Los Angeles

NASA/JPL/NIMA. "AmericaSRTM-NorthLosAngeles-picasa.jpg" Online Image. Shuttle Radar Topography Mission. 20 Jan. 2006 143kb. 886x375px. <http://photojournal.jpl.nasa.gov/jpegMod/PIA03376_modest.jpg>

Los Angeles

This image shows a perspective view created by draping a Landsat image over the elevation framework from an SRTM data set for the city of Los Angeles. It was created from an original map produced from data obtained by NASA's Shuttle Radar Topography Mission (SRTM). Using Google's free Picasa2 program, the color, contrast, and lighting were enhanced. It was then sharpened to obtain the image above. The original image can be viewed at the NASA link above.

Los Angeles, Calif., is one of the world's largest metropolitan areas with a population of about 15 million people. The urban areas mostly cover the coastal plains and lie within the inland valleys. The intervening and adjacent mountains are generally too rugged for much urban development. This in large part because the mountains are "young", meaning they are still building (and eroding) in this seismically active (earthquake prone) region. Earthquake faults commonly lie between the mountains and the lowlands. The San Andreas fault, the largest fault in California, likewise divides the very rugged San Gabriel Mountains from the low-relief Mojave Desert, thus forming a straight topographic boundary between the top center and lower right corner of the image. We present two versions of this perspective image from NASA's Shuttle Radar Topography Mission (SRTM): one with and one without a graphic overlay that maps faults that have been active in Late Quaternary times (white lines). The fault database was provided by the U.S. Geological Survey.

The Landsat image used here was acquired on May 4, 2001, about seven weeks before the summer solstice, so natural terrain shading is not particularly strong. It is also not especially apparent given a view direction (northwest) nearly parallel to the sun illumination (shadows generally fall on the backsides of mountains). Consequently, topographic shading derived from the SRTM elevation model was added to the Landsat image, with a false sun illumination from the left (southwest). This synthetic shading enhances the appearance of the topography. Landsat has been providing visible and infrared views of the Earth since 1972. SRTM elevation data matches the 30-meter (98-foot) resolution of most Landsat images and substantially helps in analyzing the large and growing Landsat image archive. This Landsat 7 Thematic Mapper image was provided to the SRTM project by the United States Geological Survey, Earth Resources Observation Systems (EROS) Data Center, Sioux Falls, S.D.

Size: View width 134 kilometers (83 miles); view distance 150 kilometers (93 miles)
Location: 34.3 degrees North latitude, 118.4 degrees West longitude
Orientation: View west-northwest, 1.8 X vertical exaggeration
Image Data: Landsat Bands 3, 2+4, 1 as red, green, blue, respectively
Original Data Resolution: SRTM 1 arcsecond (30 meters or 98 feet), Landsat 30 meters (98 feet)
Graphic Data: earthquake faults active in Late Quaternary times
Date Acquired: February 2000 (SRTM), May 4, 2001 (Landsat).

NASA/JPL/NIMA. Shuttle Radar Topography Mission. 20 Jan. 2006 <http://photojournal.jpl.nasa.gov/jpegMod/PIA03376_modest.jpg>