scholarly journals Processing of GRAS/METOP radio occultation data recorded in closed-loop and raw-sampling modes

2011 ◽  
Vol 4 (6) ◽  
pp. 1021-1026 ◽  
Author(s):  
M. E. Gorbunov ◽  
K. B. Lauritsen ◽  
H.-H. Benzon ◽  
G. B. Larsen ◽  
S. Syndergaard ◽  
...  
Keyword(s):  
Lower Troposphere ◽  
Satellite System ◽  
Negative Bias ◽  
Statistical Validation ◽  
Height Range ◽  
Maximum Value ◽  
Atmospheric Sounding ◽  
Occultation Data ◽  
Global Navigation Satellite ◽  
The Tropics

Abstract. Instrument GRAS (Global Navigation Satellite System Receiver for Atmospheric Sounding) on-board of the Metop-A satellite was activated on 27 October 2006. Currently, Metop-A is a fully operational satellite with GRAS providing from 650–700 occultations per day. We describe our processing of GRAS data based on the modification of our OCC software, which was modified to become capable of reading and processing GRAS data. We perform a statistical comparison of bending angles and refractivities derived from GRAS data with those derived from ECMWF analyses. We conclude that GRAS data have error characteristics close to those of COSMIC data. In the height range 10–30 km, the systematic refractivity difference GRAS–ECMWF is of the order of 0.1–0.2 %, and the standard deviation is 0.3–0.6 %. In the lower troposphere GRAS refractivity and bending angle indicate a negative bias, which reaches its maximum value in the tropics. In particular the retrieved refractivity is biased by up to 2.5 %. The negative bias pattern is similar to that found in the statistical validation of COSMIC data. This makes it probable that the bias should not be attributed to the instrument design or hardware.

scholarly journals Processing of GRAS/METOP radio occultation data recorded in closed-loop and raw-sampling modes

2011 ◽  
Vol 4 (1) ◽  
pp. 1061-1077 ◽  
Author(s):  
M. E. Gorbunov ◽  
K. B. Lauritsen ◽  
H.-H. Benzon ◽  
G. B. Larsen ◽  
S. Syndergaard ◽  
...  
Keyword(s):  
Lower Troposphere ◽  
Satellite System ◽  
Negative Bias ◽  
Statistical Validation ◽  
Height Range ◽  
Maximum Value ◽  
Atmospheric Sounding ◽  
Occultation Data ◽  
Global Navigation Satellite ◽  
The Tropics

Abstract. Instrument GRAS (Global Navigation Satellite System Receiver for Atmospheric Sounding) on-board of the Metop-A satellite was activated on 27 October 2006. Currently, Metop-A is a fully operational satellite with GRAS providing from 650–700 measurements per day. We describe our processing of GRAS data based on our OCC software, which was modified to become capable of reading and processing GRAS data. We perform a statistical comparison of bending angles and refractivities derived from GRAS data with those derived from ECMWF analyses. We show that GRAS data have error characteristics close to those of COSMIC data. In the height range 10–30 km, the systematic refractivity difference GRAS-ECMWF is of the order of 0.1–0.2%, and the standard deviation is 0.3–0.6%. In the lower troposphere GRAS refractivity and bending angle indicate a negative bias, which reaches its maximum value in the tropics. In particular, the retrieved refractivity is biased by up to 2.5%. The negative bias pattern is similar to that found in the statistical validation of COSMIC data. This makes it probable that the bias should not be attributed to the instrument design or hardware.

scholarly journals Preliminary validation of the refractivity from the new radio occultation sounder GNOS/FY-3C

2016 ◽  
Vol 9 (2) ◽  
pp. 781-792 ◽  
Author(s):  
Mi Liao ◽  
Peng Zhang ◽  
Guang-Lin Yang ◽  
Yan-Meng Bi ◽  
Yan Liu ◽  
...  
Keyword(s):  
Radio Occultation ◽  
Weather Prediction ◽  
Satellite System ◽  
Navigation Satellite ◽  
Near Surface ◽  
Vertical Range ◽  
New Radio ◽  
Atmospheric Sounding ◽  
Occultation Data ◽  
Global Navigation Satellite

