Data from several AVIRIS flight lines were examined to assess instrument stability and response. Both scene and in-flight calibration data were analyzed statistically. The data clearly indicates that, although the instrument output was noisy and unstable at the time of the data acquisition, valuable spectral signatures can still be extracted and analyzed. Some first order calibration corrections can be performed by forcing internal consistency within the data. AVIRIS data are delivered in band-interleaved-by-line format, but high efficiency routines were developed which access the data as either image or spectral planes and enable effective statistical and visual examination of both AVIRIS scenes and ancillary files. Two methods were used to extract spectral information from segment 4 of the Kelso Dunes flight. Both successfully identified at least three distinct spectral signatures, but neither has positively identified a specific material

Eliason, Eric M.

Kieffer, Hugh H.

Mullins, Kevin F.

Soderblom, Laurence A.

Torson, James M.

English

NASA Technical Reports Server

R A D I O M E T R I C  PERFORMANCE OF A V I R I S :  ASSESSMENT FOR AN A R I D  R E G I O N  
GEOLOGIC TARGET 
HUGH H. KIEFFER, E R I C  M. ELIASON, K E V I N  F. MULLINS, LAURENCE A. 
SODERBLOM, AND JAMES M. TORSON; U.S. Geologica l  Survey, F l a g s t a f f ,  
Ar izona,  USA 
ABSTRACT 
examined t o  assess i n s t r u m e n t  s t a b i  1 i t y  and 
response. 
were analyzed s t a t i s t i c a l l y .  
i n d i c a t e  t h a t ,  a l t hough  t h e  i ns t rumen t  o u t p u t  was 
n o i s y  and uns tab le  a t  t h e  t i m e  o f  da ta  a c q u i s i t i o n ,  
v a l u a b l e  spec t ra l  s i g n a t u r e s  can s t i  11 be e x t r a c t e d  
and analyzed. 
c o r r e c t i o n s  can be performed by f o r c i n g  i n t e r n a l  
cons i s tency  w i t h i n  t h e  data. 
de l  i v e r e d  i n  band-i n t e r l  eaved-by-1 i ne format,  ~ <but we 
haw? developed highi ’ef f icency rout inek,Ahhich access 
t h e  data as e i t h e r  image o r  s p e c t r a l  p lanes and enable 
e f f e c t i v e  s t a t i s t i c a l  and v i s u a l  examinat ion o f  b o t h  
A V I R I S  scenes and a n c i l l a r y  f i l e s .  
i n f o r m a t i o n  f r o m  segment 4 o f  t h e  Ke lso  Dunes 
f l i g h t .  Both s u c c e s s f u l l y  i d e n t i f i e d  a t  l e a s t  t h r e e  
d i s t i n c t  s p e c t r a l  s igna tu res ,  b u t  n e i t h e r  has 
p o s i t i v e l y  i d e n t i f i e d  a s p e c i f i c  m a t e r i a l .  
Data f rom seve ra l  A V I K I S  f l i g h t  l i n e s  were 
Both scene and i n - f l i g h t  c a l i b r a t i o n  da ta  
h e  da ta  c l e a r l y  
Some f i r s t  o r d e r  c a l i b r a t i o n  
A V I R I S  da ta  a r e  
J.. - P l :  tu\ . 
Two methods were used t o  e x t r a c t  s p e c t r a l  
I N TRODUC T I  ON 
v a r i o u s  c a l i b r a t i o n  f i l e s  t h a t  accompany a l l  A V I R I S  f l i g h t s  f o r  
seve ra l  1987 t a r g e t s  (TABLE 1). S t a t i s t i c a l  parameters were 
c o l l e c t e d  f o r  coherent and random n o i s e  p a t t e r n s ,  o f f s e t  and g a i n  
d r i f t s ,  and i n t e n s i t y  s h i f t s ;  some o r  a l l  o f  t hese  problems e x i s t  
i n  every f l i g h t  l i n e  we i n v e s t i g a t e d .  
performance were used t o  r e j e c t  bands w i t h  l ow  s i g n a l  - t o - n o i s e  
r a t i o s .  
