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Journey through the birth, growth and maturity of X-ray astronomy

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Research in Astronomy and Astrophysics 2019年第10期19卷 1-16页

作者： Prahlad Chandra Agrawal MU-DAE centre of Excellence in Basic Sciences Mumbai University Campus at Vidhyanagari

In this biographical account, I recall my scientific journey that began in 1961 when I joined as a Physics Trainee in the BARC Training School and after one year course was admitted in TIFR as a Research Associate. During 1962–1967, I worked on determination of the He^3 /He^4 ratio in cosmic rays using a gas Cerenkov counter and also used a scintillation + solid Cerenkov detector to measure flux of protons and helium nuclei in primary cosmic rays. I also developed a large area scintillation-Cerenkov detector with a spark chamber between them for measuring charge composition of primary cosmic rays. I joined the X-ray astronomy programme in 1967 initiated by Prof. B. V. Sreekantan and played a leading role in developing a balloon borne hard X-ray instrument for studying time variability and energy spectra of cosmic X-ray sources. We carried out a series of balloon experiments and studied temporal intensity variation and energy spectra of X-ray objects like Sco X-1, Cyg X-1, etc. Results on rapid intensity changes and spectra appeared in a series of publications based on which I obtained a Ph.D. degree in 1972. Immediately afterwards, I joined Prof. Gordon Garmire at Caltech as a Research Fellow (a post-doctoral position) to work with him on the low energy component of HEAO A-2 experiment. The instrument was developed and successfully realised. Working on this satellite experiment was a thrilling experience which exposed me to the technical complexities of space instruments. The HEAO-1 satellite was launched in 1978. During 1978–1979, Guenter Riegler and I, working at JPL, reported detection of intense soft X-rays from several classes of extragalactic and Galactic objects like new BL Lacs, a new AM Her binary, coronal X-rays from active stars, etc. After returning to TIFR, I developed a rocket experiment with K. P. Singh to map the spatial and spectral distribution of the Soft Diffuse X-ray Background. At the same time, I also designed 15 cm deep Xenon filled Proportio

关键词： TIFR-X-ray Astronomy by balloons-rockets and satellites-Indian Astronomy Satellite ASTROSAT

Integrity monitoring of fixed ambiguity Precise Point Positioning(PPP)solutions

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Geo-Spatial Information Science 2013年第3期16卷 141-148页

作者： Altti JOKINEN Shaojun FENG Wolfgang SCHUSTER Washington OCHIENG Chris HIDE Terry MOORE Chris HILL Department of Civil and Environmental Engineering Imperial College London Centre for Transport StudiesLondon SW72AZUK Nottingham Geospatial Institute(NGI) University of NottinghamNottingham NG72TUUK

Traditional positioning methods,such as conventional Real Time Kinematic(cRTK)rely upon local reference networks to enable users to achieve high-accuracy *** need for such relatively dense networks has significant cost *** Point Positioning(PPP)on the other hand is a positioning method capable of centimeter-level positioning without the need for such local networks,hence providing significant cost benefits especially in remote *** paper presents the state-of-the-art PPP method using both GPS and GLONASS measurements to estimate the float position solution before attempting to resolve GPS integer *** monitoring is carried out using the Imperial College Carrier-phase Receiver Autonomous Integrity Monitoring method.A new method to detect and exclude GPS base-satellite failures is developed.A base-satellite is a satellite whose measurements are differenced from other satellite’s measurements when using between-satellite-differenced measurements to estimate *** failure detection and exclusion methods are tested using static GNSS data recorded by International GNSS Service stations both in static and dynamic processing *** results show that failure detection can be achieved in all cases tested and failure exclusion can be achieved for static *** the kinematic processing cases,failure exclusion is more difficult because the higher noise in the measurement residuals increases the difficulty to distinguish between failures associated with the base-satellite and other satellites.

