It's been a long time between Exams - your first was at the end of Section 1. But, if you have worked your way through most (hopefully, all) of the Sections in between, your expertise has grown significantly. In this Final Exam, you will find similarities with the themes pursued in the first exam but with more sophisticated questions and interpretations to be handled. Once again, Landsat imagery will be the principal data type but with TM rather than MSS images to work on. Since you became familiar with one part of the U.S. - central Pennsylvania - in the earlier exam, we will make it easier for you by staying in the same geographic region. The emphasis in this Exam is, again, on visual interpretation of the features and contents of a scene.

To tie in with that first exam, recall your experiences with this MSS full scene, with Harrisburg near its left center.

The Landsat MSS false color composite that includes both Harrisburg, the capital, and Bloomsburg on the Susquehanna River

You should remember that the major river is the Susquehanna and that the upper part of the scene is dominated by the Valley and Ridge subprovince of the Appalachian Mountains. Now, as a transition to a TM scene, shown below is an enlargement (thus, somewhat fuzzy) of a subscene from the MSS image lying in the upper central area:

Enlargement of the Harrisburg MSS scene that covers Bloomsburg and its vicinity to the south.

In the top center, where the Susquehanna bends sharply north, is the town of Bloomsburg, the writer's (NMS) present home, and the focal point of this second Exam. In the MSS subscene, it is very hard to pick out, being just a small bluish spot.

Now, lets introduce the TM scene on which this exam is based - it is extracted from a larger (full) image taken on June 17, 1987, comprising about 40% of the latter image. We will this time work mainly with the natural color version made by the IDRISI software program.

Natural color (Bands 1,2,3 = B,G,R) subscene extracted from the June 17, 1987 TM full scene of north- central Pennsylvania; Bloomsburg is near center.

1-1: Try to fit the TM subscene into the MSS subscene, using several landmarks. Roughly, what percentage of the TM subscene is present (overlaps) the MSS subscene? ANSWER

It should help, too, to get your bearings by relating the subscene to the Pennsylvania State Official Road Map. The area of that map reproduced below, and includes some locations outside the TM image but several of these will come into play near the end of the Exam. Use the Susquehanna River to fit the TM subscene to the map.

Map of the study area for this Exam extracted from the PA State Road Map.

Bloomsburg is almost "dead center" within the above TM subscene image. Lets talk about this place for a bit. First, we show a further enlargement of it and surrounding countryside. Several small clouds are in the image; you should remember how to recognize them.

Segment of the TM subscene chosen to enlarge the area around Bloomsburg.

And, now we supplement the view with a higher resolution false color aerial photo, at a scale of approximately 1 inch to the mile (~1:62,500), taken in September of 1988. Bloomsburg is at the bottom.

False color aerial photograph of the Bloomsburg area.

To feel more at home in this small urban area, here are two ground pictures: 1) looking at Bloomsburg from across the Susquehanna River, where we see that part of the town is perched on a hillside, and

View to the north looking at the Town of Bloomsburg, and the bridge across the Susquehanna River.

2) a view of Main Street looking east, with the edge of the Bloomsburg University campus barely visible at the far end.

Main Street in Bloomsburg.

(NOTE: The Landsat subscene we are using became available to the writer in early October, 2000. A week later I made a tour of the region depicted in the subscene expressly to take ground photos. Fall was well underway. This is why so many of the photos you will see have the lovely yellows, reds, and browns in the deciduous foliage.)

Bloomsburg, the county seat of Columbia County, has a population of about 11000 within its city limits. It surrounding "suburbs" raise the population by another 5000 or so. It is, officially, the only incorporated area in the State of Pennsylvania that is entitled to call itself a "TOWN". During the academic year, Bloomsburg University, a 4-year college that is one of the 11 State System of Higher Education establishments, adds another 6800+ to the residents. Bloomsburg has a local symphony orchestra (university students/staff) plus towns people) and a resident drama theater of fine repute. Once a year, in late September, the town puts on the largest State Fair in Pennsylvania. Bloomsburg, for part of the 1830s, was the iron-producing center of the U.S., using iron extracted from sedimentary red beds plus coal from the southern part of the TM subscene, and limestone from beds along the river. Today, a number of industries (auto carpets; clothing; aircraft parts) have factories within the town or nearby within the river floodplain. The current center of shops and services has shifted to a 5 mile strip along U.S. Highway 11 which runs through the town and then eastward as the main road, as shown below:

The new commercial district for Bloomsburg, along U.S. Route 11.

