Modified photometric analyzer and enlarged beam splitter for studying simulated lunar surfaces and opposition effect on moo

Halajian, J. D.

Spagnolo, F. A.

English

NASA Technical Reports Server

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GRUMMAN RESEARCH DEPARTMENT MEMORANDUM RM-297 
c _____-.IIIIc 
PHOTOMETRIC MEASUREBENTS OF ' SIMUIAmD LUNAR SURFACES 7 
J. D. Halajian 
F. A. Spagnolo 
Geo-Astrophysics Section 
October 1965 
L 
Quarterly Progress Report on NASA Contract No. NAS 9-3182 
Approved by: &FH4g 
Charles E. Mack Jr. 
Director of Research 
https://ntrs.nasa.gov/search.jsp?R=19660002893 2020-03-16T22:15:27+00:00Z
SUMMARY 
This report i s  i n  par t ia l  fulfi l lment of t h e  reporting 
requirements on Contract No. NAS 9-3182. It is  t h e  first 
quarterly progress report on t h e  extension of t h e  work on 
"Photometric Measurements of Simulated Lunar Surfaces" and 
covers t h e  work performed i n  t h e  period from July 1, 1965 t o  
September 30, 1965. 
Work accomplished to  date includes a number of important 
modifications on t h e  Photometric Aaalyzer which were necessi- 
ta ted by t h e  nature of tke contractual experiments. Prel imi-  
nary test runs show significant improvements i n  the  quali ty 
of t h e  test  data, particularly near t h e  critical, zero-degree 
phase area where t h e  "opposition effect" on t h e  moon h a s  been 
recently ob served. 
A c t u a l  experimental and ana ly t ica l  work has j u s t  begun 
and i s  now under way. 
ii 
TABUS OF CONTENTS 
I t a  Page 
Introduction .......................................... 1 
Project Sta tus  ........................................ 2 
-
Modifications and Improvements of the  Grrtmman 
Photogletric Analyzer .................................. 3 
Discussion of Test Results ............................ 6 
PreliDIinary Analytical Approach to Phases I1 and I11 .. 8 
References ............................................ 11 
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INTRODUCTION 
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In  t h i s  f i r s t  quarterly progress report on the extension 
t o  t h e  Contract on "Photometric Measurements of Simulated Lu- 
nar Surfaces," w e  present an account of the redesign, modifi- 
cation and calibration of the Grramnan Photometric Analyzer 
t h a t  had t o  be made prior t o  the performance of the  contrac- 
t u a l  experiments. W e  a l so  present some preliminary measure- 
ments and discuss br ie f ly  our approach t o  the  analytical  phase 
of t h e  program. 
Work accomplished under the  original contract is  reported 
i n  d e t a i l  i n  Ref. 1. 
laboratory measurements of 'katural,'' "ar t i f ic ia l ,"  and "con- 
trolled" models i n  an attempt to reprodyce the lunation curves 
of t h e  moon (measured with integrated v is ib le  l ight)  and infer  
cer ta in  physical properties of t h e  lunar surface. Work to be 
performed i n  t h e  extension t o  t h e  original contract i s  as de- 
fined i n  l'Proposal B" of Ref. 2 and consists of three parts, 
namely, "spectral" brightness VS. phase angle measurements of 
some of the  natural specimens t h a t  passed the  photometric test 
under in tegra l  lighting, analytical and/or experimental asses- 
sment of "suspended particles" as a lunar photometric model 
and f inal ly ,  investigations of "contrived" models i n  an attempt 
t o  formulate t h e  reflection laws of t h e  moon i n  terms of t h e  
This work consisted essentially of t h e  
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geometry and albedo of its surface elements and t o  account 
f o r  some of t h e  photometric pecul iar i t ies  recently reported 
i n  t h e  literature. 
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PROJECT STATUS 
A number of important instrumental modifications and im- 
provements necessitated by t h e  new phQtarn@tri.c and polarimet- 
ric experiments have been successfully completed a f t e r  consid- 
erable analysis, rework and calibration. Some of t h i s  work i s  
described i n  t h e  next sec t ion  of t h i s  report, but t h e  major 
(Ref .  3) Eo be released soon. 
T e s t  runs t o  assess t h e  ffimprovedff beam s p l i t t e r  have 
been made on Hawaiian volcanic cinder No. 1. The results are 
c lear ly  superior t o  those obtained with the old beam spl i t ter  
and show st r iking s imilar i ty  to Gehrels' lunar observation of 
t h e  "opposition effect." A c t u a l  work on t h e  contractual ex- 
periments and analysis has begun and is currently proceeding 
sat isfactor i ly .  Barring major instnmental  setbacks, which 
are possible but not likely, w e  expect to complete t h e  "spec- 
tral" measurements phase of t h e  contractual experiments during 
t h e  next reporting period. 
