photomet Documentation
Isis 2 Documentation
photomet Documentation
PHOTOMET - Perform photometric corrections on a cube. Photometrically normalize an image cube for mosaicking or other applications. Users can choose options for the following three aspects of the calculation independently: 1) Surface photometric function model type and parameter values. See the documentation for parameter FUNC. 2) Atmospheric photometric function model type and parameter values. See the documentation for parameter ATMOS. 3) Type of normalization to be performed (e.g., simulation of an image by shaded relief calculation, or equalization of albedo contrasts, topographic shading, or a combination, with or without accounting for an atmosphere. See the documentation for parameter GENMOD. Note that this program trims the output cube at incidence angles greater than or equal to 90 degrees and emission angles greater than or equal to 90, except for some topo models. This is because without a topographic model of the surface it isn't possible to return a meaningful photometric correction with incidence or emission angles over 90 degrees. References cited in individual help entries: 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 spectroscopy 3: 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 photo- clinometry and other applications. Icarus, 92, pp. 298-311. Tanaka, K. L., and and Davis, P. A., 1988, Tectonic History of the Syria Planum Provice of Mars, J. Geophys. Res., 93, 14,893. 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 PROGRAMMER: K Teal Thompson, U.S.G.S., Flagstaff, AZ
| Parm | Description | Default |
|---|---|---|
| FROM | Input cube name | NONE |
| SFROM | Input subcube specifier | -- |
| TO | Output cube name | NONE |
| GENMOD | Type of normalization performed
NONE No photometry (trim only)
SHADE Shaded relief model
ALBEDO Albedo contrasts uniform
TOPO Topo shading uniform
MIXED Mixed: albedo at low inc
Blending to topo at high
SHDAT Shaded relief with atmos
ALBAT Albedo with atmosphere
TOPAT Topo shading with atmos
LUNAR Special lunar model
USER User-specified calc
| ALBEDO |
| PHOTODEM | Use inc/ema/phase angles from DEM vs ellipsoid? (YES/NO) | NO |
| PHOTOBKP | Read inc/ema/phase angles from backplanes? (YES,NO) ________________________________ Surface photometric fn params | NO |
| FUNC | Type of photometric function model used for surface: LAMBER, LOMSEL, MIN, LUNLAM, MN_EMP, LL_EMP, HAPHEN, HAPLEG, HAPH_S, HAPL_S, USER, NONE | LUNLAM |
| K | Minnaert exponent for MIN | -- |
| L | Lunar-Lambert weight for LUNLAM | -- |
| DATAFILE | File containing table of parameter values vs. phase for LL_EMP, MN_EMP | -- |
| WH | Single-scattering albedo for HAPHEN, HAPLEG, HAPH_S, HAPL_S | -- |
| HH | Opposition surge width for HAPHEN, HAPLEG | -- |
| B0 | Opposition surge strength for HAPHEN, HAPLEG | -- |
| THETA | Macroscopic surface roughness in degrees, for HAPHEN, HAPLEG | -- |
| HG1 | Henyey-Greenstein asymmetry parameter for single particle phase function in HAPHEN, HAPH_S | -- |
| HG2 | 2nd Henyey-Greenstein parameter controls mix of +HG1, -HG1 components for HAPHEN, HAPH_S | -- |
| BH | Coefficient of P1(cos(phase)) in Legendre single particle phase function for HAPLEG, HAPL_S | -- |
| CH | Coefficient of P2(cos(phase)) in Legendre single particle phase function for HAPLEG, HAPL_S | -- |
| USRARA | Up to 9 variables to be passed to user subroutine for FUNC=USER | -- |
| OBJNAM | Name of user-supplied photometric subroutine ________________________________ Atmospheric photometric params GENMOD=ALBAT, TOPAT, SHDAT only | -- |
| ATMOS | Type of atmospheric scattering model I1 1st approx. Isotropic I2 2nd approx. Isotropic A1 1st approx. Anisotropic A2 2nd approx. Anisotropic H1 1st approx. Hapke H2 2nd approx. Hapke | H2 |
| TAU | Normal atmospheric optical depth (estimated actual value) | -- |
| TAUREF | Reference value of TAU to which image will be normalized. | 0.0 |
| WHA | Single-scattering albedo of atmospheric particles. | -- |
| WHAREF | Reference value of WHA to which image will be normalized. Optional, defaults to WHA. | -- |