Settlements began to appear in Columbia County area in the mid- to late 1700s, established mostly by Quakers who then left for points west and north by the end of that century. Bloomsburg as a hamlet dates to about 1785 and its present street plan was laid out in 1805. The University was founded as a teachers college in 1838. The county has one of the largest numbers of covered bridges in the U.S. The county is traversed by Interstate 80, which runs from just west of New York City to just east of San Francisco; it passes Bloomsburg about a mile and a half north.

Two neighboring communities (boroughs) on the Susquehanna, similar in size, are Berwick (about 12 miles east) and Danville (10 miles west); the latter is the site of the Geisinger Medical Center. Find them on the map and then in the full subscene - they have a pinkish color. Catawissa and Elysburg are smaller settlements.

1-2: Based on area within the subscene, what is the principal landuse and a major source of income? ANSWER

1-3: About 14 km (8.5 miles) south of Bloomsburg is a large green area shaped something like a "U" lying on its side; what do you think this is? ANSWER

1-4: The green area continues and expands to the south and east. Assuming you deduced that this is heavily forested hilly terrain, what do you think its main use is today? Careful, this is a tricky question. ANSWER

1-5: Go back to the enlarged area centered on Bloomsburg and to the aerial photo just below it. Leading out of the west side of Bloomsburg is a road (State Route 42) that eventually meets Interstate 80 at a cloverleaf intersection. Describe the area just to the northeast of the intersection as it appears in the TM enlargement, and again as it appears in the aerial photo. There is a difference. Speculate on what now occupies this area. ANSWER

1-6: In the enlarged subscene there is some water besides the River. It appears again in the aerial photo. Where is it? With its odd shape, it does not appear to be natural. Any thoughts on its origin? ANSWER

We will turn now to a trio of black and white aerial photos that pass over Bloomsburg. They were acquired on April 18, 1994, so the trees were in an early stage of leafing. The photos are adjacent, so stereo is possible. We reproduce one of these on this page, but since you will be asked to print these out, and the Exam page is long, a link to a separate page has just the pair on it, for easy printing. After the printout, just hit the browser BACK button to return to the Exam.

Black and white aerial photo showing Bloomsburg and the countryside.

After cutting the stereo photos apart and aligning them properly, if you have a stereoscope or can see 3-D with the unaided eye examine the topography around and both north and south of Bloomsburg.

1-7: Start with the pair: 5539-136 and 5539-137. Locate the major hills in the scene. Where are the high areas in the immediate Bloomsburg area? Are some of the farms located on rolling terrain? There is a wooded area just south of the Interstate and southeast of the Columbia Mall that is medium gray, with dark spotches within; any ideas as to what these specks are (other area show this feature, sometimes being larger and continuous)? Why is the Susquehanna in 136 so bright? Can you approximate the time of day when the photo run was made? ANSWER

1-8: Now examine 5539-137 paired with 5539-138. A major tributary to the Susquehanna - Fishing Creek - joins the big river west of Bloomsburg; near the juncture, describe the topography and also the topography along the west bank of the Susquehanna south of the confluence. What is the topography on the immediate south side of the Susquehanna across from Bloomsburg? Does the farmland further south seem higher than that north of Bloomsburg? Account for the pattern of alternating and curved light and dark patterns in several of the fields. ANSWER

Digitized elevation data (DEM) have been combined with part of the subscene to generate a perspective version of the terrain. You should now be familiar enough with the subscene and key landmarks to recognize the major features in this oblique view.

A perspective view of the Bloomsburg area made by merging the TM subscene with DEM data for elevation.

1-9: Concentrating on the town of Bloomsburg itself as displayed in aerial photos (and, if you wish, checking also the false color aerial photo), what are the cluster of light patterns with square corners found in the western side of town? Why are there two ovals nearby? Can you find the University? Take a guess as to what is the covering material on Route 11 east of town and what is the identity of an isolated medium-dark straight line near the bridge across the river; what is the bridge surface itself? ANSWER

Now we are going sightseeing around the full scene. But what you see below is greatly enlarged - you will have to scroll with your vertical and horizontal buttons to get to the different features, labelled A through L. You will be asked to identify each, starting with A, and then go to the answer page to learn if you are right, to see a scene or two that shows the feature, and to read a bit of descriptive background. Wander through the super-scene now and then find the first question below it.

A very large rendition of the full TM subscene.

1-10:Identify the features to the left of the red A, and then B. ANSWER

1-11:What is just next to C?ANSWER

1-12:There are some fields next to D. Here is one. See if you can locate it in the enlarged subscene.ANSWER

Fields southwest of Catawissa, PA..

