DEA Surface Reflectance NBART (Sentinel-2B MSI)

DEA Surface Reflectance NBART (Sentinel-2B MSI)

Geoscience Australia Sentinel-2B MSI NBART Collection 3

Version:

3.2.1 (Latest)

Product types:

Baseline, Raster

Time span:

30/06/2017 – Present

Update frequency:

Daily

Product ID:

ga_s2bm_ard_3

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About

DEA Surface Reflectance Nadir corrected Bidirectional reflectance distribution function Adjusted Reflectance Terrain corrected (NBART) Sentinel-2B Multispectral Instrument (MSI) is part of a suite of Digital Earth Australia’s (DEA) Surface Reflectance datasets that represent the vast archive of images captured by the US Geological Survey (USGS) Landsat and European Space Agency (ESA) Sentinel-2 satellite programs, which have been validated, calibrated, and adjusted for Australian conditions — ready for easy analysis.

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Key details

Collection

Geoscience Australia Sentinel-2 Collection 3

DOI

10.26186/146569

Licence

Creative Commons Attribution 4.0 International Licence

Publications

  • Li, F., Jupp, D. L. B., Reddy, S., Lymburner, L., Mueller, N., Tan, P., & Islam, A. (2010). An evaluation of the use of atmospheric and BRDF correction to standardize Landsat data. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 3(3), 257–270. https://doi.org/10.1109/JSTARS.2010.2042281

  • Li, F., Jupp, D. L. B., Thankappan, M., Lymburner, L., Mueller, N., Lewis, A., & Held, A. (2012). A physics-based atmospheric and BRDF correction for Landsat data over mountainous terrain. Remote Sensing of Environment, 124, 756–770. https://doi.org/10.1016/j.rse.2012.06.018

Background

This is a sub-product of DEA Surface Reflectance (Sentinel-2B MSI). See the parent product for more information.

Reflectance data at top of atmosphere (TOA) collected by Sentinel-2B MSI sensors can be affected by atmospheric conditions, sun position, sensor view angle, surface slope and surface aspect.

Surfaces with varying terrain can introduce inconsistencies to optical satellite images through irradiance and bidirectional reflectance distribution function (BRDF) effects. For example, slopes facing the sun appear brighter compared with those facing away from the sun. Likewise, many surfaces on Earth are anisotropic in nature, so the signal picked up by a satellite sensor may differ depending on the sensor’s position.

These inconsistencies need to be reduced or removed to ensure the data can be compared over time.

What this product offers

This product takes Sentinel-2B MSI imagery captured over the Australian continent and corrects the inconsistencies across the land and coastal fringe. It achieves this using Nadir corrected Bi-directional reflectance distribution function Adjusted Reflectance (NBAR).

In addition, this product applies terrain illumination correction to correct for varying terrain.

The resolution is a 10/20/60 m grid based on the ESA level 1C archive.

Technical information

Top of atmosphere reflectance measurements

Sentinel-2 series sensors measure top of atmospheric reflectance, which is a composite of:

  • surface reflectance

  • atmospheric condition

  • interaction between surface land cover, solar radiation and sensor view angle (BRDF effect)

  • land surface orientation relative to the imaging sensor (terrain illumination).

It has been traditionally assumed that satellite imagery displays negligible variation in sun and sensor view angles. However, these can vary significantly both within and between scenes, especially in different seasons and geographic regions (Li et al. 2010, 2012).

Surface reflectance correction models

This product represents standardised optical surface reflectance using robust physical models to correct for variations and inconsistencies in image radiance values.

It delivers modelled surface reflectance from Sentinel-2B MSI data using physical rather than empirical models. This ensures that the reflective value differences between imagery acquired at different times by different sensors will be primarily due to on-ground changes in biophysical parameters rather than artefacts of the imaging environment.

This product is created using a physics-based, coupled Bidirectional Reflectance Distribution Function (BRDF) and atmospheric correction model that can be applied to both flat and inclined surfaces (Li et al. 2012). The resulting surface reflectance values are comparable both within individual images and between images acquired at different times.

For more information on the BRDF/Albedo Model Parameters product, see NASA MODIS BRDF/Albedo parameter and MCD43A1 BRDF/Albedo Model Parameters Product.

Sentinel-2 archive

To improve access to Australia’s archive of Sentinel-2 data, several collaborative projects have been undertaken in conjunction with industry, government and academic partners. These projects have enabled implementation of a more integrated approach to image data correction that incorporates normalising models to account for atmospheric effects, BRDF and topographic shading (Li et al. 2012). The approach has been applied to Sentinel-2 imagery to create baseline surface reflectance products.

The advanced supercomputing facilities provided by the National Computational Infrastructure (NCI) at the Australian National University (ANU) have been instrumental in handling the considerable data volumes and processing complexities involved with the production of this product.

