Study of the mesosphere using wide-field twilight polarization measurements: Early results beyond the polar circle

This paper discusses the results of early measurements of temperature and dust in the mesosphere on the basis of wide-field twilight sky polarimetry, which began in 2015 in Apatity (North of Russia, 67.6° N, 33.4° E) using the original entire-sky camera. These measurements have been performed for the first time beyond the Polar Circle in the winter and early spring period. The general polarization properties of the twilight sky and the procedure for identifying single scattering are described. The key results of the study include the Boltzmann temperature values at altitudes higher than 70 km and the conclusion on a weak effect of dust on scattering properties of the mesosphere during this period.     

Polarization Studies of Contribution of Aerosol Scattering to the Glow of Twilight Sky

The paper is devoted to studies and a quantitative estimation of the influence of scattering of direct solar radiation by particles of tropospheric aerosols in the period of light twilight, close to sunrise and sunset. Polarization measurements of the twilight sky in two broad spectral bands lying near the standard bands V and R form the basis of these studies. The measurements were carried out in 2002 and 2003 at the Southern Laboratory (Crimea) of the Sternberg Astronomical Institute. The twilight period during which the single aerosol scattering becomes significant is isolated. The character of its influence on the intensity and polarization of the twilight sky is demonstrated. A method is suggested to evaluate polarization of the single aerosol scattering and its contribution to the general brightness of the twilight sky background. The method is based on differential characteristics of the background near the zenith and on their correlations with each other.     

Analysis of the direction of the twilight sky background polarization as a tool for selecting single scattering

The direction of the twilight sky background polarization on the celestial sphere far from the solar vertical depends on the ratio of single and multiple scattering contributions. Variations in the polarization direction during twilight reflect the evolution of the properties and background emission components and can be used to control the procedure of selecting single scattering. This makes it possible to specify the temperature measurements according to the molecular scattering of solar emission and the contribution of dust scattering in the upper mesosphere. The results of the temperature measurements during the observations in 2011–2015 have been presented.     

Investigations of the Background Stratospheric Aerosol Using Multicolor Wide-Angle Measurements of the Twilight Glow Background

The first results of multiwave measurements of twilight background and the all-sky camera with a color (RGB) CCD matrix conducted in the spring and summer of 2016 in Central Russia (55.2° N, 37.5° E) have been discussed. The observations reveal the effect of aerosol scattering at heights of up to 35 km, which is substantially enhanced in the long-wave part of the spectrum (R band with an effective wavelength of 624 nm). An analysis of the behavior of the sky color during light period of twilight with allowance for the absorption by ozone in the Chappuis bands make it possible to restore the angular dependences of the intensity of the aerosol scattering of the light. This is used to determine the parameters of the lognormal distribution of aerosol particles over their sizes with a mean radius of 0.08 μm and a width of 1.5–1.6 for the stratospheric height interval.     

Multicolor Polarimetry of the Twilight Sky: The Role of Multiple Light Scattering as a Function of Wavelength

This paper is devoted to the investigation of the role of multiply scattered light of different wavelengths in clear twilight, as well as to the influence of multiple scattering and scattering by atmospheric aerosol particles on the polarization of the twilight sky background during this period. The work is based on wide-angle polarimetric CCD-observations of the twilight sky near zenith in the U, B, V, and R bands, which were carried out in summer 2000 at the South Laboratory of the Moscow Shternberg Astronomical Institute. Based on the data obtained, we have determined the fraction of single-scattered light in clear twilight in the zenith for the U, B, and V bands and have estimated the lower limit of this value for the R band. The analysis of color and polarimetric evolution of the sky background was made taking into account single and multiple scattering properties. The characteristic height of the upper boundary of the tropospheric aerosol layer in the Earth's atmosphere was also obtained.     

Studies of the stratosphere aerosol layer based on polarization measurements of the twilight sky

The paper is devoted to an analysis of observational manifestations of the aerosol layer in the Earth’s stratosphere and to a method of determining their optical properties. It is based on polarization measurements of the twilight sky background in the zenith vicinity and in a broad spectral band with an effective wavelength of 5250 Å. An increased abundance of the stratosphere aerosol was found in December 2006 for the first time in several years of observation. The suggested method allows one to determine the ratio of radiation scattering coefficients by the stratosphere aerosol and by air molecules, as well as the degree of polarization of aerosol scattering in the stratosphere. The appearance of the stratosphere aerosol is associated with explosive eruption of Rabaul volcano having occurred in the beginning of October 2006.     

