming end of the MODIS era. It addresses the following topics:

• End of MODIS operations
• VIIRS data options for the atmospheric science user community
• Mapping of NASA MODIS products to NASA Atmosphere Team VIIRS products
• Other aerosol and cloud property contemporary sources

End of MODIS Operations

The NASA Earth Observing System (EOS) platforms, Terra and Aqua, each carry a MODIS instrument that have been successfully in operation since 2000 and 2002, respectively. NASA plans to stop science data collection from the Aqua and Terra MODIS instruments in Sept 2027 and Feb 2027 respectively. After ending satellite operations, NASA will develop a final MODIS v8.0 calibration that will support the last reprocessing cycle to produce the full v8.0 MODIS data collection.

Further, due to fuel limitations, Terra and Aqua are currently drifting from their closely controlled morning and afternoon sun-synchronous orbits. This orbital drift results in their respective earlier and later equatorial-crossing mean local times (MLT). The Terra and Aqua home pages provide interactive plots showing current and projected changes in MLTs and altitudes. Users should monitor these MLT changes and assess the impact on their specific science goals and applications.

Finally, the NASA Earth Science Division has invested in developing, testing, and producing continuity products for instruments on the Suomi National Polar-orbiting Partnership (SNPP) and Joint Polar Satellite System (JPSS) satellite series. These instruments are designed to provide observations suitable for continuing NASA EOS data records. The LAADS DAAC encourages Aqua MODIS data users to explore using similar NASA data products from VIIRS on the NASA-NOAA SNPP, NOAA-20, and NOAA-21 platforms, which operate in sun-synchronous MLT orbits similar to Aqua. No follow-on MODIS-like instrument with an orbit at the Terra morning equatorial-crossing MLT exists in the current or planned NASA-managed Earth observation missions.

VIIRS Data Options for the Atmospheric Science User Community

As the Terra MODIS and Aqua MODIS missions transition into their decommissioning phases (Phase-F), natural concerns exist in the user community about what other current and future products will likely serve as practical replacements. The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument was first launched aboard the NOAA-NASA pathfinder mission called Suomi NPP in 2011. The VIIRS instrument has since been deployed on NOAA-20 and NOAA-21 missions, with additional instruments scheduled for launch on JPSS-3 (NOAA-22) and JPSS-4 (NOAA-23).

The VIIRS instrument observes and collects global satellite observations that span the visible and infrared wavelengths across land, atmosphere, cryosphere, and oceans. As a primary imager on the SNPP and the JPSS platform series, its visible and infrared spectral channels are designed to vastly improve upon two of its operational predecessors, the Advanced Very-High Resolution Radiometer (AVHRR) and the Operational Linescan System (OLS). As a natural successor to the MODIS instruments, VIIRS offers several improvements that include a wider swath width and higher spatial resolutions. However, VIIRS offers 22 spectral bands between 0.4 µm to 12.5 µm (including 8 dual-gain bands) while MODIS has 36 bands between 0.4 µm to 14.5 µm. Importantly for MODIS atmosphere product users, VIIRS lacks key CO₂ and water vapor Infrared (IR) absorption bands, which are critical for temperature and moisture profiling. The VIIRS instrument's Signal-to-Noise Ratio (SNR) and Noise-Equivalent Temperature Differences (NE∆T), when normalized to the same spatial scale and radiance levels. With on-board spatial aggregation, VIIRS M-bands (0.75 km) do not suffer significantly from MODIS' edge-of-swath bow-tie effect. The following table portrays some of the basic differences between VIIRS and Aqua MODIS.

Mapping of NASA MODIS Atmosphere Products to Those in the VIIRS Era

In anticipation of the time when both MODIS missions are decommissioned, the NASA-funded MODIS-VIIRS atmosphere science teams have developed continuity products that use common algorithms that are applied to VIIRS and Aqua MODIS observations. Continuity products are designed to sustain the long-term observational records. To ensure a commonly applicable continuity approach to data is maintained across the VIIRS and Aqua MODIS missions, the continuity products use a minimum set of spectral channels that are common, or approximately so, to both the VIIRS and MODIS instruments.

The NASA Atmosphere Team continuity effort generates five core atmospheric product suites*:

N-20 = NOAA-20, N-21 = NOAA-21

*Currently, cloud products are produced from both VIIRS and Aqua MODIS while Deep Blue Aerosol products are produced from VIIRS only. Additional new platform/instrument sources are planned for the future.

