SISTER: EMIT L2A Resampled Surface Reflectance and Uncertainty 60 m V002

Generated by the Space-based Imaging Spectroscopy and Thermal pathfindER (SISTER) activity in support of the NASA Earth System Observatory's Surface Biology and Geology (SBG) mission, this dataset utilizes existing airborne and spaceborne sources to generate prototype data products spanning terrestrial ecosystems, inland and coastal aquatic ecosystems, hydrology, and geology. The objective of SISTER is to mature many of the workflows, algorithms, and data products envisioned for SBG, lay the groundwork to develop a robust cal/val network, and build a vigorous and expansive user community ahead of launch. This dataset contains experimental Level 2A resampled surface reflectances and reflectance uncertainties at 60-m spatial resolution derived from data measured by NASA's Earth Surface Mineral Dust Source Investigation (EMIT) instrument. For the purposes of SISTER, only a handful of scenes have been selected from this mission, with a temporal range between 2022-08-10 and 2023-03-25 and a spatial coverage that is global in scale. EMIT measures reflected radiance at ~7.5 nanometer (nm) intervals in the visible to shortwave infrared spectral range between 381 and 2493 nm. The raw EMIT data are first processed to L1B calibrated radiance by the Imaging Spectroscopy Group at Jet Propulsion Laboratory (JPL) and then ingested into the SISTER platform for further downstream analysis. This collection was derived from native spectral resolution surface reflectances and reflectance uncertainties using a spectral resampling algorithm. Spectral resampling was performed in a two-step process. First, bands were aggregated and averaged to the closest resolution to the target resolution (10 nm). Next, a piecewise cubic interpolator was used to interpolate the spectra to the target wavelength spacing. The output products are provided in ENVI format with values expressed as percentages in the range 0-1.

For this dataset, there are 135 total files, including 15 flight lines, of reflectance and uncertainty in ENVI binary and header pairs as well as experimental product generation traceability files in JSON file formats, and a quicklook image for each flight line. 

This dataset contains experimental Level 2A resampled surface reflectances and reflectance uncertainties at 60-m spatial resolution derived from data measured by NASA’s Earth Surface Mineral Dust Source Investigation (EMIT) instrument. For the purposes of SISTER, only a handful of scenes have been selected from this mission, with a temporal range between 2022-08-10 and 2023-03-25 and a spatial coverage that is global in scale.

Project:  SISTER 

The Space-based Imaging Spectroscopy and Thermal pathfindER (SISTER) is a NASA project aimed at prototyping workflows and generating SBG-like data products in efforts to sustain and build the community to increase prospects for major scientific discovery post launch.

These data are associated with experimental products run by the SISTER Science Team as pre-launch modeling tools and data for algorithm development are investigated. The SISTER files for the Composite Release ID (CRID) 002 experimental run contain 29 separate collections (Table 1) that include five instruments and six data products (with the exception of the DESIS instrument). The output range for all sensors except DESIS is 400-2500 nm, while the DESIS output range is 400-990 nm. 

Table 1. Summary of SISTER Sensors, Products, and Coding for all CRID 002 outputs available as separate datasets.

