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Lab Six
Using NASA's Near Earth Observatory (NEO): The Role of Snow Cover in Shaping Climate
The Role of Snow Cover in Shaping Climate
In this lab, you will investigate satellite images displaying land surface temperature, snow cover, and reflected shortwave radiation data from the NASA Earth Observation (NEO) website.
Download, explore, and animate these images using ImageJ, a public domain image analysis program from the National Institutes of Health (NIH). Then use the web-based analysis tools built into NEO to observe, graph, and analyze the relationship between the three variables.
Lab authors: Betsy Youngman, Carla McAuliffe, Rita Freuder, Jeff Lockwood, Kevin Ward, David Herring, Brooke Carter, Holli Riebeek Science Education Resource Center
Step 1: Download and Install the ImageJ Software
Once there, click the link that appears directly below the name of your computer's operating system (e.g., Mac, Linux, Windows). This action will transfer a compressed file of the software to your computer. Your browser should automatically expand the file, creating an ImageJ folder on your computer's hard drive.
Note to Windows Users: It is recommended that you install ImageJ in the Documents directory, rather than in the Program Files directory. For security reasons, Windows 7 and Windows Vista do not allow programs to alter themselves by writing files to the Program Files directory. If ImageJ is installed in the Program Files directory, then the update function in Step 2 below will not work properly. In addition, if you are a Windows Vista user, be sure to choose the correct version of ImageJ (either 32-bit or 64-bit) for your computer.
Step 2: Select and Download the NEO Data
Go to the NASA Earth Observations (NEO) website and display the Energy Dataset, Reflected Shortwave Radiation image for January 1, 2009 to January 31, 2009.
- Show Me How
1. Go to the NASA Earth Observations (NEO) website. The NEO website opens in a new browser window. Be sure to use a Web browser that is both Flash and Java enabled. NEO organizes datasets into five categories: Ocean, Atmosphere, Energy, Land, and Life. Click the Energy tab in the top menu.
2. Locate the Reflected Shortwave Radiation dataset in the list and click it.
3. The display window loads the most recent monthly map of Reflected Shortwave Radiation. Under "View by date", select "1 mo". Under "Select Year" select 2009, then use the slider to select the month of January 2009.
Examine the January 1, 2009 to January 31, 2009 image of Reflected Shortwave Radiation.
This image shows how much incoming shortwave radiation is reflected by Earth's surface. Reflected energy is measured in Watts/m2 (the amount of energy per square meter). Higher values indicate more reflected solar radiation. Lower numbers show areas of less reflected solar radiation. The amount of reflected solar radiation is affected both by the amount of incoming solar radiation, which can be zero during the Arctic winter, and the reflectivity of the surface.
As you view these images, consider what factors are affecting the reflectance of the light and how the amount of reflectance varies both across the Earth's surface and through the seasons. Also consider how Earth's ability to reflect incoming sunlight impacts its energy balance and temperature.
Click About this dataset to learn more details about what the map is showing.
- Show Me How
1. The About this dataset link is located in the lower left below the map.
When the text box opens, use the information in it plus your observations to answer the following questions about the dataset:
What areas are the brightest?
What areas are the darkest?
How would you define reflected shortwave radiation in terms of brightness?
Download the January 1, 2009 to January 31, 2009 image at a resolution of 0.5 degrees and save it as 01_sw_radiation.jpg. Repeat the process for all twelve months of 2009 until you end up with a total of twelve images, named from 01_ sw_radiation.jpg to 12_ sw_radiation.jpg.
If you have difficulty obtaining the images, then click on the button below and download and save the ones that open up.
Click each thumbnail to open the full size image in a larger window. Then right-click or control-click to choose file Save Image As... Do not rename the files. Keep them as 01_ sw_radiation.jpg, 02_ sw_radiation.jpg,etc.
January 2009
February 2009
March 2009
April 2009
May 2009
June 2009
July 2009
August 2009
September 2009
October 2009
November 2009
December 2009
Step 3: Animate the NEO Data with ImageJ
Launch ImageJ by double-clicking its icon ImageJ Icon Small on your desktop (Mac or PC) or by clicking the icon in the dock (Mac) or the Start menu (PC).
Choose File > Import > Image Sequence... and navigate to the Reflected Shortwave Radiation folder where you stored the monthly images.
Select the folder containing the images or the first image in the sequence and then click the Open button. Specify the Sequence Options. Start with the first image and increment by 1 and then click OK.
All twelve images will be imported into a stack named Reflected Shortwave Radiation. The individual images in a stack are called "slices" in ImageJ. The image below shows the first of the twelve total slices (1/12). The width and height of the stack in pixels, and the size of the stack, in this case 12 MB, are displayed at the top of the window just below the name of the stack.
