Digital Earth Australia Glossary

This glossary provides definitions for the terms we use at DEA, including technical terms and program-specific terms. (They are in alphabetical order.)

Acquisition

An image captured by a satellite sensor.

Advanced Land Observing Satellite (ALOS)

A Japanese satellite launched in 2006. After five years of service, the satellite lost power and ceased communication with Earth, but remains in orbit.

Advanced Spaceborne Thermal and Reflection radiometer (ASTER)

An imaging instrument onboard Terra, the flagship satellite of NASA’s Earth Observing System (EOS) launched in December 1999. ASTER data is used to create detailed maps of land surface temperature, reflectance, and elevation.

For more information, see NASA: ASTER.

Advanced Very-High Resolution Radiometer (AVHRR)

A radiation-detection sensor that can be used for remotely determining cloud cover and the surface temperature. AVHRR instruments are carried by the National Oceanic and Atmospheric Administration (NOAA) family of polar orbiting and European MetOp satellites.

For more information, see ESA: AVHRR.

Aerosol optical depth

Aerosol optical depth is a measure of the extinction of the solar beam by dust and haze.

For more information, see NASA Earth Observatory.

Albedo

The fraction of light that a surface reflects. Albedo is measured on a scale of 0-1, with 1 indicating that all light has been reflected by the surface.

Algorithm

In the context of remote sensing, algorithms generally specify how to determine higher-level data products from lower-level source data. For example, algorithms prescribe how atmospheric temperature and moisture profiles are determined from a set of radiation observations originally sensed by satellite sounding instruments.

Ancillary datasets

Data which enhance processing and utilisation of remote sensing instrument data. Ancillary datasets are used to assist in the analysis and classification of e.g. ARD by providing supporting data on conditions at the time of satellite data acquisition, such as aerosol and water vapour concentrations.

Amazon Web Services (AWS)

One of the two environments used for hosting Digital Earth Australia. Amazon Web Services is a commercial cloud computing provider. Used by Digital Earth Australia for our JupyterHub Sandbox and Web Mapping Services.

Analysis Ready Data (ARD)

Satellite data that has been processed to a minimum set of requirements and organised into a form that allows immediate analysis and interoperability through time and with other datasets.

Application Programming Interface (API)

A software intermediary that allows two applications to talk to each other. The Open Data Cube API gives programmers full access to the capabilities of the Cube, allowing query and advanced data retrieval.

Atmospheric correction

The process of removing the effects of the atmosphere on the reflectance values of images taken by satellite or airborne sensors.

Australian Geoscience Data Cube (AGDC)

A collaborative prototype project between Geoscience Australia, CSIRO and NCI, which aimed to provide better public access to NASA’s extensive Landsat archive. The AGDC has since been superseded by Digital Earth Australia.

Australian Research Environment (ARE)

The ARE is an interface for using the data and software available on the NCI. It is a replacement for the old VDI system.

For more information, see Australian Research Environment.

Azimuth

The angle of an object’s position from true north.

Azimuthal exiting (degrees)

The angle between true north and the exiting direction in the slope geometry.

Azimuthal incident (degrees)

The angle between true north and the incident direction in the slope geometry.

Band

Each remote sensing instrument (i.e. a satellite) can observe the Earth at multiple wavelengths. A single, discrete wavelength interval or range is referred to as a band.

Barest Earth

An estimate of the spectra of the barest state (i.e. least vegetation) observed from imagery of the Australian continent collected by the Landsat 5, 7, and 8 satellites.

Bidirectional Reflectance Distribution Function (BRDF)

Bidirectional reflectance distribution function is a theoretical concept that describes the relationship between light and an opaque surface. It uses a target’s irradiance geometry and the remote sensing system’s relative angle to the target.

Bidirectional Reflectance Distribution Function (BRDF) / Albedo Parameter

The Bidirectional Reflectance Distribution Function (BRDF)/Albedo parameters provide:

• coefficients for mathematical functions that describe the BRDF of each pixel in the seven MODIS ‘Land’ bands (1- 7); and

• albedo measurements derived simultaneously from the BRDF for bands 1-7 as well as three broad bands (0.4-0.7, 0.7-3.0, and 0.4- 3.0 micrometers).

For more information see: NASA.

