Measurements and Calibration of Tropospheric Delay at Goldstone from the Cassini Media Calibration System
Abstract
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 experiments, the MCS surpasses the requirement of the Cassini Gravitational Wave Experiment (residual ASD <1.1 x 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.
- Publication:
-
Interplanetary Network Progress Report
- Pub Date:
- August 2004
- Bibcode:
- 2004IPNPR.158A...1K