photomet

This program performs photometric correction on image pixels acquired under different illumination and viewing geometries by adjusting the brightness and contrast such that the resulting image appears as if obtained under uniform conditions. The photometric correction is applied to each pixel by computing a photometric model based on local photometric angles and a set of parameters that defines the model. Currently, no default values are assigned for any parameter names in the ISIS3 version of photomet.

Photometric angles can be computed from the following:

• SPICE information stored in the image labels
• User-entered values for parameter names
• Incidence angle, emission angle, and phase angle backplanes
• Photometric angle files generated by the user

This program sets all pixels that have an incidence angle and/or emission angle greater than or equal to 90 degrees to NULL pixel values, regardless of the photometric angles resulting from using a topographic model.

The user must select a photometric model and a normalization model, with the option of adding an atmospheric model. Each of these models has a set of parameters that specifies its operation, which the user must provide. The different models can be mixed and matched to produce variations of the photometric correction.

• You may enter the desired parameters by using the program GUI, which is recommended
• A PVL file containing the photometric parmeters may be used if you opt to use the "frompvl" parameter
• Within the GUI you may select a PVL file, and in addition, select the "frompvl" drop-down menu and photomet will load the values from the PVL file into the appropriate parameter names in the GUI for you. Note, if more than one model type for phtname, atmname, or normname parameters are in the PVL file, then the parameter values for the first model type encountered by the program are loaded. Review the parameter values to make sure the correct options are selected and have correct values before executing the program.
• Values also can be entered manually at the command line

Note: If any parameter names are entered into the GUI after specifying "frompvl", the new values entered into the GUI will take precedence over the values entered in the PVL file.

There are three aspects of a photometric correction that should be considered when running the photomet program:

1. The surface photometric function model type that describes the planetary surface. Any one of the surface photometric functions can be used in combination with any of the normalization type models and optionally an atmospheric photometric model.
2. The atmospheric photometric function model type used when atmospheric scattering is present. The models that end with "1" use a first order scattering approximation, and those that end with "2" use a second order approximation; the second order has slower processing time because it uses more iterations and a quadratic equation versus fewer iterations and a linear equation used in the first order approximation.
3. The type of normalization applied to the image to equalize the albedo or the topographic contrasts, or a combination of the two. One of the available modes must be selected.

The intent of topographic normalization is to correct for the variation in incidence, emission, and phase angles within and between images. Topographic normalization involves both a multiplicative correction that adjusts the contrast for a unit slope to reference conditions, and an additive correction to keep the average brightness uniform.

In practice, the albedo may be nonuniform, so a multistep process is used:

1. Photomet is run in albedo mode, which decreases the brightness variations across the individual image and removes any additive atmospheric contribution.
2. The output image in step 1 is divided by a low-pass-filtered version of itself, which removes the albedo variations if they have broader spatial scales than the topographic shading as is often the case.
3. And finally, photomet is run again in topography mode on the output image from step 2, which reverses the albedo normalization of the first pass and then applies the topographic normalization.

In the absence of an atmosphere, the "albedo mode" is very simple: the image is divided by the photometric model evaluated at the actual angles and then multiplied by the model at a reference geometry. If an atmosphere is present, the additive component of the atmospheric scattering is subtracted at the real conditions before a multiplicative step, and added back as calculated for the standard conditions at the end. The "mixed mode" of normalization is used for images that span very large ranges of incidence angles. In the mixed mode, the albedo correction is applied at small incidence angles where albedo variations dominate topographic shading, and the topographic normalization is performed at large incidence angles where the reverse is true. A user-specified parameter "incmat" controls the incidence angle at which a smooth transition from one type of normalization to the other takes place.

The normalization models that use an atmospheric correction are albedoatm, shadeatm, and topoatm. If using the GUI interface photomet will automatically exclude all atmospheric models for normaliztion types that do not require an atmospheric correction.

Question: What happens if the normalization model I chose does not perform an atmospheric correction although I have an atmospheric model defined in my PVL file?
Answer: If you have chosen a normalization model that does not perform atmospheric correction, then the image is normalized without applying the atmospheric correction.

New Developments

A new parameter name "chngpar" was added to photomet to allow the user to enter a string consisting of parameter names and values outside of the PVL files. This string replaces any parameter already defined. This is useful when one or two parameter values change for each image but all the other parameter values remain the same.

The parameter name "ZEROB0STANDARD" was shortened to "ZEROB0ST," but the longer name will still work for backward compatibility. The default is to get the user setting for "ZEROB0ST" from the PVL file. If no PVL file exists and the user does not specify a "FALSE" or "TRUE" option, the program will automatically default to "TRUE" to follow the default setting in previous photomet versions. PLEASE NOTE: This change was actually not added because the ability to support aliases (or deprecated) values has not been fully implemented in ISIS. As a result, you must use the full ZEROB0STANDARD parameter name.

The parameter name "INCMAT" is no longer required when the "ALBEDO" normalization model is selected. The parameter name will still appear in the GUI for backward compatibility, but does not need to be defined by the user in the GUI or on the command line.

A set of photomet PVL templates for Mars and other planetary bodies developed in ISIS2 are now available in $ISIS3DATA/base/templates/photometry/ directory. There are also additional examples of PVL files for different photometric models under "Example PVL files," later in this document.

Note: The NoNormalization model has been removed because it duplicated the functionality of the shade model. Use shade with incref=0 and albedo=1.0 instead.

The program photemplate can be used to set up the PVL file containing the selected options for photomet.

The tables below show the models and their related parameter requirements along with the ISIS2 default values. The ISIS2 default values are only meant to serve as possible initial values to test backward compatibility since there are no default values defined in ISIS3.

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SURFACE PHOTOMETRIC FUNCTION MODELS

Available photometric function models and required parameter names

Name	Required parameter names
Hapkehen	B0, hg1, hg2, hh, theta, wh
Hapkeleg	Theta, wh, bh, ch, hh, b0, zerob0st
Lambert	None
LommelSeeliger	None
LunarLambert	L
LunarLambertEmpirical	Phaselist, llist, phasecurvelist
LunarLambertMcEwen	None
Minnaert	K
MinnaertEmpirical	Phaselist, klist, phasecurvelist

Photometric model parameter names and settings

Name	Description	ISIS2 default	Valid range
B0	Hapke opposition surge component	0.0	0 <= value
Bh	Hapke Legendre coefficient for single particle phase function	0.0	-1 <= value <= 1
Ch	Hapke Legendre coefficient for single particle phase function	0.0	-1 <= value <= 1
Hg1	Hapke Henyey Greenstein coefficient for single particle phase function	0.0	0 <= value <= 1
Hg2	Hapke Henyey Greenstein coefficient for single particle phase function	0.0	0 <= value <= 1
Hh	Hapke opposition surge component	0.0	0 <= value
K	Minnaert function exponent	1.0	0 <= value
L	Lunar-Lambert function weight	1.0	No limit
Theta	Hapke macroscopic roughness component	0.0	0 <= value <= 90
Wh	Hapke single scattering albedo component	0.5	0 < value <= 1
Zerob0st	Flag to set opposition surge B0 to zero	True	True or False
Phaselist	Phase list for empirical functions	None	String
Llist	Exponent list of limb darkening values	None	String
Klist	Exponent list of limb darkening values	None	String
Phasecurvelist	Phase curve list of brightness values	None	String

