Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986 
Optimal Thematic Mapper bands and transformations for discerning 
metal stress in coniferous tree canopies 
C.Banninger 
Institute for Image Processing and Computer Graphics, Research Centre Joanneum, Graz, Austria 
ABSTRACT: A statistical analysis of multitemporal Landsat Thematic Mapper (TM) data acquired 
from a pine and a spruce tree stand growing in copper-lead-zinc enriched soils helped define 
the TM spectral bands and transformations best suited for detecting metal stress in conifer 
ous tree canopies. Based on four Landsat TM scene dates, the first principal component (PC1) 
and the band difference BD1 rank the highest of thirty-one single and transformed TM bands 
examined, followed by the TM brightness index (TMB) and Thematic Mapper bands 5 and 7. 
1 . INTRODUCTION 
To effectively employ geobotanical re 
mote sensing techniques in mineral explora 
tion, a simple and expedient approach is 
required that will help define suitable tar 
get areas for follow-up examination by ground- 
based exploration methods. Plants growing in 
soils containing toxic concentrations of 
heavy metals normally undergo changes that 
alter both their physiological make-up and 
their external appearance. These changes to 
a plant are detectable by remote sensing 
means, and in particular by the Thematic 
Mapper sensor system on board Landsat 4 and 
5. Both single and transformed TM bands have 
been employed to monitor the state of vege 
tation growth and the condition of its 
health, although these have been applied in 
most studies on a singular basis and may not 
have been the most suitable band or trans 
formation for the purpose or task at hand. 
The question still remains as to which The 
matic Mapper bands and transformations are 
best at defining metal-related stress in 
vegetation stands. 
To help answer this question - at least 
with respect to coniferous forests - thirty- 
one single and transformed Thematic Mapper 
spectral bands (TABLE 1) for each of four 
Landsat scene dates of two mineralised forest- 
covered area's in southwestern Spain and south 
eastern Austria were statistically evaluated 
to determine the most effective TM bands and 
transformations for metal stress detection. 
The transformed TM bands employed in the 
analysis are configured to enhance or better 
define important plant-energy relationships 
associated with plant growth and health. 
A brief description of the test sites, 
ground and Thematic Mapper data utilised in 
the study, and the analytical and statisti 
cal approaches employed in the evaluation 
of these data sets is presented in the fol 
lowing sections. A more comprehensive des 
cription of these topics can be found in 
Banninger 1984, 1985a, b, c, and 1986. 
2. DESCRIPTION OF TEST SITES, GROUND DATA 
COLLECTION, AND THEMATIC MAPPER SCENES 
A mature, densely wooded pine and spruce 
forest comprise the Spanish and Austrian test 
sites. High concentrations of copper, lead, 
and zinc occur in the soils at both test sites, 
and soil metal isopleth maps derived from the 
soil sample data provided the means to relate 
the soil geochemistry to the overlying tree 
canopies, and subsequently to the Thematic 
Mapper canopy radiance values. Soil metal 
values for the Spanish test site range from 
26-153 ppm for copper, 30-325 ppm for lead, 
and 39-205 ppm for zinc; for the Austrian 
test site, copper values range from 20-940 
ppm, lead values from 10-10,000+ ppm, and 
zinc values from 60-6300 ppm. No overt mani 
festations of stress are present in the two 
test site tree stands. 
Thematic Mapper canopy radiance values 
employed in the study consisted of January 
1983 and August 1984 acquired scene data for 
the Spanish test site and June and August 1984 
acquired scene data for the Austrian test 
site. Atmospheric haze corrections were ap 
plied to all scene radiance values before 
their computational use. 
3. STATISTICAL ANALYSIS AND RESULTS 
A linear regression analysis of the two 
ground and four Landsat scene data sets pro 
vided the basis for evaluating the thirty- 
one TM bands and transformations. Landsat 
canopy pixel radiance values were regressed 
against Landsat pixel metal values, after 
first transforming the soil metal data con 
tained in the isopleth maps to their corre 
sponding TM test site pixels. A dot grid 
scaled to the dimensions of the instantane 
ous field of view of the Thematic Mapper 
sensor system was used to obtain the average 
copper, lead, and zinc values for each pixel 
position. 
Pearson product moment correlation coef 
ficients (r-values) for the higher ranking 
TM bands and transformations of each of the 
four Landsat scene dates extend to a maximum 
of r=-0.80 and r=-0.68 for the January and 
August Spanish scene dates, and up to r=-0.73