測(cè)繪工程畢業(yè)設(shè)計(jì)外文翻譯

1、<p><b>　　外文資料譯文及原文</b></p><p><b>　　中文翻譯</b></p><p><b>　　摘要</b></p><p>　　根據(jù)當(dāng)前大地測(cè)量、地球物理、空間物理和導(dǎo)航等領(lǐng)域的科學(xué)研究和工程應(yīng)用中的若干重要GPS科研項(xiàng)目的需要，近年來，我們系統(tǒng)研究了電離層延遲的

2、高精度模擬和改正方法。本文報(bào)告的內(nèi)容，是我們研究工作的部分貢獻(xiàn)，主要涉及基于GPS的電離層監(jiān)測(cè)及延遲的高精度改正的理論與方法的研究：如何通過修正靜、動(dòng)態(tài)單、雙頻用戶的電離層延遲影響，進(jìn)一步改善GPS 測(cè)量的精度和可靠性；增強(qiáng)型GPS廣域差分系統(tǒng)的電離層模擬及利用GPS監(jiān)測(cè)電離層的理論和方法等方面</p><p>　　關(guān)鍵詞：GPS的電離層監(jiān)測(cè)，電離層延遲，GPS廣域差分</p><p>　

3、　本文主要包括兩方面的內(nèi)容：</p><p>　　一、研究背景的一般性描述及相關(guān)基礎(chǔ)研究的系統(tǒng)總結(jié)和介紹,主要涉及：地球電離層研究意義, 地球電離層探測(cè)技術(shù)與相關(guān)理論研究的內(nèi)容,現(xiàn)代大地測(cè)量中電離層問題的由來、嚴(yán)重性與新課題, 地球電離層的基本特性及其對(duì)電波傳播的影響，GPS定位的基本理論與方法，電離層延遲對(duì)GPS測(cè)量的影響，GPS的電離層延遲改正的基本方法，基于GPS的電離層研究的基本原理與方法等。進(jìn)而論述了解

4、決GPS的電離層延遲影響的重要性和切入點(diǎn)。</p><p>　　二、具體研究工作的系統(tǒng)報(bào)告，主要集中在以下幾方面: </p><p>　?、傺芯咳绾卫脝闻_(tái)雙頻GPS接收機(jī)的觀測(cè)信息確定電離層延遲改正模型，為小范圍的單頻用戶服務(wù)；</p><p>　?、谘芯咳绾螌?shí)時(shí)分離GPS觀測(cè)中的儀器偏差與電離層延遲；</p><p>　　③研究如何建立較

5、大區(qū)域的電離層格網(wǎng)模型，進(jìn)而初步設(shè)想利用中國(guó)地殼運(yùn)動(dòng)觀測(cè)網(wǎng)絡(luò)深入研究我國(guó)領(lǐng)域的電離層的電子濃度變化規(guī)律；</p><p>　　④研究單頻用戶在不利條件下，如何更好地利用電離層延遲改正信息；</p><p>　?、菅芯坷肎PS監(jiān)測(cè)隨機(jī)電離層擾動(dòng)的基本理論和框架方案；</p><p>　?、扪芯咳绾尉C合顧及電離層的周日、季節(jié)和年變化，進(jìn)一步提高利用GPS模擬電離層延遲

6、的能力；</p><p>　　⑦研究如何實(shí)現(xiàn)星載單頻GPS低軌衛(wèi)星的精密測(cè)軌中的電離層延遲改正要求。</p><p>　　1. (局部)電離層延遲的高精度提取</p><p>　　系統(tǒng)論述和分析了影響利用GPS觀測(cè)精確提取電離層延遲信息的各類因素。通過對(duì)有關(guān)模型和方法問題的深入研究，進(jìn)一步提高了利用GPS提取電離層延遲信息的精度。主要包括：</p>&

7、lt;p>　　（1）將參數(shù)固定的三角級(jí)數(shù)函數(shù)電離層模型，擴(kuò)展為更適用于理論研究和實(shí)際應(yīng)用的參數(shù)可調(diào)型廣義形式，實(shí)現(xiàn)了根據(jù)電離層延遲時(shí)空變化特征，選擇不同的特征參數(shù)模擬電離層延遲的影響。試算結(jié)果表明，它能較好地反映電離層活動(dòng)特性，提高了局部電離層延遲模擬能力，適用于DGPS系統(tǒng)修正其服務(wù)區(qū)域內(nèi)的單頻GPS用戶的電離層延遲。</p><p>　?。?）設(shè)計(jì)了幾種不同的計(jì)算方案，用于分析儀器偏差對(duì)確定電離層延遲的

