Introduction to IDL-ENVI

Harm Bartholomeus

IDL-ENVI?!?

IDL = Interactive Data Language Progamming language

ENVI = ENvironment for VIsualisation Plug in module for IDL Made for visualisation and analysis of remote

sensing data

2 programs in your taskbar, both are needed:

IDL-ENVI 4.8

The most important button: e.g. unmixing

IDL-ENVI is one of the few programs which provides a good HELP-module. Use it!

Although the interface may differ from Erdas Imagine, the processes and possibilities are practically the same.

The hyperspectral modules of IDL-ENVI are much better.

IDL-ENVI: Basics

ENVI-files don’t have a specific extension, but are always combined with a .hdr file. This contains the header information, eg. number of rows and columns, projection etc.

ENVI supports practically all file formats. Img-files can be read immediately.

IDL-ENVI: BasicsDisplay an image: 3 windows

-Main window (1)

-Scroll window (2)

-Zoom window (3)

1

2 3

Choose the right display to show your image (existing or new)

IDL-ENVI: Processing

IDL-ENVI: Processing

Input file:

- Spatial and spectral subsets can be made when choosing the input file.

- A mask can be used to leave certain objects/areas out of the analysis.

IDL-ENVI: Continuum removal

Apply a continuum removal on the HyMap image. The depth of the dip between green and NIR is related to the chlorophyll content of the object. Which spectral subset should be used? Compare the chlorophyll absorption of the

different landcover types Compare these results with the result of the Red

Edge

IDL-ENVI: Linear Spectral Unmixing

Apply Linear Spectral Unmixing on the HyMap image. Define endmembers:

• Image or field spectra? • Which objects?• How many objects?

Unmixing:• Constraints, use them or not?• Analysing the results. The values, what do they mean?

Acceptable?

IDL-ENVI v Erdas Imagine: TerminologyIDL-ENVI Erdas Imagine

ROI (region of interest)

AOI (area of interest)

Display Viewer

Most terms are self-explanatory, use the HELP-function!!

Just try!

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