A wideband microwave airborne imaging system for hydrological studies

The development of the NOAA Polarimetric Scanning Radiometer (PSR) system commenced in the fall of 1995, with the first-generation system operated on the NASA P-3B aircraft to study passive microwave ocean surface wind signatures in March, 1997. The PSR system consist of sets of polarimetric radiometers housed within standardized gimbal-mounted scanhead drums. Each scanhead is rotatable by a gimbaled positioner so that the radiometers can view any angle within 70° elevation of nadir and at any azimuthal angle (1.32π sr solid angle), as well as external hot and ambient calibration targets. The configuration supports conical, cross-track, along-track, fixed-angle stare, and spotlight scan modes. Scanheads are designed for in-flight operation without the need for a radome (i.e. in contact with the aircraft slipstream), thus allowing precise calibration and imaging without superimposed radome signatures. The conical scan mode allows the full Stokes´ vector to be imaged without polarization mixing. The PSR has been used in several successful airborne missions, demonstrating the first 2-dimensional ocean surface wind vector mapping, high-resolution hurricane rainband imaging and satellite rainfall rate validation, C-band soil moisture imaging, high-resolution sea-ice mapping, and ocean internal wave imaging. Since its inaugural mission there have been several new hardware developments that have extended the capability of the PSR system in terms of the observable spectrum, polarizations, and compatibility with various aircraft. Currently in progress are developments which will provide the capability to perform wideband airborne hydrological studies with a single suite of synchronized, compatible sensor heads. This suite will include the PSR/CX, PSR/S, and PSR/L scanheads, which collectively extend the capabilities of the original PSR/A scanhead. Four positioners are anticipated to be available for operation in 2003. Each assembly (scanhead and positioner) was designed for integration into several aircraft, including the NASA DC-8, Orion P-3B, and WB-57F, Scaled Composites´ Proteus, Airplatforms, Inc. Canberra B-6, U.S. Navy P-3A, and NASA ER-2. Upon completion, the PSR system will provide passive polarimetric microwave imagery at most of the channel- s in the range of 1.4 to ∼800 GHz that are useful for spaceborne or airborne hydrological remote sensing. Studies planned using the system include vapor-to-runoff phase monitoring of precipitation, estuarian runoff and mixing, targeted forecasting, and cirrus generation by convection.