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MODIFICATIONS AND IMPROVEMENTS OF THE 
GRUMMAN PH(ITmTR1C ANALYZER 
Considerable time and effort  has been spent during t h e  
period covered by t h i s  report t o  modify and improve t h e  Grumman 
Photometric Analyzer. Although t h i s  work was necessitated by 
t h e  nature of the experiments t o  be performed under t h i s  con- 
tract and the  "Polarimetric" contract, No, NAS 9-4942, it has  
been carried through under in-house funding and is  described 
i n  d e t a i l  i n  a G m n  non-contractual report  (Ref. 3). Briefly, 
t'ne am'iysis and rewolf'K of t h e  experhen-i set-up descriloed in  
t h e  above referenced report  include t h e  following items: 
1, Light source analysis and comparison t o  solar  source; 
correction by f i l t e r s  
F i l t e r  analysis and comparison t o  Gehrels, UGI, and 
UBV systems 
2. 
3. Photomultiplier comprative spectral responses 
4 Photomultiplier spectral  characteristics 
a) a t  room temperature 
b) as a function of applied voltage 
c) a t  dry ice temperature 
d) a t  l iquid n i t rogen  temperature 
e) 
F i l t e r  transmission character is t ics  and comparison t o  
manufacturers' data 
as a function of various photomultipliers of the 
same type 
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F i l t e r  temperature character is t ics  and instrumental 
heating character is t ics  
Astronomical data photometric systems and comparison 
t o  t h e  Grumman system 
Camparison of filters among themselves 
@ti-mechanical modifications of t h e  Photometer/ 
Polarimeter 
equally important improvement of the photcxnetric ana- 
lyzer t h a t  i s  not discussed in  Ref. 3 i s  the  widening of t h e  
beam s p l i t t e r  t o  enable a more meaningful simulation and study 
of t h e  "opposition effect" recently reported i n  t h e  literature. 
As has  been explained i n  a previous report  (Ref. l ) ,  t h e  Gruman 
Photometric Analyzer makes use of a beam s p l i t t e r  t o  generate 
photometric functions which pass  through zero phase angle. 
Furthermore, t h i s  beam spl i t ter  is  mounted i n  such a way t h a t  
it can be replaced readily with a complete f i rs t -surface m i r -  
r o r  of the  same s i z e  f o r  use a t  phase angles greater than 
about 6 O .  A second first-surface mirror inclined 45' about 
an axis normal t o  t h e  source axis and a l s o  normal t o  t h e  axis 
of t h e  f irst  mirror is provided t o  de-polarize t h e  source fo r  
other than zero phase region. 
Astrophysical data reported by Gehrels e t  a1 (Ref.  4) have 
shown a very pronounced "opposition" e f fec t ,  much sharper near 
zero phase angle than earlier data, 
on measurements of the  lunation photometric function much closer 
These new data a r e  based 
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t o  zero degrees phase angle than had been reported previously. 
By comparison with the Grimnnan Photometric analyzer data taken 
on many models it can be seen t h a t  t h i s  trend toward a sharp 
peak exists i n  the  laboratory data also,  but because t h e  va l id  
data taken through the  beam s p l i t t e r  are effect ively confined 
t o  about 
over a range of Q0 phase angle cannot be verified.  Further- 
more, t h e  in te rva l  of time t h e  beam s p l i t t e r  takes t o  travel 
t h i s  narrow angular distance i s  not suf f ic ien t  t o  allow t h e  
recorder t o  respond i n  time to  the actual brightness sensed by 
the  photometer. To increase the  Grumman capabi l i ty  of reading 
out t he  slope and peak of this s igni f icant  part of the  photo- 
metric signature of a model, a large beam s p l i t t e r  has been 
built-up especially fo r  t h i s  range. The large beam s p l i t t e r  
i s  used so le ly  f o r  readings nea r  zero phase angle and is  re- 
moved and replaced with a mirror fo r  readings a t  larger  phase 
angles. 
cover is  = 7 O  t o  + 1 3 O  as can be seen from sample reaordings, 
Fig, 3c. 
collimated source arm i s  s h m  as Fig, 1. 
l* degree phase angle, the exact shape of t h e  curve 
& 
The approximate range which t h i s  beam s p l i t t e r  w i l l  
A photograph of the u n i t  attached t o  the  ro ta t ing  
The ro ta t ing  source of t h e  Analyzer has a l s o  been provided 
w i t h  accommodation for  6 filters or  5 f i l t e r s  and a clear space, 
manually selectable from f l o o r  level as shown i n  Fig. 2. The 
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I f i l t e r s  a r e  inserted between t h e  diffuser disks and t h e  f i e l d  
stop. The source radiance has  been improved by a large factor  
by use of a 1 KW tungsten-iodine lamp and two quartz diffuser  
disks i n  series whereas  flashed opal diffusers  of greater  den- 
s i t y  had been used previously. 
