性能优异的美国陆地卫星—7

1972年美国“陆地卫星”(Landsat)首次入轨运行至今,已经连续27年为全世界广大用户提供了高分辨率、多光谱的遥感数据。美国有关方面经过5年多的努力,终于在今年4月15日发射了Landsat-7资源卫星,以代替已经工作15年、性能老化的Landsat-5,从而将Landsat计划推向21世纪。4月18日,收到了卫星获取的第1幅图像。经过75～90天的在轨调试后将向各国地面站发送数据。Landsat-7与以前的Landsat在获取数据的地理范围、空间分辨率、校正精度和光谱特性等方面足够一致,从而为研究全球变化和其他应用研究奠定了基础。与Landsat-4、5一样,Landsat-7按…     

千呼万唤始出来：美国陆地卫星—7发射成功

1999年4月15日,陆地卫星-7(Landsat-7)用一枚德尔他-2火箭从范登堡空军基地发射升空,进入了一条高705km、倾角98.2°的太阳同步轨道。Landsat-7是美国航宇局(NASA)“地球使命计划”中的一部分,又是美国“国防气象卫星计划”(DMSP)和“泰罗斯”(Tiros)卫星的继承卫星,同时也是NASA1972年开始实施的Landsat计划中的最后一颗卫星。这颗卫星的发射,标志着一个时代——即大型、昂贵的Landsat系列地球观测卫星时代行将结束,NASA的下一步将发展较小、较便宜和研制周期较短的地球观测卫星。Landsat-7的主承制商是洛马公司。卫星总经费约需8…     

美国“陆地卫星数据连续性任务”卫星拟于今年发射

美国"陆地卫星数据连续性任务"(LDCM)卫星是陆地卫星-5、7(Landsat-5、7)的后续任务,卫星发射入轨后将成为"陆地卫星"系列中的第8颗,并更名为陆地卫星-8。"陆地卫星数据连续性任务"的目标是保持"陆地卫星"数据的连续性,为农业、水资源管理、灾害响应、科学研究、国家安全和其他领域提供多光谱图像数据。美国航天机构表示,争取能在2012年12月前发射"陆地卫星数据连续性任务",以降低该卫星发射入轨前出现"陆地卫星"数据断     

欧洲发射地球资源卫星同时搭载发射4颗小型卫星

阿里安空间公司于1991年7月用“阿里安40”火箭发射欧空局(ESA)的“欧洲地球资源卫星(ERS-1)”,并附带发射美、法、德、英的4颗小型实验卫星。 ERS-1发射至倾角98.5°、高度785km的太阳同步极轨道上。由于阿里安空间公司发射至极轨的卫星频率每年还不足1次,因此,它至今还没有能独立经营的跟踪管理站,必须依靠美国的支援。将用美国家海洋大气局(NOAA)设置在阿拉斯加州费尔班克斯的遥测接收专用站,编入最初确认卫星入轨的程序中。同时发射的小型卫星分离机构安装部件由法国马特拉公司研制。称为“阿里安辅助     

空间活动大事记

6日苏联发射宇宙1908卫星,它是电子侦察卫星。 14日法国马特拉公司研制的,1985年5月发射的Telecom-1B电信卫星的控制系统失灵。该星的工作由Telecom-1A接替。 15日苏联用一枚火箭发射了6颗卫星:宇宙1909～1914。 20日苏联发射进步34货运飞船。 26日苏联发射照像侦察卫星宇宙1915。 30日苏联发射Meteor 2-17气象卫     

俄罗斯将发射高分辨率资源卫星

资源-DK1（Resurs—DK1）是俄罗斯新型民用地球观测卫星,能向地面站传送分辨率为1m的图像。卫星由俄罗斯航天局投资,由萨马拉火箭航天中心（即位于萨马拉的原“进步”中央特种设计局）设计、建造和运营,其商业数据的发行商是航天局下属的Sovinformsputnik公司。Resurs—DK1卫星计划于2005年下半年由联盟号火箭发射,卫星主要用于接收和传输有关地球自然资源及突发事件的即时数据。     

