How to Calibrate NLAPS Landsat Data in ENVI
According to the USGS, all Landsat data are currently processed through their LPGS system. These datasets contain metadata in a MTL.txt file, which accompanies all data files. Some available Landsat 4 and 5 data were processed using the NLAPS system. NLAPS metadata is contained in a .WO file, which accompanies all data files.
ENVI's Radiometric Calibration tool is not able to calibrate Landsat data processed using the NLAPS system. But these data can be calibrated using ENVI Classic. Here are the steps to radiometrically calibrate NLAPS Landsat data in ENVI Classic:
1. Open ENVI Classic (for example, on Windows, go to the Start menu and choose All Programs > ENVI 5.2 > Tools > ENVI Classic).
2. In ENVI Classic, open the NLAPS data by choosing File > Open External File > Landsat > NLAPS, then selecting one of the .H* files in the dataset. ENVI Classic will open all of the image files in the current directory.
3. From the main ENVI menu, choose Basic Tools > Preprocessing > Calibration Utilities > Landsat Calibration.
4. In the resulting Landsat Calibration Input File dialog, select the Landsat dataset you just opened, and click OK.
5. In the ENVI Landsat Calibration dialog, ENVI will have determined the calibration parameters from the metadata and populated the dialog. Check these parameters to make sure they match your understanding of your dataset.
6. To see the gain and offset values that ENVI read from the metadata, click the Edit Calibration Parameters button. These are the values that the Radiometric Calibration tool in the default ENVI interface cannot read from NLAPS datasets.
7. Select the Calibration Type. Note that selecting Reflectance will calibrate the data to the top-of-atmosphere reflectance, not surface reflectance. If you plan to apply an atmospheric correction like FLAASH to the data, to correct for surface reflectance, you will want to choose Radiance.
8. Enter an output filename for the calibrated data, then click OK.
Review 12/3/14 by PS and KK