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) range. 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 2A Surface Reflectance and Uncertainty (EMITL2ARFL) Version 2 data product provides surface reflectance data in a spatially raw, non-orthocorrected format. Each EMITL2ARFL granule consists of two Network Common Data Format Version 4 (netCDF-4) files at a spatial resolution of 60 meters (m): Reflectance (EMIT_L2A_RFL) and Reflectance Uncertainty (EMIT_L2A_RFLUNCERT). The Reflectance file contains surface reflectance maps of 285 bands with a spectral range of 381-2493 nanometers (nm) at a spectral resolution of ~7.5 nm. These are all contained within a single science dataset layer/variable. Aerosol optical thickness and water vapor values are also included within their own separate variables. The Reflectance Uncertainty file contains uncertainty estimates captured as per-pixel, per-band, posterior standard deviations.

Each netCDF-4 file holds a location group containing geometric lookup tables (GLT) which are orthorectified images that provide relative x- and y-reference locations from the raw scene, enabling projection of the data. In addition to the GLT layers, the file also contains latitude, longitude, and elevation variables. The latitude and longitude coordinates are based on the World Geodetic System 84 (WGS-84) ellipsoid. Elevation data included in each granule are sourced from Shuttle Radar Topography Mission (SRTM) v3 data and resampled to match EMIT’s 60 m spatial resolution.

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

Known Issues:

• Data acquisition gap: From September 13, 2022, through January 6, 2023, a power issue on the ISS caused a pause in EMIT 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.