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Radio Occultation Climate Data Records and Application

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A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Earth Observation Data".

Deadline for manuscript submissions: closed (26 April 2024) | Viewed by 6921

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Dr. M Mainul Hoque

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Institute of Solar-Terrestrial Physics, German Aerospace Center (DLR), Kalkhorstweg 53, 17235 Neustrelitz, Germany
Interests: GNSS ionosphere sounding; space weather; space climate; satellite navigation; geodesy; remote sensing
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Shuanggen Jin

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Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China
Interests: GNSS meteorology; remote sensing; space/planetary exploration
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Special Issue Information

Dear Colleagues,

Radio occultation (RO) is a method for exploring planetary atmospheres. It was initially used to study atmospheres of other planets, such as Venus or Mars. With the availability of GNSS (Global Navigation Satellite System, such as GPS, GLONASS, Galileo, BeiDou, QZSS), it has been used more recently to study Earth’s atmosphere. The basic concept of this RO method is a space-based LEO (Low Earth Orbit) instrument that tracks radio signals transmitted from a GNSS spacecraft while they pass through Earth’s atmosphere (limb sounding). The RO observations are primarily used to study the neutral atmosphere, but also allow ionospheric soundings up to the LEO altitude (or even plasmasphere monitoring when considering zenith signals collected for LEO Orbit Determination purposes). Although refraction of the radio wave in the ionosphere is determined mostly by the electron concentration, the path of the signal in the neutral atmosphere is determined by air pressure, temperature, and humidity.

The first GPS based instrument for Earth observations was GPS/Meteorology (GPS/MET), launched in April 1995 as a proof-of-concept experiment to demonstrate the usefulness of the RO technique. It had only limited temporal coverage, but from 2001 on-wards, continuous RO measurements of the Earth’s atmosphere exist, more recently also making use of all GNSS constellations.

RO data have a large potential for climate related assessments, as the core measurement is based on the measurements of precise time information provided by atomic clocks. Different instruments can be combined to generate long-term datasets. With more than two decades of continuous RO observations being available now, neutral atmospheric data has also been included in the latest Assessment Report 6 of the Intergovernmental Panel on Climate Change (IPCC). Several RO groups provided climate data records to this report, to cover information on long-term temperature trends in the middle to upper atmosphere.

This Special Issue is inviting contributions covering radio occultation climate data records, as well as use of such records in, e.g., re-analysis, or applications of such records for climate related studies. These contributions can make use of neutral atmospheric observations, and/or ionospheric ones.

Dr. M Mainul Hoque
Prof. Dr. Shuanggen Jin
Guest Editors

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Keywords

radio occultation
climate data records
long term trend of climate data
RO sounding of ionosphere and plasmasphere
neutral atmospheric retrieval
temperature profile
water vapour
re-analysis
climate models

Published Papers (5 papers)

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17 pages, 2861 KiB

Open AccessArticle

Sea Surface Roughness Determination from Grazing Angle GPS Ocean Observations and Scatterometry Simulations

by Per Høeg and Anders Carlström

Remote Sens. 2023, 15(15), 3794; https://doi.org/10.3390/rs15153794 - 30 Jul 2023

Viewed by 846

Abstract

Measurements of grazing angle GNSS-R ocean reflections combined with meteorological troposphere data are used for retrieval of ocean wave heights and surface roughness parameters. The observational results are compared to multiphase screen simulations for the same atmosphere conditions. The retrieved data from observations and simulations give equal results within the error bounds of the methods. The obtained ocean mean wave-heights are almost proportional to the square of the wind speed when applying a first-order approximation model to the high-wave-number part of the measured GNSS-R power spectra. The spectral variances from the measurements link directly to the ocean surface roughness, which is also verified by the performed multiple phase-screen wave propagation simulations. Thus, grazing angle GNSS-R techniques are an efficient method for determining the ocean state and the conditions in the boundary layer of the troposphere. Full article

(This article belongs to the Special Issue Radio Occultation Climate Data Records and Application)

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11 pages, 1094 KiB

Open AccessCommunication

Real-Time Tomographic Inversion of Truncated Ionospheric GNSS Radio Occultations

by Germán Olivares-Pulido, Manuel Hernández-Pajares, Enric Monte-Moreno, Haixia Lyu, Victoria Graffigna, Estel Cardellach, Mainul Hoque, Fabricio S. Prol, Riccardo Notarpietro and Miquel Garcia-Fernandez

Remote Sens. 2023, 15(12), 3176; https://doi.org/10.3390/rs15123176 - 19 Jun 2023

Viewed by 1151

Abstract

This paper presents a new way of combining Abel inversion and the Chapman model with a linearly increasing scale height to retrieve ionospheric electron density vertical profiles from truncated-sounding radio-occultation data. A linear Vary–Chap model is used to cover the blind region due to data truncation, with parameters estimated by enumeration of the possible values in a grid centered around a set of parameters compatible with ionospheric physics. The resulting electron density is estimated with its corresponding error from the linear least-squares solution presenting the smaller post-fit residual on the input GNSS carrier-phase measurements. The results, tested on a set of representative GNSS RO measurements obtained by COSMIC/FORMOSAT-3, show that this method can retrieve EDVPs with a predominant absolute and relative error of

10^{10} e^{-} m^{- 3}

and 5%, respectively, and in less than 10 s per profile, which makes this method suitable for near real-time applications in upcoming missions such as EUMETSAT Polar System-Second Generation. Full article

