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.

This paper presents enhanced data products from an airborne ultra-wideband frequency modulated (FM) microwave radar capable of measuring cm-scale of snow cover thickness from high altitude (>1.3 km above ground level, AGL). We use advanced radar hardware combined with a custom synthetic aperture radar (SAR) algorithm applied in post-processing to demonstrate a unique capability of retrieving snow cover depth values down to ~5 cm over a <35-m footprint from altitudes as high as 5,800 m AGL. The improved detection capabilities presented here will be advantageous to maximize mapping coverage while maintaining fine granularity during high altitude surveys.

This letter presents an experimental study on the use of ultrawideband (UWB) probing radar as a new type of sensor to efficiently and nondestructively measure plant structure for breeding applications, focusing here on wheat canopy height. Wheat canopy height is an important morphological and developmental phenotype that indicates plant growth and it is related to biomass. Currently, taking manual measurements of canopy height is labor-intensive and has become a bottleneck for genomic selection and breeding programs. Other recently proposed noncontact methods only sense the top of the canopy, thereby having to make assumptions about the elevation of the base of the canopy. We propose the use of UWB radar as a phenotyping sensor for measuring a variety of plant characteristics. A direct measurement of wheat canopy height is investigated with the capability of sensing both the top and the bottom of the canopy simultaneously. To test this idea, we developed a 2–18-GHz frequency-modulated-continuous-wave (FMCW) radar prototype and a mobile phenotyping platform. The sensor was tested by collecting near-nadir coherent radar measurements of wheat canopies of breeding plots at different growth stages. The performance to detect both the top and bottom of the canopy was examined at different frequency bands.

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.

We designed a Ka-band prototype radar altimeter operated at a center frequency of 35 GHz with a 6 GHz bandwidth. The instrument was intended for fine-resolution verification and validation of space borne altimetry datasets. We installed it onboard the NASA C-130 aircraft in conjunction with two other wideband microwave instruments and collected airborne altimetry data over Greenland land ice and arctic sea ice during the 2015 NASA Operation IceBridge arctic campaign. Apart from the major application of verification and calibration of satellite-based measurements, data from this instrument can be used to derive snow grain size because of the dominant effect of volume scattering in radar signatures. In this paper, we briefly describe the system design and the installation on the NASA C-130, discuss the observed penetration depths of Ka-band signals into the snowpack, present sample results of optical-equivalent snow grain size estimates from radar measurements over the dry snow zone using a simplified snowpack model. We show that the observed penetration depths and the snow grain size estimates from the airborne Ka-band radar retrievals agree well with the model and in-situ snow-pit measurements.

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.

Snow in mountainous areas provides freshwater resources for lower basins and coastal areas. Snow layering at mountain summits contains information about local seasonal snow accumulation and climate history. Knowledge of snow depths is required to estimate the snow water equivalent. However, monitoring spatial distribution and temporal changes in snow depth and accumulation over remote mountains and glaciers in wide areas is challenging because of limited accessibility for in-situ measurements. As a part of NASA Operation IceBridge missions, we took airborne radar measurements of snow over Alaskan mountains, icefields and glaciers in late May of 2018, with a compact frequency-modulated continuous wave radar system, operating from 2 GHz to 8 GHz and installed on a Single Otter aircraft. In this paper, we describe the radar instrument, its installation onto the platform, the data collection and processing activities, and report the major results from these surveys. We observed seasonal snow depth between ~0.3 m to ~15 m for elevations above sea level from ~1726 m to ~3624 m. We successfully mapped snow accumulation layers to depths exceeding ~85 m below the surface at high-elevation summits of Mount Wrangell and Bona. The traced snow depth profiles over glaciers and accumulation layers at mountain summits point to the utility of these data to the study of water resource management, hydrology modelling, and regional climate change.

