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Forward Scatter RADAR

JayJay
edited May 2015 in RADAR Discussions
This is the easiest of all (Space) RADAR. Forward Scatter RADAR is reflection of the RF Energy from distant transmitters facilitating the monitoring of only the space over a line between a transmitter of convenience and the receiver, not nearby local activity. This technique generally requires Carrier Wave reception with a dedicated Receiver for Audio detection and/or the Spectral display of a Software Defined Radio of over the horizon illumination sources (Transmitters) typically requiring custom-built high gain antennae pointing above the horizon at the transmitter of interest. Forward Scatter reflections are effectively dimensionless, consisting of narrow Doppler modulation of the reflected transmitter's energy over time. Being that the energy from the forward scatter is arriving at the receiving antennae from above the horizon, the antennae may be physically shielded from local terrestrial RF with several different techniques, some applied together:
  1. Placing the Antennae where a local obstruction like a building or thick forest attenuates local RF sources.
  2. Placing a Faraday Fence of at least 1.5 times the wavelength of interest one half wavelength from the antennae, between the antennae, perpendicular to the offending source.
  3. Placing the Antennae below the level of the ground, behind a berm, hill, or mountain between the antennae and the offending RF source.

Comments

  • JayJay
    edited May 2015
    The Navy Space Surveillance System

    A complete system for satellite detection and tracking, now decommissioned after more than 50 years in continuous operation, this PDF White Paper circa 1959, discusses details of the NAVSPASUR Space Fence. Before its decommissioning, it was the most attractive, powerful, and useful Forward Scatter RADAR system on Earth. NAVSPASUR was used by Amateurs for detecting Satellites and Meteor activity in much of North America.
  • JayJay
    edited May 2015
    CAD scale model of earth-space in relation to my receiver. Even thought the NAVSPASUR RADAR has been decommissioned, this drawing gives the enthusiast for Forward Scatter observations a good idea how Forward Scatter scales to the size of the Earth, the scale of meteor activity, the scale of Satellites to the Earth, and the relative scale to the enthusiast's receiver positions and antennae pointing orientation. During the several years observing this huge RADAR System's reflections, I successfully recorded reflections of The Moon, over-dense Meteor trail clouds lasting 10 minutes, a Meteor Storm of 5 meteors per second, the International Space Station over 1000 miles away, the very brief passing of a Near-Earth Asteroid, Sporadic-E reflections, Geomagnetic Storms, Solar Wind, Mesospheric clouds, and lightning from storms 700 miles over the horizon.
    image
  • JayJay
    edited May 2015
    A passive FPAA based RF scatter meteor detector

    My Comment: While this is a comprehensive White Paper, no attempt is made by the authors to guide the enthusiast toward a working prototype; no mention of what to purchase, what equipment was used to meet the challenge of building a working prototype, or any mention of the actual apparatus to accomplish effective reception. No references or pictorials are given showing actual bench top working prototypes or the reception radio. Included in the Paper are low resolution monochromatic screen shot graphics of vetted prerecorded meteor activity. The authors are obviously accomplished Engineers and Academics, but neglect presenting their work so it may be reproduced for public consumption; depending on already installed and working receivers and antenna. Thus, unless the enthusiast possesses significant experience in Hardware and Software development skills, the paper is merely an Academic curiosity.

    Abstract from the Paper: In the article we (the authors) present a hardware meteor detector. The detection principle is based on the electromagnetic wave reflection from the ionized meteor trail in the atmosphere. The detector uses the ANADIGM field programmable analogue array (FPAA), which is an attractive alternative for a typically used detecting equipment - a PC computer with dedicated software. We implement an analog signal path using most of available FPAA resources to obtain precise audio signal detection. Our new detector was verified in collaboration with the Polish Fireball Network - the organization which monitors meteor activity in Poland. When compared with currently used signal processing PC software employing real radio meteor scatter signals, our low-cost detector proved to be more precise and reliable. Due to its cost and efficiency superiority over the current solution, the presented module is going to be implemented in the planned distributed detectors system. 
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