关键词： Precise Point Positioning(PPP) integrity ambiguity resolution failure exclusion

Revealing Storage-area Relationship of Open Water in Ungauged Subalpine Wetland-Napahai in Northwest Yunnan, China

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Journal of Mountain Science 2013年第4期10卷 553-563页

作者： LI Jie HU Jin-ming DENG Wei HUANG Sheng-li JIA Hai-feng ZHU Chun-ling LUO Huai-xiu Asian International Rivers centre Yunnan University Institute of Mountain Hazards and Environment Chinese Academy of Sciences ASRC Research and Technology Solutions US Geological Survey (USGS) Earth Resources Observation and Science (EROS) 47914 252nd Street Sioux Falls

Mountains and plateaus in Southwest China contain many subalpine and alpine wetlands, with significant hydroecological functions. But ungauged or poorly gauged conditions limit the study and understanding of hydrological regimes of these wetland types. This study selects an ungauged subalpine wetland-Napahai in Northwest Yunnan, China-as a case for developing a practical approach to revealing its storage-area relationship of open water. A Trimble R8 GNSS (Global Navigation satellites Systems) RTK (Real-time Kinematic system) and sonar fathometer were used to survey fine-resolution elevation data and generate a digital elevation model of the Napahai Wetland. Forty-four Landsat images from 1987 to 2011 were collected, and the Normalized Difference Water Index was used to classify open water features in the area. The area of open water in Napahai was calculated for each phase. With these data and a developed conceptual model, the storage of open water for each phase was estimated using ArcGIS tools. Both storage and area of open water showed significant intra-annual and inter-annual variations. In the rainy season, the monthly change of average storage of open water in Napahai showed about 1-2 months lag behind mean monthly rainfall. The storage-area relationship of open water was well fit by a power function equation (R 2 ≈0.91, n=44). This study indicates that if detailedelevations are available for similarly ungauged subalpine wetlands in Southwest China, researchers can use this practical approach to estimate multi- temporal areas and storages and reveal the storage-area relationship of open water in the wetlands. The study provided valuable information of this case wetland for optimizing its hydro-ecological managements and a new method to wetland researchers and managers for the hydrological study of similarly ungauged wetland complex.

关键词：中国西南地区高山湿地水域面积区域关系存储区纳帕海滇西北全球导航卫星系统

Precise Orbit Determination for the FY-3C Satellite Using Onboard BDS and GPS Observations from 2013, 2015, and 2017

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Engineering 2020年第8期6卷 904-912页

作者： Xingxing Li Keke Zhang Xiangguang Meng Wei Zhang Qian Zhang Xiaohong Zhang Xin Li School of Geodesy and Geomatics Wuhan UniversityWuhan 430079China German Research centre for Geosciences(GFZ) Potsdam 14473Germany National Space Science Center Chinese Academy of SciencesBeijing 100190China Beijing Key Laboratory of Space Environment Exploration Beijing 100190China

Using the FengYun-3C(FY-3C)onboard BeiDou Navigation Satellite System(BDS)and Global Positioning System(GPS)data from 2013 to 2017,this study investigates the performance and contribution of BDS to precise orbit determination(POD)for a low-Earth orbit(LEO).The overlap comparison result indicates that code bias correction of BDS can improve the POD accuracy by 12.4%.The multi-year averaged one-dimensional(1D)root mean square(RMS)of the overlapping orbit differences(OODs)for the GPS-only solution is 2.0,1.7,and 1.5 cm,respectively,during the 2013,2015,and 2017 *** 1D RMS for the BDS-only solution is 150.9,115.0,and 47.4 cm,respectively,during the 2013,2015,and 2017 periods,which is much worse than the GPS-only solution due to the regional system of BDS and the few BDS channels of the FY-3C *** the BDS and GPS combined solution(also known as the GC combined solution),the averaged 1D RMS is 2.5,2.3,and 1.6 cm,respectively,in 2013,2015,and 2017,while the GC combined POD presents a significant accuracy improvement after the exclusion of geostationary Earth orbit(GEO)*** main reason for the improvement seen after this exclusion is the unfavorable satellite tracking geometry and poor orbit accuracy of GEO *** accuracy of BDS-only and GC combined solutions have gradually improved from 2013 to 2017,thanks to improvements in the accuracy of International GNSS Service(IGS)orbit and clock products in recent years,especially the availability of a high-frequency satellite clock product(30 s sampling interval)since ***,the GC POD(without GEO)was able to achieve slightly better accuracy than the GPS-only POD in 2017,indicating that the fusion of BDS and GPS observations can improve the accuracy of LEO *** combined POD can significantly improve the reliability of LEO POD,simply due to system *** increased contribution of BDS to LEO POD can be expected with the launch of more BDS satellites and with further improvements in

