http://www.globalsecurity.org/wmd/world/israel/nuke-test.htm

"In addition to detection satellites, the United States maintains a global network for detecting other atomic explosion phenomena, including sound waves, seismic shock waves traveling through Earth, and hydroacoustic pulses traversing Earth's oceans. Of these, the best data were from the hydroacoustic signals collected on devices called hydrophones. The hydrophone data indicated signals both from a direct path and from a reflection of the Antarctic's Scotia Ridge. Analyses of these signals conducted by the Naval Research Laboratory confirmed that they had been generated at a time and location consistent with the Vela 6911 detection and that their intensity was consistent with a small nuclear explosion on, or slightly under, the ocean's surface.

More evidence came from a Los Alamos researcher using a radio telescope for an unrelated project in Arecibo, Puerto Rico, detected a traveling ionospheric disturbance - a ripple in Earth's upper atmosphere - moving south to north during the early morning hours of September 22, 1979, something researchers had never before witnessed.

But such evidence was discounted by the White House panel.

In 1979, this analysis had been vigorously challenged by the Carter administration. The challenge was driven by a general mistrust in aging satellites and an unwillingness to accept the efficacy of other evidence. Instead, the Carter administration assembled a panel of scientists from academia to review the data. After their review, the panel concluded that, lacking independent collaborative data to support a nuclear origin of the signals, the original interpretation of the satellite data could not be justified. The panel said the flash could have been caused by a combination of natural events, specifically a micrometeorite impact on the detector sunshade, followed by small particles ejected as a result of the impact.

But Los Alamos scientists were not dissuaded. "The whole federal laboratory community came to the conclusion that the data indicated a bomb," Los Alamos scientist Dave Simons said. "But in the administration's view, because the evidence was weak, they took exception to the information and our analysis. ... It was unsettling because we were quite thoroughly convinced of our interpretation," Simons said.

Los Alamos scientists remained convinced that the flash was a nuclear detonation and invested substantial effort in analyzing the signal. Subsequently, Los Alamos researchers published an unclassified paper describing the characteristics of optical signals caused by nuclear explosions.

In February 1980, CBS News was the first to suggest that Israel helped South Africa conduct a nuclear test. CBS received information from "informed sources," but until now, no South African government official was willing to lend the report any credibility.

In 1981 TIROS-N plasma data and related geophysical data measured on 22 September 1979 were analyzed by Los Alamos to determine whether the electron precipitation event detected by TIROS-N at 00:54:49 universal time could have been related to a surface nuclear burst (SNB). The occurrence of such a burst was inferred from light signals detected by two Vela bhangmeters approx. 2 min before the TIROS-N event. The precipitation was found to be unusually large but not unique. It probably resulted from passage of TIROS-N through The precipitating electrons above a pre-existing auroral arc that may have brightened to an unusually high intensity from natural causes approx. 3 min before the Vela signals. On the other hand, no data were found that were inconsistent with the SNB interpretation of the 22 September Vela observations. In fact, a patch of auroral light that suddenly appeared in the sky near Syowa Base, Antarctica a few seconds after the Vela event can be interpreted (though not uniquely) as a consequence of the electromagnetic pulse of an SNB.

In an 20 April 1997 article that appeared in the Israeli Ha'aretz Daily Newspaper, South African Deputy Foreign Minister Aziz Pahad confirmed for the first time that a flare over the Indian Ocean detected by an American satellite in September 1979 was from a nuclear test. This statement was confirmed by the American Embassy in Pretoria, South Africa, as an accurate account of what Pahad officially acknowledged. The article said that Israel helped South Africa develop its bomb designs in return for 550 tons of raw uranium and other assistance.

With Pahad's revelation, Los Alamos National Laboratory scientists said this controversy can at last reach closure. Original analyses conducted by Los Alamos scientists and others in the US intelligence community said the flash could only be from a nuclear test. Now, their studies had been vindicated."