History of Remote Sensing: A Landsat Image - Lecture Material - Completely GPS, GIS dan Remote Sensing tutorial - facegis.com
History of Remote Sensing: A Landsat Image

The picture below is a Landsat full image, from October 1972, shown both as individual bands and as a false color composite. We display below a succession of MSS bands 4 through 7 (bands 1-3 were assigned to the RBV), comprising images of a very well known region in the eastern U.S. Beneath these four images, is a false color composite, made from bands 4, 5, and 7, of this scene, here extended southward to include the southern tip of a peninsula that includes the town of Cape May (a clue).

Note 1: By convention, Landsat and most other satellite system images are normally oriented with North towards the top. However, because of the ninety-nine degree orbital inclination, the north direction is not vertical but is a few degrees inclined relative to the perpendicular to the top and bottom margins of the printed image.

Note 2: The lettering at the bottom of each image (probably not readable on your screen) is the standard annotation placed on Landsat images produced at NASA, EROS, and most commercial facilities. The information recorded, from left to right, includes the calendar date of acquisition, the latitude-longitude coordinates of the scene principal and nadir points, the sensor type, the elevation and azimuth positions of the Sun, and the Scene (Frame) identification number (I.D.) starting with the particular Landsat (1 through 5) and ending with the specific band (or band combination if in color).

Before you look at the second paragraph beneath this image set, we challenge you to try to identify what geographic area is shown here.

Landsat MSS October 10, 1972
Landsat image of New Jersey and New York City (October 10, 1972) - MSS Band 4

MSS Band 4

Landsat image of New Jersey and New York City (October 10, 1972) - MSS Band 5

MSS Band 5

Landsat image of New Jersey and New York City (October 10, 1972) - MSS Band 6

MSS Band 6

Landsat image of New Jersey and New York City (October 10, 1972) - MSS Band 7

MSS Band 7

These bands plus a small part of the next image to the south joined (mosaicked) to them can be combined to make a standard false color composite using the three Band combinations as shown below the image:

False Color composite made from bands 4 (blue), 5 (green) and 7 (red) above, for the October 10 New York/New Jersey scene plus an extension down to Cape May, NJ

MSS Band 4 = Blue

MSS Band 5 = Green

MSS Band 7 = Red

If you correctly identified the scene, then in the individual bands, you saw much of New Jersey along with New York City and the west end of Long Island in the upper right corner and Philadelphia at just left of the image center. The color composite extends the coverage to the northern Delmarva Peninsula, flanked by the northern Chesapeake Bay (bottom left) and Delaware Bay (bottom center) and Cape May (bottom right). These two urban regions, along New Jersey cities along the Hudson River, appear in light to medium gray-blue tones in Band 5 (red). In Band 7 (IR), the central areas of these metropolitan complexes are in dark tones, owing largely to the prevalence of asphalt streets and dark (usually asphalt) roofs, together with few trees and little other vegetation. In Bands 6 and 7, the urban scene contrasts with the lighter tones associated with high reflectance vegetation in the countryside. Water is dark in Bands 6 and 7 but lighter in Bands 4 and 5, in part because of silt and other sediments (more reflective). In contrast, among the brightest features in both individual-band and color composite scenes are the sandy beaches and soils comprising the ocean side of the barrier islands lining the New Jersey coast.

Vegetation in this October 10, 1972 scene is still actively growing (mostly green in natural color, but some trees are beginning to get their autumn colors), so its spectral distribution indicates an overall brightness in the Band 6 and 7 images. We can compare the dark tones of the fold belt ridges in the upper left in Band 5 with their corresponding light tones (from high reflectances related to tree leaves; this ridges are heavily forested) in Band 7. Surfaces dominated by vegetation are shown in several shades of red in the false color composite. Harvested (fallow) fields appear in blue tones, similar to those characterizing the cities. The large, darker area in New Jersey east of Philadelphia is the Pine Barrens, marked by evergreens that grow well in the sandy soils (Note the appearance of these trees in each of the four bands; in color, they are reddish brown; evergreens are bright but not as much as deciduous trees).

