Professor at the University of Portland (Oregon), specialist in the adaptation of cities to climate change, Vivek Shandas founded a research laboratory on sustainable urban areas (Sustaining Urban Places Research lab). His team drew temperature maps in 24 cities in the United States and around the world. Until then, studies of urban heat islands relied on data obtained by stations of public institutions or satellites. The researcher was the first to collect data using mobile sensors deployed by “citizen scientists”.
You have developed a so-called “transverse mobile” approach to measuring heat. What is it about ?
I would first like to recall how we measure temperatures. It’s less immediate than it sounds. When it comes to large areas, such as cities, there are three methods available. The first is to set up a measuring station somewhere. This is what the cities do. Usually they have three to five such places in operation. These are very good measurements over time, but not enough to get a sense of the variations between neighborhoods.
The second method, which has existed for twenty-five years, is the satellite. The sun sends out energy-rich shortwave radiation. The surface absorbs it and eventually returns heat to the environment through long-wave radiation, which is captured by satellite sensors. You can see certain elements: the parks, the difference between the asphalt and the roofs of buildings. The problem is, the pixels are very large: squares of 90 meters by 90 meters, or 1 kilometer, or 5 kilometers. It does not represent what an individual feels when walking.
The transversal mobile approach makes it possible to collect a lot of data. On a very hot day for example, like the end of June in Portland, we take measurements while moving; we do not remain static like the official stations. This allows you to see how building geometry or construction differences affect temperature. You can also measure humidity, which is not the case with satellites.
How does it work?
We have very precise temperature sensors. We designed them ourselves to be very easy to use. The sensor is a circular device. Air enters from one side. Inside there is a very sensitive thermometer which measures humidity and temperature, once per second. It is coupled with a small GPS unit which records the location of the data. It can be attached to a bicycle or installed on the passenger seat side of a car. People take readings just before sunrise, then at 3 p.m. and then at 7 p.m., which allows us to have the full cycle of temperatures.
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