Sensor	Product	Sensor_Level_Product
AVIRIS Classic	Resampled Surface Reflectance and Uncertainty	AVCL_L2A_RSRFL
	Corrected Surface Reflectance	AVCL_L2A_CORFL
	Fractional Cover	AVCL_L2B_FRCOV
	Aquatic Pigments	AVCL_L2B_AQUAPIG
	Vegetative Biochemical Traits	AVCL_L2B_VEGBIOCHEM
	Snow Grain Size	AVCL_L2B_SNOWGRAIN
AVIRIS Next Gen	Resampled Surface Reflectance and Uncertainty	AVNG_L2A_RSRFL
	Corrected Surface Reflectance	AVNG_L2A_CORFL
	Fractional Cover	AVNG_L2B_FRCOV
	Aquatic Pigments	AVNG_L2B_AQUAPIG
	Vegetative Biochemical Traits	AVNG_L2B_VEGBIOCHEM
	Snow Grain Size	AVNG_L2B_SNOWGRAIN
DESIS	Resampled Surface Reflectance and Uncertainty	DESIS_L2A_RSRFL
	Corrected Surface Reflectance	DESIS_L2A_CORFL
	Fractional Cover	DESIS_L2B_FRCOV
	Aquatic Pigments	DESIS_L2B_AQUAPIG
	Vegetative Biochemical Traits	DESIS_L2B_VEGBIOCHEM
PRISMA	Resampled Surface Reflectance and Uncertainty	EMIT_L2A_RSRFL
	Corrected Surface Reflectance	EMIT_L2A_CORFL
	Fractional Cover	PRISMA_L2B_FRCOV
	Aquatic Pigments	PRISMA_L2B_AQUAPIG
	Vegetative Biochemical Traits	PRISMA_L2B_VEGBIOCHEM
	Snow Grain Size	PRISMA_L2B_SNOWGRAIN
EMIT	Resampled Surface Reflectance and Uncertainty	EMIT_L2A_RSRFL
	Corrected Surface Reflectance	EMIT_L2A_CORFL
	Fractional Cover	EMIT_L2B_FRCOV
	Aquatic Pigments	EMIT_L2B_AQUAPIG
	Vegetative Biochemical Traits	EMIT_L2B_VEGBIOCHEM
	Snow Grain Size	EMIT_L2B_SNOWGRAIN

Related Datasets:

See SISTER datasets with the Composite Release ID (CRID) version 002 (filter e.g.: V002)

Townsend, P., M.M. Gierach, P.G. Brodrick, A.M. Chlus, H. Hua, O. Kwoun, M.J. Lucas, N. Malarout, D.F. Moroni, S. Neely, W. Olson-Duvall, J.K. Pon, S. Shah, and D. Yu. 2023. SISTER: Composite Release ID (CRID) Product Generation Files, 2023. ORNL DAAC, Oak Ridge, Tennessee, USA. https://doi.org/10.3334/ORNLDAAC/2231

• SISTER_CRID_002.json - SISTER Composite Release ID (CRID) file contains details of repositories and versions used for this V002 run.
• SISTER_log.txt – SISTER file providing ancillary information which lists and explains file/scene  addition or removal between version releases. 

Spatial Coverage: Selected scenes/flight lines across the globe

Spatial Resolution: 60 m

Spectral Resolution: 10 nm

Temporal Resolution: One-time estimates

Temporal Coverage: 2022-08-10 to 2023-03-25

Site Boundaries: Latitude and longitude are given in decimal degrees.

Site	Westernmost Longitude	Easternmost Longitude	Northernmost Latitude	Southernmost Latitude
EMIT Lines	-122.7249	148.8407	43.7720	-37.7688

Data File Information

There are 135 total files including 15 flight lines of reflectance and uncertainty for each flight line in ENVI binary and header pairs with an associated quicklook image of reflectance, as well as processing product generation information for experimental reproducibility. For the 15 flight lines, there are nine files per flight line.

File naming convention: 
SISTER_<instrument>_<processing_level>_<product>_<flight_id>_<ver>_<subproduct>.<ext>, where 

• <instrument> = the spectroscopy instrument that provided input radiance (Table 3)
• <processing_level> = the NASA Earthdata Data Processing Level
• <product> = the SISTER Project data product (Table 2)
• <flight_id> = flight line identifier, <YYMMDD>T<HHMMSS>, encoding the date and time by year (YY), month (MM), day (DD), and the UTC hour, minute, and second for the start of flight. 
• <ver> = the SISTER processing version, also known as the CRID
• <subproduct> = 'UNC' included for data that are the uncertainty files
• <ext> = file extension

Example file name:

• SISTER_EMIT_L2A_RSRFL_V2_20130612T181031_002.bin
• SISTER_EMIT_L2A_RSRFL_V2_20130612T181031_002_UNC.bin

The ENVI header (.hdr) (https://www.l3harrisgeospatial.com/docs/enviheaderfiles.html) for each ENVI holds metadata for the binary data file, including: 

• number of samples (columns), lines (rows), and bands 
• band information: wavelength and fwhm
• data type (4 = Float32, 5=Float64), interleave type, and byte order 
• map info: projection and datum, coordinates for x y reference points, pixel size, and map units 
• file metadata: sensor type, start and end acquistion time, and bounding box

Table 2. The outputs of the L2A spectral resampling PGE use the following naming convention and produce the following data products. The naming convention for these files follow the same pattern as described above.