The functions are defined as follows, where phase is the phase angle, and u0 and u are the cosines of the incidence and emission angles, respectively:

Lambert

FUNC=u0

LommelSeeliger

FUNC=u0/(u0+u)

Minnaert

FUNC=u0**K * u**(K-1)

LunarLambert (Lunar-Lambert, "lunar" part is Lommel-Seeliger)

FUNC=(1-L)*u0 + 2*L*u0/(u0+u)

MinnaertEmpirical

FUNC=B(phase) * u0**K(phase) * u**(K(phase)-1)

LunarLambertEmpirical

FUNC=B(phase) * ((1-L)*u0 + 2*L*u0/(u0+u))

---

ATMOSPHERIC PHOTOMETRIC FUNCTION MODELS

Available atmosphereic functions and required parameter names

Function model name	Required parameters
Anisotropic1	Bha, hnorm, nulneg, tau, tauref, wha
Anisotropic2	Bha, hnorm, nulneg, tau, tauref, wha
HapkeAtm1	Hga, hnorm, nulneg, tau, tauref, wha
HapkeAtm2	Hga, hnorm, nulneg, tau, tauref, wha
Isotropic1	Hnorm, nulneg, tau, tauref, wha
Isotropic2	Hnorm, nulneg, tau, tauref, wha

Atmospheric models parameter names and settings

Name	Description	ISIS2 Default	Valid Range
Bha	Coefficient of the single particle Legendre phase function	0.85	-1 <= value <= 1
Hga	Coefficient of single particle Henyey Greenstein phase function	0.68	-1 < value < 1
Hnorm	Atmospheric shell thickness normalized to the planet radius	0.003	0 <= value
Nulneg	Specifies if negative values after removal of atmospheric effects will be set to NULL	NO	YES or NO
Tau	Normal optical depth of the atmosphere	0.28	0 <= value
Tauref	Reference value of tau to which the image will be normalized	0.0	0 <= value
Wha	Single scattering albedo of atmospheric particles	0.95	0 < value < 1

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PHOTOMETRIC NORMALIZATION MODELS

Available photometric normalization functions and required parameter names

Function name	Normalization function type	Required parameter names
Albedo	Albedo contrasts uniform	Albedo, incref, thresh
AlbedoAtm	Albedo with atmosphere	Incref
Mixed	Albedo at low incidence blended to topo at high incidence	Albedo, incmat, incref, thresh
MoonAlbedo	Special Lunar model	Bsh1, d, e, f, g2, h, wl, xb1, xb2, xmul
Shade	Shaded relief model	Albedo, incref
ShadeAtm	Shaded relief with atmosphere	Albedo, incref
Topo	Topographic shading uniform	Albedo, incref, thresh
TopoAtm	Topographic shading with atmosphere	Albedo, incref

Normalization model parameter names and settings

Name	Description	ISIS2 default	Valid range
Albedo	Albedo to which the image will be normalized	1.0	No limit
Bsh1	Albedo dependent phase function normalization parameter	0.08	0 <= value
D	Albedo dependent phase function normalization parameter	0.14	No limit
E	Albedo dependent phase function normalization parameter	-0.4179	No limit
F	Albedo dependent phase function normalization parameter	0.55	No limit
G2	Albedo dependent phase function normalization parameter	0.02	No limit
H	Albedo dependent phase function normalization parameter	0.048	No limit
Incmat	Specifies incidence angle where albedo normalization transitions to incidence normalization	0.0	0 <= value < 90
Incref	Reference incidence angle to which the image will be normalized	0.0	0 <= value < 90
Thresh	Sets upper limit on amount of amplification in regions of small incidence angle	30.0	No limit
Wl	Wavelength in micrometers of the image being normalized	1.0	No limit
Xb1	Albedo dependent phase function normalization parameter	-0.0817	No limit
Xb2	Albedo dependent phase function normalization parameter	0.0081	No limit
Xmul	Used to convert radiance to reflectance or apply a calibration fudge factor	1.0	No limit

Example PVL files:

    Example 1:
  
    Object = PhotometricModel
      Group = Algorithm
        PhtName = Lambert
      EndGroup
    EndObject
    Object = NormalizationModel
      Group = Algorithm
        NormName = Shade
	Incref = 0.0
	Albedo = 1.0
      EndGroup
    EndObject
  
    --------------------------------
    Example 2:
  
    Object = PhotometricModel
      Group = Algorithm
        PhtName = Minnaert
	K = 0.5
      EndGroup
    EndObject
    Object = NormalizationModel
      Group = Algorithm
        NormName = Albedo
	Incref = 0.0
	Incmat = 0.0
	Albedo = 1.0
	Thresh = 30.0
      EndGroup
    EndObject
  
    --------------------------------
    Example 3:
  
    Object = PhotometricModel
      Group  = Algorithm
        PhtName = Hapkehen
	Wh = 0.52
	Hh = 0.0
	B0 = 0.0
	Theta = 30.0
	Hg1 = 0.213
	Hg2 = 1.0
      EndGroup
    EndObject
    Object = AtmosphericModel
      Group = Algorithm
        AtmName = hapkeatm2
	Hnorm = 0.003
	Tau = 0.28
	Tauref = 0.0
	Wha = 0.95
	Hga = 0.68
      EndGroup
    EndObject
    Object = NormalizationModel
      Group = Algorithm
        NormName = albedoatm
	Incref = 0.0
      EndGroup
    EndObject

    --------------------------------
    Example 4 (Used to process Clementine UVVIS filter "a" data):
  
    Object = PhotometricModel
      Group  = Algorithm
        PhtName = LunarLambertMcEwen
      EndGroup
    EndObject
    Object = NormalizationModel
      Group = Algorithm
        NormName = MoonAlbedo
	D = 0.0
	E = -0.222
	F = 0.5
	G2 = 0.39
	H = 0.062
	Bsh1 = 2.31
        Wl = 1.0
        Xb1 = 1.0
        Xb2 = 1.0
      EndGroup
    EndObject
  
    --------------------------------
    Example 5 (Used to process Clementine UVVIS filter "b" data):
  
    Object = PhotometricModel
      Group  = Algorithm
        PhtName = LunarLambertMcEwen
      EndGroup
    EndObject
    Object = NormalizationModel
      Group = Algorithm
        NormName = MoonAlbedo
	D = 0.0
	E = -0.218
	F = 0.5
	G2 = 0.4
	H = 0.054
	Bsh1 = 1.6
        Wl = 1.0
        Xb1 = 1.0
        Xb2 = 1.0
      EndGroup
    EndObject
  
    --------------------------------
    Example 6 (Used to process Clementine UVVIS filter "cde" data):
  
    Object = PhotometricModel
      Group  = Algorithm
        PhtName = LunarLambertMcEwen
      EndGroup
    EndObject
    Object = NormalizationModel
      Group = Algorithm
        NormName = MoonAlbedo
	D = 0.0
	E = -0.226
	F = 0.5
	G2 = 0.36
	H = 0.052
	Bsh1 = 1.35
        Wl = 1.0
        Xb1 = 1.0
        Xb2 = 1.0
      EndGroup
    EndObject

    --------------------------------
    Example 7 (Used for Mars red filter data to apply empirical photometric models):
    
    Object = PhotometricModel
    # For Mars red filter images
    # The phase angles at which the coefficient values for the Lunar Lambert 
    # Empirical (LunarLambertEmpirical) L and the Minnaert Empirical K approximation are 
    # calculated, along with the brightness (phase curve) values at those
    # points (ALL ON ONE LINE!)

