共查询到20条相似文献，搜索用时 21 毫秒
1.
William M. Irvine 《Icarus》1975,25(2):175-204
Methods for solving radiative transfer problems within the extended visible spectrum in planetary atmospheres are reviewed for use by the nonspecialist. Emphasis is placed on rapid, approximate procedures for the determination of such quantities as the plane and spherical (Bond) albedo, surface illumination, absorbed energy, limb darkening, phase curve, and spectra. Precise numerical methods and analytical results are also discussed. Recent approaches to such complications as atmospheric inhomogeneity and reflection from a porous regolith are described briefly. 相似文献
2.
B. Ruiz Cobo 《Astrophysics and Space Science》1998,263(1-4):331-334
During the last years, inversion techniques have become one of the most powerful tools to obtain, from spectropolarimetric
data, the stratification of physical quantities (temperature, pressure, velocity fields, magnetic field, etc.) describing
different structures in the solar atmosphere.
The SIR code (Stokes Inversion based on Response functions), developed at the Instituto de Astrofísica de Canarias (IAC),
is internationally acknowledged nowadays at the most sophisticated and accurate inversion method. The main results derived
from its application to the study of the solar photosphere, are presented. Two recent extensions are reported as well: inversion
under NLTE conditions, and the MISS code (Multiline Inversion of Stellar Spectra).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
We present a study of the effects of atmospheric seeing on quantities derived from observations of solar polarized light –
specifically, the vector magnetic flux and quantities derived from its magnitude and direction. Data from the Imaging Vector
Magnetograph (‘IVM’) at the U. Hawaii/Mees Solar Observatory, are degraded by various degrees by applying a blur function
to the ‘incoming light’, simulating a range of seeing conditions. A quantitative study of the resulting effects on derived
quantities including total magnetic flux, vertical electric current density and magnetic shear angles, are discussed as a
function of the imposed degradation. The generality of the seeing effects is explored by comparing the results from two different
active regions; we find that the results are comparable for those quantities directly computed from the magnetic flux vector
(e.g., summed, as in total flux) but less so for those quantities involving higher-order calculations (e.g., derivatives,
as in vertical currents). We suggest that for temporal series data from any instrument, a method such as that which we outline
here, be applied in order to model the uncertainties imposed on the data (in addition to instrumental uncertainties, etc.)
due to seeing variations. 相似文献
4.
Accelerometer measurements made by Spirit and Opportunity during their entries through the martian atmosphere are reported. Vertical profiles of atmospheric density, pressure, and temperature with sub-km vertical resolution were obtained using these data between 10 and 100 km. Spirit's temperature profile is ∼10 K warmer than Opportunity's between 20 and 80 km. Unlike all other martian entry profiles, Spirit's temperature profile does not contain any large amplitude, long wavelength oscillations and is nearly isothermal below 30 km. Opportunity's temperature profile contains a strong inversion between 8 and 12 km. A moderate dust storm, which occurred on Mars shortly before these two atmospheric entries, may account for some of the differences between the two profiles. The poorly known angle of attack and unknown wind velocity may cause the temperature profiles to contain errors of tens of Kelvin at 10 km, but these errors would be an order of magnitude smaller above 30 km. On broad scales, the two profiles are consistent with Mars Global Surveyor Thermal Emission Spectrometer (TES) pressure/temperature profiles. Differences exist on smaller scales, particularly associated with the near-isothermal portion of Spirit's profile and the temperature inversion in Opportunity's profile. 相似文献
5.
Ian W. Roxburgh 《Astrophysics and Space Science》2010,328(1-2):3-11
I discuss several asteroseismology diagnostic techniques that can be applied to the high quality data on stellar oscillations obtained, and to be obtained in the future, from ground based and space based experiments. In particular I discuss techniques using the representation of oscillation frequencies in terms of inner and outer phase shifts which can be used both for model fitting and inversion procedures to probe the inner structure of stars, and hence to test and improve our modelling. 相似文献
6.
