WMOD00593

• Contract/Permit #: 14-06-D-7052
• Title: Ecological Impacts of Snowpack Augmentation in the San Juan Mountains, Colorado
• Date: 3/1/1976
• State: CO
• Weather Modification - Doc Type: Report

MAPPING METHODS

Two methods were employed. Detailed maps having 35
cover type categories were produced by conventional
air photointerpretation. However, the lack of
adequate contemporary aircraft coverage for the
entire target area justified the use of satellite
data. Computer-aided analysis techniques using
LANDSAT-l data produced a logogramatic map of
generalized vegetation for 9,644 km2 (2.5 million
acres) (Hoffer, Fleming, and Krebs 1974).

Detailed Vegetation Maps

Detailed vegetation maps of the San Juan Mountains
were originally prepared at a scale of 1:24,000.
These maps are filed at the Institute for Arctic and
Alpine Research (INSTAAR) for use by interested
persons. The coding system for the cover type
categories is given in Table 1. The area of detailed
mapping covers 14 USGS 7~' quadrangle maps along a
belt near the southern border of the San Juan Mountains
(Figure 2). Using these maps, spatial relationships
of plant communities and topographic features become
apparent. The cover type categories chosen (Table 1)
represen4 recurring plant communities and provide
manageable information without confusing detail.

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Figure 2.

Area covered.by detailed vegetation maps
at a scale of 1:24,000.

U.S. Forest Service and U.S. Geological Survey air
photography were used for the preliminary maps. Mark
Hurd's quadrangle-centered 1971 series of air photo-
graphic map documents were acquired from the Colorado
Office of State Planning for portions of the study
area. To obtain aircraft coverage for the entire
area, however, would have been prohibitively expensive.
Acquisition of NASA mission coverage (National Aero-
nautics and Space Administration Aixcraft Mission
Center) of infrared and color positive films in support
of the LANDSAT-l and Sky lab investigations (contract
numbers NAS5-21880 and NAS9-13380, respectively) solved
this problem. The NASA flights used in the vegetation
mapping were Mission 213 (September 1972), Mission 238
and Mission 239 (June 1973), and Mission 248 (August
1973).

Field-verified cover type standards were noted on pre-
liminary maps and used in photointerpretation to in-
crease accuracy in the laboratory. The Hurd photog-
raphy facilitated both photointerpretation and spat~al
correction when transferring the cover type boundar1es
to the base maps. National Aeronautics and Space
Administration (NASA) color infrared imagery (Mission
248, Roll 24, and Mission 238, Roll 48) aided in
identification of mapping units. The photointer-
pretive results from the color infrared aircraft
coverage were delineated directly on the Hurd photo-
graphs. Correct placement of boundaries was insured
by keying on geographic points and topographic features
visible on the two types of aircraft coverage (Figure 3).

For portions of several quadrangles, complete Hurd
coverage was not available; in these cases, photo-
interpretation was based strictly on the NASA
coverage.
NASA Color Infrared Aerial Photography
(of differing scales) ~

Field Check Standards 4 ~ Photo Interpretation

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Hurd Photo absent Hurd Photo

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Interpolation of Scale Directly Spatial Correction onto

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Finished Produc ts
1) Mylar Overlay
2) USGS Topographic Base Map

Figure 3. Vegetation mapping methods.

The color and hue of the various cover types are
distinctive on the color infrared film (Table 2).
However, accurate photointerpretation in areas of
shadow requires an awareness of both topographic
features and elevation (Krebs and Groeneveld 1974).

The final colored vegetation map at 1:120,000 (in
map pocket) was compiled from the detailed vege-
tation maps and portrays a generalized trend of
vegetation changes. The following combined cover
type ca~egories were used; coniferous, deciduous,
deciduous-coniferous, meadow-grassland-agricultural,
tundra, creek community, water, bare rock-bare soil,
and urban. The code system (Table 1) used on the
detailed maps was designed for combination of
categories. For example, all codes in the 220s
represent coniferous forest, 230s represent
deciduous-coniferous forests, and 160s represent
agricultural lands. This coding system permitted
translation into the classification terminology of
the generalized map at a smaller scale, and it per-
mitted formation of new complexes which represent
vegetation entities of composite character. Some
funds for production of the maps were provided by
NASA contract NAS5-21880, NASA contract NAS9-13380,
NASA Grant NGL-06-003-200.

Translation from detailed to generalized vegetation
must correspond to an accurate portrayal as closely
as the scale permits. If a cover type occupies only
a very small area, it is usually suppressed alto-
gether. But there are cases when a small area is
enlarged enough to be visible on the smaller scale
map. This applies to instances where portrayal of
special cover types contributes to a better under-
standing of the map as a whole. For example, because
of the importance of creek communities and bare rock-
bare soil areas in an ecological overview, these
units are exaggerated for their inclusion on the
smaller scale map. Often the deciduous-coniferous

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