Abstract
The Earth Polychromatic Imaging Camera (EPIC) onboard the Deep Space Climate Observatory (DSCOVR) provides multispectral images of the sunlit disk of Earth since 2015 from the L1 orbit, approximately 1.5 million km from Earth toward the Sun. The NASA’s Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm has been adapted for DSCOVR/EPIC data providing operational processing since 2018. Here, we describe the latest version 2 (v2) MAIAC EPIC algorithm over land that features improved aerosol retrieval with updated regional aerosol models and new atmospheric correction scheme based on the ancillary bidirectional reflectance distribution function (BRDF) model of the Earth from MAIAC MODIS. The global validation of MAIAC EPIC aerosol optical depth (AOD) with AERONET measurements shows a significant improvement over v1 and the mean bias error MBE = 0.046, RMSE = 0.159, andR= 0.77. Over 66.7% of EPIC AOD retrievals agree with the AERONET AOD to within ± (0.1 + 0.1AOD). We also analyze the role of surface anisotropy, particularly important for the backscattering view geometry of EPIC, on the result of atmospheric correction. The retrieved BRDF-based bidirectional reflectance factors (BRF) are found higher than the Lambertian reflectance by 8–15% at 443 nm and 1–2% at 780 nm for EPIC observations near the local noon. Due to higher uncertainties, the atmospheric correction at UV wavelengths of 340, 388 nm is currently performed using a Lambertian approximation.
Highlights
The Earth Polychromatic Imaging Camera (EPIC) is a 10-channel Charge Coupled Device (CCD) onboard the Deep Space Climate Observatory (DSCOVR) satellite that orbits around the Sun–Earth Lagrange-1 (L1) point with a distance of about 1.5 million kilometers from the Earth
The current paper focuses on cloud detection, aerosol retrieval and atmospheric correction over land, and provides the list of reported data products
Over 66.72% of Multi-Angle Implementation of Atmospheric Correction (MAIAC) EPIC aerosol optical depth (AOD) agree with AERONET within the expected error (EE) of ±(0.1 + 0.1AOD)
Summary
The Earth Polychromatic Imaging Camera (EPIC) is a 10-channel Charge Coupled Device (CCD) onboard the Deep Space Climate Observatory (DSCOVR) satellite that orbits around the Sun–Earth Lagrange-1 (L1) point with a distance of about 1.5 million kilometers from the Earth (http://epic.gsfc.nasa.gov). The main limitations stem from the limited angular sampling of EPIC prohibiting deriving the selfconsistent BRDF model in the full hemisphere of angles of incidence and reflection, and from the growing uncertainties of the ancillary MODIS BRDF model at high SZA/VZA in application to EPIC Both Lambertian and scaling algorithms reproduce well the spatial pattern and the RGB color of the EPIC TOA images while, respectively, underestimating and overestimating the true BRF, especially at high zenith angles. The “direct term” algorithm shows rapidly growing uncertainties at high zenith angles As it depends on the absolute ancillary BRDF model, this approach is prone to spatial and spectral distortions in the resulting RGB BRF images. The DSCOVR orbit became less constrained and allows the range of angles ∼2–12° from the exact backscattering since March 2020
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