Choose File > Save As... to save the stack as Reflected_Shortwave_Radiation.tif.
Choose Image > Stacks > Animation > Animation Options... to set the speed of the animation to five frames per second.
- Show Me How
1. Choose Image > Stacks > Animation > Animation Options...
2. Specify the Sequence Options. Use all twelve slices, beginning with the first slice and incrementing by one. Do not scale the images. Turn on (check) the Sort Names Numerically option and click OK.
Use the play/pause button at the lower left part of the window to start and stop the animation.
If you had difficulty creating or saving the stack, then use the Reflected_Shortwave_Radiation stack by clicking the button below. To download and save the Reflected_Shortwave_Radiation stack, on a PC, right-click on the link and on a Mac, control-click on the link. Then choose File > Save As... and navigate to where you want to save the stack.
Reflected Shortwave Radiation.tif (TIFF 8.9MB Jun14 10)
Experiment with changing the speed of the animation. Step through or animate the Reflected Shortwave Radiation images from January 2009 through December 2009. Carefully observe the changes that occur during the year and then answer the following questions:
◦ What regions of the Earth are have the most reflected short wave radiation each month of the year? These regions appear "bright" on the map.
◦ How does this change in the amount of reflected short wave radiation relate to the seasons?
◦ Which months of the year have the largest area of reflected short wave radiation in the Arctic regions of Canada and Siberia, Russia?
◦ Canada is heavily forested with evergreen trees, so the cause of this reflected solar radiation is not soil or desert. What might be causing this reflection of the light?
The high level of reflected solar radiation moves with the seasons. The more incoming solar radiation, the more there is to reflect. The combination of high levels of spring sunlight and highly reflective snow cover creates a time of high reflective solar radiation in April in the Northern Hemisphere. The months of the year in the Arctic with the highest level of reflected solar radiation are March, April, and May. The time in the Canadian Arctic with the highest level of reflected solar radiation are in the spring when the snow cover is still extensive and the incoming solar radiation is high. Due to its high Albedo or reflectivity, it is the snow and ice that cause the high levels of reflected solar radiation.
Step 4: Explore Additional NEO Data
Use the same procedure as in Step 1 of Part 2 to go to the NASA Earth Observations (NEO) website and display the Land Dataset, Snow Cover (MODIS) image for January 1, 2009 to February 1, 2009. Click on the Land tab under the map and select the Snow Cover (MODIS) dataset.
Note: Be sure you have selected "Snow Cover (MODIS)" and NOT the "Snow Cover & Sea Ice Extent" dataset.
- Show Me Where to Find the Snow Cover (MODIS) dates in NEO
Click on the Land tab and then select the Snow Cover (MODIS) dataset.
Examine the January 1, 2009 to February 1, 2009 image. Satellites can detect snow cover due to its high amount of reflectivity. Areas with higher snow cover are "brighter." In the NEO images, the amount of snow is given as a percentage of cover. 100% cover would mean areas with no bare patches. In areas with 50% cover, half of the ground is covered with snow while the other half is vegetation or soil, both of which are less reflective.
Look at the About this dataset window beneath the image to learn more details about what the map is showing.
Select the Intermediate level of information. Use the information in the text box to answer the following questions about the data set:
◦ Why is snow important (beyond it is fun to play in)?
◦ What percentage of light is reflected by snow vs. bare ground?
◦ What influence might this have on the Earth's energy balance?
Snow is a key source of water for the Earth. It provides water for drinking and for crops. Snow typically reflects 80% or more of the sunlight that falls onto it. Bare Earth only reflects 5-40% of the sunlight. Because it is highly reflective, snow plays an important role in the Earth's energy balance. Without snow and ice, Earth's surface temperature would be higher.
The Northern Hemisphere is the most snow covered region on Earth during the months of December to February. However, snow cover follows seasonal patterns. From June through August, snow cover in the Southern Hemisphere increases, especially in places of high elevation like the Andes Mountains. In general, winters are less harsh and there is less snow cover in the Southern Hemisphere when compared to the Northern Hemisphere. This is because the Northern Hemisphere has more of its area covered by land masses. Additionally, snow cover in the Southern Hemisphere is influenced by the moderating affect of the oceans. The largest snow cover in the Arctic regions of Canada and Siberia occurs during the months of December through February.
Land surface temperature is measured at the surface of the Earth, directly on the surface material whereas surface air temperature is measured at a height of one to two meters above the ground. Surfaces on Earth heat and cool differently. It is important to monitor them in order to predict weather and climate.
