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AEDC-TR-65-170 


nov iz m 

JAN t 9 -ft** 








HEMISPHERICAL REFLECTANCE OF 
METAL SURFACES AS A FUNCTION OF 
WAVELENGTH AND SURFACE ROUGHNESS 


R. C. Birkebak 

Georgia Institute of Technology 
and 

J. P. Dawson, B. A. McCullough, and B. E. Wood 

ARO, Inc. 


October 1965 


PROPERTY pc I|. s AIR FORCE 
AF r '~ 1 'TV.RY 
AF 40(600)1200 

AEROSPACE ENVIRONMENTAL FACILITY 
ARNOLD ENGINEERING DEVELOPMENT CENTER 
AIR FORCE SYSTEMS COMMAND 
ARNOLD AIR FORCE STATION , TENNESSEE 




















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AEDC-TR-65-170 


HEMISPHERICAL REFLECTANCE OF 
METAL SURFACES AS A FUNCTION OF 
WAVELENGTH AND SURFACE ROUGHNESS 


R. C. Birkebak 

Georgia Institute of Technology 
and 

J. P. Dawson, B. A. McCullough, and B. E. Wood 

ARO, Inc. 


AP • HE DC 


AEDC-TR-65-170 


FOREWORD 


The research reported herein was sponsored by Arnold Engineering 
Development Center (AEDC), Air Force Systems Command (AFSC), 
Arnold Air Force Station, Tennessee, under Program Element 61445014, 
Project 8951, Task 895104. 

The results of research presented were obtained by ARO, Inc. (a 
subsidiary of Sverdrup and Parcel, Inc.), contract operator of the AEDC 
under Contract AF40{600)-1200. The work was conducted under ARO 
Project Number SW2407, and the manuscript was submitted for publica¬ 
tion on July 21, 1965. 

The authors wish to acknowledge the Heat Transfer Laboratory, 
Department of Mechanical Engineering, University of Minnesota for their 
contribution to this report by supplying test surfaces and suggestions on 
data reduction. 

This technical report has been reviewed and is approved. 

Donald R. Eastman, Jr. 
DCS/ Research 


Harold L. Rogler 
1/Lt, USAF 

Aerospace Sciences Division 
DCS/Research 


li 



AEDC-TR-65-170 


ABSTRACT 


Measurements of the hemispherical reflectance of metallic surfaces 
with controlled surface roughness were made using a sulfur infrared 
integrating sphere and a Beckman DK2A spectrometer. The surfaces 
studies were ground glass and nickel coated with films of aluminum, 
gold, platinum, and nickel. The data indicate that beyond a certain ratio 
of surface roughness to incident wavelength, cr 0 /lA = 1, the normalized 
data for aluminum, gold, and platinum may be represented by a single 
curve. This was true for the unidirectional as well as the isotropic 
roughnesses, although the nickel data deviate from this curve. The 
causes for this deviation are believed to be associated with high surface 
stresses caused by changes in the crystalline structure and are discussed 
in this report. 


