An At-Sensor Calibrated Radiance RGB image (bands 36, 22, 10) and data cube showcasing spectral signatures of the data from the EMITL1BRAD product over Libya, Africa on August 17, 2022.
View full-size imageThe Earth Surface Mineral Dust Source Investigation (EMIT) instrument measures surface mineralogy, targeting the Earth’s arid dust source regions. EMIT is installed on the International Space Station (ISS) and uses imaging spectroscopy to take mineralogical measurements of sunlit regions of interest between 52° N latitude and 52° S latitude. 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 1 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 4 (NetCDF4) 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, which are held within a single science dataset layer (SDS). The Observation file contains viewing and solar geometries, timing, topographic, and other information related to the observation.
Each NetCDF4 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 resampled to EMIT’s spatial resolution.
Each granule is approximately 75 kilometer (km) by 75 km, nominal at the equator, and some granules near the end of an orbit segment reaching 150 km in length.
| Characteristic | Description |
|---|---|
| Collection | EMIT |
| DOI | 10.5067/EMIT/EMITL1BRAD.001 |
| File Size | ~1.8 GB |
| Temporal Resolution | Varies |
| Temporal Extent | 2022-08-09 to Present |
| Spatial Extent | Global (52 °N to 52 °S Latitude) |
| Coordinate System | Geographic Latitude and Longitude |
| Datum | World Geodetic System (WGS84) |
| File Format | NetCDF4 |
| Geographic Dimensions | 74.5 km x 76.8 km |
| Characteristic | Description |
|---|---|
| Number of Science Dataset (SDS) Layers | 10 |
| Columns/Rows | 1242 x 1280 |
| Pixel Size | 60 m |
| SDS Name | Description | Units | Data Type | Fill Value | No Data Value | Valid Range | Scale Factor |
|---|---|---|---|---|---|---|---|
| radiance1 | Radiance Data, (12804x1242x285) | μW/cm²/sr/nm | 32-bit floating point | -9999.00 | N/A | N/A | N/A |
| obs2 | 3D array with band parameters specified, (12804x1242x11) | N/A | 32-bit floating point | -9999.00 | N/A | N/A | N/A |
| glt_x3 | Geometric lookup table – x values | N/A | 32-bit signed integer | -9999 | 0 | 1 to 1242 | N/A |
| glt_y3 | Geometric lookup table – y values | N/A | 32-bit signed integer | -9999 | 0 | 1 to 2559 | N/A |
| lat3 | Latitude | Degree | 64-bit floating point | -9999.0000 | N/A | -90 to 90 | N/A |
| lon3 | Longitude | Degree | 64-bit floating point | -9999.0000 | N/A | -180 to 180 | N/A |
| elev3 | Elevation | Meters | 64-bit floating point | -9999.0000 | N/A | N/A | N/A |
| radiance_wl1 | Wavelength centers | Nanometers | 32-bit floating point | -9999.00 | N/A | N/A | N/A |
| radiance_fwhm1 | Full width at half maximum | Nanometers | 32-bit floating point | -9999.00 | N/A | N/A | N/A |
| observation_bands2 | Array of strings indicating the name of each observation band | N/A | N/A | N/A | N/A | N/A | N/A |
1 EMIT_L1B_RAD
2 EMIT_L1B_OBS
3 EMIT_L1B_RAD and EMIT_L1B_OBS
4 Scenes have at least 1280 rows. To prevent small scenes, scenes at the end of an orbit segment will have up to 2559 rows.
| Band Name | Units | Comments | |
|---|---|---|---|
| Path length | meters | Distance between sensor and ground | |
| To-sensor azimuth | Degree | 0 to 360 degrees clockwise from N | |
| To-sensor zenith | Degree | 0 to 90 degrees from zenith | |
| To-sun azimuth | Degree | 0 to 360 degrees clockwise from N | |
| To-sun zenith | Degree | 0 to 90 degrees from zenith | |
| Solar phase | Degree | Degrees between to-sensor and to-sun vectors in principal plane | |
| Slope | Degree | Local surface slope as derived from Digital Elevation Model (DEM) in degrees | |
| Aspect | Degree | Local surface aspect 0 to 360 degrees clockwise from N | |
| Cosine(i) | N/A | Apparent local illumination factor based on DEM slope and aspect and to sun vector, 0 to 1 | |
| UTC Time | Hours | Fractional hours since UTC midnight | |
| Earth-sun distance (AU) | Astronomical Units | Distance between the Earth and the Sun. |
** All geometry products in the observation dataset are calculated using SRTM as a surface.
Quality information for the EMITL1BRAD Version 1 data product is not provided.