I-21: Try your hand at picking out other major landmarks in the scene (use an atlas for help in recognizing their locations). ANSWER

I-22: Although it may be a "pain" scrolling up and down repeatedly, we suggest you pick out various features in each of the four MSS band images and note how they appear, in terms of gray levels (and shapes) in each band; in other words, compare. Also, describe the overall appearance of each band relative to the others. Do this mentally, or write it down if you wish. This is a worthwhile task, as it will give you a "feel" for the general nature of each of the four bands that represent the continuum of spectral intervals from 0.4 to 1.1 µm. ANSWER

As a preview of change detection, compare the October 1972, Band 7 image above with the one below, which was taken on April 18, 1978. Because it's a time in the Spring in which trees and other vegetation in the eastern U.S. have not yet leafed out there are especially dark ridges whose tones result from low rock and soil reflectances that dominate the radiances because of the absence of leaves). This seasonal effect results in a reduction in brightness over much of the areas in the lowlands where the fields remain fallow prior to emergence of growing vegetation. Many of the brighter areas in this April image do correlate with some field crops that were planted earlier; small bright patches in the Pine Barrens are sand pits - highly reflective in all bands.

Landsat image of New Jersey and New York City (April 18, 1978) - MSS Band 7

The reader may have noticed that in the two black and white Landsat-1 images near the top of this page there is a gray bar and some annotation on the bottom. This is a common format used in most renditions of early Landsat images and in some more recent versions. (Throughout the Tutorial this information is usually cropped off to reduce image size; it is almost unreadable on Internet pages anyway). We show another image (North Africa) here which contains all normally peripheral information included in photo prints of Landsat imagery:

A full-sized Landsat-1 image containing gray bars (top & bottom) and annotation; the region shown is in North Africa and shows large igneous plutons (dark).

The annotation contains valuable information. Here is an enlargement of the annotation in the above image:

Annotation and gray bar extracted from the African image.

The first writing on the very left of the annotation row is the date of scene acquisition. This is followed by two groups of letters/numbers that define: a. the latitude-longitude coordinates of the principal point (format center), then b. latitude-longitude coordinates of scene nadir point (nadir refers to a line from the platform vertical to the ground). Next to the right is the identification of sensor (MSS) and Band (7). Then comes the elevation of the Sun (angle above horizon) and the Sun's location (azimuth defining Sun's position above the horizon geographically relative to true North), both at the time of scene acquisition. The next string of alphanumerics contains specialized information including spacecraft heading (189°), then (G), location of the receiving station (here, Goldstone in California), followed by I-N-D-IL for I = full size, N = normal processing, D = definitive accuracy for image center, 1L = 1 for linear mode for spacecraft data transmission (2 would be compressed mode), and L for low gain (H would be high gain) signal amplification level. NASA ERTS signifies that this product was made by NASA's ERTS (Landsat) satellite. The farthest right alphanumerics, E-1106-09183-7 specifies ERTS (E) followed by the mission number (1 for ERTS-1), plus 106 for the number of days after launch, -09183, the hour (09), minute (18), and second (7), all local time of observation (for scene center). The last, 01, is known as the regeneration number. Below the gray bar are three numbers that mark the longitudes (here E = east of Greenich, London) in degrees and minutes as these intersect the bottom of the image frame; these numbers appear at the top again, shifted left because of the orbital inclination.

In ordering Landsat imagery, information in the annotation can be helpful. There is another aid that users often use instead. For the Landsat program, the Worldwide Reference System (WRS) was established. This is a grid with near up and down lines called the Path trace and horizontal lines the Row coordinates. We show this map of the coordinate system, realizing that on the Internet, the numbers and words appear too small to be readable:

The master map for the WRS-2 coordinates.

Look at a small part of the Path-Row system that crosses this map:

Path-Row coordinates for a Landsat scene in Ohio.

For Landsats 1-3, there are 251 Paths (001 to 251), the same number of orbits needed by these spacecraft to image the Earth in one 18-day cycle. There are 120 Rows, with 1 starting near the North Pole (80°47'), 60 coinciding with the Equator, and 120 in high south polar latitude. Path 001 is set at an equatorial crossing point of 64°36'

WRS-1 refers to the coordinate set used for the first three Landsat. WRS-2 denotes use by Landsats 4, 5, and 7. Because of the lower orbital altitude, this map contains 233 Paths. When the above Ohio scene is ordered, its location can be specified as Path = 19, Row = 31. Then a time-of-year date is selected, and, usually, a limit (in percent) of cloud cover (anything below that is acceptable).

Source: http://rst.gsfc.nasa.gov