Initial Assessment of the COSMIC-2/FORMOSAT-7 Neutral Atmosphere Data Quality in NESDIS/STAR Using In Situ and Satellite Data

Abstract

A COSMIC-1/FORMOSAT-3 (Constellation Observing System for Meteorology, Ionosphere, and Climate-1 and Formosa Satellite Mission 3) follow-on mission, COSMIC-2/FORMOSAT-7, had been successfully launched into low-inclination orbits on 25 June 2019. COSMIC-2 has a significantly increased Signal-to-Noise ratio (SNR) compared to other Radio Occultation (RO) missions. This study summarized the initial assessment of COSMIC-2 data quality conducted by the NOAA (National Oceanic and Atmospheric Administration) Center for Satellite Applications and Research (STAR). We use validated data from other RO missions to quantify the stability of COSMIC-2. In addition, we use the Vaisala RS41 radiosonde observations to assess the accuracy and uncertainty of the COSMIC-2 neutral atmospheric profiles. RS41 is currently the most accurate radiosonde observation system. The COSMIC-2 SNR ranges from 200 v/v to about 2800 v/v. To see if the high SNR COSMIC-2 signals lead to better retrieval results, we separate the COSMIC-2–RS41 comparisons into different SNR groups (i.e., 0–500 v/v group, 500–1000 v/v group, 1000–1500 v/v group, 1500–2000 v/v group, and >2000 v/v group). In general, the COSMIC-2 data quality in terms of stability, precision, accuracy, and uncertainty of the accuracy is very compatible with those from COSMIC-1. Results show that the mean COSMIC-2–RS41 water vapor difference from surface to 5 km altitude for each SNR groups are equal to −1.34 g/kg (0–500 v/v), −1.17 g/kg (500–1000 v/v), −1.33 g/kg (1000–1500 v/v), −0.93 g/kg (1500–2000 v/v), and −1.52 g/kg (>2000 v/v). Except for the >2000 v/v group, the high SNR measurements from COSMIC-2 seem to improve the mean water vapor difference for the higher SNR group slightly (especially for the 1500–2000 v/v group) comparing with those from lower SNR groups.

An Analysis Study of FORMOSAT-7/COSMIC-2 Radio Occultation Data in the Troposphere

“…Statistically, the rate of penetration below 1 km is about 40% for FS3 and 80% for FS7. Similar statistical results are also found in [7,10].…”

“…In the lower troposphere, RAOB has maximum deviations of about 1.5 °C and 2.2 hPa from the FS7 RO temperature and vapor pressure, respectively. A negative difference up to − hPa in the lower troposphere is present for RAOB, and the negative moisture deviation below 2 km is in agreement with the verification in [10], which may be associated with the tracking uncertainty due to the superrefraction from FS7 [7,[9][10]. Generally, the absolute magnitudes of temperature and vapor pressure differences are less than 0.5 °C and 1 hPa, respectively, in the troposphere.…”

“…Before the comparisons with multiple datasets, more accurate independent observations should be used to quantify the data quality of FS7 wet RO retrievals. RAOB as a ground-truth measurement is useful for verification as described in [10], despite few being available over the ocean. For verification on oceanic RO soundings, the Central Weather Bureau (CWB) took two flights to obtain the in situ observations with DROP, which were released at times closer to the occurrence of RO soundings.…”

“…The negative biases in the lower troposphere may be caused by SR, tracking depth and noise, and fluctuations of refractivity, etc., as discussed in [9]. The authors of [10] compared FS7 RO refractivity with Vaisala RS41 radiosonde data, which is currently the most accurate radiosonde observation and showed a negative difference in the lower troposphere. The negative biases further transfer to the RO wet products (the descendant data) after One-Dimensional Variational (1DVAR) retrieval ( https://cdaac-www.cosmic.ucar.edu/cdaac/doc/documents/1dvar.pdf).…”

Looking for Earthquake Precursors From Space: A Critical Review

“…From IVM measurements of the ion velocity, it is also possible to estimate the electric field. The FORMOSAT-7/COSMIC-2 mission offers the unique capabilities: 1) to carry simultaneously both vertical soundings of the ionospheric and in-situ plasma observations; and 2) to provide measurements with a constellation of six satellites (Ho et al, 2020). These features will allow investigating pre-, co-and post-seismic phenomena with a high-resolution (in time and space) measurements at low latitude (Liu et al, 2020b).…”