Raw EPIC Data Calibration

Cede, Alexander; Huang, Liang; McCauley, Gavin; Herman, J. R.; Blank, Karin; Kowalewski, M. G.; Marshak, Alexander

doi:10.3389/frsen.2021.702275

Cited by 7 publications

(2 citation statements)

References 31 publications

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“…Particularly, it resulted in more accurate estimation of solar/view angles for each EPIC pixel thereby improving radiance simulations and reducing errors in ozone retrievals. EPIC version 3 Level 1 data have been also corrected for the darkcurrent signal, flat-field, and stray-light contamination (Cede et al, 2021). In-flight EPIC radiometric calibrations are done by comparing EPIC measured albedo for each wavelength channel with coincident, scene-matched measurements from Suomi National Polar Partnership (SNPP) Ozone Mapping and Profiler Suite (OMPS) Nadir Mapper (Herman et al, 2018).…”

Section: Epic Total Ozonementioning

confidence: 99%

Evaluation of Version 3 Total and Tropospheric Ozone Columns From Earth Polychromatic Imaging Camera on Deep Space Climate Observatory for Studying Regional Scale Ozone Variations

Kramarova

Ziemke

Huang

et al. 2021

Front. Remote Sens.

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Discrete wavelength radiance measurements from the Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Imaging Camera (EPIC) allows derivation of global synoptic maps of total and tropospheric ozone columns every hour during Northern Hemisphere (NH) Summer or 2 hours during Northern Hemisphere winter. In this study, we present version 3 retrieval of Earth Polychromatic Imaging Camera ozone that covers the period from June 2015 to the present with improved geolocation, calibration, and algorithmic updates. The accuracy of total and tropospheric ozone measurements from EPIC have been evaluated using correlative satellite and ground-based total and tropospheric ozone measurements at time scales from daily averages to monthly means. The comparisons show good agreement with increased differences at high latitudes. The agreement improves if we only accept retrievals derived from the EPIC 317 nm triplet and limit solar zenith and satellite looking angles to 70°. With such filtering in place, the comparisons of EPIC total column ozone retrievals with correlative satellite and ground-based data show mean differences within ±5-7 Dobson Units (or 1.5–2.5%). The biases with other satellite instruments tend to be mostly negative in the Southern Hemisphere while there are no clear latitudinal patterns in ground-based comparisons. Evaluation of the EPIC ozone time series at different ground-based stations with the correlative ground-based and satellite instruments and ozonesondes demonstrated good consistency in capturing ozone variations at daily, weekly and monthly scales with a persistently high correlation (r2 > 0.9) for total and tropospheric columns. We examined EPIC tropospheric ozone columns by comparing with ozonesondes at 12 stations and found that differences in tropospheric column ozone are within ±2.5 DU (or ∼±10%) after removing a constant 3 DU offset at all stations between EPIC and sondes. The analysis of the time series of zonally averaged EPIC tropospheric ozone revealed a statistically significant drop of ∼2–4 DU (∼5–10%) over the entire NH in spring and summer of 2020. This drop in tropospheric ozone is partially related to the unprecedented Arctic stratospheric ozone losses in winter-spring 2019/2020 and reductions in ozone precursor pollutants due to the COVID-19 pandemic.

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Section: Epic Total Ozonementioning

confidence: 99%

Evaluation of Version 3 Total and Tropospheric Ozone Columns From Earth Polychromatic Imaging Camera on Deep Space Climate Observatory for Studying Regional Scale Ozone Variations

Kramarova

Ziemke

Huang

et al. 2021

Front. Remote Sens.

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“…The measurements are 2 × 2 pixels aggregated onboard except for the blue (443 nm) band. The standard calibration of the EPIC's raw imagery includes the dark, latency, temperature, stray-light and flat-field corrections (Cede et al, 2021). To track the post-launch changes and on-orbit trending of calibration, the EPIC's calibration is continuously updated using the underflight comparisons with other Earth observing instruments, e.g., Moderate Resolution Imaging Spectroradiometer (MODIS), Visible Infrared Imaging Radiometer Suite (VIIRS), Ozone Mapping and Profiler Suite (OMPS) on Suomi National Polarorbiting Partnership (SNPP) satellite etc.…”

Section: Introductionmentioning

confidence: 99%

Atmospheric Correction of DSCOVR EPIC: Version 2 MAIAC Algorithm

Lyapustin¹,

Wang

et al. 2021

Front. Remote Sens.

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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, and R = 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.

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