We have developed the P-band Signals of Opportunity (SoOp) sensor based on the Unmanned Aircraft System (UAS) to remotely sense Snow Water Equivalent (SWE) and Root Zone Soil Moisture (RZSM). The P-band UAS SoOp sensor for Hydrology (UASHydro) would operate on the S2 aircraft developed by Black Swift Technologies for sensing of SWE and RZSM with a spatial resolution of about 10m. Root-zone soil moisture and snow water storage in land are critical parameters of the water cycle. The long-term goal of our development would be to use small UAS to perform regional high resolution observation of two key hydrological measurements to improve the estimation of terrestrial water storage for water management, crop production and forecasts of natural hazard. The UASHydro concept utilizes passive receivers to detect the reflection of strong existing P-band radio signals at the 360-380 MHz band from geostationary Mobile Use Objective System (MUOS) communication satellites launched by the US Navy. The SWE remote sensing measurement principle using the P-band SoOp is based on the propagation delay (or phase change) of radio signals through the snowpack. The time delay of the reflected signal due to the snowpack with respect to snow-free conditions is directly proportional to the snowpack SWE, while the soil moisture can be retrieved from the reflectivity at the P-band frequencies for MUOS. We have been conducting ground-based campaigns to test the instrumentation and data processing methods at the Fraser Experimental Forest in Colorado since February 2016. The field campaign data has provided support to the measurement concept. To install the SoOp technologies on the UAS, a lightweight antenna has been built and interfaces with the S2 built by Black Swift Technologies have been completed. A set of flights have been planned starting April 2018 through the end of 2018 in Colorado.
We have developed the HydroCube mission concept with a constellation of small satellites to remotely sense Snow Water
Equivalent (SWE) and Root Zone Soil Moisture (RZSM). The HydroCube satellites would operate at sun-synchronous 3-
day repeat polar orbits with a spatial resolution of about 1-3 Km. The mission goals would be to improve the estimation
of terrestrial water storage and weather forecasts. Root-zone soil moisture and snow water storage in land are critical
parameters of the water cycle. The HydroCube Signals of Opportunity (SoOp) concept utilizes passive receivers to detect
the reflection of strong existing P-band radio signals from geostationary Mobile Use Objective System (MUOS)
communication satellites. The SWE remote sensing measurement principle using the P-band SoOp is based on the
propagation delay (or phase change) of radio signals through the snowpack. The time delay of the reflected signal due to
the snowpack with respect to snow-free conditions is directly proportional to the snowpack SWE. To address the
ionospheric delay at P-band frequencies, the signals from both MUOS bands (360-380 MHz and 250-270 MHz) would be
used. We have conducted an analysis to trade off the spatial resolution for a space-based sensor and measurement accuracy.
Through modeling analysis, we find that the dual-band MUOS signals would allow estimation of soil moisture and surface
roughness together. From the two MUOS frequencies at 260 MHz and 370 MHz, we can retrieve the soil moisture from
the reflectivity ratio scaled by wavenumbers using the two P-band frequencies for MUOS. A modeling analysis using
layered stratified model has been completed to determine the sensitivity requirements of HydroCube measurements. For
mission concept demonstration, a field campaign has been conducted at the Fraser Experimental Forest in Colorado since
February 2016. The data acquired has provided support to the HydroCube concept.
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