Aggregate images in time

The Aggregate images in time block allows you to create one image from multiple images across a time period. 

This is done by creating a new image with values for each band derived from each of the pixel values from the aggregated images. 

The values for each pixel in the image are determined by the method:

• Median: selects the middle value
• Mean: creates an average from each value
• Sum: calculates the total of all the values
• Min: selects the minimum value
• Max: selects the maximum value
• Mode: selects the most common value
• Earliest: takes the pixel from the oldest image
• Most recent: takes the pixel from the most recent image
• Last: takes the pixel from the last image in the collection (usually the same as ‘earliest’)
• Maximise Index (greenest pixel): finds the image in the image collection with the highest value for a chosen band, and uses the values from this image as the values for each band. For example, you might use this to find the image in the image collection with the ‘greenest’ pixel with the highest NDVI (using the Calculate index block).
• Count: Counts every pixel that has a value (including zero). Parts of an image that have been masked out won’t have a value.

You can choose to combine the images by frequency:

• Over entire time period: create one image for the entire time period. 
• By year
• By month
• By week
• By day
• By hour
• By minute

By default, all frequencies will create one image for each of those periods. For example, selecting ‘By week’ creates one image for every 7 days.

To create an image for each fortnight, select By week and create a new image for every 2 weeks

To create one image for every season (in a four-season model), select By month and create a new image for every 3 months.