Optical properties of the undisturbed mesosphere from wide-angle twilight sky polarimetry

The paper describes the first results of all-sky polarization measurements of the twilight background started in central Russia in the very beginning of summer 2011. Time-frequency data of the sky intensity and polarization over a wide range of sky point zenith distances are used to separate single and multiple scattering and construct the altitude dependence of the scattering coefficient and polarization in the mesosphere (altitudes from 60 to 90 km) at different angles. The undisturbed structure of the mesosphere without noticeable aerosol stratification on observation days makes it possible to estimate the temperature of the atmosphere at these altitudes.     

Scattering function of tropospheric aerosol according to the data of polarimetry of the twilight and night sky background

The paper contains the photometric and polarimetric analysis of the sky background near the zenith during the twilights and the nights of different years and seasons. The period of enhanced tropospheric aerosol content during the summer 2009 is noticed. The aerosol scattering of solar emission is separated from the total twilight sky background, and similar data on lunar emission is taken from the night sky background. The results are compared with the data of relatively clear troposphere of winter 2006. The observational data are used to construct the polarization scattering function of tropospheric aerosol particles during the nighttime.     

Longitudinal dependence of the H<Superscript>+</Superscript> concentration distribution in the plasmasphere according to <Emphasis Type="Italic">INTERBALL-1</Emphasis> satellite data

The paper has presented a study of the dependence of the H⁺ ions concentration in the plasmasphere on geographic longitude. A vast database of measurements of the cold plasma density by the Alpha-3 instrument on board the INTERBALL-1 satellite has been used for the study. Based on these measurements, a dependence of the H⁺ ions concentration in the filled magnetic flux tube in the plasmasphere in the equatorial plane under quiet geomagnetic conditions has been obtained as a function of geographic longitude. Studies have been performed for two seasons, summer and winter. It has been shown that, during the summer in the near-midnight sector, the minimum in the H⁺ concentration falls within geographic longitudes of 270°–315°. The ratio of the concentration of H⁺ ions at various longitudes could reach a factor of three. During the winter, in the near-noon sector, the maximum of the H⁺ ions concentration falls within longitudes of 180°–225°, whereas the concentration ratio could reach a factor of 2.2.     

Estimating the accuracy of the technique of reconstructing the rotational motion of a satellite based on the measurements of its angular velocity and the magnetic field of the Earth

The paper has studied the accuracy of the technique that allows the rotational motion of the Earth artificial satellites (AES) to be reconstructed based on the data of onboard measurements of angular velocity vectors and the strength of the Earth magnetic field (EMF). The technique is based on kinematic equations of the rotational motion of a rigid body. Both types of measurement data collected over some time interval have been processed jointly. The angular velocity measurements have been approximated using convenient formulas, which are substituted into the kinematic differential equations for the quaternion that specifies the transition from the body-fixed coordinate system of a satellite to the inertial coordinate system. Thus obtained equations represent a kinematic model of the rotational motion of a satellite. The solution of these equations, which approximate real motion, has been found by the least-square method from the condition of best fitting between the data of measurements of the EMF strength vector and its calculated values. The accuracy of the technique has been estimated by processing the data obtained from the board of the service module of the International Space Station (ISS). The reconstruction of station motion using the aforementioned technique has been compared with the telemetry data on the actual motion of the station. The technique has allowed us to reconstruct the station motion in the orbital orientation mode with a maximum error less than 0.6° and the turns with a maximal error of less than 1.2°.     

The analysis of measurements of quasi-stationary electrical fields in the near-surface zone of the <Emphasis Type="Italic">Mir</Emphasis> orbital complex

The quasi-stationary electrical fields have been measured in the near-surface zone of the Kvant module of the Mir orbital complex using vibration-type sensors of the Zond-Zaryad instrument. The analysis of measurements has shown that, depending on the spacecraft’s surface section shape (an octagon), four areas of the electrical fields configuration (and of the plasma component density) were revealed in the spacecraft vicinity: a ram with angular extension of about 120° (±60°), two side areas with angular extension of about 60° each, and a wake with angular extension of about 120° (±60°). The electrical field in the ram has a small absolute value. In the side areas, the electrical field can have either a negative or positive value, and it is smaller in magnitude than that in the ram. The electrical field in the wake has a three-petal structure (and an even more complicated structure is also possible): the negative value of the field (with angular extension of about 45°), the positive value of the field (with angular extension of about 30°), and, again, the negative value of the field (with angular extension of about 45°). Absolute value of the field in the wake is at least an order of magnitude higher than that in the ram and on the side surfaces.     

