This paper presents snow sounding images produced using data collected with C3/Group 2 class Aurelia X6 Pro Hexacopter integrated with a nadir-looking $2-8 \text{GHz}$ ultra-wideband frequency modulated continuous wave (FMCW) radar. First, we apply Synthetic Aperture Radar (SAR) processing methods in the along-track direction to a dataset collected in Greenland during the summer of 2024, resulting in a much improved data product showing distinct snow accumulation layers to depths exceeding 30-meters below the surface. Next, the improved data processing methods were also applied to data collected during measurements of opportunity taken over repeat passes before and after a significant snowfall event in Lawrence Kansas, USA, in the winter of 2025. The before and after snowfall images are presented and successfully demonstrate snow layer interface detection over ground near the theoretical range resolution limit of the radar. Approximately 10 cm of snowfall was detected from an altitude of 75 m above ground level (AGL). The significance of this work focuses on demonstrating a cost effective small form-factor radar integrated with a commercially available small Unmanned Aerial System (sUAS) as versatile tool for snow depth retrieval compared to competing technologies, including comparable radars operating on fixed-wing aircraft, while maintaining outstanding electrical performance.

Accurate mapping of fire perimeters and reconstruction of fire evolution are essential for fire behavior analysis, fire spread modeling and prediction, and wildland fire situational awareness. In this article, we present a new method for generating unitemporal fire perimeter maps and reconstructing grassfire evolution using low-altitude, multitemporal thermal infrared (TIR) imagery from a small unmanned aircraft system (UAS). The proposed method is novel in its ability to correct spatiotemporal variations of fire perimeters caused by longitudinal and lateral overlapping in structure-from-motion-stitched orthomosaics. It offers a simple and robust approach for mapping a large wildland fire using only a single UAS. In addition, this approach significantly reduces manual processing efforts while improving the temporal fidelity of fire representation, providing a cost-effective solution to produce spatiotemporally consistent fire representations to support modeling, analysis, and fire operations. The effectiveness of the proposed method is demonstrated and evaluated using a TIR UAS dataset collected during a 30-acre prescribed grassfire at the Anderson County Prairie Preserve, Kansas.

This paper presents initial images from a side-looking Synthetic Aperture Radar (SAR) collected using a $12-18 \text{GHz}$ ultra-wideband frequency modulated continuous wave (FMCW) radar integrated into a C3/Group-2 class Aurelia X6 Hexacopter. We performed SAR processing with motion compensation on data collected in the spring of 2025 in Lawrence KS, USA. The Hexacopter operated at a nominal altitude of 75 m above ground level (AGL) with a 45° radar look angle. We successfully generated preliminary SAR images that correlate well with visible spectrum satellite imagery of the area near the Clinton International Model Airport. This paper focuses on data processing considerations leading to the SAR images. The significance of this investigation is demonstrating the ability to produce high resolution SAR images using data from a cost-effective FMCW radar with ultra-wideband capabilities integrated with a commercially available unmanned aerial system (UAS). Continued efforts are being made to collect additional data using a two-receive-channel version of the FMCW radar and evaluate single-pass interferometric SAR (InSAR) processing techniques.

This paper presents an analysis of the bed detecting capabilities of an ice sounding radar integrated onto a small, unmanned aircraft system (UAS). We evaluated the average signal-to-noise ratio (SNR) and signal-to-interference ratio (SINR) of radar measurements collected by the UAS over Greenland's Helheim Glacier in 2022 and compared those to radar measurements collected over the same region using a radar-equipped Twin Otter around 2008. The statistical analysis presented of the SNR and the SINR shows that both systems have comparable bed detection capabilities. While the average SNR for all points considered is more than 20 dB higher for the Twin Otter system, the average SINR of both has a similar value. The overall average SINR is 9.79 dB for the UAS and 9.19 dB for the MA. As it is discussed in the paper, the lower SNR of the UAS system is attributed to its lower operating frequency, while the comparable SINR depends on various factors. The results of this paper have implications on planning and design of future field deployments.