8、影響的特點(diǎn)。研究表明，儀器偏差對(duì)求解電離層延遲的影響遠(yuǎn)大于觀測(cè)噪聲的影響，給電離層延遲觀測(cè)值帶來高達(dá)數(shù)米的系統(tǒng)誤差。利用GPS觀測(cè)數(shù)據(jù)求解電離層模型或直接計(jì)算斜距電離層延遲時(shí)，都須慎重處理儀器偏差，不應(yīng)簡(jiǎn)單把其作為噪聲處理;</p><p>　?。?）利用相位平滑測(cè)碼數(shù)據(jù)進(jìn)一步精化了儀器偏差分離方法，探討了儀器偏差的穩(wěn)定性。研究發(fā)現(xiàn)，新方法可有效克服噪聲對(duì)分離儀器偏差的影響，而且儀器偏差相對(duì)穩(wěn)定并可有效進(jìn)行測(cè)段間

9、及數(shù)日間預(yù)報(bào)。</p><p>　?。?）基于實(shí)時(shí)平均去噪和碼、相位觀測(cè)數(shù)據(jù)的加權(quán)聯(lián)合處理的思想，提出了一種實(shí)時(shí)分離儀器偏差和求解電離層延遲量的新方案。算例表明，新方法通過采用平均去噪分離方法后處理相位平滑測(cè)碼數(shù)據(jù)，求出儀器偏差并對(duì)需要實(shí)時(shí)處理儀器偏差的觀測(cè)數(shù)據(jù)進(jìn)行預(yù)報(bào)改正，直接利用觀測(cè)值確定電離層延遲量，待估參數(shù)少、能消除儀器偏差的大部分影響，具有較好的精度，可作為WAAS及其他GPS網(wǎng)絡(luò)系統(tǒng)確定電離層延遲的可

10、行的參考方案。</p><p>　　2. 一種構(gòu)建大規(guī)模(區(qū)域性和全球性)高精度格網(wǎng)電離層模型的新方法</p><p>　　——站際分區(qū)法及其在中國(guó)的初步實(shí)現(xiàn)</p><p>　　在系統(tǒng)深入研究了格網(wǎng)電離層模型建立原理與方法的基礎(chǔ)上，為避免基準(zhǔn)站網(wǎng)的幾何結(jié)構(gòu)對(duì)模型精度估計(jì)的影響，充分顧及電離層延遲影響的局部特性，進(jìn)一步提高格網(wǎng)電離層模型的構(gòu)建精度，提出了一種新的格網(wǎng)

11、電離層模型構(gòu)建方法——站際分區(qū)格網(wǎng)法。在以上研究的的基礎(chǔ)上，估計(jì)了利用地殼運(yùn)動(dòng)觀測(cè)網(wǎng)絡(luò)的基準(zhǔn)網(wǎng)建立格網(wǎng)電離層模型的精度，初步探討中國(guó)域內(nèi)擬建立的廣域差分GPS增強(qiáng)系統(tǒng)，采用格網(wǎng)電離層模型提供電離層改正信息的可行性及有待進(jìn)一步研究的問題。</p><p>　　3. 不利條件下為WAAS的單頻GPS用戶提供電離層延遲改正</p><p>　　的新方法——APR-I方案</p>&

12、lt;p>　　在正常條件和平靜電離層區(qū)域，WAAS能夠滿足單頻用戶的電離層延遲改正要求，但當(dāng)用戶無法正常獲取電離層延遲改正信息時(shí)，如在差分系統(tǒng)突然中斷信息發(fā)送或用戶步入無法正常接收差分改正信息的位置等不利條件下，單頻GPS接收機(jī)不能有效進(jìn)行實(shí)時(shí)電離層延遲改正，尤其在電離層活動(dòng)異常區(qū)域如電離層擾動(dòng)條件下，實(shí)時(shí)差分改正效果將受到嚴(yán)重影響。這些問題在WAAS的實(shí)際運(yùn)行中是難以避免和必須解決的。而以往的研究結(jié)果，均為后處理方法，不能滿足(