iii 



AEDC-TR-65-170 


CONTENTS 

Page 

ABSTRACT. iii 

NOMENCLATURE. vi 

I. INTRODUCTION. 1 

II. TEST SURFACES. 2 

III, MEASUREMENT TECHNIQUES AND PROCEDURES ... 2 

IV. RESULTS AND DISCUSSION. 3 

V. CONCLUSIONS. 6 

REFERENCES . 7 

ILLUSTRATIONS 

Figure 

1. Photomicrographs of Aluminum-Coated Ground Glass. 9 

2. Reflectance Definition and Coordinates. 10 

3. Biangular Reflectance Correlations. 11 

4. Hemispherical-Angular Reflectance, Ground 

Glass Substrate. 12 

5. Hemispherical-Angular Reflectance, Nickel 

Substrate. 13 

6. Hemispherical-Specular Function versus Optical 

Roughness Ratio. 14 

7. Unidirectional Surface Roughness Effects. 15 

TABLES 

I. Root-Mean-Square Roughness of Metal-Coated Ground 

Glass Surface. 16 

II. Root-Mean-Square Roughness of Ground Nickel Surface , . 17 

III. Calculated Specular Ray Reflectance from Information 

in Ref. 2. 18 


v 


















AEDC-TR-65-170 


NOMENCLATURE 

a Parameter connected to the rms slope M of the surface 

contour through the relation/M 

9 Angle between reflected radiation and surface normal 

A. Wavelength 

p Reflectance 

u Root-mean-square surface roughness 

<f> Angle of reflected radiation measured in plane of 

reflecting surface 

\fr Angle between incident radiation and surface normal 

v Solid angle 

SUBSCRIPTS 

ah Angular - hemispherical 

ba Biangular 

ha Hemispherical - angular 

i Incident 

m Mechanical 

o Optical 

p Smooth polished surface 

r Reflected 

s Specular 

V Viewing direction 


vi 



AEDC-TR-65-170 


SECTION I 
INTRODUCTION 


Radiative reflectance of a material has been shown to be a function 
of surface roughness (Refs. 1 and 2) and surface contaminants. There¬ 
fore, the relationship between these factors must be known for accurate 
heat balance studies. 

Until recently, a theory relating the surface roughness and reflect¬ 
ance has been lacking. In 1954 Davies proposed a mathematical model 
which would predict the scattering of microwaves from disturbed water 
surfaces. In 1961 Bennett and Porteus applied Davies' theory to 
reflected light from metal surfaces of specific roughnesses and verified 
its application in the infrared region for the case of near normal inci¬ 
dence and specular reflectance. 

Several experimental investigations of the relationship between the 
roughness of surfaces and the specular or diffuse reflectance have been 
reported (Refs. 3 and 4). Radiation in the visible and near infrared 
region was used, and the reflectance was measured for various angles 
of incidence. In the visible regime, the surface irregularities are com¬ 
parable in magnitude to the radiation wavelength, and the specular 
reflectance is also a function of the rms surface roughness and slope 
(Refs. 1 and 5). In the infrared, the specular reflectance is primarily 
a function of the rms surface roughness. Using the Davies-Bennett 
theory, the optical surface roughness may be calculated from infrared 
reflectance data, and the rms slope may be obtained from visible re¬ 
flectance measurements. 

In a recent paper by Birkebak and Eckert (Ref. 2), biangular, 
specular, and hemispherical-angular reflectance measurements of 
roughened aluminum and nickel surfaces were discussed in terms of 
the surface roughness, u 0 , and wavelength, \ . In their conclusions, 
the authors recommended additional studies be made of the effects of 
surface material on the hemispherical-angular reflectances. This 
report expands the surface material effects on the hemispherical- 
angular reflectance in terms of new measurements and additional cal¬ 
culations, The discussion centers around the wavelength range where 
the hemispherical-angular reflectance is essentially constant and inde¬ 
pendent of the optical surface roughness ratio, a c /A . The test surfaces 
studied were films of aluminum, gold, platinum, and nickel applied on 
roughened substrates of glass and pure nickel. 


1 



AEDC-TR-6 5-170 


SECTION H 
TEST SURFACES 


The test surfaces were prepared by a standard optical grinding 
technique using aluminum oxide grinding compounds of various grit 
sizes. In this technique, the sample is free to rotate around its own 
center while moving back and forth across the rotating grinding wheel. 

Ground glass was chosen as the substrate material because it ob¬ 
tains a very irregular surface in the grinding process. All ground sur¬ 
faces were coated simultaneously with an evaporated metal film to a 
thickness of approximately 8 x 10 - 6 in. The irregular structure of the 
surfaces can be seen in the photomicrographs (Fig. 1). In the following 
tables and figures, the various samples are identified by their surface 
roughness, cr m , which was measured mechanically with a Cleveland 
Model BK6101 roughness indicator. The rms mechanical and optical 
surface roughnesses for metal-coated glass samples are given in Table I. 

The nickel surfaces were prepared using the same techniques 
described for the ground glass surfaces. The mechanical and optical 
surfaces' roughnesses are given in Table II. 

A metal-coated polished glass sample and a polished nickel sample 
were used as reference surfaces in their respective measurements 
(Ref. 2). The surface irregularities of these samples were an order of 
magnitude smaller than those of the smoothest roughened sample. 