This article presents the adaptation and integration of the University of Kansas' Multichannel Coherent Radar Depth Sounder for operation onboard the NASA Gulfstream V aircraft during the closing phase of Operation IceBridge. The mission objectives included measuring ice sheet thickness in Antarctica, imaging deep internal layers, and mapping glaciers along their flowline. First, we discuss the development of a custom four-element antenna array designed under tight structural constraints to support operation over the 236-254 MHz frequency range. We document the development of the antenna elements, feed structure, fiberglass composite fairing, and ground plane considerations for integration onto a carbon fiber composite panel. We also provide a summary of modifications to the radar electronics to support operation over the above band. This includes the implementation of a compact multichannel radar transmitter capable of a maximum peak transmit power of 1 kW per channel. Next, we discuss results from test flights over the Gulf of Mexico, conducted to assess the impulse response and sensitivity of the system and in-flight radiation pattern of the realized antenna array. Last, we discuss how the radar was used to survey the Antarctic coast in the Western Pacific Ocean Sector approximately between Davis Sea and Dumont d'Urville Sea. We completed 19 flights within 1 month, during which we collected a total of 5.5 terabytes of raw data covering similar to 21 000 km. The radar measured a maximum ice thickness of 4.484 km and mapped ice stratigraphy with a vertical resolution smaller than 10 m. Overall, the radar development, integration, and performance are satisfactory, and the field campaign is a success.

This paper presents a reconfigurable, low-cost ultra-wideband microwave radar front-end and radar demonstrator designed for nadir-looking measurements of layered media (e.g. snow or vegetation) from either a fast-moving ground-based platform or a C-3 class unmanned aerial system (UAS). The radar demonstrator uses a frequency modulated continuous-wave (FMCW) architecture and can be configured to operate in either the 2-8 GHz or in the 12-18 GHz range, providing fine vertical resolution while offering a significantly reduced weight, size, and power consumption with respect to prior implementations. We have demonstrated the operation of the system in the 2-8 GHz and 12-18 GHz bands in the laboratory; in the 2-8 GHz band using a surface-based setup in Antarctica; and in the 2.6-7 GHz band on local flight tests onboard an Aurelia X6 Pro UAS equipped with 3-D printed antennas. This paper provides an overview of the radar front-end and demonstrator design and implementation, and a summary of the different tests completed to document their performance.

Electromagnetic compatibility is a crucial factor to consider for reducing potential safety concerns while designing and operating unmanned aerial vehicles (UAVs). Radio frequency (RF) signals transmitted by nearby electronic systems, such as Wi-Fi hotspots or cellphone and television broadcast base stations, may interfere with a small UAV's command and control (C2) links, subsystems, and sensors. The interference comes through communication pathways or coupling of the RF electric field. We conducted various tests using two different UAVs to assess the impacts of radio frequency interference (RFI) on their functionality and operational safety. We used software-defined radios to generate RFI signals spanning from 60 MHz to 6 GHz. We established the signal-to-noise ratio thresholds for stable, unstable, and disrupted C2 link connections for both models operating at 2.4-2.5 GHz and identified in-band and adjacent-band RFI scenarios in which the C2 links of one UAV model may be disturbed. We also discovered that RFI signals emitted at very high frequency (VHF) bands utilized by television broadcasting channels had adverse effects on both UAVs. We identified the VHF bands and electric field strengths that adversely affected the UAV's C2 link connection and compass. We conducted flight and shielding experiments to further confirm our findings, and finally, we provide recommendations for reducing the UAV's vulnerability to RFI.

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.

One of the key components of this research has been the mapping of Antarctic bed topography and ice thickness parameters that are crucial for modelling ice flow and hence for predicting future ice loss and the ensuing sea level rise. Supported by the Scientific Committee on Antarctic Research (SCAR), the Bedmap3 Action Group aims not only to produce new gridded maps of ice thickness and bed topography for the international scientific community, but also to standardize and make available all the geophysical survey data points used in producing the Bedmap gridded products. Here, we document the survey data used in the latest iteration, Bedmap3, incorporating and adding to all of the datasets previously used for Bedmap1 and Bedmap2, including ice bed, surface and thickness point data from all Antarctic geophysical campaigns since the 1950s. More specifically, we describe the processes used to standardize and make these and future surveys and gridded datasets accessible under the Findable, Accessible, Interoperable, and Reusable (FAIR) data principles. With the goals of making the gridding process reproducible and allowing scientists to re-use the data freely for their own analysis, we introduce the new SCAR Bedmap Data Portal (https://bedmap.scar.org, last access: 1 March 2023) created to provide unprecedented open access to these important datasets through a web-map interface. We believe that this data release will be a valuable asset to Antarctic research and will greatly extend the life cycle of the data held within it. Data are available from the UK Polar Data Centre: https://data.bas.ac.uk (last access: 5 May 2023​​​​​​​). See the Data availability section for the complete list of datasets.