Dynamics of polar boundary of the auroral oval derived from the IMAGE satellite data

Based on a new database on positions of the auroral oval boundaries including measurements made by the IMAGE satellite in 2000–2002 with correct determination of the glow boundaries, statistical estimations of the latitudinal position of the polar cap boundary (PCB) are obtained depending on the IMF B _y and B _z , and the PCB evolution during a magnetic storm is analyzed. At zero IMF in the noon (midnight) sector, PCB is located approximately at 80° (76°) CGMLat. The PCB displacement along the noon-midnight meridian is controlled by the IMF B _z , and in the noon (midnight) sector it is equal to 0.45° (0.15°) CGMLat when B _z changes by 1 nT. The PCB displacement along the dawn-dusk meridian depends on the IMF B _y , and it equals 0.1° CGMLat when B _y changes by 1 nT. Accordingly, the north polar cap as a whole is shifted to the dawn (dusk) side at B _y > 0 (B _y <0). After northward turn of the IMF during the storm’s recovery phase, the PCB on the dayside is shifted to the north practically without time delay. The night boundary requires 25 h or more in order to be shifted to the pole to a latitude corresponding to B _z > 0.     

基于航迹关联的抗角闪烁跟踪算法研究

角闪烁背景下，高分辨雷达在近距离跟踪阶段存在不能精确跟踪的问题。针对此问题，分析了基于距离高分辨的单脉冲测角方法，并在此基础上，结合距离向强散射点的幅度特征，提出了一种基于航迹关联的抗角闪烁跟踪算法。算法首先对和通道、方位差通道、俯仰差通道的回波信号分别进行脉压和相参积累；然后在和通道的高分辨一维距离向上实现目标强散射点的检测，依据幅度进行排序并输出各点的距离信息和角度信息；最后利用联合集成概率数据互联算法作为目标跟踪滤波算法进行跟踪。本文通过对ku波段实测数据中入射余角为60°~69°的近距离跟踪部分进行分析，将所提算法与卡尔曼滤波跟踪算法进行了对比，仿真结果表明，本文算法使多目标跟踪的精度得到了提高，具有更好的角闪烁抑制性能。     

跨介质航行器弹性舵翼空化流固耦合仿真分析

跨介质航行器水中航行过程中的流固耦合效应是影响航行稳定性和结构安全性的关键问题。基于径向基函数法和模态叠加方法,开展跨介质航行器水中运动过程中空化流动与结构振动的耦合仿真,对航行器三角型截面舵翼的流固耦合效应进行研究,分析了不同攻角下的空泡形态以及舵翼与空化流动的相互作用。分析结果表明,在来流攻角为2°～6°时,航行器及舵翼几乎被包在超空泡内部。当来流攻角为8°时,舵翼的自由端会穿透空泡界面,使其所受水动力比小攻角条件下大一个量级,振动特征也更为复杂。     

Solution of the flyby problem for large space debris at sun-synchronous orbits

the paper considers the flyby problem related to large space debris (LSD) objects at low earth orbits. The data on the overall dimensions of known last and upper stages of launch vehicles makes it possible to single out five compact groups of such objects from the NORAD catalog in the 500–2000 km altitude interval. The orbits of objects of each group have approximately the same inclinations. The features of the mutual distribution of the orbital planes of LSD objects in the group are shown in a portrait of the evolution of deviations of the right ascension of ascending nodes (RAAN). In the case of the first three groups (inclinations of 71°, 74°, and 81°), the straight lines of relative RAAN deviations of object orbits barely intersect each other. The fourth (83°) and fifth (97°–100°) LSD groups include a considerable number of objects whose orbits are described by straight lines (diagonals), which intersect other lines many times. The use of diagonals makes it possible to significantly reduce the temporal and total characteristic velocity expenditures required for object flybys, but it complicates determination of the flyby sequence. Diagonal solutions can be obtained using elements of graph theory. A solution to the flyby problem is presented for the case of group 5, formed of LSD objects at sun-synchronous orbits.     

