A spectral index emphasizes a specific phenomenon (such as a tree species) in an image and may minimize other factors that make the phenomenon harder to identify (such as variations in soil). To do this, a spectral index mathematically combines the spectral reflectance values of two or more wavelengths (called bands) from a multiband image. The normalized difference vegetation index (NDVI) is a common example, but spectral indices can be used to evaluate vegetation health, identify burn scars, measure moisture, and identify land cover, among other applications.
Indices can be used for visualization, in which case the values are symbolized to make them easier to understand visually. They are also used for analysis, with the raw index values as input (detecting change in vegetation health over time, for example).
Spectral indices are useful for a variety of applications, but the logistics of applying the index to an image (or collection of images) can be confusing.
ArcGIS provides methods to access and apply these algorithms using tools, raster functions, and shared templates on ArcGIS Online to create persisted or on-the-fly derived products. Options for applying spectral indices to imagery in ArcGIS include the following:
- The Imagery tab in ArcGIS Pro includes an Indices drop-down menu with 15 commonly used indices. Using these indices is straightforward—select the raster, select an index, and apply the index.
- ArcGIS Online includes the ArcGIS Spectral Index Library, which contains ready-to-apply raster function templates for about 20 indices, configured to support both visualization and analysis. Apply them to your imagery in ArcGIS Pro or in a custom app, either locally or using the server. ArcGIS Enterprise users can also apply them (through ArcGIS Image Server) using the Map Viewer Classic web interface.
- You can use the Band Arithmetic or Calculator raster functions. Raster functions apply calculations directly to the raster pixels displayed on your screen, visualizing results on the fly, and can be included in longer or automated processing chains. The Band Arithmetic raster function includes about 20 predefined indices.
- You can use the Raster Calculator geoprocessing tool, which produces a new, persistent output raster and is compatible with ModelBuilder.
- Spectral indices (in the form of function chains) can also be included as a part of an image service. If you view an image service using an attached index (in ArcGIS Pro or a web app), the processing is applied on the server, and results are visualized on the fly.
Explore the following resources to learn more about working with spectral indices in ArcGIS. (Not sure where to start? Look for the star by Esri's most helpful resources.)
Note:
To edit or apply functions to mosaic dataset items, you need ArcGIS Desktop Standard or Desktop Advanced. The Calculator raster function and the Raster Calculator tool require ArcGIS Image Analyst or the ArcGIS Spatial Analyst extension for ArcGIS Pro.
The Raster Calculator tool also requires the ArcGIS Spatial Analyst extension for ArcGIS Pro.
To run raster analysis on your ArcGIS Enterprise portal, you need ArcGIS Image Server with raster analytics configured.
Imagery Workflows resources
Review the community-supported tools and best practices for working with and automating imagery and remote sensing workflows:
- Explore the ArcGIS Spectral Index Library, which provides a collection of more than 20 ready-to-apply indices for various well-known sensors.*
ArcGIS help
Review the following links on reference materials for ArcGIS products:
- Learn how to apply a spectral index raster function to an imagery layer using the Indices gallery in the Tools group on the Imagery tab in ArcGIS Pro.
- Learn about raster functions, which are helpful for visualizing spectral indices in ArcGIS.
- Learn about the Band Arithmetic raster function in ArcGIS Pro, which allows you to apply custom or preset spectral indices to imagery layers. Alternatively, you can also create custom spectral indices using the Calculator raster function. Both can be included in longer or automated raster function chains.
- Learn about the Raster Calculator tool.
- For ArcGIS Enterprise users, learn how to use distributed, server-side raster analysis in your portal to apply raster functions that have been invoked using ArcGIS Pro. You can also learn about configuring your portal for raster analysis.
ArcGIS blogs, articles, story maps, and technical papers
Review the following supplemental guidance about concepts, software functionality, and workflows:
- Read a blog about the ArcGIS Spectral Index library, including why you should use it and how to get started.
Videos
Review the following Esri-produced videos that clarify and demonstrate concepts, software functionality, and workflows:
- Watch this video to see how to get started working with the ArcGIS Spectral Index Library. (4 minutes)
- (External resource) Watch this video from Jarlath O'Neil-Dunne explaining the difference between raster functions and geoprocessing tools. (6 minutes)
- (External resource) Watch this video from Geo 2004 about creating spectral indices in ArcGIS Pro. (6 minutes)
Training and tutorials
Review the following guided lessons and tutorials based on real-world problems and key ArcGIS skills:
- In this tutorial, you'll use distributed raster analysis, spectral indices, and a series of ArcGIS tools to calculate landslide risk for communities affected by wildfires. (1.5 hours)*
- In this tutorial, you'll assess burn scars using geoprocessing tools to calculate a spectral index from satellite imagery. (2 hours)
Developer resources
Review the following resources and support for automating and customizing workflows:
- Developers can apply spectral indices using the REST protocol. The export image operation performed on an image service resource supports a variety of request parameters, including the rendering rule. See raster function json objects for the syntax and examples of how indices can be applied to image services through REST.
Esri Community
Use the online imagery community to connect, collaborate, and share experiences:
- Visit the Imagery and Remote Sensing community to connect, collaborate, and share experiences regarding spectral indices.