These new missions have included Taiwan/US Formosat-7/Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (COSMIC-2), the European Space Agency (ESA)/European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT)/US Sentinel-6, and commercial RO missions from GeoOptics Inc. (Pasadena, CA, USA) and Spire Global Inc. (Boulder, CO, USA) [30]. The NOAA has included GNSS RO data as one of the crucial long-term observables for weather and climate applications, just as those from IR and MW measurements [30; 31]. The NOAA National Center for Environmental Prediction (NCEP) has assimilated RO data from NOAA missions (i.e., COSMIC-2 and Sentinel-6) and partners' missions (i.e., Korea Multi-Purpose Satellite/Airrang-5 (KOMPSAT-5), Meteorological Operational Satellite-A, -B, and -C (Metop-A, -B, and -C)) into their NWP system. Around 10 K daily occultation profiles were ingested into the NCEP global NWP system. These RO data have demonstrated apparent impacts on the NCEP global NWP, especially in the lower stratosphere [29]. The International Radio Occultation Working Group (IROWG) from the World Meteorology Organization (WMO) recommend that the optimal occultation number for NWP and climate applications is at least 20 K per day, with a uniform spatial and temporal distribution [30]. To include more GNSS RO data in its NWP systems, the NOAA initiated the Commercial Weather Data Pilot (CWDP) program to assess the quality of the commercial GNSS RO data available on the market. After two rounds of pilot studies, the CWDP decided to award the first Indefinite Delivery Indefinite Quantity (IDIQ) contract to GeoOptics and Spire Incs. in 2020. Unlike nationally supported RO missions with more expensive receivers and larger antennae (see below), GeoOptics and Spire used CubeSats. Using the miniature 6U CubeSat version onboard the Community Initiative for Cellular Earth Remote Observation (CICERO) satellites, GeoOptics can collect from approximately 1000 to 2000 occultation profiles per day. While GeoOptics data are collected from a few CubeSats, Spire GNSS RO data are collected from over thirty CubeSats. Currently, Spire can collect around 20 K occultation profiles per day. COSMIC-2 used the TriG (Global Positioning System--GPS, GALILEO, and GLObal Navigation Satellite System--GLONASS) RO Receiver System (TGRS) receiver. The Spire STRATOS RO antenna-receiver payload can track GNSS signals from GPS, GLONASS, GALILEO, and Quasi-Zenith Satellite System (QZSS). Ref. [30] stated that whether RO data from commercial CubeSats are of the same quality as those from other previous validated RO missions (i.e., Formosa Satellite Mission 3-Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC-1 hereafter) [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20], COSMIC-2 [21], etc. ), so that we can still use them for climate and weather prediction studies [5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19], is the most pressing issue for the RO community. The specific questions we need to answer include the following:  
1. Does lower signal-noise ratio (SNR) commercial CubeSat RO data lead to lower precision and more significant observation errors? The SNR is defined as the magnitude of the RO signals divided by the noise level from the receiver in the voltage-to-voltage unit (\(v/v\)). The SNR of the RO signal is one of the critical parameters that indicates the quality of RO measurements (i.e., time delay and excess phases) and Level 2 (L2) data products (i.e., bending angle (BA), refractivity, temperature, and moisture profiles). When RO signals are stronger or the noise level is smaller, the magnitude of the SNR will be larger, which may indicate an improved observation quality. While COSMIC-1 and COSMIC-2 used an antenna of two feet, the antenna from CubeSat is only one foot. Figure 1 depicts the SNR histograms of Spire, COSMIC-2, and KOMPSAT-5 for different GNSS RO emitters. The sample numbers are normalized to the maximum number of the SNR bin.