Backpropagation Processing of GPS Radio Occultation Data

Ao, C. O.; Hajj, G. A.; Meehan, T. K.; Leroy, S. S.; Kursinski, E. R.; Juárez, Manuel Torre de la; Iijima, B. A.; Mannucci, A. J.

doi:10.1007/978-3-540-38366-6_57

Cited by 8 publications

(2 citation statements)

References 12 publications

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“…Moreover, the bias was shown to be larger in the tropics, suggesting a possible correlation with water vapor abundance. A negative refractivity bias in the lower troposphere has also been reported recently for a small set of CHAMP and SAC‐C data [ Wickert et al , 2001; Ao et al , 2003; Marquardt et al , 2003; Hajj et al, submitted manuscript, 2002].…”

Section: Introductionsupporting

confidence: 72%

Lower troposphere refractivity bias in GPS occultation retrievals

et al. 2003

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[1] Analysis of atmospheric occultation data from the GPS Meteorology experiment has revealed that the refractivity retrievals in the lower troposphere were systematically smaller than those obtained with numerical weather prediction models. It has been suggested that the bias was due to a combination of atmospheric multipath, critical refraction, and receiver tracking errors. In this paper, we show that a similar bias exists in the CHAMP and SAC-C data and describe the characteristics of the bias based on over 6700 soundings from October 2001. Retrievals obtained using the recently introduced canonical transform method are shown to markedly reduce the refractivity bias; however, a significant bias still remains below 2 km altitude. To better understand the underlying causes of the bias, we perform an end-to-end simulation study that incorporates full-wave signal propagation and realistic receiver tracking effects using an ensemble of atmospheric profiles. We find that atmospheric ducting effects associated with the top of the planetary boundary layer (PBL) at 1-2 km altitude would cause retrieval errors at and below the PBL even in the absence of the receiver errors. Furthermore, current implementation of the receiver tracking algorithm based on an enhanced version of the phase-locked loop could introduce additional errors under the low signal-to-noise ratio conditions that are often encountered in the lower troposphere. The latter problem is expected to be resolved in the near future through the adoption of open-loop tracking and the removal of the navigation modulation from the GPS signal.INDEX TERMS: 3360

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Section: Introductionsupporting

confidence: 72%

Lower troposphere refractivity bias in GPS occultation retrievals

et al. 2003

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“…The LEO (Low Earth Orbit) satellites CHAMP and SAC-C launched in 2000, carry a new generation of Global Positioning System (GPS) receivers to perform radio occultation soundings of the ionosphere and neutral atmosphere. Up to date, occultations in the order of 10 5 have been gathered (see e.g., Ao et al 2003).…”

Section: Introductionmentioning

confidence: 99%

A Global Distribution of the Stratospheric Gravity Wave Activity from GPS Occultation Profiles with SAC-C and CHAMP

Torre

Tsuda

Hajj

et al. 2004

Journal of the Meteorological Society of Japan

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We have analysed the gravity wave activity using temperature profiles retrieved from the GPS occultation experiments on board the SAC-C and CHAMP satellites. By dividing the latitude and longitude ranges, here considered in individual cells, the variability of wave energy as a function of altitude observed in both hemispheres during October, November and December 2001 is presented. Some features were repeatedly observed during the three months. Nevertheless, as most available occultations were occurred during November, we begin showing results from this month. Significant differences detected during October are only pointed out at midlatitudes, provided that sufficient number of occultations are available. A significantly larger wave activity at 40-60 N with respect to 40-60 S is detected during this month. Differences between both the hemispheres are discussed and compared with previous results. Wave activity enhancements at equatorial regions above Brazil, Indonesia and India are found to be correlated with outgoing longwave radiation data. Vertical fluctuations with lengths above and below 3.5 km are considered separately, in order to identify the contribution of Kelvin and Rossby-gravity waves. In both cases, for long and short fluctuations and at the upper troposphere as well as at the lower stratosphere, there is a height interval of several kilometers where a systematic enhanced wave activity is observed. Its average height is progressively decreasing with increasing latitude, same as the height variation in the tropopause location. Longitudinal enhancements are also detected mainly around the equator and at midlatitudes. A clear signature is observed locally in the Southern Hemisphere (SH) at midlatitudes and 70-65 W, for vertical wavelengths longer than 3.5 km. It corresponds to mountain waves forced by the Andes Range, observed whenever occultations are available in this cell.

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