1-1: Once you have located 2 or 3 towns, and one or
more rivers, finding the rest should be easy. Some difficulty may occur if your
map is at a notably scale, but use the patterns of very dark blotches in 7 -
these are the urban areas (but small lakes - black in this band - can be confusing).
BACK
1-2: There are innumerable possibilities. Some you
may have found - if not, look now - are the Schuylkill River, the head of Chesapeake
Bay, the Chesapeake and Delaware Canal, Blue Mountain; Sunbury, Hazleton, Lewisburg,
and Carlisle, PA; the Delaware River near Easton, the Lehigh River passing Allentown,
South Mountain (partly in Maryland). On your map, some of the mountain ridges
north of Blue Mountain may be named. BACK
1-3: The towns and rivers are easiest to locate in
MSS 7. They are also well displayed in the False Color Composite, the towns
being dark blue. The towns and rivers are much more difficult to spot in MSS
5. Actively growing vegetation is dark in band 5. Forests, in particular, are
thick along the ridges and mountains so that these stand out as uniformly dark.
Band 5 also tends to highlight agricultural field patterns - some crops are
still active and show as medium grays whereas other fields have been plowed
by mid-October (or the corn has dried out), so that they appear in lighter tones.
In the color composite, the speckled red and light tan denote these two crop
states. BACK
1-4: I think you will agree that the match between
geological patterns and those in Band 5 is strong. BACK
1-5: It has been printed with what may be an "over-intense"
red tone. The date in October 11, about the time of Fall when at least some
trees have begun to turn to autumn colors (the peak at this latitude is generally
about October 20-25). One might expect that chlorophyll has started to diminish
and reflectance in the Near-IR has commenced to drop, so that redness could
be decreasing. This is all speculative, since the writer wasn't on the scene
in 1972. But, check the next question. BACK
1-6: At the very left is
the date of image acquisition; the first set of latitude/longitude
coordinates describes the geographic position of the
scene; the second set of coordinates denotes the nadir
point location, as though the spacecraft was pointing
straight down (it usually isn't owing to slight deviations
known as pitch, roll, and yaw); the notation SUN EL
refers to the Sun's elevation above the horizon at
the time of day the scene was imaged; AZ is an azimuth
value, with O being north, 90° being east, and
in this case 150° referring to a direction of
the Sun's rays coming from a position S 30° E;
the next grouping of numbers describes some characteristics
of the spacecraft's orbit (we will normally not be
concerned with this); finally, towards the right is
the sequence NASA ERTS E-1088-15185 - ERTS is the
early name for Landsat, the 1 in 1088 refers to ERTS-1
(Landsat-), 88 is the 88th day, and the 15185 concerns
the hour, minute, and ten second values of the time
of acquisition, referenced to Greenwich time. BACK
1-7: The intensity of red has become notably more
subdued, and in fact, has a yellowish tinge. This is about the tone one would
expect from trees being near their peak as fall foliage and crops being brownish
where not harvested. The blue of the Susquehanna River, and the Delaware River
to its east, is the mark of a heavy silt load. Apparently, there was a major
storm a day or so earlier that washed huge quantities of mud and other runoff
into the principal streams. BACK
1-8: The blues associate maily with the agricultural
fields in the valleys and plains. At this time in June, most crop plantings
have yet to emerge, so the bulk of the fields consists of soil, which will commonly
appear bluish in the standard false color composite. The largest valley, just
below Blue Mountain, is the Great Valley, also known as the Lebanon Valley,
which consists mainly of Lower Paleozoic limestones. Below it is the Piedmont,
more hilly terrain made up mainly of metamorphic rocks (note the dendritic drainage
pattern superimposed on it. The lower right corner of the image is part of the
wide Coastal Plains that continue for 100+ miles eastward to the Atlantic Ocean.
