Summary of noise levels and transfer functions

Table 2:

Noise sources and contributions (expressed as Allan deviation [23

] at 1000 s integration) in Cassini-era precision Doppler tracking GW observations. This table is adapted from [1

, 22

]. SEP: sun-earth-probe (solar elongation) angle; SNR: signal-to-noise ratio of the downlink. Models of the spectra of the individual noises are given in [105



Noise source	$σ y$ [1000 s]	Comment


Frequency standard	$≃$ 8 $×$ 10^–16	fundamental noise source [1 , 22 ]
Antenna mechanical	$≃$ 2 $×$ 10^–15	DSS 25 (34-m antenna) under favorable conditions [19 ]
Ground electronics	$≃$ 2 $×$ 10^–16	measured in controlled test, DSS 25 [1 ]
Plasma phase scintillation	$<$ 10^–15, for Ka-band and SEP $∘ > 150$	$σy$ depends on SEP; dispersive; scales as square of radio wavelength; see Figure 10
Stochastic spacecraft motion	$≃$ 2 $×$ 10^–16	Cassini in quiet cruise [122 , 123 ]; see Figure 13 Update
Receiver thermal noise	few $×$ 10^–16	depends on link SNR and detector bandwidth [23 ]
Spacecraft transponder noise	$≃$ 10^–16	preflight tests of Cassini Ka-band translator [1 , 22 ]
Tropospheric scintillation (raw)	$<$ 3 $×$ 10^–15 to $≃$ 30 $×$ 10^–15	variable; nondispersive [20 , 71 ]
Tropospheric scintillation (corrected)	$<$ 1.5 $×$ 10^–15 to $≃$ 3 $×$ 10^–15	under favorable conditions [19 ]; median conditions in connected-element interferometry tests [90 ]

4.10 Summary of noise levels and transfer functions