Cloud Mask: The Continuity MODIS-VIIRS Cloud Mask (MVCM) algorithm is used to produce the Cloud Mask (CLDMSK) product. This provides an ideal example of how the original MODIS product is extended to continue in the VIIRS era by using only those channels that are common to both instruments. The MVCM algorithm effectively extends the MODIS MYD35 cloud mask product into the VIIRS era, resulting in four continuity CLDMSK products: one from MODIS onboard Aqua and three from VIIRS onboard SNPP, NOAA-20, and NOAA-21.

Cloud Properties: The original MODIS cloud-top and cloud optical properties algorithms benefitted from certain MODIS-specific channels that are absent on VIIRS, including thermal infrared, water vapor, and CO2 absorption channels. Additionally, a spectral offset between the MODIS 2.13 µm and VIIRS 2.25 µm shortwave infrared (SWIR) channels, in which ice and liquid cloud absorption differs, preclude directly porting those algorithms to benefit VIIRS observations. The commonly applicable CLDPROP algorithm provides a continuity approach between MODIS and VIIRS, relying on spectral channels that are common to both instruments.

Dark Target Aerosol & Deep Blue Aerosol: The MODIS era introduced two separate aerosol retrieval algorithms. The Dark Target (DT) algorithm focused on oceans and dark vegetative surfaces, while the Deep Blue (DB) algorithm originally focused on bright land surfaces. Both algorithms provide global data on Aerosol Optical Depth (AOD) and related aerosol properties. Together, they provide complementary coverage, enabling robust global aerosol characterization across diverse surface types.

The Dark Target aerosol product (AERDT) is provided for VIIRS only (currently from SNPP and NOAA-20). AERDT continuity products are not produced for Aqua MODIS. The Deep Blue aerosol product (AERDB) relies on two sub-algorithms: Deep Blue over land, and the Satellite Ocean Aerosol Retrieval (SOAR) algorithm over ocean. The AERDB (L2 and L3) is only produced for VIIRS from SNPP and NOAA-20.

Water Vapor: The SNPP VIIRS does not have sounding channels; however, it does offer some spectral bands to help integrate total column water vapor under clear-sky conditions. To compensate for its lack of water vapor absorption channels, this product benefits from water vapor soundings from two additional sounder instruments that are co-located with VIIRS aboard the SNPP platform: Advanced Technology Microwave Sounder (ATMS) and Cross-track Infrared Sounder (CrIS).

The water vapor product is derived by adapting the MODIS atmospheric profile algorithm and assisted by sounding-based measurements from ATMS and CrIS. This approach enables the SNPP VIIRS Level-2 water vapor products to provide global clear-sky total column water vapor properties at a high spatial resolution. These products extend the long-term record of observations that began with MODIS on the Terra and Aqua platforms.

The table below provides the landing-page links to all the VIIRS atmosphere products that are available from the LAADS DAAC.

VIIRS Atmospheric Science Products from the LAADS DAAC

MODIS versus VIIRS Atmosphere Products: A Visual Comparison of a Handful of Products

The following images provide a visual comparison of aerosol, cloud mask, cloud properties, and water vapor retrievals between MODIS- and VIIRS-derived products. Two points to bear in mind about the following comparisons include the following:

• The products being compared are not identical and are not based on coincident observations.
• The MODIS and VIIRS products being compared do have differences in spatial coverages and temporal resolutions as well as data observation times.

Other Aerosol and Cloud Property Contemporary Sources

Other contemporary atmospheric remote sensing data orbital platforms include Geostationary Earth Orbit (GEO) missions, for instance, the NOAA Geostationary Operational Environmental Satellites (GOES) and the Japanese Himawari series. A NASA Low-Earth Orbiting (LEO) satellite mission called, the Plankton, Aerosol, Cloud ocean Ecosystem (PACE), was launched on February 8, 2024. Aerosol and cloud products from the PACE mission are still in their evaluation and implementation phases. The PACE Data Products Table provides an update on product status.

The LAADS DAAC manages two suites of NASA aerosol products that were generated for the first time from GEO satellite sources. The following two GEO-LEO project pages contain more details:

• GEO-LEO Dark Target Aerosol MEaSUREs project
• GEO-LEO Deep Blue Aerosol ESROGSS project

The GEO-LEO Dark Target Aerosol suite was produced through a NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) project and covers January 2019 through December 2022 timespan. The GEO-LEO Deep Blue Aerosol suite was produced through a NASA Earth Science Research from Operational Geostationary Satellite Systems (ESROGSS)-funded project that covers May 2019 through April 2020.