Georeferencing of Scanned Aerial Imagery and Change Detection

Transcription

1 Georeferencing of Scanned Aerial Imagery and Change Detection For: Janet Finlay GISC9231- Remote Sensing John Bull B.Sc Candidate GIS-GM Candidate 3 Jasmin Crescent St. Catharines, Ontario

2 Table of Contents Table of Figures Introduction Aerial Images (19, 20, 21)[Figure 1] Aerial Images (H20-1, H20-2, H22-25, H22-91) Satellite Imagery (IKONOS Multispectral Imagery)[Figure 9] Change Detection Conclusions Bibliography... 23

3 Table of Figures Figure 1: 1934 aerial images overlaid on top of raster imagery... 2 Figure 2: Wedge shaped feature at location A... 4 Figure 3: Linear feature at location B... 5 Figure 4: Pond at location C... 6 Figure 5: Feature at location E... 8 Figure 6: 1921 aerial images overlaid on top of raster imagery... 9 Figure 7: Ship identified in Lock 12 of the third canal Figure 8: Construction of fourth canal Figure 9: False-colour composite image of third and fourth canals in Figure 10: Roads crossing the third canal instead of lift bridges Figure 11: Vegetation growth in an old lock in canal three Figure 12: Outline of Fuller Plan Figure 13: Fuller Plan in Figure 14: Fuller Plan in Figure 15: Fuller Plan in

4 1. Introduction Georeferencing is done in ESRI s ArcGIS through the use of control points. Control points are a set of user defined spots that are used to align an image or to tie one image down to another. For this project we had aerial imagery from 1921 and 1934 that we georeferenced, or tied down, to a satellite image from By selecting a point on the aerial image and then selecting where that point is on the corresponding satellite image we create control points that the software then uses to fit our aerial image onto our satellite image. The key for georeferencing is to choose locations that are easily identifiable such as intersections but also locations that are spread evenly across the aerial image. The rubber-sheet approach to tying down images works best when control points have a full spatial coverage. Once the aerial images were georeferenced and tied down to the satellite image, a set of questions was answered for each set of aerial images as well as the satellite image. The questions consisted mostly of identifying features. Lastly, a section has been included that performed a change detection analysis. This section provides changes to the locks, as well as a certain land segment, over the years 1921, 1934, and

5 Aerial Images (19, 20, 21)[Figure 1] Figure 1: 1934 aerial images overlaid on top of raster imagery 2.1. What was the operational status of each of the canals in 1934? Why do you draw this conclusion? Judging by the three provided air photos it appears as if the west canal (canal four) was the 2

6 one that was in use in Neither canal has a visible boat passing through giving definitive evidence that it was being used at that time however the east canal has a very rough texture in each of its locks as opposed to the smooth texture of the west canal; this evidence suggests the east canal is not full with water and is therefore not operational. Other research (Westwater, 2010)shows that canal four opened the same year that canal three was shut down, 1932, which further proves that only the west canal was operational Referring to A Welland Canals 1934 (JPEG), what is the wedge shaped formation at location A? What are the striations? The wedge-shaped formation at location A is a large mound of dirt created from the excavation of land to build canal four. The striations on the dirt mound are created from the machinery that was doing the excavation (Transport Canada, 1916); the steam shovels or dragline excavators that were working on the project released the dirt slowly in lines creating the striations we see in the images. The following elements of image interpretation explain why: a. Shape: The feature is wedge-shaped and appears to disperse away from the canal indicating that the point of highest elevation is closest to the canal. The feature s shape is also resembles an alluvial fan indicating that the hill may be made of a sediment-rich material, such as excavated earth. b. Size: The feature is very large, stretching the length of two locks in the north-south direction. This large size may be attributed to the large amount of dirt that was needed to be removed from this section of the canal; the fourth canal created these locks to climb the escarpment in a very short distance so therefore lots of earth had to be removed. c. Pattern: The striations on the large feature show a linear pattern extending out from the point of highest elevation. This pattern indicates the dirt may have been released in a long linear pattern so that the hill would not be extremely high. It also could be from the dirt running down the hill along its angle of repose. d. Tone: The feature has some bright spots but for the most part it is what I would consider a medium colour in this panchromatic range. To me this is indicative of a feature that is comprised of natural materials such as dirt. e. Texture: The feature has a very coarse or rough texture with a large spectral variability across it. This high variability is due to the roughness of the excavated dirt that has been placed there. f. Shadow: The feature does not cast much of a shadow apart from a small section on the eastern side of the feature. This would normally represent that there is not much relief associated with the feature but since this feature has such a gradual drop in relief the lack of shadow is probably not from a lack of height. g. Association: The feature is located right beside the newly built canal indicating that the large feature could have been created during its creation. The feature also has two access roads that appear to come from the canal itself indicating that trucks or excavators were using these roads to climb out of the canal and dump their dirt onto the feature. 3

