Sacramento Glows With Urban Heat

July 01, 1998

California's capital city glows in its own summer heat in this false-color infrared image taken as part of the interagency Urban Heat Island Pilot Project (UHIPP). Sacramento is the second of three cities being surveyed in UHIPP. Baton Rouge, Louisiana, was the first city to be studied in May and the third city to be studied, Salt Lake City, Utah, is scheduled for mid-July.

In this "quick look" image - which has not been calibrated or corrected - white and red are hot, and blue and green are cool. North is up. The hottest spots are buildings, seen as white rectangles of various sizes, and a railyard (orange) to the top right (east) of the Sacramento River flowing from top to bottom (the American River cuts across the top right corner). The state capital is the red spot in the green rectangle to the right center of the river. A significant number of cool areas are present, including the American River Parkway at top right. Interstate 5, running north to south along the East Side of the Sacramento River, and US 50, from left to bottom right are also visible.

The image was taken Monday, June 29, at 1 p.m. local time by the ATLAS imager aboard a NASA Lear 23 jet equipped with various sensors and cameras for UHIPP.

From surface temperature estimates, the white areas are about 60 degrees C (140 degrees F), said Dr. Jeff Luvall, the principal investigator at NASA's Marshall Space Flight Center. Dark areas (vegetation) are approximately 29 to 36 degrees C (85-96 degrees F). Since the image has not been calibrated, absolute temperatures will change after calibration, but the relative temperature differences between surface types will not.

Atmospheric profiles of temperature, relative humdity, and pressure were measured with a balloonborne instument package called a radiosonde to calibrate the ATLAS measured surface temperatures. Additional roof surface temperatures were taken with a handheld "heat spy," an infrared themometer to help calibrate the ATLAS thermal measurements. Scattered around the city on three rooftops were instruments which measured the visibility or transmissivity of the atmosphere to aid in the calibration of the visible data.

The image clearly demonstrates the principle behind UHIPP, that the differences in cooling and heating between the natural and manmade surfaces can affect city temperatures.

"Urban forests are important to keeping cities cool," Luvall said. "What's important are both the extent and arrangement of these forests."

Luvall said that it is important to note that this is a quick-look image that has not be corrected for atmospheric interference or fully calibrated with ground sensor data.

In addition to ATLAS and the "heat spy" instruments on the ground, the study uses images from a 23x23 cm (9x9 in) film camera aboard the Lear 23 and sensors aboard weather satellites.

The Global Hydrology and Climate Center (GHCC) in Huntsville, Ala., working with the U.S. Environmental Protection Agency and several local governments, is conducting UHIPP. The GHCC is a joint venture by NASA/Marshall, the Universities Space Research Association, and the Space Science and Technology Alliance of the State of Alabama. UHIPP follows the successful Urban Heat Island Experiment in Atlanta in May 1998.

NASA/Marshall Space Flight Center--Space Sciences Laboratory

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