Abstract. As a new member of the space-based radio occultation sounders, the GNOS (Global Navigation Satellite System Occultation Sounder) mounted on Fengyun-3C (FY-3C) has been carrying out atmospheric sounding since 23 September 2013. GNOS takes approximately 800 daily measurements using GPS (Global Positioning System) and Chinese BDS (BeiDou navigation satellite) signals. In this work, the atmospheric refractivity profiles from GNOS were compared with the ones obtained from the co-located ECMWF (European Centre for Medium-Range Weather Forecasts) reanalysis. The mean bias of the refractivity obtained through GNOS GPS (BDS) was found to be approximately −0.09 % (−0.04 %) from the near surface to up to 46 km. While the average standard deviation was approximately 1.81 % (1.26  %), it was as low as 0.75 % (0.53 %) in the range of 5–25 km, where best sounding results are usually achieved. Further, COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) and MetOp/ GRAS (GNSS Receiver for Atmospheric Sounding) radio occultation data were compared with the ECMWF reanalysis; the results thus obtained could be used as reference data for GNOS. Our results showed that GNOS/FY-3C meets the design requirements in terms of accuracy and precision of the sounder. It possesses a sounding capability similar to COSMIC and MetOp/GRAS in the vertical range of 0–30 km, though it needs further improvement above 30 km. Overall, it provides a new data source for the global numerical weather prediction (NWP) community.

scholarly journals Sensitivity of airborne radio occultation to tropospheric properties over ocean and land

2017 ◽  
Author(s):  
Feiqin Xie ◽  
Loknath Adhikari ◽  
Jennifer S. Haase ◽  
Brian Murphy ◽  
Kuo-Nung Wang ◽  
...  
Keyword(s):  
Land Surface ◽  
Radio Occultation ◽  
Multipath Propagation ◽  
Method Comparison ◽  
Lower Troposphere ◽  
Virgin Islands ◽  
Negative Bias ◽  
Full Spectrum ◽  
Bending Angle ◽  
The Tropics

Abstract. Airborne radio occultation (ARO) measurements collected during a ferry flight at the end of the PRE-Depression Investigation of Cloud-systems in the Tropics (PREDICT) field campaign from the Virgin Islands to Colorado are analyzed. This long flight at ~ 13 km altitude provided intercomparisons of bending angle retrieval techniques over a range of environments that may have different levels of atmospheric multipath propagation interference. Two especially well-adapted radio-holographic bending angle retrieval methods, full-spectrum-inversion (FSI), and phase-matching (PM), were compared with the standard geometric-optics (GO) retrieval method. Comparison of the ARO retrievals with the near-coincident ECMWF reanalysis-interim (ERA-I) profiles shows only a small root-mean-square (RMS) refractivity difference of ~ 0.3 % in the drier upper troposphere from ~ 5 km to 13 km over both land and ocean. Both the FSI and PM methods improve the ARO retrievals in the moist lower troposphere and reduce the negative bias found in the GO retrieval due to the multipath problem. In the lowest layer of the troposphere, the ARO refractivity using FSI shows a negative bias of about –2 %. The increase of the refractivity bias occurs below 5 km over the ocean and below 3.5 km over land, corresponding to the approximate altitude of large vertical moisture gradients above the ocean and land surface, respectively. In comparisons with radiosondes, the FSI ARO soundings capture well the height of layers with sharp refractivity gradients but display a negative refractivity bias inside the boundary layer. Three spaceborne radio occultation profiles within 300 km of the flight track shows a slightly larger RMS refractivity difference of ~ 2 %. Analysis of the 12 ARO events that were simultaneously recorded from both the top and side-looking antennas, indicates that high precision of the ARO measurements can be achieved corresponding to an RMS difference better than 0.2 % in refractivity (or ~ 0.4 K). The surprisingly good quality of recordings from a very simple antenna on top of an aircraft increases the feasibility of developing an operational tropospheric sounding system.

scholarly journals Preliminary validation of refractivity from a new radio occultation sounder GNOS/FY-3C

2015 ◽  
Vol 8 (9) ◽  
pp. 9009-9044 ◽  
Author(s):  
M. Liao ◽  
P. Zhang ◽  
G. L. Yang ◽  
Y. M. Bi ◽  
Y. Liu ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Radio Occultation ◽  
Weather Prediction ◽  
Satellite System ◽  
Navigation Satellite ◽  
Near Surface ◽  
Vertical Range ◽  
New Radio ◽  
Atmospheric Sounding ◽  
Global Navigation Satellite

