Title: The Ultra-Wideband Software-Defined Radiometer (UWBRAD) for Ice Sheet Internal Temperature Sensing: Instrument Status and Experiment Plans
Presenting Author: Alexandra Bringer
Organization:The Ohio State University
Co-Author(s): Joel Johnson

Abstract:
The Ultra-Wideband Software-Defined Radiometer (UWBRAD) is currently being developed under the support of the NASA Instrument Incubator Program (IIP). The UWBRAD instrument will provide measurements of ice sheet thermal emission over the frequency range 0.5-2 GHz for the purpose of remotely sensing internal ice sheet temperature information. Physical temperature plays an important role in influencing stress-strain relationships in the ice sheet volume, and therefore impacts ice sheet dynamics including deformation and flow across the ice sheet base. No methods currently exist for remotely sensing ice sheet internal temperatures; the only measured information at present is obtained from a small number of deep ice core sites. Previous studies have shown the potential of multi-frequency brightness temperature measurements from 0.5-2 GHz to obtain deep ice sheet temperature information. These studies have investigated forward model predictions of brightness temperatures given assumed ice sheet internal temperatures, electromagnetic permittivity, and other physical parameters such as density and particle grain size. Accordingly, the UWBRAD instrument is being developed to provide brightness temperature observations over 0.5-2 GHz using multiple frequency channels and full-bandwidth sampling of each channel. The UWBRAD system includes three primary subsystems: the antenna, a multi-channel analog front end, and a multi-channel digital backend. Because the frequency range 0.5-2 GHz is not a protected portion of the spectrum, UWBRAD is being designed to allow brightness temperature observations in the presence of interfering sources. This goal is to be achieved by separating the observed bandwidth into 13 separate channels, each of which is sampled at 250 MSPS (i.e. fully Nyquist sampled), so that advanced radio frequency interference (RFI) detection and mitigation methods can be applied. This process will enable UWBRAD to identify open portions of the spectrum that can be used for radiometric observations even in the presence of other transmitting sources. The UWBRAD antenna is designed to provide nadiral brightness temperature measurements with a near constant antenna pattern over the 0.5-2 GHz range. A conical spiral design has been selected for this purpose. The antenna has only a moderate gain of ~ 10 dB by design to ensure that all frequency channels observe approximately the same spatial region. The impact of the antenna pattern on brightness temperature measurements is also incorporated into the retrieval process. UWBRAD is to be deployed in 2016 in airborne observations of the Greenland ice sheet, including overflights of multiple ice core locations to provide in-situ temperature information. The project team is conducting extensive simulation studies of UWBRAD observations in order to develop temperature retrieval methods from multi-frequency brightness temperature measurements. Initial retrieval studies have shown the ability of the system to provide information on ice temperatures at 10 m depth, averaged over depth, as well as temperature profile information. At present, a detailed simulation study of UWBRAD measurements over the expected Greenland flight path is in process. Results from these simulations are also being compared to the 1.4 GHz brightness temperature measurements available from the SMOS and Aquarius satellites. The presentation will provide an overview of the current UWBRAD instrument development status, test results, and project experiment plans. Results from the Greenland simulation study will be reported and interpreted for the information they provide on the expected science information to be acquired from the 2016 campaign. A discussion of future UWBRAD deployment opportunities, including measurements in Antarctica, will also be provided.