On the approximation of H-function for anisotropic scattering. I.A-Rayleigh’s phase function
S. Ka b a n ja t a n d S. K . Ba r m a n
Department of Mathematics^ Vniversitif of North Bengal, WeM Bengal, {Beceived 8 December 1972)
One of Karaiijai’s approximate forms for tlio //-function for isotropic scattering has beoji (jxtended to anisotropic; scattering. The pliaso function considered in this paper is the Rayleigh's pliaso function.
Comparison of calcu]at(;d results witli, the exact values given by Chandrasekliar shows good agreement. Results |iav(‘ beem applied to find diffuse reflection according to the Rayleigh’s pha>se function.
Indian J . Phya. 48, 126-132 (1974)
1. Introdttctton
Ih e solution of most of the problems of radiative transfo)’ in semi-infinite plane parallel atmosphere involve Chandrasc^.kJiar's //-function which is solution of the integi'al ecjuation
H { f ,) . . I ,1//'.
0 r-//
( 1 1
and is bmimlcd in the entire half-i)Jane Ji(Z) 0. nhore the cliaraeteristie func
tion »//{//) is an oven potynoinial in // satisfyiiiR the condition
/ '/'(/0d/< < L (2)
The case of equality m (
hj. (2) is the conservative cas(». On rean-anaiiur oq. (1)
H{/i) (3)
To get an exact solution of eq. (3) wo are to find out first, a first approxi
mation to ^.function and then to substitute it in the right hand side of eq. (3) and to continue the iterative process so long as the difference lietween two successive iterates is negligible.
when llio scattering is isotropic with albwlo w, we Jiavo
= constant = a>/2.
126
(4)
On the approxim ation o f H -fu n ction etc. 127 Thus for isotropic eonsorvativo case
= h 1). ... (5)
Different approximate forms for the £f-function for isotropic scattering have already boon considered by workers in tliis line, e.g. Abu-Shumays (1966a, 19666, 1967), Karanjai (1968a, 19686, 1969), Karanjai & Sou (1970, 1971), Harris (1957), Van de Hulst (1957), ChandrasekJiar & Breen (1947), Chamlborlain & Kuiper (1956), Chamberlain & McEIroy (1966), Sobolev (1949), Savodoff (1952), Stibbs iV: Weir (1959). In the above-referred works everyone considered the case of isotropic scattering. In this series of papers wo like to extend 4iff®i*^ut approxi
mate forms to the case of anisotropic scattering and tabulatj& the -function and some otluM* related functions witli different phase functions. Since the //-function is a function of both w and /i we denote the function by II{w,/i) instead of i/(//).
Here in this paper w(^ consider the approximate form (Karanjai 1972, Abu-
♦Sliumays 1967)
H{u), fi) — l+a/^+^/i*7 ... (6)
where a and 6 are constants to bo determined, for anisotropic scattering with Rayleigh’s phase functions, according to which //(e^,//), and
are defined in terms of the characteristic functions
^ {1 + 1/819(1- --3 (2 ^ o>)//H I f I
and
respectively.
3a»
8"
3co
... (6a)
... (6l>)
... (6c)
Case / . Whefi the first approximate for the II-function is given hy eq. (6) and ike characteristic function is given by eq. (6a). Determination of the. constants a and b.
The H-function satisfies the following conditions (Chandrasekliar 1960) :
i) / H{w, = 1 - [ 1 - 2 / i/r{/i)d/i]* , ... (7)
-) ^1—2 ^ ^i^(/t)d/t j* / H{w,
Substituting for and from oq. (6) and (6a) into eq. (7) we get 128 S. Karanjai and S. K . Barman
where
K, = PJP,, S _ 2(1-.-t)
A = [^ 1 - 2 / i>(/<)d//y 1 - j ' ,
P, ---
9(1 J 3(2—0)) 1
^ 8 " ‘ 5 3
9(1^^.) 1 3(2-0)) 1
8 6 8 4
9(J-o;) 1 3(2-0)) 1 8 ’ 7 “ S' ' 5
■I-
+
8 3 ’
... (9)
(9a) (9b) (9c)
(9d)
(9o)
• (»f)
• (9g) Substituting for and <,>(/-/) from eq. (H) and (6a) into oq. (8) and using eq. (9) wo got
where
Ti¥+TJ)+Tz = 0, ... (10)
!Ti (w/4)/?/, ... (10a)
n = A(P,-P,K,H(wl2)R,P„ ... (10b)
7*3 = ^(P3 + P3Jf,)-f(w/4)/?i2-P3, ... (10c)
A = Pi+Peifi,. ... (lOd)
J?3 - P^-P,K„ ... (lOo)
p 9(l-<c) 1 3(2-£o) 1 9 1
’ 8 ‘ 8 8 • 6 + 8 ■ 4’ ... (lOf) jj 9(1 oi) 1 3(2—o)) 1 9 1
* 8 9 8 • 7 + 8 - 6 - ... (lOg)
Eq. (9) and (10) give the constants a and b.
O n the a p p ro xim a tion o f H -fuw stion etc.
129
Second approximation formula :Substituting for H{u}, fi) and from eq. (6) and (6a) into eq. (3) we get the second approximation formula as
1 H(oj,p)
where
= 1- pca [■ 9 2
1
(11)
(12)
Case II, When the first approximate for the H~function is given by eq, (6) and the characteristic function is given by eg, (66). Determhudion of the ronstants a and b.
and
Following tlie same procedure as has been done in case I, we get
a ^ K ^ --K 4 > , ... (13)
Tj6 2 + T ,6 + T 3 = = 0 , ... (14)
whore S, and R^ arc given by the equations (9a), (9b), (9c), (lOd) and (lOe), respectively, and
^ = ( * - ? » ) ■ Po = 2/15, P i - 1/12, Pa = 2/36, Ps = 1/24, P , = 2/63, P, = (3a*/16)Pg*,
P* = A(P^-P^Kt)+{^wlS)BiB^, P, « ^(P,+P,iCj)+(3«/16)i?i*-i>g.
