1,1,1,3,4- 1Sapienza University of Rome, Department of Mechanical and Aerospace Engineering, Italy (flavia.giuliani@uniroma1.it)
- 2University of Maryland, Baltimore County, MD 21250, USA
- 3NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
- 4NASA Jet Propulsion Laboratory, Pasadena, CA 91109, USA
The Venus Emissivity, Radio Science, InSAR, Topography, And Spectroscopy (VERITAS) mission, a Discovery class mission selected by NASA in 2021, is designed to answer fundamental questions about Venus’s geological activity and evolution, internal structure, and potential evidence of past or present interior water. VERITAS will carry two instruments – an X-band interferometric SAR (VISAR) and a near-infrared imaging spectrometer (VEM) – as well as a gravity science experiment to address these scientific objectives.
The VERITAS gravity science experiment will produce a global gravity map of significantly higher and more uniform spatial resolution than that achieved by the Magellan mission. Numerical simulations predict that VERITAS will achieve a gravity field spatial resolution between 85 and 120 km, with 90% of the planet mapped at a resolution better than 106 km. Additionally, VERITAS will retrieve important parameters related to Venus’s tidal response and rotational state, providing key constraints on its interior structure.
The gravity science investigation will rely on radio tracking data composed of range and Doppler measurement, collected via two coherent and simultaneous radio links in X and Ka bands. Thanks to the state-of-the-art quality of Doppler tracking data, the system is expected to deliver Doppler accuracy of approximately 18 μm/s at 10 second integration time, for Sun-Probe-Earth (SPE) angles above 15°.
Previous simulations were performed under the reasonable assumption of white noise (uncorrelated measurements) in the tracking data. In this work, we present a more realistic analysis incorporating colored noise components (i.e. correlated measurement, with frequency dependent characteristics) into the Doppler error model. We quantify their impact on gravity field recovery and evaluate the validity of the white noise assumption.
Our analysis was carried out using JPL’s MONTE Orbit Determination software. The enhanced noise model includes contributions from both signal propagation effects and instrumentation noise from ground and onboard systems. Noise sources may be stationary or time-varying (e.g. seasonal variations in the troposphere, SPE dependence in plasma), and exhibit either white or colored spectral profiles (e.g. plasma, frequency and timing systems). Colored components were generated using the algorithm described by [1] and incorporated into the filtering process via a whitening procedure applied prior to estimation, which normalizes residuals, flattens the power spectral density and decorrelates the measurement, since filtering processes in orbit determination typically assume uncorrelated measurements.
We present comparative results for the white-noise and colored-noise scenarios, focusing on gravity field recovery up to degree 220 in spherical harmonics.
The methodology developed for this study is not limited to VERITAS and can be applied to other radio science experiments.
[1] Timmer, J. and Koenig, M. (1995). On generating power law noise. Astronomy and Astrophysics, 300:707.
How to cite: Giuliani, F., De Marchi, F., Durante, D., Cascioli, G., Iess, L., Mazarico, E., and Smrekar, S.: Modeling Colored Noise in Doppler Tracking Data: Mapping Venus’s Gravity Field with VERITAS, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–12 Sep 2025, EPSC-DPS2025-739, https://doi.org/10.5194/epsc-dps2025-739, 2025.
