The Water Observations from Space (WOfS) viewer provides a summary of surface water observations across Australia overlayed on a Google Earth background, which provides basic location search functionality.
The information displayed over the Google Earth background is the WOfS surface water summary. This shows how often water was seen across Australia as a percentage of how often the Landsat satellites were able to clearly see the Earth at each point. An area is considered to have been "clearly seen" if the satellite sensor was working correctly, and the location was not covered by cloud or shadows at the time of observation.
WOfS is shown in a colour scheme indicating frequently observed water (high percentages) in purple and blue, down through greens to infrequently observed water (low percentages) in yellows, and finally to very low percentages in red.
This means that water that is often found in a location, such as in a dam or lake, will appear purple or blue. Water that is found in areas that might dry up or in areas that the satellite can't always see (such as narrow river channels), will be in the green shades. Water that is found in an area very rarely (such as from flooding) will show up in red colours, with the biggest, rarest events as the darkest red.
Occasionally the detection system mistakes shadows from clouds and hills as water, so there are some errors where a shadow is mistakenly detected as water, that also appears in red.
WOfS works poorly in dense urban areas such as cities, where the medium resolution of the Landsat satellites and frequent shadows from large buildings creates errors in water detection.
WOfS also contains more errors in areas where clouds are more frequent, such as along mountainous and coastal areas. This is due to the inability for an automated process to correct for shadows 100% of the time. Occasionally cloud and terrain shadows will be mistaken for water and appear in the WOfS result.
WOfS works best on large, open flood plains such as along Australia's inland rivers.
More information about a point location can be obtained by left-clicking on the point in the viewer. This brings up a results "bubble" that provides four pieces of information:
The confidence probability is a measure of how confident we are that a location flagged as water is truly water. The confidence information was created by comparing the WOfS with other data, to see how well it matched known water areas from other sources. These sources are:
The higher the confidence at a location, the more the water result correlates with the confidence factors. However the confidence factors also contain errors, and hence can produce an overstated confidence in some areas such as cities, where the confidence factors are not as useful.