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26 2. DEVELOPMENT OF THE FABRY-PEROT DOPPLER IMAGING SYSTEM Electric Lenses Fluorescent Screen IZ\Ju / / : / Photocathode Micro Channel Plates Figure 2.6. Diagram of the photon imaging head (Pill) detector [after Nakajima, 1993] while the fringes of an auroral emission of 01557.7 nm with a peak emission altitude of —105 km cover a region of approximately 350 km in diameter. This system was used for observations of thermospheric wind velocities at Syowa Station, Antarctica in 1990. From the analysis of the obtained data, large variations in the neutral thermospheric temperatures and wind velocities during an auroral breakup event on 11 September 1990 were reported INakajima, 1993, Nakajima et al., 1995]. 2.3.2 Correction of the image distortion caused by the photon imaging head The photon imaging head (PIH) used in the prototype FPDIS is a highly sensitive two-dimensional photon detector (Model C2166-01, Hamamatsu Photonics Corp.) which consists of a photocathode, a pair of electric lenses, two-stage microchannel plates, and a fluorescent screen, all assembled in a vacuum tube. A schematic diagram of the PHI is shown in Figure 2.6. A slight (less than 5%) geometric distortion was found in the obtained PHI images. Its cause was aberrations of the electric lenses. Precise correction of this distortion is essential to derive thermospheric temperatures and wind velocities from interference-image data. The collection methods called 'the grid calibration' and 'the two-dimensional plane- spline-interpolation', were given by Nakajima [1993] and Nakajima et al. [1995J. In the grid calibration, a precise optical grid is placed on the focal plane in the foreoptics of the FPDIS, and images of the grid which is weakly illuminated by a diffused He-Ne laser / / / z
2. DEVELOPMENT OF THE FABRY-PEROT DOPPLER IMAGING SYSTEM 27 are taken. Next, X and Y coordinates at the intersections of vertical and horizontal grid lines in the image are obtained, and the two-dimensional plane-spline-interpolation method is applied to interpolate the X and Y coordinates over the whole region of the image. Figure 2.7(a) shows an example of the grid image used for the grid calibration, while Figure 2.7(b) shows an image corrected by the two-dimensional plane-spline-interpolation method. It is found that distorted and curved grid lines are mapped to straight lines that are orthogonal to each other. As described above, the correction procedures for the PIH images are very complicated, and may reduce the accuracies in derivation of thermospheric winds and temperatures. To solve this image distortion problem, we need a different type of imaging detector. In the model developed in 1993, we adopted the proximity focused photon counting imager (PFPCI) which has no electric lenses. Details about the PFPCI are described in Section 2.4.4. 2.3.3 Problems in the image integration The PHI was operated in the photon counting mode because the luminosity of auroral emission is usually less than 106 photons/mm2/s. This mode detects an incident photon as a single photon spot on the output fluorescent screen. A typical diameter of this spot is approximately 60 ,um. Images are then produced by summation of individual photons on the CCD chip. The exposure time of the CCD is selectable among 0.53, 1.06, 2.13, 4.26, and 8.58 s. Then, a thresholding procedure which eliminates CCD thermal and readout noises and an integration procedure are needed to obtain the etalon fringes of the incident light, as shown in Figure 2.8(a). However, photon spots sometimes overlap each other as shown in Figure 2.8(b), since the PHI detects too many photons in the case of bright aurora even if the minimum exposure time of 0.53 s is selected. In this case, obtained fringe peaks are deformed because overlapped photon spots are counted as one spot by a simple thresholding procedure. To solve this problem, a new image processing system has been adopted for the new version of the FPDIS developed in 1993. Details about this system are described in Section 2.4.5.
Page 1 and 2: A Study on Middle-scale Variations
Page 3 and 4: Abstract The solar wind energy inje
Page 5 and 6: Contents Acknowledgments Abstract i
Page 7 and 8: 6 Discussions CONTENTS 6.1 Nighttim
Page 9 and 10: x LIST OF FIGURES 2.10 2.11 2.12 2.