| BHA | Used only with ATMOS=A1, A2. Coeff of P1(phase) in single particle Legendre phase fn. | -- |
| BHAREF | Used only with ATMOS=A1, A2. Reference value of BHA to which image will be normalized. Optional, defaults to BHA. | -- |
| HGA | Used only with ATMOS=H1, H2 Coeff of single particle Henyey-Greenstein phase fn. | -- |
| HGAREF | Used only with ATMOS=H1, H2 Reference value of HGA to which image will be normalized. Optional, defaults to HGA. | -- |
| HNORM | Atmospheric shell thickness normalized to planet radius. Default 0.003 is for Mars. | 0.003 |
| NULNEG | If TRUE, negative values after removal of atmospheric effects will be set to NULL. ________________________________ Parameters for trimming, used in any mode but esp GENMOD=NONE | NO |
| INC | Incidence angle boundary in degrees, must be < 90 | -- |
| EMA | Emission angle boundary in degrees, must be < 90 | -- |
| TRIMANG | Distance (deg) of trim from center at CLAT, CLON | -- |
| CLAT | Latitude of center of trim with TRIMANG parameter | -- |
| CLON | Longitude of center of trim with TRIMANG parameter | -- |
| RLAT | Latitude range for trim | -- |
| RLON | Longitude range for trim ________________________________ Parameters for various modes | -- |
| ALBEDO | Albedo of output for GENMOD= SHADE, TOPO, MIXED, SHDAT, TOPAT | -- |
| INCMAT | For GENMOD=MIXED, inc angle where albedo & topo contrasts will be made equal | -- |
| INCREF | Reference incidence angle to which image photometry will be normalized (not trimmed) For SHADE, ALBEDO, SHDAT, ALBAT, use 0 (default) For TOPO, TOPAT use 30 | 0.0 |
| THRESH | Maximum factor by which to increase image contrast Important for GENMOD=TOPO, MIXED ________________________________ Parameters for GENMOD=LUNAR | 30.0 |
| MOONOPT | Choose a particular lunar option PHOTOM, ALBEDO, or NOALBEDO | PHOTOM |
| D | Empirically derived coefficient Used only with MOONOPT=ALBEDO | -- |
| E | Empirically derived coefficient Used only with MOONOPT=ALBEDO | -- |
| F | Empirically derived coefficient Used only with MOONOPT=ALBEDO | -- |
| G2 | Empirically derived coefficient Used only with MOONOPT=ALBEDO | -- |
| XMUL | Used to convert radiance to reflectance or apply calibration fudge factor Used only with MOONOPT=ALBEDO | -- |
| WL | Wavelength in micrometers Used only with MOONOPT=ALBEDO | -- |
| H | Empirically derived coefficient Used only with MOONOPT=ALBEDO | -- |
| BSH1 | Empirically derived coefficient Used only with MOONOPT=ALBEDO | -- |
| XB1 | Empirically derived coefficient Used only with MOONOPT=ALBEDO | -- |
| XB2 | Empirically derived coefficient Used only with MOONOPT=ALBEDO |
ADDITIONAL NOTES:
| Parm | Description |
|---|---|
| FROM | Filename of input cube. The input cube can be in camera geometry (Level 1) or any map projection. |
| SFROM | SFROM specifies the subcube using a single string for all three dimensions of the cube. The order of the three dimensions is always "samples:lines:bands". If a dimension is left blank, all the data for that dimension is selected. The default value of NULL for SFROM selects the entire cube. Any application below can be used for any dimension. To select specific data from any dimension: "10-100(3):11,12,15-20:1-10(2)" = This example will select every third sample starting with sample 10 thru 100. It selects lines 11 and 12, and 15-20. It selects every other band, starting with band 1 thru 10. There are special characters that can be used for selecting a subcube efficiently, such as "*","#", and "~". For examples type "help sfrom" in TAE. **NOTE** For more examples and explanation of the many features of the SFROM parameter, tutor the sfrom.pdf or refer to Introduction To ISIS, Section 6, of the ISIS User's Manual ** |
| TO | Filename of output cube. |