13、準(zhǔn))實(shí)時(shí)處理電離層擾動(dòng)的要求。</p><p>　　針對(duì)這種狀況，我們通過設(shè)計(jì)能有效結(jié)合電離層延遲絕對(duì)量和相對(duì)變化量的抗差遞推過程，提出了一種可在以上不利條件下有效實(shí)時(shí)改正單頻GPS用戶電離層延遲的方法—APR-I方案。</p><p>　　1）構(gòu)建APR-I方案的理論依據(jù)</p><p>　　WAAS正常運(yùn)轉(zhuǎn)和正常條件下可提供高精度的電離層延遲改正信息(絕對(duì)量)，

14、而WAAS所服務(wù)區(qū)域內(nèi)的單頻GPS接收機(jī)在不利條件下也能有效提供電離層延遲變化量(相對(duì)量)，且在不考慮噪聲影響，可直接計(jì)算任意兩觀測(cè)歷元間的電離層變化量的近似值。</p><p>　　2）提出APR-I方案</p><p>　　通過設(shè)計(jì)能有效結(jié)合電離層延遲絕對(duì)量和相對(duì)變化量的抗差遞推過程，研究了一種新的單頻GPS電離層延遲改正方案(稱為APR方案,即Absolute Plus Relati

15、ve Scheme)；給出了APR-I方案的精度估計(jì)公式；分析實(shí)施APR-I方案的有效途徑。</p><p>　　研究表明，新方案既保留正常條件下差分電離層延遲信息的精確改正效果，也確保了在不利條件下單頻GPS用戶的電離層延遲改正效果。APR-I方案的實(shí)施，不需改變WAAS原有的整體設(shè)計(jì)思想，對(duì)硬件無新的要求，只需對(duì)用戶GPS軟件稍加改進(jìn)，實(shí)施簡(jiǎn)便，是WAAS和單頻GPS用戶均可接受和易于實(shí)現(xiàn)的。</p&g

16、t;<p>　　4. 檢測(cè)隨機(jī)信號(hào)的新理論——變樣本自協(xié)方差估計(jì)的提出</p><p>　　及其在GPS監(jiān)測(cè)隨機(jī)電離層擾動(dòng)中的應(yīng)用</p><p>　　根據(jù)GPS時(shí)序觀測(cè)的特點(diǎn)，通過設(shè)計(jì)先研究樣本時(shí)序變化時(shí)隨機(jī)電離層折射的自協(xié)方差估計(jì)的統(tǒng)計(jì)特性，再探討利用GPS實(shí)時(shí)監(jiān)測(cè)電離層活動(dòng)的新方法的思路，從基礎(chǔ)理論的提出到框架方案的建立，系統(tǒng)深入研究了利用GPS監(jiān)測(cè)隨機(jī)電離層擾動(dòng)的基本

17、理論與方法。具體包括：</p><p>　　1）研究變樣本自協(xié)方差估計(jì)(ACEVS)理論</p><p>　　從一般的數(shù)學(xué)意義上建立了ACEVS的基本模型，并在進(jìn)一步擴(kuò)展白噪聲理論的基礎(chǔ)上，得到了ACEVS估計(jì)的理論和簡(jiǎn)化解式，即變樣本自協(xié)方差估計(jì)的統(tǒng)計(jì)模型參數(shù)估計(jì)解式，進(jìn)而建立了隨機(jī)信號(hào)擾動(dòng)的診斷準(zhǔn)則。</p><p>　　2）ACEVS估計(jì)應(yīng)用于GPS電離層監(jiān)測(cè)

18、的可行性的理論證明與模擬分析</p><p>　　不僅從理論上證明了ACEVS應(yīng)用于GPS電離層監(jiān)測(cè)的可行性，而且利用雙頻GPS數(shù)據(jù)也成功地模擬了隨機(jī)電離層折射的ACEVS估計(jì)的特性，并發(fā)現(xiàn)，變樣本自協(xié)方差估計(jì)的統(tǒng)計(jì)特性對(duì)隨機(jī)電離層延遲變化是敏感的；初步討論和分析了GPS觀測(cè)提供的TEC變化也適用于ACEVS方法應(yīng)用條件.</p><p>　　3）建立利用GPS監(jiān)測(cè)隨機(jī)電離層擾動(dòng)的框架方案

