The Earth Surface Mineral Dust Source Investigation (EMIT) is an Earth Ventures-Instrument (EVI-4) Mission aboard the International Space Station (ISS). EMIT’s prime mission was designed to map surface mineralogy of arid dust source regions using imaging spectroscopy in the visible and short-wave infrared (VSWIR). EMIT uses imaging spectroscopy to take mineralogical measurements of sunlit regions of interest between 52° N latitude and 52° S latitude. During the prime mission, the EMIT team focused on using surface reflectance to resolve absorption features of iron oxides, clays, sulfates, carbonates, and other dust-forming minerals in Earth's dust source regions. In the extended mission, EMIT’s core measurements remain the same, but acquisitions expand to sample all regions observable from the ISS orbit, supporting efforts across the atmosphere, biosphere, cryosphere, geosphere, hydrosphere, and more. An interactive map showing the regions being investigated, current and forecasted data coverage, and additional data resources can be found on the VSWIR Imaging Spectroscopy Interface for Open Science (VISIONS) EMIT Open Data Portal.

The EMIT Level 2B Fractional Cover and Uncertainty (EMITL2BFRCOV) Version 2 data product provides a series of fractional cover estimates, associated uncertainty metrics, and one quality control (QC) flag mask variable. The fractional cover estimates are derived from the EMIT L2A Estimated Surface Reflectance and Uncertainty Version 2 (EMITL2ARFL) data product, while the QC flag mask variable is derived from EMITL2ARFL Version 2, EMIT L2A Masks (EMITL2AMASK) Version 3, and non-EMIT landcover and water body inputs. For more details about inputs used for this data product, see Sections 4.3 and 4.5 of the Algorithm Technical Basis Document (ATBD).

Each EMITL2BFRCOV granule consists of seven Cloud Optimized GeoTIFF (COG) files at 60 meter (m) spatial resolution: Photosynthetic Vegetation (PV) Fractional Cover (EMIT_L2B_FRCOVPV) and Uncertainty (EMIT_L2B_FRCOVPVUNC), Non-photosynthetic Vegetation (NPV) Fractional Cover (EMIT_L2B_FRCOVNPV) and Uncertainty (EMIT_L2B_FRCOVNPVUNC), Bare Soil Fractional Cover (EMIT_L2B_FRCOVBARE) and Uncertainty (EMIT_L2B_FRCOVBAREUNC), and QC Flags (EMIT_L2B_FRCOVQC). A browse image is also available.

Each granule is approximately 75 kilometers (km) by 75 km, nominal at the equator with some granules at the end of an orbit segment reaching 150 km in length.

Known Issues

• Data acquisition gap: From September 13, 2022, through January 6, 2023, a power issue outside of EMIT caused a pause in operations. Due to this shutdown, no data were acquired during that timeframe. Outside of this period, regular short-term gaps in coverage are expected depending on the solar and sensor geometry.
• Data pixel misidentification: Pixels along cloud edges and in cloud shadows may be incorrectly identified as high NPV pixels.
• Missing QC water pixels: Major inland lakes that should be classified as QC water pixels may not be included due to them being absent from an input dataset used in the production of this data product.
• QC pixel misidentification: Water, cloud, and snow/ice pixels may be misidentified based on normalized snow difference index, pixel brightness, or pixel shading.
• For more information on these topics check the Known Issues Section of the ATBD.