| PHOTODEM | Determines if incidence and emission angles based on a digital elevation model (DEM) will be used instead of the angles for the reference ellipsoid in calculations of the surface photometry. Even if PHOTODEM=YES, the incidence angles for the ellipsoid will be used in the atmospheric part of the calculation (if any); the phase angle is the same for both DEM and ellipsoid. If PHOTODEM=YES and PHOTOBCK=NO, then the FROM image labels will be searched for the PHOTO_DEM keyword and the keyvalue found will be used as the name of a DEM file used to calculate the angles on the fly. If the keyword is not found or the file is not found, an error will occur. The PHOTO_DEM keyword is set in the labels using the levsetlab program. The DEM file must contain values of planetary radius rather than height relative to the reference surface. If PHOTODEM=YES and PHOTOBCK=YES, then the program will attempt to read the DEM-derived incidence and emission angle backplanes from the FROM file. These backplanes can be created by running levsetlab to set the PHOTO_DEM keyword and then running levgeoplane or lev1geoplane. |
| PHOTOBKP | Determines if the incidence, emission, and phase angles
will be read from image backplanes rather than calculated
on the fly for each pixel. The backplanes needed depend
on the value of PHOTODEM and GENMOD selected, and if the
required planes are not found, an error will occur. The
backplanes can be created by running levgeoplane or
lev1geoplane. If PHOTODEM=YES then levsetlab must first
be run to set the PHOTO_DEM keyvalue in the labels to the
name of the DEM file to be used in calculating surface
photometric angles.
Setting PHOTOBCKP=YES is the only way to run photomet on
Level 2 image mosaics. All backplanes needed for the
intended processing must be created for each Level 1 image
separately. They will then be propagated through the
map projection and mosaicking steps.
The required backplanes are as follows. "Atmosphere?"
is "yes" for the set of GENMOD modes using the atmosphere
(SHDAT, ALBAT, and TOPAT) and "no" for the remaining modes.
PHOTODEM PHOTOBCK Atmosphere? Required backplanes
________ ________ ___________ ___________________
either NO either none
NO YES either INC, EMA, PHASE
YES YES no DEMINC, DEMEMA, PHASE
YES YES yes INC, DEMINC, EMA, DEMEMA,
PHASE
|
| GENMOD | This parameter governs the type of normalization that will be applied to the image. Any surface photometric function (FUNC) and atmosphere model (ATMOS) can be used with any mode, though only the atmospheric modes SHDAT, ALBAT and TOPAT make use of the atmospheric model, and modes NONE and LUNAR ignore both the atmosphere and surface function. The modes include those familiar from PICS and early ISIS (PHOTOM) and several new modes: NONE No photometry (trim image based on incidence and emission angles and latitude and longitude only) SHADE The surface photometric function is evaluated at the geometry of the image FROM in order to calculate a shaded relief image of either the ellipsoid or DEM data. The radiance of the model surface is set to ALBEDO at incidence angle INCREF and zero phase. The image data are not used. ALBEDO This is the normalization mode familiar from PICS and early ISIS programs PHOTOM. 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 0. 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, however, it will be amplified more in regions of low incidence angle and will not appear uniform. This mode does not incorporate any corrections for atmospheric scattering. TOPO This mode is used to normalize topographic shading to uniform contrast regardless of incidence angle, as described by Kirk et al. (2000). Such a normalization would exaggerate albedo variations at large incidence angles, so this mode is used as part of a three step process in which (1) the image is temporarily normalized for albedo; (2) a highpass divide filter is used to remove regional albedo variations; and (3) the image is renormalized with TOPO mode to undo the first normalization and equalize topographic shading. The reference state in the first step MUST have INCREF=0 because this is what is undone in the final step. If there are no significant albedo variations, step (2) can be skipped but step (1) must not be. Example pdf: procedure local albedo real body !Do first pass with albedo option photomet from=c4400357.lv1 to=c4400357.1stpass