SECTION III 

MEASUREMENT TECHNIQUES AND PROCEDURES 


The angular-hemispherical technique (ah) was employed in the re¬ 
flectance measurements in the visible and near infrared region. This 
technique is shown in Fig. 2a. The incident radiation is contained in the 
solid angle Au^, and the radiation, which is reflected hemispherically, 
is measured. The hemispherical-angular technique (ha) was used in the 
infrared measurements. In this technique (Fig, 2b), the test surface is 
irradiated hemispherically, and the energy reflected in a particular solid 
angle, Au r , is measured. Previous investigations (Refs. 2 and 4) have 
shown that the two techniques are equivalent if the angles and Au^ are 
equal to the angles 9 V and Aw r . The solid angles Aui and Au r , used in 
this study, were approximately equal, and ^ = approximately 15 deg and 
9 y = 10 deg. This difference in ^ and By was caused by the different 


2 



A EDC-T R-65-T70 


geometries of the two systems; however, no difference was noted in the 
data in the overlap region. 

Two techniques were employed in measuring the hemispherical - 
angular and angular-hemispherical reflectance. The first system was 
identical to that described in Ref. 2. It consisted of an integrating 
sphere, a radiation source, a focusing mirror, and a monochromator. 
The sample was uniformly radiated by the source and multiple reflec¬ 
tions from the sulfur interior of the integrating sphere. The energy 
reflected at an angle of 6 V = 10 deg from the normal was viewed by a 
mirror. This energy was focused on the entrance slit of the mono¬ 
chromator and the intensity measured by the detector. The second sys¬ 
tem employed was a standard Beckman DK-2A spectrophotometer with 
a magnesium oxide-coated integrating sphere attachment. The angle of 
incident energy was approximately 15 deg from the normal. 

Using either technique, the test surface was placed in the inte¬ 
grating sphere. The surface was irradiated, and the energy reflected 
was measured as a function of wavelength. The reflectance of each 
roughened surface was compared to the respective polished sample and 
to a standard sample. The standard samples used were magnesium 
oxide in the 0. 35- to 2. 7-ju range and flowers of sulfur from 1. 5 to 1 5 /j . 


SECTION IV 

RESULTS AND DISCUSSION 


According to Birkebak and Eckert (Ref. 2) in their discussion on 
the hemispherical-angular reflectance, Pha> the theory of Davies (Ref. 3) 
indicates that p^ a is independent of wavelength for A < cr 0 . The results 
(Ref. 2) shown in Fig. 3 for the biangular reflectance normalized with 
respect to the specular ray reflectance indicate that over a threefold 
range of surface roughness and fourfold change of wavelength that the 
results are independent of wavelength. 

The ratio of the hemispherical-angular reflectance of the rough 
surface to that of a polished sample of the same material plotted versus 
the optical roughness ratio, o Q f A, is shown in Figs. 4 and 5 for alumi¬ 
num, gold, nickel, and platinum. The aluminum surface approaches the 
asymptotic hemispherical-angular reflectance value about twice that of 
the nickel value (open symbols. Figs, 4 and 5). The variation of the 
hemispherical-angular reflectance with film material is the subject of 
the remaining section of this report. 


3 



AEDC-TR-6 5-170 


In order to evaluate this effect, the test surfaces studied in Ref. 2 
(evaporated films of pure aluminum on ground glass and roughened 
nickel samples) were restudied. Using these test samples as substrate 
surfaces, evaporated films of gold, platinum, and nickel were deposited 
and the reflectances measured as a function of wavelength from 0. 5 to 2p , 

The data are presented as the ratio of the hemispherical-angular 
reflectance of a roughened surface to that of a perfectly smooth surface 
(a Q = 0. 003p ) of the same material, Pha.1 Pha, p versus the ratio of the 
optical rms roughness to wavelength, o 0 f\, where a 0 was determined 
previously in Ref. 2 and given in Tables I and II, 

Since the nickel surfaces had been exposed to excessive handling, 
they were restudied after having been cleaned. There was no indication 
that any major change had occurred in the roughness distribution at the 
wavelengths used. The results are shown in Fig. 5 (solid points), and 
satisfactory agreement is obtained where the two sets of data overlap. 

The hemispherical-angular reflectance results* of gold and plati¬ 
num on ground glass agree within 2 percent with those of aluminum 
(Fig. 4). The results for gold on a nickel substrate show a change in 
hemispherical-angular reflectance by a factor of 2 as compared to 
nickel and are in fair agreement with those of gold on ground glass. 

