{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T02:49:38Z","timestamp":1760150978953,"version":"build-2065373602"},"reference-count":33,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2022,2,1]],"date-time":"2022-02-01T00:00:00Z","timestamp":1643673600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100002261","name":"Russian Foundation for Basic Research","doi-asserted-by":"publisher","award":["20-05-00189 A"],"award-info":[{"award-number":["20-05-00189 A"]}],"id":[{"id":"10.13039\/501100002261","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Multiple radio occultation (RO) missions are currently providing observations that are assimilated by the world\u2019s leading numerical weather prediction centers. These RO missions use the same signals originating from the Global Navigation Satellite Systems (GNSS), but they have different satellite designs and sizes with different antennas and receivers. This results in different noise levels for different missions. Although the amplitude data are characterized by the Signal-to-Noise Ratio (SNR), the noise, to which they are normalized, is not the real Noise Floor (NF) of the RO observations. We study the statistical distributions of the SNR and NF for RO missions including COSMIC, COSMIC2, METOP-A, METOP-B, METOP-C, and Spire. We demonstrate that different missions have different NF values and different NF and SNR distributions, sometimes multimodal. We propose to use the most probable NF value as an SNR normalization constant in order to compare the SNR values from different RO missions.<\/jats:p>","DOI":"10.3390\/rs14030691","type":"journal-article","created":{"date-parts":[[2022,2,1]],"date-time":"2022-02-01T22:16:18Z","timestamp":1643753778000},"page":"691","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":8,"title":["Noise Floor and Signal-to-Noise Ratio of Radio Occultation Observations: A Cross-Mission Statistical Comparison"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-2738-0547","authenticated-orcid":false,"given":"Michael","family":"Gorbunov","sequence":"first","affiliation":[{"name":"A. M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Pyzhevsky Per. 3, 119017 Moscow, Russia"},{"name":"Spire Global, Inc., 1690 38th Street, Boulder, CO 80301, USA"},{"name":"Hydrometcenter of Russia, 13, Building 1, Bolshoy Predtechensky Lane, 123376 Moscow, Russia"}]},{"given":"Vladimir","family":"Irisov","sequence":"additional","affiliation":[{"name":"Spire Global, Inc., 1690 38th Street, Boulder, CO 80301, USA"}]},{"given":"Christian","family":"Rocken","sequence":"additional","affiliation":[{"name":"Spire Global, Inc., 1690 38th Street, Boulder, CO 80301, USA"}]}],"member":"1968","published-online":{"date-parts":[[2022,2,1]]},"reference":[{"key":"ref_1","unstructured":"Sokolovskiy, S., Schreiner, W., Weiss, J., Zeng, Z., Hunt, D., and Braun, J. (2019, January 19\u201325). Initial Assessment of COSMIC-2 Data in the Lower Troposphere. Proceedings of the Joint 6th ROM SAF Data User Workshop and 7th IROWG Workshop, Elsinore, Denmark."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"e2019GL086841","DOI":"10.1029\/2019GL086841","article-title":"COSMIC-2 Radio Occultation Constellation: First Results","volume":"47","author":"Schreiner","year":"2020","journal-title":"Geophys. Res. Lett."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Ho, S.P., Zhou, X., Shao, X., Zhang, B., Adhikari, L., Kireev, S., He, Y., Yoe, J.G., Xia-Serafino, W., and Lynch, E. (2020). Initial Assessment of the COSMIC-2\/FORMOSAT-7 Neutral Atmosphere Data Quality in NESDIS\/STAR Using In Situ and Satellite Data. Remote Sens., 12.","DOI":"10.3390\/rs12244099"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"e2020JA028028","DOI":"10.1029\/2020JA028028","article-title":"The Early Results and Validation of FORMOSAT-7\/COSMIC-2 Space Weather Products: Global Ionospheric Specification and Ne-Aided Abel Electron Density Profile","volume":"125","author":"Lin","year":"2020","journal-title":"J. Geophys. Res. Space Phys."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"109","DOI":"10.1007\/s10291-009-0142-3","article-title":"Metop-GRAS in-orbit instrument performance","volume":"14","author":"Bonnedal","year":"2010","journal-title":"GPS Solut."