F i r s t ,  a d e t a i l e d  s t a t i s t i c a l  a n a l y s i s  was performed on t h e  
These measures o f  
Table 1. Data Used i n  This Work 
F1 i gh t  Target Date Data Used 
~~~ ~~~ 
Mof f e t t  F i  e l  d 
Mountain Pass 
Hebro 
S i e r r a  Foothi  11 s 
Kelso Dunes 
Lake Powell 
Grand Canyon 
San Francisco Bay 
6/25/87 
7130187 
8/01/87 
91 14/87 
9/14/87 
9/18/87 
9/18/87 
10/13/87 
~~~ ~~~ ~ ~~ 
Ca l ib .  o n l y  
Cal ib.  o n l y  
Cal ib.  o n l y  
Cal ib .  o n l y  
Cal ib.  & image 
Cal ib.  o n l y  
Cal ib .  & image 
Cal ib.  & image 
30 
https://ntrs.nasa.gov/search.jsp?R=19890012786 2020-03-20T02:33:47+00:00Z
NO1 SE LEVEL ANALY S I  S 
average and s tandard d e v i a t i o n  values were ob ta ined  f o r  each o f  t h e  
f o u r  separate i n t e r n a l  i n t e n s i t y  1 eve1 s ( F i  gure 1). H i  stograms o f  
raw DN and o f  t h e  abso lu te  second d i f f e r e n c e  o f  t h e  raw DN were 
generated. Using l i n e a r  i n t e r p o l a t i o n  o f  t h e  corresponding 
DN, and t h e  median and mean abso lu te  second d i f f e r e n c e  were 
computed. S i m i l i a r  r o u t i n e s  were run on t h e  dark c u r r e n t  and image 
done on raw A V I K I S  data. 
Pre- and p o s t - f l i g h t  c a l i b r a t i o n  f i l e s  were processed and 
L u i l i u l u L l v L  ~ s n m a o l a + 4 ~ , n  h i c t n n r a r n s  I 1 l d u u y l  U t l l  , t h e  1 and 99 p e r c e n t i l e  p o i n t s  ~f t h e  r a w  
c:1..c I cnw. L y l i l c l l L  C n n m n n f  4 o f  t h e  Kelsc D ~ n e s  f l i g h t .  Al 1 analyses were 
A V I R I S ,  
50.0 
40.0 
30.0 
20.0 
10.0 
0.0 
-10.0 
-28.8 
-30.0 
-40.0 
-50.0 
(prc-posl ddrk for 4 flights / 00-MV- 4 09.08827 
I E 
Lake Powell 
Moffet t  
Grand Canyon 
Kelso 
BAN) NUBER 
F i g u r e  1. The d i f f e r e n c e  between the p re -  and p o s t - c a l i b r a t i o n  
dark c u r r e n t s  a r e  compared f o r  f o u r  A V I R I S  f l i g h t s .  
a r e  a c t u a l l y  cen te red  on zero bu t  each has been p r o g r e s s i v e l y  
o f f s e t  v e r t i c a l l y  by 10 DN. 
A l l  f o u r  p l o t s  
A s imp le  measure o f  d e t e c t o r  noise i s  one-hal f  t h e  median 
a b s o l u t e  va lue  o f  t h e  second d i f f e r e n c e  ( f o r  Gaussian n o i s e  t h i s  i s  
n e a r l y  i d e n t i c a l  t o  t h e  s tandard d e v i a t i o n ) .  This parameter v a r i e s  
s t r o n g l y  w i t h  d e t e c t o r ,  even w i t h i n  each o f  t h e  f o u r  
spectrometers.  Typical  va lues a r e  4.5, 2.5, 3.2, and 2.7 f o r  
spect rometers A, B, C and D, r e s p e c t i v e l y .  For t h e  most respons ive  
d e t e c t o r s  i n  each spectrometer,  t h e  s i g n a l - t o - n o i s e  r a t i o  (SNR) f o r  
t h i s  measure o f  no i se  i s  approx imate ly  150, 55, 100, and 60 f o r  t h e  
f o u r  spectrometers.  A r e v e a l i n g  parameter i s  t h e  "sc ience - to -no ise  
r a t i o " ,  based on t h e  v a r i a t i o n  o f  r e f l e c t i v i t y  w i t h i n  a scene, 
31 
r a t i o e d  t o  the n o i s e  l e v e l .  This parameter i s  on t h e  o r d e r  o f  20 
t o  30 f o r  a l l  f o u r  spectrometers.  
data. 
t e n  p i x e l s  f l o w  across t h e  image. 
t h e  coas t  o f  Oregon) no i se  w i t h  t h e  p e r i o d  o f  14.16 p i x e l s  was 
s h i f t e d  i n  phase by 10.5 samples between l i n e s .  