Second Approximation formula ;
The second approximation formula is obtained as
where is given by eq. (12).
6
(13a) (13b) (13c) (13d) (14a) (14b) (14c) (14d) (14e)
(15)
130 S. K aranjai and S. K . Barman
Case 111. When the first apirroxmatc for the H-funetion is given by eq.
(6) and the characteristic function is given by cq. (6c). Determination of the constants a and b.
Following the Bamo prociMiuro as has boon doiio in oaso T, wc got
a = ^ K ^ -K .jK ••• (16)
and
Tjb^+T.,b+T^=^(), ... (17)
where, a« ))efoze A\, A'j, S, AV and are, respectively, given by the oq.
(9a), (9b), (9c), (lOd) and (lOe) and
n = 8/15, P, - 1 / 6 , P, = 8/105,
Pa - 1/24, P4 = 8/316, Pi = (3 /64)A2*.
= ^(P,-P3A2)-f-(3o>/32)iJiA2 1\ = J (P ,+ P 3 Ai)+ (3«/6 4)Ai*-P 2 . Second approximation formula :
The second approximation forjnula is obtaiiuMi as 3<u/(
... (16a)
... (16b) ... (16c) ... (16d) ... (17a) ... (I7b) ... (17c) ... (17d) ... (17e)
1 = 1- • [(A) 2/0-t-/.,) \-a{I^—2I.j-\-I^-\-b{l2—2 /4 + /j)J (18) i/< *'(«,/«)" 32
where i „ is again given by eq. (12).
2. Discussions
Values of the il-function, viz., H(w, y), y), and iP*>(w, y ) have been calculated with the second approximation formulae given, respectively, by the eq. (11), (16) and (18) for w = 1 and /< = 0(0-2)l. In table 1 wo give the results obtained by our calculalions. Table 2 contains those values obtained by Chandrasekhar (1960). Comparison of our results with those o f Chandra
sekhar shows that maximum error in //(to, y) is less than 0 005 per cent, and those ni f/<‘ >(tt>,/t) and H<^^w,y) are loss than 0 000006 per cent.
On the approxim ation o f H -function etc. 131 Tablo 1. Valuer of ^-functions calciilatod with eq. (11), (15) and (18)
with ci> ~ 1 H(/t)
0.0 1.000000 1.000000 l.OOOOOO
0.2 1.478628 1.013613 1.024467
0.4 1.879236 1.021314 1.032S43
0.6 2.264615 1.026522 1.036W7
0.8 2.642940 1.030274 1.0»9961
1.0 3.017684 1.033116 1.0411^6
3 2, Values of .fl^-functions given by Chandraaokliar (19
m / i )
0.0 1.000000 1.000000 1.000000
0.2 1.48009 1.01362 1.02448
0.4 1.88106 1.02131 1.03236
0.6 2.26660 I .02662 1.03679
0.8 2.64503 1.03028 1.03966
1.0 3.01973 1.03312 1.04170
3. Application
diffuse refloction in accordance with Rayleigh's phase function (con
servative ease, oi — 1*0) is given by
9>o) ='
I
+ [(l-//2)H '2>(//)ir(l-//,® )»'«(/01onR 2(94„-5»j ... (19) wJiore
= jff(//)(3—c//,), ... (19a)
... (19b) and //(//), are defined in terms o f thc' cliaracteristic functions giv^on by equations (6a), (fib) and (6c) with a> 1.
The constants c and q are related to tJxe moments of the iEf-function by
and
a,q = 2/3a,
.. (19o) .. (19d)
132 S. Kaxanjai and 8. K. Bannan
For illuBtratioii we consider two caaes only
case (i) /^o ^ and - 0"
case (ii) /<o ~ *^‘8
The diffuse reflection for the above two cases have been calculated and given in table 3.
Table 3. Diffuse reflection for Rayliegh’s phase function
case (i) case (ii)
0.0 0.6377063 0.6675300
0.2 0.7163045 0.6906563
0.4 0.7402489 0,7459697
0.0 0.7583574 0.7839645
0.8 0.7808479 0.8135706
1.0 0.8383860 0.8383860
Rbferences Abu-Shumaya I. K. 1966a N u d . ftc. Eng. 26, 430.
19666 T h e m . Harvard Vnivermtu.
1967 N m l Sc. Eng. 27, 607.
Buabridgt! I. W. 1953 M .N . 113, 52.
Chandrasekhar S. & Breen F. H. 1947 A p .J . 106, 143.
Chandrasekhar S. 1960 Radiative Transfer (Dover Publ.) Chamberlain .T. W. & Kuiper G. 1956 A p .J . 124, 399.
Chamberlain. ,T. W. & McElroy M. B. 1966 A p .J . 144. 114S.
Harris D. 1957 A p .J . 126. 408.
Hulst H. C. Van de 1952 The Atmosphere o f the Earth and Planets. Erl. 0. Kuifrer, Chap. HI.
Karanjai S. 1968a In d . J . Theo. P h ys. 16, 85.
19686 .7. North Bengal University See. M ath. p. 17.
1969 Thesis, North Bengal University.
1972 In d . J . Theo. P hys. 20, 63.
Karanjai S. & Sen M. 1970 P .A .S .J .22, 235.
1971 Astrophys. Space, Sc.13, 267.
Sobolev V. V. 1949 A str. J . ( V .S .8 .R .) 26, 129.
Savedoff M. P. 1952 A p .J . 115, 509.
Stibbs D. W. N. & Weir R. E. 1959 M .N . 119, 512.