Lela Prashad, CEO and Co-Founder of NiJeL, a data science company focused on environmental and social sustainability; former director (2006-2011) of the 100 Cities Project at Arizona State University’s School of Earth and Space Exploration
Research interests: Connecting satellite remote sensing data with ground-based monitors to build a more complete picture of urban environments and how people locally experience these environments.
Research highlights: The end of June and beginning of July in New York City this past summer were sizzling, with temperatures in Central Park soaring into the 90s four straight days. Meanwhile, the temperature in Islip, NY, 53 miles away on Long Island, reached the 90s only one time during this same period. While Islip’s location closer to the Atlantic Ocean likely helped mitigate the high temperatures experienced in New York City, another factor in Islip’s favor may have been that it lacks the extremely high density of people and pavement found in The Big Apple.
Temperature data measured by instruments aboard Earth observing satellites and at ground level show that urban areas tend to have higher average temperatures than the more rural areas around them. These warmer urban areas are called “urban heat islands.” When temperature data are combined with socioeconomic data (such as census data), population clusters that may be affected by higher urban temperatures are easy to identify.
The ability to combine remotely sensed satellite data with socioeconomic and other demographic data is a powerful tool for exploring the impact humans have on Earth. This combination of satellite and ground-based data also is key component of Lela Prashad’s research into how people live in and experience urban environments.
Much of Prashad’s research centers on exploring the impact of urban heat islands. The increased heat seen in urban areas is caused by numerous factors, including high amounts of concrete and asphalt (which retain and slowly dissipate heat) and higher concentrations of vehicles with internal combustion engines (which produce greenhouse gasses that trap heat). According to the U.S. Environmental Protection Agency, impacts of urban heat islands include:
- Increased energy consumption;
- Elevated emissions of air pollutants and greenhouse gases;
- Compromised human health and comfort; and
- Impaired water quality
As Prashad notes, NASA data are the foundation for her work on cities and provide numerous advantages in her studies. Satellite data and imagery allow her to study a complete region at multiple scales and resolutions, provide repeatable coverage at known times, and enable her to acquire data across political boundaries.
An important satellite data source for Prashad is the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). ASTER is one of five instruments aboard the Terra Earth observing satellite (launched in 1999), and is a partnership between NASA, Japan’s Ministry of Economy, Trade and Industry, the National Institute of Advanced Industrial Science and Technology in Japan, and Japan Space Systems (J-spacesystems). ASTER collects data in 14 different wavelengths (ranging from visible to thermal infrared) that are used to create detailed maps of land surface temperature, emissivity (a measure of the ability of an object to radiate energy), reflectance (a measure of how well a surface is able to reflect light or other radiation striking the surface), and elevation. Prashad supplements ASTER data with data from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard the Terra and Aqua satellites (primarily land surface temperature and emissivity products) along with imagery from the joint NASA/U.S. Geological Survey (USGS) Landsat series of satellites.