l=.44 genmod=albedo atmos=i1 func=lunlam incref=0.0 !Do divide filter boxfilter from=c4400357.1stpass to=c4400357.filter filter=div samp=51 line=51 band=1 !Get average dn after the divide filter for topo model avg_sd from=c4400357.filter option=avg avg=albedo !Do second pass with topo option photomet from=c4400357.filter to=c4400357.ll.top.lv1 l=.44 genmod=topo func=lunlam albedo=&albedo incref=30.0 end-proc MIXED Mixed albedo/topo w/o atmosphere This mode will do albedo normalization over most of the pla- net but near the terminator it will normalize topographic contrast to avoid the "seams" that can occur with the usual albedo normalization. The two effects will be joined seamlessly at incidence angle INCMAT. This parameter must be adjusted to give the best equalization of contrast at all incidence angles. Parameter ALBEDO 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. SHDAT The surface photometric function is used to simulate an image by relief shading, as for SHADE, but the effects of atmospheric scattering are also included in the calculation. ALBAT Albedo normalization with atmosphere. For each pixel, a model of atmospheric scattering (Kirk et al., 2000, 2001) 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 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 mode ALBEDO, if topographic shading is present, it will be amplified more at high incidence angles and will not appear uniform. TOPAT Topographic normalization with atmosphere. As with the similar TOPO mode, this option is used in the final step of a three-step process: (1) normalize with mode ALBAT, INCREF=0, and TAUREF=0 to temporarily remove atmosphere and normalize albedo variations; (2) use highpass divide filter to remove albedo variations; and (3) normalize with TOPAT mode to undo temporary normalization and equalize topographic shading. See also documentation for TOPO, ALBAT modes. LUNAR Special lunar mode similar to current ALBEDO mode that does iterative, self-consistent solution for normal albedo and appropriate phase correction for that normal albedo. This mode ignores FUNC and ATMOS and the values of the "normal" photometric parameters that go with them. See MOONOPT for further information. A published reference for this model is not currently available. |
| FUNC | This parameter selects the type of photometric function
model used to describe the planetary surface. Any surface
photometric function can be used in combination with any
of the operational modes (GENMOD) and, for the modes that
include correction for atmospheric scattering, any type
of atmospheric photometric model (ATMOS). The parameters
used differ between the photometric functions.
PHOTOMETRIC FUNCTIONS
TAE Full name Parameters
___ _________ __________
LAMBER Lambert none
LOMSEL Lommel-Seeliger ("lunar") none
LUNLAM Lunar-Lambert function L
MIN Minnaert function K
LL_EMP Lunar-Lambert empirical DATAFILE
MN_EMP Minnaert function DATAFILE
HAPHEN Hapke - Henyey-Greenstein WH,HG1,HG2,
HH,B0,THETA
HAPLEG Hapke - Legendre WH,BH,CH,
HH,BH,THETA
HAPH_S Hapke - Henyey-Gr. smooth WH,HG1,HG2
HAPL_S Hapke - Legendre smooth WH,BH,CH
USER User-linked subroutine USRARA,OBJNAM
NONE Trim only none
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
Lommel-Seeliger
FUNC=u0/(u0+u)
Minnaert
FUNC=u0**K * u**(K-1)
Lunar-Lambert ("lunar" part is Lommel-Seeliger)
FUNC=(1-L)*u0 + 2*L*u0/(u0+u)
Minnaert empirical
FUNC=B(phase) * u0**K(phase) * u**(K(phase)-1)
Lunar-Lambert empirical
FUNC=B(phase) * ((1-L)*u0 + 2*L*u0/(u0+u))
Used with the two empirical functions, the file
named in DATAFILE contains a table of triplets of
phase, B(phase), and K(phase) or L(phase). These
values will be spline-interpolated to calculate B
and K or L at the needed phase angles. The program
pho_emp_global can be used to calculate values of
B and K or L that will provide a fast approximation
to Hapke's model with any particular set of parameter
values. See description of DATAFILE for formatting
of the file and examples and McEwen (1991) for the
original description of these fast approximate
photometric functions.
