Metop-GRAS in-orbit instrument performance

Bonnedal, M.; Christensen, Jacob; Carlström, Anders; Berg, Anders

doi:10.1007/s10291-009-0142-3

Cited by 45 publications

(57 citation statements)

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“…To address premature signal loss GNSS-RO receiver tracking algorithms based on closed feedback loops were replaced by "open-loop" techniques (see e.g. Sokolovskiy, 2001b;Sokolovskiy et al, 2006;Ao et al, 2009;Bonnedal et al, 2010;Wang et al, 2016). If a receiver operates in open-loop mode the feedback loop is opened and the NCO producing the replica signal is steered (in part or fully) from model parameters.…”

Section: Closed-loop and Open-loop Signal Trackingmentioning

confidence: 99%

“…This model takes into account the expected signal dynamics from both, the transmitter and receiver orbits, clocks biases and drifts as well as the signal propagation characteristics in the lower troposphere. The latter are typically obtained from an atmospheric climatology (Sokolovskiy, 2001b;Bonnedal et al, 2010).…”

Section: Closed-loop and Open-loop Signal Trackingmentioning

confidence: 99%

“…Compared to O/L methods employed by space-based GNSS-RO receivers, which are based on predetermined code and carrier parameters derived from atmospheric climatologies (Sokolovskiy, 2001b;Sokolovskiy et al, 2006;Ao et al, 2009;Bonnedal et al, 2010), the OpenGPS O/L technique creates a different O/L model during the initialization phase (elevation angles between +2 and 0 • ) for each setting event. Thus, diurnal variations in the atmospheric refractivity field may be better accounted for in the O/L model.…”

Section: A2 Opengps Receiver Softwarementioning

confidence: 99%

“…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%

“…Whereas the "fly wheeling" tracking method of JPL's "Blackjack" GPS receivers mounted on CHAMP and GRACE Hajj et al, 2004) showed some progress, significant improvements with respect to probing of the planetary boundary layer (PBL), in particular at low latitudes, were obtained with the introduction and implementation of open-loop (O/L) tracking (or raw-sampling) techniques (see e.g. Sokolovskiy, 2001b;Sokolovskiy et al, 2006;Ao et al, 2009;Bonnedal et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

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Open-loop GPS signal tracking at low elevation angles from a ground-based observation site

Beyerle

Zus

2017

Atmos. Meas. Tech.

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Abstract. 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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Section: Closed-loop and Open-loop Signal Trackingmentioning

confidence: 99%

Section: Closed-loop and Open-loop Signal Trackingmentioning

confidence: 99%

Section: A2 Opengps Receiver Softwarementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Open-loop GPS signal tracking at low elevation angles from a ground-based observation site

Beyerle

Zus

2017

Atmos. Meas. Tech.

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Interference from terrestrial sources and its impact on the GRAS GPS radio occultation receiver

Isoz

Buehler

Kinch³

et al. 2014

Radio Sci.

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It is well known that terrestrial GPS/Global Navigation Satellite Systems (GNSS) receivers are vulnerable and have suffered from intentional and unintentional interference sources. Unfortunately, space‐based GPS/GNSS receivers are not exempt from radio frequency interference originating from the Earth. This paper explores data recorded by the GNSS Receiver for Atmospheric Sounding (GRAS) instrument onboard MetOp‐A in September 2007, which is assumed to be representative of the typical environment for GPS/GNSS instrumentation in LEO orbit. Within these data it is possible to detect both pulsed interference and variations in the background noise. One plausible source of the pulsed interference is identified. We also show that neither the pulsed interference nor the variations in the background noise degrades the performance of the higher level products from GRAS.

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Observation, analysis, and modeling of deep radio occultation signals: Effects of tropospheric ducts and interfering signals

et al. 2014

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GPS radio occultation (RO) signals are sometimes observed very deep in the Earth's shadow.To investigate these phenomena, one of the FORMOSAT-3/COSMIC RO receivers was set to track RO signals deep below the limb, down to a height of straight line À350 km on 5-6 October 2010. Analysis of the spectrograms revealed the existence of two types of signals below À200 km, RO signals induced by tropospheric propagation and interfering signals not transmitted by the occulted GPS. The RO signals induced by tropospheric propagation arrive from impact heights corresponding to inversion layers. Wave optics modeling of RO signals showed that deep signals exist when the refractivity gradient exceeds critical (super-refraction). The existence of such signals is a diffractional phenomenon, which offers a new quality control parameter to identify occultations that may be affected by super-refraction. This is important for RO data assimilation in weather models in the moist lower troposphere because assimilation of RO data affected by super-refraction is an ill-conditioned problem. Detection of the tropospheric ducts also may be useful for evaluation of radio wave propagation conditions. For infinitely horizontally extended ducts, the deep signals are extended in duration, have amplitudes of about 0.1%, and exist for only elevated ducts. For ducts of limited horizontal extension, the deep signals are shorter in duration, have amplitude of about 1%, and may exist for both elevated and surface ducts. The interfering signals were found in about half of occultations. Based on frequency modeling, in most cases, the interfering signal was identified with non-occulted GPS. The disturbance of retrieved bending angle induced by an interfering signal from a non-occulted GPS in a region of strong defocusing and significant spectral spread of RO signal was modeled and determined to be quite large, up to 10% of bending angle. However, the probability of occurrence of such interference (not estimated), generally, must be low. Removal of the interfering signal by high-pass filtering was tested, but it introduced a disturbance of bending angle of about the same magnitude as the interfering signal itself.

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Metop-GRAS in-orbit instrument performance

Cited by 45 publications

References 1 publication

Open-loop GPS signal tracking at low elevation angles from a ground-based observation site

Open-loop GPS signal tracking at low elevation angles from a ground-based observation site

Interference from terrestrial sources and its impact on the GRAS GPS radio occultation receiver

Observation, analysis, and modeling of deep radio occultation signals: Effects of tropospheric ducts and interfering signals

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