A comparison of polarization jet characteristics at the greatly separated stations Yakutsk and Podkamennaya Tunguska

Characteristics of the polarization jet (PJ) are considered on the basis of measurements made in 1989–1992 at the ionospheric stations Yakutsk (L = 3.0, λ = 129.6°) and Podkamennaya Tunguska (L = 3.0, λ = 90.0°) separated in longitude. Using the data of these stations, the result obtained earlier (that the formation of PJ during disturbances in the near-midnight sector occurs at the expansion phase of a substorm) is confirmed. At isolated magnetic disturbances with AE > 500 nT in the 11:00–16:00 UT interval, the PJ band covers an MLT sector of 3 h between the Yakutsk and Podkamennaya Tunguska stations. The time of the PJ beginning at the Podkamennaya Tunguska station for the majority of events is 45–60 min behind the PJ beginning at the Yakutsk station. This corresponds to the westward motion of a PJ source with a velocity of ～3 MLT h per hour.     

Thermal structure of dayside plasmasphere according to the data of Tail and Auroral Probes, and Magion-5 satellite

We consider the results of measurements of density and temperature of cold plasma in the dayside sector of the plasmasphere. The measurements were made by Interball-1 (Tail Probe) in November 1995, by Interball-2 (Auroral Probe) in August 1996 (the periods close to the solar cycle minimum), and by the Magion-5 satellite in June 2000 (this period is close to the solar cycle maximum). It was shown by the measurements in the dayside sector of the plasmasphere that, contrary to expectations of model distributions of temperature in the plasmasphere [1, 2], under quiet geomagnetic conditions the temperature of hydrogen ions of the cold plasma filling the plasmasphere was observed to increase at altitudes 5000 km < H < 10000 km. Its altitude gradient was equal to ～0.5 deg/km, the geomagnetic latitude being variable within the limits 10° < λ < 40°. The maximum values of temperature of protons, as measured by Tail Probe and Auroral Probe deep in the plasma-sphere, were equal to ～4000–6000 K. According to the data obtained by the Magion-5 satellite in the depth of the plasmasphere, these temperatures varied within the limits 7500–8500 K. These results can be considered as some indication of a dependence of the plasmasphere thermal structure on the phase of the solar cycle. In the region 2.5 < L < 5 and at geomagnetic latitudes λ < 40°, drops of the ion temperature were regularly observed with values reaching ～2000 K.     

Investigation of oxygen O2(a1Δg) emission on the nightside of Venus: Nadir data of the VIRTIS-M experiment of the Venus Express mission

The paper is devoted to studies of the oxygen 1.27 μm emission on the Venus nightside using nadir measurements with the imaging spectrometer VIRTIS. A map of the emission distribution in coordinates latitude-local time is drawn for the southern hemisphere, equatorial region, and low latitudes of the northern hemisphere on the basis of observations in the period from June 2006 to January 2008 (more than 600 runs). As it has been noted before, strong spatial and time variations of the emission were observed. Two maxima of the emission are found: the first one (expected) is observed near the antisolar point, and the second one (near 23:00 LT) is seen at latitudes of 30°–60° in the southern hemisphere. The average value of the emission intensity measured according to the nadir data is 1.0 ± 0.4 MR. The emission with the intensity exceeding the average one by a factor of 2–3 was detected at different times almost over the entire nightside of the southern hemisphere.     

Determining Spacecraft Motion from Four Star Sensor Measurements

The BOKZ-M60 star sensor (a module that measures the coordinates of stars) has been designed for determining the parameters of the orientation of the intrinsic coordinate system relative to the inertial system from observations of stellar sky sections. The methods and results of processing of measurements by a set of four BOKZ-M60 sensors on the Resurs-P satellite no. 2 have been described. The time interval at which the satellite was in orbital orientation exceeds three orbital revolutions (19003 s). The joint processing of measurements by the four sensors conducted at the same time instants allowed the sensors to be associated with the universal coordinate system. With a root-mean-square error of less than 0.4′′ for each angle of rotation around its axes, this system is consistent with the model of the satellite’s rotational motion. The position of the universal system with respect to the instrumental coordinate system of the satellite was determined from the angular velocity measurements. Here, the root-mean-square errors for the values determined by the angles of rotation of the universal system around its axes were 0.044°, 0.051°, and 0.18°. The low-frequency (with frequencies less than 0.05 Hz) variations in the positions of intrinsic sensor coordinate systems relative to the universal system do not exceed 10′′. These are periodic variations with a fundamental frequency equal to the orbital frequency. The root-mean-square values of high-frequency components of these variations do not exceed 18′′.     

晨昏时段大气辐射对成像有效信噪比的影响

从成像有效信噪比的角度出发,利用MODTRAN辐射传输软件,分析计算了晨昏时段大气辐射的分布特点及其对成像的潜在影响。结果表明选择近红外成像谱段,可有效抑制大气背景辐射,实现晨昏时段一定观测倾角下的目标探测能力。