Hapke - Henyey-Greenstein
Complete Hapke (1981; 1984; 1986) photometric 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.
Hapke - Legendre
Similar to the previous except that the single particle
phase function is a two-term Legendre polynomial with
coefficients BH and CH.
Hapke - Henyey-Greeenstein smooth
Substantially simplified version of Hapke-Henyey-Greenstein
function that omits the opposition effect as well as the
(very slow) macroscopic roughness correction. For a smooth
model with opposition effect, use the full Hapke-Henyey
function with THETA=0.
Hapke - Legendre smooth
Simplified Hapke model with Legendre single particle phase
function, no opposition surge, and no roughness correction.
McEwen (1991) has compiled Hapke parameter estimates for
many planets and satellites from a variety of sources.
The following Hapke parameters for Mars are 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)
Band WH B0 HH HG1 HG2
Red 0.52 0.025 0.170 0.213 1.000
Green 0.29 0.290 0.170 0.190 1.000
Blue 0.16 0.995 0.170 0.145 1.000
Kirk et al. (2000) found that Mars whole-disk limb-darkening
data of Thorpe (1973) are consistent with THETA=30, but
results of Tanaka and Davis (1988) based on matching
photoclinometry of local areas to shadow data are more
consistent with THETA=20 when the domain of the fit is
restricted to small emission angles (=< 20 degrees).
User
To make the user subroutine copy the source code skeletons:
$ISISDATA/my_pht_userF.F
$ISISDATA/my_pht_user_bind_F.c
$ISISDATA/make_my_pht_user
to your area.
The binder my_pht_user_bind_F.c is written in C programming
language. The subroutine my_pht_userF.F is written in For-
tran programming language. It is in this file that the user
must replace the existing test Lunar-Lambert code with the
desired photometric calculations. The make file
make_my_pht_user is then used to build the object from the
source files my_pht_user_bind_F.c and my_pht_userF.F.
bug{151}> make -f make_my_pht_user
where "bug{151}>" represents the command line prompt.
|
| K | Exponent that governs limb-darkening in the Minnaert
photometric function: FUNC=u0**K * u**(K-1). Values
generally fall in the range from 0.5 ("lunar-like",
almost no limb darkening) to 1.0 (Lambert function).
|
| L | Weight that governs limb-darkening in the Lunar-Lambert photometric function: FUNC=(1-L)*u0 + 2*L*u0/(u0+u). Values generally fall in the range from 0 (Lambert function) to 1 (Lommel-Seeliger or "lunar" function). |
| DATAFILE | User datfile from which photomet loads the photometric func- tion parameters for the Minnaert empirical (MN_EMP) and lunar-Lambert empirical (LL_EMP) functions, which use a table to describe how the parameters of the empirical function vary with phase angle. Program pho_emp_global can be used to calculate the parameter values that best approximate a Hapke model with a given set of parameters. The file may contain sets of values for both functions, generally intended to represent the same Hapke model (same planetary surface). Here is an example for Mars. Some carriage returns have been added to make this example fit into the PDF documentation and must be removed if the file is to be used. ################################################## ## File: ~/$ISISDATA/photom.marsred.sav ## ## Description: This file is the Mars lookup ## ## file for default photometric correction ## ## parameters for the photometric correction ## ## program, "photomet". This file contains ## ## Lunar-lambert and Minnaert empirical fits ## ## to a Hapke model for Mars in the red band ## ## wh=0.52, hh=b0=0, theta=30.0, hg1=0.213, ## ## hg2=1.0. Parameters are based on Johnson ## ## et al. (1999) Hapke fits to MPF IMP images## ## of Mermaid dune, with opposition surge set## ## to zero and roughness adjusted to 30 deg ## ## based on Kirk et al. (2000) ## ## Author: Randolph L Kirk ## ## Data: Randolph L Kirk ## ## Date of Last Revision: 2003 Jul 07 ## ################################################## ## Use # at the beginning of the line for ## ## comments. ## ## Use , to delineate the coefficient values. ## ## New line starts new