Radar Range Measurements Research Articles

ACCURACY ANALYSIS OF AIRCRAFT POSITIONING USING NAVIGATIONAL DATA FROM AVIA-W RADAR

The paper presents an analysis of the accuracy of determination of parameters of the position of aircraft using data from the AVIA-W radar. In the first place, the authors determined the position of the aircraft as well as the range and azimuth parameters by the AVIA-W radar, located in Dęblin. This was followed by a determination of the absolute position error of the aircraft and the determination of the range and azimuth measurement error by the AVIA-W radar. The research test was carried out using a Diamond DA40 NG aircraft on which a GPS satellite receiver was mounted in order to determine the flight reference position. In addition, the range and azimuth measurements for the aircraft were acquired from the AVIA-W radar. Navigational calculations were conducted for polar and rectangular planar coordinates. Based on the performed research, the azimuth error was found to be –1.4o, while the radar range measurement error was equal to –0.04 km. The conducted research is experimental in its character. In the future it will be repeated and extended to the GCA-2000 radar, which is also located at Dęblin military airfield.

Method of 2-D Range-Doppler Imaging for Plasma Wake Based on Range Walk Correction

When a hypersonic vehicle flies in the atmosphere, plasma sheath and trails are configured around the vehicle due to aerodynamic heating and ablation, which distort the radar echo signal and then influence the target range information and Doppler frequency extracted from the echoes. In order to examine the impact of plasma laminar wake on radar detection, this article is primarily aimed to establish a laminar wake echo model based on a linear frequency-modulated continuous wave (LFMCW) radar, which takes into account the reaction control system of laminar wake by employing the Born approximation solution and the characteristics of the inhomogeneous and nonunique velocity of the wake medium. An echo signal processing method is also developed, in which the stretch processing technique is combined with the keystone transform of the target range walk correction. Such a treatment not only reduces the sampling rate and bandwidth, but also eliminates the cross-range cells phenomenon caused by hypersonic; finally, the range-Doppler (RD) image of the wake is achieved by 2-D fast Fourier transform (2-D FFT) processing, and radar range and velocity measurement results in the presence of plasma are obtained.

Wideband and Efficient 256-GHz Subharmonic- Based FMCW Radar Transceiver in 130-nm SiGe BiCMOS Technology

This article proposes a fully integrated single-channel bistatic frequency-modulated continuous-wave (FMCW) radar transceiver (TRX) that operates at a center frequency of 256 GHz. The main focus of this work is to realize a wideband and efficient radar TRX that offers high resolution of target detection in the short-range FMCW radar sensing application. The radar TRX chip is designed and manufactured using the 130 nm silicon–germanium (SiGe) bipolar complementary metal-oxide-semiconductor (BiCMOS) technology which offers heterojunction bipolar transistors (HBTs) with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{\mathbf {T}}/f_{\mathbf {MAX}}$ </tex-math></inline-formula> of 300/500 GHz. The transmitter (TX) of the radar TRX is based on a fundamentally operated multiplier-by-8 chain architecture that offers a 3-dB bandwidth of around 65 GHz with a saturated output power of −5.4 dBm. On the other hand, the receiver (RX) is based on a subharmonic architecture that provides a conversion gain (CG) of 10.4 dB with an average noise figure (NF) of 23.5 dB. This TRX is realized with two integrated on-chip folded dipole antennas. The antenna offers high antenna gain and radiation efficiency due to the use of the selective localized backside etching (LBE) technique. This chip consumes 305 mW of power from a 3.3-V supply and occupies a silicon area of 3.3 mm2. The radar range measurement is performed in an anechoic chamber, and it shows the maximum dynamic range (DR) of around 34 dB at 1-m range of the target.

Dechirp‐receiving radar target detection based on generalized Radon‐Fourier transform

The dechirp-receiving radar measures range by the frequency difference between the target echo and the reference signal. It can operate at a low sampling frequency while transmitting a wideband signal, which simplifies the radar hardware. However, when detecting high-speed and highly maneuvering targets, residual video phase (RVP), frequency mismatch, frequency modulation (FM) rate mismatch, and across range-Doppler unit (ARDU) problems occur after dechirp receiving, which cause difficulties in integrating the target echo and result in severe performance loss. To solve these problems, the dechirp generalized Radon-Fourier transform (DGRFT) and an algorithm for its fast implementation are proposed. The DGRFT compensates for the frequency and FM rate mismatch in the fast-time domain and the RVP in the fast-time frequency domain, and then implements joint envelope and phase compensations to overcome the ARDU phenomenon. After these compensations, the target echo can be effectively integrated. Experiments with simulated and measured data show that the performance of the DGRFT is better than that of the conventional moving target detector.