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"2255","DOI":"10.5194\/amt-4-2255-2011","article-title":"Analysis of GPS radio occultation data from the FORMOSAT-3\/COSMIC and Metop\/GRAS missions at CDAAC","volume":"4","author":"Schreiner","year":"2011","journal-title":"Atmos. Meas. Tech."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"336","DOI":"10.1016\/j.asr.2010.07.028","article-title":"GRAS radio occultation on-board of Metop","volume":"47","author":"Andres","year":"2011","journal-title":"Adv. Space Res."},{"key":"ref_8","first-page":"375","article-title":"Case Study of Impact of Assimilating MetOp GPS Radio Occultation Observation on Top of COSMIC Data on Typhoon Forecast","volume":"50","author":"Hsieh","year":"2018","journal-title":"J. Aeronaut. Astrnaut. Aviat."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"1031","DOI":"10.5194\/amt-11-1031-2018","article-title":"An intercomparison of stratospheric gravity wave potential energy densities from METOP GPS radio occultation measurements and ECMWF model data","volume":"11","author":"Rapp","year":"2018","journal-title":"Atmos. Meas. Tech."},{"key":"ref_10","unstructured":"Irisov, V., Duly, T., Nguyen, V., Masters, D., Correig, O.N., Tan, L., Yuasa, T., and Ector, D. (2018, January 10\u201314). Recent radio occultation profile results obtained from Spire CubeSat GNSS-RO constellation. Proceedings of the AGU Fall Meeting, Washington, DC, USA."},{"key":"ref_11","unstructured":"Irisov, V., Ector, D., Duly, T., Nguyen, V., Nogues-Correig, O., Tan, L., and Yuasa, T. (2018, January 10\u201314). Atmospheric Radio Occultation Observation from Spire CubeSat Nanosatellites. Proceedings of the AMS Annual Meeting, Washington, DC, USA."},{"key":"ref_12","unstructured":"Gorbunov, M., Koval, O., and Kirchengast, G. (2019, January 19\u201325). Kirkwood Distribution Function and its Application for the Analysis of Radio Occultation Observations. Proceedings of the Joint 6th ROM SAF User Workshop and 7th IROWG Workshop, EUMETSAT ROM SAF, Elsinore, Denmark."},{"key":"ref_13","unstructured":"Irisov, V., Nguyen, V., Duly, T., Nogues-Correig, O., Tan, L., Yuasa, T., Masters, D., Sikarin, R., Gorbunov, M., and Rocken, C. (2019, January 19\u201325). Radio Occultation Observations and Processing from Spire\u2019s CubeSat Constellation. Proceedings of the Joint 6th ROM SAF User Workshop and 7th IROWG Workshop, EUMETSAT ROM SAF, Elsinore, Denmark."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"3772","DOI":"10.1002\/qj.3872","article-title":"An assessment of GNSS radio occultationdata produced by Spire","volume":"146","author":"Bowler","year":"2020","journal-title":"Q. J. R. Meteorol. Soc."},{"key":"ref_15","unstructured":"Kursinski, E.R. (2019, January 19\u201325). Weather & Space Weather RO Data from PlanetiQ Commercial GNSS RO. Proceedings of the Joint 6th ROM SAF Data User Workshop and 7th IROWG Workshop, Elsinore, Denmark."},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Chang, H., Lee, J., Wang, Y., Breitsch, B., and Morton, Y.J. (2020, January 21\u201325). Preliminary Assessment of CICERO Radio Occultation Performance by Comparing with COSMIC I Data. Proceedings of the 33rd International Technical Meeting of the Satellite Division of The Institute of Navigation, Online.","DOI":"10.33012\/2020.17754"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"954","DOI":"10.1002\/2014RS005436","article-title":"Observation, analysis, and modeling of deep radio occultation signals: Effects of tropospheric ducts and interfering signals","volume":"49","author":"Sokolovskiy","year":"2014","journal-title":"Radio Sci."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"D22111","DOI":"10.1029\/2010JD014058","article-title":"On the uncertainty of radio occultation inversions in the lower troposphere","volume":"115","author":"Sokolovskiy","year":"2010","journal-title":"J. Geophys. Res."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"L14816","DOI":"10.1029\/2006GL026112","article-title":"GPS profiling of the lower troposphere from space: Inversion and demodulation of the open-loop radio occultation signals","volume":"33","author":"Sokolovskiy","year":"2006","journal-title":"Geophys. Res. Lett."},{"key":"ref_20","first-page":"RS4010","article-title":"Analysis of wave fields by Fourier integral operators and its application for radio occultations","volume":"39","author":"Gorbunov","year":"2004","journal-title":"Radio Sci."