(This article belongs to the Special Issue Radio Occultation Climate Data Records and Application)

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20 pages, 5773 KiB

Open AccessArticle

Assessment of GRAS Ionospheric Measurements for Ionospheric Model Assimilation

by M. M. Hoque, F. S. Prol, M. Hernandez-Pajares, R. Notarpietro, L. Yuan, G. Olivares-Pulido, V. Graffigna, A. Von Engeln and C. Marquardt

Remote Sens. 2023, 15(12), 3129; https://doi.org/10.3390/rs15123129 - 15 Jun 2023

Viewed by 969

Abstract

We conducted a study to assess the GNSS (Global Navigation Satellite System) Receiver for Atmospheric Sounding (GRAS) ionospheric data quality by processing Radio Occultation (RO) observations of ionospheric products. The main objective of the study is to validate ionospheric data generated at EUMETSAT, such as ionospheric bending angle profiles, amplitude and phase scintillations, topside Total Electron Content (TEC) from MetOp-A GRAS instrument as well as generating and validating new ionospheric products derived from GRAS RO observations such as the TEC, rate of TEC and vertical electron density profiles. The assessment is conducted by comparing and evaluating the systematic differences between similar products from other Low Earth Orbit (LEO) satellite missions or from ground-based ionospheric measurements. The study confirms that the GNSS topside and RO observations recorded by the GRAS instrument onboard MetOp satellites are of good quality and are a valuable source of data for ionospheric research. Full article

(This article belongs to the Special Issue Radio Occultation Climate Data Records and Application)

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17 pages, 7318 KiB

Open AccessArticle

Study of Ionospheric Bending Angle and Scintillation Profiles Derived by GNSS Radio-Occultation with MetOp-A Satellite

by Fabricio S. Prol, M. Mainul Hoque, Manuel Hernández-Pajares, Liangliang Yuan, Germán Olivares-Pulido, Axel von Engeln, Christian Marquardt and Riccardo Notarpietro

Remote Sens. 2023, 15(6), 1663; https://doi.org/10.3390/rs15061663 - 20 Mar 2023

Cited by 1 | Viewed by 1631

Abstract

In this work, a dedicated campaign by MetOp-A satellite is conducted to monitor the ionosphere based on radio-occultation (RO) measurements provided by the onboard GNSS (Global Navigation Satellite System) Receiver for Atmospheric Sounding (GRAS). The main goal is to analyze the capabilities of the collected data to represent the bending angle and scintillation profiles of the ionosphere. We compare the MetOp-A products with those generated by other RO missions and explore the spatial/temporal distributions sensed by the MetOp-A campaign. Validation of dual frequency bending angles at the RO tangent points, S4 index, and Rate of the Total electron content Index (ROTI) is performed against independent products from Fengyun-3D and FORMOSAT-7/COSMIC-2 satellites. Our main findings constitute the following: (1) bending angle profiles from MetOp-A agree well with Fengyun-3D measurements; (2) bending angle distributions show a typical S-shape variation along the altitudes; (3) signatures of the sporadic E-layer and equatorial ionization anomaly crests are observed by the bending angles; (4) sharp transitions are observed in the bending angle profiles above ~200 km due to the transition of the daytime/nighttime in addition to the transition of the bottom-side/top-side; and (5) sporadic E-layer signatures are observed in the S4 index distributions by MetOp-A and FORMOSAT-7/COSMIC-2, with expected differences in magnitudes between the GPS (Global Positioning System) L1 and L2 frequencies. Full article

(This article belongs to the Special Issue Radio Occultation Climate Data Records and Application)

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14 pages, 3724 KiB

Open AccessTechnical Note

A New Method of Electron Density Retrieval from MetOp-A’s Truncated Radio Occultation Measurements

by M. Mainul Hoque, Liangliang Yuan, Fabricio S. Prol, Manuel Hernández-Pajares, Riccardo Notarpietro, Norbert Jakowski, German Olivares Pulido, Axel Von Engeln and Christian Marquardt

Remote Sens. 2023, 15(5), 1424; https://doi.org/10.3390/rs15051424 - 03 Mar 2023

Cited by 4 | Viewed by 1477

Abstract

The radio occultation (RO) measurements of the Global Navigation Satellite System’s (GNSS’s) signals onboard a Low Earth Orbiting (LEO) satellite enable the computation of the vertical electron density profile from the LEO satellite’s orbit height down to the Earth’s surface. The ionospheric extension experiment performed by the GNSS Receiver for Atmospheric Sounding (GRAS) receiver on board MetOp-A provides opportunities for ionospheric sounding but with the RO measurements only taken with an impact parameter height below 600 and 300 km within two different experiments, although MetOp-A was flying at an orbit height of about 800 km. Here, we present a model-assisted RO inversion technique for electron density retrieval from such kind of truncated data. The topside ionosphere and plasmasphere above the LEO orbit height are modelled by a Chapman layer function superposed with an exponential decay function representing the plasmasphere. Our investigation shows that the model-assisted technique is stable and robust and can successfully be used to retrieve the electron density values up to the LEO height from the truncated MetOp-A data, in particular when observations are available until 600 km. Moreover, this model-assisted technique is also successful with the availability of a small number of observations of the topside above the peak density height. For observations available only up to 300 km, the accuracy of the retrieved profile is comparable to the one obtained by the data truncated at a 600 km height only when the peak electron density lies below the 250 km altitude level. Full article

(This article belongs to the Special Issue Radio Occultation Climate Data Records and Application)

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