DN2TOA

Description

Parameters

Parameter descriptions

Input: Input image

Specifies the name of the input image from one of the supported sensors (see the ASENSOR parameter description).

The input image can be a raw image, an orthorectified image, or the output haze-free image from HAZEREM.

Source background options

Specifies, potentially with Source Background Values, which pixels in the source image are to be considered background (NoData) pixels. In general, if a pixel is considered NoData, the application handles the pixel in a special manner.

See the Source Background Values parameter for specific examples.

Source background values

Sensor

Optionally specifies the name of the sensor used to capture the input image.

See the Function Details section for a list of supported sensors.

If this parameter is not specified, the function checks for the PlatformName metadata tag at the file level.

If this parameter is not specified and the PlatformName metadata tag is not found, the function will error.

Calibration file name

Optionally specifies the path and name of the text file that contains, for each band, the calibration coefficients used to transform the values from the image to absolute at-sensor radiance values. This information is typically provided with the data set as an offset and a gain for each channel.

7      c0       c1 [mW/cm2 sr micron]
1   -0.0500   0.0778700
2   -0.2600   0.0798800  
3   -0.3000   0.0621600
4   -0.5500   0.0639700
5   -0.1150   0.0126200 
6    0.3200   0.00372047
7   -0.0420   0.00438900

The atcor\cal\ folder in the CATALYST Professional installation directory contains sample calibration files for every sensor supported by the atmospheric correction functions (MASKING, ATCOR, ATCOR_T). Each row in a calibration file lists the calibration coefficients for each sensor band; the bands are listed in increasing band order.

Ensure that the offset (c0) and gain (c1) values correspond to the scene. These values must be provided in the expected units for the specific sensor (shown at the top right of the calibration file).

If this parameter is not specified, DN2TOA reads the RadiometricTransOffset, RadiometricTransGain, and RadiometricTransUnits metadata tags for each channel in the input file. If the Calibration File (CFILE) parameter is not specified, or if the coefficients cannot be derived from the metadata, DN2TOA errors.

Solar zenith (degrees)

Specifies the solar zenith angle (0-90 degrees) at the time of image acquisition.

If this parameter is not specified and none of the combinations of metadata tags are found in full, this function errors.

Output units

Optionally specifies the output units for the atmospherically corrected image.

Output

Specifies the name of the output file to receive the computed reflectance image.

Details

DN2TOA generates a Top Of the Atmosphere (TOA) image that can be used for further processing, such as masking and atmospheric correction.

This function converts imagery from digital number to at-satellite reflectance (Top of the Atmosphere reflectance). This step is required before calculating radiometric transformations such as the Tasseled Cap transformation or Normalized Difference Vegetation Index, which require at-satellite reflectance input instead of digital numbers.

DN2TOA supports imagery stored in any GDB-supported format. For more information, refer to GDB file formats in the Technical Reference section of the CATALYST Professional Online Help.

The generated TOA image can be used to determine the seed and lowest threshold for cloud detection by MASKING.

References

Chander, G.; Markham, B.; Helder, D. Summary of Current Radiometric Calibration Coefficients for Landsat MSS, TM, ETM+ and EO-1 ALI Sensors. Remote Sensing of Environment, 113, 893-903.