Your smartphone can make science better. The SatCam project wants to improve space-based tools scientists use to study the atmosphere. The SatCam app lets you send ground truth reports of cloud cover so scientists can check weather satellites' accuracy.
Modis is Nasa’s Moderate Resolution Imaging Spectroradiometer, an instrument carried by the Terra and Aqua Earth-observation satellites. It collects light in the infrared and visible spectrum leaving Earth. That light was radiated or reflected by Earth’s surface, the plants and buildings on the surface, or the clouds floating above it. That light changes depending on the physical and chemical variables on the ground and in the air. Scientist study the data collected by Modis to understand those variables and produce better models of Earth’s dynamic systems.
The Modis team processes the data as a service to other scientists. One of these services is a cloud mask - a pixel-by-pixel measure of whether the sky is clear or cloudy in a Modis image. Cloud cover is a major source of error in remote sensing analysis. The cloud mask lets researchers use the best data for studying the atmosphere or Earth’s surface. The mask lets researchers studying clouds know where the clouds are. More importantly, researchers can program cloud masks into an algorithm to automatically analyze the right data as it processes billions of pixels.
Cloud masks are part of the foundation for scientists’ work. Naturally, scientists want those masks to be as accurate as possible, but the mask-generating algorithms are only as good as the assumptions and models built into their code. Snow, urban development, or multiple layers of different cloud types could lead the Modis algorithms to produce bad data. Researchers at the University of Wisconsin’s Space Science and Engineering Center want to understand the accuracy of cloud masks produced by Modis and the similar Viirs instrument on the Suomi NPP satellite. Checking the data is easier said than done. The researchers must compare the data with ground truth - what kinds of cloud and what surface conditions are actually present - across the United States. It’s too big a job to do themselves, so they turned to amateurs for help.
The SatCam app for iOS lets you collect and report that ground truth. It uses your iPhone’s GPS to let you know when Terra, Aqua, or Suomi NPP satellites are overhead. You use the app to take a picture of the sky and your surroundings. After you classify the degree of cloud cover and the kind of landscape, the app adds time and location data. The app downloads the satellite imagery so you can compare your observations to the view from space. In an interview with Wisconsin Public Radio, Modis science team member Liam Gumley said that he designed SatCam “so a scientist could use it or a kid in sixth grade could use it.” UW’s Cooperative Institute of Meteorological Satellite Studies incorporates SatCam into its education outreach programs. Teachers who participate in the Earth Science Information Partners Workshop learn how to incorporate SatCam and other iOS apps into their science curriculum. They can then borrow an iPad from the iPad Library at UW’s Climate Literacy Ambassadors Project.
The SatCam team updated the app (PDF report) to align it with Nasa’s S’Cool education program which lets students provide ground truth for the Ceres satellite-based climate experiment. They also changed the code and back-end systems to make ports to Android easier.