This paper presents recent updates to the CReSIS radar sensor package and the platforms supporting these sensors. These sensors cover a wide frequency range (14 MHz to 38 GHz). The specific frequency bands are chosen to balance between bandwidth available and signal penetration. The wide frequency range is also used for measuring different phenomenology. CReSIS has integrated these radar systems, including antennas, on a wide variety of fixed wing crewed aircraft, several UAV platforms, and for ground-based applications. The software for processing the radar data is now open source and an overview of the capabilities and how to access and use the software are presented. Finally, example data products which explore the new capabilities of the sensors and platforms are given.

The basal topography of most of the glaciers that drain the ice caps of the Canadian Arctic Archipelago is largely unknown. To measure the basal topography, NASA Operation IceBridge flew a radar depth sounder in a wide swath mode with three transmit beams to image the glacier beds during three flights over the archipelago in 2014. We describe the measurement setup of the radar system, the algorithms used to process the data to produce a 3D image of the glacier bed, show digital elevation model (DEM) results of the beds, and provide a basic assessment of the tracking algorithm used to extract the DEM.

We have developed an unmanned aerial system consisting of a compact sounding radar operating in the frequency bands of 14 and 35 MHz integrated into a fixed-wing UAV for remote surveys of glaciers and ice-sheets. The system is capable of collecting coherent sounding measurements along multiple parallel tracks. With the use of differential GPS for precise trajectory determination, we demonstrate multipass SAR array processing. The system was recently deployed by CReSIS personnel in the spring of 2016 to survey the Russell glacier in Greenland. This paper reports on the instrumentation including the integration of the radar, antennas, and aircraft; the survey flights in Greenland; and results from measurements collected at 35 MHz.

In the above paper[1], there is an error inTable I. The value “30” in the bottom row, fifth column should be “350.” The corrected table is provided here.

We present an ultrawideband frequency-modulated continuous-wave radar for airborne measurements of snow thickness. The radar operates over a frequency range of 2-18 GHz and is capable of about 1.4-cm range resolution at a nominal survey altitude of 500 m. The system was installed on a Twin Otter and used to collect data to demonstrate the capability of fine-resolution measurements of snow thickness over both sea ice and land near Barrow, AK. Data collected over a relatively smooth water surface, a lead, were used to deconvolve system effects to reduce range sidelobes and obtain close-to-ideal range resolution. Radar data collected over snow covered sea ice and land from the field campaign showed that we can map air-snow and snow-ice interfaces of thin and thick snow. The radar-derived snow thickness data are in a very good agreement with the in situ measured data with a correlation of 0.88.

In this paper, we present the development of a multi-channel VHF/UHF ultra-wideband airborne radar sounder and imager for measurements of polar ice sheets. The radar was developed at the Center for Remote Sensing of Ice Sheets (CReSIS) for operation onboard the German Alfred Wegener Institute (AWI) Basler BT-67 aircraft. The system operates from 150 to 600 MHz corresponding to a vertical resolution of 33 cm in free space. The radar is equipped with three 4-m long 8-element antenna subarrays installed under the fuselage and both wings to support 8 transmit and 24 receive channels. The radar waveform from each transmit channel can be configured individually to enable real-time transmit beamforming for wide-swath ice bed imaging of up to 10 km wide. The radar system was deployed to Greenland in the spring of 2016 as a part of the joint AWI/CReSIS test campaign to conduct measurements over glaciers. Sample radar data from this field campaign are presented to illustrate the capability of the radar.

Prof. Richard Moore introduced me to FM-CW radars on my first day at the University of Kansas as a graduate student in 1979 and asked me to put together a radar using laboratory test equipment. I put it together, but it did not provide the results we wanted for detecting buried pipes. This was mainly because of the lack of suitable inexpensive RF and digital technologies at that time. Prof. Moore was a strong advocate for using ultra-wideband FM-CW radars. We are able to implement what he taught me because of recent advances in RF microwave and digital technologies, allowing us to develop the ultra-wideband radars Prof. Moore envisioned for remote sensing of snow and ice. We developed ultra-wideband radars for airborne measurements over ice and snow. One of these radars operates over a frequency range of 150-600 MHz for sounding ice sheets, imaging the ice-bed interface, and mapping internal layers in polar firn and ice; additional radars operate over the frequency ranges of 2-8 and 12-18 GHz for airborne measurements of the thickness of snow over sea ice and land and surface elevation measurements, respectively.