Although t h e  f i l ters are shielded by t h e  diffuser  disks 
and a cer ta in  amount of s t ructural  shielding, t h e  thermal prob- 
lem resul t ing from t h e  use of a 1 KW lamp is severe. T r i a l  of 
a dense red filter shuwed a temperature of about 200' F a t  t h e  
surface of t h i s  f i l t e r .  This part icular  f i l t e r  cracked. Temp- 
erature  fluctuations of such a degree can r e s u l t  i n  color 
changes as w e l l  as mechanical fa i lure .  
reviewed from a thermal  standpoint and improved by providing 
high absorptivity radiation h e a t  sink surfaces fo r  t h e  f i l t e r  
and improving t h e  conduction t ransfer  paths.  A blower has  
been used throughout t o  c i rcu la te  a i r  through t h e  source assem- 
bly. The f i l t e r s  have been placed adjacent t o  t h e  source 
rather than t h e  photaneter phototube fo r  reasons of convenience 
and timesaving i n  operation. 
a l lev ia ted  by t h e  use of f i l t e r s  which have law radiation ab- 
sorption. 
The design has  been 
The f i l t e r  problem could a l s o  be 
DISCUSSION OF TEST RESULTS 
To evaluate t h e  performance of t h e  new, improved, beam 
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s p l i t t e r ,  a test run w a s  made on t h e  Hawaiian volcanic cinder 
No. 1 a t  Oo,  30" and 60" viewing angles as shown i n  Fig. 3a 
t o  C. 
A canparison wi th  similar curves on t h e  same specimen ob- 
tained by t h e  old, narrower beam s p l i t t e r  as presented i n  Fig. 
17 of Ref .  1, indicates  a significant improvement i n  t h e  quali ty 
of t h e  data obtained. 
measured by t h e  old beam spl i t ter  w a s  only about 10 per cent 
grea te r  than t h e  1.0 normalization point on t h e  ordinate of 
t h e  curve whereas the corresponding value measured by t h e  new 
beam s p l i t t e r  i s  i n  excess of 30 per cent not counting t h e  fact 
t h a t  a t  t h e  normal viewing position t h e  brightness surge a t  
zero degree phase was so intense t h a t  the  recording pen went 
off  t h e  paper, as may be seen i n  Fig. 3a. 
The brightness peak, a t  zero degree phase, 
I n  addition to measuring t h e  brightness peak more accur- 
a te ly ,  t h e  new beam s p l i t t e r  reveals t h e  change i n  t h e  slope 
of t h e  photometric curve i n  t h e  region where t h e  opposition 
effect takes place and thus, permits d i r ec t  comparison with 
t h e  measured lunar data i n  t h i s  region. 
Gehrels '  data (Ref. 4) w i t h  our new measurements i s  more s t r ik -  
ing than w i t h  t h e  previous measurements obtained through t h e  
old beam s p l i t t e r .  
The s imi la r i ty  of 
The demonstration of t h e  new beam s p l i t t e r  i l l u s t r a t e s  
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again t h e  importance of adequate or  refined instruments i n  
lunar model-matching experiments . 
nary resu l t s ,  t h e  time and e f fo r t  spent i n  improving t h i s  
par t icu lar  aspect of our photometric analyzer appear t o  have 
been jus t i f ied .  
Judging f ran  t h e  prelimi- 
PRELIMINARY ANALYTICAL APPROACH TO PHASES I1 AND 111 
While experimental models are being constructed t h e  ana- 
l y t i c  work associated with Phases I1 and I11 w a s  i n i t i a t e d  
during t h e  f i r s t  reporting period and w i l l  continue through- 
out t h e  remaining portion of t h e  present contract. The ro l e  
of shadowing i s  being investigated fo r  various suspended par- 
t icle configurations within which multiple scat ter ing and dif-  
f rac t ion  e f fec ts  are neglected. 
