Determining the mass balance of Antarctica by satellite gravimetry, altimetry and input-output methods is still suffering from large discrepancies between methods, especially for East Antarctica. Error sources for the different estimation methods include GIA for GRACE/GRACE-FO, firm compaction for satellite altimetry, and poorly known interior snow fall and grounding line mass flux for outlet glaciers in the input-output method. To narrow down uncertainties for the latter, an international SCAR project “RINGS” was initiated in 2023, aiming as a primary goal to cover all major unmapped outlet glaciers with new radar ice thickness data in the coming years. A unique multi-disciplinary airborne remote sensing RINGS campaign was carried out as part of a first circumnavigation of Antarctica 2024/25, using a Twin-Otter as dedicated science aircraft. The airborne campaign instruments included a 30 GHz deep ice sounding radar, a 5 GHz broadband snow radar, along with scanning lidar, nadir and side-looking imagery, and gravimetry, as well as atmosphere monitoring sensors for chemistry and aerosols. In the presentation we outline the results of the RINGS airborne campaign, the impact on the input-output method of the new outlet glacier thicknesses, and compare the changes to current GRACE/GRACE-FO mass balance results.

In this paper we present the design of a reconfigurable radar flight tested on an ultra-long endurance UAS (Unmanned Aerial System). The radar consists of a common digital backend and swappable RF (radio frequency) front ends. Given this development was designed to support ice and snow measurements in polar regions, two RF modules were fabricated and integrated into the system for testing. A low-Very High Frequency (VHF) RF subsystem operating from 60-80 MHz was developed for ice sounding, while a 2-8 GHz subsystem is to support snow thickness and near-surface ice measurements. This paper provides a brief overview of the various radar subsystems, laboratory test results, aircraft integration, and flight-test results.

We present a dual- band radar instrument package for measurements during the SWIDA-RINGS mission - a large international scientific collaboration to circumvent Antarctica and collect new airborne data along the continent's grounding line -. The radar instrument package consists of a similar to 30-MHz radar depth sounder for ice thickness measurements and a microwave radar with multi-gigahertz bandwidth for mapping seasonal snow accumulation. We integrated the radar electronics and antennas onto a Twin Otter aircraft equipped with a gravimeter, a scanning lidar, optical cameras and an atmospheric sampling apparatus. This unique instrument combination will provide critical data to fill knowledge voids on the Antarctic Ice Sheet margins and general dynamics. This paper provides a brief overview of the SWIDA-RINGS mission and its objectives; a description of the dual-band radar instrument setup and aircraft integration efforts; and sample preliminary radar results from a logistically complex field campaign conducted in Antarctica during the 2024/2025 Austral Summer season.

Airborne ice-sounding radars typically operate in the low-to mid-VHF spectrum. Most ice sounding missions require large cross-track arrays to reduce clutter from rough surfaces, necessitating antennas to be mounted on aircraft wings. The mechanical response of the airframe can affect the radar system performance due to the displacement and vibrations of both the wing and the antennas. This paper investigates the vibrational response of wing-mounted 70 MHz antennas developed by the Center for Remote Sensing and Integrated Systems (CReSIS) at the University of Kansas. A finite element model validated with experimental measurements is used to predict the antenna response in flight. From an analysis of the radar data from a recent flight test, it is apparent the airframe vibrations due to the engine are observed in the signal. Future study is recommended to further characterize this effect including impacts on beam forming and means to mitigating the response.

A major airborne remote sensing campaign with multifrequency radar, lidar, imagery and gravimetry was carried out in a circumnavigation of Antarctica in the 2024/25 season, as a major contribution to the recent SCAR RINGS initiative. The primary purpose of the campaign was to measure ice thickness along the grounding line, to secure better data on Antarctic mass balance by the input-output method, and thus adding more reliable information to solve the discrepancies between space-based mass balance estimates of Antarctica, but also to monitor upper ice layers, providing input data for models, and adding improved gravity measurements to rectify earlier geophysical surveys. The airborne campaign was based on a 30 GHz deep ice sounding radar, along with a 5 GHz broadband snow radar of University of Kansas, along with scanning lidar, nadir and side-looking imagery and gravimeters, and even included atmosphere chemistry and aerosol monitoring sensors in cooperation with EPFL, Switzerland. The logistics involved two Twin-Otters (one for science and one for logistics), helicopters (used for access to national bases), as well as logistics support from a Brazilean-chartered icebreaker, hosting a complimentary scientific program with a.o. shallow ice coring and oceanography. The presentation will show some first results of the campaign, and also highlight the usefulness of private-public cooperation in the extensive and costly field program.

The Center for Oldest Ice Exploration (COLDEX) project is exploring Antarctica to find a continuous ice record from the present to 1.5 million years ago and document the midPleistocene transition, which occurred similar to 1 million years ago. The current longest ice record is 800,000 years old. This work describes a new 600-900 MHz UHF radar to help address this challenge with a 1) much larger, 22.8 m or 57-wavelength, cross-track antenna array and 2) higher transmit power, than prior renditions. Survey flights on a Basler aircraft were conducted from the South Pole in 2022-2023 and in 2023-2024. In this work, we provide an overview of the design requirements, the radar system architecture, and antenna array implementation. We also present preliminary results from aerial surveys conducted in Antarctica.

