Georeference RADARSAT

Use Georeference RADARSAT to georeference RADARSAT data with embedded geolocation point information. You can use the geolocation points associated with each line of RADARSAT data to georeference the data to a specified map projection. You can use all of the geolocation points from the file, or specify how many points to extract from the data for georeferencing.

Note: Not all RADARSAT files contain embedded geolocation points. If your RADARSAT data does not have geolocation points, you will be unable to georeference the file.

Note: If a RADARSAT-2 file includes a valid GeoTIFF header, map information will be available upon opening the file.

1. Select File > Open As > Radar Sensors > RADARSAT from the menu bar.

• For RADARSAT-2 data in CEOS format, select the data file (typically named dat_01.001). For RADARSAT-2, select an image file in GeoTIFF format (image_<n>.tif, one for each polarization channel).

2. Select Geometric Correction > Georeference by Sensor > Georeference RADARSAT from the Toolbox. The Input File dialog appears.

3. Select an input file and perform optional spatial and spectral subsetting, then click OK. The Extract RADARSAT GCP Parameters dialog appears.

   Use the settings in this dialog to select an output projection and to specify how to extract geolocation points from the RADARSAT file:

• Select Output Projection For Registration: Choose the projection into which to warp the data. The default projection is UTM (if map information is available).
• X Pixel Size/Y Pixel Size: Set the output data pixel size in units of degrees, meters, or feet. The units to use depends on the units used for the selected projection. If your input image does not have a pixel size defined, the default values are 12.5 meters for both x and y. If pixel size data is included in your file, those values appear in the X and Y Pixel Size fields.

• Number of Lines to Skip: Use this option to optimize either the accuracy or the processing speed of the geolocation point extraction.

  The larger the value in this field, the fewer number of points are extracted. In this case, processing is faster but the accuracy is more approximate.

  If you choose a smaller value for the number of lines to skip, the processing time increases but the accuracy is improved. The default value is 100.

• Enter Output GCP File Name: Allows you to optionally save the extracted GCPs in a file with a specified name.
4. Click OK. The Registration Parameters dialog appears.

5. The Registration Parameters dialog allows you to further refine the warp method, resampling technique, background value, and output parameters.

   In the Enter Output Filename field, enter the filename for your georegistered image.

6. Click OK. ENVI adds the resulting output to the Layer Manager.