Group - Doppler spectroscopy


 

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Doppler spectroscopy, also known as radial velocity measurement, is a spectroscopic method for finding extrasolar planets. It involves the observation of Doppler shifts in the spectrum of the star around which the planet orbits. It is extremely difficult to directly observe extrasolar planets because they are very faint at interstellar distances, although the first claims of direct observations were made in 2004 and 2005. As a result, planets outside of our solar system are usually discovered using indirect methods, through the effect of the planet on an object that is easier to observe, such as the parent star. Successful methods include Doppler spectroscopy, astrometry, pulsar timing, transits, and gravitational microlensing. Almost all of the known extrasolar planets have been discovered using Doppler spectroscopy. Otto Struve proposed in 1952 the use of powerful spectrographs to detect distant planets. He described how a very large planet, as large as Jupiter, for example, would cause its parent star to wobble slightly as the two objects orbit around their center of mass. He predicted that the small Doppler shifts to the light emitted by the star, caused by its continuously varying radial velocity, would be detectable by the most sensitive spectrographs as tiny red shifts and blue shifts in the star's emission. However, the technology of the time produced radial velocity measurements with errors of 1,000 m/s or more, making them useless for the detection of orbiting planets. The expected changes in radial velocity are very small – Jupiter causes the Sun to change velocity by about 13 m/s over a period of 12 years, and the Earth's effect is only 0.1 m/s over a period of 1 year – so long-term observations by instruments with a very high resolution are required.  



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     Related Documents

  • Doppler angle and flow velocity mapping by combined Doppler shift and ...

  • Abstract: Accurate estimation of flow velocity requires measurement of Doppler angle, which is not available in general clinical applications. We describe a novel method of direct Doppler angle and flow velocity mapping that uses a conventional single-beam optical Doppler tomography system. The Doppler angle is estimated by combination of Doppler shift and Doppler bandwidth measurements, and flow velocity is calculated from the Doppler shift and the estimated Doppler angle. In vivo study of lip microvascularization demonstrates that this method is capable of providing both flow speed and flow direction ...

  • Quantifying Doppler angle and mapping flow velocity by a combination o...

  • Abstract: Recently we introduced a novel procedure that estimates Doppler angle and flow velocity simultaneously by combining Doppler-shift and Doppler-bandwidth measurements with a conventional single-beam optical Doppler tomography device. Here we validate this method experimentally with two Intralipid flow setups that correspond to fixed Doppler angle and fixed flow speed. One set of data has a fixed flow speed of 53.6 mm/s with a Doppler angle that changes from 56 degrees to 90 degrees; the other has a fixed Doppler angle of 80 degrees with flow speed that changes from 18.5 to 141.9 mm/s. As obtaine...

  • [Ultrasound Doppler sonography in obstetrics. A comparison between sim...

  • Abstract: 120 pregnant women between the 26th and 42nd week of gestation have been examined using simple Doppler-units with pulsed- or continuous-wave technique and duplex Doppler-units (combined B-mode and pulsed-wave Doppler). The umbilical and uterine arteries were measured with both units in a semi-recumbent position at the same time by the same examiner. Only ideal flow profiles were taken to calculate the S/D-ratio. Our results were correlated to the fetal outcome, to all cases of pre-eclampsia and to all cases of intra-uterine growth retardation. Except in one of these cases we got the majority o...

  • [Doppler effect in cardiology. Continuous Doppler, pulsed Doppler, Dop...

  • Abstract: Echocardiography has contributed to the exploration of the heart by providing much information, and it has even given rise to new semiological concepts. However, abnormalities of intracardial blood flow, notably shunts and regurgitations, could only be diagnosed indirectly from their effects on cardiac cavities. A new step forward was the advent of pulsed and continuous doppler ultrasound, since from that moment it has been possible to demonstrate abnormal blood flows, to measure their velocity and to determine, albeit with some reservation, such crucial values as pressure gradients. Yet even ...

  • [The significance of the Doppler techniques -- "color Doppler" and "po...

  • Abstract: The eyeball is perfectly suited for ultrasound examination due to its location and structure. The ultrasound examination including the "color Doppler" and "power Doppler" option was performed in 59 patients. Ophthalmologists requested ultrasound examination in those patients mainly in order to confirm and differentiate retinal ablation or because of opacity of vitreous body of the eye. The ultrasound examination was performed with a Logiq 500 f-y GE unit equipped with a 7.5 MHz linear transducer and a 7.5 MHz linear transducer and a Hitachi 415 EUB applied. Primary retinal ablation was diagnos...

  • Comparison of Doppler echocardiography, color M-mode Doppler, and Dopp...

  • Abstract: To overcome the limitations of mitral inflow parameters for predicting pulmonary capillary wedge pressure (PCWP), combined indices (with Doppler tissue imaging or color M-mode Doppler) have been developed. This study was aimed to compare the accuracy of these indices to predict PCWP. Sixty-one patients were studied. The best correlations with PCWP were found for indices that combined isovolumic relaxation time with flow propagation velocity (color M-mode) or early diastolic velocity of the lateral mitral annulus (Doppler tissue). Both closely tracked changes in PCWP. The color M-mode-derived i...

  • Clinical utility of Doppler echocardiography and tissue Doppler imagin...

  • Abstract: BACKGROUND: Noninvasive assessment of diastolic filling by Doppler echocardiography provides important information about left ventricular (LV) status in selected subsets of patients. This study was designed to assess whether mitral annular velocities as assessed by tissue Doppler imaging are associated with invasive measures of diastolic LV performance and whether additional information is gained over traditional Doppler variables. METHODS AND RESULTS: One hundred consecutive patients referred for cardiac catheterization underwent simultaneous Doppler interrogation. Invasive measurements of LV...

  • Assessment of Doppler velocimetry of the fetal umbilical artery by mul...

  • Abstract: The Doppler signal of blood flow originates from the sonographic scattering from the circulating red blood cells. However, the physics of blood flow is complex as expressed by the Bernoulli equation, and the flow velocity at different positions in the laminar flow of the same vessel is variable. Using multigate spectral Doppler scanning, we recorded multiple Doppler flow signals over a segment of the umbilical artery and compared the results with traditional pulsed Doppler ultrasonography. The intraobserver variations of the pulsatility index, the resistive index, and the systolic-to-diastolic...

  • [Spectro-temporal mapping (STM)]

  • Abstract: In recent years, various kinds of time-varying spectral analysis which estimate the frequency content of a signal as a function of time have been proposed. Spectro-temporal mapping (STM) is one of such methods with elaborate modification of a simple fixed period analysis. Merits and demerits of this method in clinical application are described in this chapter. Certain technical aspects pertinent to the interpretation of STM were also discussed. In conclusion, STM in present form is inferior to time domain analysis for the prediction of serious ventricular arrhythmias. But it has some usefulnes...



























 

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