Martin Ummenhofer

A multi-frequency hybrid passive radar concept for medium range air surveillance

A MFH-PR concept has been presented. The rationale for pursuing such a hybrid unit has been explained in terms of enhancing detection range and coverage over conventional PRs. The important distinctions between MFNs and SFNs have been analysed. Section VI has described the advantages of signal reconstruction and has shown that, in certain situations, adequate interference suppression can be achieved without use of additional adaptive filters. An important consideration of MFH-PR is the potential range coverage extension. This has been demonstrated in Section VII using an advanced radar planning tool. Frequency and spatial diversity have been discussed in the context of improving tracking performance. The military utility of a MFH-PBR has also been discussed in Section XIII.

Evaluation of the ambiguity function for passive radar with OFDM transmissions

The presence of clutter in passive radar returns imposes a minimum floor level on the ambiguity surface, masking weak returns and reducing dynamic range. When the illuminating signal is a form of OFDM, orthogonality between subcarriers can be exploited to produce a zero floor within certain delay bins. In this paper we compare and contrast several such ambiguity processing techniques for general OFDM signals. The methods are applied to simulated and real DVB-T passive radar returns having a wide range of delays. It is shown that an OFDM-specific method can outperform a standard pulse-Doppler processing method under certain conditions. An example is provided using real German DVB-T data from Fraunhofer FHR.

Passive radar components of ARGUS 3D

Combining the detection range capability of passive radar using FM radio emissions with the range resolution obtained through the use of DVB-T signals and the elevation coverage capability provided by DAB Tx yields a high-performance hybrid passive radar sensor. Increasing the coherent integration time of the high-resolution DVB-T component in a track-before-detect approach, cued by the Doppler information obtained through the FM radio component, provides high-range resolution at extended detection ranges. In addition, the DAB-using component, cued by Doppler information provided by FM radio, extends the high-resolution detection volume to elevation ranges not illuminated by DVB-T. The heart of such a hybrid passive radar sensor will be the cued track-before-detect procedure, which is currently being developed at Fraunhofer Institute for High Frequency Physics and Radar Techniques in Wachtberg, Germany.

Passive radar based control of wind turbine collision warning for air traffic PARASOL

PARASOL is a passive radar based system to activate the collision warning lights of wind power plant on demand in order to increase acceptance of renewable energies in the population and avoid the attraction of birds by light emissions. The system design is composed of three passive radar sensors providing the location of potential targets by the measurement of time-difference-of-arrival (TDOA) of direct and reflected echo signals and calculation the TDOA ellipsoid intersections. A key issue is the proper siting of the sensors with respect to the DVB-T transmitters of opportunity and the wind park dimensions.

Doppler estimation for DVB-T based Passive Radar systems on moving maritime platforms

PR (Passive Radar) systems using digital broadcasting services such as DVB-T (Digital Versatile Broadcasting - Terrestrial) transmission as illuminators represent surveillance solutions which have rapidly evolved and matured over recent years. PR systems typically use coherent integration time in the order of a few hundred milliseconds to acquire enough dynamic for the detection of moving objects. This is done under the assumption that both the illuminator of opportunity and the receiver stay static during this time period. However, advances in miniaturization of high performing computers and data storage devices allowed the design of PR systems that are compact enough to be operated onboard of moving platforms such as cars [1] and airplanes [2], [3]. Deploying PR systems on maritime platforms could enable covert surveillance of small land or sea based targets in littoral environment. A receiver mounted on such a platform may be subjected to highly non-linear motions. In this case a reference signal generated under the assumption of a static scenario may de-correlate from measured Doppler shifted surveillance channel and consequently degrade the PR systems detection performance. Compensation of these detrimental effects requires highly sampled and accurate measurements of the vessels Doppler shift with respect to the transmitter. To study these effects a two channel PR system for DVB-T broadcast reception has been deployed on a small boat to acquire platform motion data in a littoral environment. Based on the data gathered in this trial, a robust method for the Doppler estimation was developed, which uses the DVB-T standards OFDM (Orthogonal Frequency Division Multiplexing) signal features. The validity of this approach is verified with data gathered simultaneously from onboard IMU (Internal Motion Units) data.

Experimental Study for Transmitter Imperfections in DVB-T Based Passive Radar

We investigate effects of transmitter imperfections in terms of time and frequency offsets on the performance of digital video broadcast-terrestrial based passive radars. To facilitate an accurate reconstruction of the transmitted waveform, transmitter imperfections need to be understood and compensated. The transmitter introduced clock imperfections are estimated and compensated via two different methods and tested on real-field measurements acquired in Germany and Australia for single frequency and multiple frequency networks.

Passive radar collision warning system PARASOL

Wind energy is an important pillar of the renewable energy mix and has been growing continuously during recent years. Its acceptance among citizens, however, is not only fostered by the environmentally friendly attitude of wind energy, but also restricted by its visual and acoustic appearance, modifying the picture of nature. In particular, at night, when the red collision avoidance illuminations print blinking lines on the sky, people feel bothered by this safety feature. Moreover, birds are attracted by the red blinking lights and may suffer fatal collisions with the blades of the wind turbines. Hence, switching on the collision avoidance illumination on demand, only when an aircraft appears within a protection sector of a wind park, is a requirement of the wind energy community.