Lab - LANDSAT TM & SPOT IMAGERY
The purpose of Lab06 is to familiarize you with interpreting Landsat Thematic Mapper and SPOT imagery. Upon completion of this lab you should be aware of the usefulness of each TM band, and the similarities and differences between TM and SPOT data.
Outline:
| Data Name | Description |
|---|---|
| GEOG111_Lab08Questions.docx | Handout to turn in |
Q1. Circle the nadir point in the air photo and discuss why. (2 point) NADIRimage.jpg
Part 2: Flight Planning
This example illustrates the various calculations involved in preparing an aerial flight plan for an area of 80mi2.
Basic information required is as follows: Desired photographic scale: 1,320ft/in Scale of base map: 1:62,500 or 1in = 5,208ft Size of area: 8 miles EW by 10 miles NS or 42,240ft by 52,800ft Average ground elevation above mean sea level (MSL): 1,200ft Average forward overlap: 60% Sidelap: 15-45%, averaging approximately 30% Negative format: 9x9in or 11,880ft by 11,880ft on the ground Camera focal length: 6in or .5ft
Items to be computed in preparing the flight plan are as follows: Flying height above ground and height above mean sea level Direction and number of flight lines Ground distance between flight lines Actual percentage of sidelap Map distance between flight lines Ground distance between exposures on each line Map distance between exposures on each line Number of exposures on each line & total number of exposures
Flight map computations:
From #1 desired scale is 1,320ft (GD) per inch (PD) 1,320ft * 12 in = 15,840in so desired scale = 1:15,840
Flying height above ground (AGL) and height above mean sea level Flying height above ground (AGL) AGL = focal length * desired scale denominator AGL = .5ft * 15,840 = 7920ft above ground
Flying height above mean sea level
7,920 + 1,200 (from #4) = 9,120ft
B. Direction and Number of Flight Lines Direction of flight lines: N-S following long dimension of tract. Number of flight lines: Assuming an average sidelap of 30% (#6), the lateral gain from one line to another is 70% of the print width, or Print width GD = negative formatscale denominator = 9in15840 = 142560 in = 11880ft (1-Average sidelap) * Print width GD 0 .70 x 11,880 = 8,316ft (lateral gain) between lines.
The number of intervals between lines is found by dividing the tract width (42,240 ft)
by the lateral gain 8,316ft. The result is
Track width = 42,240ft = 5.08 or 5 intervals and 6 flight lines.
Lateral gain 8,316ft
C. Ground Distance between Flight Line (Tract width) 42,240ft = 8,448ft GD between flight lines (Intervals) 5
D. Actual Percent of Sidelap Actual percent of sidelap, assuming exterior flight lines are centered over tract boundaries:
Sidelap%= (Print width GD (ft)-GD between flight lines (ft))/(Print width GD (ft))*100
Sidelap%=(11,880-8,488)/11,880*100=28.9%
E. Map Distance between Flight Lines Map scale = 1:62,500
1 Map Distance 1 inch x inches
= =
62,500 Ground Distance 5,208ft 8,448ft
= 1.62in between flight lines on map
F. Ground Distance between exposures on each line Assuming an average forward overlap of 60%, the spacing between successive exposures is 40% of the print width or:
0.40 * 11,880ft = 4,752ft
G. Map Distance between exposures on each line
1 Map Distance 1 inch x inches
= =
62,500 Ground Distance 5,208ft 4,752ft
OR scale of base map = distance between exposure on map
40% of print width
H. Number of exposures on each line and total number of exposures Number of intervals between exposures is found by dividing tract length (52,800ft) by 4,752 = 11.11 intervals. This would require 12 exposures inside the area, assuming that the first exposure is centered over one tract boundary.
In addition, two extra exposures are commonly made at the ends of each line. Thus, a total of 12 + 2 + 2 = 16 exposures would be taken on each flight line.
So, the total number of exposures required to cover the entire tract is:
6 lines * 16 exposures/line = 96 exposures
Part 3
Assume you get a job, after acing this class, and are a well-paid Projects Coordinator for a local photogrammetric consulting firm. Your task is to set up a flight plan for an over-flight near Lawrence, Kansas. Use the following information to plan the mission.
