Ice-penetrating radars are a valuable tool for studying subsurface processes and conditions on Earth’s ice sheets. Vast amounts of ice-penetrating radar data have been collected from coherent chirped airborne ice-penetrating radar systems. Operating these airborne radar sounders is resource intensive, requiring large teams and significant financial resources. Here, we present a coherent chirped ground-based ice-penetrating radar system that can leverage the wealth of processing methods built for coherent chirped airborne radar data at a much lower cost. Our system is based on a commercially available software-defined radio (SDR) and open-source radar code platform, enabling widespread community adoption and use of the system. Furthermore, use of the SDR platform increases flexibility of the system and allows for easy reconfiguration of specific intrinsic radar and survey parameters. We present the architecture of our system alongside data it collected on the McMurdo Ice Shelf in Antarctica and at Summit Station in Greenland. We estimate the bed echo SNR it would achieve throughout Antarctica, which can be used to guide survey design. Finally, we discuss potential future system architectures which the system can be easily adapted to.

We explore and present a range of strategies for quantifying and mitigating the effects of receiver saturation in ice-penetrating radars. Ice-penetrating radars must be able to detect very weak reflected signals while maintaining dynamic ranges greater than 120 dB or more. Historically, ice-penetrating radars have done this by increasing pulse length, increasing transmit power, and interleaving short and long pulses to improve dynamic range. In most ice-penetrating radar architectures, steps are taken to prevent receiver saturation. Here we investigate the performance trade-offs associated with receiver saturation, and explore techniques to impact the negative effects of receiver saturation.

Ice-penetrating radar (IPR) instruments are a widely used tool to understand the structure and dynamics of Earth’s ice sheets and glaciers. Originally primarily designed to image the bedrock beneath ice, IPR systems are now being used for a wider range of scientific investigations. At the same time, new hardware architectures and customized radar systems are emerging. This combination of factors makes it worth re-visiting common assumptions about the noise characteristics of IPR systems and the phase coherence of measured reflections. In this work, we explore what it means for an IPR instrument to be coherent, how architectural choices in the design of software-defined radio-based instruments may impact phase coherence, and what instrument specifications should be considered for IPR applications that rely on measurements of small phase changes.

Airborne 0.5–2 GHz brightness temperatures were collected along a transect of the Priestley Glacier, Northern Victoria Land, Antarctica that coincides with previously acquired 189–199 MHz depth sounding radar data from NASA’s Operation IceBridge (OIB). The measured brightness temperature spectra evolve from negative spectral gradients (brightness temperature decreases with frequency) over the inland ice sheet and upper reach of the outlet glacier toward positive spectral gradients in the central region of the glacier. The spectra then increase almost linearly with frequency over the floating portion of the glacier terminus. The positive spectral gradients are more similar to sea ice on the ocean as compared to the grounded interior ice sheet. Comparison with modeling studies at Ross Ice Shelf sites where physical temperature has been measured in boreholes shows that positive gradients are to be expected where glacier ice overlies a water base. Calculations of radar reflectivity support the assumption of patchy regions of basal water and help to resolve ambiguities associated with processes such as interface roughness and near-surface firn layering.

Here we show the initial design and results from MAPPERR: The Multi-frequency Active Passive Polar Exploration Radar-Radiometer. MAPPERR addresses fundamental limitations in traditional ice-penetrating radar sounders and microwave radiometers stemming from non-unique contributions of different glaciological conditions. By utilizing active radar channels at 2, 22, 330, and 1000 MHz MAPPERR is designed to disentangle basal roughness and basal material conditions, while also providing important constraints on englacial temperature via measurements of attenuation. Passive radiometer channels at 330 and 1000 MHz provide additional constraints on englacial temperature via measurements of thermal emission and attenuation. Here, the system design is described and initial field results from campaigns in Svalbard, Iceland, and Antarctica are presented.

Measurement of ice-sheet thermal state via microwave remote sensing techniques has the potential to provide critically needed observations on englacial temperature at the local and continental scale. Better constraints of the vertical englacial temperature structure are needed to improve understanding of thermomechanical processes, ice rheology, and basal sliding, and to reduce uncertainty in interpretations of basal conditions such as material, roughness, and thermal state. We investigate the potential to combine active and passive microwave remote sensing techniques, namely ice-penetrating radar sounding and microwave radiometry, to enable more precise, accurate, and robust measurement of ice-sheet thermal state across widely varying thermal regimes. We simulate the effects of englacial temperature profiles on the attenuation and brightness temperature and explore the performance tradeoffs for joint radar-radiometer system architectures. Our analysis shows that active and passive microwave measurements have complementary sensitivities to englacial temperature as a function of depth, and that a ground-based joint radar-radiometer system can reduce the requirements and complexity demanded of each single instrument.

