We developed a multichannel wideband synthetic aperture radar (SAR) that operates over a frequency range of 190-450 MHz for measurements over the ice sheets in Antarctica and Greenland. The antenna-array, which consists of eight elements housed in a certified external structure for a BASLER aircraft, was used for measurements during the 2013-2014 Antarctic field season. We performed measurements with this system in conjunction with two ultra-wideband radars operating over a frequency range of 2-8 GHz and 12-18 GHz on Siple Coast ice streams in West Antarctica during December 2013 and January 2014. We sounded ice thicker than 2 km with a signal-to-noise ratio (SNR) of more than 20 dB in an area with two-way ice loss of about 27 dB/km. The same system also simultaneously mapped near-surface internal layers with submeter resolution from the ice-surface to a depth of about 1100 for 1200 m thick ice. In this paper, we provide a detailed overview of the radar instrumentation and signal processing algorithms and present a few sample results. The radar will be operated over a frequency range of 150-550 MHz with a 24-element antenna-array for wide-ranging measurements over the Greenland and Antarctic ice sheets, starting around August 2015.

The concept of multi-input multi-output (MIMO) radar has drawn considerable attention in recent years. One of the key technologies to enable the MIMO radar is to design the orthogonal signals to support simultaneous transmission from multiple antennas, because the orthogonality characteristics have a keen impact on the performance of the MIMO radar. In this paper, a novel approach to generate and process mutually orthogonal waveforms based on orthogonal frequency division multiplexing (OFDM) signals is proposed. The ambiguity function of the suggested waveforms is derived and analyzed based on the statistical derivation. A corresponding multi-channel signal processing scheme at the receiver part is proposed to eliminate the Doppler influence and suppress the cross-channel interference. Numerical simulation results based on the Monte Carlo method are presented to validate the theoretical derivation and analysis. The findings indicate that the interchannel interference for moving targets can be eliminated and that the proposed interleaved OFDM signals are a suitable waveform set for the MIMO radar applications.

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.

Significant progress has been made in the development of next-generation ice-sheet models to simulate the response of large ice sheets in a warming climate and to determine their contribution to sea level rise over the next century. Good progress has also been made in characterizing the bed topography of a few key outlet glaciers in Greenland and Antarctica. These new models and data have been used to generate sea level rise projections of between 26 and 98 cm by the end of this century. However, there is still a need to better understand both ice-stream dynamics near the grounding lines and ice-shelf-ocean interactions, as well as to incorporate this understanding into improved models to reduce the large uncertainly in sea level rise predictions. We developed an ultra-wideband radar that operates over a frequency range of 150-450 MHz for fine-resolution measurements over the ice sheets in Antarctica and Greenland. This radar was developed specifically to obtain measurements over ice shelves and fast-flowing glaciers. The current antenna-array, which consists of eight elements, is housed in a certified antenna structure for a Basler aircraft. It will be soon expanded to 24 elements to cover a wider frequency range (150-600 MHz). During December 2013 and January 2014, we collected data over a few ice streams and glaciers in Antarctica. This paper will provide an overview of the radar, antenna array and results from the 2013-2014 deployment in Antarctica, as well as our plans for a larger array and wider bandwidth system.

We developed a compact radar for use on a small UAV to conduct measurements over the ice sheets in Greenland and Antarctica. It operates at center frequencies of 14 and 35 MHz with bandwidths of 1 MHz and 4 MHz, respectively. The radar weighs about 2 kgs and is housed in a box with dimensions of 20.3 cm x 15.2 cm x 13.2 cm. It transmits a signal power of 100 W at a pulse repletion frequency of 10 kHz and requires average power of about 20 W. The antennas for operating the radar are integrated into the wings and airframe of a small UAV with a wingspan of 5.3 m. We selected the frequencies of 14 and 35 MHz based on previous successful soundings of temperate ice in Alaska with a 12.5 MHz impulse radar [Arcone, 2002] and temperate glaciers in Patagonia with a 30 MHz monocycle radar [Blindow et al., 2012]. We developed the radar-equipped UAV to perform surveys over a 2-D grid, which allows us to synthesize a large two-dimensional aperture and obtain fine resolution in both the alongand cross-track directions. Low-frequency, high-sensitivity radars with 2-D aperture synthesis capability are needed to overcome the surface and volume scatter that masks weak echoes from the ice-bed interface of fast-flowing glaciers. We collected data with the radar-equipped UAV on sub-glacial ice near Lake Whillans at both 14 and 35 MHz. We acquired data to evaluate the concept of 2-D aperture synthesis and successfully demonstrated the first successful sounding of ice with a radar on an UAV. We are planning to build multiple radar-equipped UAVs for collecting fine-resolution data near the grounding lines of fast-flowing glaciers.

This paper addresses the concept of digital channelizer as a promising solution to overcome the real-time signal detection and analysis challenges for radar signal interception. By employing digital channelizer after high-speed ADC, the intercepted broadband signals can be divided into numbers of sub-channel signals, the signal detection and analysis tasks can then be performed at lower speed after decimation in sub-channels. The sub-channel signal detection and parameter measurement modules are developed to perform signal processing tasks. A realization example based on multi-FPGA chips and its test results are presented to consolidate the proposed signal interception receiver structure.