The land-surface flux model (PROGSURF) designed jointly at the Universities of Vienna and Budapest is reviewed; it belongs to the broad spectrum of PILPS1 models. PROGSURF comprises one vegetation layer and three soil layers. Temperature prediction is made by the heat conduction equation in conjunction with the force-restore method. Turbulent heat fluxes are parameterized by gradient laws using the resistance concept. The formula for the canopy surface resistance involves both a parameter describing atmospheric demand and one describing moisture availability. Soil moisture prediction is made with Richards' equation. PROGSURF is tested in off-line mode for the Cabauw data set. The observed annual mean values of the state and flux quantities at the earth's surface are well reproduced. For example, the model yields latent and sensible heat fluxes of −35.3 and −2.4 W/m2, respectively; evapotranspiration and runoff is −449 and 326 mm/yr; and root zone soil moisture content is 0.344 m3/m3. Further, the seasonal changes of water and energy balance components are well simulated. The sensitivity of PROGSURF to the canopy resistance formulation is analysed. We find that the atmospheric demand is largely represented by the saturation value of the evapotranspiration/soil moisture curve with maximum summer impact upon the annual value and further that the moisture availability is represented by the slope of the evapotranspiration curve. Both saturation value and slope control the amplitude of the seasonal fluctuation of the water balance components; at Cabauw site the saturation value is the governing parameter. These results fit satisfactorily into the other PILPS models. In particular, we are able to reproduce with PROGSURF the total variability of most other PILPS models by simply changing the atmospheric demand and soil moisture availability parameters. PROGSURF presently serves to simulate observed surface fluxes for an atmospheric diagnostic model. 相似文献
7.
Benton C. Clark 《Icarus》1978,34(3):645-665
Converging lines of evidence suggest that a significant portion of the Martian surface fines may consist of salts and smectite clays. Salts can form stoichiometric hydrates as well as eutectic solutions with depressed freezing points; clays contain bound water of constitution and adsorb significant quantities of water from the vapor phase. The formation of ice may be suppressed by these minerals in some regions on Mars, and their presence in abundance would imply important consequences for atmospheric and geologic processes and the prospects for exobiology. 相似文献
8.
作者结合射电天文和气象实测资料,使用大气层结模型和反演法,数值计算了大气中云的含水量和云天大气对射电源毫米波辐射总衰减的改正。其结果优于均匀气温模型和两层大气模型的结果以及跟踪太阳法的结果。 相似文献
9.
推导了GPS无线电掩星振幅观测反演地球大气技术中Abel积分变换中的天顶补偿项 ,定性地说明了天顶补偿项对计算过程和反演剖面的影响。 相似文献
10.
Straylight effects in solar intensity images have been framed in a well-established mathematical formulation (Chae et al., 1998a, b). Many procedures can be applied to recover the point spread function (PSF) and correct the atmospheric and instrumental distortions. Concerning velocity data, some procedures to make corrections for straylight have been addressed. Many experiments infer the velocity as the mean displacement of a spectral line and build a Dopplergram as a nonlinear combination of the intensity images sampled at different wavelengths. Unfortunately, often only the final products are available and it is not possible to apply an appropriate correction to the individual intensity images. A standard procedure to correct for the straylight has been applied to a time-series of velocity data and the results have been controlled in the single Dopplergram (that seems to be good) and in a power spectrum at the atmospheric frequencies (where any correction should reduce the power). These frequencies are characteristic of the observing site and typically in the range of the g modes: this means that no long run from a network would decrease their contribution to the noise. The results show that the correction procedures, based on the intensity and velocity gradients, are not reliable if controlled in the power spectrum. This conclusion has led to a change of the acquisition procedure at the Kanzelhöhe Solar Observatory, where now the individual intensity images that build the Dopplergram are stored. 相似文献
11.