Jammer avoidance for dual-function radar-communications using FSK and independent null steering

In this paper, we propose a novel method for dual-function radar-communication(DFRC) system. Our focus is on radar being used for communications in parallel to conventional target tracking and/or surveillance assignment. In the proposed setup, the main beam is directed toward the targets as primary radar function, whereas, communication is performed through the sidelobes as secondary function. In addition, the nulls are used to avoid the jammers. A sophisticated null steering feature has been incorporated to deal with the moving jammers. In this null shifting, only the proposed null will be shifted, whereas, rest of the antenna radiation pattern including main beam and the other sidelobes will remain undisturbed. We also propose a new information embedding to transmit the communication signal in the radar emission by using the frequency shift keying (FSK) as orthogonal waveforms to transmit binary information towards the communication receivers and analyzing the impact of the FSK signals on the radar range measurements. Simulations are carried out and the results indicate the validity and performance of the proposed idea in terms of interference mitigation as well as Bit Error Rate (BER).

Real‐Time Thermospheric Density Estimation via Radar and GPS Tracking Data Assimilation

AbstractAs the number of man‐made Earth‐orbiting objects increases, satellite operators need enhanced space traffic management capabilities to ensure safe space operations. For objects in Low Earth orbit, orbit determination and prediction require accurate estimates of the local thermospheric density. In previous work, the estimation of thermospheric densities using two‐line element data and a reduced‐order model for the upper atmosphere was demonstrated. In this study we demonstrate an approach for density estimation using radar and GPS tracking data. For this, we assimilate the tracking data in a dynamic reduced‐order density model using a Kalman filter by simultaneously estimating the orbits and global density. We used the radar range and range rate measurements of 20 objects and the GPS position measurements of 10 commercial satellites. The estimated density was validated against accurate SWARM density data and compared with NRLMSISE‐00, JB2008, and two‐line element (TLE)‐estimated densities. We found that the estimated densities are significantly more accurate than NRLMSISE‐00 and JB2008 densities. In particular, using the GPS data of 10 satellites, we obtain density estimates with a daily 1‐σ error of only 5% compared to 14% and 22% for empirical models and 10% for TLE‐estimated density. These accurate density estimates can be used to improve orbit determination and the use of real‐time tracking data would enable real‐time density estimation.

The precision of radar-derived subglacial bed topography: a case study from Pine Island Glacier, Antarctica

AbstractRecent advances in the measurement of bedforms beneath active ice streams have been made using ground-based grid profiling using impulse radar systems operating with centre frequencies in the 3–5 MHz range. Surveys of Rutford Ice Stream and Pine Island Glacier have shown that features such as mega-scale glacial lineations with topographic relief of as little as 3 m can be traced for many kilometres downstream under more than 2 km of fast-moving ice. In the discussion of these data, it is often asked ‘How is it possible to map such fine-scale topography with such a low-frequency radar’. In answering that question, the key point is the distinction between the precision of a radar range measurement to a single, isolated reflective interface and the ability to resolve the presence of two closely-spaced interfaces of similar reflectivity (commonly referred to as the vertical resolution). This paper will discuss and illustrate this distinction and use the case study of data acquired over Pine Island Glacier to examine the limits of precision of the radar range measurement.

A Planar Differential Wide Fan-Beam Antenna Array Architecture: Modular high-gain array for 79-GHz multiple-input, multiple-output radar applications

This article proposes a planar, wide fan-beam differential, corporate-fed patch antenna array architecture for automotive radar applications that mitigates the multipath and multiple reflections effects of its conventional series-fed counterpart. The proposed array architecture offers the merits of wide beamwidth in azimuth, high gain, yet, is applicable in multiple-input, multiple-output (MIMO) configurations. Two 8 × 1 arrays were developed, built, and measured at the 77-81-GHz band. In design 1, the width of driven 50-Ω patch is optimized for the widest beamwidth and the array feeding network employs impedance transformers for matching. The experimental verification showed an azimuthal half-power beamwidth (HPBW) of 70° with a 15-dBi gain. In design 2, the interelement spacing is increased for wider beamwidth and less mutual coupling, and the feeding network transformers were eliminated to mitigate scattering and radar cross section (RCS) in turn. A 130° azimuthal HPBW was measured. A 2 × 2 MIMO radar hardware was built, employing the proposed array architecture on a scalable radar platform to validate its applicability in MIMO radars. For the sake of comparison, another reference demonstrator with conventional series-fed arrays was built. Frequency-modulated continuous-wave (FMCW) radar range and angle measurements were performed where multiple reflections and multipath effects were mitigated.

