scholarly journals Full Spectrum Inversion of radio occultation signals

Radio Science ◽  
2003 ◽  
Vol 38 (3) ◽  
pp. n/a-n/a ◽  
Author(s):  
Arne Skov Jensen ◽  
Martin S. Lohmann ◽  
Hans-Henrik Benzon ◽  
Alan Steen Nielsen
Keyword(s):  
Radio Occultation ◽  
Full Spectrum ◽  
Spectrum Inversion

scholarly journals Application of window functions for full spectrum inversion of cross-link radio occultation data

Radio Science ◽  
2006 ◽  
Vol 41 (3) ◽  
pp. n/a-n/a ◽  
Author(s):  
Martin S. Lohmann ◽  
Arne Skov Jensen ◽  
Hans-Henrik Benzon ◽  
Alan Steen Nielsen
Keyword(s):  
Radio Occultation ◽  
Cross Link ◽  
Full Spectrum ◽  
Window Functions ◽  
Occultation Data ◽  
Radio Occultation Data ◽  
Spectrum Inversion

scholarly journals Application of the full spectrum inversion algorithm to simulated airborne GPS radio occultation signals

2016 ◽  
Vol 9 (10) ◽  
pp. 5077-5087 ◽  
Author(s):  
Loknath Adhikari ◽  
Feiqin Xie ◽  
Jennifer S. Haase
Keyword(s):  
Measurement Errors ◽  
Vertical Structure ◽  
Radio Occultation ◽  
Lower Troposphere ◽  
Signal Amplitude ◽  
Systematic Bias ◽  
Geometric Optics ◽  
Full Spectrum ◽  
Bending Angle ◽  
Spectrum Inversion

Abstract. With a GPS receiver on board an airplane, the airborne radio occultation (ARO) technique provides dense lower-tropospheric soundings over target regions. Large variations in water vapor in the troposphere cause strong signal multipath, which could lead to systematic errors in RO retrievals with the geometric optics (GO) method. The spaceborne GPS RO community has successfully developed the full-spectrum inversion (FSI) technique to solve the multipath problem. This paper is the first to adapt the FSI technique to retrieve atmospheric properties (bending and refractivity) from ARO signals, where it is necessary to compensate for the receiver traveling on a non-circular trajectory inside the atmosphere, and its use is demonstrated using an end-to-end simulation system. The forward-simulated GPS L1 (1575.42 MHz) signal amplitude and phase are used to test the modified FSI algorithm. The ARO FSI method is capable of reconstructing the fine vertical structure of the moist lower troposphere in the presence of severe multipath, which otherwise leads to large retrieval errors in the GO retrieval. The sensitivity of the modified FSI-retrieved bending angle and refractivity to errors in signal amplitude and errors in the measured refractivity at the receiver is presented. Accurate bending angle retrievals can be obtained from the surface up to ∼ 250 m below the receiver at typical flight altitudes above the tropopause, above which the retrieved bending angle becomes highly sensitive to the phase measurement noise. Abrupt changes in the signal amplitude that are a challenge for receiver tracking and geometric optics bending angle retrieval techniques do not produce any systematic bias in the FSI retrievals when the SNR is high. For very low SNR, the FSI performs as expected from theoretical considerations. The 1 % in situ refractivity measurement errors at the receiver height can introduce a maximum refractivity retrieval error of 0.5 % (1 K) near the receiver, but the error decreases gradually to ∼ 0.05 % (0.1 K) near the surface. In summary, the ARO FSI successfully retrieves the fine vertical structure of the atmosphere in the presence of multipath in the lower troposphere.

scholarly journals Analysis of vertical wave number spectrum of atmospheric gravity waves in the stratosphere using COSMIC GPS radio occultation data

2011 ◽  
Vol 4 (8) ◽  
pp. 1627-1636 ◽  
Author(s):  
T. Tsuda ◽  
X. Lin ◽  
H. Hayashi ◽  
Keyword(s):  
Gravity Waves ◽  
Radio Occultation ◽  
Temperature Fluctuations ◽  
Ground Level ◽  
Wave Number ◽  
Radiosonde Data ◽  
Small Scale ◽  
Vertical Resolution ◽  
Full Spectrum ◽  
Gps Radio Occultation

Abstract. GPS radio occultation (RO) is characterized by high accuracy and excellent height resolution, which has great advantages in analyzing atmospheric structures including small-scale vertical fluctuations. The vertical resolution of the geometrical optics (GO) method in the stratosphere is about 1.5 km due to Fresnel radius limitations, but full spectrum inversion (FSI) can provide superior resolutions. We applied FSI to COSMIC GPS-RO profiles from ground level up to 30 km altitude, although basic retrieval at UCAR/CDAAC sets the sewing height from GO to FSI below the tropopause. We validated FSI temperature profiles with routine high-resolution radiosonde data in Malaysia and North America collected within 400 km and about 30 min of the GPS RO events. The average discrepancy at 10–30 km altitude was less than 0.5 K, and the bias was equivalent with the GO results. Using the FSI results, we analyzed the vertical wave number spectrum of normalized temperature fluctuations in the stratosphere at 20–30 km altitude, which exhibits good consistency with the model spectra of saturated gravity waves. We investigated the white noise floor that tends to appear at high wave numbers, and the substantial vertical resolution of the FSI method was estimated as about 100–200 m in the lower stratosphere. We also examined a criterion for the upper limit of the FSI profiles, beyond which bending angle perturbations due to system noises, etc., could exceed atmospheric excess phase fluctuations. We found that the FSI profiles can be used up to about 28 km in studies of temperature fluctuations with vertical wave lengths as short as 0.5 km.

scholarly journals Analysis of vertical wave number spectrum of atmospheric gravity waves in the stratosphere using COSMIC GPS radio occultation data