t h e  individual particles being considered are assumed, as i n  
R e f .  5, t o  be opaque, macroscopic, generalized surfaces of 
revolution of uniform albedo. Also, f o r  simplicity, each 
elementary surface element is assumed t o  exhibi t  the  d i f fus ive  
For purposes of general i ty  
reflective behavior of a "Lambertian" surface. 
t h e  analysis  developed i n  Ref. 5 resides  i n  t h e  f a c t  t h a t  it 
lends itself t o  canputer analyses i n  which t h e  per t inent  param- 
e t e r s  can be varied. 
known geometries (cylinders, spheres, planar surfaces) are eas i ly  
obtained and can be readi ly  compared t o  other more complicated 
The u t i l i t y  of 
Furthermore, r e su l t s  fo r  spec i f ic  w e l l -  
0 
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shapes. 
ter ing function reduces t o  t h e  r e su l t  previously obtained by 
Schoenberg (Ref. 6 )  and l a t e r  used by Hapke (Ref. 7) who con- 
sidered t h e  scattering of l i g h t  from a medium comprised of 
randomly oriented opaque particles w i t h  rough surfaces. 
t o  t h e  increased d i f f icu l t ies  encountered i n  t h e  geametrical 
analysis f o r  
it appears a t  t h i s  point that it w i l l  probably be necessary t o  
l i m i t  t h e  number of layers to j u s t  a few. 
For t h e  spherical case t h e  individual par t ic le  scat- 
Owing 
these models as one increases t h e  number of layers, 
W i t h  reference t o  Phase 111 of t h e  present study, t h e  dan- 
inant ro l e  of shadowing is being studied fo r  various contrived 
tridimensional models. 
obtained fo r  t h e  configuration consisting of a series of sus- 
pended horizontal %ambertian" elements of uniform albedo, sep- 
arated by a fixed distance. The brightness vs. phase curve fo r  
one case (viewing angle E, equal t o  zero) bears a remarkable 
resemblance t o  one recently suggested i n  the  Interim Report of 
t h e  original contract (Ref. 1). 
m o d e l  has  been completed for  a l l  ViaJing angles as w e l l  as vari- 
able l inear  dimensions, no numerical results have been obtained 
fo r  cases other than E = 0.  Analytical work along these l i nes  
w i l l  be extended t o  include a s  many of t h e  contrived configur- 
a t ions as is possible and i n  particular t h e  T 
Preliminary numerical resu l t s  have been 
Though t h e  analysis fo r  t h i s  
or "thumb tacks" 
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model. 
certain cases. 
described above, w i l l  be par t icular ly  useful i n  assessing the  
analytical resul ts .  
"Composite" albedo effects  w i l l  a l s o  be considered f o r  
I n  t h i s  connection, t h e  "improved" beam s p l i t t e r ,  
ACKNOWLEIXXMENT 
It is  a p l e a a r e  t o  thank again H.B, Hallock, J, Grusauskas 
and D.R. Lamberty of Servo Engineering for t h e i r  valuable con- 
t r ibu t ion  and painstaking ef for t s  i n  rebuilding and recalibrating 
the Photometric Analyzer and performing t h e  experiments. 
10 
1. 
2. 
3. 
4. 
5. 
6. 
7. 
REFEREMXS 
Halajian, J.D.,"Photometric Measurements of Simulated 
Lunar Surfaces," GrraPman Research Department Report 
RE-219, July 1965. 
''Photanetric Measurements of Simulated Lunar Surfaces," 
Grtrrmman Research 
65-83NAS, June 1965. 
(Interim Report on NASA Contract NAS9-3182) 
Technical Proposal RP-255, F i l e  No. 
Egan, W.G. e t  al ,  "Search fo r  a Lunar Surface W e 1  0-  
Appendix A: 
Equipment," Grumman Research Department Memorandum 
RM-304 ( in  preparation) . 
Analysis of Photometric and Polarimetric 
Gehrels,  T., Coffeen, T., and Owings, D., "Wavelength 
Dependence of Polarization of t h e  Lunar Surface", The 
Astrmnmical Journal, V a l ,  69, No, 10, December 1964. 
Look, D.C., "General Expression for  Lambert Diffuse Re- 
flection," JOSA. V a l .  55, No. 4, April 1965. -
Van de Hulst, H.C., Ligh t  Scattering by Small P a r t i c l e s ,  
Wiley, New York, 1957. 
Haplce, B.W., 'A Theoretical Photometric Function fo r  t h e  
Lunar Surface," Center for Radiophysics and Space Research, 
Cornel1 University, Report No. 138, February 1963. 
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Photometric measurements of simulated lunar surfaces Quarterly progress report, Jul. 1 - Sep. 30, 1965

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