The Landsat series of satellites is the longest running program capturing earth resource imagery. The other key factor is revisit frequency, or the amount of time between when a satellite captures an image. This means that to capture satellite pictures for all of north Australia, many orbits and hundreds of images would be required. The on-ground resolution has significant implications for a satellite’s ability to accurately map on-ground features.Įvery Landsat orbit (overpass) captures imagery along a 185km-wide path. The graphic to the right shows the on-ground resolution or pixel size of three earth resource satellites (1) MODIS with each pixel 250×250 metres, Landsat 28×28 metres and the Sentinel 2 satellite with a 10 x 10 metre resolution. The temporal frequency is also referred to as the revisit frequency. Temporal (time) refers to how long a satellite has been capturing imagery (extent) and how frequently it captures imagery (resolution).Spatial extent refers to the on-ground width of a satellite image overpass.Spatial resolution refers to the on-ground size of a pixel in a satellite image.This is described in terms of resolution and extent. Spatial (space) in the context of satellite data refers to the size of the image.Key to understanding satellite data are their spatial, temporal and spectral characteristics. The following explanation will focus on the two satellites most commonly used in fire mapping and monitoring across northern Australia. The satellites cannot always ‘see’ fires, so understanding their limitations is key to their effective use. It is important when using information derived from these satellites to understand the type of information each provides and how it can be used. There are many Earth resource satellites, each with different sensor and orbit characteristics. These satellites orbit/circle the Earth in a known and consistent way so they pass over the same spot on the earth’s surface at regular intervals. These Earth Resource satellites are specifically designed to measure aspects of the earth’s surface using on-board ‘sensors’ (cameras). The image below, from the MODIS satellite, shows smoke coming from many fires in the Top End of Australia in July 2015. Pictures (raster images) of the earth’s surface captured from satellites orbiting the earth are a vital tool for natural resource management.
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