Uncertainties in retrieving microphysical properties of rain profiles using ground‐based dual‐frequency radar

AbstractDual‐frequency radar (DFR) could improve the accuracy of estimating the microphysical properties of rain profiles. Unfortunately, factors that cause inaccuracies in retrieved rain profiles include uncertainties in raindrop size distribution (DSD) parameterizations, DFR retrieval methods and radar measurement errors. The primary objective of this study was to assess the uncertainties in retrieving rain profiles to offer insight into application considerations for ground‐based DFRs in China. The uncertainties caused by DSD models are assessed by comparing attenuation coefficients and rain rates from DFR algorithms with those directly derived from DSD spectra from disdrometers. Then, based on a DSD model, the impacts of retrieval methods, radar range resolution, measurement error and errors in temperature on DFR retrievals are explored by comparing the rain profiles obtained using DFR algorithms with those directly output from the Weather Research and Forecasting model. Overall, the impact of measurement error on the DFR retrievals is relatively significant for both the forward retrieval method and the iterative backward retrieval method and should be eliminated in practical applications. At an individual uncertainty level, the impact of DSD parameterizations on the retrievals from the dual‐frequency technique is less than ±10% bias when the shape factor μ of the gamma distribution ranges from 2 to 4. The retrieved rain profiles from the forward retrieval method are relatively sensitive to radar range resolution and the retrieval performance can be improved with increasing the range resolution, while the iterative backward retrieval method exhibits stable retrieval performance. The impact of temperature errors on the retrieved rain profiles is negligible.

Target Positioning With Surveillance Radar by the Estimation of Atmospheric Refractivity Profile

The positioning of a target with radar measurements could be inaccurate because of the atmospheric refraction effects. We present a technique for determining the refractivity parameters using known position information of cooperative targets. The estimated refractivity parameters are then used to find the position of a noncooperative target, along with its radar range and angle measurements. The performance of the proposed algorithm is assessed by comparing the mean squared error of the estimate with the Cramer–Rao lower bound as well as by testing the algorithm with real field data. Ground-based military surveillance radar can adopt the proposed algorithm and benefit when there are some cooperative flying aircraft while there is no external refractivity information such as radiosonde data.

LaIF: A Lane-Level Self-Positioning Scheme for Vehicles in GNSS-Denied Environments

Vehicle self-positioning is of significant importance for intelligent transportation applications. However, accurate positioning (e.g., with lane-level accuracy) is very difficult to obtain due to the lack of measurements with high confidence, especially in an environment without full access to a global navigation satellite system (GNSS). In this paper, a novel information fusion algorithm based on a particle filter is proposed to achieve lane-level tracking accuracy under a GNSS-denied environment. We consider the use of both coarse-scale and fine-scale signal measurements for positioning. Time-of-arrival measurements using the radio frequency signals from known transmitters or roadside units, and acceleration or gyroscope measurements from an inertial measurement unit (IMU) allow us to form a coarse estimate of the vehicle position using an extended Kalman filter. Subsequently, fine-scale measurements, including lane-change detection, radar ranging from the known obstacles (e.g., guardrails), and information from a high-resolution digital map, are incorporated to refine the position estimates. A probabilistic model is introduced to characterize the lane changing behaviors, and a multi-hypothesis model is formulated for the radar range measurements to robustly weigh the particles and refine the tracking results. Moreover, a decision fusion mechanism is proposed to achieve a higher reliability in the lane-change detection as compared to each individual detector using IMU and visual (if available) information. The posterior Cramer–Rao lower bound is also derived to provide a theoretical performance guideline. The performance of the proposed tracking framework is verified by simulations and real measured IMU data in a four-lane highway.