      Group = Algorithm
	PhtName = LunarLambertEmpirical
	PhaseList = "0.,10.,20.,30.,40.,50.,60.,70.,80.,90.,100.,110.,120.,130.,140.,150.,160.,170.,180."
	LList = "0.946,0.748,0.616,0.522,0.435,0.350,0.266,0.187,0.118,0.062,0.018,-0.012,-0.027,
	   -0.035,-0.036,-0.037,-0.031,-0.012,-0.010"
	PhaseCurveList = "0.1578,0.1593,0.1558,0.1484,0.1391,0.1292,0.1194,0.1099,0.1008,0.09176,
	   0.08242,0.07234,0.06165,0.05106,0.04091,0.03137,0.02171,0.01038,0."
      EndGroup

      Group = Algorithm
	PhtName = MinnaertEmpirical
	PhaseList = "0.,10.,20.,30.,40.,50.,60.,70.,80.,90.,100.,110.,120.,130.,140.,150.,160.,170.,180."
	KList = "0.518,0.595,0.660,0.709,0.753,0.796,0.837,0.875,0.904,0.922,0.926,0.935,0.954,0.986,
	   1.019,1.063,1.099,1.095,1.090"
	PhaseCurveList = "0.1574,0.1582,0.1546,0.1470,0.1375,0.1273,0.1174,0.1077,0.09797,0.08750,
	   0.07594,0.06466,0.05471,0.04665,0.03935,0.03339,0.02642,0.01482,0."
      EndGroup
    EndObject 


  References:

  Chandrasekhar, S., 1960.  Radiative Transfer. Dover, 393 pp.
  Hapke, B. W., 1981. Bidirectional reflectance spectroscopy 1: Theory. J. 
     Geophys. Res., pp. 86,3039-3054.
  Hapke, B., 1984. Bidirectional reflectance spectroscopy3: Corrections for 
     macroscopic roughness. Icarus, 59, pp. 41-59.
  Hapke, B., 1986. Bidirectional reflectance spectroscopy 4: The extinction 
     coefficient and the opposition effect. Icarus, 67, pp. 264-280.
  Johnson, J. R., et al., 1999, Preliminary Results on Photometric Properties of 
     Materials at the Sagan Memorial Station, Mars, J. Geophys. Res., 104, 8809.
  Kirk, R. L., Thompson, K. T., Becker, T. L., and Lee, E. M., 2000. 
     Photometric modelling for planetary cartography. Lunar Planet. Sci., XXXI, 
     Abstract #2025, Lunar and Planetary Institute, Houston (CD-ROM).
  Kirk, R. L., Thompson, K. T., and Lee, E. M., 2001. Photometry of the martian 
     atmosphere:  An improved practical model for cartography and photoclinometry.
     Lunar Planet. Sci., XXXII, Abstract #1874, Lunar and Planetary Institute, 
     Houston (CD-ROM).
  McEwen, A. S., 1991. Photometric functions for photoclinometry and other 
     applications.  Icarus, 92, pp. 298-311.
  Thorpe, T. E., 1973, Mariner 9 Photometric Observations of Mars from November 
     1971 through March 1972, Icarus, 20, 482.
  Tomasko, M. G., et al., 1999, Properties of Dust in the Martian Atmosphere from
     the Imager on Mars Pathfinder, J. Geophys. Res., 104, 8987.
  

Description

This is the input filename that will be photometrically corrected.

Type	cube
File Mode	input
Filter	*.cub

Description

This output file will contain the results of the photometric correction.

Type	cube
File Mode	output
Pixel Type	real

Description

This text file contains the parameter names and values to be used to perform the photometric correction.

Type	filename
File Mode	input
Default Path	$base/templates/photometry
Internal Default	None Specified
Filter	*.pvl

Description

Chngpar is used to enter a string of parameter names and values enclosed in quotes that will be added to or replaces the pre-defined parameter values. PLEASE NOTE: Any parameter names used in the CHNGPAR string input MUST be spelled out completely and without any errors. Otherwise, they will be ignored by the program.

Example:
photomet from=f1.cub to=pho.cub frompvl=my.pvl chngpar="tau=0.5 tauref=30"

Type	string
Default	None
Internal Default	None

Description

The maximum number of degrees allowed for the emission angle in order to retain the data. This number must be between 0.0 and 90.0.

Type	double
Default	90.0
Minimum	0.0 (inclusive)
Maximum	90.0 (inclusive)

Description

The maximum number of degrees allowed for the incidence angle in order to retain the data. This number must be between 0.0 and 90.0.

Type	double
Default	90.0
Minimum	0.0 (inclusive)
Maximum	90.0 (inclusive)

Description

This specifies if the image will be trimmed based on the photometric angles obtained from the ellipsoid (default) or the DEM surface.

The ellipsoid is retrieved from the IAU/NAIF target body file, which is defined within the cube's kernel group as the TargetAttitudeShape. If this parameter is set to false, then the photometric angles will be obtained from the ellipsoidal surface.

The photometric angles obtained from the DEM surface (shape model) for each pixel are obtained using an ellipsoid defined by the radius obtained from the DEM shape model. Note that photomet does not trim using local slopes.

Type	boolean
Default	FALSE

Description

The incidence, emission, and phase angles are determined based on the source defined by the user. The available options are listed below:

ELLIPSOID (default)

The photometric angles for each pixel are obtained using an ellipsoid defined by the radius obtained from the DEM shape model.

DEM

The photometric angles for each pixel are obtained using the DEM shape model (if one is defined in the image labels). The surface roughness is taken into account to calculate a surface normal, which is used to calculate the photometric angles. i.e. slope, local emission, local incidence.

CENTER_FROM_IMAGE

The photometric angles are obtained from the center of the input image using the ellipsoid shape model. These angles are applied to every pixel in the input file. This option is best for images where the photometric angles do not vary much and when faster processing is desired.

CENTER_FROM_LABEL

The photometric angle keywords are obtained from the label of the input image, and applied to every pixel in the file. The keywords "IncidenceAngle," "EmissionAngle," and "PhaseAngle" must be in the image labels. This option is best for images where the photometric angles do not vary much and when faster processing is desired.

CENTER_FROM_USER

The photometric angles are obtained from the values defined for IncidenceAngle, EmissionAngle, and PhaseAngle parameter names. These angles are applied to every pixel in the file. This option is best for images where the photometric angles do not vary much and when faster processing is desired.

BACKPLANE

The photometric angles are obtained from separate cube files, which contain the information for each pixel in the input file. These angles are applied to every pixel in the file. This option is best for images that will be processed through the same steps many times with different photometric settings because the photometric angles are not recomputed each time for every pixel. This option is also used for images that do not have a camera model associated with them. If no camera model is available, then create files that contain the photometric angle information for each pixel in the input file with fx or another program. It is very important that the new files have the same number of samples and lines as the input file.

