An Estimated Surface Reflectance RGB image (bands 36, 22, 10) and data cube showcasing spectral signatures of the data from the EMITL2ARFL product over Libya, Africa on August 17, 2022.View full-size image
The 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 2A Estimated Surface Reflectance and Uncertainty and Masks (EMITL2ARFL) Version 1 data product provides surface reflectance data in a spatially raw, non-orthocorrected format. Each EMITL2ARFL granule consists of three Network Common Data Format 4 (NetCDF4) files at a spatial resolution of 60 meters (m): Reflectance (EMIT_L2A_RFL), Reflectance Uncertainty (EMIT_L2A_RFLUNCERT), and Reflectance Mask (EMIT_L2A_MASK). 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, which are held within a single science dataset layer (SDS). The Reflectance Uncertainty file contains uncertainty estimates about the reflectance captured as per-pixel, per-band, posterior standard deviations. The Reflectance Mask file contains six binary flag bands and two data bands. The binary flag bands identify the presence of features including clouds, water, and spacecraft which indicate if a pixel should be excluded from analysis. The data bands contain estimates of aerosol optical depth (AOD) and water vapor.
Each NetCDF4 file holds a location group containing a geometric lookup table (GLT) which is an orthorectified image that provides relative x and y reference locations from the raw scene to allow for projection of the data. Along with the GLT layers, the files will 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.
|File Size||~1.8 GB|
|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)|
|Geographic Dimensions||74.5 km x 76.8 km|
|Number of Science Dataset (SDS) Layers||13|
|Columns/Rows||1242 x 1280|
|Pixel Size||60 m|
|SDS Name||Description||Units||Data Type||Fill Value||No Data Value||Valid Range||Scale Factor||Offset|
|reflectance1||Reflectance, Multiband Array (12806x1242x285)||N/A||32-bit floating point||-9999.00||N/A||N/A||N/A|
|reflectance_uncertainty2||Reflectance Uncertainty, (12806x1242x285)||N/A||32-bit floating point||-9999.00||N/A||N/A||N/A|
|mask3||Mask||N/A||32-bit floating point||-9999.00||N/A||N/A||N/A|
|band_mask3||Per-wavelength mask||N/A||8-bit unsigned integer||241||N/A||N/A||N/A|
|glt_x5||Geometric lookup table – x values||N/A||32-bit signed integer||-9999||0||1 to 1242||N/A|
|glt_y5||Geometric lookup table – y values||N/A||32-bit signed integer||-9999||0||1 to 2559||N/A|
|lat5||Latitude||Degree||64-bit floating point||-9999.0000||N/A||-90 to 90||N/A|
|lon5||Longitude||Degree||64-bit floating point||-9999.0000||N/A||-180 to 180||N/A|
|elev5||Elevation||Meters||64-bit floating point||-9999.0000||N/A||N/A||N/A|
|wavelengths4||Wavelength grid||Nanometers||32-bit floating point||-9999.00||N/A||N/A||N/A|
|good_wavelengths4||Wavelengths where reflectance is useable||N/A||8-bit unsigned integer||241||N/A||0, 1||N/A|
|fwhm4||Full width at half maximum||Nanometers||32-bit floating point||-9999.00||N/A||N/A||N/A|
|mask_bands3||Array of strings indicating the name of each observation band||N/A||N/A||-9999.00||N/A||N/A||N/A|
4 EMIT_L2A_RFL and EMIT_L2A_RFLUNC
5 EMIT_L2A_RFL, EMIT_L2A_RFLUNC, and EMIT_L2A_MASK
6 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 Number||Band Name||Band Description|
|0||Cloud Flag||Cloud Coverage|
|1||Cirrus Flag||Dense Cirrus clouds|
|2||Water Flag||Water bodies|
|3||Spacecraft Flag||Spacecraft or space station components that intersect the EMIT field of view|
|4||Dilated Cloud Flag||Cloud coverage + buffer|
|5||AOD550 (unitless)||Aerosol Optical Depth at 550 nm estimates|
|6||H₂O (g/cm²)||Water Vapor estimates|
|7||Aggregate Flag||Aggregated binary flag of bands 1 through 5|
Quality information for the EMITL2ARFL Version 1 data product is not provided.