da ta  i t s e l  f. The 1 ow-1 eve1 p re -ca l  i b r a t i o n  da ta  has an approximate 
square-wave p a t t e r n  w i t h  amp l i t ude  o f  4 t o  6 DN w i t h  a p e r i o d  o f  26 
p i x e l s .  The dark l e v e l  ( 1  p i x e l  pe r  l i n e )  shows h i g h  frequency 
noise,  obvious, ab rup t  l e v e l  s h i f t s  on t h e  o r d e r  o f  5 p i x e l s ,  and 
d r i f t s  on t h e  order  o f  a few DN per  minute. I n  u n i f o r m  scenes, 
some o f  t h e  more obv ious l e v e l  s h i f t s  correspond t o  s h i f t s  i n  t h e  
dark c u r r e n t  f i l e .  
There a r e  severa l  k i n d s  o f  p e r i o d i c  n o i s e  w i t h i n  t h e  A V I K I S  
I n  a wavelength "movie", waves w i t h  a p e r i o d  on t h e  o r d e r  o f  
I n  a u n i f o r m  area ( t h e  ocean o f f  
There are a l s o  severa l  p a t t e r n s  o f  n o i s e  i n  t h e  c a l i b r a t i o n  
COHERENT N O I S E  
A V I K I S  subscene and on-board c a l i b r a t i o n  da ta  acqu i red  d u r i n g  t h e  
Kelso Dunes f l i g h t .  
un i fo rm f l  a t - f i e l d  t a r g e t  f o r  s tudy o f  coherent  n o i s e  a t  b r i g h t n e s s  
l e v e l s  above dark c u r r e n t .  The on-board c a l i b r a t i o n  c o n s i s t e d  of  
i ns t rumen t  data acqu i red  w i t h  t h e  f o r e - o p t i c s  s h u t t e r  c l o s e d  and 
t h e  i n t e r n a l  c a l i b r a t i o n  lamp e i t h e r  t u r n e d  o f f  p r o v i d i n g  dark 
c u r r e n t  data,  o r  a t  h i g h  and low i n t e n s i t y  l e v e l s  p r o v i d i n g  a 
f l a t - f i e l d  a t  d i f f e r e n t  i ns t rumen t  DN o u t p u t  l e v e l s .  
512 samples o f  a l i n e  f o r  a l l  224 s p e c t r a l  channels. Because a 
uni form-radiance f i e l d  was used, ampl i tudes o f  a l l  t h e  'Fou r ie r  
components can be a t t r i b u t e d  t o  e i t h e r  random o r  coherent  F o u r i e r  
no i  se (except  zero f requency).  Typical  background-f  requency 
ampl i tudes due t o  random n o i s e  f o r  t h e  f o u r  spect rometers f a l l  
w i t h i n  t h e  range .5  t o  1.0 DN f o r  most d e t e c t o r s .  Some o f  t h e  
d e t e c t o r s  w i t h  a 1 ower s i g n a l  - t o - n o i  se r a t i o  have n o t i  c a b l y  h i g h e r  
F o u r i e r  ampl i tudes a t  random f requencies.  These i n c l u d e  d e t e c t o r s  
97, 113, 131 t o  136, and 210. 
Coherent no i se  was modeled by F o u r i e r  t rans fo rms  o f  a u n i f o r m  
A subscene o f  t h e  dune f i e l d  p r o v i d e d  a 
A one-dimensional f a s t  F o u r i e r  t r a n s f o r m  (FFT) was a p p l i e d  t o  
P r o - c a l .  h i a h  intensity broad band.  Kelso f l i a h t  fi;,dp': 
Wavelength l p i x e l s / c y c l e l  
F i g u r e  2. 
scan l i n e  f o r  d e t e c t o r  C, band 129. The t r a n s f o r m  i s  o f  t h e  Kelso 
Dunes f l  i g h t  pre-ca l  i b r a t i o n  da ta  acqu i red  w i t h  t h e  f o r e - o p t i c s  
s h u t t e r  c l o s e d  and t h e  i n t e r n a l  c a l i b r a t i o n  lamp a t  t h e  h i g h  
i n t e n s i t y  l e v e l .  Because a un i fo rm- rad iance  f i e l d  was used, t h e  
h igh -amp l i t ude  F o u r i e r  components can be a t t r i b u t e d  t o  coherent  
no ise.  
p i x e l s / c y c l e  and i s  t y p i c a l  o f  most o f  t h e  d e t e c t o r s  i n  
spect rometer  C. 