Land surface temperature warms and cools as the seasons change on Earth. As the incoming solar radiation increases in the spring and summer months, the temperature generally increases. However, the warming in the spring is delayed in snow covered areas, because the snow reflects a large percentage of the incoming solar radiation back out to space.
Before you begin, create a Snow Cover folder to hold the twelve images you will download.
Go to the NASA Earth Observations (NEO) website and download the Snow Cover (MODIS) January 1, 2009 to February 1, 2009 image at a resolution of 0.5 degrees and save it as 01_snowcover.jpg. Repeat the process for all twelve months of 2009 until you end up with a total of twelve images, named from 01_snowcover.jpg to 12_snowcover.jpg.
If you need help downloading the images, follow the same procedure as in Part 2, Step 3.
To animate the Snow Cover images using ImageJ, follow the same procedure as in Part 3 with the Reflected Shortwave Radiation images.
If you had difficulty creating or saving the stack, go to this link: Snow Cover stack (Snow.tif). To download and save the Snow Cover stack, on a PC, right-click on the link and on a Mac, control-click on the link. Then choose File > Save As... and navigate to where you want to save the stack.
Experiment with changing the speed of the animation. Step through or animate the Snow Cover images from January 2009 through December 2009. Carefully observe the changes that occur during the year and then answer the following questions:
◦ What regions of the Earth are the most snow covered each month?
◦ How does this change in relationship to the seasons?
◦ Which months of the year have the largest area of snow cover in the Arctic regions of Canada and Siberia, Russia?
Use the same procedure as in Step 1 of Part 2 to go to the NASA Earth Observations (NEO) Web site and display the Land Dataset, Land Surface Temperature (Day) (MODIS) image for January 1, 2009 to February 1, 2009. click on the Land tab under the map and select the Land Surface Temperature (Day) (MODIS) dataset. Note: Check your selection carefully as there are three other Land Surface Temperature datasets besides this one.
- Show me where to find the Land Surface Temperature (Day) (MODIS) dataset in NEO
Click on the Land tab and then select the Land Surface Temperature [Day] dataset.
Note: there are a number of data sets with similar names, make sure you select the one named exactly Land Surface Temperature [Day]
Examine the January 1, 2009 to February 1, 2009 image. Imagine a summer evening while you are walking barefoot on a warm sidewalk, sandy beach, or pool deck. That warmth that you feel in your feet, came from the Sun's rays shining on Earth during the day and warming its surface. Some surfaces hold that warmth longer than others. Can you think of a place that is always cool on a summer day? A grassy lawn would be one example. Satellites can detect the temperatures of these surfaces on the Earth. Some areas change temperatures dramatically over the course of a year.
Read the About this dataset window beneath the image to learn more details about what the map is showing.
Choose the Intermediate level, by clicking more detail. Use the information in the text box to answer the following questions about the data set:
◦ How is land surface temperature different than surface air temperature?
◦ Why do scientists monitor land surface temperature?
Before you begin, create a Land Surface Folder to hold the twelve images you download.
Go to the NASA Earth Observations (NEO) website and download the Land Surface Temperature (Day) (MODIS) January 1, 2009 to February 1, 2009 image at a resolution of 0.5 degrees and save it as 01_landsurface.jpg. Repeat the process for all twelve months of 2009 until you end up with a total of twelve images, named from 01_landsurface.jpg to 12_landsurface.jpg.
If you need help downloading the images, follow the same procedure as in Part 2, Step 3.
To animate the Land Surface images using ImageJ, follow the same procedure as in Part 3 with the Reflected Shortwave Radiation images.
If you had difficulty creating or saving the stack, then use the Land Temperature stack (Landtemp.tif) provided in the link below. To download and save the Land Temperature stack, on a PC, right-click on the link and on a Mac, control-click on the link. Then choose File > Save As... and navigate to where you want to save the stack.
Landtemp.tif (TIFF 8.9MB Jan13 10)
Experiment with changing the speed of the animation. Step through or animate the Land Surface Temperature (Day) images from January 2009 through December 2009. Carefully observe the changes that occur during the year and then answer the following questions:
◦ What regions of the Earth are the warmest each month?
◦ How does this change in relationship to the seasons?
Step 5: Analyze Relationships Between Datasets
Select the April 2009 Reflected Shortwave Radiation Map for Analysis
Go to the NASA Earth Observations (NEO) website. Click on the Energy tab under the map to display the Energy tab in the top menu. Then select the Reflected Shortwave Radiation dataset.
In the window that opens, find the "View by Date" button and select 1 month (1 mo).
Find the "Select Year" button and select 1990.