《天文和天体物理学研究(英文版)》2020,(6)
In this article,we present detailed seasonal,monthly and daily statistics of temperature difference in the surface layer at the Muztagh-ata site based on the temperature measurements at two heights of 2 m and6 m.We find that temperature inversion occurs frequently at our site during nighttime,especially during the cold season.Strong temperature inversion always represents stable atmospheric turbulence,which is crucial for an optical observatory.By analyzing the behavior of temperature inversion and its correlation with wind and cloud amount,one conclusion can be made that radiation inversion is the main reason for the existence of temperature inversion in the surface-layer at the Muztagh-ata site. 相似文献
12.
《Chinese Astronomy and Astrophysics》2005,29(2):223-233
The Abel integral transformation in GPS/LEO occultation technique requires the atmospheric index of refraction n to be a single-valued function of the refractional radius a. This condition is broken when the vertical refractivity gradient is less than a critical value dN/dr∼-0.16 N-units m−1, and it is called superrefraction. The Abel integral transformation is no longer valid under this condition, and, if the classical Abel transformation is still formally applied, then a negative refractivity bias occurs in results. The physical characteristics and mathematical expression of the superrefraction phenomenon in the lower troposphere are described. In the frame of a general Abel integral transformation, the inversion algorithm of the atmospheric profiles in and below the superrefraction layer is discussed. Under a simple assumption of the constant vertical gradient of refractivity in the sampling interval, the simulation calculation is carried out on UK High Resolution Radiosonde Data. The computational results have verified the relationship between the negative refractivity bias and the superrefraction phenomenon, as well as the validity of the general Abel transformation proposed. 相似文献
13.
Bjarne S. Haugstad 《Icarus》1978,35(3):410-421
Turbulence in planetary atmospheres leads to both fluctuating and systematic errors in atmospheric profiles derived from Doppler measurements during radio occultation. If the upper atmospheres of Venus and Jupiter are about as turbulent as the earth's troposphere, we deduce rms fractional errors in temperature and pressure of less than ～ 10?2 for the Mariner 10 and Pioneer 10/11 occultation experiments. Fractional systematic errors are typically of the order of 10?6. These estimates depende rather weakly on quantities characterizing the atmosphere and the occultation, and it is conjectured that turbulence-induced errors in atmospheric profiles derived from Doppler measurements are always very small in the weak scattering limit 相似文献
14.
The effective level of line formation for spectroscopic absorption lines has long been regarded as a useful parameter for determining average atmospheric values of the quantities involved in line formation. The identity of this parameter has recently been disputed. Here we reestablish the dependence of this parameter on the average depth at which photons are absorbed in a semi-infinite atmosphere and show that the mean depths derived by others are similar in nature and behavior. 相似文献
15.
Thomas E. Thorpe 《Icarus》1978,36(2):204-215
The Viking Extended Mission has experienced two major dust storms that have changed the global photometric properties of Mars. Large quantities of atmospheric dust arising from the June 5, 1977, storm have been observed at very low phase angles to measure the opposition effect. These particles yield only a small increase in brightness at 0° phase angle with the least enhancement seen in violet light. The phase function is well modeled by nonspherical particles with a spectrally dependent single scattering albedo. It is doubtful, therefore, that atmospheric dust plays a significant role in the reported blue light brightness surge. Such particles as surface structure combined with a lunar photometric function could, however, produce the wavelength-dependent backscattering observed during the 1967 and 1969 oppositions under clearer conditions. 相似文献
16.
17.
S. -I. Akasofu D. Weimer
T. Iijima
B. -H. Ahn
Y. Kamide
《Planetary and Space Science》1990,38(12):1533-1540On the basis of records from meridian chains of magnetometers and the KRM inversion method, we have deduced a number of ionospheric quantities, including the distribution of the electric potential, field-aligned currents, the ionospheric currents and its equatorial counterpart and the relationship between the AE index and the cross-polar cap potential. In this paper, we examine the results thus obtained in the light of compatible data which are deduced from satellite observations. It is shown that both results agree fairly well, proving the validity of the polar ionospheric parameters deduced from both the ground-based and satellite-based data. Several important implications of the results are pointed out. 相似文献
18.
