Reprocessing the Pioneer Venus radio occultation data

RIU-Planetary Research is reprocessing original data from the Pioneer Venus Orbiter radio science experiment ORO which were recorded between 1979 and 1988. These valuable raw open-loop data are available from the PDS (Planetary Data System). However, the original processed atmospheric and ionospheric profiles from the Venus atmosphere are not available on the PDS.

A limited selection of original ORO profiles, primarily comprising electron density profiles, with only a few temperature profiles, was obtained from an NSSDC server and published by Withers et al. (2020) on a Boston University server.

We are using state-of-the-art software code along with an updated version of the Venus gravity field (Konopliv et al., 1999) and newly processed PVO orbit data provided as SPICE kernels.

The longer open-loop observation sets consist of ingress data (at two-way) and egress data (at one-way). The uplink was performed at S-band, while the downlink was coherent dual-frequency S-band and X-band. The X-band downlink was activated just before entering occultation, resulting in a relatively short baseline.

We shall present atmospheric and ionospheric profiles derived from S-band and differential Doppler recordings, respectively, processed from the original Pioneer Venus Orbiter raw open-loop data sets. We will then compare these profiles with VEX-VeRa radio occultation profiles obtained under comparable observation conditions, as well as with the few existing original PVO profiles retrieved from the Boston University server account (Withers et al., 2020).

The VEX-VeRa profiles show excellent agreement with the reprocessed ORO profiles under similar observation conditions. However, the few original ORO profiles exhibit a noticeable altitude shift of several kilometers, most likely caused by the less precise PVO orbit solution available at the time of observation.