DEA Water Observations Statistics (Landsat)

Water Observations from Space Statistics 25m 2.1.5

Version
2.1.5 flat-square
Product ID
wofs_summary, wofs_annual_summary, wofs_apr_oct_summary, wofs_nov_mar_summary
Program
Digital Earth Australia
Collection
Geoscience Australia Landsat Collection 2
Resource type
Derivative
Published Date
09/05/2017

Background

This is one of the Water Observations from Space suite of products, which gives summaries of how often surface water was observed by the Landsat satellites for various periods (per year, per season and for the period from 1986 to the present).

WO-STATS is created from the WO_25_2.1.5 product and provides information on how many times the Landsat satellites were able to clearly see an area, how many times those observations were wet, and what that means for the percentage of time that water was observed in the landscape. 

What this product offers

This product consists of the following datasets:

  • Clear Count: how many times an area could be clearly seen (ie. not affected by clouds, shadows or other satellite observation problems)
  • Wet Count: how many times water was detected in observations that were clear
  • Water Summary: what percentage of clear observations were detected as wet (ie. the ration of wet to clear as a percentage)

As no confidence filtering is applied to this product, it is affected by noise where misclassifications have occurred in the WOfS water classifications, and can be difficult to interpret on its own. The confidence layer and filtered summary are contained in the WO-FILT-STATS product, which provides a noise-reduced view of the water summary.

WO-STATS is available in multiple forms, depending on the length of time over which the statistics are calculated. At present the following are available:

  • WO-STATS: statistics calculated from the full depth of time series (1986 to present)
  • WO-STATS-ANNUAL: statistics calculated from each calendar year (1986 to present)
  • WO-STATS-NOV-MAR: statistics calculated yearly from November to March (1986 to present)
  • WO-STATS-APR-OCT: statistics calculated yearly from April to October (1986 to present)

Applications

  • Helps understand where flooding may have occurred in the past, to inform emergency management and risk assessment.
  • Provides an indication of the permanence of surface water in the Australian landscape by showing where water is observed rarely in comparison to where it is often observed, informing water management and mapping.
  • Can assist with wetland analyses, water connectivity and surface-ground water relationships.
  • The annual product provides information on how surface water changes per year across Australia, and is useful for drought analysis.
  • The seasonal product is useful for understanding the differences in water availability between the summer and winter periods across Australia.

Related products

Publications

Mueller, N., Lewis, A., Roberts, D., Ring, S., Melrose, R., Sixsmith, J., Lymburner, L., McIntyre, A., Tan, P., Curnow, S., & 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

Data access

Link to data AWS
Link to maps DEA Maps
Web services OWS
eCat record 121074
Product ID wofs_summary, wofs_annual_summary, wofs_apr_oct_summary, wofs_nov_mar_summary
CMI RESTful node ID 143
NCI project code fk4
Access constraints

WO_STATS_2.1.5 is available under CC-BY 4.0. The code for WOfS and its derivatives is available through GitHub under Apache 2.0 Open licensing.

Security classification Unclassified
Update frequency periodic

Access notes

DEA Maps

To view and access the data interactively:

1) Visit DEA Maps.

2) Click 'Add data'.

3) Select 'Surface water' > 'Water Observations from Space'.

4) Select which products you would like to display and click 'Add to the map'.

Technical information

As no confidence filtering is applied to this product, it is affected by noise where misclassifications have occurred in the WOfS water classifications, and hence can be difficult to interpret on its own. The confidence layer and filtered summary are contained in the WO-Fil-STATS product, which provide a noise-reduced view of the water summary.

WO-STATS is available in multiple forms, depending on the length of time over which the statistics are calculated. At present the following are available:

  • WO-STATS: statistics calculated from the full depth of time series (1986 to present)
  • WO-STATS-ANNUAL: statistics calculated from each calendar year (1986 to present)
  • WO-STATS-NOV-MAR: statistics calculated yearly from November to March (1986 to present)
  • WO-STATS-APR-OCT: statistics calculated yearly from April to October (1986 to present)

In previous versions of WOfS, the basic water classifications, statistical summaries and confidence products were contained within one product with several datasets. As of version 2.1.5, WOfS is split into three products: Water Observation Feature Layers (WO_25_2.1.5), Summary Statistics (WO-STATS_25_2.1.5), and Filtered Summary Statistics (WO-Fil-STATS_25_2.1.5).

Accuracy and limitations

Please refer to the SR-N_25_2.0.0 Product Description (GA, 2013) for the accuracy and limitations of the atmospheric, BRDF and topographic shading processing sequence. Please refer to Mueller et al. 2016 for details on the accuracy and limitations of WOfS and WOfS-STATS.

WO-STATS provides a summary of water classification results from the WOfS product for all of Australia. As WOfS cannot perfectly filter out misclassifications due to clouds, cloud shadows and issues to do with satellite sensor problems (such as the Landsat 7 SLC-Off failure), the summary also contains these misclassifications. In general misclassifications occur in the very low frequency observations and so can cause a misrepresentation of flooded areas. Misclassifications can also be caused by the presence of vegetation covering the water or within the water.

Relevant websites

References

Mueller, N., Lewis, A., Roberts, D., Ring, S., Melrose, R., Sixsmith, J., Lymburner, L., McIntyre, A., Tan, P., Curnow, S., & 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

Lineage

This product is created from the WOfS water classification (Water Observations 2 (Landsat)). Every pixel location in WO_25_2.1.5 is analysed statistically to derive the count of clear observations, the count of clear-wet observations and then calculate the percentage of clear observations that were also wet. This provides a 'normalised' water frequency product for all of Australia.

Processing steps

  1. Water Observation from Space (WOfS) - statistics

Major algorithms

Schema / spatial extent

DEA Albers Raster Schema

Update frequency asNeeded
Temporal extent
Min. longitude -1943830.00
Max. longitude 2170690.00
Min. latitude -1119030.00
Max. latitude -4856630.00
Coordinate reference system Australian Albers / GDA94 (EPSG: 3577)
Cell size X 25.00
Cell size Y 25.00

Owner

Commonwealth of Australia (Geoscience Australia)

Principal contributors

Norman Mueller, Adam Lewis, Dale Roberts

Subject matter experts

Norman Mueller

License

CC BY Attribution 4.0 International License

Rights statement

© Commonwealth of Australia (Geoscience Australia) 2015. Creative Commons Attribution 4.0 International License.