Sizing up the City
Are you exploring any cities this summer? Rain or shine, urban planners use Landsat to take stock of city growth & its environmental impact.
What Landsat Sees
Do you have a favorite summer resort town? Have you noticed it change over the years? Landsat has been imaging our planet for almost fifty years and recording the growth of cities and towns around the planet.
When the first Landsat launched in 1972, Cancún, Mexico was a little-known seaside village, but it’s first hotel opened two years later and over the last five decades it has been transformed into a world-known vacation destination hosting millions of visitors each year. Today, the city’s economic success must be balanced with the environmental costs of pollution, erosion, and ecosystem decline.
The natural color Landsat images here show the massive growth of Cancún between 1985 (left) and 2019 (right). Use the slider to see the bright white area of paved city expand into the tropical forests west of Cancún’s lagoon.
Hotels line the shoreline of Cancún, Mexico. Photo credit: Michelle Raponi from Pixabay
Islands in Our Midst
Have you ever heard of an Urban Heat Island? In the summertime, city dwellers often dream of escaping from the hot city—their Urban Heat Island—to an actual island.
This summer a humid heatwave hit Tokyo as the 2021 Summer Olympics began, with temperatures over 90ºF. Global warming has made heatwaves in Japan’s capital more frequent. And the city’s urban growth has contributed to rising temperatures as paved and built regions absorb sunshine and reradiate heat, creating an Urban Heat Island.
The image on the right is derived from TIRS, the thermal instrument on Landsat 8. It shows land surface temperatures throughout Tokyo in August 2019. The image on the left is a natural color image of the city created with Landsat 8’s Operational Land Imager (OLI) sensor. Landsat 9 will carry two similar instruments, OLI-2 and TIRS-2.
Areas covered with vegetation and water typically stay much cooler, and Tokyo’s green spaces are noticeably less hot. Fortunately, the Olympic Village is on the harbor and stays a little cooler with help from sea breezes.
Land Surface Temperatures of Tokyo in August 2019. Image credit: NASA Earth Observatory
Urban Runoff
Have you ever watched stormwater rush down a street gutter during a summer thunderstorm? That flow of draining water gets faster and deeper when rain can’t soak into the ground.
Paved highways, streets, parking lots, sidewalks, and rooftops are all considered impervious surfaces because water cannot typically soak through them. When cities grow, so does the amount of impervious surface area. This has big implications for stormwater runoff, as well as city temperatures.
Landsat satellites can reliably map the amount of impervious land cover in urban areas. In the Landsat-derived map shown here, the dark blue areas show where impervious surfaces are located in the Washington, D.C. metropolitan area (2010). Using Landsat’s long archive, urban planners can calculate the expansion of impervious surfaces and better prepare for the increased water runoff that comes with it.
As the amount of impervious surfaces increase, so does the amount of water runoff during storms. Source: Green Infrastructure Guidance for Flood Reduction
City From Above
This false-color image of Dallas, Texas was one of the earliest images collected by Landsat 1. The image was acquired on July 25, 1972, just two days after launch, by the Multispectral Scanner System (MSS) aboard the satellite (originally known as the Earth Resources Technology Satellite). Red shades on this image indicate vegetation, brown areas are bare ground, and silvery shades are urban areas.
The MSS was an experimental, secondary instrument aboard Landsat 1. The primary instrument was a television-style camera system called a Return Beam Vidicon, or RBV. But an early electrical malfunction caused the RBV to be shut off for the life of the mission, but not before it was outshone by the MSS which used new fiber-optic technology, recorded energy from four different spectral bands, and relayed that information digitally back to Earth.
The MSS had many naysayers, but once the data got to the ground, it was clear that the MSS was a superior instrument. Virginia Norwood, the Hughes engineer who conceptualized and led the build of the instrument, was not surprised: “I never had doubts about the MSS, because I designed it and knew it would work.”
01 / 05
Postcards from Camp Landsat
Whatever you do for summer fun, wherever you go to relax, Landsat is there. Landsat data helps people manage, protect, and preserve some of your favorite places on Earth.
Collect all nine postcards from Camp Landsat continuing with Week 5: Cities & Suburbs !
The adventure continues at Camp Landsat with lots of fun and fascinating Landsat facts and activities.