Type	combo
Default	ELLIPSOID
Internal Default	ELLIPSOID
Option List:	Option Brief Description ELLIPSOID Get angles from ELLIPSOID The photometric angles for each pixel are obtained using an ellipsoid defined by the radius obtained from the DEM surface (shape model). Exclusions PHASE_ANGLE_FILE INCIDENCE_ANGLE_FILE EMISSION_ANGLE_FILE PHASE_ANGLE INCIDENCE_ANGLE EMISSION_ANGLE DEM Get angles from DEM The photometric angles for each pixel are obtained using the DEM surface (shape model). Exclusions PHASE_ANGLE_FILE INCIDENCE_ANGLE_FILE EMISSION_ANGLE_FILE PHASE_ANGLE INCIDENCE_ANGLE EMISSION_ANGLE CENTER_FROM_IMAGE Get angles from center of image The photometric angles are obtained from the center of the input image using the ellipsoid shape model. Exclusions PHASE_ANGLE_FILE INCIDENCE_ANGLE_FILE EMISSION_ANGLE_FILE PHASE_ANGLE INCIDENCE_ANGLE EMISSION_ANGLE CENTER_FROM_LABEL Get angles from image label The keyword values for "IncidenceAngle," "EmissionAngle," and "PhaseAngle" are extracted from the image labels and used for the photometric angles to apply to every pixel. Exclusions PHASE_ANGLE_FILE INCIDENCE_ANGLE_FILE EMISSION_ANGLE_FILE PHASE_ANGLE INCIDENCE_ANGLE EMISSION_ANGLE CENTER_FROM_USER Get the angles from user The photometric angles are obtained from the user and applied to every pixel in the file. Exclusions PHASE_ANGLE_FILE INCIDENCE_ANGLE_FILE EMISSION_ANGLE_FILE Inclusions PHASE_ANGLE INCIDENCE_ANGLE EMISSION_ANGLE BACKPLANE Get the angles from separate file(s) The photometric angles are obtained from separate backplane band(s) or file(s) which contain the angle information for each pixel in the input image file. Exclusions PHASE_ANGLE INCIDENCE_ANGLE EMISSION_ANGLE

Description

This file must contain the phase angle information for the input cube.

Type	cube
File Mode	input
Pixel Type	real
Internal Default	No file

Description

This file must contain the incidence angle information for the input cube.

Type	cube
File Mode	input
Pixel Type	real
Internal Default	No file

Description

This file must contain the emission angle information for the input cube.

Type	cube
File Mode	input
Pixel Type	real
Internal Default	No file

Description

The center phase angle to use if the CENTER_FROM_USER option is chosen.

Type	double
Default	0.0
Minimum	0.0 (inclusive)
Maximum	180.0 (inclusive)

Description

The center incidence angle to use if the CENTER_FROM_USER option is chosen.

Type	double
Default	0.0
Minimum	0.0 (inclusive)
Maximum	90.0 (inclusive)

Description

The center emission angle to use if the CENTER_FROM_USER option is chosen.

Type	double
Default	0.0
Minimum	0.0 (inclusive)
Maximum	90.0 (inclusive)

Description

Specify the name of the surface photometric function model to apply to the input image. The available options are the following:

FROMPVL

Gets the photometric model from the PVL file. If the required parameter names and values are missing from the PVL file, either add them to the PVL file, or enter the values at the command line or use the GUI to enter the values.

LAMBERT

A simple photometric model which predicts that light incident on a surface is scattered uniformly in all directions; the total amount of reflected light depends on the incidence angle of the illumination. This function does not depend upon the outgoing light direction.

HAPKEHEN

Derive model albedo using the complete Hapke model with Henyey-Greenstein single-particle phase function whose coefficients are hg1 and hg2, plus single scattering albedo wh, opposition surge parameters hh and b0, and macroscopic roughness theta. For a smooth model with opposition effect use theta=0.

The table below shows the Hapke parameters for Mars from Johnson et al. (1999) for IMP data of Photometry Flats (soil) and may be reasonably representative of Mars as a whole. Note that (hg1, hg2=1.0) is equivalent to (-hg1, hg2=0.0).

Parameter settings for Mars

Band	Wh	B0	Hh	Hg1	Hg2
Red	0.52	0.025	0.17	0.213	1.0
Green	0.29	0.29	0.17	0.19	1.0
Blue	0.16	0.995	0.17	0.145	1.0

HAPKELEG

Derive model albedo using complete Hapke model with Henyey Legendre two-term Legendre polynomial phase function whose coefficients are bh and ch, plus single scattering albedo wh, opposition surge parameters hh and b0, and macroscopic roughness theta.

LOMMELSEELIGER

This model takes into account the radiance that results from single scattering (scattering of collimated incident light) and does not take into account the radiance that results from multiple scattering (scattering of diffuse light which has made its way indirectly to the same position by being scattered one or more times). This model depends on the incidence and emission angles.

LUNARLAMBERTMCEWEN

This model was developed specifically for use with the Moon, and designed to be used in conjunction with the MoonAlbedo normalization model.

LUNARLAMBERTEMPIRICAL, LUNARLAMBERT, MINNAERTEMPIRICAL, and MINNAERT

These models combine a weighted sum of the LommelSeeliger and Lambert models. Given a suitable value for the LunarLambert function weight, L, these models fit the true reflectance behavior of many planetary surfaces equally well as the Hapke model. These models also depend on the incidence and emission angles.

Type	combo
Default	FROMPVL
Internal Default	FROMPVL
Option List:	Option Brief Description FROMPVL Get from photomet PVL Get photometric model from the PVL file. Add missing parameters to the PVL file, or enter the values at the command line or use the GUI to enter the values. Exclusions THETA WH HG1 HG2 HH B0 ZEROB0STANDARD BH CH L K PHASELIST KLIST LLIST PHASECURVELIST LAMBERT Lambert Photometric Model Simple photometric model which predicts that light incident on a surface is scattered uniformly in all directions. Exclusions THETA WH HG1 HG2 HH B0 ZEROB0STANDARD BH CH L K PHASELIST KLIST LLIST PHASECURVELIST HAPKEHEN Hapke-Henyey-Greenstein Photometric Model Derive model albedo using complete Hapke model with Henyey-Greenstein single-particle phase function. Exclusions BH CH L K PHASELIST KLIST LLIST PHASECURVELIST Inclusions THETA WH HG1 HG2 HH B0 ZEROB0STANDARD HAPKELEG Hapke Legendre Polynomial Photometric Model Derive model albedo using complete Hapke model with Henyey Legendre two-term Legendre polynomial phase function. Exclusions HG1 HG2 L K PHASELIST KLIST LLIST PHASECURVELIST Inclusions THETA WH BH CH HH B0 ZEROB0STANDARD LOMMELSEELIGER Lommel-Seeliger Photometric Model This model takes into account the radiance that results from single scattering (scattering of collimated incident light). Exclusions THETA WH HG1 HG2 BH CH HH B0 ZEROB0STANDARD L K PHASELIST KLIST LLIST PHASECURVELIST LUNARLAMBERTEMPIRICAL Lunar Lambert Empirical Photometric Model This model combines a weighted sum of the LommelSeeliger and Lambert models. Exclusions THETA WH HG1 HG2 BH CH HH B0 ZEROB0STANDARD K L KLIST Inclusions PHASELIST LLIST PHASECURVELIST LUNARLAMBERTMCEWEN Lunar Lambert-McEwen Photometric Model This model was designed for the Moon to be used in conjunction with the MoonAlbedo normalization model. Exclusions THETA WH HG1 HG2 BH CH HH B0 ZEROB0STANDARD L K PHASELIST KLIST LLIST PHASECURVELIST LUNARLAMBERT Lunar Lambert Photometric Model This model combines a weighted sum of the LommelSeeliger and Lambert models. Exclusions THETA WH HG1 HG2 BH CH HH B0 ZEROB0STANDARD K PHASELIST KLIST LLIST PHASECURVELIST Inclusions L MINNAERTEMPIRICAL Minnaert Empirical Photometric Model This model combines a weighted sum of the LommelSeeliger and Lambert models. Exclusions THETA WH HG1 HG2 BH CH HH B0 ZEROB0STANDARD K L LLIST Inclusions PHASELIST KLIST PHASECURVELIST MINNAERT Minnaert Photometric Model This model combines a weighted sum of the LommelSeeliger and Lambert models. Exclusions THETA WH HG1 HG2 BH CH HH B0 ZEROB0STANDARD L PHASELIST KLIST LLIST PHASECURVELIST Inclusions K

