An overview of radar soundings of the martian ionosphere from the Mars Express spacecraft

The Mars Express spacecraft carries a low-frequency radar called MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) that is designed to study the subsurface and ionosphere of Mars. In this paper, we give an overview of the ionospheric sounding results after approximately one year of operation in orbit around Mars. Several types of ionospheric echoes are commonly observed. These include vertical echoes caused by specular reflection from the horizontally stratified ionosphere; echoes from a second layer in the topside ionosphere, possibly associated with O⁺ ions; oblique echoes from upward bulges in the ionosphere; and a variety of other echoes that are poorly understood. The vertical echoes provide electron density profiles that are in reasonable agreement with the Chapman photo-equilibrium model of planetary ionospheres. On the dayside of Mars the maximum electron density is approximately 2 × 10⁵ cm⁻³. On the nightside the echoes are often very diffuse and highly irregular, with maximum electron densities less than 10⁴ cm⁻³. Surface reflections are sometimes observed in the same frequency range as the diffuse echoes, suggesting that small isolated holes exist in the nightside ionosphere, possibly similar to those that occur on the nightside of Venus. The oblique echoes arise from upward bulges in the ionosphere in regions where the crustal magnetic field of Mars is strong and nearly vertical. The bulges tend to be elongated in the horizontal direction and located in regions between oppositely directed arch-like structures in the crustal magnetic field. The nearly vertical magnetic field lines in the region between the arches are thought to connect into the solar wind, thereby allowing solar wind electrons to heat the lower levels of the ionosphere, with an attendant increase in the scale height and electron density.     

纪念毛泽东主席视察T-7M火箭45周年

196 0年 5月 2 8日毛泽东主席视察了上海机电设计院 (北京空间机电研究所的前身 )负责研制的T - 7M火箭。在毛泽东主席那次视察 4 5周年之际 ,回顾和论述了那次视察的背景、情况和意义。     

返回散射电离图干扰噪声的消除方法

返回散射电离图干扰噪声的消除方法程晓梅,郭保华（中国电波传播研究所,新乡４５３００３）关键词返回散射探测,射频干扰,电离图在返回散射探测中,回波信号来自广延的地面散射［１］,遭受到很大的传播损耗,所以典型的返回散射回波信号要比其他探测方式的回波信号弱...     

Solar wind velocity measurements near the sun using Ulysses radio amplitude correlations at two frequencies

Measurements of solar wind velocity have been derived from simultaneous coronal sounding observations of radio amplitude scintillations at both S-band and X-band during the solar conjunction of the Ulysses spacecraft in August 1991. The signal amplitude was recorded with an averaging time of 1 s. A cross-correlation analysis between S- and X-band amplitude fluctuations shows that the fluctuation signature at S-band appears to be shifted to earlier times with respect to the X-band recording. The time difference is proportional to the coronal separation of the ray paths and inversely proportional to the apparent velocity of plasma inhomogeneities across the ray paths. Preliminary estimates of solar wind speed obtained using model calculations of the differential refraction are found to lie near the expected transition from subsonic to supersonic velocities at solar offset distances of the order of 6–8 R. As a byproduct of the investigation, we find that the transition from weak to saturated scintillation occurs at about 16 R for S-band and 7 R for X-band.     

机载GNSS掩星观测反演大气折射率廓线研究

作为星载掩星技术的推广,基于飞机平台的无线电掩星技术备受关注。为了将机栽掩星技术更好地应用到工程实践中,文章通过介绍机载掩星探测的基本原理和主要特点、模拟仿真,对机载掩星的反演算法进行了探讨,并给出模拟结果：包括利用STK仿真软件生成仿真场景;采用3维射线追踪技术模拟机载无线电掩星,预报掩星事件出现的时间、仰角,模拟信号传播特征;详细研究大气层内折射率反演技术并给出反演结果。研究结果表明,模拟仿真对机载掩星工程化实现是有益的。最后展望了机载掩星探测的发展趋势,提出了弱掩星信号的捕获跟踪、飞机平台的精度定位测速以及反射信号的抗干扰三项技术及工程化中需解决的技术难点。     

