Landsat Collection 2 Level 2 product processing requires auxiliary atmospheric characterization data from multiple external sources. Landsat 8 and Landsat 9 surface reflectance data acquired on October 1, 2023, and onward will utilize a different source of atmospheric characterization data than what has been used previously.
Atmospheric Auxiliary Data Changes Affect Landsat 8-9 Level 2 Surface Reflectance Processing
Landsat 8 and 9 Collection 2 surface reflectance is processed using the Land Surface Reflectance Code (LaSRC) (Vermote et al., 2016) which requires near contemporaneous auxiliary ozone and water vapor data.
For the Landsat 8 and Landsat 9 scenes acquired prior to October 1, 2023, the auxiliary ozone and water vapor data are derived from Moderate Resolution Imaging Spectroradiometer (MODIS) onboard NASA Terra and Aqua. The daily water vapor is extracted from 0.05-degree MODIS Aerosol Optical Thickness (MOD09CMA and MYD09CMA) and ozone is extracted from 0.05-degree Surface Reflectance Climate Modelling Grid (CMG) (MOD09CMG and MYD09CMG) products. Terra and Aqua began drifting in April and July 2021, respectively, and both have been imaging at a lower orbit altitude with changing Mean Local Time (MLT) equatorial crossing time since 2022.
Given the aging spacecrafts and drifting orbits, the USGS conducted studies of alternative auxiliary data sources for continuity of Landsat Surface Reflectance product. The auxiliary data from the Visible Infrared Imaging Radiometer Suite (VIIRS) sensor onboard NOAA-21, NOAA-20 and Suomi-NPP indicated minimal impact on the continuity of Landsat 8 and 9 Surface Reflectance product.
The image below shows the timeseries of the average Level-2 surface reflectance and 95% confidence interval over WRS-2 Path39/Row37 for the red spectral band (Band 4) when utilizing MODIS and VIIRS atmospheric characterization auxiliary data. For additional information about the impact expected please see Crawford et al. (2023) or the Landsat Science Team presentation.
For the Landsat 8 and Landsat 9 scenes acquired October 1, 2023, and onward, the surface reflectance data will be processed utilizing ozone and water vapor datasets retrieved from NOAA’s VIIRS Aerosol Daily L3 Global 0.05-degree Climate Modeling Grid (CMG). Currently the NOAA-20 (designated as JPSS-1 prior to launch) is the primary source of VIIRS CMG product (VJ104ANC), and if unavailable, the Suomi-NPP data (VNP04ANC) will be used. Once the CMG products from NOAA-21 (designated as JPSS-2 prior to launch) are made public, the data from NOAA-21 (VJ204ANC) will take the priority. The NOAA VIIRS CMG product used for Landsat 8/9 Collection 2 Level 2 Surface Reflectance processing are accessed from NASA's Level 1 and Atmosphere Archive & Distribution System Distributed Active Archive Center (LAADS DAAC).
Users can determine which auxiliary data source (MODIS or VIIRS) was used to generate a surface reflectance product by looking at the <DATA_SOURCE_OZONE> and <DATA_SOURCE_WATER_VAPOR> fields in the Level 2 metadata file.
Information about the VIIRS aerosol daily L3 global 0.05-degree CMG that will be used in Landsat Level 2 processing starting October 1, 2023, can be found on the Landsat Collection 2 Atmospheric Auxiliary Data webpage.
Please contact USGS EROS Customer Services with any questions about this announcement and the atmospheric auxiliary data.
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