19、</p><p>　　綜合ACEVS理論及相關(guān)的結(jié)論和GPS時(shí)序采樣的特點(diǎn)，初步給出一種基于GPS的電離層擾動(dòng)監(jiān)測(cè)的框架方案。</p><p>　　以上方法盡管是針對(duì)實(shí)時(shí)監(jiān)測(cè)要求提出的，但它完全可用于后處理情況。電離層擾動(dòng)的GPS探測(cè)方案，主要分后處理和實(shí)時(shí)兩種情況，靜、動(dòng)態(tài)實(shí)時(shí)方案基本相同，差別主要取決于硬件要求。試驗(yàn)結(jié)果表明，利用ACEVS研究基于GPS的隨機(jī)電離層活動(dòng)的監(jiān)測(cè)方法的設(shè)想

20、是基本可行的；所給出的框架方案可作為設(shè)計(jì)各類利用單臺(tái)(靜、動(dòng)態(tài))雙頻GPS接收機(jī)監(jiān)測(cè)電離層活動(dòng)的方法的參考方案之一。</p><p>　　5. 利用GPS數(shù)據(jù)精確模擬電離層延遲的新構(gòu)想</p><p>　　——電離層蝕因子法及初步實(shí)現(xiàn)</p><p>　　提出了IPP點(diǎn)的電離層蝕因子及其影響因子的概念，給出了簡(jiǎn)便的計(jì)算方法，進(jìn)而提出了一種利用GPS數(shù)據(jù)確定電離層延遲

21、改正模型的新方法——電離層蝕因子法。電離層蝕因子及其影響因子，能夠根據(jù)電離層隨周日、季節(jié)、半年和周年的變化，將適應(yīng)于不同季節(jié)的電離層延遲模型有效結(jié)合起來。研究表明，利用蝕因子法模擬的電離層延遲的改正精度與利用電離層無關(guān)觀測(cè)的消除電離層延遲的精度很接近，使得單頻GPS觀測(cè)的電離層延遲的改正精度有望實(shí)現(xiàn)突破性提高，從而接近雙頻GPS觀測(cè)自校正電離層延遲的精度。同時(shí)，由于它具有很好的描述和區(qū)分電離層日間和夜間的能力，所以很適合模擬高動(dòng)態(tài)低軌衛(wèi)

22、星的星載單頻GPS觀測(cè)數(shù)據(jù)的電離層延遲的變化特性。</p><p>　　6. 高精度修正星載單頻GPS低軌衛(wèi)星的電離層延遲的新對(duì)策</p><p>　　——APR-II方案，即空基APR方案</p><p>　　分析了現(xiàn)有方法無法保證高精度和高可靠性地進(jìn)行電離層分層這一嚴(yán)重不足；利用實(shí)測(cè)數(shù)據(jù)模擬全球電離層模型和建立高精度區(qū)域格網(wǎng)電離層模型，初步分析了在全球范圍內(nèi)尋找

23、若干個(gè)電離層結(jié)構(gòu)和活動(dòng)相對(duì)較有規(guī)律的局部區(qū)域的可行性；設(shè)計(jì)了在選定的局部電離層區(qū)域，聯(lián)合處理地基和低軌空基用戶的GPS觀測(cè)數(shù)據(jù)有效進(jìn)行電離層分層的具體方法，給出了相應(yīng)的精度估計(jì)公式。初步的精度估算和試算結(jié)果表明，這種在局部區(qū)域進(jìn)行有效電離層分層的設(shè)想及給出的實(shí)施方法是可行的。進(jìn)而系統(tǒng)性地提出了一種用于星載單頻GPS接收機(jī)精密測(cè)軌中電離層延遲改正的綜合方法—APR-II方案。地面GPS數(shù)據(jù)進(jìn)行的兩個(gè)初步模擬計(jì)算結(jié)果顯示，利用APR-II可

24、滿足低軌衛(wèi)星等低軌航天器精密測(cè)軌時(shí)的電離層延遲的高精度改正要求。</p><p><b>　　外文原文</b></p><p><b>　　Abstract</b></p><p>　　Recently, according to the requirements of some important GPS researc

25、h subjects in the fields of Geodesy, Geophysics, Space-Physics and navigation in China, we studied systematically how to correcting the effects of the ionosphere on GPS, with high-precision and accuracy. As the parts of

26、the main contributions, the research projects focus mainly on how to improve GPS surveying by reducing ionospheric delay for dual/single frequency kinematic/static users: high accuracy correction of ionospheric </p>

27、;<p>　　Keywords:GPS ionospheric monitoring, ionospheric delay, GPS Wide Area Differential</p><p>　　The main contents of this Ph.D paper consist of two parts:</p><p>　　Fisrt part---the out