These results indicate that the surface materials of aluminum, gold, 
and platinum do not affect the normalized hemispherical-angular reflect¬ 
ance. However, the discrepancy between ground nickel, gold, plati¬ 
num, or aluminum remains to be explained. 

To resolve this peculiar behavior of nickel, sputtered films of pure 
nickel were applied to some of the ground glass samples. The data 
(Fig. 5) agree within experimental error with the results in Ref. 2 for 
pure nickel surfaces. Therefore, it must be concluded that the cause is 
primarily associated with the nickel surfaces (Ref. 6). 

Further examination of the results in Ref. 2 reveals that when the 
angular-hemispherical reflectance is normalized with respect to the 
specular ray direction, both the aluminum on ground glass and nickel 
surfaces give similar results as shown in Fig. 6. This indicates, as is 
shown in Fig. 3, that the roughness characteristics of the two materials 
are similar. 

Considering all of the above facts, the difference between the ab¬ 
solute hemispherical-angular reflectances of nickel and other surfaces is 


*It was assumed that the optical roughness o 0 is independent of the 
film material. 


4 



A E DC* TR-65-170 


thought to be associated with high surface stresses caused particularly 
by changes in the crystalline structure of the nickel (Ref. 6). These 
changes could result from the grinding process, contamination of the 
surface by the grinding compounds (inclusion of grinding grit into the 
surface), and by the sputtering process used to apply the thin film in 
the case of ground glass substrate. The situation of highly stressed 
thin films of nickel on glass substrates has been observed in work on 
microminiature electronic circuits (Ref. 6). This causes large varia¬ 
tions in the physical properties. 


According to Davies (Ref. 5), the angular-hemispherical reflect¬ 
ance of a roughened surface to a perfectly smooth surface for <r 0 /A > 1.0 
is 

- ^ - ah - = , I- - -1 / / [ (cos 6 f cos i£) 2 ] e” z (sin QA$A<f>) 

P ah.p 32,7 L °o J ° ° 


2 


1/2 


/a\ S ( sin Q cos dt — sin {p ) 1 

V <T 0 J L ( cos Q + cos 


+ sin 3 6 sin 2 tj> 

J? 


( 1 ) 


Three curves calculated using values of a 2 /a 0 2 of 10, 15, and 20 are 
shown in Fig. 3 for the distribution function of reflected radiation, and 
a value of 15 best describes the experimental results. Equation (1) is 
normalized with respect to the reflectance in the specular ray direction 
by 



( 2 ) 


Equation (2) is for cos 6 = cos ^ = 1.0 which approximates the experi¬ 
mental conditions cos 10 deg = 0.985. Using a2/cr 0 2 of 10, 15, and 20, 
calculations of Pah/Pba s are shown in Fig. 6. Again the value of 
a2/o 0 2 = 15 agrees'most closely with the experimental results. Finally, 
Eq. (2) is used to calculate the specular ray reflectance for the various 
values of a2/cr 0 2 . The results are given in Table III and are not in agree¬ 
ment with the experiment. For nickel the experimental value is approxi¬ 
mately 0. 001, and for aluminum it is between 0. 002 and 0. 003. It 
appears that Davies' equation is off by a factor of four, if agreement 
with the aluminum data is the desired result. If this is the case, for 
a 2 /cr 0 2 = 15, the specular ray reflectances are in agreement with the 
aluminum results when the correction is applied. 


The preceding discussion has been centered around surfaces of 
isotropic roughnesses. Russell (Ref. 3) presents angular-hemispherical 
reflectances for surfaces with unidirectional roughness prepared by 
sanding the surface in one direction with various grades of emery paper. 


5 



AEDC-TR-65-170 


Samples of pure copper and of stainless steel were prepared. The 
results of Ref. 3 are normalized according to the procedure presented 
in this report, and the mean roughness height, measured by a profilom- 
eter, is used in the roughness ratio. The final result is shown in Fig. 7, 
and the trend of unidirectional roughness is similar to the isotropic 
results. The results of Ref. 3 for copper between the wavelengths of 
0. 5 to 0. 7p have not been included because over this wavelength range 
the reflectance changes from approximately 40 to 90 percent, and it is 
difficult to obtain good results where the reflectance changes rapidly 
with wavelength. 


