Authors: Jia Huang (SSL/UCB), Davin E. Larson (SSL/UCB), Orlando Romeo (SSL/UCB), Mingzhe Liu (SSL/UCB), Roberto Livi (SSL/UCB), Ali Rahmati (SSL/UCB), Phyllis Whittlesey (SSL/UCB), Samer T. Alnussirat (SSL/UCB), Sam Badman (CfA), The SWEAP/FIELDS team

A key science goal for Parker Solar Probe (PSP) is to measure the angular momentum loss rate of the Sun due to non-radial outflow of the solar wind. Inside the subsonic region, the corona is expected to approximately co-rotate. This results in a significant transverse velocity component in the solar wind that is most significant in the near Sun region. As of orbital Encounters 22 and 23, PSP reached within ~9.8 solar radii (R_S) of the Sun, and additionally the extremely large transverse spacecraft velocity (191 km/sec at perihelion) brings the aberrated solar wind ion distribution almost fully in the FOV of the SPAN-Ion instrument, resulting in a much better determination of the solar wind velocity. Accurate determination of the transverse velocity is biased by instrumental issues. We have re-evaluated relative geometric values for the SPAN-Ion anodes to improve systematic uncertainties in the transverse velocity of both proton and alpha particles that have not been accounted for in previous studies. We also apply forward modeling techniques to account for the unmeasured portion of the SPAN-I FOV. In addition, we will examine alternative methods to derive the transverse solar wind velocity with the best FOV coverage to date.