7 Figure 2: Wedge shaped feature at location A 2.3. Again, referring to A Welland Canals 1934 (JPEG), what is the linear feature at location B? What was its status in 1934 (was it actively being used)? What is your evidence? The linear feature at location B is the remnants of the Blue Ghost Tunnel which was a train tunnel that ran under canal three. The following elements of image interpretation explain why: a. Shape: The feature is linear and is slightly wider than most of the surrounding roads. The linear shape of the feature indicates that it is probably used for some sort of transportation either for cars or trains. b. Size: The feature is very long as it spans from the canal to the west over to the edge of the 4

8 air photo to the east. This also indicates that the feature is probably used for transportation. c. Pattern: There is not much of a pattern associated with the feature as it is fairly simply. The lack of pattern does not really help in the identification of the feature. d. Tone: The feature has two very distinct and opposite tones. One line is a very bright white whereas a line just to the south of it is very dark. These two different tones could represent two different features, for example the dark feature could be the train tunnel whereas the lighter feature could be a service road that runs parallel to the tunnel. e. Texture: The feature has a fairly smooth texture which could indicate it being constructed of a man-made material such as cement or pavement. f. Shadow: There is little to no shadow associated with this feature indicating that the feature probably runs along the ground such as a road or train tracks. g. Association: The linear feature stops abruptly at the water and then picks back up on the other side indicating that the feature is probably a tunnel that goes under the canal. The feature also appears to split away from the train tracks that are north of the feature. Figure 3: Linear feature at location B The Blue Ghost Tunnel was not actively being used in 1934; it was closed completely in 1915 after only being operational for thirty-nine years (HH Paranormal Inc., 2011). 5

9 2.4. Again, referring to A Welland Canals 1934 (JPEG), why do you suppose the pond at C existed? The pond at location C appears to exist due to some sort of pumping system coming from the fourth canal. The pond is located at the end of some fan-shaped features that could be pumping out sediment and water from the fourth canal. A dark linear feature northwest of the pond (arrow pointing to it) could also be part of the pumping system directed from the canal. The tone of the pond is very dark as well indicating that it could be a very muddy or murky water due to its large amount of sediment. Figure 4: Pond at location C 6

10 2.5. Again, referring to A Welland Canals 1934 (JPEG), what is area E? The feature located at area E could be a large dirt hill, similar to the wedge at location A, which has been flattened or groomed to a flat elevation. The following elements of image interpretation explain why: a. Shape: The feature is an odd polygon shape but yet it has very definitive boundaries indicating to me that it is probably man-made or groomed using some sort of machinery and that it is not just a natural feature. b. Size: The feature, similar to the wedge at location A, is rather large. It is slightly larger than the wedge though which makes me think that it is possibly a similar feature that has been groomed and spread out over a slightly larger area. c. Pattern: The feature has sort of a linear striation pattern that is similar to a groomed farmer s field. This is why I believe the field to have been groomed by some sort of machinery to flatten it. d. Tone: The feature itself has mostly a mid-tone but has multiple spots with much brighter tones. This appears to me as if it is mostly comprised of dirt, with the lighter toned areas representing a lighter or drier sand or dirt. e. Texture: The texture of the feature is fairly coarse. There are limited smooth areas and the striations add to the coarseness of the overall feature. This coarseness again leads me to believe the feature is comprised mainly of loose, groomed dirt. f. Shadow: The feature has little to no shadow indicating to me that the feature is probably very low lying and does not contain any real relief. g. Association: As noted earlier the feature somewhat resembles a farmer s field that has recently been groomed, but due to the proximity of the canal I can t see this being correct. The feature has a road running along the west edge of it which could have been used my machinery when dumping and grooming in the feature. 7

