Satellite Product Comparisons
Next, you’ll learn to use satellite imagery and products to analyse cloud heights and thicknesses, and compare land and ocean features. But first, let’s make sure that you know which products to use for different situations. Note: From here on out, we’ll refer to images and products simply as “products.”
Here, you will view all products for a different case and answer a series of questions. You can select pairs of products to view and compare - notice which features you can and cannot see on each product. Then, scroll below the product area and answer the questions. Use the “Arrow” buttons to move between questions. After you have finished all of the questions, use the “Next” button to proceed to the next section.
Instructions: Select a product for each set of radio buttons. The first product will display, with a slider over it. Move the slider to see the second image. To change one or both images, select a different product for each radio button.
Question 1 of 8
Why does the visible image (natural colour RGB) only show data on the right side of the image?
The correct answer is c.
The visible sensor only senses within the visible portion of the spectrum. At night, it does not receive enough radiation return to produce a useful image.
Please make a selection.
Question 2 of 8
Which of the following RGBs use the visible channel and thus are not available at night? Compare the visible image with the RGBs to figure this out.
The correct answers are b, d.
Since the severe convection and natural colour RGBs are partly made from the visible channel, they are not useful at night.
Please make a selection.
Question 3 of 8
Which other products let you identify the low clouds/fog on and south of the coasts of Côte d’Ivoire, Ghana, Togo, and Benin? (If you’re unfamiliar with this area, consult a map.) Use the night microphysics RGB to find the area, then compare it to the other products.
The correct answers are b, d.
While the night microphysics RGB is the ideal product to use, if you were without it, you would want to use channels that have helped make up the night microphysics product: infrared imagery or products made predominantly from these channels.
Please make a selection.
Question 4 of 8
Select the severe convection RGB and find the most active convection. Then compare the RGB to the visible, infrared, and water vapour images. Which channel does the best job of highlighting the most active convection?
The correct answer is c.
Water vapour imagery sees the mid- to upper-troposphere. Typically, the upper levels of the troposphere are relatively dry, so any convection breaking into this layer contains much higher amounts of water vapor and will contrast dramatically with the other features. This makes WV imagery useful for identifying the cold cloud-tops associated with severe convection. In fact, the WV channel (and differences of it) is so useful for detecting severe convection that it’s used in the severe convection RGB.
IR imagery can be just as useful for identifying severe convection when it’s enhanced to highlight the colder cloud tops.
Overall, it’s best to use the severe convection RGB for this type of analysis. But if you need a backup or it’s nighttime, use WV or enhanced IR imagery.
Please make a selection.
Question 5 of 8
View the dust RGB. Pink tones indicate dust in north-central Niger, northern Chad, Eritrea/Djibouti/Yemen/the Red Sea, and northern Namibia. But two of these areas are not actually dust. Which products can help you verify this? (Compare these products to the dust RGB to figure this out.)
The correct answers are a, f.
If you compare the visible and natural colour products with the dust RGB, you’ll see that the “dust” area in northern Namibia is actually a dry lake bed, and the area in northern Chad is the Tibesti Mountains. These have been highlighted on the image below in bright green.
Both areas show up in dust RGB imagery because of the transition from nocturnal cooling to diurnal heating. As the day goes on, it becomes clearer that they are not dust.
Please make a selection.
Question 6 of 8
During the day, which features can only be identified with the natural colour RGB? (View this RGB and compare it with the other products to figure this out.)
The correct answers are b, c, e.
Only the natural colour RGB can clearly show grasslands/forests, flooded areas, and ice clouds. You can see this by comparing Lake Victoria, the grasslands/forests north of it, and any of the cyan-coloured clouds on the natural colour RGB with the other imagery.
Please make a selection.
Question 7 of 8
Using visible imagery over Ethiopia, the cloud mass there is uniform in color and it is difficult to pick out details of the cloud tops and relative cloud heights. This is caused by the sun angle. Now view the products listed below, and identify those that can be used to differentiate the heights of these clouds over Ethiopia.
The correct answers are a, b, c, d, e, and f.
These six products are made from infrared channels (including water vapour, which is in the infrared range) or channel differences (partly or in whole), which provide information about cloud top temperature and thus, cloud height. Even though the night microphysics RGB is calibrated for night-time use, it is still capable of seeing cloud height differences during the daytime hours, just not as easily at low-levels like it can at night.
Please make a selection.
Question 8 of 8
Which of these four products lets you see the relative cloud levels most distinctly?
The correct answer is a.
In general, the IR channel does a better job of differentiating cloud-top heights, and this is especially useful when low-level clouds are present.
The severe convection RGB can be useful for differentiating cloud-top heights with rapidly changing brightness temperatures, but the severe convection RGB cannot see low-level clouds well.
If the image in question were taken overnight, the infrared and dust RGB would be the only useful products from the list. The night microphysics RGB (not listed above) would be the most useful for comparisons if this image was taken overnight.
Please make a selection.
Be sure that you have answered all of the questions before proceeding to the next section where we will talk more specifically about how to differentiate cloud heights and thicknesses, dust, and land cover vs. water features.