2 Notation, Acronyms, and Conventions
Table 1Update* defines some acronyms used in this article. Since it is always clear from context, I use the same symbol for theoretical statistical quantities (e.g., underlying spectra) and estimates derived from finite data sets (e.g., sample spectra). All power spectra are twosided.Symbol 
Meaning 
acf 
autocorrelation function 
AMC 
Advanced Media Calibration system (see Section 4.3) 
DOY 
dayofyear, i.e., January 20 = DOY 020 
DSN 
Deep Space Network, the NASA/JPL spacecraft communications and tracking network with antennas at complexes in Australia, Spain, and the United States 
DSS 
Deep Space Station (identifier for specific antennas in the DSN, e.g., “DSS 25”) 
f 
Fourier frequency 
FTS 
Frequency and Timing System, the reference for twoway Doppler tracking 
Kaband 
a deep space communications frequency 32 GHz

KaT 
Cassini’s “Kaband Translator” which accepts an uplink Kaband signal and phasecoherently translates it to a downlink Kaband signal for retransmission to earth 
LISA 
Laser Interferometer Space Antenna, a future lowfrequency GW observatory [24*] 
oneway 
Doppler tracking where the downlink is referenced to an oscillator on the spacecraft 
Sband 
a deep space communications frequency 2.3 GHz 
scintillation 
phase fluctuation due to wave propagation in a random medium [106*, 79*, 40*, 99*, 71*] 
SEP angle 
sunearthprobe angle, the apparent solar elongation angle of the spacecraft 
S_{x}(f) 
power spectrum of x(t), i.e., Fourier transform of [73*, 89*] 
T 
duration of an observation 
T_{2} 
twoway light time between earth and spacecraft 
threeway 
Doppler tracking where the received downlink is coherently referenced to an uplink signal from another station 
twoway 
Doppler tracking where the downlink is coherently referenced to the uplink signal 
Xband 
a deep space communications frequency 8.4 GHz 
x y 
convolution of time series x(t) and y(t) [34] 
y(t) 
generic time series of fractional frequency, [23*]

radio frequency 

Allan deviation, fractional frequency stability at integration time [23*] 

angle between GW propagation direction and earthspacecraft vector; = cos() 
