CONTRIBUTED P A P E R Atmospheric Media Calibration for the Deep Space Network Automatic calibration systems have been developed for tracking spacecraft on inter-planetary missions; the systems account for communication delays due to atmospheric effects. By Yoaz E. Bar-Sever , Christopher S. Jacobs , Stephen Keihm, Gabor E. Lanyi , Charles J. Naudet , Hans W. Rosenberger , Thomas F. Runge , Alan B. Tanner, and Yvonne Vigue-Rodi ABSTRACT | Two tropospheric calibration systems have been developed at the Jet Propulsion Laboratory (JPL) using different technologies to achieve different levels of accuracy, timeliness, and range of coverage for support of interplanetary NASA flight operations. The first part of this paper describes an automated GPS-based system that calibrates the zenith tropo- spheric delays. These calibrations cover all times and can be mapped to any line of sight using elevation mapping functions. Thus they can serve any spacecraft with no prior scheduling or special equipment deployment. Centimeter-level accuracy is provided with 1-h latency and better than 1-cm accuracy after 12 h, limited primarily by rapid fluctuations of the atmospheric water vapor. The second part describes a more accurate line- of-sight media calibration system that is primarily based on a narrow beam, gain-stabilized advanced water vapor radiome- ter developed at JPL. We discuss experiments that show that the wet troposphere in short baseline interferometry can be calibrated such that the Allan standard deviation of phase residuals, a unitless measure of the average fractional frequency deviation, is better than 2  10 15 on time scales of 2000 to approximately 10 000 s. KEYWORDS | Calibrations; Deep Space Network (DSN); GIPSY; GPS; interplanetary; navigation; spacecraft; troposphere; very long baseline interferometry (VLBI); water vapor radiometer (WVR) I. INTRODUCTION The delays experienced by radiometric signals due to refractive index variations in the Earth’s troposphere can be a limiting error source in spacecraft tracking, very long baseline interferometry (VLBI), and radio science applica- tions. Detailed studies of present-day operational space- craft tracking techniques (Doppler, range, and VLBI) indicate that the uncalibrated troposphere delay is a major source of astrometeric error [1]. Radio science experi- ments, such as the Cassini gravitational wave experiment, that involve signal propagation between Earth and the spacecraft will be affected by the tropospheric phase fluctuations and require accurate calibration [2]. VLBI astrometric measurements indicate that the coherence time of observations is limited and the delay-rate is dominated by the phase fluctuations induced by the Earth’s troposphere [3], [4]. To address these tropospheric errors, the Jet Propulsion Laboratory (JPL) has developed two troposphere calibration systems using different technolo- gies to serve different levels of need for accuracy, timeliness, and range of coverage. Section II describes an automated GPS-based system that calibrates the zenith troposphere to support Deep Space Network (DSN) tracking of NASA-JPL interplane- tary spacecraft. These calibrations cover all times and can be mapped to any desired line of sight using appropriate elevation mapping functions. Thus they can serve any DSN user without requiring any prior scheduling or special equipment deployment. They provide centimeter-level zenith-equivalent accuracy with 1-h latency and better than 1-cm accuracy after 12 h, limited primarily by the inhomogeneous distribution and rapid fluctuations of the atmospheric water vapor. Section III describes a complementary system for calibrating the fluctuating line-of-sight wet delay using Manuscript received January 22, 2007; revised May 9, 2007. This work was supported by the National Aeronautics and Space Administration. The authors are with the Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 USA (e-mail: Yoaz.E.BarSever@jpl.nasa.gov; Chris.Jacobs@jpl.nasa.gov; Steve.Keihm@jpl.nasa.gov; Gabor.E.Lanyi@jpl.nasa.gov; Charles.J.Naudet@jpl.nasa.gov; Hans.Rosenberger@jpl.nasa.gov; Thomas.F.Runge@jpl.nasa.gov; Alan.Tanner@jpl.nasa.gov; Yvonne.Vigue-Rodi@jpl.nasa.gov). Digital Object Identifier: 10.1109/JPROC.2007.905181 2180 Proceedings of the IEEE | Vol. 95, No. 11, November 2007 0018-9219/$25.00 Ó2007 IEEE