Ninoslav Majurec

Airborne L-Band Radio Frequency Interference Observations From the SMAPVEX08 Campaign and Associated Flights

Statistics of radio frequency interference (RFI) observed in the band 1398-1422 MHz during an airborne campaign in the United States are reported for use in analysis and forecasting of L-band RFI for microwave radiometry. The observations were conducted from September to October 2008, and included approximately 92 h of flight time, of which approximately 20 h of “transit” or dedicated RFI observing flights are used in compiling the statistics presented. The observations used include outbound and return flights from Colorado to Maryland, as well as RFI surveys over large cities. The Passive Active L-Band Sensor (PALS) radiometer of NASA Jet Propulsion Laboratory augmented by three dedicated RFI observing systems was used in these observations. The complete system as well as the associated RFI characterization approaches are described, along with the resulting RFI statistical information and examinations of specific RFI sources. The results show that RFI in the protected L-band spectrum is common over North America, although the resulting interference when extrapolated to satellite observations will appear as “low-level” corruption that will be difficult to detect for traditional radiometer systems.

Software defined radar studies of human motion signatures

The detection and monitoring of human motion with radar has numerous applications in surveillance, urban military operations, search-and-rescue, and other areas. Recent studies have shown that movements of humans generate unique micro-Doppler signatures that can be exploited to classify human motions. This motivates an improved understanding of human Doppler signatures. Numerous simulations and measurements of human “dismount” signatures has been performed in the past, but most have been focused on a single radar center-frequency and have not taken polarization effects into consideration. In this paper, human modeling and motion measurements using multiple radar frequencies are proposed to explore the impact of the radar frequency on human range/Doppler signatures. Furthermore, ground effects on human targets are investigated using a four path model. The OSU Software defined radar (SDR) system, which can be tuned from 2GHz to 18 GHz with 500MHz bandwidth, was used for the measurements. This radar can operate at two frequencies simultaneously, allowing for dual frequency human measurements. Also, different polarizations are considered to understand human Doppler signatures. Modeling efforts are based on a finite dielectric cylinder approximation, so that the human body is modeled as a collection of dielectric cylinders. Scattering signatures are computed neglecting scattering interactions among these cylinders.

Software-defined radar for MIMO and adaptive waveform applications

The development of a software-defined radar testbed is described. The testbed is to be used to explore advanced techniques such as multiple-input multiple-output radar and adaptive waveforms. The system features a fully programmable, dual-channel, arbitrary pulsed waveform generator with a quadrature downconverting receiver. The system can generate waveforms of up to 500 MHz instantaneous bandwidth at a center frequency tunable from 2–18 GHz. The RF front end features two independent transmit and receive channels that can be multiplexed between four dual-polarized transmit and four dual-polarized receive antennas.

Comparison of Model Predictions With Measurements of Ku- and Ka-Band Near-Nadir Normalized Radar Cross Sections of the Sea Surface From the Genesis and Rapid Intensification Processes Experiment

A comparison of model predictions with measurements of near-nadir normalized radar cross sections (NRCSs) of the sea surface at Ku- and Ka-bands is reported. Measurements of Airborne Precipitation Radar Second Generation (APR-2) from near nadir to 25 ° incidence angle, along with simultaneous wind truth from dropsonde observations, are compared with predictions of the “cutoff-invariant” two-scale model of sea scattering with the overall goal of assessing the model for possible future use in the APR-2 calibration process. The performance of the model as a function of wind speed and incidence angle is therefore emphasized. The measured data set, acquired primarily during the 2010 “Genesis and Rapid Intensification Processes” (GRIP) experiment, includes wind speeds from approximately 5 to 45 m/s. Model comparisons are limited by uncertainties in the wind fields due to limited dropsonde coverage; the data set is separated into “more reliable” (containing wind speeds of 5-20 m/s) and “less reliable” (wind speeds of 5-45 m/s) wind truth categories accordingly. Because a model of the sea spectrum is required for cutoff-invariant model predictions, comparisons with measured data are performed for three differing sea spectrum descriptions. It is found that a bias of less than ~ 1 dB over the wind speed range 5-40 m/s and a standard deviation less than 1 dB over the wind speed range 10-40 m/s can be achieved when using the “unified” sea spectrum description of Elfouhaily The model also provides error levels that are near uniform with respect to both incidence angle and wind speed.