The bulges in the river are water behind dams that, having backed up, spread
laterally. The best known of these is the Conowingo Dam (about 2/3rds of an
inch upstream from the Susquehanna mouth at the Chesapeake Bay). Possibly on
your screen you may see a thin white line which is the concrete top of the dam,
used as a major roadway (U.S. Highway 1). BACK
1-9: The amount of blue in the valleys has diminished
significantly. This simply means that many crops are sufficiently "up" or mature
to add their high reflectances to Band 7. Some fields remain fallow (blue; but
some blue coincides with the towns). The blue color on the left (west) side
of the Susquehanna River is an influx of sediment (silt) mainly from the Juniata
River upstream (somewhat hidden by a cluster of clouds), probably the result
of runoff after an earlier storm. BACK
1-10: It snowed in the mountains down through the
Great Valley, as indicated by the white tones in the upper left diagonal part
of the image. One peculiar feature is a white line that ends in a second curved
linear with a bump at the end. One can only speculate as to its cause: the white
line is probably a highway in which the snow hasn't been cleared; the bump may
be a frozen lake but its linear is a mystery. No such puzzle in the Susquehanna
River about 30 mile southeast of Harrisburg: it is just frozen over and may
be snow covered (minor snowfall may have occurred in the Piedmont but doesn't
affect the reflectance. Note a rather hazy condition in the Piedmont; this could
be a low level atmospheric haze from the cold. The other dramatic feature is
the sharpness with which the ridges stand out; this is because the low Sun angle
(21°) produces distinct shadows that contrast with the snowy ridges, thus highlighting
these mountains. Snow can be distinguished from some cloud types, such as cumulus,
which will cast shadows. Low-lying stratus or nimbus clouds, if extending more
or less continuously, could be confused with snow except, in this case, one
can see the ridges and thus know those areas are cloudfree. BACK
1-11: The RB-57 photo looks overly blue as it was
printed. This results from an excessive amount of light at lower visible wavelengths
reflected from the atmosphere; this can be reduced using a blue haze filter.
There is considerable pinkish-red color in the scene, which relates to vegetation
of several kinds. Even in February, grassy areas may be active enough in growth
to influence the Near-IR reflectance; other reddish areas are farms with winter
wheat in early stages. But the moountains and hills show as dark bluish-black,
resulting from reflectance of both soil and bare trees. The prominent stream
with strong meanders is Conodoguinet Creek. To its north is Interstate 81; other
roads are Interstate 83 and 283, the Pennsylvania Turnpike, and State Highways
11, 15, and 581. Harrisburg itself shows extensive street patterns; look close
and you can see in the downtown the State Capitol Building and associated state
government offices. The principal towns west of the Susquehanna are Camp Hill,
Lemoyne, and New Cumberland. In the left center is a large square with white
elongate buildings: this is a U.S. Navy Supply Center. BACK
1-12: Set up a ratio equation: 1:141,000/1:1,000,000
= X/115. The answer is 16.2 miles. BACK
1-13: The big difference is that the vegetation in
the hills and ridges is reddish in the MSS composite in contrast to the dark
blue-black of the aerial photo. Most of the major roadways are discernible in
the Landsat subscene. But, note the huge gap in Interstate 81. In 1972, this
road was still being built and this segment had not been started. One cannot
see individual buildings in the MSS scene. The U.S. Navy yard buildings are
not visible individually (they are in TM images). The crop fields, nearly all
being, several pixels in size, are evident in the MSS; a few can be matched
to those in the aerial photo. Note the dark slanted parallel lines. These are
certain of the scan lines, which can be largely removed by special computer
processing. BACK
1-14: The July scene is much more reddish, as vegetation
is at its prime. Interstate 81 has been completed. Some buildings in the U.S.
Navy complex seem resolvable. As we say earlier, the Susquehanna River shows
a siltation band along its left bank but not to the east. This, again, is probably
a contribution from the Juniata River that empties into the Susquehanna about
8 miles to the north. BACK
1-15: In May, only winter wheat was growing extensively.
