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ENVI

Radiometric Calibration

Radiometric Calibration

Calibrating Images Tutorial

Use Radiometric Calibration to calibrate image data to radiance, reflectance, or brightness temperatures.

You can also write a script to perform calibration using the ENVICalibrateRaster routine. Or, use ENVIApplyGainOffsetTask to apply custom gains and offsets to a raster that will be input to a custom calibration routine.

The following table lists the calibration options that are available by sensor type. Use the File > Open menu option to select the metadata files listed in the table.

Sensor

Calibration Options

Metadata File to Open

Radiance

Reflectance

Brightness
Temperature

ALOS AVNIR-2 and PRISM Level-1B2 data

 

HDR*.txt

AlSat-2A

 

 

.dim

DMC DIMAP

 

.dim
EO-1 ALI

 

Use the File > Open As > Optical Sensors > EO-1 > HDF4 menu option and select a *_HDF.L1G file. A *_MTL.L1G file must be in the same directory.

EO-1 Hyperion Level-1R

 

Use the File > Open As > Optical Sensors > EO-1 > HDF menu option and select an .L1R file. Calibration metadata is hard-coded into the application and not read from any metadata files.
Gaofen-1

 

Use the File > Open As > Optical Sensors > CRESDA > GF-1 menu option and select an .xml file.

GeoEye-1

 

.til

IKONOS

 

metadata.txt

KOMPSAT-3

 

 

*_aux.xml

Landsat TM, ETM+, and Landsat-8 OLI/TIRS data

*_MTL.txt, *WO.txt, *.met

OrbView-3

 

.tif

Pleiades-HR 1A, 1B Primary and Ortho (single or mosaic)

 

 

DIM*.xml

Pleiades-HR DIMAP V2 (JPEG2000, TIFF)

 

DIM*.xml

QuickBird

 

.til

RapidEye Level-1B and -3A (TIFF, NITF)

 

*_metadata.xml

A NITF/NSIF license is required to open NITF files.

ResourceSat-2

 

 

.h5

Sentinel-2

 

*.xml

Sentinel-3

 

 

*.xml

SPOT DIMAP

 

DIM*.xml

SSOT DIMAP

 

 

METADATA.DIM

TripleSat/DMC3

 

*.xml, *.dim

UrtheCast Theia

 

 

*.xml

WorldView

 

.til
Ziyuan-1-02C

 

Use the File > Open As > Optical Sensors > CRESDA > ZY-1-02C menu option. Select from the following files: *.orientation.xml opens the MUX-PAN data product with metadata, *-MUX.xml opens multispectral data with metadata, *-PAN.xml opens panchromatic data with metadata, and *.xml opens the HRC data product (images with two parallel cameras) with metadata.
Ziyuan-3A

 

Use the File > Open As > Optical Sensors > CRESDA > ZY-3 menu option. Select from the following files: *.orientation.xml opens the TLC data product (images with nadir, forward, backward view) with metadata, *.xml opens multispectral data with metadata, *-NAD.xml opens TLC nadir-view data with metadata.

ENVI automatically calibrates the following data types as follows:

  • Göktürk-2: Radiance
  • MODIS/ASTER Simulator (MASTER): Radiance
  • NPP VIIRS
  • RASAT: Radiance
  • SkySat-1 and -2: Radiance
  • ASTER Level-1B: ENVI converts byte-scaled radiance data into floating-point radiance units. For Level-1A data, it performs a complete calibration to radiance. The units of the output ASTER radiance are W/m2/μm/sr.
  • MODIS Level-1B through 4 (HDF-EOS): ENVI converts the 16-bit data to radiance floating-point data in units of W/m2/μm/sr. It also automatically computes emissivity and reflectance data without units.

Follow these steps to perform radiometric calibration:

  1. From the Toolbox, select Radiometric Correction > Radiometric Calibration.
  2. Select an input file from one of the sensors/formats listed in the table above.
  3. Perform optional spatial subsetting.
  4. If you are using Landsat data, choose one of the following options:
  5. Click OK. The Radiometric Calibration dialog appears.
  6. From the Calibration Type drop-down list, select one of the following options:
    • Radiance: This option is available if the image has gains and offsets for each band. ENVI reads these values from metadata from the sensors listed above. Radiance is computed using the following equation:

    ENVI expects gains and offsets to be in units of W/(m2 * sr * µm). If so, then radiance will be in units of W/(m2 * sr * µm).

    WorldView-3 calibration coefficients are based on the DigitalGlobe 2014 Calibration Season Version 1, released 06 March 2015.

    • Reflectance: Top-of-atmosphere (TOA) reflectance (0 to 1.0). This option is available if the image has gains, offsets, solar irradiance, sun elevation, and acquisition time defined in the metadata. ENVI reads these values from metadata from the sensors listed above.

      If the input file contains metadata for reflectance gains and offsets, ENVI uses those values to calibrate the data to TOA reflectance. With Landsat-8 files, ENVI scales the reflectance gains and offsets by the sine of the sun elevation.

      If the input file does not contain metadata for reflectance gains and offsets, ENVI computes TOA reflectance using the following equation:
    • Where:

      = Radiance in units of W/(m2 * sr * µm)

      = Earth-sun distance, in astronomical units.

      = Solar irradiance in units of W/(m2 * µm)

      = Sun elevation in degrees

    • Brightness Temperature: This option is only available for Landsat-8, ETM+, and TM thermal imagery. Brightness temperatures (in Kelvin) are computed as follows:
    • Where:

      and = Calibration constants, in Kelvin. ENVI reads these values from the Landsat metadata.

Note: To edit or override values for gains, offsets, earth-sun distance, solar irradiance, sun elevation, or acquisition time (for example, if you believe the vendor metadata are incorrect), use the ENVI application programming interface (API) to read the imagery, then set the METADATA_OVERRIDE keyword to ENVI::OpenRaster to set your own metadata values.

  1. From the Output Interleave drop-down list, select an interleave option for the calibrated image:
    • BSQ: Band sequential
    • BIL: Band interleaved by line
    • BIP: Band interleaved by pixel
  2. From the Output Data Type drop-down list, select a data type for the calibrated image:
    • Float: Floating-point
    • Double: Double-precision floating-point
    • Uint: 16-bit unsigned integer
  3. To output radiance in different units than W/(m2 * sr * µm), enter a multiplicative Scale Factor to get the calibrated image in your desired units. Otherwise, leave the default value of 1.00.
  4. If you are calibrating an image for input into FLAASH, click the Apply FLAASH Settings button. This will create a radiance image with the following properties, which are required for input into FLAASH:
    • BIL interleave
    • Floating-point data type
    • Scale factor of 0.1. This scales the output to units of µW/(cm2 * sr * nm).
  5. This saves you time from having to perform all of these conversions individually. You can import the calibrated image directly into FLAASH. Because this process converts the data type to floating-point and combines all bands into a single file, the time to create an output file will increase significantly and the progress bar may pause at 25%.

  6. Select an output folder and filename for the calibrated image.
  7. Enable the Display Result option to automatically display the calibrated image upon completion.
  8. Click OK.



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