Due to interferences from pervasive electromagnetic emissions, the likelihood of irregular performance and possibly loss of control of an unmanned aircraft system (UAS) grows as small commercial drones are deployed in more applications. The UAS electromagnetic compatibility has therefore become a crucial factor to consider in UAS design and operation to minimize any potential safety issues. A UAS may experience radio frequency interference (RFI), a subset of a broader range of electromagnetic interference (EMI), through its communication link or capacitive coupling of the RF electrical field. We conducted measurements both outside and within a chamber to assess the impacts of front-door and back-door RFI on the C2 (command and control) link and the subsystem components of two distinct drone models. In this paper, we describe the measurement setup and procedures, present the results, and analyze the safe distances of the drones from RFI sources such as cellphone base stations and airport surveillance radar (ASR) under the impacts from these two types of RFI in this study.

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.

Abstract. Over the past 60 years, scientists have strived to understand the past, present and future of the Antarctic Ice Sheet. One of the key components of this research has been the mapping of Antarctic bed topography and ice thickness parameters that are crucial for modelling ice flow and hence for predicting future ice loss and ensuing sea level rise. Supported by the Scientific Committee on Antarctic Research (SCAR), the Bedmap3 Action Group aims not only to produce new gridded maps of ice thickness and bed topography for the international scientific community, but also to standardize and make available all the geophysical survey data points used in producing the Bedmap gridded products. Here, we document the survey data used in the latest iteration, Bedmap3, incorporating and adding to all of the datasets previously used for Bedmap1 and Bedmap2, including ice-bed, surface and thickness point data from all Antarctic geophysical campaigns since the 1950s. More specifically, we describe the processes used to standardize and make these and future survey and gridded datasets accessible under the ‘Findable, Accessible, Interoperable and Reusable’ (FAIR) data principles. With the goals to make the gridding process reproducible and to allow scientists to re-use the data freely for their own analysis, we introduce the new SCAR Bedmap Data Portal (bedmap.scar.org, last access: 18 October 2022) created to provide unprecedented open access to these important datasets, through a user-friendly webmap interface. We believe that this data release will be a valuable asset to Antarctic research and will greatly extend the life cycle of the data held within it. Data are available from the UK Polar Data Centre: https://data.bas.ac.uk.

The National Aeronautics and Space Administration (NASA)’s Operation IceBridge (OIB) was a 13‐year (2009–2021) airborne mission to survey land and sea ice across the Arctic, Antarctic, and Alaska. Here, we review OIB’s goals, instruments, campaigns, key scientific results, and implications for future investigations of the cryosphere. OIB’s primary goal was to use airborne laser altimetry to bridge the gap in fine‐resolution elevation measurements of ice from space between the conclusion of NASA’s Ice, Cloud, and land Elevation Satellite (ICESat; 2003–2009) and its follow‐on, ICESat‐2 (launched 2018). Additional scientific requirements were intended to contextualize observed elevation changes using a multisensor suite of radar sounders, gravimeters, magnetometers, and cameras. Using 15 different aircraft, OIB conducted 968 science flights, of which 42% were repeat surveys of land ice, 42% were surveys of previously unmapped terrain across the Greenland and Antarctic ice sheets, Arctic ice caps, and Alaskan glaciers, and 16% were surveys of sea ice. The combination of an expansive instrument suite and breadth of surveys enabled numerous fundamental advances in our understanding of the Earth’s cryosphere. For land ice, OIB dramatically improved knowledge of interannual outlet‐glacier variability, ice‐sheet, and outlet‐glacier thicknesses, snowfall rates on ice sheets, fjord and sub‐ice‐shelf bathymetry, and ice‐sheet hydrology. Unanticipated discoveries included a reliable method for constraining the thickness within difficult‐to‐sound incised troughs beneath ice sheets, the extent of the firn aquifer within the Greenland Ice Sheet, the vulnerability of many Greenland and Antarctic outlet glaciers to ocean‐driven melting at their grounding zones, and the dominance of surface‐melt‐driven mass loss of Alaskan glaciers. For sea ice, OIB significantly advanced our understanding of spatiotemporal variability in sea ice freeboard and its snow cover, especially through combined analysis of fine‐resolution altimetry, visible imagery, and snow radar measurements of the overlying snow thickness. Such analyses led to the unanticipated discovery of an interdecadal decrease in snow thickness on Arctic sea ice and numerous opportunities to validate sea ice freeboards from satellite radar altimetry. While many of its data sets have yet to be fully explored, OIB’s scientific legacy has already demonstrated the value of sustained investment in reliable airborne platforms, airborne instrument development, interagency and international collaboration, and open and rapid data access to advance our understanding of Earth’s remote polar regions and their role in the Earth system.

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.

