James Park

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.

Experimental Demonstration of Adaptive Infrared Multispectral Imaging using Plasmonic Filter Array

In our previous theoretical study, we performed target detection using a plasmonic sensor array incorporating the data-processing technique termed “algorithmic spectrometry”. We achieved the reconstruction of a target spectrum by extracting intensity at multiple wavelengths with high resolution from the image data obtained from the plasmonic array. The ultimate goal is to develop a full-scale focal plane array with a plasmonic opto-coupler in order to move towards the next generation of versatile infrared cameras. To this end, and as an intermediate step, this paper reports the experimental demonstration of adaptive multispectral imagery using fabricated plasmonic spectral filter arrays and proposed target detection scenarios. Each plasmonic filter was designed using periodic circular holes perforated through a gold layer, and an enhanced target detection strategy was proposed to refine the original spectrometry concept for spatial and spectral computation of the data measured from the plasmonic array. Both the spectrum of blackbody radiation and a metal ring object at multiple wavelengths were successfully reconstructed using the weighted superposition of plasmonic output images as specified in the proposed detection strategy. In addition, plasmonic filter arrays were theoretically tested on a target at extremely high temperature as a challenging scenario for the detection scheme.

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.

Joint analysis of radio frequency interference from SMOS measurements and from airborne observations

The Soil Moisture and Ocean Salinity (SMOS) mission has been providing L-band brightness temperature observations since its launch in November 2009. SMOS observations are being utilized for soil moisture and ocean salinity estimation. However, the mission has been affected by significant levels of radio frequency interference caused by anthropogenic sources of radiation in the 1400–1427 MHz band. SMOS has only one frequency channel and measures brightness temperatures with 1.2 seconds time resolution, therefore the detection and mitigation of RFI is challenging, especially for low-level RFI. One possible approach for RFI detection involves use of the fully polarimetric properties of SMOS measurements. In this paper, an examination of the characteristics of SMOS measurements over the USA is first reported. SMOS measurements from Fall 2010 are then compared with RFI source information obtained from a Fall 2008 airborne campaign called SMAPVEX08 (which supported NASAs Soil Moisture Active/Passive (SMAP)). The SMAPVEX08 “ground truth” information on RFI sources is used to examine possible RFI detection strategies using SMOS polarimetric data. Although the study is limited by possible changes in source properties in the intervening two year period, the results suggest that polarimetry can be used as an indication of some RFI sources, but may not reflect the RFI characteristics of a region in general.

Measurements and simulations of multi-frequency human radar signatures

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 range-Doppler signatures using both measurements and models, in particular focusing on the impact of the radar frequency to enable an understanding of any advantages in the use of multiple radar frequencies.

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.

High temperature measurements of AlON using a CO2 laser

IR sensors continue to be a powerful tool for a broad range of sensing applications including night vision, surveillance and other mission functions. Sensors are often exposed to challenging scenarios such as targeting under extreme conditions including detection under extremely high temperature and speed, such as in hypersonic applications. Thermal protection is vital for sensor performance under unfavorable conditions. Transparent ceramic is one of the window materials used against thermal impact due to its excellent optical transmission, transparency, and durability under extreme conditions. In this paper, we focus on investigating the behavior of Aluminum Oxynitride (AlON) optical ceramics at high temperatures. AlON has been reported to have transparency and transmission over 80% from the UV all the way to the mid-wave IR cutting off around 5μm. A 25.4mm × 25.4mm × 6mm square and 1.5mm × 1.5mm × 10.16mm AlON samples were heated up to ~907K. A 50W CO2 laser was used as a heating source for the material under test (MUT). Significant thermal distribution was measured using a long-wave IR thermal camera to observe the MUT surface. In addition, heating results show that there was severe thermal stress in the MUT. We are currently optimizing the optical beam dimensions and projection shape towards a sample in order to minimize the stress and heat towards 1273K. Finally, we validated our experimental results with thermo-optic simulations and modeling.

High-temperature material characterization for multispectral window

A microwave cylindrical cavity combined with a laser has been investigated to characterize the temperature dependence of widow materials in the Air Force Research Laboratory (AFRL). This paper discusses the requirements of high temperature RF material characterizations for transparent ceramic materials, such as ALON, that can potentially be used for multispectral windows. The RF cylindrical resonator was designed and the numerical model was studied to characterize the dielectric constant of materials. The dielectric constant can be extracted from the resonant frequency shift based on the cavity perturbation method (CPM), which is sensitive to the sample size and shape. Laser heating was applied to the material under test (MUT), which could easily be heated above 1000°C by the laser irradiation, in order to conduct CPM at high temperature. The temperature distribution in a material was also analyzed to investigate the impact of the thermal properties and the sample shape.

Optimal design of IR sensor's spectral bands for material classification

The spectral matched filtering is based upon the principle of forming a superposition of basis functions such as a set of sensors spectral bands to perform target classification. We report a band-engineering routine, which is critical to find the optimal design setting for each sensor band to improve the estimation of targets signature such as reflectance of material. The quality of engineered sensors spectral bands is validated as they apply to the various material classification problems.