28、line of research background and the systematic introduction and summarization of the previous research results of this work. </p><p>　　Second part---the main contribution and research results of this paper a

29、re focused on as follows:</p><p>　　(1) How to use the measurements of a dual frequency GPS receiver to determine the ionospheric delay correction model for single frequency GPS of a local range;</p>&

30、lt;p>　　(2)    How to separate the instrumental biases with the ionospheric delays in GPS observation;</p><p>　　(3) How to establish a large range grid ionosphere model and use the GPS data

31、of Chinese crust movement observation network to investigate the change law of ionospheric TEC of  China area; </p><p>　　(4) How to improve the effectiveness of correcting ionospheric delays for WAAS’s

32、users under adverse conditions.</p><p>　　(5) How to establish the basic theory and the corresponding framework of monitoring the stochastic ionospheric disturbance using GPS</p><p>　　(6) How to

33、improve the modelling ability of ionospheric delay according to its diurnal, seasonal, annual variations based on GPS;</p><p>　　(7) How to meet the demand of correcting the ionospheric delay of  high-pr

34、ecision orbit determination for low-earth satellite using a single frequency GPS receiver</p><p>　　1 Extracting (local) ionospheric information from GPS data with high-precision </p><p>　　T

35、he factors are systematically described and analyzed which limit the precision of using GPS data to extract ionospheric delays. The precision of determining ionospheric delay using GPS is improved based on the further re

36、search of the related models and methods. The main achievements of this work include the some aspects as follows:</p><p>　　(1) Based on a simple model with constant number of parameters, which consists of a

37、set of trigonometric series functions, a generalized ionospheric model is constructed whose parameters can be adjusted. Due to the property of selecting the different parameters according to the change law of ionospheric

38、 delay, the new model has better availability in the field of the related theoretic research and engineering application. The experimental results show that the model can indicate the characterist</p><p>　　(

39、2) Different calculating schemes are designed which are used to analyze in detail the characteristics of the effect from instrumental bias (IB) in GPS observations on determining ionospheric delays. IB is different from&

40、#160; noise in GPS observations. The experimental results show that the effect of IB is much larger than that of the noise on estimating ionospheic delay, and  IB can cause ionospheric delay measurements to include

41、systematic errors of the order of several meters. Therefore, one must</p><p>　　(3) Stability of IB is studied with a refined method for separating it from ionospheric delay using multi-day GPS phase-smoothed

42、 code data. The experimental results show that, by using averaging of  noise with phase-smoothed code observation，the effect of noise on separating IB from ION can be efficiently reduced, and  satellite bias pl

43、us receiver bias are relatively stable and may be used to predict the IBs of the next session or even that of the next several days.</p><p>　　(4) A new algorithm about static real time determination of ionos

44、pheric delay is presented on the basis of the predicted values of IB and the technique of real time averaging of noise and weighted-adjustment of dual P-code and carrier phase measurements. The preliminary results show t

45、hat the new method, which is by post-processing phase-smoothed code data to calculate the IB and then with them to predict and to correct the IB of data needed to remove its effects  in real time in the next observa

46、</p><p>　　2  A method of constructing large range (regional and global) high-precision grid ionospheric model─—the Different Area for Different Stations (DADS) and its application in China</p>&l

47、t;p>　　Based on the systematic and further research of the principle and methods of establishing grid ionospheric model (GIM), a new method of establishing a GIM ----- Different Areas for Different Stations (DADS) is i

48、nvestigated which is advantageous for considering the local characters of ionosphere, avoiding the effects of the geometrical construction of GPS reference network on estimating the external precision of the GIM, and imp

49、roving the precision of calculating model parameters. The above resul</p><p>　　3 A method of efficiently correcting ionospheric delays for WAAS’s users under typical adverse conditions ——the Absolute Plus Re

50、lative Scheme (APR-I)</p><p>　　The commonly used WAAS’s DIDC received by single frequency GPS receivers can usually provide the effective correction of  the ionospheric delays for the users under normal

51、 conditions and in the fields of calm ionosphere. However, the ionospheric delays cannot be efficiently accounted for during those periods when the WAAS cannot broadcast the DIDC values to users, or when the receivers ca

52、nnot receive the DIDCs for whatever reason. The ionospheric delay corrections will be less well known in case</p><p>　　For this, a new ionospheric delay correction scheme for single frequency GPS data—the AP