Cloud Optimised GeoTIFF (COG)

A data file format optimised for efficient workflows on the cloud and partial file access.

Collection

All products downstream of the rawest form of the main input data (telemetry), produced sequentially and processed with consistent algorithms/code/inputs/outputs.

Collection 2 (C2)

Digital Earth Australia’s second collection of Landsat data. Now superseded by Collection 3. Note that there was no DEA Collection 2 of Sentinel 2 products.

Collection 3 (C3)

The third collection of Digital Earth Australia’s Landsat or Sentinel 2 data, and the most up-to-date collection available.

Collection upgrade

The reproduction of the collection, including all downstream products, with the initial input being the rawest form (telemetry). Collections are updated when there are fundamental changes and upgrades to the data suite that make it incompatible with the existing collection. Therefore, a collection upgrade is more akin to a movie franchise reboot than a re-release.

Committee on Earth Observations, Systems Engineering Office (CEOS-SEO)

Established in 1984, CEOS is the primary forum for the international coordination of space-based Earth observations. The SEO performs historical coverage analyses using the data archives for the Landsat, Sentinel-1, and Sentinel-2 missions.

Commonwealth Scientific and Industrial Research Organisation (CSIRO)

An Australian federal government agency responsible for scientific research.

For more information, see CSIRO.

Copernicus Australasia Regional Data Hub

Copernicus Australasia is a regional hub supporting the Copernicus Program. The Copernicus Australasia Regional Data Hub provides free and open access to data from Europe’s Sentinel satellite missions for the following South-East Asia and South Pacific region.

For more information, see Copernicus Australasia.

Copernicus Programme

The Copernicus Programme, established in 2014, is the European Union (EU)’s Earth observation programme coordinated and managed by the European Commission in partnership with the European Space Agency (ESA), the EU Member States and EU Agencies.

For more information, see Copernicus Programme.

Dataset

A related set of files composed of separate elements that can be manipulated as a unit. It is an instantiation of a product.

Digital Earth Australia (DEA)

A Program of Geoscience Australia that uses spatial data and images recorded by satellites orbiting our planet to detect physical changes across Australia. DEA prepares these vast volumes of Earth observation data and makes it available to governments and industry for easy use. DEA is the Australian implementation of the Open Data Cube.

For more information, see the DEA website.

DEA Notebooks

An open-source repository containing Jupyter notebooks, tools and workflows for geospatial analysis with Open Data Cube and xarray.

For more information, see the GitHub repository.

DEA Sandbox

The Digital Earth Australia Sandbox is a learning and analysis environment for getting started with DEA and the Open Data Cube. It includes sample data and Jupyter notebooks that demonstrate the capability of the Open Data Cube.

For more information, see the getting started wiki.

Digital Earth Africa (DE Africa)

A sister project to Digital Earth Australia but for the African Continent.

For more information, see Digital Earth Africa.

Dynamic range

The range between the maximum and minimum amount of input radiant energy that an instrument can measure.

Earth Observation (EO)

The process of acquiring observations of the Earth’s surface via remote sensing instruments. These can include satellite-based observations, as well as drone or aerial images.

Enhanced Thematic Mapper Plus (ETM+)

The sensor aboard Landsat 7 that picks up solar radiation reflected by or emitted from the Earth. It is an enhanced version of the Thematic Mapper.

For more information, see NASA Enhanced Thematic Mapper Plus.

Ephemeris

A table of satellite orbital locations for specific time intervals. The ephemeris data helps characterise the conditions under which remotely sensed data is collected and is commonly used to correct the sensor data before analysis.

European Space Agency (ESA)

The European Space Agency is a European intergovernmental collaboration focussed on the development of Europe’s space capability. The ESA is a partner of the Copernicus Programme.

Exiting angle (degrees)

The angle between a ray reflected from a surface and the line perpendicular to the surface at the point of emergence.

Final

A stage in DEA’s dataset maturity lifecycle. DEA’s best quality ARD, produced using high quality ancillary datasets derived from observed data.

For more information, see DEA dataset maturity.

Fractional Cover (FC)

Fractional Cover (FC) is a DEA product that uses an algorithm to split the landscape into three parts, or fractions;

• green (leaves, grass, and growing crops),

• brown (branches, dry grass or hay, and dead leaf litter), and

• bare ground (soil or rock).

