Derivation of Shortwave Radiometric Adjustments for SNPP and NOAA-20 VIIRS for the NASA MODIS-VIIRS Continuity Cloud Products

Kerry Meyer,Fred Nagle,Robert Holz,Steven Platnick,Steve Dutcher,Greg Quinn

doi:10.3390/rs12244096

Abstract

Climate studies, including trend detection and other time series analyses, necessarily require stable, well-characterized and long-term data records. For satellite-based geophysical retrieval datasets, such data records often involve merging the observational records of multiple similar, though not identical, instruments. The National Aeronautics and Space Administration (NASA) cloud mask (CLDMSK) and cloud-top and optical properties (CLDPROP) products are designed to bridge the observational records of the Moderate-resolution Imaging Spectroradiometer (MODIS) onboard NASA’s Aqua satellite and the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the joint NASA/National Oceanic and Atmospheric Administration (NOAA) Suomi National Polar-orbiting Partnership (SNPP) satellite and NOAA’s new generation of operational polar-orbiting weather platforms (NOAA-20+). Early implementations of the CLDPROP algorithms on Aqua MODIS and SNPP VIIRS suffered from large intersensor biases in cloud optical properties that were traced back to relative radiometric inconsistency in analogous shortwave channels on both imagers, with VIIRS generally observing brighter top-of-atmosphere spectral reflectance than MODIS (e.g., up to 5% brighter in the 0.67 µm channel). Radiometric adjustment factors for the SNPP and NOAA-20 VIIRS shortwave channels used in the cloud optical property retrievals are derived from an extensive analysis of the overlapping observational records with Aqua MODIS, specifically for homogenous maritime liquid water cloud scenes for which the viewing/solar geometry of MODIS and VIIRS match. Application of these adjustment factors to the VIIRS L1B prior to ingestion into the CLDMSK and CLDPROP algorithms yields improved intersensor agreement, particularly for cloud optical properties.

Highlights

The twin Moderate-resolution Imaging Spectroradiometer (MODIS) instruments onboard the National Aeronautics and Space Administration’s (NASA) Earth Observing System (EOS) Terra and Aqua satellites to date have provided an extraordinary 20+ (Terra) and 18+ (Aqua) year record of Earth observations that have enabled a broad range of investigations of the Earth’s oceans, land and atmosphere [1,2,3,4]
These Collection 6 (C6)-derived adjustment factors are only shown for the Suomi National Polar-orbiting Partnership (SNPP) Visible Infrared Imaging Radiometer Suite (VIIRS) M5 and M7 channels since the C6.1 RVS correction for Aqua MODIS was applied only to the VIS/NIR channels [17], and C6.1 reprocessing was completed prior to National Oceanic and Atmospheric Administration (NOAA)-20 launch
NOAA-20 VIIRS was found to be in better agreement with Aqua MODIS, generally within 2%, whereas SNPP VIIRS can be up to 5% brighter than Aqua MODIS (e.g., 0.67 μm (M5))

Summary

Introduction

The twin Moderate-resolution Imaging Spectroradiometer (MODIS) instruments onboard the National Aeronautics and Space Administration’s (NASA) Earth Observing System (EOS) Terra and Aqua satellites to date have provided an extraordinary 20+ (Terra) and 18+ (Aqua) year record of Earth observations that have enabled a broad range of investigations of the Earth’s oceans, land and atmosphere [1,2,3,4]. Given the uncertainties of current satellite imagers, including MODIS, observational records of more than 2–3 decades are required to detect cloud feedbacks [5]. Continuing these satellite geophysical data records beyond MODIS is a desirable goal. NASA has pursued extending the EOS MODIS geophysical data products to the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument onboard the United States’ new generation of polar orbiting weather satellites, beginning with the joint NASA/National Oceanic and Atmospheric Administration (NOAA) Suomi National Polar-orbiting Partnership (SNPP, launched in late 2011) and continuing with NOAA-20 (launched in late 2017) and beyond, with the ultimate goal of obtaining a merged climate data record that provides continuity between the various imagers. VIIRS, similar to MODIS, provides multispectral narrowband observations from the visible (VIS) to the infrared (IR), and the early afternoon equatorial crossing times of SNPP and NOAA-20 (both roughly 13:30 local solar time (LST), though in different orbital planes) are similar to that of Aqua (roughly 13:35 LST)

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