1-13:There are several patches of dark green to the left of E. We will tell you that they are not natural woods. They represent a seasonal product that is an important commodity produced in this part of Pennsylvania. Take a shot at saying what they contain.ANSWER

1-14:You are standing at point F looking south: What do you expect to see? Then, you are at point G looking west, and once more what do you see? Where is the high points (in elevation) in the green pattern in this vicinity? ANSWER

1-15:Looking around at point H in the subscene, there are several patterns of thin, regular lines that may be straight in segments. They don't appear to be roads since those are curved as they follow the topography, ranging between valleys and the need to climb over hills. What might these straight patterns be?ANSWER

1-16:All around the red I are irregular patterns that have a purplish color, mixed with some black. Hark back to the first Exam during which this pattern was evident (look at the MSS image above) and was explained. With this hint, you should be able to identify these patterns.ANSWER

1-17:Red J is on Catawissa Mountain. Here is a photo of it west end seen from the north. There is a long dark curved line about half way up its slope. What might it be?ANSWER

Catawissa Mountain seen from the uplands to its north.

1-18: In the forests that extend from Catawissa Mountain to the east and south, there are several patches of lighter green. Find them and explain their nature.ANSWER

1-19: What's at red K? If you were standing on the bridge there looking northeast up the Susquehanna River, what special feature is in the river (near L)?ANSWER

We now return to the original TM subset of data, which the writer (NMS) obtained after all of the above was completed. Using the 7 TM band images, various renditions were produced using the IDRISI for Windows package. The first product is a false color composite made from TM1 = Blue; TM3 = Green; TM4 = Red (not quite the usual false color rendition):

False color composite of the TM subscene, using the combination 1,3,4 as R,G,B.

1-20: While this appears to be a typical standard false color composite, it has two unusual or anomalous variations from the norm. Can you specify them?ANSWER

Although we will not ask a formal question, look at just two of the bands from the TM set: Band 4 (left or top) and Band 7 (right or bottom). At first glance, they seem almost to have a negative-positive relation - what is light in one is dark in the other and vice versa. But a few features don't show that reversal. Look for them.

TM Band 4 TM Band 7

Band 6, the thermal band, is shown next. Its 120 m resolution was resampled to a repetitive 4 adjacent pixels of 30 m each to allow direct registration with the 30 m pixel size for the other bands.

TM Band 6, the thermal image of the region around Bloomsburg.

1-21: Conduct a general analysis of this image in terms of relating warmer (light tones) and cooler (darker tones) areas to specific features.ANSWER

It should be obvious to you that vegetation is one of the dominant features/materials in the subscene. By June 17 the deciduous trees, by far the most prevalent large vegetation, are fully leafed. Grasses are also growing well. In this part of Pennsylvania, in June many crops were just planted (commonly in May) and are not yet beyond their early stages of growth. So, when one drives across the countryside, these fields probably show some signs of the planting but from space the background soil occupies a higher percentage of a farmland pixel than the vegetative material it is nurturing.

One quick way to assess the relative proportions of vegetation-dominated terrain from other land uses is to ration the Near IR band to one of the visible bands, usually the red band. Here, we present a ratio of 4/2 (the highly reflective IR band to the green band):

Black and white image made by dividing Band 4 pixels by Band 2 pixels, and then doing a Histogram Equalization stretch.

1-22: Comment on the most readily apparent information in this image. A colorized rendition will appear in the answer. ANSWER

page 3-4), we introduced the NDVI as a sensitive means of recognizing vegetation at several levels of type, density, health, etc. The Index is, as you may recall, the ratio of Near Ir - Red to Near IR + Red (for Landsat, SPOT, AVHRR, etc.). IDRISI allow this calculation and has a special color palette to display the resulting image. Here it is:

NDVI map of the TM subscene; vegetation in green; other materials in yellow and red.

1-23: This a rather strange-looking (almost displeasing) appearance. There seem to be just four distinct colors. Comment on what you think this NDVI image is telling you. ANSWER

IDRISI can rapidly calculate Principal Components. The resulting images can be informing or can offer little new or understandable insights into the scene's feature content. Using this image processing program, the 7 TM bands were incorporated into PCA and the seven resulting component images were examined. Individually, most revealed little added information. Various combinations of three PC images were tried - most failed to develop presentable composites when various IDRISI palettes were applied. Here is a colorful exception made by displaying PC1 = blue; PC4 = green; PC2 = red, applied to a large segment extracted from the full TM subscene. Below it is an enlargement of the area around Bloomsburg.

