Los Alamos National Laboratory
Jim Danneskiold or John Gustafson, 505-667-7000
FIRST RESULTS FROM NONPROLIFERATION SATELLITE EXPAND KNOWLEDGE OF LIGHTNING, TIPPs
SAN FRANCISCO, Dec. 9, 1997 -- Just three months after its launch, Los Alamos National Laboratory's FORTE satellite is detecting many thousands more radio bursts from lightning strikes and other phenomena than previously reported.
Initial data from FORTE, presented today in a poster session at the semi- annual meeting of the American Geophysical Union, should help researchers locate from space the mysterious and powerful radio bursts called trans- ionospheric pulse pairs, or TIPPS. The data also will help solve questions about the conection between TIPPS, whose origins aren't well understood, and thunderstorm activity, said researcher Bob Franz of Los Alamos' Nonproliferation and International Security Division.
FORTE, which stands for Fast On-orbit Recording of Transient Events, is a lightweight satellite designed to test technology to monitor compliance with arms control treaties. FORTE's instruments detect, record and analyze bursts of radio energy and light arising from near Earth's surface, and gather data on the physics of lightning and the ionosphere.
A joint project of the Department of Energy's Los Alamos and Sandia national laboratories, FORTE was launched August 29 into a polar orbit about 480 miles above Earth.
TIPPs, first reported in 1993 by the Blackbeard radio experiment on board Los Alamos' ALEXIS satellite, are powerful radio impulses -- a hundred times stronger and a thousand times briefer than the radio emissions generated by lightning. They are believed to come from an altitude of three to 10 miles in the vicinity of thunderstorm complexes.
"Where Blackbeard detected about 1,000 very bright, spectacular TIPPs over the past four years, FORTE can detect 1,000 a day, and is seeing TIPPs that were otherwise buried in the radio noise," Franz said. "We're also working on ways to pinpoint the location of TIPPs from space for the first time."
Due to its better sensitivity, FORTE's detectors also are spotting lightning strikes at a much higher rate than Blackbeard, leading Franz and his colleagues to speculate that radio frequency emissions from lightning may be taking place at a higher rate than previously believed.
"It may be that a lot of what we're seeing is inter-cloud lightning, rather than cloud-to-ground lightning," Franz said. "Inter-cloud lightning rates really haven't been measured accurately before."
FORTE is revolutionary because it integrates a wide-field optical imager that can locate lighting flashes and a sensitive radio frequency sensor system on the same platform.
The optical imagers allow researchers on the ground to pinpoint a lightning flash within six miles, roughly the size of single thunderstorm cell.
"We've already seen the trail of lightning locations as FORTE tracks a thunderstorm over just a few minutes of satellite motion," Franz said.
This precision and the integrated way that FORTE looks at both natural and man-made radiofrequency and optical signals may help researchers determine whether TIPPs are associated with a corresponding optical pulse, Franz said.
To come up with a precise location for TIPPs, Los Alamos scientists are studying the characteristics of the signals detected by FORTE, then feeding the signals into a computer model that includes other ionospheric data from satellites and ground stations. They use the model to study changes in the time between the two pulses of the TIPP -- a gap of about 50 millionths of a second -- that depend on the geometry between the satellite and the source of the TIPP. The model yields a location, which then can be correlated with locations of optical pulses.
Los Alamos scientists are using another major FORTE instrument, an event classifier, to distinguish the inherent structures of radio frequency signals in the 30-300 megahertz range, which includes commercial television, FM radio, aircraft navigation and communication bands. Weeding these out from lightning and signals from rogue nuclear weapons tests is a key to future nonproliferation satellites.
FORTE receives radio frequency signals via a novel, 35-foot-long antenna that has two arrays set at right angles to each other. The antenna, which was coiled up like a Slinky toy in a foot-high canister aboard the satellite, was unfurled last month.
Data from FORTE eventually will aid scientists studying global climate effects, where the lightning flash rate within a thunderstorm can be related to the precipitation rate. The associated radio frequency emission data can help explain the atmospheric breakdown mechanisms that lead to lightning discharges.
The improved detection technology on FORTE is the first step toward an autonomous radio frequency detection system that performs reliably in the electromagnetically noisy environment of near-Earth space. Known as the V- sensor, for Verification, the sensor is proposed to fly on a future mission of the Global Positioning System, or GPS.
FORTE's structure, made entirely of graphite-reinforced epoxy, weighs just 90 pounds, so more payload goes into orbit. The new process developed for building FORTE by Los Alamos and Composite Optics Inc. of San Diego allows the satellite to be snapped together like a model aircraft, an assembly method that is two-thirds faster and 60 percent less expensive than other methods.
The seven-foot-tall satellite, which weighs 470 pounds fully loaded, carries three decks with aluminum honeycomb cores and composite facing to support the onboard instruments. Launch cost was about $15 million, while development and construction of the satellite cost about $35 million.
FORTE is the second satellite built by Los Alamos. The first one, ALEXIS, was launched in 1993 and still operates, well past its one-year projected lifetime. ALEXIS carries X-ray telescopes and a radio burst detection experiment, Blackbeard, that provides a less sophisticated version of FORTE's ability to correlate lightning-induced radio frequency pulses with flashes of light.
FORTE information is online at:
http://nis-www.lanl.gov/nis-projects/forte/index.html.
Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy. -30-
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