FC provides a representation of the proportions of living vegetation, dry and dying vegetation (including deciduous trees during autumn, dying grass, etc.), and bare soils across the Australian continent for any point in time in the Landsat archive since 1987.

For more information, and for details of the methodology, see DEA Fractional Cover.

Gain

A general term used to denote an increase in signal power in transmission from one point to another, usually expressed in decibels. It can also be used to represent the multiplier used to transform satellite image digital numbers to measures of at-sensor radiance.

Geoscience Australia (GA)

Geoscience Australia is the national public-sector geoscience organisation. It is the government’s technical advisor on all aspects of geoscience and is the custodian of geographic and geological data. Digital Earth Australia is a program of Geoscience Australia.

For more information, see Geoscience Australia.

Geomedian

Geometric median is a robust high-dimensional statistic that maintains relationships between spectral bands, while producing a multidimensional median over a timeseries of satellite images.

The Geometric Median provides information on the general conditions of a landscape over a timeseries.

For more information, see Geomedian.

Google Earth Engine (GEE)

A Google-based platform for analysis and visualisation of geospatial datasets.

Geographic Information System (GIS)

A system that manages and visualises spatially referenced data.

High and Low Tide Imagery (HLTC)

Previously called High and Low Tide Composites. DEA High and Low Tide Imagery is a Digital Earth Australia product providing cloud-free imagery mosaics of Australia’s coast, estuaries and reefs at low and high tide.

For more information, see DEA High and Low Tide Imagery.

High Performance Computing (HPC)

The practice of aggregating computing power in a way that delivers much higher performance than one could get out of a typical desktop computer or workstation in order to solve large problems in science, engineering, or business.

Incident angle (degrees)

The angle between a ray incident on a surface and the line perpendicular to the surface at the point of incidence.

Interim

A stage in DEA’s dataset maturity lifecycle. Interim production means that one or more ancillary datasets were not available at the time of production, and the dataset has instead been corrected using a combination of NRT climatological ancillaries, and final observed ancillaries.

For more information, see DEA dataset maturity.

Intertidal Elevation

Previously called National Intertidal Digital Elevation Model (NIDEM). A DEA product derived from DEA Intertidal Extents that maps the elevation of the Australian intertidal zone relative to Mean Sea Level.

For more information, see DEA Intertidal Elevation.

Intertidal Extents

Previously called Intertidal Extents Model (ITEM). DEA Intertidal Extents is a DEA product that maps the relative extent of the Australian intertidal zone at regular intervals of the observed tidal range.

For more information, see DEA Intertidal Extents.

Indexing

The process of registering a dataset with associated metadata (in a folder or at a URI) to an Open Data Cube instance so that it is searchable and accessible through the datacube API.

Jupyter notebooks

A computational “notebook” that allows code to be run and presented alongside explanatory documentation, figures, scientific notation etc.

JupyterLab

An interactive web-based user interface for editing and running Jupyter notebooks. JupyterLab is used as an analysis environment on both the DEA Sandbox and the NCI’s ARE.

Landsat

A joint NASA/USGS program of medium resolution satellites that have been collecting publicly available Earth observation data continuously since 1972.

For more information, see Landsat Science.

Land Cover Classification Scheme (LCCS)

The Land Cover Classification Scheme was developed by the United Nations Food and Agriculture Organization to provide a consistent framework for the classification and mapping of land cover.

For more information, see LCCS.

Median Absolute Deviation (MAD)

Median Absolute Deviation, used as a form of standard deviation for the geomedians.

The Median Absolute Deviation provides information on how a landscape is changing over a timeseries.

For more information, see MAD.

Moderate Resolution Imaging Spectroradiometer (MODIS)

A sensor aboard NASA’s Terra and Aqua satellites. MODIS instruments view the entire Earth’s surface every 1-2 days, acquiring data in 36 spectral bands. It plays a vital role in the development of validated, global, interactive Earth system models which aim to accurately predict global change.

For more information, see NASA: MODIS.

MultiSpectral Instrument (MSI)

The MSI is carried on the Sentinel-2 satellites. Light reflected up to the MSI instrument from the Earth and its atmosphere is collected by a three-mirror (M1, M2 and M3) telescope and focused, via a beam-splitter, onto two Focal Plane Assemblies: one for the ten very-near infrared wavelengths and one for the three shortwave infrared wavelengths.

