Abstract
The Combined ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) MODIS (Moderate Resolution Imaging Spectroradiometer) Emissivity over Land (CAMEL) Version 2 (V002) has been available since March 2019 from the NASA LP DAAC (Land Processes Distributed Active Archive Center) and provides global, monthly infrared land surface emissivity and uncertainty at 0.05 degrees (~5 km) resolution. A climatology of the CAMEL V002 product is now available at the same spatial, temporal, and spectral resolution, covering the CAMEL record from 2000 to 2016. Characterization of the climatology over case sites and IGBP (International Geosphere-Biosphere Programme) land cover categories shows the climatology is a stable representation of the monthly CAMEL emissivity. Time series of the monthly CAMEL V002 product show realistic seasonal changes but also reveal subtle artifacts known to be from calibration and processing errors in the MODIS MxD11 emissivity. The use of the CAMEL V002 climatology mitigates many of these time dependent errors by providing an emissivity estimate which represents the complete 16-year record. The CAMEL V002 climatology’s integration into RTTOV (Radiative Transfer for TOVS) v12 is demonstrated through the simulation of IASI (Infrared Atmospheric Sounding Interferometer) radiances. Improved stability in CAMEL Version 3 is expected in the future with the incorporation of the new MxD21 and VIIRS VNP21 emissivity products in MODIS Collection 6.1.
Highlights
Land surface emissivity is a critical variable in a multitude of Earth science studies and applications
The climatology described in this paper is based on the MEaSUREs CAMEL V002, which is available from the National Aeronautics and Space Administration (NASA) Land Processes Distributed Active Archive Center (LP DAAC)
Climatology ances or the inter-channel correlation of the observations needed for data assimilation four selected case sites, chosen for their are diverse representations of land cover ty purposes to account for the lack of independence between the spectral observations [36]
Summary
Land surface emissivity is a critical variable in a multitude of Earth science studies and applications. One of the significant advantages of the CAMEL HSR dataset is that it provides an estimate of the surface emissivity for the entire thermal infrared region, including channels used for sounding the atmosphere, at a spatial resolution higher than current hyperspectral infrared sounding instruments. The CAMEL HSR product and its precursor, the UWIREMIS dataset, are actively used by the numerical weather prediction (NWP) community in research into the use of infrared satellite observations over land for weather forecasting. The climatology was derived from the CAMEL V002 monthly product for the period 2000–2016, making it a better representation of the full NASA Earth Observing System satellite record This RTTOV emissivity update was released in RTTOV version 12.3 and includes both an update to the error covariance matrix as well as a snow correction option in the emissivity module. The paper is broken down as follows: Section 2 describes the data and software, Section 3 highlights changes in CAMEL from V001 to V002, Section 4 describes the methodology, Section 5 shows analyses of the climatology dataset, Section 6 demonstrates its use in RTTOV, and Section 7 compares the CAMEL and ECOSTRESS datasets
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