Assessing the potential for measuring Europa's tidal Love number h2 using radar sounder and topographic imager data

The tidal Love number h2 is a key geophysical measurement for the characterization of Europa's interior, especially of its outer ice shell if a subsurface ocean is present. We performed numerical simulations to assess the potential for estimating h2 using altimetric measurements with a combination of radar sounding and stereo imaging data. The measurement principle exploits both delay and Doppler information in the radar surface return in combination with topography from a digital terrain model (DTM). The resulting radar range measurements at cross-over locations can be used in combination with radio science Doppler data for an improved trajectory solution and for estimating the h2 Love number. Our simulation results suggest that the absolute accuracy of h2 from the joint analysis of REASON (Radar for Europa Assessment and Sounding: Ocean to Near-surface) surface return and EIS (Europa Imaging System) DTM data will be in the range of 0.04–0.17 assuming full radio link coverage. The error is controlled by the SNR budget and DTM quality, both dependent on the surface properties of Europa. We estimate that this would unambiguously confirm (or reject) the global ocean hypothesis and, in combination with a nominal radio-science based measurement of the tidal Love number k2, constrain the thickness of Europa's outer ice shell to up to ±15 km.

An improved single-point track initiation using GMTI measurements

A ground moving target indicator (GMTI) radar measures range, azimuth, and Doppler or range-rate of a target. The range-rate measurement, which is the key measurement of a GMTI radar, is used to differentiate a ground moving target from clutter when the radial velocity of the target exceeds the minimum detectable velocity (MDV). The range and azimuth measurements provide an accurate estimate of the target position. A number of track initiation algorithms using GMTI measurements are known at present. All track initiation algorithms set the initial velocity to zero and a large prior covariance for velocity is used based on the maximum target speed. The range-rate measurement is then used to update the target velocity or state. The range-rate measurement contains only the component of the target velocity along the radar line-of-sight (RLOS) and no component of velocity in the perpendicular direction is measured. As a result, existing track initiation algorithms produce a bias in the velocity estimate. This paper first corrects two errors in the single-point (SP) track initialization part of the paper [29] using the range-rate measurement to obtain the initial velocity estimate and associated covariance. Secondly, we present an improved track initiation algorithm based on a heading-parameterized multiple model (HPMM) method that uses the sign of the range-rate measurement, prior knowledge of target maximum speed, and MDV. The proposed algorithm reduces the bias in the initial velocity estimate and the superior performance of the algorithm is demonstrated using Monte Carlo simulations.

An innovative navigation scheme of powered descent phase for Mars pinpoint landing

Pinpoint landing (within 100m from the target) is essential for future Mars exploration missions. This paper deals with one aspect of the pinpoint landing architecture—the navigation performance improvement during the powered descent phase, and proposes an innovative navigation scheme to obtain the vehicle complete and accurate states. On the basis of dead reckoning relying on the Inertial Measurement Unit, measurements of the Integrated Doppler Radar are adopted to correct the vehicle velocity and altitude. Distance between the vehicle and one Mars Orbiter as well as their line-of-sight relative velocity is measured by a radio sensor, and integrated in the filter to correct the vehicle horizontal position. The innovative navigation system is based on an Extend Kalman Filter. Two observation schemes are developed. One considers measurements of the Integrated Doppler Radar and radio range measurement. Another further considers radio velocity measurement. The performance of the innovative navigation scheme is greatly influenced by the position of the Mars Orbiter with respect to the target. Stochastic analyses are performed to obtain optimal locations of Mars Orbiter. Finally, the innovative navigation scheme performances are assessed through stochastic simulations. Its performance improvements are demonstrated by comparison with the Integrated Doppler Radar only navigation scheme.

