## 1 Introduction  
The analysis of ground deformation at volcanoes has long been considered a crucial monitoring technique. Although geodetic systems such as Global Positioning Systems (GPS) can be used to determine ground motion, the logistical challenges of field monitoring--including high costs and the vulnerability of monitoring equipment near active volcanic vents--have rendered remote sensing a valuable addition for monitoring volcanic deformation. Interferometric Synthetic Aperture Radar (InSAR), in which the differences in phase of two or more temporally spaced synthetic aperture radar (SAR) images are used to determine surface deformation, has become a highly desirable measure of centimeter-scale deformation over large areas. This has allowed scientists to make measurements of volcanic deformation at otherwise unmonitored, or unexpectedly deforming, volcanoes (e.g., [1; 2; 3; 4; 5]).  
Using InSAR, much work has been devoted to connecting volcanic eruptions with geodetic signatures for eruption forecasting [6]. This has led to several inferences about the characteristics of magmatic plumbing systems and reservoirs (e.g., [5; 7; 8; 9; 10; 11; 12]). Some volcanoes have been known to show no deformation prior to eruption, while others deform without erupting, or exhibit deformation unrelated to magmatic intrusions, suggesting complex relationships between eruption behavior and resulting deformation (e.g., [13; 14]). Here, we use satellite and aerial radar images to measure surface displacements following explosive eruptions in May 2010 at Pacaya volcano in Guatem. L-band (wavelength = 23.6 cm) Advanced Land Observing Satellite-1 (ALOS-1) satellite imagery, available from 2008 to 2011, is compared to and supplemented with L-band (wavelength = 23.8 cm) Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) aerial data, available since 2011.  
UAVSAR is a miniaturized polarimetric synthetic aperture radar (SAR) system designed for repeat pass deformation measurements on aerial platforms. Unique from typical Uninhabited Aerial Vehicle (UAV) sensors, which are unmanned platforms, the UAVSAR radar pod is mounted beneath a Gulfstream-III plane and flown by pilots over a specific path requested by NASA-approved researchers. While the radar is collecting data, on-board operators use Platform Precision Autopilot (PPA) to control the plane so it can fly the same flight path within a 10 m diameter tube for hundreds of kilometers at a time [15]. This is important to scientists who want to track changes on the surface of the earth from one flight to the next to study features like glaciers, earthquakes, volcanoes, and landslides using repeat-pass InSAR. The L-band radar onboard the UAVSAR operates at a central frequency of 1217.5 MHz to 1297.5 MHz, with a bandwidth of 80 MHz. The nominal flight altitude for UAVSAR is 12,500 m, and the typical image swath width is >23 km. The spatial resolution of the resulting UAVSAR single-look-complex (SLC) imagery are \(\sim\)1.7 m in range and \(\sim\)0.8 m in azimuth. More information on flight planning and operations is available on the UAVSAR website ([[http://uavsar.jpl.nasa.gov/](http://uavsar.jpl.nasa.gov/)]([http://uavsar.jpl.nasa.gov/](http://uavsar.jpl.nasa.gov/))). We discuss the utility of this precise topography change monitoring technique for volcanic activity and use it to augment standard satellite techniques.