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"RS3009","DOI":"10.1029\/2003RS002899","article-title":"Geometrical optics phase matching of radio occultation signals","volume":"39","author":"Jensen","year":"2004","journal-title":"Radio Sci."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"853","DOI":"10.5194\/amt-14-853-2021","article-title":"Generalized canonical transform method for radio occultation sounding with improved retrieval in the presence of horizontal gradients","volume":"14","author":"Gorbunov","year":"2021","journal-title":"Atmos. Meas. Tech."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1159","DOI":"10.1029\/90JA02125","article-title":"Extension of MSIS thermosphere model into the middle and lower atmosphere","volume":"96","author":"Hedin","year":"1991","journal-title":"J. Geophys. Res."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"441","DOI":"10.1029\/1999RS002273","article-title":"Modeling and inverting radio occultation signals in the moist troposphere","volume":"36","author":"Sokolovskiy","year":"2001","journal-title":"Radio Sci."},{"key":"ref_25","unstructured":"Gorbunov, M.E., and Sokolovskiy, S.V. (1993). Remote Sensing of Refractivity from Space for Global Observations of Atmospheric Parameters, Max\u2013Planck Institute for Meteorology. Report 119."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"109","DOI":"10.5194\/amt-8-109-2015","article-title":"Generation of a bending angle radio occultation climatology (BAROCLIM) and its use in radio occultation retrievals","volume":"8","author":"Syndergaard","year":"2015","journal-title":"Atmos. Meas. Tech."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"622","DOI":"10.1134\/S0001433816060050","article-title":"Statistically average atmospheric bending angle model based on COSMIC experimental data","volume":"52","author":"Gorbunov","year":"2016","journal-title":"Izv. Atmos. Oceanic Phys."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"1084","DOI":"10.1029\/2002RS002800","article-title":"Simulation studies of GPS radio occultation measurements","volume":"38","author":"Beyerle","year":"2003","journal-title":"Radio Sci."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"675","DOI":"10.1080\/01431160010030091","article-title":"Back-propagation and radio-holographic methods for investigation of sporadic ionospheric E-layers from Microlab-1 data","volume":"23","author":"Gorbunov","year":"2002","journal-title":"Int. J. Remote Sens."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"3-1","DOI":"10.1029\/2001GL013398","article-title":"Detection of high-altitude ionospheric irregularities with GPS\/MET","volume":"29","author":"Sokolovskiy","year":"2002","journal-title":"Geophys. Res. Let."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"507","DOI":"10.2151\/jmsj.2004.507","article-title":"Inversion and Error Estimation of GPS Radio Occultation Data","volume":"82","author":"Kuo","year":"2004","journal-title":"J. Meteorolog. Soc. Jpn."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"171","DOI":"10.1016\/S1364-6826(97)00056-4","article-title":"Modeling the impact of the Earth\u2019s oblateness on the retrieval of temperature and pressure profiles from limb sounding","volume":"60","author":"Syndergaard","year":"1998","journal-title":"J. Atmos. Sol. Terr. Phys."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"247","DOI":"10.1007\/BF02838657","article-title":"Correction on effect of Earth\u2019s oblateness in inversion of GPS occultation data","volume":"8","author":"Xiaohua","year":"2005","journal-title":"Geo Spat. Inform. Sci."}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/14\/3\/691\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T22:12:27Z","timestamp":1760134347000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/14\/3\/691"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2022,2,1]]},"references-count":33,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2022,2]]}},"alternative-id":["rs14030691"],"URL":"https:\/\/doi.org\/10.3390\/rs14030691","relation":{},"ISSN":["2072-4292"],"issn-type":[{"type":"electronic","value":"2072-4292"}],"subject":[],"published":{"date-parts":[[2022,2,1]]}}}