A mosaic is a composite image created by combining the most appropriate pixels from a collection of ​source images. A common use case is to create cloud-free images for applications that are not time-dependent. There are a number of approaches.

​

Real Pixel Mosaics

​

These are cloud-filtered mosaics based on time series data where a specific non-cloudy pixel is selected from a time series. The resulting product will be made up of pixels from different times, and the overall composite may have varying cloud cover percentage throughout, as these algorithms only consider the time series for each individual pixel, meaning cloud cover percentage may vary between pixels. Common selection techniques include:

​

Most Recent / Least Recent Pixel 

A cloud-free mosaic using the most recent (newest) or least recent (oldest) clear pixel in a time series.

​

Maximum Value Composite (MVC)

A cloud-free mosaic based on the maximum value of an index (e.g. NDVI) in a time series. This type of mosaic is best for agriculture or forest detection in a time series. In some cases, the minimum value composite is also desired.

​

Synthetic Pixel Mosaics

​

These are cloud-filtered mosaics produced using an algorithm to determine the desired spectral combination. Two common algorithms are:

​

Median Mosaic

Creates cloud-filtered mosaics using the "middle" spectral response of each band in a time series. Since the bands can vary independently, the result is often a "synthetic" product that is not representative of any particular time. This type of mosaic is also possible with radar data.

Geomedian Mosaic

A new algorithm developed by Geoscience Australia (GA) that creates a synthetic mosaic, similar to a median, but which is more representative of the spectral relationship between bands.