Radiometric Conversion module

Name	Caption
Input Scenes	Input scene folder
Output Folder	Output folder
Overwrite Results	Overwrite existing results
Send Email	Email notification settings
Convert To	Radiometric conversion to apply
Create Angle Files	Whether to create angle files
Use Default	Whether to use default offset and factor coefficients
Non-Thermal Coefficients: Offset	Offset coefficient for non-thermal bands
Factor	Factor coefficient for non-thermal bands
Thermal Coefficients: Offset	Offset coefficient for thermal bands
Factor	Factor coefficient for thermal bands
Output File Type	Output file type
Output File Options	Output file options
Output Data Type	Type of output data
Raster Channels	List of channels

Parameter descriptions

Input Scenes

The path and name of a folder containing valid GDB-supported images.

The channels of each image must be calibrated radiometrically in radiance or reflectance.

This parameter can be specified by using any of the following:

Path and name of a folder of input images; for example, C:\data
Path and name of a folder with a wildcard to filter the imagery by file name or type; for example, C:\data\*_PAN.pix
You can also specify an MFILE as input. An MFILE is a text file with an .mfile file name extension. For more information on this type of file, see About the MFILE format.

Output Folder

The path and name of the folder to which to write the output files.

Overwrite Results

Select this check box to overwrite the existing output files, if any exist. If this check box is left clear, and an output file exists in the relevant folder, the status of the job displays a message informing you of the existence and name of the output file. The message is also written to the event log of the job.

Send Email

If necessary, you can set up CATALYST Enterprise to send an email notification on job start and job completion.

With this check box selected, an email message is sent to each address specified in the Email Addresses box after the job starts and on completion.

You can specify one or more addresses, and each must be separated by a comma or a semi-colon. The email address of the user currently logged in displays by default.

Convert To

The radiometric conversion to apply.

You can select from the following:

Radiance: Converts pixel values with radiometric-calibration information to radiance.
Thermal channels are converted to emissive radiance. The supported input-calibration types are radiance and reflectance. The input reflectance can be relative (still affected by the effects of the solar zenith angle) or absolute, with the solar elevation angle effects removed. The input radiances are transferred as is, with only pixel values converted, if required.
Reflectance: Converts pixel values with radiometric-calibration information to reflectance.
Thermal channels are converted to thermal brightness temperature in degrees Kelvin. The supported input-calibration types are radiance and reflectance. The input reflectance can be relative (still affected by the effects of the solar zenith angle) or absolute, with the solar elevation angle effects removed.

Create Angle Files

Select this check box to create and use angle files during processing.

For more information about angle files, and how they are used in processing, see About angle files.

Note: If your input imagery is orthorectified, make sure the check box is clear.

Use Default

Select this check box to use the default coefficients to convert the computed values to digital numbers (DN) before writing them to the output file.

For more information about the default coefficients, including how they are calculated, see About default coefficients.

Non-Thermal Coefficients: Offset

The offset coefficient by which to convert the computed values for non-thermal bands to digital numbers (DN).

If you specify a value for this parameter, you must also specify a value in the corresponding Factor box to the right (non-thermal coefficients).

Factor

The factor coefficient by which to convert the computed values for non-thermal bands to digital numbers (DN).

Thermal Coefficients: Offset

The offset coefficient by which to convert the computed values for thermal bands to DNs.

If you specify a value for this parameter, you must also specify a value in the corresponding Factor box to the right (thermal coefficients).

Factor

The factor coefficient by which to convert the computed values for thermal bands to DNs.

Output File Type

The format of the output file.

You can select from the following formats:

Output File Options

The options to apply when creating the output file or files. The available options are specific to the file format; in each case, the default of no options is allowed.

For more information on the options available for the output file type you specify, see GDB-supported file formats.

Output Data Type

The type of data to write to the output channels; that is, the bit depth of the pixel.

You can select from the following data types:

8U: 8-bit unsigned integer
16U: 16-bit unsigned integer
16S: 16-bit signed integer
32R: 32-bit real

Raster Channels

A comma-delimited list of channels; for example, 1,2,5.

This parameter is optional. If you do not specify a value, all of the channels in the input files is used.

Details

General job details

Preprocessing requirements

Before running this module, the following requirements must be met to ensure the job processes successfully and produces accurate results:

Input scenes
The input scenes can be raw or orthorectified imagery. With raw images, you can opt to create angle files. Angle files cannot be created for orthos; therefore, with this type of input imagery, make sure the Create angle files check box is clear before running the job.
The scenes to process must have the necessary metadata; that is, the following metadata tags must be available:
- RadiometricTransformationGain
- RadiometricTransformationBias
- RadiometricTransformationQuantity
- RadiometricTransformationUnits
Output folder
The name of the folder to which to write the output file or files.

Module details

The Radiometric Conversion module reads the input folder for valid image data to convert. For each valid file found, the module creates a child radiometric-conversion job. Each child job converts a given file to either radiance or reflectance.

