Brief description
The seasonal fractional cover product shows representative values for the proportion of bare, green and non-green cover, created from a time series of Sentinel-2 imagery. It is a spatially explicit raster product, which predicts vegetation cover at medium resolution (10 m per-pixel) for each 3-month calendar season across Eastern and Central Australia from 2016 to present. The green and non-green fractions may include a mix of woody and non-woody vegetation.
This model was originally developed for Landsat imagery, but has been adapted for Sentinel-2 imagery to produce a 10 m resolution equivalent product.
A 3 band (byte) image is produced:
- band 1 - bare ground fraction (in percent),
- band 2 - green vegetation fraction (in percent),
- band 3 - non-green vegetation fraction (in percent).
The no data value is 255.
Notes
Supplemental InformationData are available as cloud optimised GeoTIFF (COG) files. COG files are easier and more efficient for users to access data corresponding to particular areas of interest without the need to download the data first.
Lineage
Summary of processing:
Sentinel 2 surface reflectance data > multiple single-date fractional cover datasets > seasonal composite of fractional cover
Further details are provided in the Methods section.
Data Creation
Image Pre-processing:
Sentinel-2 data was downloaded from the ESA as Level 1C (version 02.04 system). Masks for cloud, cloud shadow, topographic shadow and water were applied as described in Flood (2017).
Fractional Cover Model:
A multilayer perceptron (MLP) model is used to estimate percentage cover in three fractions – bare ground, photosynthetic vegetation (PV) and non-photosynthetic vegetation (NPV) from surface reflectance, for every image captured within the season. The MLP model was trained with Tensorflow using Landsat TM, ETM+ and OLI surface reflectance and a collection of approximately 4000 field observations of overstorey and ground cover. The field observations covered a wide variety of vegetation, soil and climate types across Australia, collected between 1997 and 2018 following the procedure outlined in Muir et al (2011). As the model is trained on Landsat imagery, the Sentinel-2 reflectance values are slightly adjusted to more closely resemble Landsat imagery, then the fractional cover model is applied. The model was assessed to predict the vegetation cover fractions with MAE/wMAPE/RMSE of:
bare - 6.9%/34.9%/14.5%
photosynthetic vegetation (PV) - 4.6%/37.9%/10.6%
non-photosynthetic vegetation (NPV) - 9.8%/25.2%/16.9%.
Data Compositing:
The method of compositing selected representative pixels through the determination of the medoid (multi-dimensional equivalent of the median) of at least three observations of fractional cover imagery. The medoid is the point which minimises the total distance between the selected point and all other points. Thus the selected point is “in the middle” of the set of points. It is robust against extreme values, inherently avoiding the selection of outliers, such as occurs when cloud or cloud shadow goes undetected. Unfortunately, due to the high level of cloud cover in some areas, often three cloud free pixels are not available, resulting in data gaps in the seasonal fractional cover image. For further details on this method see Flood (2013).
Notes
CreditWe at TERN acknowledge the Traditional Owners and Custodians throughout Australia, New Zealand and all nations. We honour their profound connections to land, water, biodiversity and culture and pay our respects to their Elders past, present and emerging.
This dataset was produced by the Joint Remote Sensing Research Program using data sourced from the European Space Agency (ESA) Copernicus Sentinel Progam.
This product captures variability in fractional cover at seasonal (i.e. three-monthly) time scales, forming a consistent time series from late 2015 - present. It is useful for investigating recent inter-annual changes in vegetation cover and analysing regional comparisons. For applications that focus on non-woody vegetation, the Landsat-derived ground cover product may be more suitable. For applications investigating rapid change during a season, the monthly composite or single-date (available on request) fractional cover products may be more appropriate.
This product is based upon the JRSRP Fractional Cover 3.0 algorithm.
Data Quality Assessment Scope
local :
dataset
1) All the data described here has been generated from the analysis of Sentinel-2 data, which has a spatial resolution of approximately 10 m in the Blue, Green, Red and Near Infra-red (NIR) bands, and 20 m in the two Short Wave Infra-red (SWIR) band. The 20 m bands have been resampled to 10 m using cubic convolution, to provide a consistent 10 m data set. The imagery is rectified during processing by the European Space Agency (ESA), and not modified spatially beyond that.<br>
2) The fractional cover model was compared to samples drawn from approximately 4000 field reference sites.
Sentinel 2 Performance and Data Quality Reports
uri :
https://sentiwiki.copernicus.eu/web/document-library#DocumentLibrary-PerformanceandDataQualityReportsLibrary-S2-Performance-DQR
Data Quality Assessment Result
local :
Quality Result
1) The Sentinel-2 Data Quality Report from ESA indicates that positional accuracy is on the order of 12 m.<br>
2) The fractional cover model predicts the vegetation cover fractions with MAE/wMAPE/RMSE of:<br>
bare - 6.9%/34.9%/14.5%<br>
PV - 4.6%/37.9%/10.6%<br>
NPV - 9.8%/25.2%/16.9%.<br>
Created: 2022-03-28
Issued: 2022-05-03
Modified: 2024-09-25
Data time period: 2015-12-01
text: Australia excluding Western Australia and South Australia
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Point-of-truth metadata URL
Sentinel 2 Level 1C Algorithms and Products
Zhu, Z., & Woodcock, C. E. (2012). Object-based cloud and cloud shadow detection in Landsat imagery. Remote Sensing of Environment, 118, 83–94. https://doi.org/10.1016/J.RSE.2011.10.028
doi :
https://doi.org/10.1016/J.RSE.2011.10.028
Flood, N. (2017). Comparing Sentinel-2A and Landsat 7 and 8 Using Surface Reflectance over Australia. Remote Sensing, 9(7). https://doi.org/10.3390/rs9070659
doi :
https://doi.org/10.3390/rs9070659
Muir, J., Schmidt, M., Tindall, D., Trevithick, R., Scarth, P., & Stewart, J. B. (2011). Field measurement of fractional ground cover: A technical handbook supporting ground cover monitoring for Australia.
uri :
https://www.researchgate.net/publication/236022381_Field_measurement_of_fractional_ground_cover
Flood, N. (2013). Seasonal Composite Landsat TM/ETM+ Images Using the Medoid (a Multi-Dimensional Median). Remote Sensing, 5(12), 6481–6500. https://doi.org/10.3390/rs5126481
- URI : geonetwork.tern.org.au/geonetwork/srv/eng/catalog.search#/metadata/13810293-c6b5-442b-bfcd-817700738e0d
- global : 13810293-c6b5-442b-bfcd-817700738e0d