Image format specifications

band01, band02, band03, band04, band05, band06, band07, band08, band8A, band11, band12

Format

GeoTIFF

Resolution

10/20/60m based on Sentinel-2 original pixel resolution

Datatype

Int16

No data value

-999

Valid data range

[1,10000]

Tiled with X and Y block sizes

512x512

Compression

Deflate, Level 6, Predictor 2

Pyramids

Levels: [8,16,32]
Compression: deflate
Resampling: GDAL default (nearest)
Overview X&Y block sizes: 512x512

Contrast stretch

None

Output CRS

As specified by source dataset; source is UTM with WGS84 as the datum

thumbnail

Format

JPEG

RGB combination

Red: band 4
Green: band 3
Blue: band 2

Resolution

X and Y directions each resampled to 10% of the original size

Compression

JPEG, Quality 75 (GDAL default)
PHOTOMETRIC colour model: YCBCR

Contrast stretch

Linear
Input minimum: 10
Input maximum: 3500
Output minimum: 0
Output maximum: 255

Output CRS

Geographics (Latitude/Longitude) WGS84

Processing steps

  1. Longitude and Latitude Calculation

  2. Satellite and Solar Geometry Calculation

  3. Aerosol Optical Thickness Retrieval

  4. BRDF Shape Function Retrieval

  5. Ozone Retrieval

  6. Elevation Retrieval and Smoothing

  7. Slope and Aspect Calculation

  8. Incidence and Azimuthal Incident Angles Calculation

  9. Exiting and Azimuthal Exiting Angles Calculation

  10. Relative Slope Calculation

  11. Terrain Occlusion Mask

  12. MODTRAN

  13. Atmospheric Correction Coefficients Calculation

  14. Bilinear Interpolation of Atmospheric Correction Coefficients

  15. Surface Reflectance Calculation (NBAR)

References

F. Li, D. L.B. Jupp & M. Thankappan (2015) Issues in the application of Digital Surface Model data to correct the terrain illumination effects in Landsat images, International Journal of Digital Earth, 8:3, 235-257, DOI: 10.1080/17538947.2013.866701

L. Wang, F. Li, I. Alam, D. Jupp, S. Oliver and M. Thankappan, “Analysis Ready Data Sensitivity Analyses,” IGARSS 2019 - 2019 IEEE International Geoscience and Remote Sensing Symposium, 2019, pp. 5642-5645, doi: 10.1109/IGARSS.2019.8898667

Accuracy

Atmospheric correction accuracy depends on the quality of aerosol data and total column water vapour available to determine the atmospheric profile at the time of image acquisition (Wang et al., 2009).

BRDF correction is based on low resolution imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS), which is assumed to be relevant to medium resolution imagery such as that captured by Sentinel-2B MSI. A single BRDF shape is applied to each Sentinel-2B tile and it does not account for changes in land cover.

The algorithm assumes that BRDF effect for inclined surfaces is modelled by the surface slope and does not account for land cover orientation relative to gravity (as occurs for some broadleaf vegetation with vertical leaf orientation).

The accuracy of the terrain correction also depend on the quality, scale and spatial resolution of the DSM data used and the co-registration between the DSM and the satellite image (Li et al., 2013). At present, 30 m resolution SRTM DSM data were used for the correction.

The algorithm depends on several auxiliary data sources:

  • Availability of relevant MODIS BRDF data

  • Availability of relevant aerosol data

  • Availability of relevant water vapour data

  • Availability of relevant DSM data

  • Availability of relevant ozone data

Improved or more accurate sources for any of the above listed auxiliary dependencies will also improve the surface reflectance result.

Quality assurance

Results from the DEA Cal/Val workflow over 17 data takes from 9 field sites were created based on both BRDF Collections 5 and 6.

The results for each collection were averaged and then compared. The comparison showed small changes in individual field sites, but overall there was no significant difference in the average results over all field sites to within 1% at most.

The technical report containing the data summary for the Phase 1 DEA Surface Reflectance Validation is available: DEA Analysis Ready Data Phase 1 Validation Project: Data Summary

Access the data

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Code sample

Learn how to use the DEA Sandbox

Get via web service

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How to access Sentinel-2 data using the Open Data Cube

This product is contained in the Open Data Cube instance managed by Digital Earth Australia (DEA). This simplified process allows you to query data from its sub-products as part of a single query submitted to the database.

Introduction to DEA Surface Reflectance (Sentinel-2, Collection 3)

How to access DEA Maps

To view and access the data interactively via a web map interface:

  1. Visit DEA Maps

  2. Click “Explore map data”

  3. Select “Baseline satellite data” -> “DEA Surface Reflectance (Sentinel-2)”

  4. Click “Add to the map”

Old versions

View previous versions of this data product.

1.0.0: DEA Surface Reflectance NBART (Sentinel-2 MSI)

Changelog

2024-02-26: Reprocessing complete

Reprocessing for the Sentinel-2 contiguity fix is complete. For a list of all scenes that were affected, download the CSV file below.

The first rows of the CSV file that lists all scenes that were affected.
A preview of the CSV file.

Download the list of affected scenes (CSV)

Acknowledgments

This research was undertaken with the assistance of resources from the National Computational Infrastructure (NCI), which is supported by the Australian Government.

Contains modified Copernicus Sentinel data 2015-present.

The authors would like to thank the following organisations:

  • National Aeronautics and Space Administration (NASA)

  • Environment Canada

  • The Commonwealth Scientific and Industrial Research Organisation (CSIRO)

  • National Oceanic and Atmospheric Administration (NOAA) / Earth System Research Laboratories (ESRL) / Physical Sciences Laboratory (PSD)

  • The National Geospatial-Intelligence Agency (NGA)

  • The United States Geological Survey (USGS) / Earth Resources Observation and Science (EROS) Center

  • Spectral Sciences Inc.