Remote Sensing Tutorial Section Exam Answers¶
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` <>`__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 Band 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 <Sect1_examq.html#1-2>`__
` <>`__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 Band 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 <Sect1_examq.html#1-3>`__
` <>`__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 <Sect1_examq.html#1-6>`__
` <>`__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 <Sect1_examq.html#1-24>`__
` <>`__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: The anthracite coal region in the Wyoming Valley and south and west, in Pennsylvania, shows up with a distinctive maroon color. The Terra interpreters claim this is due to iron discolorations. The writer (NMS), living near this region, recognizes that there is some iron compounds that give a yellowish color to soils. BUT, he contends that the reddish signature is caused mainly by the coal wastes, which tend to give a blackish tone, as we have seen in other images covering the area. There are several other places in the MISR image where this maroon color prevails. In at least one, iron in the soils is obvious when touring the area. Thus, there seems to be an ambiguity - two different causes. This is commonplace, in fact, often the norm, in multiband space images: a given color does not represent just one material or feature; several different explanations can be proposed, and each may be right for its particular location.**BACK**
` <>`__1-27: 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**
` <>`__1-28: 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**
` <>`__1-29: 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**
` <>`__1-30: 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**
` <>`__1-31: 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**
` <>`__1-32: The most obvious difference is associated with scale and resolution. For example, the Seasat image, having been acquired from a high altitude, does not show the same details as the SLAR image - the agricultural fields south of Blue Mountain are hard to find and the Conodoguinet Creek is very hard to pick out. Note that islands in the Susquehanna visible in SLAR are not discernible in the SAR image. Both scenes were illuminated from the south, as suggested by the south slopes of the fold mountains being brighter in each image. **BACK**