Satellite radar altimeter (RA) measurements are important for continued monitoring of rapidly changing polar regions. In 2010, the European Space Agency launched CryoSat-2 carrying SIRAL, a Ku-band RA with objectives of determining the thickness and extent of sea ice and the topography of the ice sheets. One difficulty with Ku-band radar surveys over snow and ice is unknown penetration of RA signal into snow cover. Improving our understanding of the interactions of RA signals with snow and ice is needed to produce accurate elevation products. To this end, we developed a low-power, ultrawideband (12-18 GHz) RA for airborne surveys to provide fine resolution measurements capable of detecting both scattering from the surface and layers within sea ice and ice sheets. These measurements provide a means of identifying the dominant scattering location of lower resolution RA measurements comparable to satellite-based instruments. We generated two products: a full-bandwidth waveform (FBW) to identify scattering targets at fine resolution and a reduced-bandwidth waveform (RBW) to represent conventional RA measurements. Retrackers are used to generate height estimates over various surface conditions for comparisons. Over ice sheets, the leading-edge tracker provided consistent ice-surface elevation measurements between the FBW and RBW results; however, there were significant differences between the results from the centroid tracker. Over sea ice, the location of the dominant return between the results from snow-covered sea ice is highly variable. This paper provides an overview of RA surveys in polar regions, a description of the CReSIS system, and a discussion of the results.

A wideband multi-channel airborne sounding and imaging radar for cryospheric remote sensing applications has been recently developed by the Center for Remote Sensing of Ice Sheets (CReSIS). The radar is designed to measure ice thickness, image the ice-bed interface, and map internal layers in ice sheets and glaciers. This newly-developed radar uses the wide bandwidth for high-resolution imaging and cross-track array processing for suppression of surface clutter. The radar was integrated onto a BT-67 aircraft and completed its first field deployment in Antarctica during the 2013/2014 Austral Summer season. This paper focuses on the development and deployment of the radar. A few sample results from the field survey in Antarctica are also presented to demonstrate the high resolution features of the radar.

This paper presents a radar sensor package specifically developed for wide-coverage sounding and imaging of polar ice sheets from a variety of aircraft. Our instruments address the need for a reliable remote sensing solution well-suited for extensive surveys at low and high altitudes and capable of making measurements with fine spatial and temporal resolution. The sensor package that we are presenting consists of four primary instruments and ancillary systems with all the associated antennas integrated into the aircraft to maintain aerodynamic performance. The instruments operate simultaneously over different frequency bands within the 160 MHz-18 GHz range. The sensor package has allowed us to sound the most challenging areas of the polar ice sheets, ice sheet margins, and outlet glaciers; to map near-surface internal layers with fine resolution; and to detect the snow-air and snow-ice interfaces of snow cover over sea ice to generate estimates of snow thickness. In this paper, we provide a succinct description of each radar and associated antenna structures and present sample results to document their performance. We also give a brief overview of our field measurement programs and demonstrate the unique capability of the sensor package to perform multifrequency coincidental measurements from a single airborne platform. Finally, we illustrate the relevance of using multispectral radar data as a tool to characterize the entire ice column and to reveal important subglacial features.

The National Aeronautics and Space Administration (NASA) initiated a program called Operation IceBridge for monitoring critical parts of Greenland and Antarctica with airborne LIDARs until ICESat-II is launched in 2016. We have been operating radar instrumentation on the NASA DC-8 and P-3 aircraft used for LIDAR measurements over Antarctica and Greenland, respectively. The radar package on both aircraft includes a radar depth sounder/imager operating at the center frequency of 195 MHz. During high-altitude missions flown to perform surface-elevation measurements, we also collected radar depth sounder data. We obtained good ice thickness information and mapped internal layers for both thicker and thinner ice. We successfully sounded 3.2-km-thick low-loss ice with a smooth surface and also sounded about 1-km or less thick shallow ice with a moderately rough surface. The successful sounding required processing of data with an algorithm to obtain 56-dB or lower range sidelobes and array processing with a minimum variance distortionless response algorithm to reduce cross-track surface clutter. In this paper, we provide a brief description of the radar system, discuss range-sidelobe reduction and array processing algorithms, and provide sample results to demonstrate the successful sounding of the ice bottom interface from high altitudes over the Antarctic and Greenland ice sheets.

