DSCOVR_EPIC_L2_AER_03 is the Deep Space Climate Observatory (DSCOVR) Enhanced Polychromatic Imaging Camera (EPIC) Level 2 UV Aerosol Version 3 data product. Observations for this data product are at 340 and 388 nm and are used to derive near UV aerosol properties. The EPIC aerosol retrieval algorithm (EPICAERUV) uses a set of aerosol models to account for the presence of carbonaceous aerosols from biomass burning and wild fires (BIO), desert dust (DST), and sulfate-based (SLF) aerosols. These aerosol models are identical to those assumed in the OMI algorithm (Torres et al., 2007; Jethva and Torres, 2011). Aerosol data products generated by the EPICAERUV algorithm are aerosol extinction optical depth (AOD) and single scattering albedo (SSA) at 340, 388 and 500 nm for clear sky conditions. AOD of absorbing aerosols above clouds is also reported (Jethva et al., 2018). In addition, the UV Aerosol Index (UVAI) is calculated from 340 and 388 nm radiances for all sky conditions. AOD is a dimensionless measure of the extinction of light y aerosols due to the combined effect of scattering and absorption. SSA represents the fraction of extinction solely due to aerosol scattering effects. The AI is simply a residual parameter that quantifies the difference in spectral dependence between measured and calculated near UV radiances assuming a purely molecular atmosphere. Because most of the observed positive residuals are associated with the presence of absorbing aerosols, this parameter is commonly known as the UV Absorbing Aerosol Index. EPIC-derived aerosol parameters are reported at a 10 km (nadir) resolution.

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LARC_ASDC Short Name: DSCOVR_EPIC_L2_AERF Version ID: 01 Unique ID: C2128176689-LARC_ASDC

Robust cloud products are critical for DSCOVR to make a significant contribution to climate studies. Building on our team’s track-record in cloud detection, cloud property retrieval, oxygen band exploitation, and DSCOVR-related studies, we propose to develop a suite of algorithms for generating the operational EPIC cloud mask, cloud height and cloud optical thickness products. Multichannel observations will be used for cloud masking; the cloud height will be developed with information from the oxygen A- and B- band pairs (780 nm vs. 779.5 nm and 680 nm vs. 687.75 nm); for the cloud optical thickness retrieval, we propose an approach that combines the EPIC 680 nm observations and numerical weather model outputs. Preliminary results from radiative transfer modeling and from proxy data applications show that the proposed algorithms are viable. Product validation will be conducted by comparing EPIC observations/retrievals with counterparts from coexisting Low Earth Orbit (LEO) and Geosynchronous Earth Orbit (GEO) satellites. The proposed work will include a rigorous uncertainty analysis based on theoretical and computational radiative transfer modeling that complements standard validation activities with physics-based diagnostics. We also plan to evaluate and improve the calibration of the EPIC O2 A- and B-band absorption channels through tracking the instrument performance over known targets, such as cloud free ocean and ice sheet surfaces. The deliverables for the proposed work include an Algorithm Theoretical Basis Document (ATBD) for peer-review, products generated with the proposed algorithms and supporting research articles. The data products, which will be archived at the Atmospheric Science Data Center (ASDC) at the NASA Langley Research Center, will provide essential inputs needed for the community to apply EPIC observations to climate research and to better interpret NISTAR observations. The proposed work directly responds to the solicitation to “develop and implement the necessary algorithms and processes to enable various data products from EPIC sunrise to sunset observations once on orbit”, and also for improving “the calibration of EPIC based on in-flight data”.

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LARC_ASDC Short Name: DSCOVR_EPIC_L2_O3SO2AI Version ID: 03 Unique ID: C2229467436-LARC_ASDC

DSCOVR_EPIC_L2_TO3_v03 is Level2 Total Ozone derived from the Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Imaging Camera (EPIC) using Level 1b version 3 inputs and version 3 ozone retrieval algorithm. The measurements from four EPIC UV channels are used to derive the global distributions of total ozone over the entire sunlit portion of the Earth. A new soft calibration technique developed based on scene matching with OMPS gives calibrated EPIC radiances. The calibrated EPIC radiances are used to derive science-quality total ozone products from EPIC that are consistent with those from other UV instruments. The retrieval algorithm uses wavelength triplets and assumes that the scene reflectivity changes linearly with wavelength. Version 3 algorithm includes several key modifications aimed to improve total ozone retrievals: a) switch to Version 3 Level 1b product with improved geolocation registration, flat field and dark counts corrections; b) replace OMI based cloud height climatology with the simultaneous EPIC A-Band cloud height; c) update absolute calibrations using polar orbiting SNPP OMPS; d) add corrections for ozone profile shape and temperature; e) update algorithm and error flags to filter data; f) add column weighting functions for each observation to facilitate error analysis. EPIC ozone retrievals accurately capture short term synoptic changes in total column ozone. With EPIC measurements from DSCOVR's vantage point synoptic ozone maps can be derived every 1-2 hours. Scene Reflectivity (clouds, aerosols, and surface) is derived as part of the ozone retrieval. The scene reflectivity in conjunction with ozone has been used to derive the amount of UV solar radiation reaching the ground, and surface UV Erythemal is also reported in these files.

