The 2025 NASA Space Apps Challenge was held on October 4-5, 2025. This challenge is now closed.

Summary

Like Alice in Wonderland, let’s travel down the rabbit hole to reveal a world that looks like our planet Earth… but not quite! Using synthetic aperture radar (SAR), we can image the world by emitting radar pulses toward Earth and recording the energy that is reflected back after the signals interact with Earth's surface. Your challenge is to download multi-frequency or multi-polarization SAR data for an interesting study area of your choice –e.g., your hometown, a tropical wetland, ice sheet, forest wildfire, flooded neighborhood, volcano eruption, etc.—and use that data to develop hypotheses about the physical drivers operating there.

Background

Earth remote sensing helps us acquire information from a bird’s eye view. Spaceborne and airborne instruments image the planet and provide Earth observations to inform decision makers in addition to field surveys conducted on the ground. Many of these instruments conduct passive remote sensing by measuring energy from the Sun that reflects off Earth, but radar instruments conduct active remote sensing to image Earth.

Active remote sensing instruments emit and receive their own sources of energy. Radar sensors use energy in the microwave band of the electromagnetic spectrum. A SAR instrument “synthesizes” a long antenna by combining a sequence of acquisitions from its actual, shorter antenna to provide higher spatial resolution data. SAR instruments send out a pulse of energy that reacts with Earth’s surface and is reflected back to the instrument and recorded. SAR instruments can be used to study forest structure, soil moisture, wetlands, ocean topography, sea ice, and more. SAR data can be collected day or night and even in cloudy weather, which allows for critical data collection during disaster events like oil spills, wildfires, hurricanes, etc. Public SAR data is available for several instruments (see Resources tab) at different spatial resolutions, polarizations, and frequencies.

Radar images are more than just typical satellite images that you may see with your Global Positioning System (GPS) app. Radar data is most sensitive to two things: roughness and moisture content (the dielectric constant). Roughness information is characterized in the backscatter of the radar signal after it bounces off Earth’s surface; the different polarizations of this backscatter can tell us about the structure, geometry, and material properties of Earth. Furthermore, since water has a high dielectric constant, SAR data also highlights water bodies, flood inundation, and soil moisture. In addition, sensors employing different frequencies/wavelengths (e.g., C-band, L-band, P-band, etc.) provide data from varying penetration depths on Earth. Analyzing the data collected by these different sensors can enable studies such as monitoring different layers of a forest canopy (e.g., branches and leaves vs. soil and litter).

Objectives

Your challenge is to peer through the looking glass… by analyzing radar remote sensing data from SAR instruments that employ different polarizations and frequencies to reveal information about physical drivers on Earth. As you climb through the mirror like Alice to a world turned upside down, you will discover that data in each frequency reveals a different clue. Oil spills are seen in one wavelength but not the others, forest canopies and understories are highlighted only in certain polarizations. More riddles await you!

What area will you pick to study? You could investigate your hometown, a tropical wetland, ice sheet, forest wildfire, flooded neighborhood, volcano eruption, etc.—wherever the rabbit hole may take you! Download freely available SAR datasets for your chosen area using the list of resources provided, and don’t forget to use SAR data with different polarizations and frequencies in your project!

What can you hypothesize about the physical drivers behind what you see (or don’t see) in the SAR data? For example, if you are looking at the Amazon Rainforest, can you tell the trees and the water apart? Which polarizations highlight each and why? Does a different radar frequency highlight certain vegetation types? If you can find multiple images taken at different times, can you detect how the forest is changing over time?

How will you present your findings? Don’t forget to focus on compelling storytelling through data visualizations. You can use any digital medium you prefer: a final report, video, presentation slides, StoryMap, or even a riddle!

Like the secret doors and riddles Alice encounters in Wonderland, the images you’ll collect in this challenge aren’t as they seem. Everything seems to be in different “colors” – why does the city look pink and white? The rivers black? “CuriouSAR and curiouSAR!” cried Alice.

Potential Considerations

You may (but are not required to) consider the following:

You can download data from different dates to show a time series and ancillary datasets (population, vegetation type, etc.) to contextualize the study area.
In addition to the SAR data, you could incorporate supplemental data such as optical images or geographic information system (GIS) data to contextualize the SAR imagery.
Your project could show how human drivers (agriculture, industry, etc.) are impacting Earth’s natural resources.
If you are familiar with your study area (e.g. it’s your hometown), you can provide personal context and stories that help explain the SAR imagery.
Consider making your project interactive (e.g. image sliders, web maps, etc.).

For data and resources related to this challenge, refer to the Resources tab at the top of the page.

Through the Radar Looking Glass: Revealing Earth Processes with SAR