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 1B At-Sensor Calibrated Radiance and Geolocation (EMITL1BRAD) Version 2 data product provides at-sensor calibrated radiance values along with observation data in a spatially raw, non-orthocorrected format. Each EMITL1BRAD granule consists of two Network Common Data Format Version 4 (netCDF-4) files at a spatial resolution of 60 meters (m): Radiance (EMIT_L1B_RAD) and Observation (EMIT_L1B_OBS). The Radiance file contains the at-sensor radiance measurements of 285 bands with a spectral range of 381-2493 nanometers (nm) and with a spectral resolution of ~7.5 nm, all held within a single variable. The Observation file contains viewing and solar geometries, timing, topographic, and other information related to the observation.

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 to allow for projection of the data. Along with the GLT layers, the files also contain latitude, longitude, and elevation layers. The latitude and longitude coordinates are presented using the World Geodetic System (WGS84) ellipsoid. The elevation data was obtained from Shuttle Radar Topography Mission v3 (SRTM v3) data and then resampled to EMIT’s spatial resolution.

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 approximately 150 km in length.

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.