关键词： FengYun-3C LEO precise orbit determination(POD) Onboard BDS and GPS BDS code bias BDS/GPS combined POD

Comparative Accuracy Assessment of Combined MODIS and NAAPS Aerosol Optical Depth with AERONET Data over North Africa

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Atmospheric and Climate Sciences 2019年第3期9卷 398-420页

作者： Clement O. Akoshile Sarafadeen Shehu-Aladodo Muawiya Sani Jibril O. Otu Benjamin T. Ajibola Physics Department University of Ilorin Ilorin Nigeria centre for Atmospheric Research NASRDA Anyigba Nigeria

Aerosol is one of the important geophysical parameters that determine the earth’s radiation budget, energy balance and hydrological cycle. The “Deep Blue” Moderate Resolution Imaging Spectro-radiometer (MODIS) Aerosol Optical Depth (AOD) retrieval algorithm was designed to complement existing “Dark Target” Ocean and Land algorithms to be able to retrieve AOD over bright land surface. Using level 2 AOD data from five Aerosol Robotic Network (AERONET) stations over the study location of North Africa (0°S - 40°N, 30°W - 60°E), comparative accuracy assessments are made for combined MODIS AOD aboard Terra and Aqua satellites and US Navy Aerosol Analysis and Prediction System (NAAPS) forecast AOD data. The aerosol transport and vertical mixing over the region are investigated at different altitudes up to 3000 m above ground level using Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT). The MODIS validation result shows highest correlation in the Sub-Sahel (0.811) followed by Sahel (0.726) and then Sahara region (0.662). Furthermore, the combined retrieval algorithm of Terra and Aqua MODIS shows statistically significant discrepancies from AERONET AOD values in term of mean, t-test value, index of agreement and fractional error. The comparison of NAAPS predicted soil dust to AERONET AOD fared best in December to February (DJF) season for the Sahel region and June to August (JJA) season for the Sahara when the dust emission and transport are at the peak. However, median ratios of NAAPS to AERONET AOD indicated bias in some island sites in the Atlantic Ocean which may be due to the presence of sea salt over the site. The analysis carried out in this study reveals that both MODIS retrieval algorithm and NAAPS model could be improved by incorporating some local aerosol sources from the study area.

关键词： Aerosol Deep Blue Dark Target Algorithm Validation

Perturbations in Earth’s Atmosphere over An Indian Region during the Total Solar Eclipse on 22 July 2009

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Journal of Meteorological Research 2019年第4期33卷 784-796页

作者： S.B.Surendra PRASAD Vinay KUMAR K.Krishna REDDY S.K.DHAKA Shristy MALIK M.Venkatarami REDDY U.Murali KRISHNA Semi-arid-zone Atmospheric Research centre(SARC) Department of PhysicsYogi Vemana UniversityKadapaAndhra Pradesh 516003India Radio and Atmospheric Physics Lab Rajdhani CollegeUniversity of DelhiDelhi 110015India Department of Applied Physics Delhi Technical UniversityDelhi 110042India

