SNOOPI: Signals of Opportunity P-band Investigation


SNOOPI is a 6U CubeSat mission that will demonstrate and validate the in-space use of P-band signals of opportunity to measure root zone soil moisture and snow water equivalent. This project will reduce the risk of utilizing this technique on future space missions, verifying important assumptions about reflected signal coherence, robustness to the RFI environment, and the ability to capture and process the transmitted signal in space.

Science Area

Root zone soil moisture (RZSM) and snow water equivalent (SWE) play critical roles in the hyrdrologic cycle, impacting agricultural food production, water management, and weather phenomena. A better understanding of RZSM could enable a breakthrough in estimating key unobserved hyrdrologic fluxes and reduce uncertainty in net ecosystem exchange (NEE), carbon balance, discharge estimates, and crop yield forecasts. With the high albedo and insulating properties of snow, monitoring SWE accumulation provides key information for climate modeling and streamflow forecasting. Despite these contributions, accurate global RZSM and SWE measurements are unattainable with current technology.


Microwave observations at P-band frequency (240-380 MHz) are needed to penetrate into the root zone of the ground, but conventional P-band radars and radiometers are prone to radio frequency spectrum access issues and require large antennas to obtain sufficient signal-to-noise ratio or spatial resolution. SNOOPI reuses signals from existing telecommunications satellites and therefore does not require a transmitter, which makes this technology much more cost effective and enables measurements in all weather conditions day and night.

SNOOPI builds on two previous ESTO projects: P/I band Multi-Frequency Reflectometry Antenna (MFRA) for U-class Constellation and SoOp-AD: Signals of Opportunity Airborne Demonstration.


  • A Low Noise Front End will receive and process signals from the antenna subsystem and provide internal circuitry and noise sources to calibrate the reflectometer.
  • A Digital Back End will combine off-the-shelf hardware with a custom designed RF/Clk/Host board modified to process P-band reflected signals to generate measurements needed for science retrieval.
  • The antenna subsystem will use a set of two commercial off-the-shelf (COTS) circularly polarized, turnstile dipole antennas tuned to 255 and 370 MHz and placed at the ends of the CubeSat.

Principal Investigator

James Garrison photoJames Garrison is a professor of Aeronautics and Astronautics at Purdue University and the Principal Investigator of on the SNOOPI mission. Jim received his Ph.D. in Aerospace Engineering Sciences from the University of Colorado Boulder, his M.S. in Aeronautics and Astronautics from Stanford University, and his B.S. in Aeronautical Engineering from Rensselaer Polytechnic Institute.

Jim’s co-investigators on this project include Jeffrey Piepmeier, Manuel Vega, and Rajat Bindlish at NASA Goddard Space Flight Center; Rashmi Shah at JPL; and, Justin Mansell at Purdue.