Manifold calibration improves parametric angle estimator accuracy and resolution performance by reducing the mismatch between the model of an array's response to directional sources and truth. This article presents nonparametric array manifold calibration for a multichannel ice-penetrating synthetic aperture radar (SAR) sounder used for imaging subglacial morphology with parametric angle estimation in tomography. In this study, we outline a methodology for identifying scatterers at known angles from multichannel imagery by aligning our measurements to an independent fine-resolution satellite-derived digital elevation model of the Arctic that extends beyond the swath of the SAR. We adopt a support statistic based on our partial knowledge of the array response to identify approximately single-source measurements in our scenes. This technique is a departure from traditional approaches to the sounder array characterization problem that require measurements of flat, specular surface reflections from a maneuvering platform. We aggregate observations of single sources and measure manifold corrections relative to our nominal model from the principal eigenvector of our array covariance. We demonstrate the application of three measured manifolds in tomography and compare performance to a nominal manifold that assumes isotropic radiators and known array geometry. We present radar-derived topography of exposed rock and sea ice in the Canadian Arctic Archipelago under the measured and nominal manifolds and report improved vertical accuracy realized with a measured manifold model assumed by the MUltiple SIgnal Classification angle estimators in 3-D image formation.

Tree heights are important input for many inventory and ecosystem models. While optical and infrared sensors such as LiDAR are widely used in forest surveys, microwave radar has the unique advantage of being able to operate in bad weather or poor visibility conditions. In this work, we employed a LiDAR combined with a compact ultra-wideband frequency modulated continuous wave (FMCW) radar onboard a Single Otter aircraft to collect data over forested areas in Alaska. While the primary focus of the mission was to map the surface elevation and snow thickness of Alaskan glaciers as a part of NASA Operation IceBridge (OIB), we recorded LiDAR and radar returns during the transit flights to analyze backscattering signatures from tree-covered areas, thereby assessing the potential application of our radar to forest and vegetation remote sensing. We analyzed these measurements and estimated the tree heights along the flight trajectory. The very good agreement between the tree height profiles from the two instruments shows promising results for wide area forestry studies using microwave radar.

Abstract. Radar sounding of the thickness of temperate glaciers is more challenging than for polar ice sheets, due to the former's greater volume scattering (englacial water), surface scattering (crevasses and debris) and dielectric attenuation rate (warmer ice). Lower frequency (~1–100 MHz) radar sounders are commonly deployed to mitigate these effects, but the lack of a synthesis of existing radar-sounding surveys of temperate glaciers limits progress in system and survey design. Here we use a recent global synthesis of measured glacier thickness to evaluate the relation between the radar center frequency and maximum thickness. From a maximum reported thickness of ~1500 m near 1 MHz, the maximum thickness sounded decreases with increasing frequency by ~500 m per frequency decade. Newer airborne radar sounders generally outperform older, ground-based ones at comparable frequencies, so radar-sounder success is also influenced by system design and processing methods. Based on globally modeled glacier thicknesses, we conclude that a multi-element airborne radar sounder with a center frequency of ≤ 30 MHz could survey most temperate glaciers more efficiently than presently available systems.

We present an ultrawideband (UWB) frequency-modulated (FM) microwave radar instrument capable of preserving cm-scale vertical resolution from a very long range (verified up to ~6 km). The system can operate either as a conventional continuous-wave FM radar (2-18 GHz) or in time-delayed stretch processing mode (2-14 GHz), providing high sensitivity, fine range resolution, and very low-range sidelobes. We present an overview of the system and laboratory test results to validate its performance. As a practical demonstration of its capabilities, we tested the system's ability to map snow cover thickness on the Arctic marine ice. We present sample results from airborne measurements carried out at altitudes between ~500 m and ~6 km above the ground level onboard a long-range fixed-wing platform.

We developed an airborne radar system capable of simultaneous operation at Ku- and Ka- bands. The system is compact and lightweight, and supports coincident altimetry measurements in both bands with ultra-wide bandwidth (up to 6 GHz). Wide-band data can be used to obtain fine vertical resolution or sub-banded to match the operational parameters of orbital instruments. We installed the system onboard a Twin Otter aircraft and collected data over the East Greenland ice sheet margin and on Arctic marine ice during a test field campaign conducted in the summer of 2019. The work was carried as an international collaboration to support the validation of ESA's CryoSat-2 and NASA's ICESat-2 measurements. In this paper, we present an overview of the instrument and its airborne test configuration and field operation; provide initial results from field trials; and outline the potential application of dual-band airborne radar data for the validation of satellite instruments.