Description

The "macroscopic roughness" of the surface as it affects the photometric behavior, used for Hapkehen or Hapkeleg. This is the RMS slope at scales larger than the distance photons penetrate the surface but smaller than a pixel. See Hapke (1986). The roughness correction, which is evaluated if theta is given any value other than 0.0, but is extremely slow. See Hapke (1986).

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	0.0 (inclusive)
Maximum	90.0 (inclusive)

Description

The Hapke single scattering albedo of surface particles, see Hapke (1981).

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	0.0 (exclusive)
Maximum	1.0 (inclusive)

Description

Asymmetry parameter used in Hapke Henyey Greenstein model for the scattering phase function of single particles in the surface. See Hapke (1981). The two parameter Henyey Greenstein function is:

P(phase)=(1-hg2) * (1-hg1**2)/(1+hg1**2+2*hg1*cos(phase))**1.5 + hg2 * (1-hg1**2)/(1+hg1**2-2*hg1*cos(phase))**1.5

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	-1.0 (exclusive)
Maximum	1.0 (exclusive)

Description

The Hapke Henyey Greenstein coefficient for single particle phase function. The second parameter of the two-parameter Henyey-Greenstein model for the scattering phase function of single particles in the surface. This parameter controls the proportions in a linear mixture of ordinary Heneyey Greenstein phase functions with asymmetry parameters equal to +hg1 and -hg1. See HG1 for the full formula.

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	0.0 (inclusive)
Maximum	1.0 (inclusive)

Description

The Hapke Legendre coefficient for single particle phase function. A two-term Legendre polynomial is used for the scattering phase function of single particles in the surface:

P(phase) = 1 + bh * p1(cos(phase)) + ch * p2(cos(phase))

Bh is not to be confused with the Legendre coefficient bha of the phase function for atmospheric particles, used when atmname=anisotropic1 or anisotropic2.

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	-1.0 (exclusive)
Maximum	1.0 (exclusive)

Description

The Hapke Legendre coefficient for single particle phase function. A two-term Legendre polynomial is used for the scattering phase function of single particles in the surface:

P(phase) = 1 + bh * p1(cos(phase)) + ch * p2(cos(phase))

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	-1.0 (exclusive)
Maximum	1.0 (exclusive)

Description

The Hapke opposition surge component. The width parameter for the opposition effect for the surface if Hapkehen or Hapkeleg is used. See Hapke (1984).

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	0.0 (inclusive)

Description

The Hapke opposition surge component. The magnitude of the opposition effect for the surface if Hapkehen or Hapkeleg is used. See Hapke (1984).

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	0.0 (inclusive)

Description

This specifies if the opposition surge component B0 is set to zero during the standard conditions phase. The program will automatically default to "true" if "ZEROB0STANDARD" is not defined in the PVL FILE when the "READFROMPVL" option is selected, and the user did not choose either "FALSE" or "TRUE" option.

Type	string
Default	READFROMPVL
Option List:	Option Brief Description READFROMPVL Get ZEROB0STANDARD value from the FROMPVL file Retrieve and set the ZEROB0STANDARD parameter from the FROMPVL file. If a FROMPVL file is not provided, then an error will occur. FALSE B0 will not be set to zero for standard conditions phase This option specifies that the opposition surge B0 will not be set to zero during the standard conditions phase. TRUE B0 will be set to zero for standard conditions phase This option specifies that the opposition surge B0 will be set to zero during the standard conditions phase.

Description

The Lunar Lambert function weight that governs limb-darkening in the lunar lambert photometric function:

Func=(1-L)*u0 + 2*L*u0/(u0+u)

The values generally fall in the range from 0 (Lambert function) to 1 (Lommel-Seeliger or "lunar" function).

Type	string
Default	None Specified
Internal Default	None Specified

Description

The Minnaert function exponent that governs limb-darkening in the Minnaert photometric function:

Func=u0**K * u**(K-1)

The values generally fall in the range from 0.5 ("lunar-like", almost no limb darkening) to 1.0 (Lambert function).

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	0.0 (inclusive)

Description

The Minnaert Empirical and Lunar Lambert Empirical function phase angle list entered as a comma delimited string describing how the parameters of the empirical function vary with phase angle. See "$ISIS3DATA/base/templates/photometry/marsred.pvl" for an example.

Type	string
Default	No List
Internal Default	No List

Description

The Minnaert Empirical function exponent list of limb darkening values entered as a comma delimited string that describes how the parameters of the empirical function vary with phase angle. See "$ISIS3DATA/base/templates/photometry/marsred.pvl" for an example.

Type	string
Default	No List
Internal Default	No List

Description

The Lunar Lambert Empirical function parameter list of limb darkening values entered as a comma delimited string that describes how the parameters of the empirical function vary with phase angle. See "$ISIS3DATA/base/templates/photometry/marsred.pvl" for an example.

Type	string
Default	No List
Internal Default	No List

Description

The Minnaert Empirical or Lunar Lambert Empirical function phase curve list of brightness values corresponding to a set of phase angles defined in the PHASELIST parameter. See "$ISIS3DATA/base/templates/photometry/marsred.pvl" for an example.

Type	string
Default	No List
Internal Default	No List

Description

This is the name of the atmospheric photometric function model to be applied. The models ending with "1" use a first order scattering approximation. Those ending with "2" use a second order scattering approximation, and are slower but more accurate than the first order scattering approximation. The atmospheric correction can be used with only three atmospheric normalization models: albedoatm, shadeatm, and topoatm. See Kirk et al. (2001).