Page 11 and 12: xii LIST OF FIGURES 4.8 Fringe prof
Page 13 and 14: xiv LIST OF FIGURES 5.23 Same as Fi
Page 15 and 16: Chapter 1 Introduction 1.1 The Eart
Page 17 and 18: 1. INTRODUCTION rate at high latitu
Page 19 and 20: 1. INTRODUCTION 5 Analogous to the
Page 21 and 22: 1. INTRODUCTION 7 thermospheric cir
Page 23 and 24: 1. INTRODUCTION 9 Okano and Kim [19
Page 25 and 26: 1. INTRODUCTION confirmed that the
Page 27 and 28: 1. INTRODUCTION 13 and EUV solar ra
Page 29: 1. INTRODUCTION 15 analytical descr
Page 32 and 33: 18 2. DEVELOPMENT OF THE FABRY-PERO
Page 52 and 53: 38 Er e Z O CE F-F-a Ur) h^-• O 0
Page 54 and 55: i 40 2. DEVELOPMENT OF THE FABRY-PE
Page 56 and 57: 42 2. DEVELOPMENT OF TI E FABRY-PER
Page 58 and 59: 44 2. DEVELOPMENT OF THE FABRY -PER
Page 60 and 61: 46 3. OBSERVATIONS 1) The adjustmen
Page 63: (b) 3. OBSERVATIONS (a) !7lasigum 1
Page 67 and 68: 3. OBSERVATIONS Table 3.1. Summary
Page 69: ____------- wind velocity line-of-s
Page 73 and 74: 3. OBSERVATIONS 59 All operations o
Page 75 and 76: Chapter 4 Procedures of Data Anal y
Page 77 and 78: 4. PROCEDURES OF DATA ANALYSIS 63 2
Page 79 and 80: -, (a) 1000 500 (b) 1000 500 0 0 4.
Page 81 and 82: as 4. PROCEDURES OF DATA ANALYSIS 6
Page 83 and 84: wind velocity v is given by 4. PROC
Page 85 and 86: 80 c..1 0 40 ,7u cn 20 0 0 4. PROCE
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Page 89 and 90: o 5000 4. PROCEDURES OF DATA ANALYS
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(a) 800 600 (i) =g-, 400 ›.- Pc C
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80 5. THER.MOSPIIERIC NEUTRAL WINDS
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8 2 5_ THERMOSPHERIC NEUTRAL WINDS
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I E 84 5. TILERMOSPHERIC NEUTRAL WI
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I 05 8 6 5. THERMOSPILERIC NEUTRAL
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88 5. THERMOSPHERIC NEUTRAL WINDS O
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Line-of-Sight Neutral Wind Velociti
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5. THERMOSPIIERIC NEUTRAL WINDS OVE
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0 Cf) CO • imme F.4 Ca) O 7-1)` c
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5. THERMOSPHERIC NEUTRAL WINDS OVER
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Chapter 6 Discussions 6.1 Nighttime
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a_ -1 7 6 5 4 3 2 -2 1 0 - 3 _4 -5
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I = - E ,---, c.) u.) a) ..... c.;
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1 (13 C 7)4 "CI ,;3 C N 0 z 0, 2 Ho
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6. DISCUSSIONS 125 is seen in numer
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6. DISCUSSIONS 6.3 Middle-scale atm
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6. DISCUSSIONS 129 15:50:00 lb:00:0
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132 6. DISCUSSIONS It is very inter
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CAD MAGNE TOGFIRM AT STOWR STA T I
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136 7. CONCLUSIONS 5) Nighttime var
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138 REFERENCES Conde, M., and R. W.
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140 REFERENCES Hernandez, G., R. W.
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142 REFERENCES Rees, D., and A. H.
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Appendix A Sequential wind data in
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Line-of-sight neutral wind velociti
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