parameter. ## ## formatting for coeffs: (f15.8) ## ## declaration for coeffs: real*8 ## ## declaration for line: character*256 ## ################################################## LUNAR_LAMBERT_EMP # number of coefficients for Empirical Lunar Lambert L approximation numllcoef=19 # the angles at which the coefficient values for Empirical Lunar Lambert L # approximation are calculated (ALL ON ONE LINE!) Count should = numllcoef. llphase =0.,10.,20.,30.,40.,50.,60.,70.,80.,90.,100.,110.,120.,130., 140.,150.,160.,170.,180. #the values for Empirical Lunar Lambert L (ALL ON ONE LINE!) lval =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 #number of coefficients for Empirical Lunar Lambert B approximation numbeecoef=19 # the angles at which the coefficient values for Empirical Lunar Lambert B # approximation are calculated (ALL ON ONE LINE!) Count shou ld = numbeecoef. bphase=0.,10.,20.,30.,40.,50.,60.,70.,80.,90.,100.,110.,120.,130., 140.,150.,160.,170.,180. #the values for Empirical Lunar Lambert B (ALL ON ONE LINE!) bval=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. END MINNAERT_EMP numkaycoef=19 kayphase =0.,10.,20.,30.,40.,50.,60.,70.,80.,90.,100.,110.,120.,130., 140.,150.,160.,170.,180. kval =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 numbeecoef=19 bphase=0.,10.,20.,30.,40.,50.,60.,70.,80.,90.,100.,110.,120.,130., 140.,150.,160.,170.,180. bval=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. END (end of DATAFILE example) |
| WH | Single-scattering albedo of surface particles, used if FUNC=HAPHEN, HAPLEG, HAPH_S, or HAPL_S. See Hapke (1981). Not to be confused with albedo WHA of the atmospheric particles. |
| B0 | Magnitude of the opposition effect for the surface, used if FUNC=HAPHEN, HAPLEG, HAPH_S, or HAPL_S. See Hapke (1984). |
| HH | Width parameter for the opposition effect for the surface, used if FUNC=HAPHEN, HAPLEG, HAPH_S, or HAPL_S. See Hapke (1984). |
| THETA | "Macroscopic roughness" of the surface as it affects the photometric behavior, used if FUNC=HAPHEN or HAPLEG. 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 will be evaluated if THETA is given any value other than 0.0, is extremely slow. |
| HG1 | Asymmetry parameter used in the Henyey-Greenstein model
for the scattering phase function of single particles
in the surface, used if FUNC=HAPHEN or HAPH_S. 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
|
| HG2 | Second parameter of the two-parameter Henyey-Greenstein model for the scattering phase function of single particles in the surface, used if FUNC=HAPHEN or HAPH_S. This parameter controls a 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. |
| BH | When FUNC=HAPLEG or HAPL_S, 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 ATMOS=A1 or A2. |
| CH | When FUNC=HAPLEG or HAPL_S, 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)) |
| USRARA | USRARA (user array) allows the user to enter up to nine real values that will be passed to the USER subroutine as working variables. Within the USER subroutine, the user must remem- ber to "label" each value of USRARA accordingly for later reference in the printer output. Also note that the values of USRARA can change or be used as constants in the USER subroutine. |
| OBJNAM | This is the name that the user has assigned to the subroutine they have supplied to evaluate their surface photometric function. |
| ATMOS | Only used with GENMOD=SHDAT, ALBAT, or TOPAT, this parameter Controls the type of model used for atmospheric photometric correction. I1, A1, H1 all use the first order scattering approximation, whereas I2, A2, H2 use the second order approximation, and so are slower but more accurate and are generally preferred. Models I1 and I2 use Chandrasekhar's (1960) solution for isotropic scattering. They require only the parameters TAU, WHA, and HNORM, plus the corresponding values at the reference condition that the image will be normalized to, TAUREF and WHAREF. Models A1 and A2 use Chandrasekhar's solution for anisotropic scattering described by a one-term Legendre polynomial. The coefficient of this term BHA and the value for the reference