SECTION V 
CONCLUSIONS 


Results of measurements of hemispherical reflectance character¬ 
istics of roughened surfaces are presented for aluminum, gold, plati¬ 
num, and nickel films on substrate materials of glass and pure nickel. 
Various surface roughnesses were obtained by standard optical grinding 
techniques. 

A single curve may be obtained showing the effects of surface rough¬ 
ness on the monochromatic hemispherical reflectance. This is accom¬ 
plished by plotting the ratio of the hemispherical reflectance of a rough¬ 
ened surface to that of a perfectly smooth surface versus the ratio of the 
rms surface roughness to incident wavelength. This treatment yields a 
single curve for aluminum, gold, platinum, and copper. The unidirec¬ 
tional roughness of the copper sample does not influence the normalized 
results. This technique thus gives a possible means of intercomparing 
reflectance measurements of samples which have been roughened by 
several different methods. The nickel data do not agree with this 
general curve, and it is believed that surface effects such as lattice 
strain, etc., are the cause of this deviation. 

The relationship between surface roughness and the wavelength of 
the incident radiation is quite evident. The data indicate that when the 
wavelength is less than the surface roughness, a 0 f X > 1, the normalized 
reflectance is essentially a constant value. Previously it was assumed 
that the reflectance would decrease as a smooth function of a Q /\. It is 
interesting to note that the reflectance becomes a constant at the same 
value of a 0 j \ as the deviation of the specular ray from the fundamental 
law of reflection occurs. Also as the wavelength becomes larger than 
the surface roughness, the reflectance approaches that of the smooth 
surface. These results were observed for the four films tested on both 
substrate materials. 


6 



AEDC-TR-65-170 


REFERENCES 


1. Bennett, H. E. and Porteus, J. O. "Relation between Surface 

Roughness and Specular Reflectance at Normal Incidence. " 
Journal of the Optical Society of America , Vol. 51, February 
1961, pp. 123-129. 

2. Birkebak, R. C. and Eckert, E. R. G. "Effects of Roughness of 

Metal Surfaces on Angular Distribution of Monochromatic 
Reflected Radiation. M Journal of Heat Transfer , Transactions 
of the ASME, Series C, Vol. 87, February 1965. 

3. Russell, D. A. "The Spectral Reflectance of Rough Surfaces in the 

Infrared. " Master Thesis, University of California, Berkeley, 
1961. 

4. Torrance, K. E. "Monochromatic Directional Distribution of 

Reflected Thermal Radiation from Roughened Dielectric Sur¬ 
faces. " Master Thesis, Mechanical Engineering Department, 
University of Minnesota, January 1964. 

5. Davies, H. "The Reflection of Electromagnetic Waves from a 

Rough Surface. " Proceedings of the Institute of Electrical 
Engineers, Vol. 101, 1954, pp. 209-213. 

6. Private Communication - Dr. R. Belser, Experimental Station, 

Georgia Institute of Technology. 


7 




{. Polished Surface 


e. 32.0-/i Aluminum Oxide 
Grinding Grit 


Aluminum Oxide 








o 


NORMAL 


INCIDENT 

RADIATION 



REFLECTED RADIATION 
^—TEST SURFACE 


a. Angulor-Hemispherical Technique 


iMAL REFLECTANCE 
'0--^/MEASURED 
■Au r 


HEMI SPHERICALLY 
IRRADIATED 

^5 



TEST SURFACE 


b. Hemispherical-Angular Technique 


Pig, 2 Reflectance Definition and Coordinates 


AEDC-TR-65-170 



COSo 


fO 


(o/A) *0.47 
(o/A ) 0 * 0.51 

(o/A) m = 0.25 - 0.43 (Ni and Al) 


