Detect Change Using Change Analysis function

Available with Image Analyst license.

Overview

The Detect Change Using Change Analysis function generates a raster layer containing pixel date-of-change information using the change analysis raster. The change analysis raster must be generated by the Analyze Changes Using CCDC tool or the Analyze Changes Using LandTrendr tool, or the CCDC Analysis raster function or the LandTrendr Analysis raster function.

For information about the CCDC method, see How Analyze Changes Using CCDC works.

For information about the LandTrendr method, see How Analyze Changes Using LandTrendr works.

Note:

This raster function can be combined with the CCDC Analysis raster function or the LandTrendr Analysis raster function in a raster function template. To produce a permanent raster output, connect the CCDC Analysis or LandTrendr Analysis function output to the Detect Change Using Change Analysis function, save as a raster function template, and use this template as the input to the Generate Raster From Raster Function tool.

Notes

The Change Type parameter indicates the information that is generated. Information is extracted from the change analysis raster. When running this tool on the output from the CCDC tools, you can choose from the following options:

• Time of latest change—The most recent date and time at which a pixel was flagged as being changed.
• Time of earliest change—The earliest date and time at which a pixel was flagged as being changed.
• Time of largest change—The date and time at which the calculated change was the most significant for a pixel.
• Number of changes—The total number of times the pixel changed.

When running this tool on the output from the LandTrendr tools, the following additional options are available:

• Time of longest change—The date at which a pixel was flagged as being changed, at the beginning or end of the longest period of change.
• Time of shortest change—The date at which a pixel was flagged as being changed, at the beginning or end of the shortest period of change.
• Time of fastest change—The date at which a pixel was flagged as being changed, at the beginning or end of the fastest period of change.
• Time of slowest change—The date at which a pixel was flagged as being changed, at the beginning or end of the slowest period of change.

The output raster is a multiband raster in which each band contains change information depending on the change type selected and the maximum number of changes specified. For example, if Change Type is set to Time of Earliest Change and Maximum Number of Changes is set to 2, the function calculates the two earliest dates when change occurred throughout the time series for every pixel. The result is a raster in which the first band contains the dates of the earliest change per pixel, and the second band contains the dates of the second-earliest change per pixel.

When applying this function on the output from the LandTrendr tools, you can choose whether to extract the date that marks the beginning of a change or the end of a change using the Segment Date parameter. For example, to understand how the most recent change in the time series started, set the Change Type to Time of latest change and the Segment Date to Beginning of segment.

Use the following filtering parameters to extract more specific dates of change from your change analysis raster:

• Filter by year—Identify changes that occurred within a specific time period, for example, if you are looking for changes that occurred in a landscape during five years of drought.
• Filter by duration—Identify changes that occurred over a given range of years, for example, if you are only looking for abrupt changes that took place over 1 or 2 years. You can calculate the duration you are interested in using the formula end year - start year +1. Gaps in the time series will be included.
• Filter by magnitude—Identify changes of a given magnitude, for example, if you are only looking for large changes in the vegetation index NDVI. Magnitude is an absolute value, so the minimum and maximum values cannot be negative. To specify directional change, use the Change Direction parameter.

Parameters

Parameter	Description
Raster	The input change analysis raster.
Change Type	Specifies the change information to calculate. Time of Latest Change—Each pixel contains the date of the most recent change for that pixel in the time series. This is the default. Time of Earliest Change—Each pixel contains the date of the earliest change for that pixel in the time series. Time of Largest Change—Each pixel contains the date of the most significant change for that pixel in the time series. Number of Changes—Each pixel contains the total number of times the pixel changed in the time series. Time of Longest Change—Each pixel contains the date of change at the end of the longest transition segment in the time series. Time of Shortest Change—Each pixel contains the date of change at the end of the shortest transition segment in the time series. Time of Fastest Change—Each pixel contains the date of change at the end of the transition that occurred most quickly. Time of Slowest Change—Each pixel contains the date of change at the end of the transition that occurred most slowly.
Maximum Number of Changes	The maximum number of changes per pixel to be calculated. The number entered corresponds to the number of bands in the output raster. The default is 1, meaning only one change date is calculated, and the output raster contains only one band. This parameter is not available when the Change Type parameter is set to Number of changes.
Segment Date	Specifies whether to extract the date at the beginning of a change segment, or the end. This parameter is available only when the input change analysis raster is the output from the LandTrendr tools. Beginning of segment—Extract the date at the beginning of a change segment. This is the default. End of segment—Extract the date at the end of a change segment.
Change Direction	Specifies the direction of change to be included in the analysis. This parameter is available only when the input change analysis raster is the output from the LandTrendr tools. All directions—All change directions are included in the output. This is the default. Increasing—Only change in the positive or increasing direction is included in the output. Decreasing—Only change in the negative or decreasing direction is included in the output.
Filter by Year	Specifies whether to limit the output by a range of years. Checked—Filter results so that only changes that occurred within a specific range of years are included in the output. Unchecked—Do not filter results by year. This is the default. If this parameter is checked, you must set the Minimum Value and Maximum Value parameters for filtering.
Filter by Duration	Specifies whether to filter by the change duration. Checked—Filter results by duration so that only the changes that lasted a given amount of time are included in the output. Unchecked—Do not filter results by duration. This is the default. This parameter is available only when the input change analysis raster is the output from the LandTrendr tools. If this parameter is checked, you must set the Minimum Duration and Maximum Duration parameters for filtering.
Filter by Magnitude	Specifies whether to filter by change magnitude. Checked—Filter results by magnitude so that only the changes of a given magnitude are included in the output. Unchecked—Do not filter results by magnitude. This is the default. This parameter is available only when the input change analysis raster is the output from the LandTrendr tools. If this parameter is checked, you must set the Minimum Magnitude and Maximum Magnitude parameters for filtering.