2004), Measurements and calibration of tropospheric delay at goldstone from the Cassini media calibration system

One and one-half years of near-continuous measurements of the troposphere-induced path delay at Goldstone have been analyzed in order to (1) characterize the troposphere-delay fluctuations in a statistical sense and (2) evaluate the path-delay calibration performance of the Media Calibration System (MCS) at DSS 25. Both the wet and dry components of delay are considered. Statistics based on 5-minute-interval MCS data indicate wet-delay temporal structure function (the expectation value of delay differences versus the time interval) values of 1 mm at 5 minutes, 5 mm at 1 hour, and 2 cm at 1 day, increasing to an asymptotic level of 3 to 4 cm for time scales greater than 2 days. At time scales of 1000 to 10,000 seconds, Allan standard deviation (ASD) computations of the wet-delay variations indicate slightly higher fluctuation levels than shown in a previous study. The differences are attributable to the inclusion of cloudy conditions in the present study. The dry-delay fluctuation levels are approximately one-third the wet-delay levels at all time scales from minutes to weeks. The ability of the MCS to accurately calibrate the delay fluctuations was assessed by comparing side-by-side results from the two redundant instrumentation sets that comprise the MCS. Based on data during the first three Cassini radio science ex-periments, the MCS surpasses the requirement of the Cassini Gravitational Wave Experiment (residual ASD < 1.1 × 10−15 s/s) at all time scales>1000 seconds. For time scales extending out to weeks, the MCS has demonstrated a precision better than 0.06 cm for monitoring zenith-equivalent delay variations during spacecraft-tracking operations