Examination of the global sampling from the current Formosat-7 Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC-2) between September 2019 and May 2021 identified 500 cases where at least two RO were in close spatial (within 200 km of each other) and temporal (10 min separation or less) proximity and receiving the same GNSS satellite telemetry. Using the nearest 30-min Global Precipitation Measurement (GPM) Integrated Merged (IMERG) precipitation products [20], heavy precipitation conditions were defined when the average precipitation rate exceeded2 mm h\({}^{-1}\) along the RO ray path. Only 50 cases (about 10%) of RO pairs were identified where one RO intersected the air mass within the heavy precipitation, and its nearby pair intersected an independent air mass path fully outside of the heavy precipitation. Figure 2 depicts one example from 5 May 2020, where the collection of RO-estimated relative humidity (RH) and temperature profiles are contrasted. In this case, three of the COSMIC-2 RO were in near-coincidence near heavy precipitation over the tropical Atlantic Ocean. Each RO captures a different environmental air mass surrounding the convection. The RO ray paths that lie outside of, but within 100 km of the main precipitation are considerably drier than the two RO that fall within the precipitation. While the relative humidity in the boundary layer below 850 hPa (where the majority of the column water vapor is concentrated) is not considerably different amongst all three RO, the relatively smaller amount of water vapor in lower free troposphere (LFT) levels within 850-200 hPa is considerably moistened when compared within the moisture structure nearby. The presence of slight variations in the 100-200 hPa temperature region (dashed lines) is noted (see Section 6 on thermal wind). Figure 1: Idealized depiction of a RO setting through a precipitating cloud, showing four ray paths whose lowest level occurs at 8, 6, 4, and 2-km height, and the on-Earth projection of the tangent point of the lowest ray (black symbol). A projection of the 200-km segment of the RO ray path (red dashed lines) nearest the surface is shown on top of the associated surface precipitation estimated by the nearby-time IMERG precipitation data product. The gray shading represents increasing water vapor mixing ratio nearer to the Earth surface. The inherently high resolutions in the vertical and “across-ray” dimension are noted, alongside the coarser path-averaged resolution in the along-ray direction. This present work extends an earlier study by the authors [21], which investigated the basic orbital characteristics of a closely spaced PRO constellation. Section 2 provides the scientific rationale for the PRO constellation observing system. In Section 3, the required number of joint precipitation-moisture profile observations is determined by sampling a large (14 year, 2006-2020) observational dataset from the earlier Formosat-3 COSMIC period. To obtain this number of profile observations, Section 4 investigates different constellation configurations through orbit simulations of PRO opportunities captured from four GNSS telemetries, the Global Positioning System (GPS) operated by the United States Space Force, the Global Navigation Satellite System (GLONASS) operated by Roscosmos, the Galileo system operated by the European Space Agency, and the BeiDou Navigation Satellite System operated by the Chinese National Space Administration (CNSA). Each simulation considers a different number of constellation satellites, satellite temporal spacing (denoted by \(\Delta t\)), orbit inclination and altitude. For each configuration, the required on-orbit time duration is determined, such that the relation between layer-averaged precipitable water vapor and precipitation can be unambiguously discriminated across different tropospheric temperature ranges.