With the miniaturization of electronic hardware, it has become possible to operate radar systems onboard small UAS, for which there can be numerous uses in different fields. However, as an antenna’s operational frequency is inherently tied to its respective geometric characteristics, the antenna size and weight has become the limiting factor in mounting these systems onto smaller aircraft. With multifunctional structures, primary structures such as the spar can simultaneously be used as antennas, saving weight and reducing necessary payload space. Using two different hybrid CFRP and GFRP spars with coax feeds in their centers, this concept was tested as an alternative wing design for the Skyhunter UAS while radiating at 200 MHz and 75 MHz. It was discovered that the antenna’s gain and resonance frequency can be significantly affected by the placement of wiring nearby, and that the routing of these cables can be manipulated to improve or change these metrics. A proposed in-flight measurement system utilizing miniaturized electronic hardware is also presented. This system is intended to capture the effect of in-flight deformation of the radiating structure and wire routing on antenna performance metrics.

We developed a multi-channel, ultra-wideband, microwave radar for swath mapping of snow layers on land, sea ice and ice sheets. The system operates in the 2-18 GHz band (up to 16-GHz bandwidth) with two nadir-looking transmitters and six receivers; and a dual-polarized, forward-looking transmitter/receiver pair. The system addresses the limitations in cross-track resolution found in prior single-channel instruments and will help improve snow thickness retrieval in areas of complex surface topography. This paper presents an overview of the radar electronics and antenna system and their installation on the NASA P-3B aircraft. We also present initial results from a short field campaign conducted in Greenland in the spring of 2022.

We present the application of novel additively manufactured hybrid rigid-flex Vivaldi antennas as transmit and receive elements for an ultra-wideband (UWB) frequency modulated continuous wave (FM-CW) radar. This paper focuses on a series of measurements performed at Ku-band (12–18 GHz) to assess the effectiveness of these 3- D printed antennas within the radar loop, under thermal and vibration stresses. First, we verified the antennas' satisfactory operation down to -32 °C and inferred that thermal cycling would have minimal effect on the impulse response of the radar system. Next, we investigated the effects and bounds of vibration stress that could be sustained by these antennas and offer recommendations to support even higher vibration levels in future design iterations. Additionally, we present a succinct overview of the antenna design and the experimental setup used to perform these measurements.

During the concluding phase of the NASA Operation IceBridge (OIB), we successfully completed two airborne measurement campaigns (in 2018 and 2021, respectively) using a compact S and C band radar installed on a Single Otter aircraft and collected data over Alaskan mountains, ice fields, and glaciers. This paper reports seasonal snow depths derived from radar data. We found large variations in seasonal radar-inferred depths with multi-modal distributions assuming a constant relative permittivity for snow equal to 1.89. About 34 % of the snow depths observed in 2018 were between 3.2 and 4.2 m, and close to 30 % of the snow depths observed in 2021 were between 2.5 and 3.5 m. We observed snow strata in ice facies, combined percolation and wet-snow facies, and dry-snow facies from radar data and identified the transition areas from wet-snow facies to ice facies for multiple glaciers based on the snow strata and radar backscattering characteristics. Our analysis focuses on the measured strata of multiple years at the caldera of Mount Wrangell (K'elt'aeni) to estimate the local snow accumulation rate. We developed a method for using our radar readings of multi-year strata to constrain the uncertain parameters of interpretation models with the assumption that most of the snow layers detected by the radar at the caldera are annual accumulation layers. At a 2004 ice core and 2005 temperature sensor tower site, the locally estimated average snow accumulation rate is ∼2.89 m w.e. a−1 between the years 2003 and 2021. Our estimate of the snow accumulation rate between 2005 and 2006 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 same year. The snow accumulation rate between the years 2003 and 2021 also showed a linear increasing trend of 0.011 m w.e. a−2. This trend is corroborated by comparisons with the surface mass balance (SMB) derived for the same period from the regional atmospheric climate model MAR (Modèle Atmosphérique Régional). According to MAR data, which show an increase of 0.86 ∘C in this area for the period of 2003–2021, the linear upward trend is associated with the increase in snowfall and rainfall events, which may be attributed to elevated global temperatures. The findings of this study confirmed the viability of our methodology, as well as its underlying assumptions and interpretation models.

In this paper, we present an improved bandwidth antenna design for the HF Sounder radar installed on the Twin Otter. This is achieved by replacing a steel tube dipole antenna with a larger and more aerodynamic carbon fiber reinforced plastic (CFRP) antenna. By replacing the original steel design with a CFRP design, a larger antenna can be supported resulting in a wider operational bandwidth. Initially several aerodynamic cross-sections were considered for the larger antenna, and a trade study was performed to compare the various designs to the original tube design. This trade study considered electrical performance, implications to aircraft performance, and assessment of the structural design. From the initial trade study, two aerodynamic shapes were considered for further assessment—an ellipse with a t/c ratio of 0.33 and a NACA 0024 airfoil. Based on this study, a 2 in. x 8 in. NACA 0024 antenna is recommended to manufacture and physically test.