A Ku-band ultra-wideband radar altimeter with 6 GHz of bandwidth has been developed for surface elevation measurements in polar ice sheets. The radar is equipped with a newly-designed chirp generator with sufficient linearity to resolve adjacent targets at ranges of 500 m or more. This capability allows the airborne radar to resolve closely spaced sub-surface reflectors and internal layers in polar firn. In this paper, we discuss the design and development of the radar and present sample results from recent field measurements over Byrd Glacier in Antarctica.

A comparison of snow depths on sea ice was made using airborne altimeters and an Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) simulator. The data were collected during the March 2006 National Aeronautics and Space Administration (NASA) Arctic field campaign utilizing the NASA P-3B aircraft. The campaign consisted of an initial series of coordinated surface and aircraft measurements over Elson Lagoon, Alaska and adjacent seas followed by a series of large-scale (100 km × 50 km) coordinated aircraft and AMSR-E snow depth measurements over portions of the Chukchi and Beaufort seas. This paper focuses on the latter part of the campaign. The P-3B aircraft carried the University of Colorado Polarimetric Scanning Radiometer (PSR-A), the NASA Wallops Airborne Topographic Mapper (ATM) lidar altimeter, and the University of Kansas Delay-Doppler (D2P) radar altimeter. The PSR-A was used as an AMSR-E simulator, whereas the ATM and D2P altimeters were used in combination to provide an independent estimate of snow depth. Results of a comparison between the altimeter-derived snow depths and the equivalent AMSR-E snow depths using PSR-A brightness temperatures calibrated relative to AMSR-E are presented. Data collected over a frozen coastal polynya were used to intercalibrate the ATM and D2P altimeters before estimating an altimeter snow depth. Results show that the mean difference between the PSR and altimeter snow depths is -2.4 cm (PSR minus altimeter) with a standard deviation of 7.7 cm. The RMS difference is 8.0 cm. The overall correlation between the two snow depth data sets is 0.59.

We present a first assessment of airborne laser and radar altimeter data over snow-covered sea ice, gathered during the National Aeronautics and Space Administration Operation IceBridge Mission. We describe a new technique designed to process radar echograms from the University of Kansas snow radar to estimate snow depth. We combine IceBridge laser altimetry with radar-derived snow depths to determine sea ice thickness. Results are validated through comparison with direct measurements of snow and ice thickness collected in situ at the Danish GreenArc 2009 sea ice camp located on fast ice north of Greenland. The IceBridge instrument suite provides accurate measurements of snow and ice thickness, particularly over level ice. Mean IceBridge snow and ice thickness agree with in situ measurements to within$\sim$0.01 and$\sim$0.05 m, respectively, while modal snow and ice thickness estimates agree to within 0.02 and 0.10 m, respectively. IceBridge snow depths were correlated with in situ measurements ($R = 0.7$, for an averaging length of 55 m). The uncertainty associated with the derived IceBridge sea ice thickness estimates is 0.40 m. The results demonstrate the retrieval of both first-year and multiyear ice thickness from IceBridge data. The airborne data were however compromised in heavily ridged ice where snow depth, and hence ice thickness, could not be measured. Techniques developed as part of this study will be used for routine processing of IceBridge retrievals over Arctic sea ice. The limitations of the GreenArc study are discussed, and recommendations for future validation of airborne measurements via field activities are provided.

