Orthrectifying ASTER L1B images using ENVI

Within ENVI:

File > Open Image File > select Aster image (.hdf file)

Basic Tools > Preprocess > Data-Specific Utilities > ASTER > Orthorectify ASTER

A 'Select File to Orthorectify' dialogue appears

As long as you have already opened the image file, a choice of 4 files appears. These are:

VNIR (3 bands)

Backward looking VNIR (1 band)

SWIR (6 bands)

TIR bands (5 bands)

When clicking on one the file information is displayed in the right-hand-side of the dialogue box. For instance, Dims: 4980 x 4200 x 3 [BSQ] tells you that you are selecting the VNIR bands (which are band sequential) which is composed of three bands. The data is in floating point - orthorectifying keeps it in floating point too.

Choose Full Scene in Spatial subset to do the whole image.

Click OK

A 'Orthorectification Parameters' dialogue window opens

Set Image respampling to nearest neighbor

Input the DEM file

Name the output file and set where to save the file. By convention I write it as 'date_VNIR_ortho'

Check output Projection and pixel size (15m for ASTER VNIR)

Click OK

The orthorectifying will proceed and once finished the files will become available in the 'Available Bands' dialogue box

N.B From the ENVI help

The ENVI Orthorectification Module requires input images to be in their native format, filenames, and directory structure, exactly as they are delivered by the data provider. For example, you cannot spatially subset a QuickBird GeoTIFF image, rename the subset, save it as a TIFF image, and read it into the ENVI Orthorectification Module. The imagery must include all associated metadata and ephemeris data. See Introduction to the ENVI Orthorectification Module for a list of supported image formats and accompanying metadata.