condition BHAREF are required in addition to the parameters also used by the anisotropic models. The anisotropy of the Legendre function is fairly weak so the Hapke models are preferred as a description of the martian atmosphere. Models H1 and H2 are an approximation for strongly anisotropic scattering that is similar in spirit 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. In particular, a one-term Henyey- Greenstein function with parameter HGA (and HGAREF in the reference condition the image is normalized to) is used. The parameters used by the isotropic models are also required. See Kirk et al. (2001). Values of the photometric parameters for Mars, adopted from Tomasko et al. (1999) are: Band WHA HGA Red 0.95 0.68 Blue 0.76 0.78 |
| TAU | Normal optical depth of atmosphere. |
| TAUREF | Normal optical depth of atmosphere assumed for the reference condition to which the image will be normalized. This would normally be 0 unless one is interested in simulating a hazy atmosphere scene. |
| WHA | Single-scattering albedo of atmospheric particles, used in all atmospheric models. Not to be confused with albedo WH of the surface particles. |
| WHAREF | Single-scattering albedo of atmospheric particles assumed for the reference condition to which the image will be normalized, used in all atmospheric models. If no value is given, WHAREF will be set equal to WHA. Not to be confused with albedo WH of the surface particles. |
| BHA | Coefficient of P1 (cosine) term of atmospheric particle phase function, used in A1 and A2 atmosphere models. Not to be confused with corresponding coefficient BH for the surface particles. |
| BHAREF | Coefficient of P1 (cosine) term of atmospheric particle phase Function in the reference condition to which the image will be normalized, used in A1 and A2 atmosphere models. If no value is given, BHAREF will be set equal to BHA. Not to be confused with corresponding coefficient BH for the surface particles. |
| HGA | Henyey-Greenestein asymmetry parameter for atmospheric particle phase function, used in H1 and H2 atmosphere models. Not to be confused with corresponding parameter HG1 for the surface particles. |
| HGAREF | Henyey-Greenestein asymmetry parameter for atmospheric particle phase function in the reference condition to which the image will be normalized, used in H1 and H2 atmosphere models. If no value is given, HGAREF will be set equal to HGA. Not to be confused with corresponding parameter HG1 for the surface particles. |
| HNORM | Atmospheric shell thickness normalized to planet radius, used to modify angles to get more accurate path lengths near the terminator. (Ratio of scale height to the planetary radius). Default value is given for Mars, which is the only planet for which the atmospheric modes are currently used. |
| NULNEG | If YES, output values that are negative will be set to NULL. Negative values are only generated in the modes including atmospheric corrections (i.e., ALBAT, TOPAT) and occur when the optical depth TAU is overestimated, so that the atmos- pheric radiance subtracted from the image is brighter than the darkest observed pixels. In this case TAU should be decreased until no negative values are obtained. It is useful to have the negative values set to NULL in the procedure shade_tau, which adjusts TAU to an optimal value. |
| INC | INC is used as an incidence angle boundary. Any pixel in the input cube that has an incidence angle greater than INC will be set to NULL on output. This has the effect of trimming near-terminator data. INC should not be set greater than 90 degrees. Not to be confused with INCREF (incidence angle to which image will be normalized) or INCMATCH (incidence angle of transition between albedo and topographic normalization when GENMOD=MIXED). |
| EMA | EMA is used as an emission angle boundary. Any pixel in the input cube that has an emission angle greater than EMA will be set to NULL on output. This has the effect of trimming near-limb data. EMA should not be set greater than 90 degres. |
