United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Las Vegas, NV 89193-3478
Research and Development
EPA/600/S4-91/027 Jan 1992
EPA Project Summary
Watershed Characterization
Using Landsat Thematic Mapper
(TM) Satellite Imagery: Blackfoot
River, Montana
K. H. Lee
This report describes a portion of a
large regional project undertaken by
the Environmental Protection Agency
(EPA) and water-quality authorities in
the States of Montana, Idaho, and
Washington to identify and analyze fac-
tors which are affecting water quality
in an Interconnecting hydrologic sys-
tem. To achieve this directive in Mon-
tana, a spatial database is being con-
structed which will contain satellite de-
rived land cover, photo-interpreted mac-
rophyte locations, climate data, topog-
raphy, hydrography, and soils. The
database will be used by EPA Environ-
mental Monitoring Systems Laboratory
(EMSL) to demonstrate the utility of a
watershed scale information manage-
ment system. This information man-
agement system is geared toward
nonpoint pollution modeling and will
evolve into a decision support mecha-
nism capable of assessing the suitabil-
ity and feasibility of various alternate
management scenarios. The data lay-
ers focus on elements required for
nonpoint source pollution modeling in
which derivation of factors for soil erod-
ibility, rainfall, topographic slope-length,
and vegetation management are gener-
ated for the watershed. A Geographic
Information System (GIS) in which to
model alternative land management
scenarios such as road building, log-
ging, and fire/burn management. The
vegetation management factor will be
partially based on land cover derived
from Landsat Thematic Mapper satel-
lite imagery. Vegetative management
factors combine vegetative cover and
soil surface conditions Into one nu-
merical factor. This report will ad-
dress only the generation of land cover
maps for the Blackfoot River Water-
shed through quantitative remote sens-
ing techniques.
This Project Summary was developed
by EPA's Environmental Monitoring
Systems Laboratory, Las Vegas, NV, to
announce key findings of the research
project that Is fully documented in a
separate report of the same title. (See
Project Report ordering Information at
back).
Introduction
This report covers the western third of
the Blackfoot River Watershed, which is
part of the greater Lake Pend Oreille Wa-
tershed. This study is a joint cooperative
effort between the U.S. EPA and the States
of Montana, Idaho, and Washington to
understand the water quality issues of the
Lake Pend Oreille watershed. This part of
the project deals with several subwater-
sheds in the western third of the Blackfoot
River Watershed, and is based in large
part upon the interpretation of satellite im-
agery.
The entire Blackfoot River Watershed
contains approximately 6,022 square kilo-
meters (2325 sq. mi.). Because of budget
restrictions, only the western third of the
area, 2,185 square kilometers (844 sq.
mi.), was classified for land cover.
Figure 1 shows the area covered by
this part of the project.
The Blackfoot River flows 132 miles
from its source near the Continental Di-
vide westward to its junction with the Clark
Printed on Recycled Paper
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Pend Oreille River
Study Location
Canada
Montana
Butte, MT
Figure 1. Remote Sensing/GIS Support for Section 525 of the Water Quality Act of 1987.
Fork at Bonner, Montana. Factors which
affect the water quality are the logging
and mining activities, road building, fires,
agriculture, unstable river banks, munici-
pal sewage effluent, and pulp mill waste.
In Idaho, Lake Pend Oreille receives all
the Clark Fork discharge; eutrophication
has been associated with the degraded
water quality of the Clark Fork.
Procedures
Digital Image Processing
A Landsat-5 Thematic Mapper (TM) digi-
tal image acquired on 20 July, 1988 was
analyzed to create a general land-cover
map for the Blackfoot River Watershed.
The Landsat-5 TM satellite sensors record
the amount of electromagnetic energy in
seven spectral bands: blue, green, and
red (visible spectrum); three reflected in-
frared (IR) bands; and one thermal IR
band. Each pixel (or cell) covers about
30 meters by 30 meters, except for the
thermal (IR) band which is 120 meters.
The steps taken in the analysis of
Blackfoot River satellite data for land-cover
characterization were: image rectification;
optimum band selection; unsupervised
classification; and accuracy assessment
of the final classified image.
...The Optimum Index Factor (OIF) indi-
cated that a four-band combination of TM
bands 3 (red), 4, 5, and 7 reflected (IR)
be used to minimize redundancy in the 7-
band data set.
Ground Control points (GCPs) taken
from topographic maps were used to re-
align the satellite data, correcting for dis-
tortions in the image. The Universal Trans-
verse Mercator (UTM) coordinate system
was used for map control.
The TM data set was rectified using
249 ground control points which yielded
an overall average locational error of 23.4
meters.
Classification System
Classification units can be selected in
two distinct ways: (1) by image interpreta-
tion based on previous general knowledge
and experience and specific knowledge of
the area by the interpreter, or by (2)
unsupervised "clustering" of similar pixels
by the computer. Spectral characteristics
of surface materials, such as soil or veg-
etation, are likely to vary from place to
place. Therefore these clusters must'be
checked to consolidate some of them hav-
ing only minor differences in spectral char-
acteristics, but which are part of the same
soil or vegetation unit. This was done,
and resulted in a total of seven major
categories, with the three subcategories,
shown below.
