more than just the vegetation are measured. To the extent that the undercover 
is darker than the vegetation, a response from the vegetation as a result of 
hevay metal stress may be masked. On the other hand, plant density or total 
biomass may be a useful indication of heavy metal stress. 
The field measurements support the laboratory studies indicating that increased 
reflectance in the visible part of the spectrum generally results from heavy 
metal stress and that changes in the near infrared part of the spectrum are 
variable and less reliable. 
AIRBORNE MULTISPECTRAL SCANNER STUDIES 
  
To exploit the clear spectral response, particularly in the visible of vegeta- 
tion to heavy metal stress, airborne multispectral scanners of the type develo- 
ped by Chiu and Collins (1978) or used by NASA (Milton, 1981) must be used. The 
lab and field studies described earlier have limited areal coverage and are 
difficult to conduct where there is poor access ; they are, therefore, 
unsuitable for a mineral exploration program. Airborne scanners permit rapid 
coverage of large areas with high spatial resolution (pixels about 20 m on a 
side) and high spectral resolution (channels as small as 1.4 nm for the Chiu 
and Collins instrument ). Experiments. reported by Birnie and Hutton (1976), 
Birnie and Dykstra (1978), Collins et al. (1977 and 1978), Collins and Chiu 
(1979), and Birnie and Francica (1981), have used the Chiu and Collins multi- 
spectral scanner and found correlations between the spectral data and vegeta- 
tion growing in mineralized areas. This author and his coworkers report increased 
reflected radiance values in the visible part of the spectrum for lodgepole pine 
(670 nm) and douglas fir (560 nm) growing on a porphyry copper deposit. While 
Collins and his coworkers report a spectral shift of 10-20 nm of the chlorophyll 
absorption edge at about 700-750 nm in a conifer forest. 
The increased reflected radiance in the visible reported by this author and 
his coworkers is consistent with heavey metal induced chlorosis. However, these 
changes may also be related to total plant density or biomass. The spectral 
shift seen by Collins and his coworkers is probably related to a decrease in 
chlorophyll content of the vegetation since, as reproted by Elvige and 
Lyon (1982), a decrease in the chlorophyll content increases the reflectance 
on the edge of the chlorophyll A absorption band (centered at 675 nm) and pro- 
duces an apparent shift of the absorption edge. 
Milton (1981) used band ratios of NASA's 24 channel scanner to map plant species 
in the East Tintic Mountains, Utah. She created a band ratio image of both 
visible and near infrared values where each of the three primary colors corres- 
ponded to one of the three major plant communities in the area. The areas 
indicated on the image to contain a paucity of vegetation also correlated with 
zones of hydrothermal alteration. Schwaller and Tkach (1980) used aerial 
photographic techniques to detect premature leaf senescence in an area of Cu 
mineralization but warned that they also detected premature senescence outside 
the miñeralized zone. 
On the basis of the limited airborne multispectral scanner work done to date, 
it appears that the yisible region («750 nm) is the most promising for detec- 
ting geobotanical stress related to chlorosis. However, overall plant density 
determinations require measurements in the near infrared. 
    
   
   
   
  
   
    
  
    
  
   
    
   
  
     
   
  
   
    
  
  
  
  
    
  
     
   
  
  
  
  
  
   
     
   
    
  
   
   
LANDSAT STUD 
The Landsat 
based and ai 
anomalies fr 
B7/B4 was be 
ted with a s 
Cu stressed 
and Lefevre. 
that correla 
This author 
Landsat digi 
Caraiba Mini 
district is 
metasediment 
dark brown c 
quartz rich 
terranes are 
because the 
other terra 
if they prod 
the Brasilia 
rence of cer 
rocks or the 
on the mafic 
Numerous inv 
of biomass d 
fact that so 
chlorophyll, 
testing a nui 
merely exami! 
example, the 
did not accu 
vegetated. S: 
complete, the) 
and the soil: 
rocks. The di 
rocks have gi 
units allows 
rocks have h' 
soils. 
When a stand: 
of Dauth and 
the darkness 
soils occur t 
must be norme 
Tucker (1979 
a strong cori 
The overall i 
units with hi 
indices (VI/* 
vegetation ir 
In many remo! 
because it me