Validation of refractivity profiles derived from GRAS raw-sampling data

Zus, Florian; Beyerle, G.; Heise, S.; Schmidt, T.; Wickert, Jens; Marquardt, Christian

doi:10.5194/amt-4-1541-2011

Cited by 12 publications

(7 citation statements)

References 32 publications

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“…From the statistical results of the rising and setting occultations of GNOS GPS, the standard deviation of the rising and setting differs up to ∼ 0.5 %. The small positive bias between 2 and 6 km in the setting occultations is identical to the result of Zus et al (2011), which used the MetOp/GRAS refractivity and ECMWF reanalysis. As for GNOS BDS, the penetration depths of the rising and setting occultations are both higher than the depths of GNOS GPS, especially in the rising occultation, whose valid height completely stops at ∼ 3 km.…”

Section: Performance In Lower Troposphere With and Without Open-loop supporting

confidence: 62%

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

Liao

Zhang²,

Yang³

et al. 2016

Atmos. Meas. Tech.

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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.

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Section: Performance In Lower Troposphere With and Without Open-loop supporting

confidence: 62%

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

Liao

Zhang²,

Yang³

et al. 2016

Atmos. Meas. Tech.

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“…In our simulation the fractional refractivity error variance is chosen to be 1% and the vertical correlation length is chosen to be 500 m. Note that we perform a simulation study and not an assimilation study (we are concerned with the functionality of the NLM, TLM, and ADJ) such that the choice of the background error covariance matrix is not crucial. The specific choice of 1% for the fractional refractivity error variance is rational insofar as it corresponds to the typical standard deviation between GPS Radio Occultation and NWM refractivity profiles [see, e.g., Zus et al, 2011]. In order to show how the uncertainty in the refractivity field grows away from the single station, we approximate the a posteriori covariance matrix through…”

Section: Minimizing a Cost Functionmentioning

confidence: 99%

A forward operator and its adjoint for GPS slant total delays

et al. 2015

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In a recent study we developed a fast and accurate algorithm to compute Global Positioning System (GPS) Slant Total Delay (STDs) utilizing numerical weather model data. Having developed a forward operator we construct in this study the tangent linear (adjoint) operator by application of the chain rule of differential calculus in forward (reverse) mode. Armed with these operators we show in a simulation study the potential benefit of GPS STDs in inverse modeling. We conclude that the developed operators are tailored for three (four)-dimensional variational data assimilation and/or travel time tomography.

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“…A number of past and current spacecrafts carry GNSS-RO payloads, e.g. the satellites GPS/Met (Kursinski et al, 1997), CHAMP (Wickert et al, 2001), GRACE Wickert et al, 2005), COSMIC (Anthes et al, 2008), Metop (Luntama et al, 2008;von Engeln et al, 2011;Bonnedal et al, 2010;Zus et al, 2011), TerraSAR-X (Beyerle et al, 2011) and TanDEM-X (Zus et al, 2014a). Already the proof-of-concept mission GPS/Met revealed the difficul-16 G. Beyerle and F. Zus: Low-elevation GPS signal tracking ties of retrieving dual-frequency carrier phase data, when the ray tangent point enters the lower troposphere (Rocken et al, 1997a).…”

Section: Introductionmentioning

confidence: 99%

Response to reviewer 1

Beyerle¹

2016

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A 1-year data set of ground-based GPS signal observations aiming at geometric elevation angles below + 2 • is analysed. Within the "GLESER" measurement campaign about 2600 validated setting events were recorded by the "OpenGPS" open-loop tracking receiver at an observation site located at 52.3808 • N, 13.0642 • E between January and December 2014. The measurements confirm the feasibility of open-loop signal tracking down to geometric elevation angles of −1 to −1.5 • extending the corresponding closed-loop tracking range by up to 1 • . The study is based on the premise that observations of low-elevation events by a ground-based receiver may serve as test cases for space-based radio occultation measurements, even if the latter proceed at a significantly faster temporal scale. The results support the conclusion that the open-loop Doppler model has negligible influence on the derived carrier frequency profile for strong signal-to-noise density ratios above about 30 dB Hz. At lower signal levels, however, the OpenGPS receiver's dual-channel design, which tracks the same signal using two Doppler models differing by 10 Hz, uncovers a notable bias. The repeat patterns of the GPS orbit traces in terms of azimuth angle reveal characteristic signatures in both signal amplitude and Doppler frequency with respect to the topography close to the observation site. Mean vertical refractivity gradients, extracted from ECMWF meteorological fields, correlate weakly to moderately with observed signal amplitude fluctuations at geometric elevation angles between +1 and +2 • . Results from multiple phase screen simulations support the interpretation that these fluctuations are at least partly produced by atmospheric multipath; at negative elevation angles diffraction at the ground surface seems to contribute.

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Validation of refractivity profiles derived from GRAS raw-sampling data

Cited by 12 publications

References 32 publications

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

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

A forward operator and its adjoint for GPS slant total delays

Response to reviewer 1

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