F o u r i e r  t r a n s f o r m  o f  t h e  f i r s t  512 samples o f  a s i n g l e  
The transform e x h i b i t s  a sharp peak a t  39.38 and 19.69 
32 
The FFTs e x h i b i t e d  severa l  sharp peaks we1 1 above background 
n o i s e  l e v e l s  f o r  t h e  f o u r  spectrometers (see Table 2 and 
F i g u r e  2). 
same f o r  t h e  dark c u r r e n t  c a l i b r a t i o n ,  low and h i g h  i n t e n s i t y  lamp 
c a l i b r a t i o n ,  and image subscene, i t  i s  assumed t o  be an a d d i t i v e  
component t o  t h e  s i g n a l  and no t  a f u n c t i o n  o f  scene b r igh tness .  
I n  most cases a l l  d e t e c t o r s  o f  a spectrometer e x h i b i t e d  t h e  
same coherent  n o i  se frequency b u t  w i t h  v a r y i n g  ampi i tude. 
Spectrometers A and B e x h i b i t e d  t h e  lowest coherent  n o i s e  l e v e l s  o f  
no l a r g e r  than  2.0 DN ampl i tude.  
d i s c e r n i b l e  above random no ise  l e v e l s  when v iewing  a scene. 
Spectrometer D had s l i g h t l y  l a r g e r  coherent n o i s e  l e v e l s  of  no 
l a r g e r  than  4.0 DN ampli tude. 
coherent  n o i s e  l e v e l  was b a r e l y  de tec tab le  above random n o i s e  
l e v e l s  i n  some detec tors .  Spectrometer C e x h i b i t e d  t h e  g r e a t e s t  
coherent  n o i s e  l e v e l s  and were v i s i b l e  w e l l  above t h e  random n o i s e  
1 eve l  s. The 39.38 and 19.39 p i x e l  s /cyc le  coherent  no i  se 1 eve l  s ,  
hav ing  ampl i tudes  as h i g h  as 8.0 and 4.0 DN r e s p e c t i v e l y ,  were 
v i s i b l e  as o b l i q u e  wave pa t te rns .  
Because t h e  coherent  no ise  l e v e l s  a r e  approx imate ly  t h e  
These n o i s e  p a t t e r n s  were n o t  
V i sua l l y ,  t h e  19.59 p i x e l s l c y c l e  
TABLE 2. Summary o f  Four ie r  Transform Resu l t s  
Noise Maxi mum 
Spectrometer ( p i  x e l  s l c y c l  e )  ( Raw DN) Commen t s 
F r equ en cy Amp1 i tude 
A 19.69 1.8 Greatest  i n  d e t e c t o r s  13, 
16, 19, 22, 24, 25, 28, 
30. 
2.12 2.0 Present i n  a l l  d e t e c t o r s  
b u t  minimal i n  10, 30, 
31, 32. 
B 
C 
D 
9.48 2.0 Ampl i tude  n e a r l y  u n i f o r m  
5.70 1.8 Ampl i tude n e a r l y  u n i f o r m  
i n  a l l  de tec to rs .  
i n  a l l  de tec to rs .  
39.38 8.0 Greates t  i n  d e t e c t o r s  126 
t o  146. Ampl i tude v a r i e s  
w ide ly  among de tec to rs .  
131,134, 139, 140, 145, 
157. 
19.69 4.0 Greatest  i n  d e t e c t o r s  
32.00 3.0 Ampl i tude v a r i e s  w i d e l y  
19.69 4.0 Ampl i tude v a r i e s  w i d e l y  
among de tec to rs .  
among de tec to rs .  
33 
WHI TEYTARGET MODEL 
An est imate o f  t h e  expected response o f  A V I R I S  t o  a u n i f o r m  
p o i n t  t a r g e t  was computed based on t h e  c a l i b r a t i o n  f i l e  s u p p l i e d  by  
JPL, a nominal atmospher ic t r a n s m i s s i o n  spectrum computed u s i n g  
LOWTRAN 7 (Alee, 1988), and t h e  s o l a r  spectrum. This r e s u l t e d  i n  a 
"WHITE" spectrum t h a t  was used t o  conver t  A V I R I S  da ta  t o  s u r f a c e  
r e f l e c t a n c e  ( K i e f f e r ,  1988). Al though a t tempts  t o  d e r i v e  
normal ized c a l i b r a t e d  s p e c t r a  u s i n g  t h e  model gave poor r e s u l t s ,  
t h e  model was u s e f u l  i n  e s t i m a t i n g  t h e  q u a l i t y  o f  d i f f e r e n t  
s p e c t r a l  regions based on expected atmospher ic t r a n s m i s s i o n  and 
i n s t  r ument performance. 