A three-dimensional coronal magnetic field is reconstructed for the NOAA active region 11158 on 14 February 2011. A GPU-accelerated direct boundary integral equation (DBIE) method is implemented which is approximately 1000 times faster than the original DBIE used on solar non-linear force-free field modeling. Using the SDO/HMI vector magnetogram as the bottom boundary condition, the reconstructed magnetic field lines are compared with the projected EUV loop structures as observed in the front-view (SDO/AIA) and the side-view (STEREO-A/B) images for the first time; they show very good agreement three-dimensionally. A quantitative comparison with some stereoscopically reconstructed coronal loops shows that the average misalignment angles in our model are at the same order as the state-of-the-art results obtained from reconstructed coronal loops. It is found that the observed coronal loop structures can be grouped into a number of closed and open field structures with some central bright coronal loop features around the polarity inversion line. The reconstructed highly sheared magnetic field lines agree very well with the low-lying sigmoidal filament along the polarity inversion line. This central low-lying magnetic field loop system must have played a key role in powering the flare. It should be noted that while a strand-like coronal feature along the polarity inversion line may be related to the filament, one cannot simply interpret all the coronal bright features along the polarity inversion line as manifestation of the filament without any stereoscopic information. 相似文献
19.
GPS/LEO掩星技术中超折射效应的修正 总被引：4，自引：3，他引：1
在GPS掩星探测地球大气技术中，Abel积分变换要求大气折射指数n是折射半径a的单值函数，当大气折射率的垂直梯度达到小于一个极限值dN／dr≈-0．16N-unit m^-1上述单值性不成立，称其为超折射，此时Abel积分变换不再适用,如果还是在形式上应用经典的Abel变换，在反演结果中就会产生负大气折射率偏差．描述了低对流层中超折射现象的物理特性和数学表示；在广义Abel积分变换的基础上，讨论了超折射层内和超折射层下的大气剖面反演算法；选择了一个简单的采样间隔内等大气折射率垂直梯度假设，对英国高分辨率无线电探空观测资料进行模拟计算，验证了负超折射与大气折射率偏差的关系，并提出的广义Abel变换的合理性. 相似文献
20.
C. Pichon A. Siebert O. Bienaymé 《Monthly notices of the Royal Astronomical Society》2002,329(1):181-194
A method for inverting the statistical star counts equation, including proper motions, is presented; in order to break the degeneracy in that equation, it uses the supplementary constraints required by dynamical consistency. The inversion gives access to both the kinematics and the luminosity function of each population in three régimes: the singular ellipsoid, the constant ratio Schwarzschild ellipsoid plane-parallel models and the epicyclic model. This more realistic model is tailored to account for the local neighbourhood density and velocity distribution.
The first model is fully investigated, both analytically and by means of a non-parametric inversion technique, while the second model is shown to be formally its equivalent. The effect of noise and incompleteness in apparent magnitude is investigated. The third model is investigated by a non-parametric inversion technique where positivity of the underlying luminosity function is explicitly accounted for.
It is argued that its future application to data such as the Tycho catalogue (and in the upcoming satellite GAIA ) could lead – provided that the vertical potential and or the asymmetric drift or w⊙ are known – to a non-parametric determination of the local neighbourhood luminosity function without any reference to stellar evolution tracks. It should also yield the proportion of stars for each kinematic component and a kinematic diagnostic to split the thin disc from the thick disc or the halo. 相似文献
The first model is fully investigated, both analytically and by means of a non-parametric inversion technique, while the second model is shown to be formally its equivalent. The effect of noise and incompleteness in apparent magnitude is investigated. The third model is investigated by a non-parametric inversion technique where positivity of the underlying luminosity function is explicitly accounted for.
It is argued that its future application to data such as the Tycho catalogue (and in the upcoming satellite GAIA ) could lead – provided that the vertical potential and or the asymmetric drift or w