Desired photographic scale: 1:24,000
Scale of base map: 1:100,000
Size of area to be covered: 7 miles EW by 10.5 miles NS
Average ground elevation above mean sea level (MSL): 450m
Average forward overlap: 65%
Sidelap: 15-45%, averaging 30%
Negative format: 9x9in
Camera focal length: 6in (.5ft)
Q2: CALCULATE THE FOLLOWING: (2points each, a total of 22) Flying height above ground (AGL) and height above mean sea level Flying height above ground (AGL) AGL = focal length * desired scale denominator AGL = .5ft * 24,000= 12,000 ft above ground
Flying height above mean sea level
12,000 + 1,476.4 = 13,476.4 ft
B. Direction and Number of Flight Lines Direction of flight lines: N-S following long dimension of tract. Number of flight lines: Assuming an average sidelap of 30% (#6), the lateral gain from one line to another is 70% of the print width, or Print width GD = negative formatscale denominator = 9in24,000 = 142560 in = 11880ft (1-Average sidelap) * Print width GD 0 .70 x 11,880 = 8,316ft (lateral gain) between lines.
The number of intervals between lines is found by dividing the tract width (42,240 ft)
by the lateral gain 8,316ft. The result is
Track width = 42,240ft = 2.93 or 3 intervals and 4 flight lines.
Lateral gain 8,316ft
C. Ground Distance between Flight Line (Tract width) 36,960 ft = 13,320 ft GD between flight lines (Intervals) 3
D. Actual Percent of Sidelap Actual percent of sidelap, assuming exterior flight lines are centered over tract boundaries:
Sidelap%= (Print width GD (ft)-GD between flight lines (ft))/(Print width GD (ft))*100
Sidelap%=(18,000-12,320)/18,000*100=31.56%
E. Map Distance between Flight Lines Map scale = 1:62,500
1 Map Distance 1 inch x inches
= =
62,500 Ground Distance 10,000 ft 12,320 ft
= 1.48in between flight lines on map
F. Ground Distance between exposures on each line Assuming an average forward overlap of 65%, the spacing between successive exposures is 35% of the print width or:
0.35 * 18,000ft = 6,300ft
G. Map Distance between exposures on each line
1 Map Distance 1 inch x inches
= =
62,500 Ground Distance 5,208ft 4,752ft
OR scale of base map = distance between exposure on map
40% of print width
H. Number of exposures on each line and total number of exposures Number of intervals between exposures is found by dividing tract length (5,280ft) by 6,300 = 8.8 intervals. This would require 9 exposures inside the area, assuming that the first exposure is centered over one tract boundary.
In addition, two extra exposures are commonly made at the ends of each line. Thus, a total of 9 + 4 = 13 exposures would be taken on each flight line.
So, the total number of exposures required to cover the entire tract is:
4 lines * 13 exposures/line = 52 exposures
Part 4 Introduction to ERDAS IMAGINE
Introduction This part will provide an introduction to the Earth Resources Data Analysis System (ERDAS) IMAGINE software that you will be using for the rest of the semester.
Step 1: Copy files to your directory Log on to the machine. Go to your directory under My Computer and create a lab04 folder. Download GEOG 526 Lab 4 Data to your Lab04 folder and unzip it.
Step 2: Accessing ERDAS IMAGINE Click on the Start button and go to All Programs ERDAS Imagine 2016 ERDAS Imagine 2016. After a moment the IMAGINE logo should come up, followed by the main IMAGINE menu, a panel across the top of the computer screen. A “viewer”, a black screen in which images are displayed, should also come up. You can resize these windows by grabbing the corners of the windows with your cursor, or you can move the windows around if you so desire.
Step 3: Displaying an Image To display an image, right click on “2D View #1” under the contents menu on the left side of the screen and click on “Open Raster Layer…”, or simply click on the open file icon at the very top left of the screen. The Select Layer to Add window should now appear. Select the E: drive from the “Look in:” dropdown menu, and double click on “Users” your directory (E:\your_name\GEOG526\Lab05). In your directory, select (highlight) the file garden9182018.img, but don’t click OK just yet. The data in this file are from a subset of SPOT’s multi-spectral sensor over western Kansas near Garden City. Look at the other information in the Select Layer to Add window under the Raster Options tab. The Display should be on True Color. Change it to Gray Scale and Display Layer 1. This allows you to display one data layer (one band/ wavelength range) in the viewer. Switch back to the File tab. At the very bottom is additional information, including the number of columns and rows and the number of bands in the image.
- How many bands are available? What are the wavelengths represented by Spot’s Multi-spectral Scanner (XS) sensor (provide the band number, name, and wavelength)? (6 points) Use your textbook or the handout for this question.
