DEA Wetlands Insight Tool (Ramsar Wetlands)

Wetlands Insight Tool Ramsar Wetlands Polygons

Version
4.0.0 flat-square
Program
Digital Earth Australia
Collection
Geoscience Australia Landsat Collection 3
Resource type
Derivative
Published Date
27/08/2021

Background

Wetlands provide a wide range of ecosystem services including improving water quality, carbon sequestration, as well as providing habitat for fish, amphibians, reptiles and birds.  Managing wetlands in Australia is challenging due to competing pressures for water availability and highly variable climatic settings.  The Wetlands Insight Tool (Ramsar Wetlands) has been developed to provide catchment managers, environmental water holders, and wetlands scientists a consistent historical baseline of wetlands dynamics from 1987 onwards. The Wetlands Insight Tool (Ramsar Wetlands) is available online through the DEA Maps website.

What this product offers

The Wetlands Insight Tool (Ramsar Wetlands) summarises how the amount of water, green vegetation, dry vegetation and bare soil varies over time within each wetland boundary. It provides the user with the ability to compare how the wetland is behaving now with how it has behaved in the past.  This allows users to identify how changes in water availability have affected the wetland. It achieves this by presenting a combined view of Water Observations from Space (DEA Water Observations), Tasseled Cap Wetness (DEA Wetness Percentiles) and Fractional Cover (DEA Fractional Cover) measurements from the Landsat series of satellites, summarised as a stacked line plot to show how that wetland has changed over time.

Wetlands Insight Tool plot for Narran Lakes Nature Reserve, NSW, showing open water, wet, green vegetation, dry vegetation and bare soil.
Wetlands Insight Tool plot for Narran Lakes Nature Reserve, NSW, showing open water, wet, green vegetation, dry vegetation and bare soil from 1987 to 2021.

 

Applications

The product is designed to support Ramsar wetland managers, catchment managers and environmental waterholders in understanding whether or not wetlands are changing over time.  In instances where the wetlands are changing, the tool allows users to identify whether the changes are gradual, rapid, once-off or cyclical in nature.  For example the response of wetlands to the following drivers can be assessed:

  • Changes in river flow volumes
  • Changes in flood frequency
  • Long term shifts in rainfall
  • Wet-season/Dry-season shifts in water availability
  • Invasive weeds
  • Environmental watering events

Care should be used when interpreting Wetlands Insight Tool (Ramsar Wetlands) results as increases/decreases in particular cover types can be associated with different processes.  For example an increase in green cover could indicate canopy recovery of desirable wetland species or an increase in the amount of invasive weeds.

Related products

Data access

CMI RESTful node ID 669
Access constraints

Creative Commons CCBY 4.0

 

Security classification Unclassified
Update frequency asNeeded
Product life span -

Technical information

Every pixel within a wetland polygon is evaluated using this decision tree at every time step, and the results are tabulated to create the input data to the stacked line plot for that wetland. The image shows a flow chart where a pixel is checked to see if it is cloudy or nodata, classified by WOfS as water, the Tasseled Cap Wetness value is greater than negative 350. if yes the pixel is classified as cloudy or notdata, then open water, then wet, and if no then the Fractional Cover of Vegetation percentage is retrieved for the pixel and the percentage of green vegetation, dry vegetation and bare soil is returned.
Logical workflow for classifying a pixel to produce the WIT stacked line plots

 

Accuracy and limitations

The accuracy of the stacked line plots is dependent on the accuracy of the underlying algorithms: Water Observations from Space (Mueller et al. 2016) and the Joint Remote Sensing Research Program's Fractional Cover algorithm (Scarth et al. 2010). 

The Tasseled Cap Wetness threshold used in the Wetlands Insight Tool has been compared with independent inundation data for one major wetland complex, however the Tasseled Cap Wetness index may under or overestimate the actual extent of inundation for individual wetlands.  The use of a consistent threshold means that the 'precision' is high, insofar as you're measuring the same aspect of the wetland at each point in time, however the accuracy with which Tasseled Cap Wetness measures free water underneath/within wetland vegetation is not quantified.

The interpretability of the results for each polygon is dependent on the accuracy of the linework that has been used to create that polygon. The line work used in the Wetlands Insight Tool (Ramsar Wetlands) comes from the 19/03/2020 revision of the Ramsar Wetlands of Australia Dataset, and has been processed by exploding large polygons into smaller polygons in QGIS. This means that sites where multiple boundaries exist have a separate plot for separate subsites, allowing users to understand the dynamics of the subsites separately. Users are able to manually combine Wetlands Insight Tool outputs accessed through DEA Maps as csvs to gain an understanding of combined sites.  