Antarctic sea ice and its snow cover are integral components of the global climate system, yet many aspects of their vertical dimensions are poorly understood, making their representation in global climate models poor. Remote sensing is the key to monitoring the dynamic nature of sea ice and its snow cover. Reliable and accurate snow thickness data are currently a highly sought after data product. Remotely sensed snow thickness measurements can provide an indication of precipitation levels, predicted to increase with effects of climate change in the polar regions. Airborne techniques provide a means for regional-scale estimation of snow depth and distribution. Accurate regional-scale snow thickness data will also facilitate an increase in the accuracy of sea ice thickness retrieval from satellite altimeter freeboard estimates. The airborne data sets are easier to validate with in situ measurements and are better suited to validating satellite algorithms when compared with in situ techniques. This is primarily due to two factors: better chance of getting coincident in situ and airborne data sets and the tractability of comparison between an in situ data set and the airborne data set averaged over the footprint of the antennas. A 2–8-GHz frequency modulated continuous wave (FMCW) radar loaned by the Center for Remote Sensing of Ice Sheets to the Australian Antarctic Division is used to measure snow thickness over sea ice in East Antarctica. Provided with the radar design parameters, the expected performance parameters of the radar are summarized. The necessary conditions for unambiguous identification of the air/snow and snow/ice layers for the radar are presented. Roughnesses of the snow and ice surfaces are found to be dominant determinants in the effectiveness of layer identification for this radar. Finally, this paper presents the first in situ validated snow thickness estimates over sea ice in Antarctica derived from an FMCW radar on a helicopterborne platform.

Currently, CSARP-Flight only works with the MCoRDS system. However, other radar systems at CReSIS would benefit from the software. Most of the systems would only need firmware changes to work properly with the software, enhancing their capabilities. Using a single software control suite on all radar systems would also facilitate operators controlling multiple systems on missions. To increase performance of CSARP-Flight, the data visualization should be modified to use OpenGL libraries instead of the current Qwt libraries. OpenGL would allow the graphics processing unit (GPU) to perform the visualizations, reducing the strain on the CPU and freeing RAM for other purposes. The combination of MCoRDS and CSARP-Flight has proven to be very beneficial to CReSIS. Airborne missions have gathered high quality data using the system which will hopefully further our understanding of ice sheets and our world.

An ultra-wideband, frequency modulated, continuous wave radar working from 2.0 to 6.5 GHz was designed, built and tested at the Center for Remote Sensing of Ice Sheets (CReSIS) at the University of Kansas to measure snow thickness over sea ice. Improvements and modifications to the existing radar, compared to previous versions, allow for snow thickness measurements from fast-moving, long-range aircraft. Over the past year, the radar has recorded snow thickness measurements over sea ice in the Arctic and Antarctic oceans as part of NASA's Operation Ice Bridge.

The Multichannel Coherent Radar Depth Sounder (MCoRDS) system was developed by the Center for Remote Sensing of Ice Sheets (CReSIS) to map the thickness of ice sheets. This radar system was used in Antarctica as one of the primary sensors for NASA's Operation Ice Bridge (OIB) during the fall of 2009. Compared to its predecessors, MCoRDS features several new capabilities which enabled it to successfully capture ice thickness measurements over multiple glaciers on an aerial platform. This paper will focus on the capabilities of MCoRDS and also provide a sample of the processed radar results.

Information on the bedrock topography below the Greenland and Antarctic ice sheets is vital to developing models of future sea-level rise. To measure the topography, advanced data acquisition and processing techniques, including Synthetic Aperture Radar (SAR), are required. This work investigates the optimal beamwidth that would enable SAR processing to maximize the signal to noise ratio of the target. Platform height above the ice surface and bedrock roughness determine the optimal beamwidth. We found that for data collected at a “typical” altitude of 867 m, the optimal beamwidth is about 8°. In the high-altitude case, we found that beamwidth did not have a significant effect on the signal-to-noise ratio. This is probably related to scattering from the ice surface.

