University of Minnesota
University of Minnesota
Islands in the Sun

First results from the temperature network

November 18, 2011Jake GrafensteinSensor networkComments Off

Will Hertel has created an image that shows the features of the Twin Cities urban heat island.

The data are from September 15, 2011 at 4:00 am CDT. Urban heat islands are generally stronger in winter and during the nighttime. While we analyze data taken over the entire 24-hour day, the data at this early hour highlight the largest difference between the downtown and outlying areas on this particular day. Will interpolated among sites that include our volunteer network along with other standard temperature recording locations (such as airports).

This is one example of the data that we will be able to analyze with this project.

Thanks to those of you who have volunteered to help us with this project. We have received addresses from hundreds of interested people and are in the process of sorting through them. We’re grateful that so many of you are willing to help! With more sites being added, these preliminary data will be improved–more sites means less interpolation between existing sites. Stay tuned…

Islands in the Sun on MPR

November 14, 2011Jake GrafensteinGeneral, Heat island, Sensor networkComments Off

Our project was mentioned in Paul Huttner’s Updraft blog on MPR on Friday, November 11,  2011.



Islands in the Sun in the Star Tribune

Our project was mentioned in a story about urban heat islands in the Star Tribune on 11/5/11.

Check it out!

Volunteer to be part of our temperature sensor network!

September 6, 2011Jake GrafensteinFeatured, Sensor networkComments Off

We are setting up a dense network of temperature sensors around the Twin Cities Metro Area to measure the spatial and temporal variability of temperatures in a variety of urban and suburban environments. The goal of the project is to learn more about the behavior of the urban heat island effect in a large northern latitude metropolitan area. We are currently determining sites based on location and land characteristics.

If you live in the Twin Cities Metro Area and are interested in participating by housing a sensor on your property please follow the link provided below. The sensors are small (several inches long) and should not detract from your backyard aesthetics. We might contact you if we think your property might fall within our criteria. Please note that your interest does not guarantee that your site will be selected—it is possible that your location will not meet our selection criteria.

If selected, we will install a temperature sensor outside your house somewhere on your property and ask that it remain for 2-4 years. There is nothing required of you—the sensor is self-contained and automatically logs readings. We must have access to the sensor every 2-3 months to download data. We will be happy to provide the data for your site to you if you are interested.

If you are interested in housing a sensor on your property, please visit the Sensor Network page. If you have any questions please do not hesitate to contact us.

Just how do we measure the urban heat island?

September 6, 2011Jake GrafensteinFeatured, Sensor networkComments Off

We use a variety of tools to study urban heat islands, including both measurements and modeling. Some observations we get from satellites as they look down on cities from space at different resolutions (just like digital cameras have different pixel sizes). In this post we’re going to talk about the measurements we are making on the ground.

We are making measurements of temperature, wind, and radiation over various surfaces such as asphalt parking lots, grass, and concrete. We measure air temperature at four heights near the ground (2m, 1m, 0.5m, and 0.25 m). We also estimate what is known as ‘skin temperature’ of these surfaces by measuring energy that radiates from the surface. This is the close to the actual temperature of the surface. In the case of an asphalt parking lot, if you walked barefoot on it in summer the skin temperature is what your foot would feel. We all know this can be much hotter than air just inches above the parking lot.

We are also measuring solar radiation as it comes through the atmosphere and warms the ground, as well as the part of this radiation that is reflected. A grassy park is cooler than an asphalt parking lot on a bright sunny day because of many differences—one of them is the fact that parking lots absorb more solar radiation than grass. The parking lot has a lower reflectivity than the grass. One way to mitigate the urban heat island effect is to increase the reflectivity of surfaces in urban areas.

Finally, we are in the process of deploying more than 100 temperature sensors to backyards around the Twin Cities Metro Area. By measuring temperature on a dense network from the downtown to outlying areas, we can better understand the make up of our urban heat island.

Funding for the Islands in the Sun project has been provided by:

The Islands in the Sun project is currently looking for volunteers to house sensor on their property. Visit the Sensors Network page for more details.

For questions about the Islands in the Sun project, please email Peter Snyder.