Most other fields were fallow. Look for a large dark field in the aerial photo
which contains a small oval race track. Also, move your eye about an inch to
see another dark field that has five sides and a clear thin strip running through
out. These two can be found in the upper right of the MSS subscene. But, they
are now white whereas most other fields are dark at this stage. What has happened:
the wheat has been harvested and the fallow fields are all now well into crop
(mostly corn and soybeans, as we shall see later). BACK
1-16: This is a large part of the famed Anthracite
Coal Belt of eastern Pennsylvania; this coal burns very hot, with high BTU energy
release, and is prized in steel-making. For well over a hundred years, this
coal was mined from underground, but in the 1930s and '40s, surface strip mining
began. Today, production is greatly reduced from underground mines, because
of high costs, but stripping still goes on to a now reduced extent. Both stripped
overburden and underground mine wastes were indiscriminantly dumped over large
areas surrounding mining operations. You will observe this characteristic black
pattern in all the full MSS 7 scenes (it is medium gray in Band 5) and in the
color composites it remains black. BACK
1-17: The elongate one is a lake. It is hard to find
in the 1972 image. This long lake is the Deer Creek Lake, formed by damming
the creek of the same name. In the 1972 image, it was just beginning to fill
with back-up water, so that it was then almost roundish. The three black spots
have developed since 1972; they are the beginning of new, local strip mining.
BACK
1-18: D and F are lakes; F is Deer Creek Lake in
a more advanced stage of fill. C is anthracite waste. The features at I, J,
and K are large areas of defoliated forests on the ridges, thus the ground controls
the reduced reflectance compared with the bright toned healthy trees. The year
1973 saw a major infestation of the leaf-eating Gypsy Moth. Areas from New England
to the Carolinas were affected. Pennsylvania was especially hard hit. The PA
State Dept. of Environmental Management was able to use Landsat imagery to delineate
areas hard hit and to identify areas in need of spraying. This saved the state
millions of dollars that would otherwise have been spent in aerial photography
and field work. BACK
1-19: The Gypsy Moth infestation had not begun in
May. It first appeared in early June. It climaxed by early July. Amazingly,
trees can re-leaf during a single growing season, so that the ridge forest had
returned to near normal by August. Now, read the fine print in the illustration.
BACK
1-20: The structural grain related to trends in the
Precambrian metamorphic rocks (running NE-SW) is surprisingly best revealed
by panel D, the snow-covered scene, in which this snow contrasts sharply against
the areas in black that mostly are vegetated low ridges. Note too that the reservoir
is frozen and snow-covered. The Fast Fourier transform image (B) improves the
definition of the ridge-rock effect that is adequately displayed in the Band
7 stretched image. This structural trend is harder to see in the Band 5 Cubic
Convolution image, where alignments of elongated medium gray represent active
vegetation associated with the ridges. The irregular dark gray pattern below
the reservoir may be a stand of evergreens or possibly (not likely) a forest
fire scar. BACK
1-21: The choice of colors, green for healthy forestland,
red for defoliated, and purple for stressed vegetation, as applied to a simple
band ratio (7/5) image which emphasizes differences in vegetation vs certain
vegetation-depleted areas, causes the eye to see these differences much more
readily than in the standard fcc image. But, there are some small patches of
reds and purples in the valleys, which may be genuine effects (the moths get
around!) but could be "false alarms". BACK
1-22: The first component image looks very like a
MSS Band 5 image. The second component strongly resembles a Band 7 image. The
third component seems fuzzier but also shows vegetation in the ridges as bright;
water also is bright (white). The fourth component image is clearly "degraded"
but the ridge pattern persists weakly; rivers disappear; the valleys are spotty
without a sensible pattern. BACK
1-23: There is a general resemblance of the PCA123
composite to the standard fcc. The red of the forested ridges has a weak bluish
overtint. The part of the scene which shows the greatest gain in information
content is in the valleys. Yellows and greenish-yellows call attention to features
that are real and need explaining (this is one of the prime advantages of some
computer-processed special images, in that they reveal through patterns and
colors objects and classes not as easily seen in standard images). BACK
1-24: On the whole, this is a believable classification.