The table below are photometric parameter values for Mars, adopted from Tomasko et al. (1999):

Band	Wha	Hga
Red	0.95	0.68
Blue	0.76	0.78

Type	combo
Default	NONE
Internal Default	NONE
Option List:	Option Brief Description NONE No Atmospheric Model No atmospheric correction will be applied. Exclusions HNORM BHA TAU TAUREF WHA HGA NULNEG ANISOTROPIC1 Anisotropic 1 atmospheric model Uses Chandrasekhar's solution for anisotropic scattering described by a one-term Legendre polynomial. Exclusions HGA Inclusions HNORM BHA TAU TAUREF WHA ANISOTROPIC2 Anisotropic 2 atmospheric model Uses Chandrasekhar's solution for anisotropic scattering described by a one-term Legendre polynomial. Exclusions HGA Inclusions HNORM BHA TAU TAUREF WHA HAPKEATM1 Hapke 1 Atmospheric Model Provides an approximation for strongly anisotropic scattering that is similar to Hapke's model for a planetary surface. The Chandrasekhar solution for isotropic scattering is used for the multiple scattering terms, and a correction is made to the singly scattered light for anisotropic particle phase function. A one-term Henyey Greenstein function is used. Exclusions BHA Inclusions HNORM HGA TAU TAUREF WHA HAPKEATM2 Hapke 2 atmospheric model Provides an approximation for strongly anisotropic scattering that is similar to Hapke's model for a planetary surface. The Chandrasekhar solution for isotropic scattering is used for the multiple scattering terms, and a correction is made to the singly scattered light for anisotropic particle phase function. A one-term Henyey Greenstein function is used. Exclusions BHA Inclusions HNORM HGA TAU TAUREF WHA ISOTROPIC1 Isotropic 1 atmospheric model Uses Chandrasekhar's solution for isotropic scattering. Exclusions HGA BHA Inclusions HNORM TAU TAUREF WHA ISOTROPIC2 Isotropic 2 atmospheric model Uses Chandrasekhar's solution for isotropic scattering. Exclusions HGA BHA Inclusions HNORM TAU TAUREF WHA

Description

This specifies if negative values after removal of atmospheric effects will be set to NULL. Negative values are only generated in modes that include atmospheric correction and occur when the optical depth "tau" is overestimated, so that the atmospheric radiance subtracted from the image is brighter than the darkest observed pixels. In this case "tau" should be decreased until no negative values are present in the output file.

Type	string
Default	READFROMPVL
Option List:	Option Brief Description READFROMPVL Get NULNEG value from the FROMPVL file Retrieve and set the NULNEG parameter from the FROMPVL file. An error is reported if a PVL file is not provided. NO Do not set negative values to NULL This option specifies not to set negative values to NULL after the removal of atmospheric effects. YES Negative values will be set to NULL This option specifies to set negative values to NULL after the removal of atmospheric effects.

Description

The normal optical depth of the atmosphere.

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	0.0 (inclusive)

Description

The reference value of tau to which the image will be normalized. This would normally be 0.0 unless one is interested in simulating a hazy atmosphere scene.

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	0.0 (inclusive)

Description

The coefficient of single particle Henyey Greenstein phase function. Henyey-Greenestein asymmetry parameter for atmospheric particle phase function, used in hapkeatm1 and hapkeatm2 atmospheric models. Not to be confused with corresponding parameter hg1 for the surface particles.

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	-1.0 (exclusive)
Maximum	1.0 (exclusive)

Description

The single scattering albedo of atmospheric particles.

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	0.0 (exclusive)
Maximum	1.0 (inclusive)

Description

The coefficient of the single particle Legendre phase function. Coefficient of p1 (cosine) term of atmospheric particle phase function, used in anisotropic1 and anisotropic2 atmospheric models. Not to be confused with corresponding coefficient bh for the surface particles.

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	-1.0 (inclusive)
Maximum	1.0 (inclusive)

Description

The atmospheric shell thickness normalized to the planet radius, used to modify angles to get more accurate path lengths near the terminator (Ratio of scale height to the planetary radius). For Mars MDIM2.1 mosaic "0.003" was defined, which is the only planet for which the atmospheric modes are currently used.

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	0.0 (inclusive)

Description

This is the name of the normalization model to be performed

FROMPVL

Get normalization model from the PVL file. If the parameter names and values are missing in the PVL file, then either add them to the PVL file, or enter the values at the command line, or use the GUI to enter the parameter values.

ALBEDOATM

Normalization with atmosphere. For each pixel, a model of atmospheric scattering is subtracted and a surface model is divided out, both evaluated at the actual geometry of the pixel. Then, the resulting value is multiplied by the surface function at the reference conditions and the atmospheric model at reference conditions is added. In normal usage, the reference condition has normal incidence (incref=0) and no atmosphere (tauref=0), but in some cases it may be desirable to normalize images to a different incidence angle or a finite optical depth to obtain a more uniform appearance. As with the albedo model, if topographic shading is present, it will be amplified more at high incidence angles and will not appear uniform.

ALBEDO

Normalization without atmosphere. Each pixel is divided by the model photometric function evaluated at the geometry of that pixel, then multiplied by the function at reference geometry with incidence and phase angles equal to incref and emission angle at 0 degree. This has the effect of removing brightness variations due to incidence angle and showing relative albedo variations with the same contrast everywhere. If topographic shading is present, it will be amplified more in regions of low incidence angle and will not appear uniform.

MIXED

Normalization without atmosphere. This option is used to perform albedo normalization over most of the planet, but near the terminator it will normalize the topographic contrast to avoid the seams that can occur with the usual albedo normalization. The two effects will be joined seamlessly at the incidence angle set for incmat. Incmat must be adjusted to give the best equalization of contrast at all incidence angles. The albedo parameter must also be adjusted so the topographically normalized regions at high incidence angle are set to an albedo compatible with the albedo-normalized data at lower incidence.

MOONALBEDO

Normalization without atmosphere specifically designed to work with lunar data using the LunarLambertMcEwen photometric function model. A photometric correction plus an albedo-dependent phase angle correction which varies with the value of each input DN will be applied. The final output value is the reflectance at incidence and phase angles of 30 degrees, and emission angle of 0 degrees.

The following are ISIS2 default values used in the past, but may be obsolete:

• D = 0.14
• E = -0.3575 * wavelength(WL) - 0.0607 if WL is less than 1.0: otherwise -0.4179
• F = 0.55
• G2 = -0.9585 * WL + 0.98 if WL is less than 1.0: otherwise 0.02
• Xmul = 1.0
• WL = get WL from labels
• H = 0.048
• BSH1 = 19.89 - 59.58 * WL + 59.86 * WL**2 - 20.09 * WL**3
• XB1 = -0.0817
• XB2 = 0.0081

SHADEATM

Normalization with atmosphere. The surface photometric function is used to simulate an image by relief shading, just like the shade model, but the effects of atmospheric scattering are also included in the calculation.

SHADE

Normalization without atmosphere. The surface photometric function is evaluated at the geometry of the image in order to calculate a shaded relief image of the ellipsoid or DEM. The radiance of the model surface is set to albedo at incidence angle defined by incref and zero phase. The image data are not used.

TOPOATM

Normalization with atmosphere. As with the topo model, this option is used in the final step of a three-step process: (1) normalize with the albedoatm model, incref=0, and tauref=0 to temporarily remove atmosphere and normalize albedo variations; (2) use divide filter to remove albedo variations and emphasize features; and (3) normalize with the topoatm model to undo the temporary normalization and equalize topographic shading.

TOPO

Normalization without atmosphere. This option is used to normalize the topographic shading to uniform contrast regardless of the incidence angle, and exagerates the albedo variations at large incidence angles. So, this model is used as part of a three-step process in which (1) the image is temporarily normalized for albedo; (2) a divide filter is applied to remove regional albedo variations and emphasize features; and (3) the image is renormalized with the topographic mode to reverse the first normalization and equalize topographic shading. The reference state in the first step must have incref=0 because this is what is reversed in the final step. If there are no significant albedo variations, step (2) can be skipped but step (1) must not be skipped.