Accurately measuring the vertical temperature profiles of ice sheets and glaciers is important for providing observational constraints on how temperature impacts ice rheology and flow. Directly measuring englacial temperature is challenging, often involving resource-intensive boreholes. Ice-penetrating radars and radiometers have been utilized independently to probe englacial temperatures, highlighting the potential of remote sensing to collect glacier- and catchment-scale temperature data. Here, we investigate the sensitivity to temperature at depth of active and passive microwave systems and highlight the benefits of combining their measurements to constrain and improve top-to-bottom temperature retrievals. These simulations allow us to understand how each instrument performs when applied to the unique electromagnetic and geophysical properties found on an ice sheet, enabling us to tailor our system design and implementation in a target-informed acquisition and analysis approach.

The Autonomous Phase-Sensitive Radio Echo Sounder (ApRES) is a relatively inexpensive ice-penetrating Frequency-Modulated Continuous-Wave (FMCW) radar that is widely utilized in the glaciological community to obtain estimates of ice-sheet basal melt, vertical strain, and compaction rates [1]. However, these instruments are designed for stationary deployments, which prevents glacier- and catchment-scale surveys [2]. To expand the range of available applications, we assess the feasibility of mobile ApRES surveys. Our in-vestigation reveals that utilizing the ApRES in this manner introduces artifacts into the raw data. This paper character-izes the two types of artifacts (Doppler Blurring and grating lobes), investigates the conditions for when they occur, and attempts to correct them by modifying synthetic aperture radar (SAR) focusing algorithms for FMCW radars. We ul-timately identify the main obstacle in focusing radargrams from mobile ApRES surveys to be grating lobes; future work that reduces the presence of this artifact could enable more widespread use of mobile ApRES surveys.

Ice-penetrating radar is the primary geophysical tool for large-scale measurements of the geometry and internal prop-erties of the Antarctic and Greenland Ice Sheets. These low-frequency radar instruments are typically mounted on crewed aircraft or towed behind snowmobiles, both of which introduce significant logistical challenges and costs. The availability of inexpensive, portable, and fully-autonomous uncrewed aerial vehicles (UAVs) promises to reduce the cost, logistical complexity, and risk of collecting ice-penetrating radar data. We introduce a chirped radar system built around a software-defined radio (SDR) that can be carried by a low-cost and easily-transportable fixed-wing UAV. The antennas for the radar are fully integrated with the wings of the UAV and have a usable frequency range from 300–450 MHz. We detail the most critical design challenges and the solutions we have chosen.

Ice-penetrating radar sounders are powerful geophysical tools for studying the englacial and subglacial conditions of Earth’s ice sheets. Data from these instruments is critical to enhancing understanding and modeling of ice-sheet dynamics and ice-sheet contributions to global sea level. Traditionally, ice-penetrating radar sounders have a single center frequency creating inherent ambiguity in their pulse-by-pulse received power due to the confounding effects of basal material and roughness. Interpreting ice-penetrating radar data in light of these ambiguities requires assumptions about the physical state of the ice sheet, large-scale empirical analyses, or ancillary data. Here, we demonstrate that a high radiometric fidelity, narrowband, multi-frequency radar sounder can overcome these issues by separating the frequency-dependent basal roughness signature from the frequency-independent basal material signature. We present a radar system architecture with three narrow frequency bands spaced orders of magnitude apart (center frequencies of 1, 10, and 100 MHz, each with 20% fractional bandwidth) and high radiometric resolution (±0.5 dB). This architecture will allow us to precisely constrain ice-sheet basal conditions on a pulse-by-pulse basis by disambiguating the effects of basal material and basal roughness in ice-penetrating radar data.

Accurately measuring the vertical temperature profiles of ice sheets and glaciers can provide critical data for numerical ice sheet models used in global sea level projections. Ice-penetrating radars and radiometers have been utilized independently in remote sensing campaigns to measure englacial ice temperatures. Here we show that by combining these two instruments, which have complimentary sensitivities to lower and upper depths of the ice column, respectively, the overall uncertainty in temperature profile retrievals can be significantly reduced. We present unified simulations of radar attenuation and radiometer brightness temperature as functions of depth and frequency to demonstrate the value in this combined active/passive remote sensing approach.

Traditional radar sounders operating at single frequencies provide inherently ambiguous information due to the impact of subsurface basal material and roughness effects on relative along-track echo power. This ambiguity forces assumptions to be made about the nature of the ice sheet in order to definitively interpret subglacial conditions on a pulse by pulse basis. Here, we show that a multi-frequency radar sounder is best suited to discriminate basal material properties by correcting for basal roughness effects. By using frequencies spanning multiple orders of magnitude (3, 30, 300 MHz), each with high radiometric resolution (±0.5dB), we establish that such an architecture will enable determination of the basal material reflectivity to within 1.5 dB for roughness scales less than λ0/4, where λ0is the reference wavelength.