The NRC Decadal Survey recommended the Surface Water Ocean Topography (SWOT) satellite mission to address terrestrial fresh water hydrology and physical oceanography science questions. The proposed effort will develop a low-cost, Ka-band, multi-temporal baseline radar sensor designed to fly on high altitude unmanned aerial vehicle (Global Hawk) and acquire phenomenology (i.e. temporal, coherence, near-nadir scattering cross-section and vegetation attenuation) measurements in support of the SWOT mission. To realize this sensor, innovations in the sensor design, transceiver digital receiver and antenna are required. The Phase I will result in a system design for these subsystems that can be realized in a Phase II effort. During the Phase I, analytic studies and modeling will be performed to demonstrate feasibility and to perform the necessary tradeoffs. Leveraging a high altitude, FPGA-based digital receiver system developed by RSS and its development system, the digital receiver capabilities will be extended and initial laboratory testing performed. The Phase II effort will realize a prototype of this sensor.At the end of the Phase I, a technology readiness level of 3 will be achieved.