We discuss results from a high-sensitivity, multichannel, very high frequency, and surface-based radar depth sounder/imager. The instrument was used to map deep internal layers and characterize basal conditions over a 240- km2grid in the vicinity of the West Antarctic Ice Sheet Divide ice core site. The ice thickness at the core site was found to be about 3470 m, and we detected internal layers to within 350 m of the ice/bed interface. Radar-detected layer stratigraphy does not show evidence of flow-induced disturbances that might complicate the depth-age relationship and the interpretation of climate history preserved in the ice. We also found that bed reflectivity over the region varies by more than 30 dB. Approximately 15 dB of this variability appears to be the result of transitions from a frozen to a thawed bed in a number of places. The remainder probably results from changes in bed roughness. Our data are important for planning drilling to the bed, as well as providing constraints and boundary conditions for regional ice-flow models.

In August of 2008 a radar survey was conducted at the NEEM site in Greenland. An example echogram showing internal layers all the way to the bed, a digital elevation map around the drill site, and a side looking synthetic aperture radar image will be presented. The echogram appears to show a fairly continuous Eemian layer where predicted by modeling. Additionally the area around the drill site is very flat although some slope variation is observed. Finally side looking SAR images show reflected power variations that need more analysis to determine their source.

Many satellite, airborne, and in situ observations have been made to better understand the mass balance of the ice sheets. Satellite missions such as GRACE, ICESat, and Cryosat provide broad coverage, but are only capable of collecting data at relatively coarse temporal and spatial resolutions. Satellite observations alone are not sufficient to fully understand all mechanisms responsible for changes in the overall ice sheet mass balance. While these are sufficient over much of the interior of the ice sheet, to understand and model the dynamics of fast flowing glaciers and the margins of the ice sheet, finer resolution data are required. Airborne platforms, especially autonomous platforms, allow for key regions of the ice sheets to be measured with fine-resolution remote sensing instruments. These platforms provide more accurate ice thickness estimates, internal layer mapping, and ice-bedrock interface imaging. To address this gap in the observations, we are designing and developing an instrumentation suite to be deployed on crewed and uncrewed aircrafts. Here we will focus on two radars in the instrumentation suite: an accumulation radar and a radar altimeter. The altimeter will be capable of measuring surface elevation and near-surface internal layers to a depth of about 10 m. The accumulation radar will be capable of measuring internal layers to a depth of about 100 m. A previously developed 150 MHz radar depth sounder/imager will be used to map layers below 100 m, as well as the ice-bedrock interface. This radar is beyond the scope of this paper. Field data collection using these systems will be performed simultaneously, providing a fine-resolution characterization of the ice sheet from surface to bedrock. The altimeter provides annual and short-term information on the accumulation, while the accumulation radar provides information on the decadal scale variability. The depth sounder provides information on the century scale variability. Initial data collection occurred during the early spring 2009 Greenland field season; additional data collection will continue during future campaigns both in Greenland and Antarctica. System refinements will allow for this suite to be deployed on uncrewed aerial vehicles (UAVs), also being developed at the Center for Remote Sensing (CReSIS) at the University of Kansas.

Sea-level rise will affect populations worldwide with considerable and lasting consequences in the not-too-distant future. Accurate measurement of fast flowing outlet glaciers in Greenland and Antarctica are of vital importance to ice sheet models that predict the course of sea-level rise. The Center for the Remote Sensing of Ice Sheets (CReSIS) has developed a suite of tools designed for use with data collected by CReSIS depth sounding radar platforms. This suite includes algorithms for removing clutter and noise from coherent radar data, and the results show successful sounding of some of these fast-flowing glaciers for the first time.

A VHF-band radar is being developed to characterize polar ice sheets and their basal conditions from a UAV developed specifically for low-altitude polar operation. The radar's 195-MHz center frequency, 30-MHz bandwidth, and 200-W transmit power will map internal layers and ice thickness with a depth resolution of less than 3 m in ice, and image the ice-bed interface. To satisfy the mass and volume constraints of the UAV, a distributed architecture was developed employing transmit/receive modules mounted on each of the eight wing-mounted wide-bandwidth Vivaldi antennas. An eight-channel digital waveform generator will be used to create transmit waveforms to simultaneously measure ice thickness and map internal layers along the nadir track, and image ice-bed interface on the left and right sides of the platform in strip-map mode.