Abstract. As a new member of space-based radio occultation sounder, the GNOS (Global Navigation Satellite System Occultation Sounder) mounted on FY-3C has been carrying out the atmospheric sounding since 23 September 2013. GNOS takes a daily measurement up to 800 times with GPS (Global Position System) and Chinese BDS (BeiDou navigation satellite) signals. The refractivity profiles from GNOS are compared with the co-located ECMWF (European Centre for Medium-Range Weather Forecasts) analyses in this paper. Bias and standard deviation have being calculated as the function of altitude. The mean bias is about 0.2 % from the near surface to 35 km. The average standard deviation is within 2 % while it is down to about 1 % in the range 5–30 km where best soundings are usually made. To evaluate the performance of GNOS, COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) and GRAS/METOP-A (GNSS Receiver for Atmospheric Sounding) data are also compared to ECMWF analyses as the reference. The results show that GNOS/FY-3C meets the requirements of the design well. It possesses a sounding capability similar to COSMIC and GRAS in the vertical range of 0–30 km, though it needs improvement in higher altitude. Generally, it provides a new data source for global NWP (numerical weather prediction) community.

scholarly journals Application of the Fengyun 3 C GNSS occultation sounder for assessing the global ionospheric response to a magnetic storm event

2019 ◽  
Vol 12 (3) ◽  
pp. 1483-1493 ◽  
Author(s):  
Weihua Bai ◽  
Guojun Wang ◽  
Yueqiang Sun ◽  
Jiankui Shi ◽  
Guanglin Yang ◽  
...  
Keyword(s):  
Magnetic Storm ◽  
Radio Occultation ◽  
Correlation Coefficients ◽  
Satellite System ◽  
Storm Event ◽  
Calibration Data ◽  
Long Term Stability ◽  
Negative Effect ◽  
Occultation Data ◽  
Global Navigation Satellite

Abstract. The rapid advancement of global navigation satellite system (GNSS) occultation technology in recent years has made it one of the most advanced space-based remote sensing technologies of the 21st century. GNSS radio occultation has many advantages, including all-weather operation, global coverage, high vertical resolution, high precision, long-term stability, and self-calibration. Data products from GNSS occultation sounding can greatly enhance ionospheric observations and contribute to space weather monitoring, forecasting, modeling, and research. In this study, GNSS occultation sounder (GNOS) results from a radio occultation sounding payload aboard the Fengyun 3 C (FY3-C) satellite were compared with ground-based ionosonde observations. Correlation coefficients for peak electron density (NmF2) derived from GNOS Global Position System (GPS) and Beidou navigation system (BDS) products with ionosonde data were higher than 0.9, and standard deviations were less than 20 %. Global ionospheric effects of the strong magnetic storm event in March 2015 were analyzed using GNOS results supported by ionosonde observations. The magnetic storm caused a significant disturbance in NmF2 level. Suppressed daytime and nighttime NmF2 levels indicated mainly negative storm conditions. In two longitude section zones of geomagnetic inclination between 40 and 80∘, the results of average NmF2 observed by GNOS and ground-based ionosondes showed the same basic trends during the geomagnetic storm and confirmed the negative effect of this storm event on the ionosphere. The analysis demonstrates the reliability of the GNSS radio occultation sounding instrument GNOS aboard the FY3-C satellite and confirms the utility of ionosphere products from GNOS for statistical and event-specific ionospheric physical analyses. Future FY3 series satellites and increasing numbers of Beidou navigation satellites will provide increasing GNOS occultation data on the ionosphere, which will contribute to ionosphere research and forecasting applications.

An Analysis of Alternatives for the COSMIC-2 Constellation in the Context of Global Observing System Simulation Experiments

2020 ◽  
Vol 35 (1) ◽  
pp. 51-66 ◽  
Author(s):  
L. Cucurull ◽  
M. J. Mueller
Keyword(s):  
System Simulation ◽  
Three Dimensional ◽  
Lower Troposphere ◽  
Weather Forecast ◽  
Satellite System ◽  
Forecast Skill ◽  
Added Value ◽  
Simulation Experiments ◽  
Global Navigation Satellite ◽  
The Impact

Abstract Observing system simulation experiments (OSSEs) were conducted to evaluate the potential impact of the six Global Navigation Satellite System (GNSS) radio occultation (RO) receiver satellites in equatorial orbit from the initially proposed Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (COSMIC-2) mission, known as COSMIC-2A. Furthermore, the added value of the high-inclination component of the proposed mission was investigated by considering a few alternative architecture designs, including the originally proposed polar constellation of six satellites (COSMIC-2B), a constellation with a reduced number of RO receiving satellites, and a constellation of six satellites but with fewer observations in the lower troposphere. The 2015 year version of the operational three-dimensional ensemble–variational data assimilation system of the National Centers for Environment Prediction (NCEP) was used to run the OSSEs. Observations were simulated and assimilated using the same methodology and their errors assumed uncorrelated. The largest benefit from the assimilation of COSMIC-2A, with denser equatorial coverage, was to improve tropical winds, and its impact was found to be overall neutral in the extratropics. When soundings from the high-inclination orbit were assimilated in addition to COSMIC-2A, positive benefits were found globally, confirming that a high-inclination orbit constellation of RO receiving satellites is necessary to improve weather forecast skill globally. The largest impact from reducing COSMIC-2B from six to four satellites was to slightly degrade weather forecast skill in the Northern Hemisphere extratropics. The impact of degrading COSMIC-2B to the COSMIC level of accuracy, in terms of penetration into the lower troposphere, was mostly neutral.