Numerical and experimental studies of target detection with MIMO radar

Spatially diverse multiple-input multiple-output (MIMO) radar systems combine multistatic measurements of the target under view into a single detection algorithm and are thereby expected to alleviate the effects of fading on target radar cross sections (RCS) as the angle of observation is varied. Previous analytical studies of target detection for this case have shown that MIMO radar detection performance can exceed that of the corresponding phased array radar if both sufficient spatial diversity and signal-to-noise ratio (SNR) are achieved. These results have been based on a statistical model for the multistatic RCS of the target that is similar to the traditional Swerling models of the monostatic RCS. The degree to which these results are applicable to specific target geometries therefore remains uncertain. To address this issue, two studies of MIMO radar target detection incorporating realistic RCS properties for specific target geometries were performed. The first study utilized a numerical method to compute the multistatic RCS of a helicopter-like target observed at center frequency 200 MHz, while the second involved radar measurements of an unmanned aerial vehicle (UAV) target at 2.75 and 4.5 GHz. MIMO radar configurations having two transmitters and either three (for the radar measurements) or four (numerical simulations) receivers were used. In both cases, multistatic received fields were combined with regulated thermal noise levels in postprocessing to study target detection performance. Because in general the azimuthal orientation of a specific target with respect to the radar is uncertain, the detection performance results shown are averaged over the azimuthal orientation angle of the target. The average over target orientation can also be interpreted as similar to an average over “trials” of a statistical target description, enabling comparisons of field properties averaged over target orientation with similar ensemble averages from the statistical models of the literature. Although detection performance curves for the specific targets considered are not identical to those predicted analytically by the statistical target model, results for these targets confirm that the MIMO radar system can achieve enhanced detection performance as compared with the corresponding phased array radar system.

Through-Wall Sensing With Multifrequency Microwave Radiometry: A Proof-of-Concept Demonstration

A proof-of-concept demonstration of through-wall sensing with microwave radiometry is described. A multifrequency microwave radiometer with 37 channels from 2.1 to 17.35 GHz was used in two experiments to observe objects through a cinder block wall of approximately 20-cm thickness. Measured data show the clear ability of the radiometer to detect thermal contrasts on the interior of the wall. A discussion of the basic physical processes involved in the measurement is provided. When compared with active systems, microwave radiometry for through-wall sensing faces significant challenges, including limitations in ranging, horizontal resolution, and corruption by radio-frequency interference, but also provides complementary capabilities, particularly with regard to thermal information. Further consideration of microwave radiometry appears warranted for applications where thermal information is of interest.

Simulation and analysis of polarimetric radar signatures of human gaits

Radar observations of human activities have a variety of applications in security, defense, and rescue operations. Range-Doppler signatures of human motions are a useful tool for retrieving information on observed activities but require an understanding of the scattering processes involved to enable interpretation. This paper presents a study of human Doppler signatures using simulations, in particular focusing on the impact of the polarization to enable an understanding of any advantages in the use of polarimetric radar. The simulation model utilized is based on an approximate scattering approach combined with a 12-cylinder description of the human body. A comparison with single polarization co-pol measurements is used to show that the model provides reasonable first-order predictions of human signatures. Further simulations for polarimetric signatures illustrate the differing contributions of individual body parts to micro-Doppler returns and suggest that multi-polarization measurements can be useful in future micro-Doppler radar systems for human observation.

High power coherent-on-receive radar for marine surveillance

In this paper we describe the development of a low cost, high power coherent-on-receiver radar. The unit has a 25kW peak transmit power and is capable of accurately measuring velocity as well as range. The design of the radar is optimized for marine surveillance, although the techniques developed have general application. The radar system is validated through a series of tests that culminate with sea surface measurements.

Airborne L-band RFI observations in the smapvex08 campaign with the L-band interference suppressing radiometer

Radio Frequency Interference (RFI) is a major concern for microwave radiometry. In September-October 2008, an airborne campaign for observing L-band RFI was conducted and included approximately fifty hours of flight time. The campaign included test flights in Grand Junction, Colorado, observations over soil moisture ground truth sites in Iowa and Maryland, transit and return flights from Colorado to Maryland, and dedicated RFI observing missions over urban areas. In this paper, the L-band digital backend and its RFI detection and mitigation algorithms are described. RFI statistics and examples from the airborne campaign are also presented.

Calibration of the UMass Advanced Multi-Frequency Radar (AMFR)

In this paper the calibration of the University of Massachusetts Advanced Multi-Frequency Radar (AMFR) is discussed in detail. The calibration is performed primarily through the use of an internal calibration path, and is confirmed through cross-calibration with another calibrated radar. Additionally, the performance of AMFR during the 2007 Canadian CloudSat/CALIPSO Validation Project (C3VP) is demonstrated with respect to calibration and instrument stability. It is shown that the calibration during the C3VP experiment was accurate to within 1.5 dB when compared with a C-band weather radar operated by Environment Canada.