Sea ice is generally covered with snow. Information about snow thickness is essential to estimate sea-ice thickness from freeboard measurements and to model ocean-ice-atmosphere interactions. This paper discusses an algorithm to measure snow thickness by processing of coincident radar and the laser altimetry data. Radar return is dominated by the reflected signal from the snow-ice interface whereas laser return by the snow-air interface. Radar data are processed to obtain an accurate estimate of range to the snow-ice interface using aircraft trajectory derived from differential Global Positioning system (GPS) and Inertial Navigation System (INS). Laser data are processed to obtain range to the snow-air interface. The snow cover thickness is estimated from the difference in the radar and laser range estimates. The snow-thickness estimates obtained from radar and laser altimeter are comparing with the in situ snow thickness data collected over the Chukchi and Beufort lines.

The objective of the PARIS NASA Instrument Incubator Project was to demonstrate successful ice thickness sounding from a high-altitude airborne radar. This paper describes key features of the system, including the radar and the processing algorithm. Test flights over the ice sheets of Greenland produced good results.

Elevation data derived from space-based altimeter measurements over landand sea-ice are key to understanding the Earth's ice mass balance. This importance is recognized by both NASA, as expressed in the laser altimeter GLAS on ICESat, and ESA, as expressed in the radar altimeter SIRAL on CryoSat. The JHU/APL Delay-Doppler Phase-monopulse (D2P) radar altimeter has shown its value as a scientific/calibration/validation instrument, and has participated in two airborne field campaigns sponsored by NASA and ESA to collect simultaneous radar and laser altimeter measurements over land and sea ice. These measurements are unique; they provide colocated, cross-calibrated, and high-precision altimetry data over a variety of geophysical ice conditions in two very different frequency regimes. In this paper, we give an overview of the CryoVEx field campaign in 2003 including basic system parameters, flight tracks, and sample waveforms from the airborne experiment.

The primary objectives of LaRA-2002 were to assemble measurements of land and sea ice with simultaneous observations from a low-altitude aircraft by laser and radar altimeters. Data from the mission was expected to illustrate similarities and differences between these two very different means of measuring surface height. These objectives were met. This paper provides an overview of the project, and includes highlights of the results.

Using ground-penetrating radars to investigate the subsurface of Mars will be a key scientific objective over the next several years, especially in light of the large possibility that water could exist within the planet. Radars operating from a few megahertz up to a gigahertz will be able to provide valuable information concerning the subsurface electrical structure at resolutions ranging from a few centimeters near the surface to a few tens of meters at greater depths. One of the major goals of the work presented was to develop a lightweight, low-power, frequency-modulated radar system that could be used to detect subsurface deposits of ice and water. An inexpensive prototype system was developed using off-the-shelf connectorized components and evaluation boards. To verify the operation of this prototype system, a preliminary experiment was conducted in Lawrence, Kansas. Next, experiments were conducted over locations containing permafrost and ice in Fairbanks, Alaska. Results from these experiments are presented.

Ground-penetrating radar (GPR) is a remote sensing technique used to obtain information on subsurface features from data collected over the surface. The process of collecting data may be viewed as mapping from the object space to an image space. Since most GPRs use broad beam width antennas, the energy reflected from a buried structure is recorded over a large lateral aperture in the image spare, migration algorithms are used to reconstruct an accurate scattering map by refocusing the recorded scattering events to their true spatial locations through a backpropagation process. The goal of this paper is to present a pair of finite-difference time-domain (FDTD) reverse-time migration algorithms for GPR data processing. Linear inverse scattering theory is used to develop a matched-filter response for the GPR problem. The reverse-time migration algorithms, developed for both bistatic and monostatic antenna configurations, are implemented via FDTD in the object space. Several examples are presented.