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What is aerial imagery?

Aerial imagery is a type of photo of the earth, taken from above by sensors mounted on satellite or airborne platforms. These include:

  • airplanes
  • helicopters, or
  • drones (Unmanned aerial vehicles).

The imagery is geo-referenced so it can used with other spatial data to understand and assess different features and attributes of a location. It is also known as ortho-imagery or ortho-photography.

How it is used

Aerial imagery is used in emergency management and sustainability planning. It also gives context and evidence to support many other spatial datasets, including Vicmap Topographic themes and Vicmap Transport.

Aerial imagery can help computers automatically locate features, such as:

  • outline of buildings from aerial imagery
  • all persistent water bodies in Victoria

It is being used more frequently as part of this machine-learning feature extraction (MLFE) process.

How it helps

Ortho imagery is also a key tool in planning for sustainable communities. It is considered a foundation dataset by ANZLIC, the Spatial Council and recognised as supporting 6 of 17 UN Sustainable Development Goals:

  • 2 (Zero H unger)
  • 6 (Clean Water and Sanitation)
  • 9 (Industry, Innovation and Infrastructure)
  • 11 (Sustainable Cities and Communities)
  • 14 (Life Below Water)
  • 15 (Life on Land)

Learn more about Fundamental Data Themes identified by the United Nations Global Geospatial Information Management (UN-GGIM).

Considerations before use

When considering using aerial imagery, there are 3 important attributes to understand:

  • spatial resolution
  • currency, or when the imagery was collected
  • the spectral bands of the imagery

Spatial resolution

Spatial resolution refers to the area of the earth covered by each pixel in the imagery. For example, a resolution of 6 cm means that each pixel in the photograph represents an area on the ground that is 6 x 6 cm.

The resolution of geospatial imagery is usually measured in centimetres. A smaller number of centimetres indicates a higher resolution which allows you to see more detail. For example, 6 cm resolution imagery allows you to see more detail than 20 cm resolution imagery. However, there is no agreed limit for what counts as “high-resolution” or “low-resolution” imagery. What is more important is that the data resolution is fit-for-purpose and sufficient to identify your features of interest.

Currency

Details about when imagery has been collected may also be a critical attribute to:

  • ensure your feature of interest will be visible. Some features may only be visible at certain times of year, for example plants or weeds that only flower in the Spring.
  • detect when something happened or changed
  • ensure that you are using the most recent imagery available

Spectral band types

Spectral bands are the wavelengths of the light or electromagnetic spectrum that a sensor is able to collect.

3-band imagery (RGB)

Most colour photographs we are familiar collect the visible wavelengths of light to make a picture. This covers Red, Green, and Blue also known as RGB or 3-band imagery.

Infrared or 4-band imagery (RGBI)

Infrared wavelengths are not visible to the human eye, but are  highly-useful  for assessing things like vegetation health or post-bushfire impacts to forests. This is often collected at the same time as the RGB wavelengths, and the result is referred to as RGBI or 4-band imagery.

Multispectral and hyperspectral sensors

There are also other sensors that are capable of collecting even more ranges of light and can be used for a large number of research purposes, such as multispectral and hyperspectral sensors. NASA’s Hyperion satellite carries hyperspectral sensors capable of detecting up to 242 spectral bands.

How we use aerial imagery data

Given the value of aerial imagery data to deliver and improve a large range of government services, the Department is very active in:

  • acquiring new data
  • maintaining the Victorian archive of aerial imagery
  • improving imagery standards across Australia

How to access aerial imagery

To access aerial imagery for Victoria:

Page last updated: 01/12/20