GNSS radio occultation profiles in the neutral atmosphere from inversion of excess phase data

• Published in: TAO : Terrestrial, atmospheric, and oceanic sciences Vol. 30; no. 2; pp. 215 - 233
• Main Authors: Hordyniec, Paweł, Huang, Cheng-Yung, Liu, Chian-Yi, Rohm, Witold, Chen, Shu-Ya
• Format: Journal Article
• Language: English
• Published: Taiwan 中華民國地球科學學會 01.04.2019; Chinese Geoscience Union (Taiwan); Springer
• Subjects: Accuracy; Air temperature; Atmosphere; Dry air; Earth orbit; Earth orbits; Excess phase; Geophysics; Global navigation satellite system; GNSS; Inversion; Low earth orbits; Lower stratosphere; Lower troposphere; Navigation; Navigation satellites; Navigation systems; Navigational satellites; Occultation; Process parameters; Profiles; Radio; Radio occultation; Radiosonde; Radiosondes; Refractive index; Refractivity; Retrieval; Satellites; Signal processing; Soundings; Stratosphere; Temperature; Temperature inversions; Troposphere; Uncertainty; Upper troposphere; Water vapor; Water vapour; Radiosonde; Excess phase; Occultation; GNSS; Refractivity; Troposphere
• ISSN: 1017-0839; 2311-7680
• DOI: 10.3319/TAO.2018.10.12.01

Long-term stability, global coverage and high resolution are characteristics that make the Global Navigation Satellite System (GNSS) radio occultation (RO) technique well-suitable to serve as anchor measurements for observing the Earth's atmosphere. The concept of occultation soundings utilizes a receiver placed on a low Earth orbit to measure the accumulated atmospheric contribution along the limb in terms of a phase delay. A high sampling rate allows to reconstruct profiles of geophysical parameters through an inversion process of occultation signals. However, such measurements require a careful processing in order to provide accurate retrievals in the neutral atmosphere. The following development describes specific aspects in radio occultation methodology implemented in the retrieval chain from phase data to profiles of dry pressure and dry temperature. Independent retrievals from near-real time measurements are compared with occultation products provided by official processing centers to demonstrate reliability of the solution. The region within the upper troposphere and lower stratosphere (UTLS) is particularly represented by a low uncertainty being within 0.5% (K). A comparison with radiosondes shows a significant contribution of a water vapor term in the lower troposphere that comes from the dry air assumption in occultation profiles of pressure and temperature. Radiosonde measurements reproduced to refractivity profiles show very high agreement with occultation soundings, which is generally below 5%. A superior accuracy of RO refractivity is observed in the upper troposphere, where retrievals are consistent with radiosondes to 1%.