2024_01_01-CONS127-A4
pdf
keyboard_arrow_up
School
University of British Columbia *
*We aren’t endorsed by this school
Course
127
Subject
Astronomy
Date
Apr 3, 2024
Type
Pages
10
Uploaded by GrandTree11471
1 Cons 127 Observing the Earth from Space Assignment 4: What Can I See? The Electromagnetic Spectrum, Wavelengths and Spectral Resolution Instructor: Chris Colton Office: FSC 2223 chris.colton@ubc.ca TA: Evan Muise (evan.muise@ubc.ca)
For this assignment you will…
•
Learn how to characterize the electromagnetic (EM) spectrum •
Understand the relationship between wavelength, frequency and energy •
Learn how the EM spectrum is used in remote sensing •
Be introduced to the spectral properties of different materials •
Understand the use of EM channels in remote sensing platforms Submit your answers in accordance with the posted Lab Quiz (in CANVAS): •
Assignment due date: Thursday, March 7
th
, 2024 at 11:59 pm Pacific Standard Time •
Answers to questions 1 through 20. The total points of the lab are 50. •
Any screenshots or supplemental attachments (if needed)
2 Part 1: The EM Spectrum As you learned in lecture, remote sensing uses different wavelengths of the electromagnetic (EM) spectrum to observe the Earth. The EM spectrum is the range of different values that the wavelength/frequency of light can take –
with the longest wavelengths and lowest frequencies represented by radio waves (10
6
μm, up to hundreds of meters in length), and the shortest wavelengths and highest frequencies represented by gamma rays (10
-6
μm, smaller than the diameter of an atom). Visit https://applets.kcvs.ca/ElectromagneticSpectrum/electromagneticS pectrum.html . This is a website that allows you to explore the EM spectrum. Use the sliding bar to examine difference regions of the visible light spectrum, which goes from 380nm to 780nm. Note how the frequency (Wave View) and energy (Photon View) change as wavelength increases or decreases. The wavelength of your cursor can be found in the white box. Explore this tool, then answer the following questions. Figure 1 Example of the visible light spectrum from the KCVS website As you can see, the difference in size of the longest and shortest EM wavelengths is 12 orders of magnitude! To put this in perspective, the distance from the Earth to the Sun is about 149,600,000,000 m (or 1.496 x 10
11
m), an order of magnitude less; so, if you visualize a micrometre as a metre, the EM spectrum is really long! Check out Episode 5 of Cosmos: A Spacetime Odyssey (It’s on Netflix, and sometimes you can find episodes on YouTube), to get immersed into the EM spectrum even further.
3 Q1. What happens as you move the cursor from violet light to red light (left to right)? (1.5 points) a)
Wavelengths get shorter b)
Wavelengths get longer c)
No change Q2. Look under Wave View as you adjust the cursor. What happens to frequency as wavelengths get shorter? (1.5 points) a)
Frequency increases b)
Frequency decreases c)
No change Q3. As you move the slider around the visible spectrum, what is the relationship between frequency and energy? (1.5 points) a)
Energy increases as frequency increases b)
Energy decreases as frequency increases c)
Energy increases as frequency decreases d)
There is no relationship and the numbers are random Q4. Set the visible spectrum to 450nm. What color is shown? (1.5 points) a)
Red b)
Blue c)
Green d)
Orange Look at the entire electromagnetic spectrum (EM) above the visible light spectrum bar. Note that γ
means “gamma”.
Q5. Which type of radiation has the longest wavelength? (1.5 points) a)
Gamma b)
Infrared c)
Microwave d)
Radio Q6. Which type of radiation has the shortest wavelength? (1.5 points) a)
Gamma b)
UV c)
X-rays d)
Radio
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
4 Except for the case of active remote sensing technologies (and thermal and night light sensors), the energy sensed by satellites and airplanes observing the Earth entirely originates from the Sun. The wavelengths that pass easily through the Earth’s atmosphere are called atmospheric windows. One obvious atmospheric window is the visible light range, which is also the range of peak output by the Sun. Explore this webpage on light and telescopes for more information on how we use the EM spectrum https://www.sciencelearn.org.nz/resources/1625-light-and-telescopes
. Then answer the following questions. Q7) Which part of the EM spectrum do optical telescopes use? (1.5 points) a)
Radio waves b)
Micro waves c)
Visible light d)
Ultraviolet waves Q8) Which type of radiation is best for astronomers to use when detecting background radiation from the origin of the universe? (1.5 points) a.