This study explores the potential applications of carbon fiber composite material for structural antennas. Carbon fiber composite materials provide excellent specific strength and stiffness; however, their electrical properties, such as conductivity, are not well established, especially in the very high-frequency (VHF) range. Knowledge of a material's conductivity is required for electrical performance estimation through simulations. Through combined experimental and simulated analysis of multiple carbon fiber antennas, the effective conductivity for a biaxial weave carbon fiber composite was determined to be between 7000 and 13 000 S/m in the VHF spectrum. Carbon fiber antenna performance is found to be particularly sensitive to the contact between the carbon fibers and the copper feed; however, radiation efficiencies (REs) of carbon fiber composite antennas are found to be within 2%–10% of a geometrically identical copper antenna, and their bandwidths are nearly identical. The electrical performance of carbon fiber composite antennas demonstrates significant promise for structural antenna applications in the VHF range.

In this letter, we present the novel design of a near‐high frequency antenna for a small unmanned aircraft systems helicopter for the intended purpose of sounding and imaging temperate glaciers. The antenna leverages concepts in the areas of efficient electrically small antennas, structural antennas, and impedance matching to create a versatile design that is small and lightweight yet robust for airborne operations and has wider bandwidth than existing designs.

. During the concluding phase of the NASA Operation IceBridge (OIB), we successfully completed two airborne measurement campaigns (in 2018 and 2021, respectively) using a compact S/C band radar installed on a Single Otter aircraft and collected data over Alaskan mountains, ice fields, and glaciers. We observed snow strata in ice facies, wet-snow/percolation facies and dry snow facies from radar data. This paper reports seasonal snow depths derived from our observations. We found large variations in seasonal radar-inferred depths assuming a constant relative permittivity for snow 10 equal to 1.89. The majority of the seasonal depths observed in 2018 were between 3.2 m and 4.2 m, and around 3 m in 2021. We also identified the transition areas from wet-snow facies to ice facies for multiple glaciers based on the snow strata and radar backscattering characteristics. Our analysis focuses on the measured strata of multiple years at the caldera of Mount Wrangell to estimate the local snow accumulation rate. We developed a method for using our radar readings of multi-year strata to constrain the uncertain parameters of interpretation models with the assumption that most of the snow layers detected 15 by the radar at the caldera are annual accumulation layers. At a 2004 ice core and 2005 temperature sensor tower site, the locally estimated average snow accumulation rate is ~2.89 m w. e. a-1 between the years 2002 and 2021. Our estimate of the snow accumulation rate between 2005 and 2006 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 same year. We also found a linear increasing trend of 0.011 m w. e. a-1 per year between the years 2002 and 2021. With this trend, we extrapolated the snow accumulation back to 1992 and 20 obtained an average accumulation rate of 2.74 w. e. a-1 between the years 1992 and 2004, which agrees well with the value of 2.66 w. e. a-1 for the same period determined from the ice core data retrieved at the caldera in 2004. The results reported here verified the efficacy of our method, its assumption, and the interpretation models.

Radar remote sensing applications for small- to medium-sized UAS have recently been expanded due to the miniaturization of electronic hardware components, but physical limitations associated with the radar antenna continue to make it difficult to meet the very restrictive payload capacities and maximum takeoff weight constraints. One technique that addresses these limitations is to utilize structural antennas, or antennas that serve as a functional aircraft structure, in addition to having sensing capabilities. Designing multi-functional systems and optimizing weight necessitates detailed analysis on the effects of system structural characteristics as well as electrical performance. This paper presents a reduced-weight design for a near-HF antenna that is integrated onto a UAS that balances electrical performance and structural requirements.

We developed a portable ultra-wideband radar system capable of reconfigurable operation in multiple frequency bands (separate or simultaneous) spanning from microwaves through millimeter waves. The instrument provides a compact solution for fine-resolution measurements of elevation changes and superficial snow/firn thickness from low-altitude, mid-sized airborne platforms. In this article, we provide an overview of the radar system design and its performance during laboratory testing. We demonstrate its application in aerial surveys of snow layer thickness at S/C bands, dual-band airborne altimetry at Ku-/Ka-bands, and present first-order comparisons with coincident airborne lidar data.

This paper presents characterization of antennas with common structural beam cross-sections that are utilized as primary wing structures of unmanned aerial systems. Three different standard beam cross-sections were designed to operate at a frequency of 200 MHz. By varying the antenna’s shape, size, and feed location, the antenna bandwidths were significantly improved by up to 92-736%. This study also explores the potential applications of a carbon fiber composite material (CFRP) to fabricate a synergistic structural antenna design. While CFRP antennas offer flexibility in manufacturing with different shapes and forms, the results showed that they are equally effective structurally and electrically as typical metallic antennas. A fabricated C-channel shaped CFRP antenna provided excellent electrical performance, in terms of return loss and gain, in the Very High Frequency (VHF) range. Experimental and simulated results of the CFRP antenna were in good agreement with each other with regards to resonating frequencies and bandwidth.