11 Figure 5: Feature at location E 8

12 Aerial Images (H20-1, H20-2, H22-25, H22-91) Figure 6: 1921 aerial images overlaid on top of raster imagery 3.1. What was the operational status of each of the canals in 1921? Why do you draw this conclusion? In 1921 the third canal was operational however the fourth canal was still being constructed and therefore was not being used yet. The first piece of evidence that the third canal was operational was the fact that it is filled with water. We can see in Figure 6 that the third canal has a very smooth texture, with a lighter tone, indicative of a canal lock being filled with water. The second reason that I feel the third canal was operational was that a ship has been identified in Lock 12 of the third canal. The ship, as can be seen in Figure 7, is easily identifiable through its tone 9

13 against the water, its shape, and the association with a canal. Figure 7: Ship identified in Lock 12 of the third canal It is also fairly easy in the 1921 aerial images to determine that the fourth canal is still under construction (Figure 8). The texture, in sharp contrast to canal three, is extremely rough and does not indicate the presence of water but more or less just rough dirt. The pattern of striations gives the appearance of dirt tracks and roads that were probably used by the construction equipment within the canal. Lastly the tone is not indicative of water whatsoever, unlike the even toned appearance of canal three, canal four has multiple different tones indicating different elevations of dirt. 10

14 Figure 8: Construction of fourth canal 11

15 Satellite Imagery (IKONOS Multispectral Imagery)[Figure 9] Figure 9: False-colour composite image of third and fourth canals in What was the operational status of each of the canals in 2003? Why do you draw this conclusion? By the year 2003, it is quite evident via the satellite imagery, that only the fourth canal is operational and that the third one has ceased operations. Although the third canal still appears to have water in many of the locks, there are a few strong reasons to suggest that it has ceased operation. Firstly, there are many sections of the canal where there are no functioning lift bridges; the canal is crossed simply by a road or basic bridge that cannot lift in the case of a ship passing through (Figure 10). Figure 10: Roads crossing the third canal instead of lift bridges 12

16 Unless the third canal has been restricted to only very small ships than this would indicate that it is no longer in operation. Secondly, there are areas of the canal where we can see that vegetation has grown or expanded into the lock choking off its width and making it virtually impossible for a ship to pass through (Figure 11). Figure 11: Vegetation growth in an old lock in canal three Lastly, multiple websites also indicate that by 2003 the only canal that was operational was canal four. Westwater (2010) for example, on his website containing the history of the Welland Canal s, indicates that the third canal was open only until 1932 and that the fourth canal has been open from 1932 until present-day. 5. Change Detection 5.1. Create a table that shows how locks 11 through 24 are/are-not visible to our remote sensing platforms in 1934 and 2003 Table 1 below indicates whether Locks 11 through 24 were visible in 1934 and 2003 as well as their condition or why they are no longer visible Imagery 2003 Imagery Lock # Visiblity Comments Lock # Visiblity Comments 11 Visible Fully visible, still partially 11 Visible Fully visible, submerged submerged in water in water 12 Visible Fully visible, some water remains in bottom of lock 12 Visible Fully visible, slightly submerged in water, does not have typical lock appearance anymore 13 Visble Fully visible but empty 13 Visible Fully visible, small amounts of water still in it 13

17 14 Visible Fully visible but empty 14 Visible Fully visible, appears to be overgrown with vegetation 15 Visible Fully visible but empty 15 Visible Fully visible, appears to be overgrown with vegetation 16 Visible Fully visible but empty 16 Visible Fully visible, appears to be overgrown with vegetation 17 Visible Fully visible and appears to have water in it 17 Partially Visible Heavily overgrown with vegetation but basic shape still exists 18 Visible Fully visible but empty 18 Visible Fully visible, surrounded by heavy vegetation 19 Partially Visible Beginning of lock is visible but the rest has been flooded to create the reservoir for the fourth canal 19 Not visible Completely gone, covered by land, vegetation and forest 20 Not Visible Not visible at all, completely submerged in the fourth canal reservoir 21 Visible Entirely visible lying in the middle of the fourth canal reservoir 22 Visible Fully visible, appears to be empty 20 Not visible Completely submerged in fourth canal reservoir 21 Visible Partly submerged in fourth canal reservoir but still visible 22 Partially Visible Partially covered with vegetation and also somewhat submerged in reservoir 23 Not Visible Outside of image 23 Not visible No longer exist, area used as Lock 7 overflow 24 Not Visible Outside of image 24 Not visible No longer exist, area used as Lock 7 overflow Table 1: Visibility of Locks 11 to 24 in 1934 and in