Type	combo
Default	FROMPVL
Internal Default	FROMPVL
Option List:	Option Brief Description FROMPVL Get model from PVL file Get the normalization model from the PVL file. Add missing parameters to the PVL file, or enter the values at the command line, or use the GUI to enter the values. Exclusions INCREF INCMAT THRESH ALBEDO ATMNAME D E F G2 XMUL WL H BSH1 XB1 XB2 HNORM TAU WHA NULNEG TAUREF HGA BHA ALBEDOATM Albedo normalization model with atmosphere Albedo normalization with atmosphere. In normal usage, the reference condition has normal incidence (incref=0) and no atmosphere (tauref=0), but in some cases it may be desirable to normalize images to a different incidence angle or a finite optical depth to obtain a more uniform appearance. Exclusions INCMAT THRESH ALBEDO D E F G2 XMUL WL H BSH1 XB1 XB2 Inclusions ATMNAME INCREF ALBEDO Albedo normalization model Albedo normalization without atmosphere. This has the effect of removing brightness variations due to incidence angle and showing relative albedo variations with the same contrast everywhere. Exclusions ATMNAME D E F G2 XMUL WL H BSH1 XB1 XB2 HNORM TAU WHA NULNEG TAUREF HGA BHA Inclusions INCREF THRESH ALBEDO MIXED Mixed normalization model Mixed normalization without atmosphere. Used for albedo normalization over most of the planet, but near the terminator it will normalize topographic contrast so the two effects will be joined seamlessly at incidence angle defined for the incmat parameter. Exclusions ATMNAME D E F G2 XMUL WL H BSH1 XB1 XB2 HNORM TAU WHA NULNEG TAUREF HGA BHA Inclusions INCREF INCMAT THRESH ALBEDO MOONALBEDO Moon albedo normalization model This model was designed specifically for use on lunar data without atmosphere. It will compute normalized albedo for the Moon, normalized to 0 degrees emission angle and 30 degrees illumination and phase angles. Exclusions ATMNAME INCREF INCMAT THRESH ALBEDO HNORM TAU WHA NULNEG TAUREF HGA BHA Inclusions D E F G2 XMUL WL H BSH1 XB1 XB2 SHADEATM Shade normalization with atmosphere The surface photometric function is used to simulate an image by relief shading, just like the shade model, but the effects of atmospheric scattering are also included in the calculation. Exclusions INCMAT THRESH D E F G2 XMUL WL H BSH1 XB1 XB2 Inclusions ATMNAME INCREF ALBEDO SHADE Shade normalization model Normalization without atmosphere. The surface photometric function is evaluated at the geometry of the image in order to calculate a shaded relief image of the ellipsoid or DEM. The radiance of the model surface is set to albedo at incidence angle defined for incref and zero phase. The image data is not used. Exclusions ATMNAME INCMAT THRESH D E F G2 XMUL WL H BSH1 XB1 XB2 HNORM TAU WHA NULNEG TAUREF HGA BHA Inclusions INCREF ALBEDO TOPOATM Topographic normalization with atmosphere Normalization with atmosphere. As with the topo atmospheric model, this option is used in the final step of a three-step process. Exclusions INCMAT THRESH D E F G2 XMUL WL H BSH1 XB1 XB2 Inclusions ATMNAME INCREF ALBEDO TOPO Topographic normalization model Normalization without atmosphere. Used to normalize topographic shading to uniform contrast regardless of the incidence angle. Such a normalization would exagerate albedo variations at large incidence angles, so this model is used as part of a three-step process. Exclusions ATMNAME INCMAT D E F G2 XMUL WL H BSH1 XB1 XB2 HNORM TAU WHA NULNEG TAUREF HGA BHA Inclusions INCREF THRESH ALBEDO

Description

This is the reference incidence angle to which the image will be normalized. Most normalization modes attempt to normalize the appearance of the surface to a set of standard conditions, in particular, a fixed incidence angle given by the incref parameter. In most cases, a value of 0 degrees is used for albedo and albedoatm normalization modes, though 30 degrees is sometimes used. Incref of 0 degrees is also the usual choice for specifying the albedo of shaded relief images calculated with shade and shadeatm normalization modes. Incref of 30 degrees is the standard value for topographic normalization modes topo and topoatm because topographic shading disappears at 0 degree incidence angle and cannot be normalized to this value.

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	0.0 (inclusive)
Maximum	90.0 (exclusive)

Description

This specifies the incidence angle where albedo normalization transitions to topographic normalization. When mixed normalization mode is selected, the image will be normalized so that albedo variation is constant for small incidence angles and topographic shading is constant for large incidence angles. This parameter must be set by trial and error to achieve the best appearance, because it depends on the relative amount of albedo variations and shading for any given planet or satellite. The value of the albedo parameter must also be adjusted for this mode to match the mean brightness of the high incidence angle region to that of the data at lower incidence angles.

Type	string
Default	None Specified
Internal Default	None Specified
Minimum	0.0 (inclusive)
Maximum	90.0 (exclusive)

Description

This sets upper limit on the amount of amplification in regions of small incidence angle. Operating modes that involve topographic normalization topo, topoatm, and mixed options will amplify variations in the input image in regions of small incidence angle where the shading in the input image is weak. Thresh is an upper limit on the amount of amplification that will be attempted. If it is set too low, low-incidence areas of the image may appear bland, but if thresh is set too high these regions may contain amplified noise rather than useful shading information.

Type	string
Default	None Specified
Internal Default	None Specified

Description

The albedo to which the image will be normalized. The value of the desired model albedo, used with shade, topo, mixed, shadeatm, and topoatm. This is the albedo (I/F value at incidence angle defined for incref and zero phase) used to simulate a shaded relief image when shade or shadeatm normalization models are used. For the other modes, it is the albedo that the image will be normalized to have. The program stats can be run to get the average albedo of an input image, but for constructing mosaics the same value of albedo should be used for all images in order to achieve a uniform result.

Type	string
Default	None Specified
Internal Default	None Specified

Description

This is the empirically derived coefficient for the albedo dependent phase function normalization parameter.

Type	string
Default	None Specified
Internal Default	None Specified

Description

This is the empirically derived coefficient for the albedo dependent phase function normalization parameter.

Type	string
Default	None Specified
Internal Default	None Specified

Description

This is the empirically derived coefficient for the albedo dependent phase function normalization parameter.

Type	string
Default	None Specified
Internal Default	None Specified

Description

This is the empirically derived coefficient for the albedo dependent phase function normalization parameter.

Type	string
Default	None Specified
Internal Default	None Specified

Description

This is the empirically derived coefficient for the albedo dependent phase function normalization parameter.

Type	string
Default	None Specified
Internal Default	None Specified

Description

This is used to convert radiance to reflectance, or apply a calibration fudge factor.

Type	string
Default	None Specified
Internal Default	None Specified

Description

The wavelength in micrometers of the image being normalized.

Type	string
Default	None Specified
Internal Default	None Specified

Description

This is the empirically derived coefficient for the albedo dependent phase function normalization parameter.

Type	string
Default	None Specified
Internal Default	None Specified

Description

This is the empirically derived coefficient for the albedo dependent phase function normalization parameter.