협동 표적 추적을 위한 확률적 데이터 연관 기반 레이더 및 ESM 센서 측정치 융합 기법의 실험적 연구

협동교전능력을 위한 표적정보 수집, 실시간 정보융합, 공동 상황인식 기능 구현을 위하여 표적 처리기법 연구는 중요하다. 이러한 표적 처리 연구 중, 표적의 추적의 문제는 센서로부터 얻어진 측정값을 사용하여 표적의 상태를 예측하는 것으로부터 시작한다. 그러나 상태 예측에 사용되는 센서의 측정값들은 불확실성을 갖고 있기 때문에 측정된 정보에 어느 정도의 신뢰성을 부여할 수 있느냐가 중요한 문제가 된다. 따라서 이를 위해 다중 센서를 이용한 기법이 요구되고, 보편적으로 사용되는 확률적 데이터연관 기법으로부터 다중 센서를 이용한 표적 추적을 위해서는 이종 센서로부터 제공된 측정값들을 처리하기 위한 정보융합 기법이 필요하다. 본 논문에서는 레이더 및 ESM 센서에서 측정된 측정값 정보융합을 통하여 확률데이터연관 필터를 이용한 표적의 트랙 추정 성능을 향상시키기 위한 방법을 구체적으로 분석하여 정보를 결합하기 위한 새로운 실시간측정값 융합 기법을 제안하고 확률데이터연관을 통해 추적할 표적의 트랙을 추정하는 방법을 분석하였다. 모의실험을 통해 제안된 기법들이 선형 혹은 회전 운동하는 모델들에 대해 향상된 추정 결과를 보여준다. Target processing mechanisms are necessary to collect target information, real-time data fusion, and tactical environment recognition for cooperative engagement ability. Among these mechanisms, the target tracking starts from predicting state of speed, acceleration, and location by using sensors' measurements. However, it can be a problem to give the reliability because the measurements have a certain uncertainty. Thus, a technique which uses multiple sensors is needed to detect the target and increase the reliability. Also, data fusion technique is necessary to process the data which is provided from heterogeneous sensors for target tracking. In this paper, a target tracking algorithm is proposed based on probabilistic data association(PDA) by fusing radar and ESM sensor measurements. The radar sensor's azimuth and range measurements and the ESM sensor's bearing-only measurement are associated by the measurement fusion method. After gating associated measurements, state estimation of the target is performed by PDA filter. The simulation results show that the proposed algorithm provides improved estimation under linear and circular target motions.

Altimeter Data Evaluation in the Coastal Gulf of Maine and Mid-Atlantic Bight Regions

Satellite altimeter sea surface height anomaly (SSHA) data accuracy and applications are rapidly maturing over the open ocean, but more attention is required where continental shelves and marginal seas are concerned. Refined radar range measurement correction approaches are needed to enhance the quality of coastal altimeter SSHA data and to enhance the potential impact that altimeter data can play in improved ocean circulation modeling and prediction. This study provides a regional assessment of satellite altimeter SSHA data from the Jason-2, Jason-1, and TOPEX/Poseidon data sets collected over the Northwest Atlantic coastal region of the United States. The validation approach follows recent studies in numerous shelf regions to address changes from standard or default data quality flagging scheme that can enhance satellite altimeter SSHA data recovery, optimal choice of de-aliasing corrections in deriving subtidal sea level time series, and validation of altimeter data using in situ tide gauge and current measurement data sets. Spatial analyses show the impact of data filtering and corrections from the coastline out onto the slope. Revised handling of the data provides a 5–10% increase in availability (from about 70% up to 80% for waters beyond 50 km from shore). The RMS differences between tide gauge and surface layer current measurements at the 60 day time scale are 3–4 cm and 6 cm/s, respectively, and of magnitude consistent with several recent coastal altimeter data validation efforts.

Imaging Geodesy—Toward Centimeter-Level Ranging Accuracy With TerraSAR-X

In this paper, we report on experiments to measure large-scale Earth surface displacements, such as those caused by solid Earth tides, with centimeter-level accuracy using TerraSAR-X radar images. With two totally different approaches, corner reflectors and image correlation techniques, we show the clear interrelation between the radar range measurements and the projection of the solid Earth tide motion vector onto the radar line of sight. Pixel location accuracies of up to 2.6-cm standard deviation can be achieved after a single calibration. We further demonstrate that solid Earth tides and tropospheric water vapor variations are the largest sources of ranging error if not compensated for. Alternatively, tropospheric water vapor can be estimated with centimeter accuracy using our proposed technique of synthetic aperture radar (SAR) image correlation and solid Earth motion compensation by the existing models. We also consider ionospheric delays which improve the results marginally in the X-band. Our results show the best ranging accuracies so far reported for spaceborne radar amplitude images and make TerraSAR-X-together with our simple compensation methodology-suitable for the imaging of centimeter-level Earth displacements. Absolute measurements of volcanoes or glaciers are possible without the use of ground equipment and without the use of SAR interferometry, thus avoiding the associated problems of phase ambiguity, phase unwrapping, and reference points.