Principal Components composite made from PC1, PC4, PC2 = Blue, Green, Red; the full TM subscene is used.

Enlargement of the PCA composite, to focus on area around Bloomsburg.

1-24: This pair of PCA images reminds me of a cross between French Impressionist painting and modern abstract art (many space images have been collected into art shows!). But most of the color patterns seem equatable to specific scene features. Try your hand at interpretation. ANSWER

Assuming you read through the answer to this last question, you should be prepared mentally to tackle this next image. It is a Supervised Classification (IDRISI system; Maximum Likelihood) of the full subscene, using all 7 TM bands and attempting to discriminate 12 classes. The proper skeptical attitude to adopt after looking at it is: Are the classes meaningful and were those set up reasonably accurate in their distribution. Before proceeding to the classification, answer this question:

1-25: Go back to the full screen plus enlargement of the TM subscene and scroll over different areas as you choose. Make a list of what you think are valid classes present in the areas represented. These could be completely different from one another or variants of the same class, such as various agricultural field uses or conditions. You should keep in mind that your selection ought to take into account the likelihood that the color variants will probably also have spectrally separable characteristics (thus, distinctive sets of DN values that will respond well to the statistical measures calculated in doing the classification). Make your list before going to the answer. ANSWER

Without further ado, here is the Supervised Classification:

Supervised Classification (Maximum Likelihood) of the TM subscene

To help you in appraising details, there is an enlargement of the classification around Bloomsburg, and the legend (color scheme) for the 12 classes is shown to its right.

Enlargement of the Supervised Classification, concentrating on the Bloomsburg area. Legend for the Supervised Classification.

1-26: Evaluate this classification (you may want to re-read pages 1-16 and 1-17 to remind yourself of the principles of classification) in terms of 1) the purpose behind it; 2) the wisdom in choosing the particular classes, and 3) an estimate (visual impression) of the accuracy in correctly picking the classes (errors of omission and commission. ANSWER

As this Exam was being conceived, I had hoped that the Geography program at Bloomsburg University had, by now, carried out a GIS study of the TM subscene (since there is a whole course on that subject that uses IDRISI's extensive GIS capability). Unfortunately, that hasn't happened as yet. But, I was steered by the course professor to Mr. Tim Murphy (a graduate of that program at BU) who now works for Columbia County as their GIS specialist. He, and the county, have kindly provided several data layers that are already in their system but the project is still continuing (a major GIS effort can take a long time), though not ready for the decision making phase. Digitized and captured into a data base so far are the roads and streams and township boundaries for the entire Columbia County, and land use maps for about half the area. Through their generosity, we can display here two thematic maps or data elements, both for the area around Bloomsburg and its immediate north. The left (or top) map is roads (red) and streams (blue) combined; the right (or bottom) map is land use categories:

GIS Data Layer showing roads (red), river/streams (blue), and township boundaries (black) Land Use map covering Bloomsburg and the rural areas to its north.

We will not ask you any questions directly pertaining to these maps. For your information, in the land use map, the land use categories are as follows: 1) Dark green = Forest; 2) Medium green = Open Field (at the Fairgrounds) or City park; 3) Light green = farm or grass lands; 4) Yellow = Low density housing; Orange = Medium density housing; 5) Brown = High density housing; 6) Pink = Schools; 7) Medium gray = Bloomsburg University; Dark gray = Roads or the Airport; 9) Red = Commercial; 10) Purple (in part) = Factories; Blue = Lake; Black = Township boundary lines; White = Not yet classified.

As we close out the Exam, we will swing westward to look at another enlargement from the full TM scene and also one covering some of the same area by the L and C band radar on SIR-C. Compare these three images:

Landsat TM Subscene

SIR-C L-band HH Subscene

SIR-C Color Composite using L and C band Images

1-27:In the Landsat subscene, identify the towns along the Susquehanna River (note the confluence of the West and North [actually from the east] Branches), using the road map above as a guide. Then, try to find them in the L-band HH middle image. Finally, how do they appear in the radar color composite? What does the purple color correspond to? ANSWER

It's time to close this rather lengthy and demanding Final Exam - almost as rigorous as a Ph.D. "written". You will have to grade yourself on how well you have done. Hopefully, good enough to feel mentally aroused and emotionally satisfied. Having worked through the main body of the Tutorial, if you assimilated the essentials you can add remote sensing to your skill mix. Let's believe that you will encounter opportunities to apply this knowledge. We close with a:


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Primary Author: Nicholas M. Short, Sr. email: [email protected]