18 5.2. Describe the changes within the lands of the Fuller Plan from 1921 through 1934 to 2003 The Fuller Plan is a small area located just south of the CN railway and enclosed by a W - shaped roadway (Figure 12). Figure 12: Outline of Fuller Plan The Fuller Plan in 1921 contained what appears to be a few small houses, some agricultural fields, and a road (Figure 13). From this it does not appear that much of a plan was in motion to alter the land-use in the area as no construction is occurring. 15

19 Figure 13: Fuller Plan in 1921 The 1934 images portray a slightly different picture for the Fuller Plan and it is in these images where it is apparent that some sort of plan is in place to change the land-use in the area. We can see in Figure 14 that much of the land appears to have been cleared, potentially for the creation of a housing subdivision, or to open up large farming plots. Whatever the reason, the agricultural plots seen in the 1921 image, are not nearly as visible in the 1934 image leading me to believe that they were not actively being farmed anymore and instead the area was being cleared for a land-use change. 16

20 Figure 14: Fuller Plan in 1934 The 2003 image shows a far different picture than the other two sets of aerial imagery. The Fuller Plan by 2003 is completely forested over with no farming occurring. There s what appears to be a parking lot in the north section of the Fuller Plan but aside from that the Fuller Plan is covered almost entirely with forest (Figure 15). 17

21 Figure 15: Fuller Plan in 2003 The changes in the land-use of the Fuller Plan were probably caused due to the construction of the fourth canal. In 1921 when the land was being used for a few small farms, the construction of the fourth canal had just begun and the land owners may have been unaware of the full plans for the canal or its full extent. By 1934, the Fuller Plan land appeared to have been cleared out with agricultural production ceasing; by this time it was evident that the reservoir for the fourth canal as well as access roads would occupy space in close proximity to the Fuller Plan. It was at this time perhaps that it was decided that a housing or farming development would probably not be wise with the close proximity to the new canal What happened to the wedge shaped landform at location A of to A Welland Canals 1934 (JPEG) that was visible in 1921 and 1934? The wedge shaped formation at location A, which can be seen in Figure 2, is gone in

22 because the dirt it was made of was either dispersed to the area around it or transported out of the area via trucks. This formation was simply the dirt remains from the construction of the fourth canal and therefore their plan was not to leave a large dirt hill there but rather to either smooth the hill out or transport the dirt to a new location. 19

23 5.4. Create two figures for your report that show the georeferenced imagery overlaid atop the IKONOS satellite image Figure 16: 1921 aerial photography overlaid on IKONOS satellite images 20

24 Figure 17: 1934 aerial images overlaid on IKONOS satellite imagery 21

25 6. Conclusions The purpose of this assignment was to complete a GIS project using remote sensing techniques and geoferencing. Using ArcGIS we were successfully able to georeference all seven images to the IKONOS satellite imagery. The images were georeferenced using control points such as intersections, bridge crossings, agricultural field corners, and lock boundaries. Throughout this project we were able to conclude multiple things about the third and fourth Welland Canals. Firstly, the third canal was operable up until 1932 when the fourth canal opened and took over as the major ship route between Lake Ontario and Lake Erie. Secondly, we were able to establish the condition of Locks 11 through 22 in 1921, 1934, and Thirdly, we were able to see the changes to a small land area known as the Fuller Plan from 1921 to Lastly, the project required the identification of small features around the third canal that had to do with the construction of the fourth canal. 22

26 7. Bibliography HH Paranormal Inc. (2011, August 14). The Blue Ghost Tunnel: Thorold, Ontario, Canada. Retrieved November 21, 2013, from Ghost Walks: Transport Canada. (1916). Welland Ship Canal General Information and Description of Work. Welland: Brock University Library. Westwater, G. (2010). 3rd Welland Canal Retrieved November 12, 2013, from Welland Canals. 23