NASA's Atmospheric Science Data Center (ASDC) has released the Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Imaging Camera (EPIC) Level 1B version 4 data product. This dataset provides calibrated, 10-channel spectroradiometric imagery of the entire sunlit face of the Earth, enabling science applications including measurements of ozone, aerosols, cloud reflectivity, cloud height, vegetation properties, and ultraviolet (UV) radiation estimates at Earth's surface.
Mission Background
NASA's Earth Polychromatic Imaging Camera (EPIC), operating onboard the National Oceanic and Atmospheric Administration's DSCOVR spacecraft, is a 10-channel spectroradiometer (317–780 nm). The mission's primary objective is to provide a unique angular perspective of Earth from the Earth-Sun Lagrange-1 (L-1) point, enabling continuous full-disk imaging of the entire sunlit face of the Earth. EPIC's position at L-1, combined with its 0.62-degree field of view and 2048×2048 pixel charge-coupled device (CCD) and 30-cm aperture Cassegrain telescope, supports a broad range of Earth science applications. Due to DSCOVR's tilted (Lissajous) orbit about the L-1 point, the apparent angular size of Earth varies from 0.45 to 0.53 degrees within its six-month orbital period. A complete set of per-band images are captured every 60 to 100 minutes, depending on the season.
About the Data Products
Accompanying instrument metadata and a series of calibrations and corrections are applied to properly convert the images to Level 1B format. The significant corrections are for flat‐fielding and stray light. Flat-fielding is based on measurements with a uniform light source to measure the differences in sensitivity for each of the 4 million pixels. The resulting correction map is applied to the estimated counts from the CCD. Stray light was measured in the laboratory using a series of small-diameter light sources entering the telescope and imaged on the CCD.
A similar set of measurements has been performed on orbit using the Moon. The illumination of pixels outside the primary diameter of the light source was measured to produce a detailed matrix map of the entire stray light function, and the resulting stray light correction was applied to every image. Other corrections are also used based on laboratory measurements. For wavelengths longer than 550 nm, there are back-to-front interference effects in the partially transparent CCD (etaloning) that must also be removed from measured radiance.
DSCOVR EPIC Level 1B Version 4 products contain calibrated and geolocated EPIC images of Earth only (no Moon or dark space objects) in the field of view with ancillary metadata. These data products are in Hierarchical Data Format version 5 (HDF5) format.