EMITL1BRAD v001

EMIT L1B At-Sensor Calibrated Radiance and Geolocation Data 60 m


PI: Robert Green

The early release of EMITL1BRAD includes a small representation of EMIT data with limited spatial and temporal coverage to provide the science community with an opportunity to become familiar with the data. Feedback is welcome and can be sent to LP DAAC User Services at lpdaac@usgs.gov.

An older version of the Algorithm Theoretical Basis Document (ATBD) has been made available for the early release. The document is being updated and will be posted as soon as reviews are complete.

Description

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). During its one-year mission, EMIT will take mineralogical measurements of sunlit regions of interest between 52° N latitude and 52° S latitude. A map of the regions being investigated can be found on the EMIT website.

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. 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.

read more

Characteristics

Collection and Granule

Collection

Characteristic Description
CollectionEMIT
DOI10.5067/EMIT/EMITL1BRAD.001
File Size~1.8 GB
Temporal ResolutionVaries
Temporal Extent2022-07-27 to Present
Spatial ExtentGlobal (52 °N to 52 °S Latitude)
Coordinate SystemGeographic Latitude and Longitude
DatumWorld Geodetic System (WGS84)
File FormatNetCDF4
Geographic Dimensions74.5 km x 76.8 km

Granule

Characteristic Description
Number of Science Dataset (SDS) Layers10
Columns/Rows1242 x 1280
Pixel Size60 m

Layers

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, (1280⁴x1242x285) 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.

Observation SDS Bands

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.

Product Quality

Quality information for the EMITL1BRAD Version 1 data product is not provided.

Known Issues

No known issues.


About the image

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 image

Documentation

User Guide
Algorithm Theoretical Basis Document (ATBD)

Using the Data

Access Data

Citation

DOI: 10.5067/EMIT/EMITL1BRAD.001