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Optical Signal Visibility & Detectability

9010-024

Power

EIRP Distance Magnitude Bandwidth CNR
1 kW 2.3 x 1018 W 10 L.Y. +23 1 Hz 34 dB
1 MW 2.3 x 1021 W 10 L.Y. +15.5 10 kHz 24 dB
1 GW 2.3 x 1024 W 10 L.Y. +8 30 MHz 19 dB
1 GW 2.3 x 1024 W 10 L.Y. +8 4.6 GHz -3 dB

Wavelength = 656 nm, 10 meter diameter T/R telescopes.

1 Light Year (L.Y.) = 9.461 x 1015 m.

Eye sensitivity = 6th magnitude.

Planckian starlight at 2nd magnitude ignored.

 

A 1 GW transmitted signal is just below the threshold for naked eye visibility in very good seeing conditions. This received signal would be strong enough for high quality "real-time" FM modulated NTSC/PAL TV signals (30 MHz bandwidth). An incoherent filter with spectral resolution of 1 part in 100,000 would have a bandpass of 0.0066 nm, equivalent to an optical bandwidth of 4.6 GHz. In this situation, the recovered CNR would be -3 dB, and thus the signal would not be detectable without further post-detection signal integration. A high-resolution spectrometer/CCD system would detect this signal because such instrumentation integrates the received signal for a considerable period of time.

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