Digital classification of multispectral im-
agery generally produces a sait-and-pep-
per appearing map. This can arise from a
nonuniform response of the sensor, pro-
cessing errors, the pixel size or mapping
unit, or the classification algorithm. In
smoothing, every pixel is spatially ana-
lyzed in conjunction with the pixels that
surround it. Smoothing is used when the
final land-cover classification is to have a
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Tablo 1. Error Matrix: Blackfoot River Watershed Subset
Reference
Forest-d Forest-s Ag Range Barren Wetland Water
C Forest-s
L Forest-s
A Ag
S Range
S Barren
E Wetland
D Water
15102
71
0
21
4
0
0
1020
2001
26
2337
41
0
85
157
43
9141
703
4
0
1
263
646
0
1638
191
0
575
38
128
62
159
26
0
0
313
69
63
329
1
121
11
0
0
0
0
0
0
2358
Overall Accuracy = 80.5%
Commission
User's Accuracy
Forest-d
Forest-s
Ag
Range
Barren
Wetland
Water
= 89%
= 68%
= 98%
= 32%
= 10%
" 100%
" 78%
minimum mapping unit such as an acre or
hectare.
The problems of converting raster data
(having a stair-case appearance) and vec-
tor data (shown as a smooth line, arcuate
or straight) are presently solved by an
intermediate file structure called SVF. The
problems of this conversion are expected
to be solved in the near future by the
utilization of raster data in a grid format in
the vector GIS.
The following classification of land-cover
features resulted from unsupervised clas-
sification combined with adequate refer-
ence information from the area.
1. Agricultural lands: cropland and pas-
ture, found in areas of low relief.
2. Barren land: bare, exposed rock.
3. Barren land (roads): including rail-
ways.
4. Forest land: having a tree crown
areal density of at least 10 percent.
A) Dense coniferous forest cover
(greater than 40%).
B) Dense deciduous forest cover (more
than 40%).
C) Old timber/thinned sites/sparse
cover (cover less than 40%; more
than ,10%).
5. Rangeland: grasses and shrubs.
6. Wetland: was difficult to distinguish
between forest and agriculture. Only
several small areas were identified.
7. Water: includes the Blackfoot River
and tributaries, lakes, and reservoirs.
Omission
Producer's Accuracy
Forest-d
Forest-s
Ag
Range
Barren
Wetland
Water
= 99%
= 36%
= 91%
= 50%
= 6%
= 13%
= 100%
Accuracy Assessment
Evaluation of the accuracy of the land-
cover classification requires comparison
between the classification results and ref-
erence data for the area. These refer-
ence data are taken from various sources.
Site-specific comparisons are made by
calculating the frequency of coincident
classes, point by point, and reporting these
values in an error matrix (confusion matrix
or contingency table).
Detailed statements of accuracy are de-
rived from the error matrix in the form of
overall and individual land-cover category
accuracies. For each class the percent
commission and percent omission errors
are calculated from the error matrix (con-
fusion matrix or contingency table).
The reference data used to evaluate
the final, classified image of the Blackfoot
River Watershed subset were taken from
photo-interpreted color airphotos (1988)
flown for a macrophyte survey, NHAP CIR
photography (1984), and soil survey
orthophoto maps (1982).
Research indicates that reference data
from at least 1 percent of any area should
be enough for a valid evaluation of the
accuracy of the interpretation. In the case
of the Blackfoot River Watershed, the ref-
erence data used covered 1 percent of
the area.
Table 1 shows the error matrix of the
study- area having an overall map accu-
racy of 80.5%. However, this does not
consider the accuracies of individual cat-
egories. Producer's accuracy (omission er-
ror) and user's accuracy (commission er-
ror) are important in assessing the reliabil-
ity of a classified image.
Commission errors are the percentages
indicating the ratio of those pixels in any
category which are correctly classified.
Omission errors are given a percentage to
indicate the probability that a reference
sample will be correctly classified.
Unsupervised classifications were ob-
tained for the eastern two-thirds of the
entire Blackfoot River Watershed. How-
ever, not enough reference data were
available (i.e., air-photos, maps, and
ground verification) for an accuracy as-
sessment to be performed for this area.
Results and Discussion
The selection of a four-band data set
containing 61 megabytes instead of the
six-band sub-scene of 91 megabytes for
the western third of the watershed re-
sulted in the elimination of 30 megabytes
f,rom computer computation for the recti-
fied area of 100 km x 100 km.
It is projected that the overall accuracy
of 80.5 percent would not be a limiting
factor in the calculation of vegetation man-
agement factors for the Blackfoot River
Watershed. The resolution of the TM im-
agery (30 meters) will probably have
greater impact on nonpoint pollution-mod-
eling as the level of detail required for
land cover can become quite specific, even
to the point of whether the ground cover
is grass or weeds. The forest class was
divided into dense and thinned cover arbi-
trarily; this estimated amount of cover
should be useful in the development of
vegetation management factors.
The Blackfoot GIS contains other the-
matic layers which are commonly avail-
able (i.e., hydrography, elevation, soils,
etc.); these combined with recent land
cover estimates will provide the EPA Re-
gions and State agencies with the build-
ing blocks on which further analyses surely
will develop. The GIS database, as con-
structed for this modeling effort, is an at-
tempt to work on a third-order watershed
where the level of detail required may not
need to be so specific. Updates are much
easier in the GIS environment as this tech-
nology facilitates the incorporation of higher
accuracy or resolution information after
baseline development. A tentative list of
management issues in the Blackfoot River
Watershed includes investigations of wa-
ter quality for fisheries management, com-
parisons of silvicultural prescriptions for
sediment yield reduction, and environmen-
tal assessment of potential impacts of pro-
posed mining activities.
•&U.S. GOVERNMENT PRINTING OFFICE: 1992 - 648-080/40126
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K. H. Lee is with Lockheed Engineering and Sciences Company, Las Vegas,
NV89119
Ross S. Lunetta is the EPA Project Officer (see below).
The complete report, entitled "Watershed Characterization Using Landsat
Thematic Mapper (TM) Satellite Imagery: Blackfoot River, Montana,"
(Order No. PB92-115237/AS; Cost: $17.00, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Las Vegas, NV 89193-3478
United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S4-91/027
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