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This work describes the design and development of a radar receiver with a large dynamic range by means of carefully designed compression. The receiver is designed for ice sounding applications on the Antarctic and Greenland ice sheets and is designed to be usable over a large frequency range (VHF and UHF) and with multiple analog-to digital converters with only minor modifications. We present the receiver design, in which we have implemented an RF-power limiting feature so that the output power is monotonically increasing with respect to the input power over a large dynamic range. This allows the receiver to operate in the nonlinear region to compress the high-power returns into the dynamic range of the analog to digital converter while still achieving good sensitivity (low noise figure) for low power signals. We discuss design considerations, hardware description, initial lab test results, the architecture of the design and results from recent field deployments. Lastly, we discuss the future work on the decompression mechanism to recover the uncompressed signals. 

The Center for Oldest Ice Exploration (COLDEX) is a US initiative funded to search for climate records over the last 5 million years, including locating sites for an accessible continuous ice core going back 1.5 million years. As part of this effort, COLDEX has mapped the southern flank of Dome A, East Antarctica using an instrumented Basler, including dual frequency radar observations of the ice sheet and ice bed, as well as potential fields measurements (see presentation by Kerr in EGU session G4.3) across two field seasons from Amundsen-Scott South Pole Station. The aerogeophysical system included both the UTIG VHF MARFA radar system operating at 52.5-67.5 MHz, as well as a new large high resolution UHF array from CReSIS operating at 670-750 MHz operating simultaneously. A goal of this project was to obtain airborne repeat interferometry for segments of the survey, as well as directly feed ice sheet models using englacial isochrons (see Singh presentation in EGU session CR5.6). These goals lead to a survey explicitly designed around ice sheet flow lines. While prior work had sampled the region at lithospheric scales, the COLDEX survey had two components - the first was to map the region at crustal scales (line spacing of 15 km), and the second was to map subareas at ice sheet scales (line spacing of 3 km). Immediate observations include an extensive basal unit and strong discontinuity in englacial stratigraphy that runs across the survey area and appears correlated with changes in bed interface properties. The airborne campaign will be used to inform follow up ground campaigns to understand processes relevant for old ice preservation. 

Abstract. During the concluding phase of the NASA OperationIceBridge (OIB), we successfully completed two airborne measurementcampaigns (in 2018 and 2021, respectively) using a compact S and C band radarinstalled on a Single Otter aircraft and collected data over Alaskanmountains, ice fields, and glaciers. This paper reports seasonal snow depthsderived from radar data. We found large variations in seasonalradar-inferred depths with multi-modal distributions assuming a constantrelative permittivity for snow equal to 1.89. About 34 % of the snowdepths observed in 2018 were between 3.2 and 4.2 m, and close to 30 % of thesnow depths observed in 2021 were between 2.5 and 3.5 m. We observed snowstrata in ice facies, combined percolation and wet-snow facies, and dry-snow facies fromradar data and identified the transition areas from wet-snow facies to icefacies for multiple glaciers based on the snow strata and radarbackscattering characteristics. Our analysis focuses on the measured strataof multiple years at the caldera of Mount Wrangell (K'elt'aeni) to estimate the localsnow accumulation rate. We developed a method for using our radar readingsof multi-year strata to constrain the uncertain parameters of interpretationmodels with the assumption that most of the snow layers detected by theradar at the caldera are annual accumulation layers. At a 2004 ice core and2005 temperature sensor tower site, the locally estimated average snowaccumulation rate is ∼2.89 m w.e. a−1 between the years2003 and 2021. Our estimate of the snow accumulation rate between 2005 and2006 is 2.82 m w.e. a−1, which matches closely to the 2.75 m w.e. a−1 inferred from independent ground-truth measurements made the sameyear. The snow accumulation rate between the years 2003 and 2021 also showeda linear increasing trend of 0.011 m w.e. a−2. This trend iscorroborated by comparisons with the surface mass balance (SMB) derived forthe same period from the regional atmospheric climate model MAR (ModèleAtmosphérique Régional). According to MAR data, which show anincrease of 0.86 ∘C in this area for the period of 2003–2021, thelinear upward trend is associated with the increase in snowfall and rainfallevents, which may be attributed to elevated global temperatures. Thefindings of this study confirmed the viability of our methodology, as wellas its underlying assumptions and interpretation models. 

This paper demonstrates the design and implementation of two dual-polarized ultra-wideband antennas for radar ice sounding. The first antenna operates at UHF (600– 900 MHz). The second antenna operates at VHF (140–215 MHz). Each antenna element is composed of two orthogonal octagon-shaped dipoles, two inter-locked printed circuit baluns and an impedance matching network for each polarization. We built and tested one prototype antenna for each band and showed a VSWR of less than 2:1 at both polarizations over a fractional bandwidth exceeding 40 %. Our antennas display cross-polarization isolation larger than 30 dB, an E-plane 3-dB beamwidth of 69 degrees, and a gain of at least 4 dBi with a variation of ± 1 dB across the bandwidth. We demonstrate peak power handling capabilities of 400-W and 1000-W for the UHF and VHF bands, respectively. Our design flow allows for straightforward adjustment of the antenna dimensions to meet other bandwidth constraints. 

This paper demonstrates the design and implementation of two dual-polarized ultra-wideband antennas for radar ice sounding. The first antenna operates at UHF (600–900 MHz). The second antenna operates at VHF (140–215 MHz). Each antenna element is composed of two orthogonal octagon-shaped dipoles, two inter-locked printed circuit baluns and an impedance matching network for each polarization. We built and tested one prototype antenna for each band and showed a VSWR of less than 2:1 at both polarizations over a fractional bandwidth exceeding 40 %. Our antennas display cross-polarization isolation larger than 30 dB, an E-plane 3-dB beamwidth of 69 degrees, and a gain of at least 4 dBi with a variation of ± 1 dB across the bandwidth. We demonstrate peak power handling capabilities of 400-W and 1000-W for the UHF and VHF bands, respectively. Our design flow allows for straightforward adjustment of the antenna dimensions to meet other bandwidth constraints. 

Abstract This paper provides an update and overview of the Center for Remote Sensing of Ice Sheets (CReSIS) radars and platforms, including representative results from these systems. CReSIS radar systems operate over a frequency range of 14–38 GHz. Each radar system's specific frequency band is driven by the required depth of signal penetration, measurement resolution, allocated frequency spectra, and antenna operating frequencies (often influenced by aircraft integration). We also highlight recent system advancements and future work, including (1) increasing system bandwidth; (2) miniaturizing radar hardware; and (3) increasing sensitivity. For platform development, we are developing smaller, easier to operate and less expensive unmanned aerial systems. Next-generation platforms will further expand accessibility to scientists with vertical takeoff and landing capabilities.