Use the slider to select April 2009.
Click the "Add to Analysis" button to add this image to the Analysis box.
You should now see one image listed in the top menu where it says "Images".
If you wish to change one or more of your selections for analysis, click on the Images button and click Remove.
Select the April 2009 Snow Cover Map for Analysis
To select another image for analysis, click on the Land button in the top menu to display the Land Datasets. Then select the Snow Cover dataset.
Use the View by Date (1 mo), Select Year (2009), and month slider to select the April 2009 image for analysis.
Click Add to Analysis to add this image to the Analysis box.
You should now have two images in the Analysis box.
Select the April 2009 Land Surface Temperature Map for Analysis
To select another image for analysis, click on the Land tab under the map to display the Land Datasets. Then select the Land Surface Temperature [Day] dataset. Note: There are a number of datasets with similar names. Make sure you select the one titled Land Surface Temperature [Day]
Select the April 2009 image for analysis.
Click "Add to Analysis" to add this image to the Analysis box.
You should now have three images in the Analysis box.
Once the three images of reflected shortwave radiation, snow cover, and land surface temperature are in the Analysis box, it becomes possible to analyze the relationship between these variables.
Click on the Analyze button on the far right of the top menu. A new Analysis window will open.
You will use the Select Area tool to select North America and Greenland. To do this you will position your cursor over the image then click and drag to draw a yellow box around all of North America and Greenland. Once you have done this, click the Launch Analysis button.
Click the Launch Analysis button. Now step through the three images by clicking on each of the thumbnails.
You will see a Warning pop-up. Click Run.
In the new window, the three images that were selected appear as thumbnails across the top. Click on each of them and as you do, observe the relationships between the three images.
- Show Me Information About the Image Composite Explorer (ICE) Tool
Click the link below to learn about ICE:
How do reflected shortwave radiation, snow cover, and temperature change as one moves north across a continent? The Plot transect button in NEO allows one to simultaneously visually and graphically explore this relationship.
While still in the Analysis window, prepare the images for analysis. In order to be able to see familiar landmarks, select the Land Surface Temperature image, and make sure that it is the one that is in view.
Click the Plot transect button.
Click and drag from South to North on the map. Experiment with different areas. Notice that as you move the cursor, a graph is generated.
Click and drag the cursor from Texas to the area in Canada just to the left (West) of Hudson Bay in Canada.
Observe the relationship between the three variables in the plotted graph. Summarize these relationships.
- Show Me
As reflected shortwave radiation increases, so does snow cover. Conversely, as reflected shortwave radiation and snow cover increase, land surface temperature drops. While there are areas where this may not be absolute, the relationship between the three is solid.
In order to emphasize the relationship between snow cover and reflected shortwave radiation are independent of latitude, plot a transect from West to East. In this case it is best to have Snow Cover as the top image.
Use the Step button to move through the images so that the Snow Cover image is in view.
Click and drag another transect, this time from West to East, in a snow covered area of Canada.
What is the relationship between the extent of Snow Cover and Reflected Shortwave Radiation?
in the second graph, comparing snow cover and reflected radiation the two lines continue to move in concert. The more snow cover, the more reflected solar radiation. Snow has a very high albedo, especially clean white snow. Snow that is dirty from dust or soot, has a lower albedo, or ability to reflect shortwave radiation, and it actually absorbs sunlight which can cause increased melting.
Scientists think of snow and ice cover similar to a mirror on the surface of the Earth. As global snow cover decreases due to global warming, it is likely that the Earth's temperatures will also increase, triggering further changes in snow cover. This is what is known as a positive feedback loop.
The consequences of decreasing snow cover include negative impacts on the both the human and animal populations of the Arctic regions. One way humans are affected is through reduced runoff from snow melt. This runoff often provides much needed water for drinking and agriculture. Furthermore, decreases in snow cover, may lead to less opportunities for winter recreation, such as skiing.
In the animal environment, the impacts are even more threatening. Decreases in snow cover negatively impact many of the animals of the Arctic including musk ox, reindeer, vole, and lemming. All of these animals have adapted to the winter habitat. The smaller animals such as lemmings and voles depend on snow to provide them with food storage locations, habitat for burrowing and critical insulation. As the population of these species declines, it can trigger a cascading impact throughout the entire delicate Arctic food web.
So while a possible decrease in severe and dangerous winter storms may be a benefit for some of the inhabitants of Northern climates, overall, the changes in the "ways of winter" will likely be negative for the Earth systems as we know them. To learn more about changes predicted for Global snow cover, read the full report on the Global Outlook for Ice and Snow from the United Nations Environment Programme.
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