Probing general relativity with radar astrometry in the inner solar system

AbstractWe describe a long-term program designed to obtain and interpret high-precision radar range measurements of a number of near-Earth objects (NEOs) that have trajectories reaching deep inside the gravitational well of the Sun. Objects in our sample have perihelion shift rates 1.5 to 2.5 times that of (1566) Icarus (10″/cy) and span a wide range of inclinations and semi-major axes, allowing for an unambiguous separation of general relativistic and solar oblateness effects. Four objects have been observed at Arecibo on at least two apparitions since 2000, with typical uncertainties of a few hundred meters. Within the next three years, we anticipate securing a total of 15 observations of 5 different NEOs. This program is expected to provide a purely dynamical measurement of the oblateness of the Sun (J2 at the 10−8 level) and to constrain the Eddington parameter β at the 10−4 level. Although our objects are selected to minimize Yarkovsky orbital drift, we also anticipate measuring Yarkovsky drift rates, which are orthogonal to the GR and J2 signatures.

Lava dome growth and mass wasting measured by a time series of ground‐based radar and seismicity observations

Exogenous growth of Peléean lava domes involves the addition of lava from a central summit vent and mass wasting on the flanks as rockfalls and pyroclastic flows. These processes were investigated at the Soufrière Hills Volcano, Montserrat, between 30 March and 10 April 2006, using a ground‐based imaging millimeter‐wave radar, AVTIS, to measure the shape of the dome and talus surface and rockfall seismicity combined with camera observations to infer pyroclastic flow deposit volumes. The topographic evolution of the lava dome was recorded in a time series of radar range and intensity measurements from a distance of 6 km, recording a southeastward shift in the locus of talus deposition with time, and an average height increase for the talus surface of about 2 m a day. The AVTIS measurements show an acceleration in lava extrusion rate on 5 April, with a 2‐day lag in the equivalent change in the rockfall seismicity record. The dense rock equivalent volumetric budget of lava added and dispersed, including the respective proportions of the total for each component, was calculated using: (1) AVTIS range and intensity measurements of the change in summit lava (∼1.5 × 106 m3, 22%), (2) AVTIS range measurements to measure the talus growth (∼3.9 × 106 m3, 57%), and (3) rockfall seismicity to measure the pyroclastic flow deposit volumes (∼1.4 × 106 m3, 21%), which gives an overall dense rock equivalent extrusion rate of about 7 m3·s−1. These figures demonstrate how efficient nonexplosive lava dome growth can be in generating large volumes of primary clastic deposits, a process that, by reducing the proportion of erupted lava stored in the summit region, will reduce the likelihood of large hazardous pyroclastic flows.

An experimental comparative study of autonomous and co-operative vehicle-follower control systems

This paper is a comparative study of the performance of constant-time-gap autonomous control systems and co-operative longitudinal control systems that use inter-vehicle communication. Analytical results show that the minimum time gap that can be achieved in autonomous control is limited by the bandwidth of the internal dynamics of the vehicle. Experimental results from typical sensors and actuators are used to show that in practice it is very difficult to achieve a time gap less than 1 s with autonomous vehicle following. This translates to an inter-vehicle spacing of 30 m at highway speeds and a theoretical maximum traffic flow of about 3000 vehicles per hour. The quality of radar range and range rate measurements pose limitations on the spacing accuracy and ride quality that can be achieved in autonomous control. Dramatic improvements in the trade-off between ride quality and spacing accuracy can be obtained merely by replacing radar range rate in the autonomous control algorithm with the difference between the measured velocities of the two cars (a rudimentary form of co-operation). As a baseline comparison, the experimental performance of fully co-operative control is presented. An inter-vehicle spacing of 6.5 m is maintained in a platoon of 8 co-operative vehicles with an excellent ride quality and an accuracy of ±20 cm. Extending this to a 10-vehicle platoon makes it possible to achieve theoretical maximum traffic flows of about 6400 vehicles per hour. Another issue of importance addressed in the paper is the need to accommodate malfunctions in radar (ranging sensor) measurements. Measurement errors can occur due to hardware malfunctions as well as due to road curves, grades and the highway environment in the case of large inter-vehicle spacing. The ability of a co-operative control system to monitor the health of the radar and correct for such errors and malfunctions is demonstrated experimentally.