ARLA/CLUSTER: Estranhos sinais de radio vindos de Saturno.

[João Costa > CT1FBF]

Strange radio waves from Saturn

A YouTube video shows the unusual radio waves from Saturn picked up by
the space probe Cassini.

The YouTube description reads:

On July 1, 2005 at 01:12 SCET-UTC, Cassini started the engine burn
required to insert the spacecraft into orbit around Saturn (SOI).

Almost 30 minutes later, Cassini was occulted by Saturn's rings as
seen from the Earth. The geometric ring occultation covered all main
ring features, starting at the outer edge of Ring A at 01:42 and
ending at the inner edge of Ring C at 02:40. From 01:12 to 03:07,
Cassini X-band radio signal (3.6 cm-wavelength) was turned on,
primarily to monitor the burn.

The sinusoidal transmitted signal was referenced to the on board
ultrastable oscillator, allowing measurement of the signal amplitude
and phase at the 70-m ground receiving station of the Deep Space
Network at Canberra, Australia. As a useful by-product, a complete
ring occultation observation, including free-space baseline, was
achieved. Because of the special orientation of the spacecraft during
the burn, the Cassini low-gain antenna was used to transmit the
signal.

Nominal radio occultations are conducted using the high-gain antenna,
hence have intrinsic free-space signal-to-noise ratio (SNR) higher by
a factor of ~10,000 than the SOI occultation. Nonetheless, clearly
detectable signal was observed during occultation by features in Rings
A, Cassini Division, and Ring C, but not Ring B. The measurements,
after reconstruction to remove diffraction effects, may be used to
obtain an optical-depth and phase-shift profiles of resolved ring
features.

Achievable radial resolution primarily depends on the
ring-opening-angle B, available free-space SNR, and occultation
geometry. We compare radial resolution achievable for the Cassini SOI
occultation (B = 24.7 deg, SNR = 10 dB-Hz) with those of the Voyager
ring occultation (B = 5.9 deg, SNR = 50 dB-Hz), and contrast the
results with those expected from nominal radio occultations during the
Cassini tour. Example optical depth profiles from the Cassini SOI
occultation are presented.

Watch Strange radio waves picked up by Cassini from Saturn
http://www.youtube.com/watch?v=Z9PAxFzxx9M

Fonte: George Boorer ZL3PN.