Isis 2 Documentation
SHADOW_TAU - Estimate optical depth tau from shadows. This program uses level-surface and shadow image intensites to estimate atmospheric optical depth tau. The input is a table with one line per image point to be modeled, listing the image ID, incidence, emission, and phase angles, and the radiances (DN in a "level 1" calibrated image) of a level unshadowed area and a nearby shadow. On output, model results for the optical depth and albedo of the surface are appended to the end of each line. The surface and atmosphere models use the same assump- tions as the "photomet" photometric correction software so the resulting optical depth estimate will be useful for processing images with that program. (In other words, the optical depth calculated by this program is model-dependent but it is exactly the model-dependent value that will produce the most effective photometric correction in "photomet".) Since the only planet this program will be used for (the only one apart from Earth with modest atmospheric optical depths) is Mars, most of the parameters default to appropriate values for Mars. 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: Randolph Kirk, U.S.G.S., Flagstaff, AZ
Parm | Description | Default |
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FROM | Input datafile name with ID/inc/ema/phase/flat/shadow | NONE |
TO | Output datafile name with Inputs/tau/albedo | NONE |
FUNC | Type of photometric function model used for surface: LAMBER, LOMSEL, MIN, LUNLAM, MN_EMP, LL_EMP, HAPHEN, HAPLEG, HAPH_S, HAPL_S | HAPHEN |
K | Minnaert exponent for MIN | 1.0 |
L | Lunar-Lambert weight for LUNLAM | 1.0 |
DATAFILE | File containing table of parameter values vs. phase for LL_EMP, MN_EMP | "$ISISDATA/photom.mars.sav" |
WH | Single-scattering albedo for HAPHEN, HAPLEG, HAPH_S, HAPL_S | 0.52 |
HH | Opposition surge width for HAPHEN, HAPLEG | 0.170 |
B0 | Opposition surge strength for HAPHEN, HAPLEG | 0.025 |
THETA | Macroscopic surface roughness in degrees, for HAPHEN, HAPLEG | 30.0 |
HG1 | Henyey-Greenstein asymmetry parameter for single particle phase function in HAPHEN, HAPH_S | -0.213 |
HG2 | 2nd Henyey-Greenstein parameter controls mix of +HG1, -HG1 components for HAPHEN, HAPH_S | 0.0 |
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 | -- |
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 |
WHA | Single-scattering albedo of atmospheric particles. | 0.95 |
BHA | Used only with ATMOS=A1, A2. Coeff of P1(phase) in single particle Legendre phase fn. | -- |
HGA | Used only with ATMOS=H1, H2 Coeff of single particle Henyey-Greenstein phase fn. | 0.68 |
HNORM | Atmospheric shell thickness normalized to planet radius. |
ADDITIONAL NOTES:
Parm | Description |
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FROM | Filename of input textfile. Input file must have image-id, inc, ema, phase, dn-flat, dn-shadow on each line. |
TO | Filename of output textfile. Output file will have image- id,inc, ema, phase, dn-flat, dn-shadow plus tau and albedo on each line. |
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 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 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). |
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. ################################################## ## File: ~/$ISISDATA/photom.mars.sav ## ## Description: This file is the Mars lookup ## ## file for default photometric correction ## ## parameters for the photometric correction ## ## program, "photomet". ## ## Author: K. Teal Thompson ## ## Data: Randy L Kirk ## ## Date of Last Revision: 2003 Feb 11 ## ################################################## ## 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 appro ximation numllcoef=19 # the angles at which the coefficient values for Empirical L unar Lambert L # approximation are calculated (ALL ON ONE LINE!) Count shou ld = 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 =0.946,0.748,0.616,0.522,0.435,0.350,0.266,0.187,0.11 8,0.062,0.018,-0.012,-0.027,-0.035,-0.036,-0.037,-0.031,-0.0 12,0.010 #number of coefficients for Empirical Lunar Lambert B approx ximation numbeecoef=19 # the angles at which the coefficient values for Empirical L unar 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.,12 0.,130.,140.,150.,160.,170.,180. #the values for Empirical Lunar Lambert B (ALL ON ONE LINE!) bval=1.000,1.010,0.987,0.940,0.882,0.819,0.756,0.697,0.639 ,0.581,0.522,0.458,0.391,0.324,0.259,0.199,0.138,0.066,0.000 END MINNAERT_EMP numkaycoef=10 kayphase =0.,20.,40.,60.,80.,100.,120.,140.,160.,180. kval = numbeecoef=0 bphase= bval= 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)) |
ATMOS | Only used with GENMOD=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 |
WHA | Single-scattering albedo of atmospheric particles, used in all atmospheric models. 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. |
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. |
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). |
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