0.60 G.G. 
0.74 NICKEL 


i|) = 10 deg 

SURFACE 

o ALUMINUM-COATED GRD GLASS 
o ALUMINUM-COATED GRD GLASS 
□ ALUMINUM-COATED GRD GLASS 
a ALUMINUM-COATED GRD GLASS 



0 deg 


0.67 

0.58 

1.04 

1.01 


1.5 

1.0 

2 



Fig. 3 Biangular Reflectance Correlations 





to 


SURFACE COATING 

A| (REF. 2) Au Pt 0 Q| |i SURFACE, \x 

o • o 0.58 9.5 

O * 0.67 5.0 

□ ■ » 1.01-1.04 22.5 

v ▼ ▼ 2.06 32.0 

1.0 .--- 



OPTICAL ROUGHNESS RATIO, o Q /A 


Fig. 4 Hemispherical-Angular Reflectance, Ground Glass Substrate 


A E DC-T R-65-170 



SURFACE COATING 


Ni (REF. 2) Au* o 0 , m SURFACE, m 



OPTICAL ROUGHNESS RATIO, o 0 /X 


Fig. 5 Hemispherical-Angular Reflectance, Nickel Substrate 


A E DC-T R-65-170 





0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 

OPTICAL ROUGHNESS RATIO, a Q IX 


Fig. 6 Hemispherical-Specular Function versus Optical Roughness Ratio 


A E DC-T R-65-170 






AEDC-TR-65-170 





CT> 


TABLE I 

ROOT-MEAN-SQUARE ROUGHNESS OF METAL-COATED GROUND GLASS SURFACE 


Average 

Grit Size, * 

M 

Mechanical 

Roughness, 

CT m,M 

Optical 

Roughness, 

a o,H 

a o 

°m 

Polished 

Surface 

Present 

Ref. 2 Study 

0.015 0.03< 

Ref. 2 
Aluminum 

Ref. 2 

9.5 

0. 36 

0.58 

1. 72 

5.0 

0.38 0.38 

0.67 

1. 76 

22.5 

0.61 0.76 

1. 04 

1. 70 

32.0 

1.47 1.27 

2. 06 

1.40 


* Aluminum oxide grinding compound 


AEDC-TR-65-170 



TABLE II 

ROOT-MEAN-SQUARE ROUGHNESS OF GROUND NICKEL SURFACE 


Average 

Grit Size, * 

Mechanical 

Roughness, 

CT m, » 

Optical 

Roughness, 

°o/ 

a o 

a m 



Present 

Ref. 2 



Ref. 2 

Study 

Nickel 

Ref. 2 

Polished 





Surface 

0.015 

0. 06< 


2.86 

9. 5 

0. 14 

0. 15 

0.40 

2.82 

5. 0 

0. 17 

0. 20 

0. 48 

2.45 

22, 5 . 

0. 315 


0. 78 


32. 0 

0. 86 

0. 76 

1. 38 

1. 70 


^Aluminum oxide grinding compo.und 



TABLE III 

CALCULATED SPECULAR RAY REFLECTANCE FROM INFORMATION IN REF. 2 


^ba 


(calculated 


ba 



Pp 1 

Eq. (2)) 
s 

Pp 

s 




Aluminum 

10 


0.0004 



15 


0.0006 

0. 0020 - 0. 0028 

20 


0. 0008 




(measured Ref. 2) 


Nickel 


0. 001 



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T ORIGIN A TIN G ACTIVITY fCofporafo author) \za REPORT SECURITY CLASSIFICATION 

Arnold Engineering Development Center (AEDC), UNCLASSIFIED 

ARO, Inc., Operating Contractor Z t> group 

Arnold Air Force Station, Tennessee _ N/A _ 

3 REPORT TITLE 

HEMISPHERICAL REFLECTANCE OF METAL SURFACES AS A FUNCTION OF 
WAVELENGTH AND SURFACE ROUGHNESS 


4 DESCRIPTIVE NOTES (Type of report and inclusive detea) 

_N/A_ 

5. AUTHORfSJ (Laat name lira! nama, initial) 


Birkebak, R. C., Georgia Institute of Technology 

Dawson, J. P. , McCullough, B. A., and Wood, B. E. ARO, Inc. 


fl. REPO RT DATE 

7a TOTAL NO. OF PAGES 

7b. NO. OF REFS 

October 1965 

24 

6 

8a. contract or grant no. 

9a. ORIGINATOR'S REPORT NUMBER^) 1 

AF40(600)-1200 



b. PROJECT NO. 8951 

AEDC-TR-65-170 

_ 


e. Program Element 61445014 

96. OTHER REPORT NOfS) (Any other numbers that may be assigned 1 
this report) 1 

Task 895104 

N/A 


10. AVAIL ABILITY/LIMITATION NOTICES 



Qualified requesters may obtain copies of this report from DDC. 