During a total solar eclipse(TSE)on 22 July 2009,atmospheric perturbations were monitored from the surface to thermosphere to understand TSE’s impact on the meteorological(temperature,relative humidity,wind speed,and wind direction)and chemical(O3 and NOx)parameters around Kadapa(14.28°N,78.42°E),a tropical semi-arid region of *** this purpose,an experiment was conducted at Yogi Vemana University Campus,Kadapa,India,to measure the temperature,wind speed,wind direction,and concentrations of ozone(O3),NO,NO2,and NOx by using the automatic weather station(AWS)and O3 *** the eclipse day(22 July 2009),the surface observations at Kadapa showed a reduction in temperature(about 1.1℃)because of the solar *** of the thermal,dynamical(wind),and chemical parameters on the TSE day with control days[preceding(21 July 2009)and succeeding(23 July 2009)the TSE]illustrated the influence of solar *** the eclipse period,the O3 mixing ratio decreased,while NO2 and NOx increased;however,NO remained *** addition,radio occultation(RO)temperature profiles from Constellation Observing System for Meteorology,Ionosphere,and Climate(COSMIC)/Formosat Satellite Mission(FORMOSAT-3)and Thermosphere,Ionosphere,and Mesosphere Energetics and Dynamics(TIMED)satellites were utilized to understand the impact of TSE on dynamics of the middle and upper atmosphere from tropopause to the *** vertical resolution COSMIC observations revealed that during the solar eclipse,tropopause was cooler with twin peaks(double tropopause).The lower thermosphere between 110 and 130 km became warmer during the TSE,which might be caused by the dynamical response of the atmosphere in this region to the solar *** experimental data have provided very fine-scale variations of the atmospheric parameters both in time and height and also constituted a new set of results on TSE for further research.

关键词： total solar eclipse (TSE) atmospheric perturbations tropopause dynamics COSMIC/FORMOSAT-3satellite radio occultation (RO) observations

Sea Ice Observations in Polar Regions: Evolution of Technologies in Remote Sensing

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International Journal of Geosciences 2013年第7期4卷 1031-1050页

作者： Praveen Rao Teleti Alvarinho J. Luis Earth System Sciences Organization National Centre for Antarctic and Ocean Research Ministry of Earth Sciences Goa India

Evolution of remote sensing sensors technologies is presented, with emphasis on its suitability in observing the polar regions. The extent of influence of polar regions on the global climate and vice versa is the spearhead of climate change research. The extensive cover of sea ice has major impacts on the atmosphere, oceans, and terrestrial and marine ecosystems of the polar regions in particular and teleconnection on other processes elsewhere. Sea ice covers vast areas of the polar oceans, ranging from ~18 × 106 km2 to ~23 × 106 km2, combined for the Northern and Southern Hemispheres. However, both polar regions are witnessing contrasting rather contradicting effects of climate change. The Arctic sea ice extent is declining at a rate of 0.53 × 106 km2·decade–1, whereasAntarcticaexhibits a positive trend at the rate of 0.167 × 106 km2·decade–1. This work reviews literature published in the field of sea ice remote sensing, to evaluate and access success and failures of different sensors to observe physical features of sea ice. The chronological development series of different sensors on different satellite systems, sensor specifications and datasets are examined and how they have evolved to meet the growing needs of users is outlined. Different remote sensing technology and observational methods and their suitability to observe specific sea ice property are also discussed. A pattern has emerged, which shows that microwave sensors are inherently superior to visible and infrared in monitoring seasonal and annual changes in sea ice. Degree of successes achieved through remote sensing techniques by various investigators has been compared. Some technologies appear to work better under certain conditions than others, and it is now well accepted that there is no algorithm that is ideal globally. Contribution of Indian remote sensing satellites is also reviewed in the context of polar research. This review suggests different primary datasets for further research on sea ice f