2011 ◽  
Vol 4 (2) ◽  
pp. 2071-2097
Author(s):  
T. Tsuda ◽  
X. Lin ◽  
H. Hayashi ◽  
Keyword(s):  
Gravity Waves ◽  
Radio Occultation ◽  
Temperature Fluctuations ◽  
Ground Level ◽  
Wave Number ◽  
Radiosonde Data ◽  
Small Scale ◽  
Vertical Resolution ◽  
Full Spectrum ◽  
Gps Radio Occultation

Abstract. GPS radio occultation (RO) is characterized by high accuracy and excellent height resolution, which has great advantages in analyzing atmospheric structures including small-scale vertical fluctuations. The vertical resolution of the geometrical optics (GO) method in the stratosphere is about 1.5 km due to Fresnel radius limitations, but full spectrum inversion (FSI) can provide superior resolutions. We applied FSI to COSMIC GPS-RO profiles from ground level up to 30 km altitude, although basic retrieval at UCAR/CDAAC sets the sewing height from GO to FSI below the tropopause. We validated FSI temperature profiles with routine high-resolution radiosonde data in Malaysia and North America collected within 400 km and about 30 min of the GPS RO events. The average discrepancy at 10–30 km altitude was less than 0.5 K, and the bias was equivalent with the GO results. Using the FSI results, we analyzed the vertical wave number spectrum of normalized temperature fluctuations in the stratosphere at 20–30 km altitude, which exhibits good consistency with the model spectra of saturated gravity waves. We investigated the white noise floor that tends to appear at high wave numbers, and the substantial vertical resolution of the FSI method was estimated as about 100–200 m in the lower stratosphere. We also examined a criterion for the upper limit of the FSI profiles, beyond which bending angle perturbations due to system noises, etc, could exceed atmospheric excess phase fluctuations. We found that the FSI profiles can be used up to about 28 km in studies of temperature fluctuations with vertical wave lengths as short as 0.5 km.

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 Validation of refractivity profiles derived from GRAS raw-sampling data

2011 ◽  
Vol 4 (7) ◽  
pp. 1541-1550 ◽  
Author(s):  
F. Zus ◽  
G. Beyerle ◽  
S. Heise ◽  
T. Schmidt ◽  
J. Wickert ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Penetration Depth ◽  
Radio Occultation ◽  
Lower Troposphere ◽  
Research Centre ◽  
Mean Deviation ◽  
Negative Bias ◽  
Altitude Range ◽  
Full Spectrum ◽  
The Mean

Abstract. Results from GRAS (GNSS Receiver for Atmospheric Sounding) RO (Radio Occultation) data recorded in RS (Raw Sampling) mode processed at the GFZ (German Research Centre for Geoscience) Potsdam are presented. The experimental processing software POCS-X includes FSI (Full Spectrum Inversion) in order to cope with multi-path regions and enables in connection with RS data to retrieve atmospheric refractivity profiles down to the Earths surface. Radio occultation events observed between 30 September and 30 October 2007 are processed and the retrievals are validated against co-located ECMWF (European Centre for Medium-Range Weather Forecasts) profiles. The intercomparison indicates good quality of the retrieved profiles. In the altitude range 8 to 25 km the standard deviation is below 1 %. The mean deviation in this altitude range tends to be negative. At 30 km the negative bias reaches about −0.4 %. Below 8 km the standard deviation increases, reaching 2.5 % at 2 km. Below 2 km the mean deviation tends to be negative, reaching −1.9 % close to the ground. The negative bias mainly stems from the tropical lower troposphere; there, the negative bias reaches −3 %. The tropospheric penetration depth obtained from RS data shows a vast improvement compared to the tropospheric penetration depth typically obtained from CL (Closed Loop) data; 50 % of all retrieved profiles reach 720 m.

scholarly journals Application of the Full Spectrum Inversion Algorithm for Airborne GPS Radio Occultation Measurements

2016 ◽  
Author(s):  
L. Adhikari ◽  
F. Xie ◽  
J. S. Haase
Keyword(s):  
Lower Troposphere ◽  
Signal Amplitude ◽  
Retrieval Algorithm ◽  
Systematic Bias ◽  
Gps Receiver ◽  
Inversion Algorithm ◽  
Full Spectrum ◽  
Bending Angle ◽  
Abrupt Changes ◽  
Spectrum Inversion

Abstract. With a GPS receiver onboard an airplane, the airborne RO (ARO) technique provides dense lower troposphere soundings over target regions. The large variation of water vapor in the troposphere causes strong signal multipath, which could lead to systematic errors in RO retrievals with the geometric optics (GO) method. The spaceborne GPS RO community has successfully applied the Full Spectrum Inversion (FSI) technique to solve the multipath problem. This paper is the first to adapt the FSI technique to the ARO measurement with its unique perspective of having a receiver traveling on a non-circular trajectory inside the atmosphere. An end-to-end simulation system is implemented to test the newly developed FSI retrieval algorithm for ARO. The forward-simulated GPS L1 signal amplitude and phase is used to test the modified FSI algorithm. The ARO FSI method is capable of reconstructing the fine vertical structure of the moist lower troposphere in the presence of severe multipath, which leads to large retrieval errors in the GO retrieval. The sensitivity of the modified FSI retrieved bending angle and refractivity to the errors in signal amplitude and the measured refractivity at the receiver is presented. Accurate bending angle retrievals can be obtained from surface up to ~250 m below the receiver, where retrieved bending angle near the receiver altitude becomes sensitive to the measurement noise. Abrupt changes in the signal amplitude do not produce a systematic bias in the FSI retrievals when the SNR is high. A 1 % Gaussian noise in refractivity at the receiver causes ~ 0.5 % refractivity error near the receiver that reduces to ~0.05 % near the surface.

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