Product description	Units	Example filename
Resampled reflectance datacube	1	SISTER_EMIT_L2A_RSRFL_V2_20110513T175417_002.bin
Resampled reflectance header file	-	SISTER_EMIT_L2A_RSRFL_V2_20110513T175417_002.hdr
Metadata  including sensor, start and end time, description, bounding box, product, and processing level	-	SISTER_EMIT_L2A_RSRFL_V2_20110513T175417_002.met.json SISTER_EMIT_L2A_RSRFL_V2_20110513T175417_002_UNC.met.json
Quicklook image	-	SISTER_EMIT_L2A_RSRFL_V2_20110513T175417_002.png
Resampled uncertainty datacube	1	SISTER_EMIT_L2A_RSRFL_V2_20110513T175417_002_UNC.bin
Resampled uncertainty header file	-	SISTER_EMIT_L2A_RSRFL_V2_20110513T175417_002_UNC.hdr
PGE runconfig: defines inputs for the dataset's runs (one file per flight line)	-	SISTER_EMIT_L2A_RSRFL_V2_20110513T175417_002.runconfig.json
PGE log (one file per flight line)	-	SISTER_EMIT_L2A_RSRFL_V2_20110513T175417_002.log

Table 3. Possible SISTER Project Instruments available in the v002 dataset

Instrument	Instrument fullname
AVCL	AVIRIS Classic
AVNG	AVIRIS Next Generation
DESIS	DLR Earth Sensing Imaging Spectrometer
PRISMA	PRecursore IperSpettrale della Missione Applicativa
EMIT	Earth Surface Mineral Dust Source Investigation

 

The 2018 National Academies’ Decadal Survey entitled, “Thriving on Our Changing Planet: A Decadal Strategy for Earth Observation from Space.” identified Surface Biology and Geology (SBG) as a Designated Observable (DO) with the following observing priorities:

* Terrestrial vegetation physiology, functional traits, and health
* Inland and coastal aquatic ecosystems physiology, functional traits, and health
* Snow and ice accumulation, melting, and albedo
* Active surface changes (eruptions, landslides, evolving landscapes, hazard risks)
* Effects of changing land use on surface energy, water, momentum, and C fluxes
* Managing agriculture, natural habitats, water use/quality, and urban development

To accomplish these priorities, the DO requires the combined use of visible to shortwave infrared (VSWIR) imaging spectroscopy and multispectral or hyperspectral thermal infrared (TIR) imagery acquired globally with sub-monthly temporal revisits over terrestrial, freshwater, and coastal marine habitats. 

This approach presents some interesting challenges. Due to the high spatial and spectral resolution, SBG is expected to generate roughly 90 TB of data products per day.  In addition, the number of existing community algorithms for processing this data is large and needs to be evaluated, and there is no particular consensus yet on standard file formats for hyperspectral data.

To help address a subset of these challenges the SBG Algorithms Working Group was formed to review and evaluate the algorithms applicable to the SBG DO. Also, the SISTER activity was created to prototype workflows and generate SBG-like data products.

This collection is one of several that include the first experimental data products produced by SISTER with the objective of generating SBG-like VSWIR imagery with 30-m spatial resolution and 10-nm spectral resolution. The scenes in the various SISTER collections include examples from the terrestrial, aquatic, snow/ice, and geologic domains, as well as from validation sites. The main purpose of these data are to provide the scientific community with prototype data products from the SBG workflow in order to get early feedback on things like useability, file formats, and metadata.

These products are still considered experimental, and no quality assement proceedure was conducted for this collection.