印度用苏联火箭发射一颗地球资源卫星

说该卫星重442公斤,任务是用电视装置和微波辐射仪来考察地球资源。卫星是在苏联的帮助下制成的。印度专家参加了发射准备工作。卫星工作正常,苏印地面站分别接收卫星数据。     

法国和西德的直播卫星

到目前为止,还需用大型地球站接收中、低功率卫星转发的电视节目。苏联和印度拥有供集体接收的电视卫星,日本的中功率广播卫星既可集体,也可个人接收,美国和加拿大仍采用大型抛物面天线接收卫星电视节目,只有法国和西德将要首先发射大功率卫星,直接用一米以下的抛物面天线接收卫星转发的电视节目。     

《宇宙开发技术总览》之四 日本的对地观测卫星

世界第一颗地球资源卫星(ERTS),即美国陆地卫星1号是1972年7月发射的,现在日本接收的是美国陆地卫星5号的遥感图象。位于日本埒玉县鸠山上的宇宙观测中心(宇宙开发事业团)把接收、处理的资料发送给全国的用户。法国的地球观测卫星(SPOT),其数据资料将用于世界性商业服务方面。为了适应这些急剧发展的世界趋势,日本正在研制以获取海洋信息为目的的海洋观测卫星MOS-1及以获取陆地信息为目的的地球资源卫星ERS-1。海洋观测卫星MOS-1的研制     

电视广播卫星在八十年代将进入实用化阶段

自1974年美国在应用技术卫星六号(ATS-6)上首次成功地利用卫星直接试验广播电视以来,加拿大、苏联和日本也相继发射了实验广播卫星。这些广播卫星主要是探讨卫星广播电视的可行性,评价卫星广播的接收质量以及传输损耗等。通过这些卫星的实验,获得了很多实际经验。实验结果分析表明,广播卫星在技术上已经成熟,八十年代将要进入实际应用阶段。评述CTS与BSE的实验 1976年1月17日发射的加拿大通信技术卫星(CTS),同步轨道     

以太阳为射电源直接测量天线G／T

介绍以太阳为射电源,直接测量扩充后中国陆地卫星地面接收站,３个数据通道天线的Ｇ／Ｔ性能．对固定通道,测量了Ｌａｎｄｓａｔ—５下行频率的Ｇ／Ｔ～α（天线俯仰角）性能曲线;对可变通道,在α＝５°、３０°时,测量了Ｌａｎｄｓａｔ—６、ＪＥＲＳ—１、ＥＲＳ—１、ＳＰＯＴ卫星、ＺＹ—１卫星下行频率的Ｇ／Ｔ性能,以及可变通道的Ｇ／Ｔ～ｆ性能曲线,最后进行了误差分析．     

Landsat image data quality studies

The July 1982 launch of Landsat-4 was immediately followed by a two-year comprehensive set of detailed investigations sponsored by the National Aeronautics and Space Administration (NASA) at Goddard Space Flight Center (GSFC). The Landsat Image Data Quality Analysis (LIDQA) research plans for these investigations were specified prior to launch, so that minimum time would be lost in assessing the performance of the long-awaited Thematic Mapper (TM) sensor that Landsat-4 carried in addition to a fourth Multispectral Scanner (MSS). The LIDQA investigations have been substantially completed, and have shown that the TM is a very good spaceborne multispectral radiometer, and has met or exceeded most of its design goals. TM's new short-wave infrared (SWIR) spectral capability yielded improved mineral and plant discrimination compared to the MSS, as anticipated by ground-based and airborne TM simulations. Moreover, the improved spatial resolution and geometric accuracy of Landsat-4 and the TM have resulted in satellite image maps exceeding 1:100,000 U.S. map accuracy standards. Finally, based on an information entropy measure, principal component analysis, and classification results, TM data has been shown to approach its theoretical limit in information content per pixel, exceeding the MSS by at least a factor of two.     

Landsat-4 orbit determination using TDRSS

This paper presents the results of a study to compare the orbit determination accuracy for a Tracking and Data Relay Satellite (TDRS) System (TDRSS)-user spacecraft, Landsat-4, obtained using a Prototype Filter Smoother (PFS), with the accuracy of an established batch-least-squares system, the Goddard Trajectory Determination System (GTDS). The results of Landsat-4 orbit determination provide useful experience for the Earth Observing System (EOS) series of satellites. The filtered and smoothed PFS orbit solutions were compared with the definitive GTDS orbit solutions for Landsat-4; the root-mean-square (RMS) solution difference was 6.6 meters.     

