Tokyo is the world’s largest metropolitan region, home to nearly 37 million people. During the past two decades, Tokyo’s population has grown by more than 7 million. The city’s growth has continued despite Japan’s overall stagnating population, mainly due to a continued trend of centralization—citizens moving out of the country and into the city.

Landsat 4 collected this first false-color image of Tokyo on Feb. 2, 1989. The upper half of Tokyo Bay is the large water body visible in a dark blue. In the middle of the image, central Tokyo appears a deep purple just north of the bay. Twenty-two years later, Landsat 5, captured this second image of Tokyo on April 5, 2011. The urban reaches of metropolitan Tokyo have grown in both distance and density, as seen where the green color of vegetation has turned to pink and purple shades of urbanization. A major expansion of Tokyo’s Haneda Airport, can be seen south of the city, on land built out into the bay. The constant circular spot of green in the dense city-center, visible on both images, is the Tokyo Imperial Palace and its gardens. (Landsat 5 TM Bands 7,4,2)

NASA and the U.S. Department of the Interior through the U.S. Geological Survey (USGS) jointly manage Landsat, and the USGS preserves a 40-year archive of Landsat images that is freely available over the Internet. The next Landsat satellite, now known as the Landsat Data Continuity Mission (LDCM) and later to be called Landsat 8, is scheduled for launch in 2013.

In honor of Landsat’s 40th anniversary in July 2012, the USGS released the LandsatLook viewer – a quick, simple way to go forward and backward in time, pulling images of anywhere in the world out of the Landsat archive.

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