DEA Water Observations Statistics (Landsat)

DEA Water Observations Statistics (Landsat)

Geoscience Australia Landsat Water Observation Statistics Collection 3

Version:

3.1.6 (Latest)

Product types:

Derivative, Raster

Time span:

1986 – present

Update frequency:

Periodically

Product IDs:

ga_ls_wo_fq_apr_oct_3, ga_ls_wo_fq_nov_mar_3, ga_ls_wo_fq_cyear_3, ga_ls_wo_fq_myear_3

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About

Digital Earth Australia (DEA) Water Observations uses an algorithm to classify each pixel from Landsat satellite imagery as ‘wet’, ‘dry’ or ‘invalid’. Combining the classified pixels into summaries, covering a year, season, or all of time (since 1986) gives the information on where water is usually, and where it is rarely.

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For help accessing the data, see the Access tab.

Apr-Oct summaries since 1986 - AWS access

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Nov-Mar summaries since 1986 - AWS access

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Annual calendar year summaries since 1986 - AWS access

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All-time summary 1986 to present - AWS access

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Code examples

Code sample

Web Services

Get via web service

Key details

Parent product(s)

DEA Water Observations (Landsat)

Collection

Geoscience Australia Landsat Collection 3

Persistent ID

146091

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

Background

These are the statistics generated from the DEA Water Observations (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).

Water Observations Statistics (WO-STATS) 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

Each dataset in this product consists of the following datasets:

  • Clear Count: how many times an area could be clearly seen (i.e. not affected by clouds, shadows or other satellite observation problems)

  • Wet Count: how many times water was detected in observations that were clear

  • Water Frequency: what percentage of clear observations were detected as wet (i.e. the ratio of wet to clear as a percentage)

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.

Technical information

As no confidence filtering is applied to this product, it is affected by noise where misclassifications have occurred in the input water classifications, and can be difficult to interpret on its own.

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:

  • DEA WO Multi-Year: ga_ls_wo_fq_myear_3: statistics calculated from the full depth of time series (1986 to present) unfiltered

  • DEA WO Calendar Year: ga_ls_wo_fq_cyear_3: statistics calculated from each calendar year (1986 to present)

  • DEA WO November to March: ga_ls_wo_fq_nov_mar_3: statistics calculated yearly from November to March (1986 to present)

  • DEA WO April to October: ga_ls_wo_fq_apr_oct_3: statistics calculated yearly from April to October (1986 to present)

In addition, a confidence-filtered Multi-Year Summary is under development, which will contain a confidence layer and subsequent filtered water frequency layer. This provides a noise-reduced view of the unfiltered multi-year summary.

Lineage

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

Each product within the WO-STATS set is derived from the available Landsat observations within the respective period: calendar years; Apr-Oct each year; Nov-Mar each year; all-of-time (first available Landsat observation in the DEA archive to the most recent).

To create the confidence layer required for the Filtered product, a logistic regression is created between the un-filtered product and information about terrain, built-up areas, and coarse national water observations. In this way the confidence reflects the likelihood that the observed water is scientifically feasible at every pixel.

Processing steps

Calculation of clear count, wet count and water summary (percentage of clear observations that are wet).

For each WO pixel through time:

  1. count the number of clear observations (ie observations not masked by pixel quality for cloud, shadows or sensor issues) to produce clear count dataset;

  2. count the number of clear observations that are wet to produce wet count dataset;

  3. create the ratio of wet to clear from the wet and clear count datasets and produce as a percentage dataset.

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

Accuracy

Please refer to the Landsat Surface Reflectance Product Description 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 Water Observations from Space (WOfS and WOfS-STATS).

WO-STATS provides a summary of water classification results from the WOfS product for all of Australia. As it 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.

Access the data

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Code sample

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Get via web service

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Access constraints

How to access the data

To view and access the data interactively:

  1. Visit DEA Maps.

  2. Click Explore map data.

  3. Select Inland water > DEA Water Observations.

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

Old versions

View previous versions of this data product.

2.1.5: DEA Water Observations Statistics (Landsat)

2.1.5: DEA Water Observations Filtered Statistics (Landsat)

Changelog

2024-01-24: Water Observations 2023 annual summary released

Product id: ga_ls_wo_fq_cyear_3

To access the updated product, see the Access tab.