The class Urban: Industrial/Commercial within Harrisburg itself associates rather
well with the business district and the governmental offices. The U.S. Navy
Supply Depot likewise stands apart from the residential areas around Camp Hill
(these appear underclassified, i.e., should be more widespread). An industrial
area along the west bank of the river has been singled out - a check of the
PA state map shows precisely that class. Some of the vegetated cropland may
actually be suburban-residential, since the writer's personal experience (I
must drive through Harrisburg everytime I go to Washington, D.C. and return)
indicates areas shown as cropland are actually built up as citified. Forestland
is largely correctly classed. BACK
1-25: The keys to the fit are the curved Interstate
81 and the distinctive curlicue lake in the center of the aerial photo. This
places it roughly in the upper left quadrant of the fcc MSS image. The southern
end of Hazleton is at the top edge near the center. The town east of the second
highway curve is McAdoo. At the bottom center is part of Tamaqua. Near the bottom
right are the towns of Coaldale and Lansford. It is surprisingly difficult to
spot mine wastes, based on their location in the Landsat image. Some of the
light tones around McAdoo and Coaldale are probably both strip mines and waste
but barren fields seem also to be present and have that light tone. (The date
of the photo is unknown but the trees in the ridges appear to be leafless, suggesting
a late Fall to early Spring time window.) BACK
1-26: Of the four cover types, vegetation is best
mapped. The amount (extent) of defoliation is probably too widespread in this
cluster analysis. Mine refuse distribution looks valid. The category "Conflict"
is a catch-all. Hazleton and several towns (in maroon; the legend shows this
class as pink - should be maroon) are included in this but most of the other
maroon spots are of unknown identity. BACK
1-27: Corn is more common. The smaller lavender areas
may be hamlets, farm building clusters, or just "false alarms". Use a magnifying
glass to verify that most field boundaries are irregular. This is largely due
to the mixed pixel effect discussed in Section 13 of the Tutorial. What is happening
is that the pixel is straddling two field types and depending on the proportion
of each will classify as one or the other type; the next pixel along the same
boundary could have a different proportion, throwing it into the other class,
so that this alternation leads to a jagged edge. Still, there are some fields
with all or part having straight boundaries; many fields actually have non-regular
(rectangular) shapes. BACK
1-28: There was no one on site when Landsat passed
overhead that day. Had there been, people in boats would have sampled the waters
in the river mouth to determine the degree (percent) of siltation. This has
actually been done (people at the University of Delaware have done this kind
of ground truthing) and gives a quantitative measure to the determination. In
the case we consider, interpretation of the varying siltation was done by noting
varying gray levels in the image and subdividing the associated DN values arbitrarily
into degrees of turbidity. BACK
1-29: The folded ridges should help you to locate
yourself. These ridges are cool because their foliage evapotranspires and thus
cools the air around them; they are also higher. The valleys are warm owing
to being lower, trapping heat, and having more human activity. The long white
curved pattern is the Wyoming Valley which includes the cities of Wilkes-Barre
and Scranton. This is a major coal-producing area, with strip mines and extensive
dark mine wastes. The natural rocks and soil are also dark. Being dark, they
absorb more of the Sun's rays and re-radiate as warm bodies (see Section 8).
The blackish area above the folded ridges is part of the Appalachian Plateau
which attains elevations of 1500 or more feet above the warmer lowlands. BACK
1-30: The eastern U.S. on this date was almost cloudfree.
The valleys appear cooler because of radiative cooling. Water, as we shall see
in Section 9, has a higher heat capacity and looses its heat more slowly than
land surfaces, so it remains warmer at night (but usually cooler in daytime).
The ridges are warmer than the valleys because they have a higher thermal intertia
(a property we will consider in Section 9); this means that the heated bedrock
(mostly sandstones) loses less heat at night than do the soils and loose debris
in the valleys.The Harrisburg area appears as a slightly lighter tone than its
surroundings; this is the "heat island" effect (see Section 9). BACK