For more information see: ESA missions - Sentinel-2.

Multispectral Scanner (MSS)

A line-scanning instrument carried by Landsat satellites that continually scans the Earth in a 185 km swath and collects data over a variety of wavelengths.

For more information, see Landsat: Multispectral Scanner.

Nadir

The point of the celestial sphere that is vertically downward from the observer and directly opposite the zenith.

Nadir-corrected BRDF Adjusted Reflectance (NBAR)

Surface reflectance data that has been corrected to remove the effects of topography and angular variation using bidirectional reflectance modelling.

Nadir-corrected BRDF Adjusted Reflectance with Terrain illumination correction (NBART)

Surface reflectance data that has been corrected to remove the effects of topography and angular variation using bidirectional reflectance modelling, as well as corrected for the effects of terrain shadow.

National Aeronautics and Space Administration (NASA)

The United States of America’s federal government’s civil space, aeronautics and space research agency.

National Computational Infrastructure (NCI)

A national facility that provides world-class, high-end computing services to Australian researchers, including those working in the data-intensive areas of climate and Earth system science.

For more information, see National Computational Infrastructure.

National Oceanic and Atmospheric Administration (NOAA)

A scientific agency within the United States Department of Commerce that focuses on the conditions of the oceans, major waterways and atmosphere.

For more information, see NOAA.

Normalised Burn Ratio (NBR)

Calculated from near-infrared (NIR) and short wave infrared (SWIR).

Normalised Difference Vegetation Index (NDVI)

Calculated from visible and near-infrared (NIR) light reflected by vegetation.

Near Infrared (NIR)

Radiation just beyond the visible light spectrum. In Landsat and Sentinel 2 Earth observation satellites, it refers to radiation between 0.7 - 0.9 micrometers.

Near real-time (NRT)

A stage in DEA’s dataset maturity lifecycle. NRT data is a less refined/calibrated dataset, which is available much sooner after satellite acquisition than standard ARD data.

For more information, see DEA dataset maturity.

Open Data Cube (ODC)

An open source geospatial data management and analysis software project. It is a global initiative to increase the value and use of satellite data by providing users with access to free and open data management technologies and analysis platforms.

At its core, ODC is a set of Python libraries and a PostgreSQL database that allows you to work with geospatial raster data.

For more information, see Open Data Cube.

Operational Land Imager (OLI)

The Operational Land Imager is carried by the Landsat 8 satellite. It measures in the visible, near infrared NIR, and short wave infrared SWIR portions of the spectrum. Its images have 15-meter (49 ft.) panchromatic and 30-meter multi-spectral spatial resolutions along a 185 km(115 miles) wide swath.

For more information, see Landsat 8.

Operational Land Imager 2 (OLI2)

The OLI-2 instrument is carried by the Landsat 9 satellite. It provides visible and near infrared / shortwave infrared (VNIR/SWIR) imagery consistent with previous Landsat spectral, spatial, radiometric and geometric qualities.

The OLI-2 instrument includes an optical telescope, Focal Plane Array / Focal Plane Electronics, calibration hardware, and instrument support electronics. OLI-2 provides data for nine spectral bands with a maximum ground sampling distance (GSD), both in-track and cross track, of 30 m (98 ft) for all bands except the panchromatic band, which has a 15 m (49 ft) GSD.

For more information, see Landsat 9 instruments.

Panchromatic band

A band that measures a wide range of light at high resolution, compared to standard multispectral bands that measure a narrow range of light at lower resolution. On Landsat 7, 8, and 9, the panchromatic band can be used to “sharpen” 30 metre visible bands to higher 15 metre resolution.

For more information, see Pansharpening Landsat.

Pixel

The minimum size area on the ground detectable by a remote sensing device. The size varies depending on the type of sensor.

Pixel quality (PQ)

A categorical assessment of the quality of an observation at the pixel level.

Polar orbit

An orbit with an orbital inclination of near 90 degrees where the satellite ground track will cross both polar regions once during each orbit. The term describes the near-polar orbits of a spacecraft.

PostgreSQL

Also known as Postgres, it is an open source object-relational database management system with an emphasis on extensibility and standards compliance. It is a high performance database engine used as both a relational and document database by the Open Data Cube.