If a channel selected for processing has no radiometric-calibration metadata, it is copied to the output file without modification, provided the type of the output file is PCIDSK (.pix). With types other than PCIDSK, only the radiometrically calibrated channels are processed. With non-calibrated channels, a warning is reported in the log with the numbers of each.

Converting to radiance
This process converts radiometrically calibrated input data to radiance. Input data can represent radiance—in which case, it is copied as is—or reflectance, and it can be relative or absolute. Relative-reflectance values still contain the effects of the solar-zenith angle, while absolute-reflectance values have these effects removed already.

If the input file contains radiances or relative reflectances, solar angles are not required. The conversion of absolute reflectances to radiances requires that the solar effects are restored; therefore, input data of this type requires knowledge of the solar-zenith angles.

Converting to reflectance
This process converts radiometrically calibrated input data to absolute reflectance. Input data can represent radiance, relative reflectance or absolute reflectance—in which case, it is copied as is. Relative-reflectance values still contain the effects of the solar-zenith angle, while absolute-reflectance values have these effects removed already.

If the input file contains absolute reflectances, solar angles are not required. The conversion of radiances and relative reflectances requires that the solar effects be removed; therefore, input data of this type requires knowledge of the solar zenith angles. The angle of solar elevation is determined by the angle files created, if selected, and, if not, it is determined by the AngleOfSolarElevation metadata tag.

Typically, absolute reflectances occur in a range of values from zero through one. However, due to causes, such as inaccurate calibration and other artifacts of processing, the actual values calculated can be outside the range. Depending on the type of output data you specify, the scaled pixel values may be truncated to fit in the range of values supported by the data type.

Note: Truncation does not replace a calculated value with a NoData pixel value.

Thermal channels are converted to the brightness temperature in degrees Kelvin, and cannot be negative. The highest values can reach hundreds—even thousands—of degrees over some phenomena, such as active fires or volcanoes.

About angle files
Angle files provides the solar and sensor viewing angles per pixel. The files are required to convert differing radiometric quantities from, for example, radiance to reflectance.

If the applicable conversion requires solar angles, and angle files are unavailable, the nominal solar angle value is extracted from image metadata.

Angle files can only be created for raw images acquired with the following sensors:

Landsat 8
Sentinel-2
Most pushbroom types

When you select to create angle files, the channels in the files are identified automatically for each input raster channel you specify, based on the angle-channel metadata tags Quantity (SolarZenithAngle) and BandDescription (AppliesToAllBands, or the standard description of individual image bands). If an angle channel cannot be identified, the corresponding channel in the input image is copied to the output image as is.

Each child job calculates the solar and satellite viewing angles (zenith angle and azimuth) for each pixel in the image.

Figure 1. Solar zenith and solar azimuth

Solar zenith and solar azimuth

The zenith angle is measured from the vector pointing vertically (at zero degrees) from the ground location of the pixel to the direction of the sun or satellite. The direction at a tangent to the nominal Earth surface has a zenith angle of 90 degrees.

The azimuth angle is measured from the vector pointing due north from the ground location of the pixel, and the ground projection of the direction to the sun or the satellite. The direction due north has an azimuth of zero degrees; the direction due east has an azimuth of 90 degrees, due south has an azimuth of 180 degrees, and due west has an azimuth of -90 degrees. The azimuth angles are stored in a range from -180 through 180.

About default coefficients
Most output channel types require that the calculated physical values be transformed with an offset and factor before being written to the output file as digital numbers (DN). To define the required linear transformation, enter the applicable values for the offset and factor. The computed DNs are clipped subsequently to fit the value range of the output channel.

With a selected check box, default values are used for the scaling offset and factor. The values used vary by the type of output data, whether you are transforming to radiance or reflectance, and whether the band is thermal or non-thermal.

The values used for each output data type are as follows:

8U: No default values are supplied; that is, you must manually enter the offset and factor.
16S or 16U: The default values depend on whether the bands are thermal or non-thermal, and whether you are transforming between DN and radiance or reflectance.
32R: The default values for each offset parameter is 0, and 1 for each factor parameter.

The offset and factor parameters are used jointly to convert the calculated radiance or reflectance values to DNs in the output file, as follows:

DN = ComputedValue × Offset + Factor
ComputedValue = calculated radiance or reflectance value

The radiometric gain and bias values stored in the channel metadata are mutually related to the offset and factor values as follows:

Gain = 1 ÷ Factor
Bias = -Offset ÷ Factor
Factor = 1 ÷ Gain
Offset = -Bias ÷ Gain

The non-calibrated channels are appended at the end of the file only for output files in the PCIDSK (.pix) format. With any other format, the channels are omitted from processing, and a warning message is displayed for each.

Job results

On successful completion of processing, the Radiometric Conversion module creates a radiometrically converted file for each valid file of input spatial data. The file is written to the specified output folder using the name of the original file, and with a file extension of the type you selected.

If you opted to create angle files, the module creates per-pixel angle files and writes them to an angle-files subfolder in the output folder. The name of the angle file is that of the input file in PCIDSK format (.pix).

Radiometric Conversion module

Description

Parameters

Parameter descriptions

Details