The 30 metre resolution of Landsat imposes an intrinsic limitation on the Wetlands Insight Tool.  Wetland areas that are small, or long and narrow in nature are likely to be inaccurate (due to inclusion of neighbouring non-wetland pixels) or difficult to interpret (stack line plots for areas with a small number of pixels have sharp steps in them).

The period of time between when Landsat 5 ceased operations (November 2011) and Landsat 8 data became routinely available (May 2013) is likely to be inaccurate.  There will be some wetlands, close to the centre of Landsat paths where Landsat 7 continued to capture suitable (gap free) data, however it is safer, as a general rule, to consider this period as 'low data quality'. Other periods where less than four observations occur in a calendar year are also considered 'low data quality'. Regions of low data quality are hashed with a pale rectangular overlay in the Wetlands Insight Tool plots. 

Wetlands Insight Tool plot for Narran Lakes Nature Reserve, New South Wales, showing variations in open water, wet, green vegetation, dry vegetation and bare soil from 1987 to 2021
Wetlands Insight Tool plot for Narran Lakes Nature Reserve, New South Wales, showing variations in open water, wet, green vegetation, dry vegetation and bare soil from 1987 to 2021

 

Quality assurance

Quality assurance was undertaken to ensure that a Wetlands Insight Tool stacked line plot was generated for every exploded polygon in the Ramsar Wetlands polygon set, where satellite data was available through Digital Earth Australia. Sites outside continental Australia may not be available in the dataset.

Software

The Fractional cover (v2) algorithm is provided courtesy of the Joint Remote Sensing Research Program. The development of the algorithm was supported by field data collection by Australian State and Territory agencies, TERN and the National Ground Cover Monitoring Program, coordinated by ABARES. The code base used to generate the Ramsar Wetlands Insight Tool results is available at https://github.com/GeoscienceAustralia/wit_tooling

Relevant websites

References

  • Scarth, P., Röder, A., Schmidt, M., 2010. Tracking grazing pressure and climate interaction - the role of Landsat fractional cover in time series analysis. In: Proceedings of the 15th Australasian Remote Sensing and Photogrammetry Conference (ARSPC), 13-17 September, Alice Springs, Australia. Alice Springs, NT.
  • Guerschman, J.P., Scarth, P.F., McVicar, T.R., Renzullo, L.J., Malthus, T.J., Stewart, J.B., Rickards, J.E., & Trevithick, R. (2015). Assessing the effects of site heterogeneity and soil properties when unmixing photosynthetic vegetation, non-photosynthetic vegetation and bare soil fractions from Landsat and MODIS data. Remote Sensing of Environment, 161, 12-26, https://doi.org/10.1016/j.rse.2015.01.021
  • Muir, J., Schmidt, M., Tindall, D., Trevithick, R., Scarth, P., Stewart, J., 2011. Guidelines for Field measurement of fractional ground cover: a technical handbook supporting the Australian collaborative land use and management program. Tech. rep., Queensland Department of Environment and Resource Management for the Australian Bureau of Agricultural and Resource Economics and Sciences, Canberra.
  • Mueller, N., Lewis, A.  Roberts, D., Ring, S., Melrose, R., Sixsmith, J., Lymburner, L., McIntyre, A.,  Tan, P., Curnow, S. and  Ip, A.(2016) 'Water observations from space: Mapping surface water from 25 years of Landsat imagery across Australia', Remote Sensing of Environment, 174, 341-352, https://doi.org/10.1016/j.rse.2015.11.003
  • Crist, E.P. (1985) 'A TM Tasseled Cap equivalent transformation for reflectance factor data', Remote Sensing of Environment, 17(3), 301-306, https://doi.org/10.1016/0034-4257(85)90102-6

Lineage

The code base used to generate the Ramsar Wetlands Insight Tool results is available at https://github.com/GeoscienceAustralia/wit_tooling

Schema / spatial extent

Australia WGS84 Raster Schema

Update frequency asNeeded
Temporal extent
Min. longitude 112.00
Max. longitude 154.00
Min. latitude -44.00
Max. latitude -9.00
Coordinate reference system WGS 84 (EPSG: 4326)

Owner

Commonwealth of Australia (Geoscience Australia)

Principal contributors

Bex Dunn, Leo Lymburner

Subject matter experts

Bex Dunn, Leo Lymburner

License

CC BY Attribution 4.0 International License

Rights statement

© Commonwealth of Australia (Geoscience Australia) 2019. Creative Commons Attribution 4.0 International License.

Acknowledgments

The Joint Remote Sensing Research Program (JRSRP) developed the Fractional Cover algorithm that is used as one of the inputs into the Wetlands Insight Tool.