An est imate o f  t h e  r e l a t i v e  g a i n  o f  each band was computed by 
deve lop ing  a " re ference"  band composed o f  t h e  sum of  DN f o r  a 
s p e c t r a l l y  cont iguous s e t  o f  low-noise,  h igh -ga in  bands. A 
cornpar is ion o f  t h e  c o e f f i c i e n t  o f  a l i n e a r  l eas t - squares  f i t  o f  t h e  
da ta  from any band t o  t h i s  r e f e r e n c e  band w i t h  t h a t  p r e d i c t e d  by 
t h e  w h i t e - t a r g e t  model g i v e s  a d i r e c t  i n d i c a t i o n  of t h e  change o f  
response o f  each de tec to r .  
SOF WARE D I  SPLAY TOOLS 
ins t rumen t ,  a new system o f  so f tware  was designed t o  handle 
cube-formatted data. 
Workstat ion i n t e r f a c e d  t o  an I V A S  d i s p l a y  system. 
program, QL3, a l l o w s  t h e  user  t o  i n t e r a c t i v e l y  examine a t h r e e -  
dimensional  cube of image data. 
ad jacen t  segments. The l e f t - h a n d  segment i s  an image o f  t h e  
s u r f a c e  (x,y)  a t  a p a r t i c u l a r  wavelength band which i s  d e f i n e d  by 
t h e  l o c a t i o n  o f  t h e  c u r s o r  i n  t h e  s p e c t r a l  ( 2 )  dimension. The 
r i g h t - h a n d  s ide i s  a s p e c t r a l  image r e p r e s e n t i n g  a l l  y p i x e l s  and 
a l l  z bands w i t h i n  an or thogonal  p lane  whose x l o c a t i o n  i s  d e f i n e d  
by t h e  cu rso r .  A graph o f  t h e  f u l l  spectrum a t  t h e  x,y p i x e l  i s  
d i s p l a y e d  on the works ta t i on .  Band images can be d i s p l a y e d  s i n g l y  
w i t h  numerous co lor -coded o v e r l a y  planes, o r  as a t h r e e  c o l o r  
composite. Various o p t i o n s  i n c l u d e  panning, pseudo-co lo ra t i on ,  
n o r m a l i z a t i o n ,  s t r e t c h i n g  and l i s t i n g s  o f  c u r r e n t  d i s p l a y  values. 
The cube d i s p l a y  s o f t w a r e  i s  designed t o  r u n  w i t h  a number of 
concu r ren t  processes t h a t  share access t o  t h e  da ta  i n  memory. 
These concurrent  processes enable one t o  i n t e r a c t i v e l y  c o l  1 e c t  and 
man ipu la te  s p e c t r a l  da ta  and s t o r e  t h e  r e s u l t s  o f  seve ra l  such 
analyses i n  t a b u l a r  form f o r  l a t e r  process ing.  Fo r  example, p i x e l s  
t h a t  match a se lec ted  spectrum can be i d e n t i f i e d  and used t o  
produce a themat ic  map o r  mask. A s e r i e s  o f  t hese  themat i c  images, 
which may be c o l o r  coded, can be o v e r l a i d  on t h e  o r i g i n a l  image t o  
d e l i n e a t e  ( o r  mask o u t )  areas w i t h  s p e c i f i c  s p e c t r a l  
c h a r a c t e r i  s t i c s .  
Given the l a r g e  q u a n t i t y  o f  da ta  produced by t h e  A V I R I S  
The s o f t w a r e  runs on a DEC Microvax Graphics 
The cube i s  d i s p l a y e d  i n  two 
The d i s p l a y  
DATA ANALYSIS 
sur faces w i t h i n  t h e  scene by suppress ing i n s t r u m e n t  g a i n  and o f f s e t  
e r r o r s  and spec t ra l  v a r i a t i o n  i n  atmospher ic t r a n s m i s s i o n  was made 
u s i n g  t h e  l i n e a r  f i t  c o e f f i c i e n t s  of  each band t o  t h e  ' ' reference' '  
band mentioned above. 
