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 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. The most important button: e.g. unmixing IDL-ENVI is one of the few programs which provides a good HELP-module. Use it!
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: Basics • Display an image: 3 windows • Main window (1) • Scroll window (2) • Zoom window (3) 1 Choose the right display to show your image (existing or new) 3 2
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: Terminology Most terms are self-explanatory, use the HELP-function!!
Just try! You won’t ruin it… © Wageningen UR