Type	string
Default	None Specified
Internal Default	None Specified

Description

This is the empirically derived coefficient for the albedo dependent phase function normalization parameter.

Type	string
Default	None Specified
Internal Default	None Specified

This example shows the photometric correction of a cube file using the hapkehen (Hapkehen) photometric model and the albedo normalization model without trimming the image data based on incidence or emission angle.

photomet from=EW0131773041G_cal.cub to=EW0131773041G_cal_hapkehen_albedo.cub frompvl=photomG.pvl phtname=hapkehen theta=9 wh=0.218651 hg1=0.178965 hg2=0.971493 hh=0.085 b0=2.7 normname=albedo incref=0 thresh=1e+31 albedo=1.0

photomet GUI

Example GUI Screenshot of GUI version of the application. The default value for the MAXEMISSION and MAXINCIDENCE parameters is 90.0. The parameter values were loaded into the appropriate parameter names using the drop-down menu for the "FROMPVL" parameter name.

Input image

Input file Parameter Name: FROM Screenshot of the input image before the photometric correction has been performed.

Example of a PVL file	The PVL file contains the photometric parameters to be applied to the input cube file. Load the PVL file parameters using the photomet GUI drop-down menu and add the additional required parameter value for "ALBEDO."

Output image

Output file Parameter Name: TO Screenshot of the output image after the photometric correction. Notice the features have consistent tones except near the limb where the pixels are brighter because it is over-corrected. A histogram stretch is applied automatically when the image is displayed, so the image appears darker due to the higher DN values at the terminator.

This example shows the photometric correction of a cube file by using the hapkehen (Hapkehen) photometric model and mixed normalization model that performs an albedo normalization for most of the planet, and transitions to a topographic normalization at 75 degrees. Adjust the INCMAT parameter value to get the best equalization of contrast at all incidence angles.

photomet 0131773041G_cal.cub to=EW0131773041G_cal_hapkehen_mixed.cub frompvl=photomG.pvl phtname=hapkehen theta=9 wh=0.218651 hg1=0.178965 hg2=0.971493 hh=0.085 b0=2.7 normname=mixed incref=0 incmat=75 thresh=30.0 albedo=0.0

photomet GUI

Example GUI Screenshot of GUI version of the application. The default value for MAXEMISSION and MAXINCIDENCE parameters is 90.0, but the INCMAT parameter is set to 75 degrees.

Input image

Input file Parameter Name: FROM Screenshot of the input image before the photometric correction has been performed.

Example of the PVL file	The PVL file containing the photometric parameters to be applied to the input cube. Load the PVL file parameters using the photomet GUI and add additional required parameter values for "INCMAT" and "ALBEDO."

Output image

Output file Parameter Name: TO Screenshot of the output image after the photometric correction. Notice the limb area was over-corrected in the previous example, but now shows more consistent tones in the output image.

This example shows the photometric correction of a cube file using the hapkehen (Hapkehen) photometric model and a mixed normalization model that performs an albedo normalization for most of the planet, but will also trim the image data beyond 75.0 degrees incidence angle. This is to show where the transition between the two types of normalization occurred in the previous example.

photomet from=EW0131773041G_cal.cub to=EW0131773041G_cal_hapkehen_mixed_trim_at75.cub frompvl=photomG.pvl maxincidence=75 phtname=hapkehen theta=9 wh=0.218651 hg1=0.178965 hg2=0.971493 hh=0.085 b0=2.7 normname=mixed incref=0 incmat=75 thresh=30.0 albedo=0.0

photomet GUI settings

Example GUI Screenshot of GUI version of the application. The MAXEMISSION is set to 90.0; the MAXINCIDENCE and INCMAT parameters are set to 75.0 degrees.

Input image

Input file Parameter Name: FROM Screenshot of the input image before the photometric correction has been performed.

Example of the PVL file	The PVL file containing the photometric parameters to be applied to the input cube file. Load the PVL file parameters using the photomet GUI and add additional required parameter values for "INCMAT" and "ALBEDO."

Output image

Output file Parameter Name: TO Screenshot of the output image after the photometric correction. Notice the limb area, where it was over-corrected in the first example, has been trimmed.

This example shows the photometric correction of a cube file by setting the maximum emission angle to 75.0 degrees and the maximum incidence angle to 85.0 degrees. The photometric model and normalization model along with the parameter values are defined in the input PVL file. This example uses a PVL file that follows the format for a previous ISIS3 release. The photomet program will recognize some older formats and parameter names, but if an error is returned, then update the settings using the latest parameter names and/or options listed in the tables under "DESCRIPTION."

photomet from=input.cub frompvl=input.pvl to=output.cub maxemission=75.0 maxincidence=85.0

photomet GUI

Example GUI Screenshot of GUI version of the application. Notice the MAXEMISSION and MAXINCIDENCE parameters are changed from the default value of 90.0.

Input image

Input file Parameter Name: FROM Screenshot of the input image before the photometric correction has been performed.

Input PVL file	The PVL file contains the input photometric parameters for the input file.

Output image

Output file Parameter Name: TO Screenshot of the output image after the photometric correction. Notice the output image has been trimmed based on the photometric angles defined by the user.

This example shows the photometric correction of a cube file by setting the maximum emission angle to 75.0 degrees and the maximum incidence angle to 85.0 degrees. The photometric model being used is MINNAERT and the normilization model is ALBEDO. The usedem parameter is describing how to trim the image. In this case the trimming is being done using the radius obtained from the DEM. The anglesource parameter describes how to calculate the photometric angles. In this example the calculation is also being done using the DEM.

photomet photomet from=uncropped.cub to=TrimmedTestAngleSourceDemUsedemFalse.cub maxemission=87.0 anglesource=dem phtname=minnaert k=0.5 normname=albedo incref=0 incmat=80 thresh=30 albedo=1.0

photomet GUI

Example GUI Screenshot of GUI version of the application. Notice the MAXEMISSION has changed from the default value of 90.0, usedem is set to it's default, and anglesource is set to DEM.

Input image

Input file Parameter Name: FROM Screenshot of the input image before the photometric correction has been performed.

Output image

Output file Parameter Name: TO Screenshot of the output image after the photometric correction. Notice the output image has been trimmed based on the photometric angles defined by the user.

A multistep process is used to apply photometric correction to Mars images:

1. Photomet is run in albedo mode, which decreases brightness variations across the individual image and removes the additive atmospheric contribution, if any;
2. The output image from step 1 is divided by a low-pass-filtered version of itself, which removes albedo variations if they have broader spatial scales than topographic shading as is often the case; and
3. Photomet is run again on the output image of step 2 in topography mode, which undoes the albedo normalization of the first pass and then applies the topographic normalization.

The final result would need to be equalized and mosaicked together.

Sample script	This script contains the three-step processing sequence of programs that need to be executed for the three test images.

Input and output images

Collage of images The images shown are subareas at 1:1 scale to emphasize the result of the photometric correction at each stage. There are four rows in the image collage containing the following: Row 1 - Calibrated images without photometric correction Row 2 - Applied Hapkehen photometric model, albedoatm normalization model and an hapkeatm2 atmospheric model Row 3 - Applied a divide filter Row 4 - Applied Hapkehen photometric model, topoatm normalization model and an hapkeatm2 atmospheric model