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Assuming that you have read the preceding Introduction to remote sensing, you should be ready to work with the basics that image interpreters apply to examining and analyzing an image . In this section we concentrate on analyzing a single Landsat image. Because this is a major learning experience for most readers, we scrutinize this image and its derivatives more intensely than most of the others in later Sections. We demonstrate and evaluate several of the routine analysis techniques used in computer processing of satellite remote sensing data (see end of page 1-16 for a brief list of books on the principles of image processing). For this subscene, Idrisi is the processing software we used to generate all image products.

TM Band 3 of Morro Bay, California

The chosen subscene lies along the central California coast about half way between San Francisco and Los Angeles, in the county of San Luis Obispo. We extracted this subscene from Landsat 5 Thematic Mapper scene 5026-31810 (Path 043; Row 035) acquired on November 19, 1984. The actual data set is part of the Education sampler offered to users by the Earth Observation Satellite (Eosat) Corp., 4300 Forbes Blvd., Lanham, Maryland 20706 (the company has now merged and is known as SpaceImaging-Eosat).To acquaint yourself with this scene, look at the black and white TM Band 3 image which you can enlarge to its full size by clicking on it .

B/W TM Band 3 image of Morro Bay, California.

TM Band 3

1-1: Locate Morro Bay on the California map in a U.S. Atlas. Familiarize yourself with the area that includes the subscene and with the surrounding region (up to about 162 km [100 miles]). ANSWER

The data display consists of a 512 x 512 pixel array (because each pixel represents 30 m [98ft] each side of the image is just over 16 kilometers [10 miles] long). Below is a histogram giving a frequency distribution of the brightness values in Band 3.

1-2: Analyze this histogram. What do its peaks represent? If the DNs shown along the abscissa were the ones used to produce a black and white image, what would it look like? ANSWER


Histogram of the TM Band 3 image shown above.


The largest town in the image is Morro Bay, a resort community of about 10,000 permanent residents, some of whom are still actively involved in commercial fishing. The town is located about 21 km (13 miles) NW of the city of San Luis Obispo, along the conspicuous road evident in the scene (the famed coastal Highway 1 which wanders along much of the California coastline but in this scene extends inland to the east). The second major road, California Highway 41, is visible as it passes through a valley between hills enroute to Atascadero 27.5 km (17 miles) to the NE of Morro Bay. Cayucos is a small residential town along the coast just north of Morro Bay. Near the bottom of the image is another large settlement, the town of Los Osos (and its northern neighbor, Baywood Park), which is popular now as a retirement community, especially the areas along hillsides with commanding views of the ocean.

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Primary Author: Nicholas M. Short, Sr. email:

Collaborators: Code 935 NASA GSFC, GST, USAF Academy
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