Process

The generation of some form of output as the result of a set of actions, which may include sub-processes.

Product

A categorical term applied to describe the output from a process. Typically, a product has an associated product definition which contains the product description and specification. An example of a product is DEA Water Observations (Landsat)

Python

The programming language used to develop the Open Data Cube and most of Digital Earth Australia. It is an easy-to-use language, which also provides simple access to high performance processing capabilities.

For more information, see Python.

Radiance

The amount of light directly detected by remote sensing instruments.

Radiometer

A device that detects and measures electromagnetic radiation.

Radiometric

Relating to, using, or measured by a radiometer. The measurement of radiation.

Raster data

An abstraction of the real world where spatial data is expressed as a matrix of cells or pixels, with spatial position implicit in the ordering of the pixels. With the raster data model, spatial data is not continuous but divided into discrete units. This makes raster data particularly suitable for certain types of spatial operations (e.g. overlays or area calculations). Unlike vector data, there are no implicit topological relationships.

Raw data

Numerical values representing the direct observations output by a measuring instrument. The values are transmitted as a bit stream in the order they were obtained.

Real time

The time in which reporting on events or recording of events is simultaneous with the events. For example, the real time of a satellite is the time in which it simultaneously reports its environment as it encounters it.

Reflectance

The measure of the proportion of light or other radiation striking a surface which is reflected off it.

Relative azimuth (degrees)

The relative azimuth angle between the sun and view directions.

Relative slope (degrees)

The relative azimuth angle between the incident and exiting directions in the slope geometry.

Remote sensing

The measurement or acquisition of information about some property of an object or phenomenon, by a recording device that is not in physical or intimate contact with the object or phenomenon under study.

Resampling

Modifying the geometry of an image, which may be from either a remotely sensed or map data source. This process usually involves rectification and/or registration.

Resolution

A measure of the amount of detail that can be seen in an image; i.e. the size of the smallest object recognisable using the detector.

In remotely sensed imagery, resolution is significant in four measurement dimensions: spectral, spatial, radiometric and temporal.

Satellite azimuth (degrees)

The angle of the satellite’s position from true north; i.e. the angle between true north and a vertical circle passing through the satellite and the point being imaged on Earth.

Satellite view or satellite zenith (degrees)

The angle between the zenith and the satellite.

Saturation

The intensity of a colour. A highly saturated colour is vivid and brilliant. To dull a colour and decrease its saturation, add small amounts of its complement, making it closer to grey.

Scene

Each satellite data swath can be divided into a series of scenes to enable the data to be handled and catalogued more easily. A scene is a defined portion of the continuous strips of data collected by satellites. Scenes are primarily used for LANDSAT satellite data.

Secure Shell (SSH)

SSH or Secure Shell is a means to access remote computers using a text based terminal interface. It comes build in with Linux, but requires additional software to use it from Windows computers.

Sentinel

A program of satellites from Europe that collect publicly available Earth observation data. Each satellite has a different purpose or capability, and together, they address six thematic areas: land, marine, atmosphere, climate change, emergency management and security.

For more information, see Copernicus: Discover our satellites.

Short-Wave Infrared (SWIR)

Radiation beyond the visible light spectrum. In Landsat and Sentinel 2 Earth observation satellites, it refers to radiation between 1.5 - 2.4 micrometers.

Solar azimuth (degrees)

The angle of the sun’s position from true north; i.e. the angle between true north and a vertical circle passing through the sun and the point being imaged on Earth.

Solar irradiance

The solar irradiance is the output of light energy from the entire disk of the Sun, measured at the Earth.

Solar zenith (degrees)

The angle between the zenith and the centre of the sun’s disc.

Solar Zenith Angle (SZA)

The angle between the local zenith (i.e. directly above the point on the ground) and the line of sight from that point to the sun.

Spatial resolution

The area on the ground that an imaging system, such as a satellite sensor, can distinguish.

See also resolution.

Spectral response

The ratio of the relative amplitude of the response of a detector and the frequency of incident electromagnetic radiation.

Spectrometer

An optical instrument that splits the light received from an object into its component wavelengths by means of a diffraction grating, and then measures the amplitudes of the individual wavelengths.

Stacking

A process that combines all data for a tile across a specific time range into a single file.

