Product catalogue
DEA Geometric Median and Median Absolute Deviation (Landsat)
<div>The DEA Geometric Median and Median Absolute Deviation products use statistical analyses to provide information on variance in the landscape over a given year. They provide insight into the “average” conditions observed over Australia in a given year, as well as the amount of variability experienced around that average. These products are useful for monitoring change detection, such as from cropping, urban expansion or burnt area mapping. </div><div><br></div><div>Satellite imagery allows us to observe the Earth with significant accuracy and detail. However, missing data — such as gaps caused by cloud cover — can make it difficult to create a complete image. In order to produce a single, complete view of a certain area, satellite data must be consolidated by stacking measurements from different points in time to create a composite image. </div><div><br></div><div>The Digital Earth Australia GeoMAD (Geometric Median and Median Absolute Deviation) data product is a cloud-free composite of satellite data compiled annually over each calendar year. </div><div><br></div><div>Large-scale image composites are increasingly important for a variety of applications such as land cover mapping, change detection, and the generation of high-quality data to parameterise and validate bio-physical and geophysical models. A number of compositing methodologies are being used in remote sensing in general, however, challenges still exist. These challenges include mitigating against boundary artifacts due to mosaicking scenes from different epochs ensuring spatial regularity across the mosaic image and maintaining the spectral relationship between bands. </div><div><br></div><div>The creation of good composite images is especially important due to the opening of the United States Geological Survey’s Landsat archive. The greater availability of satellite imagery has resulted in demand to provide large regional mosaics that are representative of conditions over specific time periods while also being free of clouds and other unwanted visual noise. One approach is to ‘stitch together’ multiple selected high-quality images. Another is to create mosaics in which pixels from a time series of observations are combined (using an algorithm). This ‘pixel composite’ approach to mosaic generation provides more consistent results than with stitching high-quality images due to the improved colour balance created by combining one-by-one pixel-representative images. Another strength of pixel-based composites is their ability to be automated, hence enabling their use in large data collections and time series datasets. </div><div><br></div><div>The DEA GeoMAD product can be used for seeing how an area of land usually looks rather than only viewing it at a single point in time. Hence you can assess the land cover and land use on a general basis rather than at a specific date. It can also be used to assess how much an area changes over time. You will notice areas like bare rock that are very stable versus those like cropping areas that change dramatically. </div><div><br></div><div>The DEA GeoMAD product combines the Geometric Median and the Median Absolute Deviation algorithms in a single package. The Geometric Median output provides information on the general conditions of the landscape for a given year. Meanwhile the Median Absolute Deviation output provides information on how the landscape is changing in the same year. </div><div><br></div>
Simple
Identification info
- Date (Creation)
- 2024-03-06T01:00:00
- Date (Publication)
- 2024-08-08T23:09:20
- Citation identifier
- Geoscience Australia Persistent Identifier/https://pid.geoscience.gov.au/dataset/ga/149305
- Citation identifier
- Digital Object Identifier/https://dx.doi.org/10.26186/149305
- Cited responsible party
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Role Organisation / Individual Name Details Publisher Commonwealth of Australia (Geoscience Australia)
Voice Author Mueller N.
External Contact Author Roberts D.
External Contact Author Emma Ai
External Contact Author Miller, J.
Internal Contact Custodian Miller, J.
Internal Contact
- Purpose
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This product provides statistical tools that utilise DEA’s time series Earth observation data to provide annual images of general conditions and how much an area changes in a given year. The geometric median part of the product provides an 'average' cloud-free image over the given year. The geometric median image is calculated with a multi-dimensional median, using all the spectral measurements from the satellite imagery at the same time in order to maintain the relationships between the measurements. The median absolute deviation part of the product uses three measures of variance, each of which provides a 'second order' high dimensional statistical composite for the given year. The three variance measures show how much an area varies from the 'average' in terms of 'distance' based on factors such as brightness and spectra. The three variance measures are: Euclidean distance (EMAD), Cosine (spectral) distance (SMAD), and Bray Curtis dissimilarity (BCMAD). They provide information on variance in the landscape over the given year and are useful for change detection applications.The GeoMAD product is useful for the following: - Land cover mapping.- Change detection and classification (such as for burn-area mapping, crop mapping, and urban area mapping).- General variance and change so that it can be used in machine learning for change detection. - Environmental monitoring.
- Status
- Completed
- Point of contact
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Role Organisation / Individual Name Details Resource provider Space Division
External Contact Point of contact Commonwealth of Australia (Geoscience Australia)
Voice Point of contact Miller, J.