Origin of coronal and interplanetary shock and particle acceleration of a flare/CME event

By using radio data from ground-based telescopes (from 270 MHz to 25 MHz), and from the Radio and Plasma Wave experiment (WAVES) on board the WIND spacecraft (1–14 MHz and several kHz-11 MHz), as well as FY -2 satellite data, the origin of coronal and interplanetary shock and particle acceleration of the 14 July 2000 flare/CME event (the Bastille day event) have been studied. Main conclusions are as follows: (1) We investigate the causal relationship between metric type 11 bursts observed by the digital IZMIRAN radio spectrograph and type II radio emissions in the frequency range from 1–14 MHz and several kHz-11 MHz observed by the WAVES/WIND. The analysis indicate that the fast CME is the origin of both coronal and interplanetary shocks. (2)According to the time profiles of Hard X-ray, and energetic particles (include proton, ³He, and ⁴He) from FY-2 satellite, it is obvious that the Bastille day event is the event, in which both impulsive and gradual phenomena occur. The energetic particles accelerated not only in flare but also in CME.     

Research on the disturbance of ballistic missile to ionosphere by using 3D ray tracing method

This study uses the 3D ray tracing to analyse ionospheric disturbance generated by a ballistic missile plume (which was simulated in our previous work). Ray tracing results show that the 6 MHz radio waves are completely reflected by the ionosphere and cannot reach the ionospheric disturbance zone. The 8 MHz radio waves partially penetrate the ionospheric disturbance zone, producing a focusing effect. Most of the 10 MHz radio waves pass through the ionosphere and the disturbance zone. The focusing effect and focus height are reduced. In the height range 65̃400 km, the ray absorption loss of reflection is greater than the transmitted ray. When the ray is reflected multiple times in the cavity formed by the plume, ray absorption loss greatly increases.     

Integrating aeromagnetic data and Landsat-8 imagery for detection of post-accretionary shear zones controlling hydrothermal alterations: The Allaqi-Heiani Suture zone,South Eastern Desert,Egypt

The Arabian-Nubian Shield (ANS) underwent a regional carbonation event with CO₂ fluxes derived from the mantle and circulated along post-accretionary shear zones, thus affecting the redistribution of gold mineralization. Formerly, the analyses of remotely-sensed data have suggested regions of gold mineralization linked to the post-accretionary structured framework, but the results were insufficient for detailed prospecting in the ANS. In this research, aeromagnetic data and Landsat-8 imagery were integrated for delineating new high potential zones of gold mineralization in the Allaqi-Heiani Suture (AHS) zone, the ANS, South Eastern Desert (SED) of Egypt. Aeromagnetic data were enhanced using the Center for exploration targeting (CET) grid enhancement technique to detect the main structures that control hydrothermal alterations in the study area. Principal Component Analysis (PCA) technique and ratios of spectral bands were applied to Landsat-8 data for mapping zones of hydrothermal alteration associated with gold mineralization. The traced structural elements from RTP, CET and Landsat-8 maps were statistically plotted and interpreted using rose diagrams. These diagrams indicated that the NW and NE trends are the most dominant in the RTP map and that the intersection zones obtained from the CET analysis are aligned along the NW-oriented trend. While the NNW, WNW and NE trends were the most dominant ones in Landsat maps. The integration of the results indicates several new high potential zones of gold and Cu/Ni mineralization types, which are mostly concentrated at the western part of the AHS zone. The hydrothermal alteration zones and associated gold mineralization are strongly linked to NW, NE, E-W and WNW trending lineaments. The approach used in this study can be applied to other parts of the ANS and other regions with similar geological conditions around the world.     