Sun-synchronous orbit

An orbit in which a satellite is always in the same position with respect to the rotating Earth at the same time of day.

Surface reflectance

The fraction of incoming solar radiation that is reflected from Earth’s surface for specific incident or viewing cases (directional, conical, and hemispherical cases).

Swath

As a satellite moves around the Earth, it observes a long strip of the Earth’s surface called a swath. Each swath is divided into a series of scenes.

Synthetic Aperture Radar (SAR)

An imaging radar mounted on an instant moving platform. The signal is responsive to surface characteristics like structure and moisture.

For more information, see: NASA - What is Synthetic Aperture Radar?.

Telemetry

The science and technology of automatic measurement and transmission of data by wire, radio or other means from remote sources (e.g. space vehicles) to receiving stations for recording and analysis.

Thematic Mapper (TM)

An advanced, multispectral-scanning, Earth resources sensor featured on Landsat 4 and 5. TM is designed to acquire data to categorise the Earth’s surface and is particularly useful for agricultural applications and identification of land use. It continuously scans the surface of the Earth, simultaneously acquiring data in seven spectral channels.

For more information, see NASA Thematic Mapper Plus.

Thematic Real-time Environmental Distributed Data Services (THREDDS)

A National Computational Infrastructure (NCI) server, which is a high-performance and high-availability installation of Unidata’s Thematic Real-time Environmental Distributed Data Services (THREDDS).

THREDDS serves many of NCI’s open data collections at the file level, as well as some aggregations. It provides many different types of services to allow individual files to be selected, as well as more advanced services such as OpenDAP, NetCDF subsetting, OGC WCS and WMS.

For more information, see NCI: Data .

Tile

Tiles are a way of dividing data products into smaller pieces to enable the data to be handled and analysed more easily. Each tile represents a specific geographic area and multiple tiles can be combined into a grid to cover larger regions. For instance, the DEA GeoMAD product is provided using 96 × 96 km grid tiles, characteristic of DEA Summary Products.

Timedelta (seconds)

The time in seconds from satellite apogee (the point of orbit at which the satellite is furthest from the Earth).

United States Geological Survey (USGS)

A scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The USGS and NASA jointly run the Landsat program of earth observation satellites.

For more information, see USGS.

Vector data

Vector data, when used in the context of spatial or map information, refers to a format where all map data is stored as points, lines, and areas rather than as an image or continuous tone picture. These vector data have location and attribute information associated with them.

Virtual Desktop Infrastructure (VDI)

The Virtual Desktop Infrastructure was a service offered by the NCI that provided a linux desktop environment for scientific computing. It has been replaced by ARE.

Visible Infrared Imaging Radiometer Suite (VIIRS)

The Visible Infrared Imaging Radiometer Suite (VIIRS) is one of the key instruments onboard the NOAA-20 spacecraft, as well as the Suomi-NPP satellite. It collects visible and infrared imagery and global observations of land, atmosphere, cryosphere and oceans.

For more information, see Joint Polar Satellite System.

Water Observation Feature Layer (WOFL)

A WO observation for one point in time

Water Observations (WO)

Previously called Water Observations from Space. A Digital Earth Australia product that classifies satellite pixels into ‘wet’, ‘dry’, or ‘invalid’ (e.g. cloudy or a poor quality observation).

For more information see DEA Water Observations.

Wavelength

The distance from crest to crest, or trough to trough, of an electromagnetic or other wave. The longer the wavelength, the lower the frequency.

Web Map Service (WMS)

A HTTP interface for requesting geo-registered map images that can be displayed in a browser application or GIS software system.

Web Feature Service (WFS)

An interface for querying, modifying and exchanging features or values in a database and retrieving features for use.

Worldwide Reference System

Landsat scenes are arranged into a worldwide grid called the World Reference System (WRS) which uses ‘path’ and ‘row’ numbers to identify the location of each scene. It is a global indexing scheme based on nominal scene centres. Learn more about the Worldwide Reference System from NASA.

xarray

An open source project and Python package for working with labelled multidimensional arrays such as those returned by the Open Data Cube.

Yet Another Markup Language (YAML)

A human-readable data storage format. It is used throughout DEA for metadata files, product definitions and other configuration files.

Zenith

The point on the celestial sphere directly above the observer, and directly opposite to nadir.