Internal Contact
- Spatial representation type
- Topic category
-
- Geoscientific information
Extent
))
Temporal extent
- Time period
- 1986-01-01 2023-01-01
- Maintenance and update frequency
- Annually
Resource format
- Title
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Product data repository: Various Formats
- Protocol
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FILE:DATA-DIRECTORY
- Name of the resource
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Data Store directory containing the digital product files
- Description
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Data Store directory containing one or more files, possibly in a variety of formats, accessible to Geoscience Australia staff only for internal purposes
- Project
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DEA – Digital Earth Australia
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- Keywords
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Satellite Images
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- Keywords
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Geomedian
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- Keywords
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Geometric Median
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- Keywords
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Median Absolute Deviation
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- theme.ANZRC Fields of Research.rdf
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EARTH SCIENCES
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- Keywords
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Published_External
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Resource constraints
- Title
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Creative Commons Attribution 4.0 International Licence
- Alternate title
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CC-BY
- Edition
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4.0
- Addressee
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Role Organisation / Individual Name Details User Any
- Use constraints
- License
- Use constraints
- Other restrictions
- Other constraints
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© Commonwealth of Australia (Geoscience Australia) 2024
Resource constraints
- Title
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Australian Government Security Classification System
- Edition date
- 2018-11-01T00:00:00
- Classification
- Unclassified
- Classification system
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Australian Government Security Classification System
Associated resource
- Association Type
- null
- Title
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DEA GeoMAD (Landsat)
Identifier
- Description
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CMI record of DEA GeoMAD (Landsat), technical name: DEA Geometric Median and Median Absolute Deviation (Landsat)
- Language
- English
- Character encoding
- UTF8
Distribution Information
- Distributor contact
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Role Organisation / Individual Name Details Distributor Commonwealth of Australia (Geoscience Australia)
Voice facsimile
- OnLine resource
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DEA GeoMAD for annual Landsat 5 observations
DEA GeoMAD for annual Landsat 5 observations
- Distribution format
-
- OnLine resource
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DEA GeoMAD for annual Landsat 7 observations
DEA GeoMAD for annual Landsat 7 observations
- Distribution format
-
- OnLine resource
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DEA GeoMAD for annual Landsat 8 and 9 observations
DEA GeoMAD for annual Landsat 8 and 9 observations
- Distribution format
-
Resource lineage
- Statement
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<div>The GeoMAD is derived from Landsat surface reflectance data. The data are masked for clouds and shadows to increase clarity and ensure the best data is used in the median calculation. </div><div><br></div><div>The three MAD layers of the GeoMAD are calculated by computing the multidimensional distance between each observation in a time series of multispectral (or higher dimensionality such as hyperspectral) satellite imagery versus the multidimensional median of the time series. The median used for this calculation is the geometric median corresponding to the time series. </div><div><br></div><div>The GeoMAD is calculated over annual time periods on Earth observations from a single sensor by default (such as the annual time series of Landsat 8 observations); however it is applicable to multi-sensor time series of any length that computing resources can support. </div><div><br></div><div>For the purposes of the default DEA product, GeoMADs are computed per calendar year per sensor for Landsat 5, Landsat 7, and Landsat 8 until 2021. GeoMADs are computed from combined sensors Landsat 8 and Landsat 9 from 2022 onwards. GeoMADs are computed using terrain-illumination-corrected surface reflectance data (Analysis Ready Data).</div><div><br></div><div>For details of the scientific algorithms implemented, see:</div><div>Roberts, D., Mueller, N., & McIntyre, A. (2017). High-dimensional pixel composites from earth observation time series. IEEE Transactions on Geoscience and Remote Sensing, 55(11), 6254-6264.</div><div>Roberts, D., Dunn, B., & Mueller, N. (2018). Open data cube products using high-dimensional statistics of time series. In IGARSS 2018-2018 IEEE International Geoscience and Remote Sensing Symposium (pp. 8647-8650).</div><div><br></div>
Metadata constraints
- Title
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Australian Government Security Classification System
- Edition date
- 2018-11-01T00:00:00
- Classification
- Unclassified
Metadata
- Metadata identifier
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urn:uuid/8b8804ae-e753-44d6-81b1-4c4328fe65d3
- Title
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GeoNetwork UUID
- Language
- English
- Character encoding
- UTF8
- Contact
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Role Organisation / Individual Name Details Point of contact Commonwealth of Australia (Geoscience Australia)
Voice Point of contact Miller, J.
Internal Contact
Type of resource
- Resource scope
- Dataset
Alternative metadata reference
- Title
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Geoscience Australia - short identifier for metadata record with uuid
- Citation identifier
- eCatId/149305
- Date info (Creation)
- 2025-07-14T02:47:28.635Z
- Date info (Creation)
- 2025-07-14T02:41:12.829Z
- Date info (Creation)
- 2024-08-06T05:32:50
- Date info (Revision)
- 2025-07-14T02:47:42.973Z
Metadata standard
- Title
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AU/NZS ISO 19115-1:2014
Metadata standard
- Title
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ISO 19115-1:2014
Metadata standard
- Title
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ISO 19115-3
- Title
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Geoscience Australia Community Metadata Profile of ISO 19115-1:2014
- Edition
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Version 2.0, September 2018
- Citation identifier
- http://pid.geoscience.gov.au/dataset/ga/122551