| RLAT | User's requested latitude range for trimming. This is the only option used for trimming mosaic's that don't have the photometric angles in the backplanes. |
| RLON | User's requested longitude range for trimming. This is the only option used for trimming mosaic's that don't have the photometric angles in the backplanes. |
| INCMAT | When GENMOD=MIXED the image will be normalized so that albedo variations are constant for small incidence angles and topographic shading is constant for large incidence angles. The transition from albedo normalization to incidence normalization occurs around incidence angle INCMAT. 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. ALBEDO must also be adjusted in this mode to match the mean brightness of the high incidence angle region to that of the data at lower incidence angles. Not to be confused with INC (trim limit on incidence) or INCREF (incidence angle to which image will be normalized). |
| INCREF | Most modes (GENMOD) attempt to normalize the appearance of the surface to a set of standard conditions, in par- ticular, fixed incidence angle given by INCREF. A value of 0 is used for albedo normalization (GENMOD=ALBEDO, ALBAT) in most cases, though 30 degrees is sometimes used. INCREF=0 is also the usual choice for specifying the ALBEDO of shaded relief images calculated with GENMOD=SHADE, SHDAT. INCREF=30 is the standard value for topographic normalization (GENMOD=TOPO, TOPAT) because topographic shading disappears at 0 incidence and cannot be normalized to this value. Not to be confused with INC (trim limit on incidence) or INCMAT (incidence angle for matching albedo and topographic contrast when GENMOD=MIXED). |
| ALBEDO | Value of the desired model albedo, used with GENMOD= SHADE, TOPO, MIXED, SHDAT, TOPAT. For SHADE and SHADAT this is the albedo (I/F value at incidence INCREF and zero phase) used to simulate a shaded relief image. For the other modes it is the albedo that the image will be normalized to have. Program "avg_sd" 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. |
| THRESH | Operating modes that involve topographic normalization (GENMOD=TOPO,TOPAT, MIXED) 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 THRESH is too high these regions may contain amplified noise rather than useful shading information. |
| MOONOPT | Choose the option the program will use. MOONOPT=PHOTOM will
perform the photometric correction. ALBEDO will perform
the photometric correction plus an albedo-dependent phase
angle correction. NOALBEDO will perform the correction
without applying the additive value B. If MOONOPT = ALBEDO,
an additional albedo-dependent phase angle correction, which
varies with the value of each input DN is performed. You
must run "photomet" with FUNC = MOONPR and choosing MOONOPT
= ALBEDO option. The final output value when the ALBEDO
option is chosen is the reflectance at incidence and phase
angles of 30 degrees and emission angle of 0 degrees. The
parameters D, E, F, G2, XMUL, WL, H, BSH1, XB1, and XB2 are
used only if MOONOPT = ALBEDO. The program will enter a
default value for each of these parameters if the planet is
the "moon" and the user leaves the parameter blank.
The lunar defaults are as follows:
D = 0.14
E = -0.3575 * 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 = will be read from the cube label
H = 0.048
BSH1 = 19.89 - 59.58 * WL + 59.86 * WL**2 - 20.09 * WL**3
XB1 = -0.0817
XB2 = 0.0081
If MOONOPT = NOALBEDO, the following correction will be per-
formed:
OUTPUT BRIGHTNESS = INPUT BRIGHTNESS * A
|
| D | Empirically derived coefficient. See MOONOPT. |
| E | Empirically derived coefficient. See MOONOPT. |
| F | Empirically derived coefficient. See MOONOPT. |
| G2 | Empirically derived coefficient. See MOONOPT. |
| XMUL | Used to convert radiance to reflectance or apply calibration fudge factor. See MOONOPT. |
| WL | Wavelength in micrometers. Can be read from label. |
| H | Empirically derived coefficient. See MOONOPT. |
| BSH1 | Empirically derived coefficient. See MOONOPT. |
| XB1 | Empirically derived coefficient. See MOONOPT. |
| XB2 | Empirically derived coefficient. See MOONOPT. |
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