The datasets in this collection were collected by EMIT, a spaceborne imaging spectrometer installed onboard the International Space Station and operated by the National Aeronautics and Space Administration (NASA). EMIT measures radiance at 7-nanometer (nm) intervals in the visible to shortwave infrared spectral range between 380 and 2500 nm at 60-m spatial resolution. The EMIT scenes in this collection are globally distributed and include vegetation, aquatic and snow targets. Image datasets were downloaded from the NASA Earthdata Search platform and ingested into the SISTER platform for further downstream processing (Figure 2).

Figure 2. Workflow diagram of the SISTER 002 production run (Click on image to view full-resolution version).

EMIT data were provided in instrument space, unprojected, and were projected to the appropriate Universal Transverse Mercator (UTM) zone using the provided per-pixel geographic coordinates at 60-m resolution. EMIT radiance datasets were then processed to surface reflectance using an optimal estimation atmospheric correction algorithm, ISOFIT (Thompson et al. 2018) with an open-source neural-network-based emulator for modelling radiative transfer (Brodrick et al., 2021). Next, spectral resampling to a 10-nm sampling interval was performed in a two-step calculation. Bands were first aggregated and averaged to the closest resolution to the target interval then a piecewise cubic interpolator was used to interpolate the spectra to the target wavelength spacing.

For all datasets in the SISTER 002 processing version (also known as the CRID), workflow components, versions, and links to source code are summarized in Table 4.

Table 4. Key SISTER workflow components, versions, and links to source code used for V002 production (Townsend et al., 2023).

software	version	url
maap-api-nasa	3.0	https://gitlab.com/geospec/maap-api-nasa/-/tags/3.0
sister-preprocess	2.1.0	https://github.com/EnSpec/sister-preprocess/releases/tag/2.1.0
sister-isofit	2.1.0	https://gitlab.com/geospec/sister-isofit/-/releases/2.1.0
sister-resample	2.0.1	https://github.com/EnSpec/sister-resample/releases/tag/2.0.1
sister-reflect_correct	2.1.0	https://github.com/EnSpec/sister-reflect_correct/releases/tag/2.1.0
sister-fractional-cover	1.2.0	https://gitlab.com/geospec/sister-fractional-cover/-/releases/1.2.0
sister-trait_estimate	1.0.0	https://github.com/EnSpec/sister-trait_estimate/releases/tag/1.0.0
sister-grainsize	1.0.0	https://github.com/EnSpec/sister-grainsize/releases/tag/1.0.0
sister-benthic-inversion-pge	1.0.0	https://github.com/EnSpec/sister-algorithm_router/releases/tag/1.0.0
sister-benthic-cover-pge	1.0.0	https://github.com/EnSpec/sister-trait_estimate/releases/tag/1.0.0
sister-aquatic-pigments-pge	1.0.0	https://github.com/EnSpec/sister-grainsize/releases/tag/1.0.0

Brodrick, P.G., D.R. Thompson, J.E. Fahlen, M.L. Eastwood, C.M. Sarture, S.R. Lundeen, W. Olson-Duvall, N. Carmon, and R.O. Green. Generalized radiative transfer emulation for imaging spectroscopy reflectance retrievals, Remote Sensing of Environment, Volume 261, 2021, 112476, ISSN 0034-4257. https://doi.org/10.1016/j.rse.2021.112476

Thompson, D.R., V. Natraj, R.O. Green, M.C. Helmlinger,B._C. Gao, and M.L. Eastwood. 2018. Optimal estimation for imaging spectrometer atmospheric correction. Remote Sensing of Environment 216, 355-373. https://doi.org/10.1016/j.rse.2018.07.003

Townsend, P., M.M. Gierach, P.G. Brodrick, A.M. Chlus, H. Hua, O. Kwoun, M.J. Lucas, N. Malarout, D.F. Moroni, S. Neely, W. Olson-Duvall, J.K. Pon, S. Shah, and D. Yu. 2023. SISTER: Composite Release ID (CRID) Product Generation Files, 2023. ORNL DAAC, Oak Ridge, Tennessee, USA. https://doi.org/10.3334/ORNLDAAC/2231