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Article

Inverting COSMIC-2 Phase Data to Bending Angle and Refractivity Profiles Using the Full Spectrum Inversion Method

1
Cooperative Institute for Satellite Earth System Studies (CISESS), University of Maryland, College Park, MD 20742, USA
2
Center for Satellite Applications & Research (STAR), NESDIS/NOAA, College Park, MD 20740, USA
3
Global Science & Technology, Inc., 7855 Walker Drive, Suite 200, Greenbelt, MD 20770, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Steven Dewitte
Remote Sens. 2021, 13(9), 1793; https://doi.org/10.3390/rs13091793
Received: 5 March 2021 / Revised: 21 April 2021 / Accepted: 26 April 2021 / Published: 5 May 2021
(This article belongs to the Section Atmospheric Remote Sensing)
The radio occultation technique provides stable atmospheric measurements that can work as a benchmark for calibrating and validating satellite-sounding data. Launched on 25 June 2019, the Constellation Observing System for Meteorology, Ionosphere, and Climate 2 and Formosa Satellite Mission 7 (COSMIC-2/FORMOSAT-7) are expected to produce about 5000 high-quality RO observations daily over the tropics and subtropics. COSMIC-2 constellation consists of 6 Low Earth Orbit (LEO) satellites in 24° inclination orbits at 720 km altitude and distributed mainly between 45°N to 45°S. The COSMIC-2 observations have uniform temporal coverage between 30°N to 30°S. This paper presents an independent inversion algorithm to invert COSMIC-2 geometry and phase data to bending angle and refractivity. We also investigate the quality of Global Navigation Satellite System (GNSS) and LEO position vectors derived from the UCAR COSMIC Data Analysis and Archive Center (CDAAC). The GNSS and LEO position vectors are stable with LEO position variations < 1.4 mm/s. The signal-to-noise ratio (SNR) on the L1 band ranges from 300–2600 v/v with a mean of 1600 v/v. The inversion algorithm developed at NOAA Center for Satellite Applications and Research (STAR) uses the Full Spectrum Inversion (FSI) method to invert COSMIC-2 geometry and phase data to bending angle and refractivity profiles. The STAR COSMIC-2 bending angle and refractivity profiles are compared with in situ radiosonde, the current COSMIC-2 products derived from CDAAC, and the collocated European Center for Medium-Range Weather Forecasts (ECMWF) climate reanalysis data ERA5. The mean bias at 8–40 km altitude among the UCAR, ERA5, and STAR is <0.1% for both bending and refractivity, with a standard deviation in the range of 1.4–2.3 and 0.9–1.1% for bending angles refractivity, respectively. In the lowest 2 km, the RO bias relative to ERA-5 shows a strong latitudinal and SNR dependence. View Full-Text
Keywords: radio occultation; Global Navigation Satellite System; excess phase; bending angle; refractivity; Full Spectrum Inversion radio occultation; Global Navigation Satellite System; excess phase; bending angle; refractivity; Full Spectrum Inversion
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MDPI and ACS Style

Adhikari, L.; Ho, S.-P.; Zhou, X. Inverting COSMIC-2 Phase Data to Bending Angle and Refractivity Profiles Using the Full Spectrum Inversion Method. Remote Sens. 2021, 13, 1793. https://doi.org/10.3390/rs13091793

AMA Style

Adhikari L, Ho S-P, Zhou X. Inverting COSMIC-2 Phase Data to Bending Angle and Refractivity Profiles Using the Full Spectrum Inversion Method. Remote Sensing. 2021; 13(9):1793. https://doi.org/10.3390/rs13091793

Chicago/Turabian Style

Adhikari, Loknath, Shu-Peng Ho, and Xinjia Zhou. 2021. "Inverting COSMIC-2 Phase Data to Bending Angle and Refractivity Profiles Using the Full Spectrum Inversion Method" Remote Sensing 13, no. 9: 1793. https://doi.org/10.3390/rs13091793

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