Microwave b.
Gamma rays c.
Infrared d.
Radio e.
X-rays Q9) According to the article, what are false colors? (1.5 points) a.
Parts of the EM spectrum we haven’t
discovered yet b.
Parts of the EM spectrum which can’t
be seen with the naked eye, but which computers can turn into visible spectrum colors c.
Colors based on non-EM spectrum information such as elevation Q10) According to the video “Detecting
light in space”, why
do the X-ray telescopes need to be put in space, but radio telescopes can be used on Earth? (The i button can be clicked to view a transcript). (1.5 points) a.
X-rays don’t
penetrate the atmosphere, but radio waves do b.
Radio waves don’t
penetrate the atmosphere, but X-rays do c.
X-rays are used to detect objects in space such as galaxy clusters, whereas radio waves are used only for objects on Earth d.
Both X-ray telescopes and radio telescopes work best in space, but either can be used on Earth
5 Part 2: Spectral signatures 1.
An extremely useful characteristic of objects is that they have unique spectral signatures: the EM wavelengths that are reflected and absorbed at different rates by different materials. Figure 2 below, shows the reflectance characteristics of various materials. An example of spectral reflectance curves is below. Go to http://gsp.humboldt.edu/olm/Courses/GSP_216/lessons/reflectance.html for an interactive version and an explanation on why each surface feature has a different reflectance curve. Use these explanations and the interactive spectral reflectance graph to answer the following questions. Figure 2 Reflectance characteristics of various features at different wavelengths. According to the section on the spectral reflectance of vegetation…
Q11. Fill in the blank: chlorophyll strongly absorbs X and Y and strongly reflect Z Scroll down to the interactive spectral reflectance graph and explore some of the different reflectance curves of various surface materials. Then set the graph to “Water”.
6 Q12. What percentage of water is reflected at 1.5 micrometers (rounded to the nearest whole number)? a)
2% b)
10% c)
0% d)
80% The reflectance curve for water is relatively low, except for a small “bump”
around 0.4 micrometers. Q13) According to the section about water, what part of the EM spectrum should this “bump” be reflecting? a)
Blue visible light b)
Red visible light c)
Near-infrared d)
Microwave Now switch the graph to “Soil”.
Notice how different this reflectance curve is to the one for water. Q14. What percentage of soil is reflected at 1.5 micrometers (rounded to the nearest whole number)? a)
48% b)
5% c)
75% d)
10% Part 3: Exploring remotely sensed images with difference combinations of the EM spectrum By now, we’ve
gone over the EM spectrum wavelengths, their uses, and the ways different materials on the Earth’s surface absorb or reflect these wavelengths. Later, we will get more into remotely sensed imagery from satellites which use these wavelengths to observe the Earth’s surface. For now, let’s get into a short exercise about the way layering these wavelengths together creates an image. Everything you see is comprised of a combination of red, green, and blue. This is how a TV works, or how a printer creates full color images using only magenta (red), yellow (green), and cyan (blue) ink. Satellites use different “bands”
of these EM spectrum wavelengths in the same way as your eyes to create different images. For example, Landsat 8 has 11 bands of all different spectral regions (Table 1) which, when combined with others, allows us to view specific earth surface processes (such as vegetation health across a landscape). Each band is assigned its spectral region, and each has its own channel which matches. For example, Band 2 is the spectral region Blue, and so its channel is known as the Blue channel. When we put the Blue Band (Band 2) in the Blue channel, the data will be read correctly, and we will see the color blue. However, if we put another band in the Blue channel, it might show up as an entirely different color since the band is not in its correct channel.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
7 Table 1 Landsat 8 bands, spectral range, spectral region, spatial resolution, and applications Band Spectral Range (μm) Spectral Region Spatial Resolution (meters) Applications 1 0.435-0.451 Deep blues and violet 30 Coastal and aerosol studies 2 0.452-0.512 Blue 30 Coastal water mapping, differentiation of vegetation and soil 3 0.533-0.590 Green 30 Assessment of vegetation vigor 4 0.636-0.673 Red 30 Chlorophyll absorption for vegetation differentiation 5 0.851-0.879 Near Infrared (NIR) 30 Biomass survey and delineation of water bodies 6 1.566-1.651 Short-Wave Infrared 1 30 Moisture content of soil and vegetation 7 2.107-2.294 Short-Wave Infrared 2 30 Improved moisture content of soil and vegetation 8 0.503-0.676 Green, Red 15 Panchromatic band. Large area mapping, urban change studies 9 1.363-1.384 Thin part of Infrared 30 Detection of cirrus cloud contamination 10 10.60-11.19 Thermal Infrared 1 100 Thermal mapping and estimated soil moisture 11 11.50-12.51 Thermal Infrared 2 100 Improve thermal mapping and estimated soil moisture Sound confusing? It takes some practice to get used to. Go to Unity WebGL Player | Band Combination Interactive (nasa.gov) for a demonstration. This is an example of five different Landsat 8 bands /spectral regions (aka EM wavelengths) on the left, with a screen and three channels to the right. The three channels are red, green, and blue. Click and drag these inputs over to a channel to create a wire. This is similar to how remote sensing scientists put different bands in different channels. First, drag the red input to the red channel, the green input to the green channel, and the blue input to the blue channel. Each input should match the color of its respective channel. This is known as a “true color
composite”.
