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 L2A Masks 60 m (EMITL2AMASK) Version 3 data product provides a series of masks designed to facilitate the identification of clear and reliable observations of the Earth’s surface in a spatially raw, non-orthocorrected format. Each EMITL2AMASK granule consists of one Network Common Data Format Version 4 (netCDF-4) file at a spatial resolution of 60 meters (m), along with a corresponding browse image. The data file (EMIT_L2A_MASK) contains seven mask bands: five binary flag bands and two data bands. The binary flag bands identify the presence of clouds, dense cirrus clouds, and water bodies, which indicate if a pixel should be excluded from analysis. The data bands provide values that describe the probability of cloud presence and the distance to the nearest cloud pixel.

The 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 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.