11. SUPPLEMENTARY NOTES 

12. SPONSORING MILITARY ACTIVITY Arnold 

N/A 

Engineering Development Center (AEDC) 
Air Force Systems Command (AFSC) 
Arnold Air Force Station. Tennessee 


13 ABSTRACT 


Measurements of the hemispherical reflectance of metallic 
surfaces with controlled surface roughness were made using a sulfur 
infrared integrating sphere and a Beckman DC2A spectrometer. The 
surfaces studied were ground glass and nickel coated with films of 
aluminum, gold, platinum, and nickel. The data indicate that beyond 
a certain ratio of surface roughness to incident wavelength, Oo/k “ 1 
the normalized data for aluminum, gold, and platinum may be 
represented by a single curve. This was true for the unidirectional 
as well as the isotropic roughnesses, although the nickel data 
deviate from this curve. The causes for this deviation are believed 
to be associated with high surface stresses caused by changes in the 
crystalline structure and are discussed in this report. 


DD 1473 


UNCLASSIFIED 
Security Classification 














UNCLASSIFIED 


Security Classification 


IS 

KEY WORDS 

reflectance 


surfaces 


wavelengths 


sulfur 


nickel 


aluminum 


gold 


platinum 



1 LINK A 

LINK B 1 

I ROLE 

WfT 

ROLE 

WT 1 



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7a. TOTAL NUMBER OF PAGES: The total page count 
should follow normal pagination procedures, i. e., enter the 
number of pages containing information. 

7b. NUMBER OF REFERENCES; Enter the total number of 
references cited in the report. 

Sa. CONTRACT OR GRANT NUMBER: If appropriate, enter 
the applicable number of the contract or grant under which 
the report was written. 

8b, 8c, & 8d. PROJECT NUMBER: Enter the appropriate 
military department identification, such as project number, 

■ subproject number, system numbers, task number, etc. 

9a. ORIGINATOR'S REPORT NUMBER(S): Enter the offi¬ 
cial report number by which the document will be identified 
and controlled by the originating activity. This numher must 
be unique to this report. 

9b. OTHER REPORT NUMbER(S): If the report has been 
asa : gned any other report numbers (either by the originator 
or by the sponsor), also enter this number(s). 

10. AVAILABILITY/LIMITATION NOTICES: Enter any lim¬ 
itations on further dissemination of the report, other than those 


imposed by security classification, using standard statements 
such as: 

(1) "Qualified requesters may obtain copies of this 
report from DDC " 

(2) "Foreign announcement and dissemination of this 
report by DDC is not authorized. ’’ 

(3) “U. S. Government agencies may obtain copies of 
this report directly from DDC. Other qualified DDC 
users shall request through 


(4) "U. & military agencies may obtain copies of this 

report directly from DDC Other qualified users 
shall request through 


(5) "All distribution of this report is controlled. Qual¬ 
ified DDC users shall request through 


If the report has been furnished to the Office of Technical 
Services, Department of Commerce, for sale to the public, indi¬ 
cate this fact and enter the price, if known, 

11. SUPPLEMENTARY NOTES: Use for additional explana¬ 
tory nates. 

12. SPONSORING MILITARY ACTIVITY: Enter the name of 
the departmental project office or laboratory sponsoring (pay* 
ing tor) the research and development. Include address. 

13. ABSTRACT: Enter an abstract giving a brief and factual 
summary of the document indicative of the report, even though 
it may also appear elsewhere in the body of the technical re¬ 
port. If additional space is required, a continuation sheet shall 
be attached. 

It is highly desirable that the abstract of classified reports 
be unclassified. Each paragraph of the abstract shall end with 
an indication of the military security classification of the in¬ 
formation in the paragraph, represented as (TS). (S), (C), or (V). 

There is no limitation on the length of the abstract. How¬ 
ever, the suggested length is from 150 to 22S words. 

14 . KEY WORDS: Key words are technically meaningful terms 
or short phrases that characterize a report and may he used as 
index entries for cataloging the report. Key words must be 
selected so that no security classification is required. Identi¬ 
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project code name, geographic location, may be used as key 
words but w'll be followed by an indication of technical con¬ 
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UNCLASSIFIED