53、R-I scheme is proposed which can efficiently address the above problems. </p><p>　　1)      The theoretic basis of constructing the APR-I Scheme </p><p>　　The WAAS can pr

54、ovide high-precision absolute ionospheric delay estimates when it operates properly. Meanwhile, a single frequency GPS receiver serviced by the WAAS can efficiently determine the relative variation of the ionospheric del

55、ays between two arbitrary epochs even under adverse conditions if without considering observation noises. </p><p>　　2)      On the APR-I Scheme</p><p>　　Based on a robus

56、t recurrence procedure and an efficient combination approach between absolute ionospheric delays and ionospheric relative changes, the APR-I scheme  is present which is an new method of correcting ionospheric delay

57、for single frequency GPS user. The formula of estimating the precision of the APR-I scheme is given. An implementation approach of the APR-I scheme is analyzed as well.</p><p>　　The experimental results disc

58、ussed above show that the APR-I scheme not only retains the characteristic of high accuracy of the DIDC from the WAAS under normal ionospheric and reception conditions, but also has relatively better correction effective

59、ness under different abnormal conditions. The implementation of this method need not change the present basic ionospheric delay correction algorithm of the WAAS. In addition, the APR-I method does not impose new demands

60、on receiver hardware, and only </p><p>　　4 A new theory of monitoring the random signal —Auto-Covariance Estimation of Variable Samples(ACEVS) and its application in using GPS to monitor the random ionospher

61、e </p><p>　　A new approach for monitoring ionospheric delays is found and developed, based on the characteristic of time series observation of GPS, an investigation of the statistical properties of the estim

62、ated auto-covariance of the random ionospheric delay when changing the number of samples in the time series, the development of the related basic theory and the corresponding framework scheme, and the further research of

63、 using GPS and the above research results to study ionosphere.</p><p>　　The concrete work is as follows:</p><p>　　1) Studied the Auto-Covariance Estimation of Variable Samples (ACEVS) </p>

64、<p>　　From a general mathematical aspect, the basic model of ACEVS is established. The theoretic and approximate solution formulas for ACEVS are derived based on the improvement of theory of white noise and then a

65、 test raw of the state of a random signal is established based on ACEVS;</p><p>　　2) Verified and modeled the possibility of using ACEVS to test the change of state of stochastic delays</p><p>　

66、　The possibility of using ACEVS to monitor ionosphere is verified in terms of theory.  Also it is found that the statistical property of ACEVS is sensitive to the change of the random ionospheric delay, on the basis

67、 of modeling the characteristics of ACEVS using a dual frequency GPS receiver. The application conditions of using ACEVS to monitor the variation of TEC extracted by GPS data are preliminarily discussed and analyzed as w

68、ell.</p><p>　　3) Established a preliminary framework scheme of using GPS to monitor the disturbance of random ionospheric delay.</p><p>　　According to ACVES and all other results of the above an

69、d the characteristic of the time series observations of GPS, a preliminary framework scheme for monitoring the disturbance of random ionospheric delay using GPS is established. Although this method is proposed for real t

70、ime monitoring, it can be easily applied to post-processing of GPS data. The framework scheme based on ACVES can be used to design many practical schemes for monitoring ionosphere variation using a (static or kinematic)

71、dual</p><p>　　5 A new method of modelling ionospheric delay using GPS data ——Ionospheric Eclipse Factor Method (IEFM) </p><p>　　The Ionospheric Eclipse Factor (IEF) and its influence factor (IFF

72、) of Ionospheric Pierce Point (IPP) is present and a simple method of calculating the IEF is also given. By combining the IEF and IFF with the local time t of IPP, a new method of modelling ionospheric delay using GPS da

73、ta —Ionospheric Eclipse Factor Method (IEFM) is developed. The IEF and its IFF can efficiently combine the different ionospheric models for different seasons according to the diurnal, seasonal and annual variations</p

74、><p>　　6 A new strategy of correcting ionospheric delay for high-precision orbit determination for low-earth satellite using a single frequency GPS receiver ---the APR-II scheme, i.e., Space-based APR scheme &l

75、t;/p><p>　　Analyzed the shortcomings of using the previous methods to divide with high accuracy the earth ionosphere into  different layers. Used GPS data to model global ionospheric TEC. Established a hig

76、h precision grid ionospheric model. Discussed the possibility of finding out some local areas whose ionospheric construction and action have relatively better obvious law with respect to the other areas on a global scale