scholarly journals Application of GPS radio occultation to the assessment of temperature profile retrievals from microwave and infrared sounders

2014 ◽  
Vol 7 (11) ◽  
pp. 3751-3762 ◽  
Author(s):  
M. Feltz ◽  
R. Knuteson ◽  
S. Ackerman ◽  
H. Revercomb
Keyword(s):  
Temperature Profile ◽  
Radio Occultation ◽  
Satellite System ◽  
Advanced Technology ◽  
Similar Time ◽  
Gps Radio Occultation ◽  
Common Reference ◽  
Spatial Coverage ◽  
Atmospheric Sounding ◽  
Global Navigation Satellite

Abstract. Comparisons of satellite temperature profile products from GPS radio occultation (RO) and hyperspectral infrared (IR)/microwave (MW) sounders are made using a previously developed matchup technique. The profile matchup technique matches GPS RO and IR/MW sounder profiles temporally, within 1 h, and spatially, taking into account the unique RO profile geometry and theoretical spatial resolution by calculating a ray-path averaged sounder profile. The comparisons use the GPS RO dry temperature product. Sounder minus GPS RO differences are computed and used to calculate bias and rms profile statistics, which are created for global and 30° latitude zones for selected time periods. These statistics are created from various combinations of temperature profile data from the Constellation Observing System for Meteorology, Ionosphere & Climate (COSMIC) network, Global Navigation Satellite System Receiver for Atmospheric Sounding (GRAS) instrument, and the Atmospheric Infrared Sounder (AIRS)/Advanced Microwave Sounding Unit (AMSU), Infrared Atmospheric Sounding Interferometer (IASI)/AMSU, and Crosstrack Infrared Sounder (CrIS)/Advanced Technology Microwave Sounder (ATMS) sounding systems. By overlaying combinations of these matchup statistics for similar time and space domains, comparisons of different sounders' products, sounder product versions, and GPS RO products can be made. The COSMIC GPS RO network has the spatial coverage, time continuity, and stability to provide a common reference for comparison of the sounder profile products. The results of this study demonstrate that GPS RO has potential to act as a common temperature reference and can help facilitate inter-comparison of sounding retrieval methods and also highlight differences among sensor product versions.

scholarly journals Validation of three different scientific ozone products retrieved from IASI spectra using ozonesondes

2012 ◽  
Vol 5 (3) ◽  
pp. 611-630 ◽  
Author(s):  
G. Dufour ◽  
M. Eremenko ◽  
A. Griesfeller ◽  
B. Barret ◽  
E. LeFlochmoën ◽  
...  
Keyword(s):  
Tropospheric Ozone ◽  
Degrees Of Freedom ◽  
Lower Troposphere ◽  
Natural Variability ◽  
Vertical Resolution ◽  
Random Errors ◽  
Research Teams ◽  
Atmospheric Sounding ◽  
Systematic And Random Errors ◽  
The Tropics

Abstract. Three scientific ozone products from the Infrared Atmospheric Sounding Interferometer (IASI) aboard MetOp-A, retrieved in three different research teams (LA, LATMOS/ULB, LISA) with different retrieval schemes, are characterized and validated using ozonesondes measurements. The characteristics of the products are analyzed in terms of retrieval sensitivity, systematic and random errors, and ability to retrieve the natural variability of ozone and focus on different partial columns from the lower troposphere up to 30 km. The validation covers the midlatitudes and the tropics and the period from January to December 2008. The products present degrees of freedom (DOF) in the troposphere between 1 and 1.2 on average in the midlatitudes and between 1 and 1.4 in the tropics. The DOF are distributed differently on the vertical depending on the profiles and the season: summer leading to a better sensitivity to the lower troposphere, as expected. The error estimates range between 10 and 20% from the lower tropospheric partial columns (0–6 km and 0–8 km for the midlatitudes and the tropics respectively) to the UTLS partial columns (8–16 km and 11–20 km for the midlatitudes and the tropics respectively) for all the products and are about 5% in the stratosphere (16–30 km) and for the column up to 30 km. The main feature that arises from the comparison with the ozonesondes is a systematic overestimation of ozone in the UTLS (between 10 and 25%) by the three products in the midlatitudes and the tropics, attributed to the moderate vertical resolution of IASI and possibly to spectroscopic inconsistencies. The ability of the products to reproduce natural variability of tropospheric ozone is fairly good and depends on the considered season and region.