An FPGA based implementation of spectral analysis (SPECAN) algorithm for ScanSAR imaging is given in this paper. In order to meet the requirements of system miniaturization and low power consumption, the whole imaging processing will be divided into several time-division stages and mapped to reusable calculation modules and control logics, an optimized processing structure in FPGA is proposed to integrate all the processing procedure in single FPGA chip. In the verification part, FPGA based processing has been compared with Matlab based off-line processing. The experimental results indicate the validity of the design and engineering applicability of the proposed structure.

A novel pair of mutually-orthogonal radar waveforms is proposed for simultaneous polarimetric measurements (SPM). The proposed waveform pair exploits the orthogonality features between different subcarriers within a single orthogonal frequency division multiplexing (OFDM) chip, and is called interleaved OFDM (I-OFDM). With I-OFDM signals the isolation limitation defined by the bandwidth time (BT) product for frequently used waveform pairs like linear frequency modulated (LFM) and phase-code modulated (PCM) signals, can be overcome. The performance features of I-OFDM signals are theoretically analyzed; the application of I-OFDM signals and the corresponding signal processing scheme in SPM are presented. A significant increase of the polarimetric measurements efficiency by utilization of the proposed I-OFDM signals has been verified by experiments using an operational radar system.

Retrieval of cloud parameters in weather radar benefits from polarimetric measurements. Most polarimetric radars measure the full backscatter matrix (BSM) using a few alternating polarized sounding signals. Using specially encoded orthogonal frequency division multiplexing (OFDM) signals however, the BSM can be measured in a single simultaneous transmission of two orthogonally polarized signals. Based on a set of parameters for weather radar, the properties of such a signal are explored and its merit as a useful capability is shown.

A novel pair of interleaved OFDM (I-OFDM) signals is proposed to overcome the limitations of existing signals for simultaneous polarimetric measurement. The proposed I-OFDM signal pair exploits the orthogonality features between different sub-carriers within a single OFDM chip, and can then yield the theoretical orthogonality. The isolation limitation defined by the BT product for linear frequency modulated (LFM) and phase-code modulated (PCM) signals thus can be overcome, the proposed waveform pair then significantly increases the efficiency for polarimetric measurements.

Combination of two existing S-band radars TARA and PARSAX into a multi-static system for weather and targets observation is discussed. The proposed combination of radars will provide unique back-and bistatic-scattered radar data simultaneously. The feasibility of the proposed combination has been verified experimentally. Analysis of the operational modes is performed and waveforms for MIMO operation are presented.

This paper presents the development of a reconfigurable receiver to undertake challenging signal processing tasks for a novel polarimetric radar system. The field-programmable gate arrays (FPGAs)-based digital receiver samples incoming signals at intermediate frequency (IF) and processes signals digitally instead of using conventional analog approaches. It offers more robust system stability and avoids unnecessary multichannel calibrations of analog circuits for a full polarimetric radar. Two kinds of dual-orthogonal signals together with corresponding processing algorithms have been investigated; the digital implementation architectures for all algorithms are then presented. Processing algorithms implemented in FPGA chips can be reconfigured adaptively regarding to different transmitted waveforms without modification of hardware. The successful development of such reconfigurable receiver extends our radar capacity and thus yields tremendous experimental flexibility for atmospheric remote sensing and polarimetric studies of ground-based targets.

A system-level simulation model has been developed to conduct the simulation of a whole full-polarimetric radar system, all parameters both in analogue part and digital part can then be optimally selected, thus the most optimal radar performance can be achieved.

The article describes the IRCTR PARSAX radar system, the fully polarimetric FM-CW radar with dualorthogonal sounding signals, which has the possibility to measure all elements of the radar targets polarization scattering matrix simultaneously, in one sweep.

This paper presents design and practical implementation of the method for cross-channel interference suppression in polarimetric LFM-CW radar with dual-orthogonal sounding signals. Simultaneously transmitted and received signals have limited orthogonality, what results in the interfering signals in the processing channels of the radar receiver. The suppression of the interfering signals is implemented in real time, characterized by simplicity and low increase of computational resources. The efficiency of the cross-channel interference suppression is demonstrated experimentally.

An FPGA-based digital receiver has been developed to perform real-time processing for the PARSAX radar. It is a fully polarimetric FMCW radar with dual-orthogonal sounding signals, which has the possibility to measure all elements of the radar targets polarization scattering matrix simultaneously, in one sweep. This paper presents the design principles including the range profile interpretation, optimal parameters selection and processing gain analysis. A novel parallel deramping processing architecture suitable for FPGA implementation is introduced; the overall digital de-ramping processing has been implemented in one chip of FPGA and verified by experimental results.

This paper outlines the work on the design of a reconfigurable receiver for the PARSAX radar. The FPGA based digital receiver samples incoming signals at intermediate frequency (IF) and processes signals digitally instead of using more conventional analog approaches. In this way it offers more robust system stability and avoids unnecessary multi-channel calibrations of analog circuits. The processing algorithms implemented in the FPGA chips can be reconfigured adaptively regarding to different transmitted waveforms, and without changing of hardware. The successful development of reconfigurable receiver has been verified by experiment and yields maximum flexibility for the whole radar system.