Isis 3 Application Documentation
Estimate optical depth using information from image shadow
Description
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
assumptions 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 photoclinometry 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
Categories
History
| Randy Kirk | 1999-11-27 |
USGS Flagstaff Original Version
|
| Sharmila Prasad & Janet Barrett | 2011-09-04 |
Isis3 Original version, shadow_tau ported from isis2 to shadowtau in isis3
|
| Janet Barrett | 2012-01-05 |
Tested code to make sure it gives the same results as the ISIS2 version.
Created app tests.
|
|
Parameter Groups
Files
|
Name
|
Description
|
| FROM |
Input Datafile
|
| TO |
Output Datafile
|
Photometric Model
|
Name
|
Description
|
| PHTNAME | Photometric Function Model |
| WH | Single Scattering Albedo |
| HH | Opposition Surge Width |
| B0 | Opposition Surge Strength |
| THETA | Surface roughness in degrees |
| HG1 | Henyey-Greenstein coefficient 1 |
| HG2 | Henyey-Greenstein coefficient 2 |
| BH | Legendre coefficient 1 |
| CH | Legendre coefficient 2 |
| ZEROB0STANDARD |
Determines if opposition surge (B0) is set to zero when standard conditions are used
|
| L | Lunar-Lambert weight |
| K | Minnaert exponent |
| DATAFILE | File containing table of parameter values vs. phase
for LL_EMP, MN_EMP
|
Atmospheric Scattering Model
|
Name
|
Description
|
| ATMNAME |
|
| WHA | Single-scattering albedo |
| HGA | Coeff of atmospheric particle Henyey-Greenstein |
| BHA | Coeff of atmospheric particle Legendre phase function
|
| HNORM | Atmospheric shell thickness |
|
Files:
FROM
Description
Input datafile name with Image ID, incidence, emission, phase angles
and values for flat and shadow
|
Type
| filename |
|
File Mode
| input |
|
Filter
|
*.txt
|
Files:
TO
Description
Output datafile name with the input Image ID, incidence, emission,
phase angles and values for flat and shadow plus the tau and albedo
values(optical depth and albedo of the surface)
|
Type
| filename |
|
File Mode
| output |
|
Filter
|
*.txt
|
Photometric Model:
PHTNAME
Description
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
phoempglobal 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).
|
Type
| combo |
|
Default
|
HAPKEHEN
|
|
Internal Default
| HAPKEHEN |
|
Option List:
|
|
Option |
Brief |
Description |
| HAPKEHEN | Hapke-Henyey-Greenstein photometric model |
Exclusions
|
| HAPKELEG | Hapke-Legendre-Polynomial photometric model |
Exclusions
|
| LAMBERT | Lambert photometric model |
Exclusions
- BH
- CH
- HG1
- HG2
- L
- K
- WH
- HH
- B0
- THETA
- DATAFILE
- ZEROB0STANDARD
|
| LommelSeeliger | LommelSeeliger photometric model |
Exclusions
- BH
- CH
- HG1
- HG2
- L
- K
- WH
- HH
- B0
- THETA
- DATAFILE
- ZEROB0STANDARD
|
| LUNARLAMBERT | Lunar-Lambert Photometric Function | Lunar-Lambert Photometric Function
Exclusions
- BH
- CH
- HG1
- HG2
- K
- WH
- HH
- B0
- THETA
- DATAFILE
- ZEROB0STANDARD
Inclusions
|
| MINNAERT | Minnaert Photometric Function | Minnaert Photometric Function
Exclusions
- BH
- CH
- HG1
- HG2
- L
- WH
- HH
- B0
- THETA
- DATAFILE
- ZEROB0STANDARD
Inclusions
|
| LUNARLAMBERTEMPIRICAL | Lunar-Lambert Empirical Photometric Function | Include Lunar-Lambert Empirical Photometric Function to
the Hapke Model
Exclusions
- BH
- CH
- HG1
- HG2
- K
- WH
- HH
- B0
- THETA
- L
- ZEROB0STANDARD
Inclusions
|
| MINNAERTEMPIRICAL | Minnaert Empirical Photometric Function | Include Minnaert Empirical Photometric Function to
the Hapke Model
Exclusions
- BH
- CH
- HG1
- HG2
- L
- WH
- HH
- B0
- THETA
- K
- ZEROB0STANDARD
Inclusions
|
|
Photometric Model:
WH
Description
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.
Photometric Model:
HH
Description
Opposition Surge Width. ZEROs are strongly advised as the simple models
#do not fit the opposition effect well
Photometric Model:
B0
Description
Opposition Surge Strength. ZEROs are strongly advised as
the simple models #do not fit the opposition effect well
Photometric Model:
THETA
Description
Small scale surface roughness in degrees. "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.
Photometric Model:
HG1
Description
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
|
Type
| double |
|
Default
|
0.213
|
Photometric Model:
HG2
Description
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.
Photometric Model:
BH
Description
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.
Photometric Model:
CH
Description
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))
Photometric Model:
ZEROB0STANDARD
Description
This determines if the opposition surge component B0 is set to zero
during the standard conditions phase.
|
Type
| string |
|
Default
| TRUE |
|
Option List:
|
|
Option |
Brief |
Description |
| FALSE |
Don't set opposition surge B0 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 |
Set opposition surge B0 to zero for standard conditions phase
|
This option specifies that the opposition surge B0 will be set to zero
during the standard conditions phase.
|
|
Photometric Model:
L
Description
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).
Photometric Model:
K
Description
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).
Photometric Model:
DATAFILE
Description
File containing table of parameter values vs. phase
for LL_EMP, MN_EMP. User datfile from which photomet loads the
photometric function 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.
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 Lare calculated Count should = numbllcoef
llphase =0.,10.,20.,30.,40.,50.,60.,70.,80.,90.,100.,110.,
120.,130.,140.,150.,160.,170.,180.
#values for Empirical Lunar Lambert
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 approximation
numbeecoef=19
#the angles at which the coefficient values for Empirical Lunar
#Lambert B approximation are calculated Count should = 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
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
MINNAERT_EMP numkaycoef=10
kayphase =0.,20.,40.,60.,80.,100.,120.,140.,160.,180.
kval =
numbeecoef=0
bphase=
bval=
|
Type
| filename |
|
File Mode
| input |
|
Filter
| *.txt |
Atmospheric Scattering Model:
ATMNAME
Description
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
|
Type
| combo |
|
Default
|
NONE
|
|
Internal Default
| NONE |
|
Option List:
|
|
Option |
Brief |
Description |
| ISOTROPIC1 | First Order Isotropic | Exclusions
Inclusions
|
| ISOTROPIC2 | Second Isotropic |
Exclusions
Inclusions
|
| ANISOTROPIC1 | First Order Anisotropic |
Exclusions
Inclusions
|
| ANISOTROPIC2 | Second Order Anisotropic |
Exclusions
Inclusions
|
| HAPKEATM1 | First Order Henyey-Greenstein |
Exclusions
Inclusions
|
| HAPKEATM2 | Second Order Henyey-Greenstein |
Exclusions
Inclusions
|
|
Atmospheric Scattering Model:
WHA
Description
Single-scattering albedo of atmospheric particles, used in
all atmospheric models. Not to be confused with albedo WH
of the surface particles.
Atmospheric Scattering Model:
HGA
Description
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.
Atmospheric Scattering Model:
BHA
Description
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.
Atmospheric Scattering Model:
HNORM
Description
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).
|
Type
| double |
|
Default
|
0.003
|