关键词： Sea Ice Satellite Remote Sensing Polar Regions Albedo

磁宁静期磁尾爆发性整体流持续时间多点卫星研究

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地球物理学报 2005年第2期48卷 252-258页

作者：马玉端曹晋滨周国成刘振兴 H.Reme I.Dandouras 中国科学院空间科学与应用研究中心 centre d'Etude Spatiale des Rayonnements 31028 Toulouse France

本文利用星簇CLUSTER的三颗卫星数据分析了磁宁静期磁尾爆发性整体流(BBFs,BurstyBulkFlows)的时间尺度,并与单个卫星的结果做了比较.事例研究表明,利用三颗卫星观测数据判断的BBFs的时间尺度比单个卫星的大一倍左右.对于三颗卫星观测... 详细信息

本文利用星簇CLUSTER的三颗卫星数据分析了磁宁静期磁尾爆发性整体流(BBFs,BurstyBulkFlows)的时间尺度,并与单个卫星的结果做了比较.事例研究表明,利用三颗卫星观测数据判断的BBFs的时间尺度比单个卫星的大一倍左右.对于三颗卫星观测到的同一个BBFs ,BBFs在晨昏方向上的摆动决定了CLUSTER的三个卫星观测到BBFs的先后次序.三颗卫星的观测也显示了BBFs的高度局域化特征.磁宁静期磁尾BBFs寿命的增大,使得BBFs携带的质量和能量的地向输运增加.这种地向输运增加的结果是:磁尾储存的能量得到较为平稳的释放,改变了亚暴起始产生的时间,为解决磁层压力平衡矛盾(PBI,PressureBalanceInconsistency)问题提供了新的思路.

关键词： BBFs 局域化输运摆动时间尺度

Changes in Barents Sea Ice Edge Positions in the Last 442 Years. Part 2: Sun, Moon and Planets

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International Journal of Astronomy and Astrophysics 2021年第2期11卷 279-341页

作者： Jan-Erik Solheim Stig Falk-Petersen Ole Humlum Nils-Axel Mö rner Retired Department of Physics and Technology UiT The Arctic University of Norway Troms&oslash Norway Akvaplan-niva The Fram Centre Troms&oslash Norway The University centre on Svalbard (UNIS) Longyearbyen Svalbard Norway Department of Geosciences University of Oslo Oslo Norway Deceased Paleogeophysics & Geodynamics Stockholm Sweden

This is the second paper in a series of two, which analyze the position of the Barents Sea ice-edge (BIE) based on a 442-year long dataset to understand its time variations. The data have been collected from ship-logs, polar expeditions, and hunters in addition to airplanes and satellites in recent times. Our main result is that the BIE position alternates between a southern and a northern position followed by Gulf Stream Beats (GSBs) at the occurrence of deep solar minima. We decompose the low frequency BIE position variations in cycles composed of dominant periods which are related to the Jose period of 179 years, indicating planetary forcings. We propose that the mechanism transferring planetary signals into changes in BIE position is the solar wind (SW), which provides magnetic shielding of the Earth in addition to geomagnetic disturbances. Increase in the solar wind produces pressure which decelerates the Earth’s rotation. It also transfers electrical energy to the ring current in the earth’s magnetosphere. This current magnetizes the earth’s solid core and makes it rotate faster. To conserve angular momentum the earth’s outer fluid mantle rotates slower with a delay of about 100 years. In addition will geomagnetic storms, initiated by solar coronal mass ejections (CMEs) penetrate deep in the Earth’s atmosphere and change pressure pattern in the Arctic. This effect is larger during solar minima since the magnetic shielding then is reduced. The Arctic may then experience local warming. The transition of solar activities to a possibly deep and long minimum in the present century may indicate Arctic cooling and the BIE moving south this century. For the North Atlantic region, effects of the BIE expanding southward will have noticeable consequences for the ocean bio-production from about 2040.

关键词： Barents Sea Ice Edge Position Cyclic and Non-Linear Changes Lunar and Solar Forcing Planetary Orbit Synchronization