EMIT L2A Estimated Surface Reflectance and Uncertainty and Masks 60 m

PI: Robert Green

The Algorithm Theoretical Basis Document (ATBD) is being updated and a new version will be posted as soon as reviews are complete.


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.

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Collection and Granule


Characteristic Description
File Size~1.8 GB
Temporal ResolutionVaries
Temporal Extent2022-08-09 to Present
Spatial ExtentGlobal (52 °N to 52 °S Latitude)
Coordinate SystemGeographic Latitude and Longitude
DatumWorld Geodetic System (WGS84)
File FormatnetCDF-4
Geographic Dimensions74.5 km x 76.8 km


Characteristic Description
Number of Science Dataset (SDS) Layers13
Columns/Rows1242 x 1280
Pixel Size60 m

Layers / Variables

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

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.

Good_Wavelength SDS Flags

Value Description
0 Bad Data
1 Good Data

Mask SDS Bands

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

Product Quality

Quality information for the EMITL2ARFL Version 1 data product is not provided.

Known Issues

  • Data acquisition gap: From September 13, 2022, through January 6, 2023, a power issue outside of EMIT caused a pause in operations. Due to this shut down, no data were acquired during that timeframe.

About the image

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.

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User Guide
Algorithm Theoretical Basis Document (ATBD)

Using the Data

Access Data


DOI: 10.5067/EMIT/EMITL2ARFL.001