was a d j u s t e d  by t h e  d e v i a t i o n  o f  t h e  re fe rence  band, a t  t h a t  p i x e l ,  
An attempt t o  e x t r a c t  s u b t l e  s p e c t r a l  v a r i a t i o n s  a long  
For  each band, t h e  response a t  each p i x e l  
34 
f rom t h e  r e f e r e n c e  band average and scaled by t h e  s lope  o f  t h e  
l i n e a r  c o r r e l a t i o n  between t h i s  band and t h e  r e f e r e n c e  band. This 
process removed t h e  i ns t rumen t  dark l e v e l  and atmospher ic a d d i t i v e  
terms, and v a r i a t i o n  i n  i n s t r u m e n t a l  gain, s o l a r  s p e c t r a l  rad iance  
and atmospher ic t ransmiss ion.  It does n o t  a m p l i f y  no i se ,  b u t  i t  
does remove any c o r r e l a t i o n  o f  spec t ra l  s i g n a t u r e  w i t h  t h e  l o c a l  
i n c i d e n c e  angle. To whatever e x t e n t  the r e f e r e n c e  bands do n o t  
rep resen t  t h e  s p e c t r a l l y  averaged b r i g h t n e s s  of  su r face  m a t e r i a l s ,  
t h i s  process has t h e  u n f o r t u n a t e  c h a r a c t e r i s t i c  o f  magn i f y ing  t h e  
s p e c t r a l  s i g n a t u r e  o t  t h e  r e f e r e n c e  bands. 
A second technique was developed t o  remove t h e  i n s t r u m e n t  and 
atmospher ic e f f e c t s  w i t h o u t  use of any a b s o l u t e  c a l i b r a t i o n  and was 
a p p l i e d  t o  a p o r t i o n  o f  t h e  Kelso Dunes da ta  s e t  (Soderblom e t  al., 
i n  p r e p a r a t i o n ) .  
and m u l t i p l i c a t i v e  e r r o r s  i n h e r e n t  i n  t h e  A V I R I S  d a t a  so t h a t  
psuedo-spect ra l  s i g n a l s  a r e  n o t  created by t h e  n o r m a l i z a t i o n  o f  t h e  
a d d i t i v e  component. 
The w h i t e - t a r g e t  spectrum mentioned e a r l i e r  was used t o  mask 
o u t  s p e c t r a l  reg ions  of l ow  response. Next, bands w i t h  excess ive 
n o i s e  o r  da ta  c l i p p i n g  were i d e n t i f i e d  and deleted.  The nex t  s t e p  
i n v o l v e d  a process t o  d e t e c t  and d e l e t e  n o i s y  spect ra,  w i t h  any 
spectrum being d e l e t e d  t h a t  had a mean-squared d e v i a t i o n  from b o t h  
i t s  l e f t  and r i g h t  ne ighbors g r e a t e r  than 10 DN. I f  two s p e c t r a  
compared w i t h i n  t h i s  t o 1  erance, t h e n  t h e i  r average was s tored.  
This cleaned-up da ta  s e t  was then  used t o  generate h is tograms of 
a l l  remain ing channels and t o  compute t h e  f i r s t  and t h i r d  
q u a r t i l e s .  F i n a l l y ,  a l i n e a r  s t r e t c h  was a p p l i e d  t o  each s p e c t r a l  
channel, t h a t  sca led t h e  w id ths  and c e n t r o i d s  of  a l l  h istograms t o  
co inc ide .  
t h e  s p e c t r a l  c h a r a c t e r  o f  t h e  sur face,  n o t  t h e  s p e c t r a l  n a t u r e  o f  
t h e  i n s t r u m e n t  o r  atmosphere. This process c o n s i d e r a b l y  improves 
t h e  a b i l i t y  t o  d i s c e r n  i n d i v i d u a l  ground u n i t s .  
process o f  comparing t h e  normal ized s p e c t r a l  f e a t u r e s  i d e n t i f i e d  i n  
t h i s  manner w i t h  absol Ute 1 abo ra to ry  spectra.  
This process d e a l s  separa te l y  w i t h  t h e  a d d i t i v e  
The s i g n a t u r e s  i n  t h e  r e s u l t i n g  s p e c t r a  a r e  dominated by  
We a r e  now i n  t h e  
REFERENCES 
Alee, Ron, Feb. 2, 1988, Personal communication. 
K i e f f e r ,  H. H., A p r i l  19, 1988, Memorandum t o  A V I R I S  p r o j e c t  
Soderblom, L. A. e t  a1 . , i n  preparat ion,  Data-Dependent 'Approaches s c i e n t i s t .  
For C o r r e c t i o n  and Ana lys i s  o f  A V I K I S  Data 
35 


Radiometric performance of AVIRIS: Assessment for an arid region geologic target

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