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ISIS 3 Application Documentation


lronacpho

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Apply general LROC NAC photometric correction to multiband cubes

Overview Parameters

Description

LROC Empirical implements a photometric correction

      I/F = F(mu, mu0,phase)
              where
                  mu0 = cos(incidence)
                  mu = cos(emission)
                  F(mu, mu0, phase) = e(A0 + A1 * phase + A2 * mu + A3 * mu0) 
    

The equation described accounts for scattering dependance on incidence, emission, and phase angles. Lunar Reflectance approximately follows this function and has been tested with repeat coverage at different illumination geometries. The exponential equation has been derived from over 760,000 NAC image tiles. More information can be found at:

http://www.hou.usra.edu/meetings/lpsc2014/pdf/2826.pdf

This application provides features that allow LROC NAC image cubes to be photometrically corrected with a properly formatted PVL input file much like that of the ISIS program photomet. This application restricts much of the options available to the more sophisticated photomet application. Below is an example input parameter file for this application:

      Object = NormalizationModel
        Group = Algorithm
          Name = LROC_Empirical
          PhotoModel = LROC_Empirical
          Incref=30.0
          Emaref=0.0
          Pharef=30.0
        EndGroup
      EndObject

      Object = PhotometricModel
        Units = Degrees
        Group = Algorithm
          Name = LROC_Empirical
          FilterName = "Broadband"
          BandBinCenter = 600.0
          A0 = -2.9811422
          A1 = -0.0112862
          A2 = -0.8084603
          A3 = 1.3248888
        EndGroup
      EndObject
  

The Normalization object is the PhotometricModel evaluated at the given Incref, Emaref and Pharef angles. The value of the Name parameter is ignored here. The Incref, Emaref, and Pharef are the incidence, emission and phase angles to be used as the photometric standard. It will be used to normalize the photometric correction parameter to these angles. The equation used to create the photometrically corrected I/F dn is:

          odn = idn * (phostd  / ph)
         
              where phostd is the photometry model evaluated at the given Incref, 
              Emaref and Pharef angles. ph is the photometric correction for the 
              incidence, emission and phase at each pixel
      

The "Center" parameter in the above equality comes from the Center keyword in the BandBin group of the input cube file specified in the FROM parameter. This keyword must exist in the input cube or an error is generated and the program aborts. BandBinCenter and BandBinCenterTolerance are contained in each Algorithm group. Only BandBinCenter is required. If BandBinCenterTolerance is not present in an Algorithm group a value of 1.0E-6 is used. All input bands in the FROM file must be matched to at least one of the Algorithm parameters otherwise an error is generated and the application is aborted.

The parameter Units is provided to specify if the phase angle is in units of degrees or radians. It does not have to exist in any group or even in the top Object section. If it does not exist, "Radians" is the default.

An additional feature of the PVL structure is that any keyword that exists in the Object section of the PhotometricModel Object is propagated to each Algorithm group when it is read in unless the keyword already exists in the Algorithm group. If a keyword exists in both the PhotometricModel object and an Algorithm group, the keyword in the Algorithm group has precedence.

Additional consequences of the photometric correction processing is any incidence angle greater than 90 degrees is set to the ISIS special Null pixel value. And, of course, any ISIS special pixel encountered on input is propagated to the output TO file without modification.


Categories


History

Victor Silva2016-08-18 Version adapted from Kris Becker's LROWACPHO application from 2010

Parameter Groups

Files

Name Description
FROM Input cube
TO Output cube
BACKPLANE Backplane Cube
PHOPAR PVL file

Photometry

Name Description
MINPHASEMinimum phase angle to trim
MAXPHASEMaximum phase angle to trim
MINEMISSIONMinimum emission angle to trim
MAXEMISSIONMaximum emission angle to trim
MININCIDENCEMinimum incidence angle to trim
MAXINCIDENCEMaximum incidence angle to trim

Other Options

Name Description
USEDEM Use DEM instead of ellipsoid for photometric angle calculations
X

Files: FROM


Description

Use this parameter to select the input file name.

Type cube
File Mode input
Filter *.cub
Close Window
X

Files: TO


Description

This file will contain the photometrically corrected image data after being corrected by with LROC_Empirical algorithm.

Type cube
File Mode output
Pixel Type real
Close Window
X

Files: BACKPLANE


Description

This file will contain the backplane data. It must have "Phase Angle", "Emission Angle", and "Incidence Angle" as the first three bands.

Type cube
File Mode input
Pixel Type real
Internal Default Calculate the photometry on the fly
Close Window
X

Files: PHOPAR


Description

This file will contain the parameters A0-A3 to use when applying the LROC Empirical photometric correction. See the main program documentation for a full description.

Type filename
File Mode input
Filter *.pvl
Close Window
X

Photometry: MINPHASE


Description

Pixels which have a phase angle less than this value will be trimmed.

Type double
Default 0.0
Minimum 0.0 (inclusive)
Maximum 180.0 (inclusive)
Less Than or Equal MAXPHASE
Close Window
X

Photometry: MAXPHASE


Description

Pixels which have a phase angle greater than this value will be trimmed.

Type double
Default 180.0
Minimum 0.0 (inclusive)
Maximum 180.0 (inclusive)
Greater Than or Equal MINPHASE
Close Window
X

Photometry: MINEMISSION


Description

Pixels which have an emission angle less than this value will be trimmed.

Type double
Default 0.0
Minimum 0.0 (inclusive)
Maximum 90.0 (inclusive)
Less Than or Equal MAXEMISSION
Close Window
X

Photometry: MAXEMISSION


Description

Pixels which have a emission angle greater than this value will be trimmed.

Type double
Default 90.0
Minimum 0.0 (inclusive)
Maximum 90.0 (inclusive)
Greater Than or Equal MINEMISSION
Close Window
X

Photometry: MININCIDENCE


Description

Pixels which have an incidence angle less than this value will be trimmed.

Type double
Default 0.0
Minimum 0.0 (inclusive)
Maximum 180.0 (inclusive)
Less Than or Equal MAXINCIDENCE
Close Window
X

Photometry: MAXINCIDENCE


Description

Pixels which have a incidence angle greater than this value will be trimmed.

Type double
Default 90.0
Minimum 0.0 (inclusive)
Maximum 180.0 (inclusive)
Greater Than or Equal MININCIDENCE
Close Window
X

Other Options: USEDEM


Description

Phase, Emission, and Incidence angles can be calculated from the ellipsoid (default) or from the DEM. The difference is that using the DEM the surface roughness is taken into account.

Type boolean
Default False
Close Window