环绕器次表层探测雷达实时处理技术

环绕器次表层探测雷达能够在环绕轨道实现行星次表层结构高分辨探测,为深入研究行星地质结构提供科学数据,由于深空探测距离地球距离非常遥远,与地球之间的数据传输率很受限制,雷达探测得到的大量原始数据无法通过数据链路传回地球,通过星上实时处理对探测数据进行变换,只回传数据量小得多的处理结果具有非常重要的意义。本文对环绕器次表层探测雷达采用的后向投影算法的实时处理技术进行了详细的分析,给出了工程实现方法。     

Validation of the operational IASI level 2 processor using AIRS and ECMWF data

The algorithms being implemented in EUMETSAT’s IASI Level 2 Product Processing Facility are validated with real case situations using AIRS data and comparing the retrieved atmospheric states with ECMWF analyses. The tests have been performed for clear-sky ocean scenes during daytime.

The Empirical Orthogonal Function (EOF) retrievals show very good performance, with retrieved atmospheric states standard deviations between 1 and 2 K in temperature and 10% and 20% in relative humidity when compared with ECMWF analysis in the troposphere. The EOF retrievals show relatively smooth profiles.

Results from an iterative retrieval show a standard deviation between 2 and 3 K in temperature and 10% and 30% in relative humidity when compared with ECMWF analyses in the troposphere. They tend to show meteorologically reasonable discontinuities in both temperature and relative humidity. This seems to be the reason why they do not compare as well with ECMWF analyses as the EOF retrievals do. Whether they are closer to reality or not will have to be tested with co-located radiosondes or similar more accurate data, which generally do not exhibit such smooth vertical profiles as ECMWF analyses do.     

Improved precision of virtual height measurements with coherent radio pulse sounding based on the maximum likelihood method

The paper describes a new technique that improves precision of the virtual height measurements by a coherent pulse sounding of the ionosphere. Proposed technique is based on the method of maximum likelihood that matches expected and observed spectral domain signatures of the signal intermixed with the noise. Computer simulations show that our technique allows measurements of the echo virtual height with ∼100 m precision even at a much coarser step of the height sampling in the sounder. In experiment, we expect an average 300 m precision of the virtual height measurements for single echoes received during periods of little spread due to ionospheric irregularities.     

Oblique-incidence ionospheric soundings over Central Europe and their application for testing now casting and long term prediction models

After a first oblique-incidence ionospheric sounding campaign over Central Europe performed during the period 2003–2004 over the radio links between Inskip (UK, 53.5°N, 2.5°W) and Rome (Italy, 41.8°N, 12.5°E) and between Inskip and Chania (Crete, 35.7°N, 24.0°E), new and more extensive analysis of systematic MUF measurements from January 2005 to December 2006 have been performed. MUF measurements collected during moderately disturbed days (17 ? Ap ? 32), disturbed days (32 < Ap ? 50) and very disturbed days (Ap > 50), have been used to test the long term prediction models (ASAPS, ICEPAC and SIRM&LKW), and the now casting models (SIRMUP&LKW and ISWIRM&LKW). The performances of the different prediction methods in terms of r.m.s are shown for selected range of geomagnetic activity and for each season.     

新型高空探测系统

研发了一种新型全自动高空探测系统,其利用GPS定位,宽波瓣天线捕捉和低噪声接收的方法替代雷达或无线电经纬仪对高空探测仪进行跟踪定位和获取信息,具有不受低仰角的限制,目标不易丢失,性能价格比高等特点,成功将GPS应用于1680 MHz遥测数据传输体制.利用该系统进行了空中大气电场的探测实验,获得了满意的探测结果.由于系统轻便、操作简单、成本较低以及良好的机动性和可靠性,在近地空间环境探测和高空大气科学探测试验及常规的气象探测中有广阔的应用前景.