Prospects of the EPS GRAS Mission For Operational Atmospheric Applications

2008 ◽  
Vol 89 (12) ◽  
pp. 1863-1876 ◽  
Author(s):  
Juha-Pekka Luntama ◽  
Gottfried Kirchengast ◽  
Michael Borsche ◽  
Ulrich Foelsche ◽  
Andrea Steiner ◽  
...  
Keyword(s):  
Global Navigation Satellite System ◽  
Weather Prediction ◽  
European Space Agency ◽  
Satellite System ◽  
Navigation Satellite ◽  
Navigation Data ◽  
Space Agency ◽  
Atmospheric Sounding ◽  
Global Navigation Satellite ◽  
Globally Distributed

Global Navigation Satellite System (GNSS) Receiver for Atmospheric Sounding (GRAS) is a radio occupation instrument especially designed and built for operational meteorological missions. GRAS has been developed by the European Space Agency (ESA) and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) in the framework of the EUMETSAT Polar System (EPS). The GRAS instrument is already flying on board the first MetOp satellite (.MetOp-A) that was launched in October 2006. It will also be on board two other MetOp satellites (MetOp-B and MetOp-C) that will successively cover the total EPS mission lifetime of over 14 yr. GRAS provides daily about 600 globally distributed occultation measurements and the GRAS data products are disseminated to the users in near-real time (NRT) so that they can be assimilated into numerical weather prediction (NWP) systems. All GRAS data and products are permanently archived and made available to the users for climate applications and scientific research through the EUMETSAT Unified Meteorological Archive and Retrieval Facility (U-MARF) and the GRAS Meteorology Satellite Application Facility (SAF) Archive and Retrieval Facility (GARF). The GRAS navigation data can be used in space weather applications.

scholarly journals Application of GPS radio occultation to the assessment of temperature profile retrievals from microwave and infrared sounders

2014 ◽  
Vol 7 (5) ◽  
pp. 5075-5094
Author(s):  
M. Feltz ◽  
R. Knuteson ◽  
S. Ackerman ◽  
H. Revercomb
Keyword(s):  
Temperature Profile ◽  
Radio Occultation ◽  
Satellite System ◽  
Advanced Technology ◽  
Similar Time ◽  
Gps Radio Occultation ◽  
Common Reference ◽  
Spatial Coverage ◽  
Atmospheric Sounding ◽  
Global Navigation Satellite

Abstract. Comparisons of satellite temperature profile products from GPS radio occultation (RO) and hyperspectral infrared (IR)/microwave (MW) sounders are made using a previously developed matchup technique. The profile matchup technique matches GPS RO and IR/MW sounder profiles temporally, within 1 h, and spatially, taking into account the unique RO profile geometry and theoretical spatial resolution by calculating a ray-path averaged sounder profile. The comparisons use the GPS RO dry temperature product. Sounder minus GPS RO differences are computed and used to calculate bias and RMS profile statistics, which are created for global and 30° latitude zones for selected time periods. These statistics are created from various combinations of temperature profile data from the Constellation Observing System for Meteorology, Ionosphere & Climate (COSMIC) network, Global Navigation Satellite System Receiver for Atmospheric Sounding (GRAS) instrument, and the Atmospheric Infrared Sounder (AIRS)/Advanced Microwave Sounding Unit (AMSU), Infrared Atmospheric Sounding Interferometer (IASI)/AMSU, and Crosstrack Infrared Sounder (CrIS)/Advanced Technology Microwave Sounder (ATMS) sounding systems. By overlaying combinations of these matchup statistics for similar time and space domains, comparisons of different sounders' products, sounder product versions, and GPS RO products can be made. The COSMIC GPS RO network has the spatial coverage, time continuity, and stability to provide a common reference for comparison of the sounder profile products. The results of this study demonstrate that GPS RO has potential to act as a common temperature reference and can help facilitate inter-comparison of sounding retrieval methods and also highlight differences among sensor product versions.

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