An experimental study of the temporal statistics of radio signals scattered by rain

A fixed-beam bistatic CW experiment designed to measure the temporal statistics of the volume reflectivity produced by hydrometeors at several selected altitudes, scattering angles, and at two frequencies (3.6 and 7.8 GHz) is described. Surface rain gauge data, local meteorological data, surveillance S-band radar, and great-circle path propagation measurements were also made to describe the general weather and propagation conditions and to distinguish precipitation scatter signals from those caused by ducting and other nonhydrometeor scatter mechanisms. The data analysis procedures were designed to provide an assessment of a one-year sample of data with a time resolution of one minute. The cumulative distributions of the bistatic signals for all of the rainy minutes during this period are presented for the several path geometries

Region-enhanced passive radar imaging

The authors adapt and apply a recently-developed region-enhanced synthetic aperture radar (SAR) image reconstruction technique to the problem of passive radar imaging. One goal in passive radar imaging is to form images of aircraft using signals transmitted by commercial radio and television stations that are reflected from the objects of interest. This involves reconstructing an image from sparse samples of its Fourier transform. Owing to the sparse nature of the aperture, a conventional image formation approach based on direct Fourier transformation results in quite dramatic artefacts in the image, as compared with the case of active SAR imaging. The regionenhanced image formation method considered is based on an explicit mathematical model of the observation process; hence, information about the nature of the aperture is explicitly taken into account in image formation. Furthermore, this framework allows the incorporation of prior information or constraints about the scene being imaged, which makes it possible to compensate for the limitations of the sparse apertures involved in passive radar imaging. As a result, conventional imaging artefacts, such as sidelobes, can be alleviated. Experimental results using data based on electromagnetic simulations demonstrate that this is a promising strategy for passive radar imaging, exhibiting significant suppression of artefacts, preservation of imaged object features, and robustness to measurement noise

Stanford telemetry monitoring experiment on Lunar Explorer 35 Final report

Explorer 35 data analysis including occultation study and antenna pattern interpretation along with electromagnetic property experiment

Remote Sensing of Ocean Winds and Waves with Bistatic HF Radar

High frequency, or HF, coastal radars collect a vast amount of data on ocean currents, winds and waves. The technology continuously measures the parameters, by receiving and interpreting electromagnetic waves scattered by the ocean surface. Formulating the methods to interpret the radar data, to obtain accurate measurements, has been the focus of many researchers since the 1970s. Much of the existing research has been in monostatic radar theory, where the transmitter and receiver are stationed together. However, a larger, higher quality dataset can be obtained by utilising bistatic radar theory, whereby the transmitter and receiver are located at separate sites. In this work, the focus is on bistatic radar, where the most commonly used mathematical model for monostatic radar is adapted for bistatic radar. Methods for obtaining current, wind and wave information from the model are then described and in the case of winds and waves, tested. Investigating the derived model shows that it does not always fit the real data well, due to undesirable effects of the radar. These effects can be incorporated into the model but then the existing methods used to obtain ocean information may not be applicable. Therefore, a new method for measuring ocean waves from the model is developed. The recent advances in machine learning have been substantial, with the neural network becoming proficient at finding the link between complexly related datasets. In this work, a neural network is used to model the relationship between the developed radar model and the directional ocean spectrum. It is shown to successfully invert both monostatic and (for the first time) bistatic HF radar data and with this success, it becomes a viable option for obtaining ocean surface parameters from radar data

An analysis of bi-directional use of frequencies for satellite communications

The bi-directional use of frequencies allocated for space communications has the potential to double the orbit/spectrum capacity available. The technical feasibility of reverse band use (RBU) at C-band (4 GHz uplinks and 6 GHz downlinks) is studied. The analysis identifies the constraints under which both forward and reverse band use satellite systems can share the same frequencies with terrestrial, line of sight transmission systems. The results of the analysis show that RBU satellite systems can be similarly sized to forward band use (FBU) satellite systems. In addition, the orbital separation requirements between RBU and FBU satellite systems are examined. The analysis shows that a carrier to interference ratio of 45 dB can be maintianed between RBU and FBU satellites separated by less than 0.5 deg., and that a carrier to interference ratio of 42 dB can be maintained in the antipodal case. Rain scatter propagation analysis shows that RBU and FBU Earth stations require separation distances fo less than 10 km at a rain rate of 13.5 mm/hr escalating to less than 100 km at a rain rate of 178 mm/hr for Earth station antennas in the 3 to 10 m range