一种低压低功耗的环形压控振荡器设计

设计了一种低压低功耗的环形压控振荡器,它由电压电流转换（V to I）电路及5级延迟单元（delay cell）组成。单位延迟单元采用改进型差分结构,提高了上升及下降速度。同时总的延迟环路采用电容滤波技术,进一步改善了相位噪声性能。分析了环形VCO的相位噪声。电路采用SMIC13V33 1P6MLOGIC工艺,电源电压为1.2 V,仿真结果显示：VCO中心频率为350 MHz,调谐范围为（200-500）MHz,谐振在350 MHz时相位噪声位为-89.5 dBc/Hz@10 kHz,输出波形峰值为0.7 V,功耗为1.2 mW。该VCO可以应用于系统时钟锁相环中。     

Surface temperature estimation in Singhbhum Shear Zone of India using Landsat-7 ETM+ thermal infrared data

Land surface temperature (LST) is an important factor in global change studies, heat balance and as control for climate change. A comparative study of LST over parts of the Singhbhum Shear Zone in India was undertaken using various emissivity and temperature retrieval algorithms applied on visible and near infrared (VNIR), and thermal infrared (TIR) bands of high resolution Landsat-7 ETM+ imagery. LST results obtained from satellite data of October 26, 2001 and November 2, 2001 through various algorithms were validated with ground measurements collected during satellite overpass. In addition, LST products of MODIS and ASTER were compared with Landsat-7 ETM+ and ground truth data to explore the possibility of using multi-sensor approach in LST monitoring. An image-based dark object subtraction (DOS3) algorithm, which is yet to be tested for LST retrieval, was applied on VNIR bands to obtain atmospheric corrected surface reflectance images. Normalized difference vegetation index (NDVI) was estimated from VNIR reflectance image. Various surface emissivity retrieval algorithms based on NDVI and vegetation proportion were applied to ascertain emissivities of the various land cover categories in the study area in the spectral range of 10.4–12.5 μm. A minimum emissivity value of about 0.95 was observed over the reflective rock body with a maximum of about 0.99 over dense forest. A strong correlation was established between Landsat ETM+ reflectance band 3 and emissivity. Single channel based algorithms were adopted for surface radiance and brightness temperature. Finally, emissivity correction was applied on ‘brightness temperature’ to obtain LST. Estimated LST values obtained from various algorithms were compared with field ground measurements for different land cover categories. LST values obtained after using Valor’s emissivity and single channel equations were best correlated with ground truth temperature. Minimum LST is observed over dense forest as about 26 °C and maximum LST is observed over rock body of about 38 °C. The estimated LST showed that rock bodies, bare soils and built-up areas exhibit higher surface temperatures, while water bodies, agricultural croplands and dense vegetations have lower surface temperatures during the daytime. The accuracy of the estimated LST was within ±2 °C. LST comparison of ASTER and MODIS with Landsat has a maximum difference of 2 °C. Strong correlation was found between LST and spectral radiance of band 6 of Landsat-7 ETM+. Result corroborates the fact that surface temperatures over land use/land cover types are greatly influenced by the amount of vegetation present.     

Interpretation of 6 and 21 cm observations of Jupiter

Observations of Jupiter's radio emission were made at a frequency of 1412 MHz (21cm) in 1977 and at 4885 MHz (6cm) in 1978 using the Westerbork Synthesis Radio telescope in the Netherlands. The thermal disk temperatures at these wavelengths yield values of 320±20 K at 21 cm and 220±8 K at 6 cm. The first value requires an overabundance of ammonia by a factor of three with respect to the solar value, the second one is in agreement with the value expected for a convective model atmosphere with solar abundances for all chemical elements. The data at this wavelength however show no or very little limb darkening on the planet, indicating that there is a layered rather than a uniformly mixed atmosphere. A sudden increase in the ammonia abundance by a factor of about three below the 210–220 K level is proposed to explain this fact and also both derived disk temperatures.     

CPT原子钟微波信号的设计和分析

根据被动型相干布居囚禁原子钟对微波信号的要求,利用小数分频锁相环技术实现了微波频率综合,并通过优化环路带宽得到最佳的输出相噪。测试结果表明:3 417 MHz微波输出在100 Hz处的相位噪声达到-80 dBc;中心频率±50 kHz范围内的杂散抑制达到54 dB,都接近于理论值。将产生的微波用于所研制的CPT原子钟,获得频率稳定度达到1 000 s内6×10-11-1/2,为目前国外商品钟水平。