hills within large broad valleys). The hills in
these areas are generally poorly depicted in the
Level 1 plots but are clearly represented in the
Level 2 data. Certain applications may require
this increased level of detail. These varied
findings are similar to those observed in the
California study area and may indicate the need
for area and application specific determinations
of DTED requirements in moderate (> 100 feet
sigma-t) to rough terrain.
Smooth Terrain (El Dorado, Arkansas) The
Arkansas study area is considered smooth terrain
with sigma-t values under 60 feet (Table 13.
Analysis of the perspective plots for the area
revealed some of the most marked differences
between the Level 1 and Level 2 data when
compared to the field photographs. The Level 2
data was at all sites superior to Level 1 in
delineating terrain features. This region is
characterized by generally smooth terrain with
occasional, albeit subtle, landscape variations.
Despite this characteristic, the Level 2 plots
revealed well defined features, such as low
ridges, gentle hills and small valleys. The
most stark differences between the Level 1 and
Level 2 perspective plots occurred at site 10
(Figure 5). In this area, the Level 2 data
exhibited nearly perfect correspondence with the
field photographs, realistically portraying the
low hills and valleys throughout the entire
depth of field (foreground to horizon) and the
gradual sloping gradient upon which the
observation point is situated. Conversely, the
Level l data is almost devoid of detail,
displaying only certain tonal changes which may
indicate the presence of terrain features. This
significant decrease in overall feature
definition in the Level 1 plots is extremely
misleading and masks the true and potentially
critical terrain variations of the area.
SUMMARY
Utilization of solely photographic source DTED
and addition of field data in the comparison
analyses were two important enhancements
incorporated in this study that were not present
in the interim report. As expected, fidelity of
all of the data, including Level 1, was
improved.
At 18 of the 24 sites evaluated (four in Iran,
four in CA, four in ME, and all six in AR), the
Level 2 data was superior to Level 1 in
virtually every aspect of terrain visualization.
It is important to note that the Level 1 data
could not adequately portray the smooth terrain
inherent at any of the Arkansas sites. However,
at the remaining six sites (especially in the
rougher terrain in Iran and California),
portions of the Level 1 plots were found to
adequately define various terrain features,
although with less overall detail than Level 2.
CONCLUSIONS
l. Based upon the completed analyses, it is
clear that the resolution inherent in DTED Level
2 (1 arc second post spacing) is required for
realistic terrain visualization in most
situations; and is absolutely critical for
portrayal of moderate (« 100 feet Sigma-t) to
smooth terrain.
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2. While varying in degree, DTED Level 2 plots
overall rendered a more realistic portrayal of
the terrain than DTED Level 1 plots. When
compared to the field photographs for each of
the 24 sites, Level 2 data consistently
exhibited better feature definition, depth of
field and enhanced representation of surface
roughness, especially microrelief.
3. DTED Level 1 data used in this study
exhibited substantially more fidelity than the
Level 1 data analyzed in the interim report.
This is directly attributable to the use of
photographic source data. Data collection from
solely photographic sources is strongly
suggested for future DTED Levels 1 and 2
production. Moreover, a mechanism to determine
the type, scale and reliability of DTED source
materials should be made available to users.
4. The fact that DTED Level 1 performed well in
some of the rougher terrain, albeit in a limited
number of sites, may indicate the need for
determination of DTED Level 1 and 2 area
production based on terrain roughness and
specific user applications/requirements.