Band Wave Length Name XS1 0.50-0.59 um green XS2 0.61-0.68 um red XS3 0.79-0.89 um near IR
After answering the above questions, click OK. Once the image is displayed, you can retrieve information regarding various characteristics of the layer by clicking on the Metadata icon under the Home tab (the icon looks like a piece of paper with an “i” in the center). After the Metadata dialogue box opens (this may take a bit!) click on the General tab and find the Layer Info data box, in this look at the Height and Width numbers.
- How many columns of data do we have? 512 Rows? 512 (2 points)
Step 4: Assigning Color Guns to Bands Reopen garden9182018.img. Under the heading Layers to Colors on the Raster Options tab of the Open Raster Layer window, we can specify which computer color gun is used to display a certain band. Make sure it is Red-3, Green-2, and Blue-1
This is telling you that we are assigning band 3 to the first “color gun”, which is red; band 2 to the second color gun, which is green; and band 1 to the third computer color gun, which is blue. If you entered layers (or bands) 1,2,3 in that order, it would assign band 1 to color gun 1 (red), band 2 to color gun 2 (green), and band 3 to color gun 3 (blue). Get it?
In the bottom of the same window, check Clear Display (this clears the data from the display window). Also click on the box Fit to Frame- you’ll want to do this every time you display an image. This displays the whole image in the window, rather than setting it to a pre-defined default zoom. Now click OK at the side of the screen. The color composite Spot image should appear.
You can change the assignment of bands to color guns by clicking on the toolbar on the top, Raster - Multispectral tab and go to Bands where you will see the three color guns to assign.
Keep in mind that these data have been “contrast stretched” to make it easier to interpret visually. This is done by the computer’s examination of a statistics file of the image to determine how it should be stretched. You will learn how to do this later.
-
The image displayed is a color composite. What type of color composite is it? Please refer to the spectral wavelength of the image bands (3 point)
Color Gun Image Band No. Wavelength Name Red 3 near IR Green 2 red Blue 1 green
Step 5: SPOT Image Change the band combinations on the image, i.e. change the band-color gun assignments. On the main menu, click the Multispectral tab. Here there is a sub-menu called “Bands”. Change the band assignments to 3 to red, 3 to green, and 3 to blue.
- What will this image look like now? And WHY? (Explain why this image displays in this color scheme - remember that all three colors were assigned the same band of data). Is it a color composite or…? What information is highlighted by this image? (3 point) (Hint: With the color composite AND band 3 displayed, look at the features and determine if they are light or dark in band 3. If they are light, that means that type of feature reflects high in that band. Recall the vegetated spectral response curve and how it reflects high or low in portions of the electromagnetic spectrum (NIR vs visible). Look at vegetated features and non-vegetated areas (water and bare soil) to help answer this question.)
Since all three color guns were assigned to the same band, the resulting image is a grayscale representation of Band 3 (near-IR), where high values (white) represent high near-IR reflectance. Near-IR reflectance highlights the vegetation.
Zoom in the image in the viewer until you can identify the cells/pixels. To investigate pixel values and the DN’s associated with them, press the Inquire “+” icon on the viewer menu under the Home tab. This brings up the “inquire cursor”. In the window that now comes up, examine the file File-pixel column. These are the reflectance values (PV’s, DN’s, etc.) for the pixel on which the cross-hairs of the cursor lie. You will see pixel values for each of the layers of your image. Move around the cursor with your mouse and watch the pixel values change.
Open garden.img with Layers to Colors: Red: 1, Green: 2 and Blue: 3. Don’t check Clear display (keep both garden.img and garden9182018.img in View 1) and order garden.img on top of garden9182018.img. Keep in mind that the bands of SPOT may or may not have been entered in the correct order, so always be aware of the wavelength range of each individual layer/spectral band you put into a gun. Image garden.img is the identical SPOT image with garden9182018.img with a different stacking order of image bands/ wavelengths. You may click on and off to check either image and change orders of bands to R,G, B guns from Raster – Multispectral for each to explore.
- Which SPOT image has its bands in the proper order? Justify your answer and, if they are not in correct order, what order are they in? (3 points) Bands 1 & 3 are reversed between the two. In garden9182018.img, the bands are in the correct order of green, red, near IR, respectively. In garden.img the near IR is in band 1 (as evidenced by high values over vegetated areas when all three guns set to Band 1) and band 3 has been switched for the green band.
There is no need to save anything from this lab, so when done you can simply close without saving. Submit your answers to the questions on blackboard.