A new image processing technique was applied to Viking Lander multispectral images. Spectral endmembers were defined that included soil, rock and shade. Mixtures of these endmembers were found to account for nearly all the spectral variance in a Viking Lander image

Adams, John B.

Smith, Milton O.

English

NASA Technical Reports Server

SPECTRAL MIXTURE MODELING: FURTHER ANALYSIS O F  ROCK AND SOIL 
TYPES AT THE V I K I N G  LANDER SITES 
John B ,  Adams and Milton 0 ,  Smith 
Department of Geological Sciences 
Univers i ty  of Washington, S e a t t l e ,  WA 98195 
We have app l i ed  a  new image-processing technique t o  
Viking Lander m u l t i s p e c t r a l  images (Adams e t  a l e ,  1986) . 
Spec t ra l  endmembers were def ined  t h a t  included s o i l ,  rock 
and shade. Mixtures of t h e s e  endmembers were found t o  
account f o r  nea r ly  a l l  of t h e  s p e c t r a l  var iance  i n  a  Viking 
Lander 1 image, thus  one s p e c t r a l  type  of s o i l  and one type  
of rock mixed i n  va r ious  propor t ions  accounted f o r  t h e  
observed "color"  d i f f e r e n c e s .  
Fur the r  work on t h e  Viking Lander 1 image has solved 
t h e  problem of t h e  na tu re  of a  minor s p e c t r a l  endmember t h a t  
we o r i g i n a l l y  i d e n t i f i e d  a s  being due t o  secondary 
i l lumina t ion  e f f e c t s ,  That endmember can now be shown t o  be 
t h e  r e s u l t  of l i g h t i n g  e f f e c t s  ( e s p e c i a l l y  n e a r - f a r / f i e l d  
s p e c t r a l  phase changes) and t h e  e f f e c t s  of a  foreground 
m i s r e g i s t r a t i o n  of t h e  t h r e e  I R  bandpass images with t h e  
t h r e e  v i s i b l e  bandpass images i n  t h e  o r i g i n a l  Viking d a t a .  
The m i s r e g i s t r a t i o n  of t h e  d a t a  i s  not  apparent when 
viewing ind iv idua l  bandpass images o r  co lo r  composites; 
however it i s  d i s t i n c t  i n  t h e  RMS ( r o o t  mean squared) e r r o r  
image which d i sp lays  t h e  accumulated e r r o r  between t h e  model 
image and t h e  r e a l  image. The p i x e l s  with high RMS e r r o r  do 
not  correspond s p e c t r a l l y  o r  s p a t i a l l y  t o  reasonable s o i l  o r  
rock types ,  however they  fo rce  t h e  in t roduc t ion  of another  
s p e c t r a l  endmember. 
The m i s r e g i s t r a t i o n  was co r rec ted  by D r .  E .  Guinness a t  
Washington Universi ty  ( S t .  Lou i s ) .  When t h e  s p e c t r a l  mixing 
model was c a l c u l a t e d  f o r  t h e  r e c t i f i e d  images us ing  rock, 
s o i l  and shade a s  endmembers t h e  RMS e r r o r  image showed only 
a  weak s p e c t r a l  phase s h i f t  from near  t o  f a r - f i e l d ,  and no 
a d d i t i o n a l  endmember was requi red .  These r e s u l t s  f u r t h e r  
emphasize t h e  usefu lness  of t h e  mixing model f o r  i s o l a t i n g  
geo log ica l ly  meaningful s p e c t r a l  var iance  from t h a t  
introduced by t h e  imaging system o r  by l i g h t i n g  e f f e c t s .  
Analysis  of o t h e r  Viking Lander 1 and 2 images shows 
t h a t  t h e  s p e c t r a l  phase e f f e c t  i s  s t rong  a t  c e r t a i n  l i g h t i n g  
geometries.  In  a l l  cases  t h e  e f f e c t  i s  expressed a s  a  
gradual  s h i f t  i n  t h e  r e f l e c t a n c e  s p e c t r a  of a l l  o b j e c t s  from 
near  f i e l d  t o  f a r  f i e l d .  The s p a t i a l  p a t t e r n s  of t h e s e  
s h i f t s  a r e  unre la ted  t o  geologica l  f e a t u r e s .  However, t h e  
phase e f f e c t  must be i s o l a t e d  and removed i n  order  t o  
compare s o i l  o r  rock s p e c t r a  i n  d i f f e r e n t  p a r t s  of an image. 
https://ntrs.nasa.gov/search.jsp?R=19870013982 2020-03-20T10:25:33+00:00Z
W e  have a p p l i e d  t h e  mixing model t o  o t h e r  Lander 1 and 
2  images u s i n g  the  same s p e c t r a l  endmembers f o r  s o i l  and 
rock  t h a t  f i t  t h e  d a t a  i n  t h e  Vik ing  Lander 1 image. The 
o b j e c t i v e  h a s  been t o  tes t  f o r  t h e  p r e s e n c e  o f  o t h e r  s o i l  
and rock  t y p e s  by a n a l y s i n g  the  RMS e r r o r  images. M a t e r i a l s  
t h a t  appea r  s p e c t r a l l y  d i f f e r e n t  from t h e  endmembers (and 
t h e i r  m i x t u r e s )  u sed  i n  t h e  model appear  b r i g h t  i n  t h e  RMS 
e r r o r  image. P r e l i m i n a r y  r e s u l t s  show t h a t  t h e  same s o i l  and 
rock  t y p e s  c a r r y  t h rough  a l l  images s t u d i e d  a t  b o t h  Vik ing  
s i tes ,  however t h e r e  a r e  impor t an t  l o c a l  e x c e p t i o n s  where 
a r e a s  o f  s p e c t r a l l y  d i f f e r e n t  r ocks  a l s o  occu r .  A s  d i s c u s s e d  
above w e  can e s t a b l i s h  t h a t  t h e s e  s p e c t r a l  d i f f e r e n c e s  a r e  
n o t  produced by l i g h t i n g  effects o r  by sys tem defects. An 
e v a l u a t i o n  of t h e  n a t u r e  and e x t e n t  o f  t h e s e  new s p e c t r a l  
rock  t y p e s  i s  underway. 
REFERENCE 
Adams, J . B . ,  Smith, M.O. ,  and Johnson, P . E . ,  S p e c t r a l  
m ix tu r e  modeling:  A new a n a l y s i s  o f  rock  and s o i l  t y p e s  a t  
t h e  V ik ing  Lander 1 s i te ,  J. G e o ~ h v s .  R e s . ,  91, 8098-8112, 
1986. 


Spectral mixture modeling: Further analysis of rock and soil types at the Viking Lander sites

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