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LARC_ASDC Short Name: DSCOVR_EPIC_L2_TO3 Version ID: 03 Unique ID: C1990753071-LARC_ASDC

DSCOVR_EPIC_L2_VESDR_02 is the Deep Space Climate ObserVatoRy (DSCOVR) EPIC Level 2 Vegetation Earth System Data Record (VESDR), Version 2 data product. It provides Leaf Area Index (LAI) and diurnal courses of Normalized Difference Vegetation Index (NDVI), Sunlit Leaf Area Index (SLAI), Fraction of incident Photosynthetically Active Radiation (400-700 nm) absorbed by the vegetation (FPAR), Directional Area Scattering Function (DASF), Earth Reflector Type Index (ERTI) and Canopy Scattering Coefficient at 443 nm, 551 nm, 680 nm and 779 nm. The VESDR files also include Solar Zenith Angle (SZA), Solar Azimuthal Angle (SAA), View Zenith (VZA) and Azimuthal (VAA) angles at the same temporal and spatial resolutions. The parameters are projected on 8 regional 10 km SIN grids and available at 65 to 110 min temporal frequency. The version 2 VESDR product is being generated from the upstream DSCOVR EPIC L2 MAIAC (version 2) surface reflectance product. FPAR, LAI, SLAI are useful for monitoring variability and change in global vegetation due to climate and anthropogenic influences, modeling climate, carbon and water cycles, and improving forecasting of near surface weather. DASF provides information critical to accounting for structural contributions to measurements of leaf biochemistry from remote sensing. The canopy scattering coefficient is the fraction of intercepted radiation that has been reflected from, or diffusely transmitted through, the vegetation. This parameter is strongly correlated with leaf albedo which in turn depends on leaf biochemical constituents. We also provide two ancillary science data products, namely, “Version 2 10 km Land Cover Type” and “Version 2 Distribution of Land Cover Types within 10 km EPIC pixel.” The products were derived from 500m MODIS land cover type 3 product (MCDLCHKM), which was generated from 2008, 2009 and 2010 land cover products (MCD12Q1, v051). A detailed description of the VESDR and ancillary science data products can be found in “VESDR Science Data Product Guide, version 2”. Section “USER'S GUIDE” provides links to this document as well as to the two ancillary science data products.

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LARC_ASDC Short Name: DSCOVR_EPIC_L2_VESDR Version ID: 02 Unique ID: C1990753227-LARC_ASDC

DSCOVR_EPIC_L3_PAR-image_01 is a view image showing data from DSCOVR_EPIC_L3_PAR, which is the Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Imaging Camera (EPIC) Level 3 photosynthetically available radiation (PAR) version 1 data product. The EPIC observations of the Earth’s surface lit by the Sun made 13 times during the day in spectral bands centered on 443, 551, and 680 nm are used to estimate daily mean PAR at the ice-free ocean surface. PAR is defined as the quantum energy flux from the Sun in the 400-700 nm range. Daily mean PAR is the 24-hour averaged planar flux in that spectral range reaching the surface. It is expressed in E.m-2.d-1 (Einstein per meter squared per day). The factor required to convert E.m-2 d-1 units to mW.cm-2.µm-1 units is equal to 0.838 to an inaccuracy of a few percent regardless of meteorological conditions. The EPIC daily mean PAR product is generated on Plate Carrée (equal-angle) grid with 18.4 km resolution at the equator and on 18.4 km equal-area grid, i.e., the product is compatible with Ocean Biology Processing Group ocean color products. The EPIC PAR algorithm uses a budget approach, in which the solar irradiance reaching the surface is obtained by subtracting from the irradiance arriving at the top of the atmosphere (known), the irradiance reflected to space (estimated from the EPIC Level 1b radiance data), taking into account atmospheric transmission (modeled). Clear and cloudy regions within a pixel do not need to be distinguished, which dismisses the need for often-arbitrary assumptions about cloudiness distribution and is therefore adapted to the relatively large EPIC pixels. A daily mean PAR is estimated on the source grid for each EPIC instantaneous daytime observation, assuming no cloudiness change during the day, and the individual estimates are remapped and weight-averaged using the cosine of the Sun zenith angle. In the computations, wind speed, surface pressure, and water vapor amount are extracted from NCEP (National Centers for Environmental Prediction) Reanalysis 2 data, aerosol optical thickness and angstrom coefficient from MERRA-2 (Modern-Era Retrospective analysis for Research and Applications, Version 2) data, and ozone amount from EPIC Level 2 data. Areas contaminated by sun glint are excluded using a threshold on sun glint reflectance calculated using wind data. Ice masking is based on NSIDC (National Snow and Ice Data Center) near real time ice fraction data. Additional information about the EPIC ocean surface PAR products can be found at the NASA DSCOVR: EPIC website: https://epic.gsfc.nasa.gov/, under “Science -> Products -> Ocean Surface” (https://epic.gsfc.nasa.gov/science/products/ocean).

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LARC_ASDC Short Name: DSCOVR_EPIC_L3_PAR-IMAGE Version ID: 01 Unique ID: C2150640573-LARC_ASDC