Metop-GRAS in-orbit instrument performance   总被引：2，自引：1，他引：1  

Magnus Bonnedal  Jacob Christensen  Anders Carlström  Anders Berg 《GPS Solutions》2010,14(1):109-120

The GRAS instrument on the Metop-A satellite provides more than 600 radio occultation measurement profiles per day. The instrument is characterized by its wide antenna coverage, high signal-to-noise ratio and an ultra-stable clock reference. The conventional dual-frequency tracking of GPS signals is under dynamic atmosphere conditions complemented by open loop tracking with sampling of the signal at a 1 kHz rate, providing an unprecedented view of the signal spectral environment. This paper presents the instrument performance as derived from analysis of in-orbit measurement data. We show that the noise figure is low enough to enable mapping of external radio noise variations over the earth’s surface. An error propagation model is presented to relate instrument characteristics to bending angle performance. This model is also used to illustrate the relation between filter bandwidth, resolution and measurement noise. The Doppler model, guiding open loop measurements, is found to be accurate to better than 20 Hz with a possibility for improvement to 10 Hz. The high performance at low altitudes enables the presence of surface reflections at the −20-dB level to be identified in more than 50% of the occultations. The potential performance improvements for next generation receivers are discussed.  相似文献   

AsteroFLAG: First results from hare‐and‐hounds Exercise #1     

W.J. Chaplin  T. Appourchaux  T. Arentoft  J. Ballot  J. Christensen‐Dalsgaard  O.L. Creevey  Y. Elsworth  S.T. Fletcher  R.A. García  G. Houdek  S.J. Jimnez‐Reyes  H. Kjeldsen  R. New  C. Rgulo  D. Salabert  T. Sekii  S.G. Sousa  T. Toutain  the rest of the asteroFLAG group 《Astronomische Nachrichten》2008,329(5):549-557

We report on initial results from the first phase of Exercise #1 of the asteroFLAG hare and hounds. The asteroFLAG group is helping to prepare for the asteroseismology component of NASA's Kepler mission, and the first phase of Exercise #1 is concerned with testing extraction of estimates of the large and small frequency spacings of the low‐degree p modes from Kepler‐like artificial data. These seismic frequency spacings will provide key input for complementing the exoplanet search data. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献