You should see an image pop up in the window which shows a scene from a Landsat image.
8 Q15) According to the caption under the Landsat image, what do these colors represent? (1 point) a)
Color differences which indicate areas in drought versus floods b)
Wavelengths which cannot be seen with the naked eyes which need to be shown through a computer c)
The closest to what you would see if you’re
flying over the area in a plane and looking down at the ground d)
California Now click reset and switch the wires so that the near-infrared is connected to the red channel, the red to the green channel, and the green to the blue channel. This is what’s
known as a “false
color composite”.
Q16) According to the caption under the Landsat image, when is this type of image useful? (1 point) a)
Detecting landslides b)
Analyzing vegetation c)
Counting boats in the Pacific Ocean d)
Finding dinosaur bones
9 Go to http://icetool-example.epizy.com/ICEtool.html . A gray panel with 4 images should display. The top three images show the bands loaded in the RGB channels. The other images show the result of combining these three channels together. You can adjust the overall image brightness (grey scale in the bottom right) or each channel brightness (red, green and blue scales) by moving the sliders. Above this grey panel there are three drop-down menus for the red, green and blue channels. You can select any band combination and click on Load. Wait a few seconds and the gray panel should reload with the new color composite image. On the right side of the panel, you can use different tools: •
Zoom/Roam: zoom in (left-click) or zoom-out (right click) in the image •
Data Probe: RGB values for a selected pixel •
Plot transect: Click, drag and release to plot a transect (RGB values along the transect). The first time you draw a transect, the result will pop-up in the center of the image and will prevent you to keep drawing. Just move the pop-up window on the side and draw the transect again. •
Outline region: Click drag and release to select a polygon region. •
Select region: Click, drag and release to select a rectangular region. •
Scatter: Plot the values of two bands in a region. You can select which bands to plot by clicking on two of the red, green or blue channel images. •
Histogram: Compute a histogram of RGB values in a region. The images displayed in the ICE tool were acquired above Vancouver by Landsat 8 on May 5th 2018. Table 1 lists the bands of Landsat 8 and their corresponding spectral ranges. This information is also displayed on the right of the ICEtool main panel. Q17: Which type of composite is this image? True colour composite False colour composite Click the box next to “Plot transect”. Left
-click and drag a short distance across the ocean (in the lower left-
hand corner, avoiding the large sediment plumes at the outlets of the Fraser River shown in light brown) to draw a line. A popup window labelled “ICE5 Transect” should appear (you can move this window over so you can see the image of Vancouver better). Take note of the 3 lines which correspond to the red, green, and blue channels. These are the spectral reflectance curves of the ocean. Use this to answer the following question. Q18: Which of the following is true about the spectral reflectance curves? A.
The blue and green channels are being reflected; the red channel is being absorbed B.
The red and green channels are being reflected; the blue channel is being absorbed C.
All three channels are being reflected D.
Only the red channel is being reflected
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
10 Now change the drop-down menus so that band05 (near infrared) is loaded into the Red Channel, band04 (red) is loaded into the Green Channel, and band03 (green) is loaded into the Blue Channel. Q19: Which type of composite is this? True colour composite False colour composite Repeat the steps for creating the transect over the ocean with this image and use the resulting ICE5 Transect window to answer the following question. This time, the sediment plumes will appear to be bright blue, rather than light brown. Q20: Which of the following is true about the spectral reflectance curves? A.
The blue and green channels are being reflected; the red channel is being absorbed B.
The red and green channels are being reflected; the blue channel is being absorbed C.
All three channels are being reflected D.
Only the red channel is being reflected