## A "GETTING ACQUAINTED" ACTIVITY

As announced on the previous Overview page, there will several tests ("exams") later on in the Tutorial to test your knowledge of information learned and skills mastered up to that time. But first, we ask you now to engage in a simple "exam" which we euphemistically call an "activity" designed just to help you ascertain what you already know through experience or common sense (intuition) about recognizing features in space imagery of several kinds and then analyzing or interpreting them based your knowledge of the everyday world.

The approach will be straightforward: We will concentrate on one region in North America and will show you a wide variety of imagery. You will be given a series of questions pertaining to these. Some you should be able to answer right off; others you may be unsure of or just don't know. But like you saw in the Overview page, there will be answers to every one that you can click to and in so doing learn by default. So here goes:

We begin by showing you a low resolution of the part of North America that contains the region to be studied. This scene was acquired by OrbView2, a satellite operated by the Orbital Imaging Corp.

Ex-1: Where are you" Name at least 4 states that are in the scene. There is a lake that you have seen before in the Overview. Name it. Take a wild guess as to why its upper half is purple.ANSWER

Now that you are oriented geographically, the next image zeroes in on the State that contains the region in that state we will concentrate on. The scene was taken by the MODIS sensor on the Terra Satellite (see Section 16).

Ex-2: What is the State. Consult an Atlas, if need be, and see what major geographic features you can name.ANSWER

Now we will focus on the more immediate region to be studied. This is a Landsat-7 natural color Thematic Mapper (TM) image:

The image below is also a TM image of this scene but was taken at a different time of the year.

Ex-3: Locate what appear to be major metropolitan areas. What colors define these? What is the body of water that lies inland from the ocean? Why are there different bluish tones in the ocean and brownish in the inland extension? What is likely to be causing the dense green areas in parts of the images? In the upper right of both is an area that you have already encountered as the Great Valley. What are the square to rectangular patterns seen in this Valley? Why are many of these patterns brown in the upper and green in the lower image?ANSWER

Although natural color imagery ties us closer to the way the Earth appears if we were in an aircraft of spacecraft, a very common color rendition (already seen for the Salt Lake City image) often has red as the dominant color. Consider this Landsat 1 image of the Bay Area in west central (the locals call it Northern) California.

Ex-4: Unless you have had previous experience with this type of rendition, known as false color, the reason for the red is probably not in your knowledge bank. Take a guess as to why. Why is the ocean black? What color dominates the cities? There are several mountain chains in the image. One is dominated by red because of forestation. Another shows much fewer trees. How do you recognize this chain? Finally, the natural color Landsat full scene has a resolution of 30 m and this false color scene has a 79 m resolution; why do the details (sharpness of features) appear about the same in spite of the resolution differences? ANSWER

Staying with the false color theme for a moment, this next image is made from the SPOT satellite (see Section 3), which has a 20 meter resolution.

Ex-5: Somewhat more detail is seen in San Francisco in this SPOT scene. Compared with the previous Landsat scenes, at 30 and 79 meter resolution, this scene helps one to locate a particular feature associated with roads. Try to find it.ANSWER

The next pair of subscenes are further enlargements of a Landsat 7 image. Examine them, and with the help of your atlas, answer the question below them.

Ex-6: Find Mount Diablo in the upper scene. Two areas east of the East Bay Coast Range are marked by a concentration of patterns typical of urban areas. They lie along U.S. Highway 50. Identify them.The writer (NMS) worked in the town further east at the Lawrence Radiation Laboratory. When I did, neither town was anywhere close to their present size. In the upper image, make a guess as to what are the patterns of green and brown in the lower San Francisco Bay north of San Jose. About what time of year was this image acquired; give reasoning. In the lower image, why are the two S.F. bridges now visible, even though this is 30 m resolution imagery.ANSWER

Here is a photograph taken by an astronaut from the Space Shuttle as he looked down at the northern part of San Francisco.

Ex-7: Comment on the details evident in this photograph. Make a guess about the scene resolution.ANSWER

Below is a medium scale aerial photograph (taken from a plane a few miles up; resolution is a few meters). Try to find out where it fits in the astronaut photo (answer below in Ex-8).

This next remarkable image has very high resolution (1+ meter) even though taken at an orbital altitude of more than 400 miles by the IKONOS satellite (Space Imaging Corp.). Note some of the individual buildings.

To help you locate this scene, consider this ground photo of the east side of San Francisco, taken from the Coit Tower in northeast S.F.

Ex-8: What part of San Francisco is shown on the right side of the aerial photo? Try to fit the IKONOS image into this photo. There is a prominent building in the IKONOS image and in the ground view that is absent in the aerial photo. Find it - perhaps you know its name. What does this tell you about the "age" of the aerial photo? In the IKONOS image the buildings seem to be leaning somewhat. What does that mean in terms of the conditions in which the IKONOS satellite was "looking" at its target?ANSWER

The imagery and photos we've seen up to now has been constructed from electromagnetic radiation within the visible light range and in several instances includes radiation from the Near Infrared. Radiation at other wavelengths can be sensed and used to form images. These parts of the spectrum include Ultraviolet, Thermal Infrared, Passive Microwave, and Active Microwave (Radar). You may not be familiar with what these images look like but the next few such images will then introduce you to their appearance. Take, for example, this one, which was made during the daytime by a sensor mounted on an aircraft:

At the other extreme, look at this image made by the HCMM satellite at nighttime that covers much of west-central California. Before reading the next question, make a guess at what type of image (in terms of the four listed in the previous paragraph) these two belong to (afterwards, go to Section 9 for a full review of this mode of remote sensing).

Ex-9: This is a "giveaway" as to identifying the type of image: Light tones indicate relative "warm" and dark tones denote relative "cold". In the daytime thermal image, try to match several of the very dark patterns to specific features (again, use an atlas to help pick out known localities). Why is much of the City in light tones? In the lower image, first find the San Francisco Bay. Why is the Bay water lighter in tone than the surrounding land? What are the wispish lighter tones in the Pacific Ocean? What is the very dark area in the upper right? How does the central part of the Great (Sacramento) Valley appear? Account for the bright tones along the sides of the Valley?ANSWER

Now to the last images we will consider (later, see Section 8). Look at both of these and then respond to the question.

Ex-10: What type of image are these two? How do the mountains appear in the left scene? (This is usually a "trademark" of this class of image.) In that scene, what do at least some of the very bright patches correspond to? Given that images produced by this sensor type can be multiband (several wavelengths) and multipolarized, speculate on how the right image is displayed in color.ANSWER

There is one very common surface feature that is not well expressed in northern California space imagery because of the ubiquitous grass and tree cover. That is a revealing display of the underlying geology. Usually, geologic rock units are most likely to be exposed and directly visible in arid to semi-arid terrain, as is common in much of the desert areas of the U.S. West. This is treated in detail in Section 2. For now, we just want you to see (without questions) how strongly exposed geologic units look from a Landsat image. We have extracted two scenes from Section 2. The first shows a part of the Waterpocket Monoclinal Fold (strata inclined in one direction) as seen from the air. The second is a Landsat false color composite of much the same area as in the picture. See if you can match several units in the photograph with their equivalent in the image.

Well, there you have it. How did you do with the 10 questions? Even if you had some difficulties in getting at the right (best) answers, simply by trying and then checking out the answers you will have picked up many of the basic ideas and principles underlying remote sensing and image interpretation. You are thus in good shape for entering the remainder of the Tutorial, starting next with the Introduction.