Isual Publications 2014

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200407 24 Lee, L. C.( 200407 ).Space program in Taiwan, 35th COSPAR Scientific Assembly, Paris, France. The National Space Program Office (NSPO) was established in 1991 to execute the space program in Taiwan. The first fifteen-year space program (1991-2006) consists of setting up infrastructure and carrying out three satellite programs (ROCSAT-1, ROCSAT-2 and ROCSAT-3). For the second fifteen-year program (2004-2018), NSPO will execute five major missions that include remote sensing satellites, broadband communication satellite, micro-satellites, international scientific cooperation programs, and sub-orbital science program. The ROCSAT-1 satellite is a low-earth orbit scientific experiment satellite launched on January 27, 1999. It carried three scientific payloads: Ocean Color Imager (OCI), Ionospheric Plasma and Electrodynamics Instrument (IPEI), and Experimental Communication Payload (ECP). The ROCSAT-2 satellite is a high-resolution remote sensing satellite to be launched in April 2004. ROCSAT-2 carries a Remote Sensing Instrument (RSI). At nadir, RSI ground resolution is 2 meter for panchromatic and 8 meter for multispectrum images with 24 km swath. In addition, it carries a science payload ISUAL (Imager of Sprites and Upper Atmospheric Lightnings). ISUAL experiment will observe the upper atmospheric transient luminous events (TLEs), such as red sprite, blue jets, and gigantic jets. The ROCSAT-3 program, also known as COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate), is an international cooperation program between NSPO and UCAR (University Corporation for Atmospheric Research) of USA. The mission goal is to launch six micro-satellites to collect atmospherically bent signals for weather prediction, global climate-change analysis, and ionosphere and gravity research. Three payloads will be carried on each satellite, including GPS Occultation Experiment (GOX), Tiny Ionospheric Photometer (TIP), and Tri-Band Beacon (TBB). ROCSAT-3 is planned for launch in late 2005.
200412 25 R. R. Hsu, Y. J. Lee, C. L. Kuo, Y. C. Wang, W. Tsay, W. Y. Wang, W. C. Chen, S. C. Wang, A. B. Chen, H. T. Su, and L.C. Lee( 200412 ).Transient luminous jets recorded in the Taiwan 2004 TLE campaign, American Geophysical Union, Fall Meeting 2004, San Francisco, USA. AE31A-0151 The gigantic jets were first reported by Su et al. [Su et al., Nature, 423, 974-976, 2003]. After nearly two years in hunting, another gigantic jet was recorded from Lulin observatory (23.47N, 120.87E, 2862m) on June 18, 2004. The newly observed event occurred above a frontal system which was stationed at Anhui province of China about 700km away. This fact indicated that gigantic jets could also occur over land. Moreover, during the 2004 Taiwan TLE campaign, several jet-like TLEs were recorded at Kenting, Taiwan (21.92N,120.85E, 116m) on the night of August 3, 2004. These events occurred over a thunderstorm located at the coast of Guandong province, China about 500km away. The luminous duration of these events lasted for ~200ms, which is shorter than the GJs and the large blue jet observed by Pasko et al [Nature, 416 , 152-154, 2002]. The upper altitude of the jet-like TLEs is ~70km, which is lower than the GJs but is the same as the large blue-jet or the trailing jets of GJs. The luminous structure of these events looks like a fountain in the dark, which is very similar to trailing jets of GJs but is different from that of the large blue jet. In the 2004 TLE campaign, we deployed a high speed ICCD with 4ms time resolution and three NTSC ICCD cameras that were equipped with different filters. In this talk, the temporal evolution of the jets, the associated electromagnetic emissions, and their spectral properties will be presented. Comparisons with the existing theoretical models will also be presented. *Work supported in part by grants from NSPO (93-NSPO(B)-ISUAL-FA09-01) and NSC (NSC93-2112-M-006-007, NSC93-2111-M-006-001) in Taiwan.
200412 26 C. L. Kuo, R. R. Hsu, L.C. Lee, H. T. Su, A. B. Chen, S. B. Mende, H. U. Frey, H. Fukunishi, Y. Takahashi, and T. Adachi( 200412 ).Heating and luminous emission of upper atmosphere due to an applied DC E-field, American Geophysical Union, Fall Meeting 2004, San Francisco, USA. AE31A-0160 TLEs are transient and luminous events occurring between thunderstorm top and the lower ionosphere. The optical emission typically lasts for several milliseconds and is from the radiative emission of excited air molecules (mostly nitrogen and oxygen). The excitation of air molecules is due to the residual electric field above thundercloud that accelerates electrons and the resultant inelastic collisions of the accelerating electrons with molecules. Based on a Boltzmann-type distribution of electron energy, heating and luminous emission of air molecules in an applied DC electric filed was computed. The computed quantities are further compared with the electron-swarm properties of air, and the average electron energy as well as the strength of the causative electric field deduced from the TLE events observed by ROCSAT-2 ISUAL and by the 2004 Taiwan TLEs campaign. * Works performed at National Cheng Kung University were supported in part by grants from NSPO (93-NSPO(B)-ISUAL-FA09-01) and NSC (NSC93-2112-M-006-007, NSC93-2111-M-006-001) in Taiwan.
200412 27 Y. Takahashi, H. Fukunishi, T. Adachi, R. R. Hsu, H. T. Su, A. B. Chen, S. B. Mende, H. U. Frey, and L.C. Lee( 200412 ).Characteristics of Elves Observed with the Array Photometer on board the ROCSAT-2 Satellite, American Geophysical Union, Fall Meeting 2004, San Francisco, USA. AE31B-0163 Elves are the very short ( phenomena at altitude of the lower ionosphere (90-100 km) with a horizontal extent of 200 _| 500 km in diameter induced by strong electromagnetic pulse from lightning discharge. It has been confirmed by multi-channel photometric measurements that the apparent motion observed from the ground site at a distance over the radius of elves is downward at quite high speed, which is well consistent with numerical calculations of electromagnetic model. Simulation studies predict that in the optical emission region of elves the electron density could be modulated by one order or more. In order to estimate the quantitative effect of elves on the ambient atmosphere/ionosphere, measurements of absolute luminosity and spectral intensity ratio between emission bands are required. For this purpose we developed high-speed multi-anode array photometers (MAPs), which have 16 channel anodes aligned in the vertical or horizontal direction with two band pass filters, and have conducted ground observations for almost one decayed. Based on the observational result we estimated the optical emission altitude precisely and found that in the very initial phase of elves events the electron energy show considerably high values compared to the time period of maximum luminosity. However, the optical extinctions and scatters by atmosphere and aerosols prevent us to calculate the absolute values of physical parameters. The well-calibrated ISUAL instruments onboard the ROCSAT-2 satellite provide us quantitative brightness information about transient luminous events in the upper and middle atmosphere. The array photometer (AP), one of the ISUAL instrument, is an application of MAP to space use, which measures intensity ratio of two colors, namely, 360-470 nm and 520-750 nm, with absolute brightness. It is found using the preliminary observational data obtained by AP that elves consist of both red (N2 1st Positive and N2 Meinel) and blue(N2 2nd Positive and N2 1st Negative) colors at magnitude of almost same order. The ISUAL recorded about 100 elves for first three months. We discuss the possible ionizing and heating effects of elves based on the initial observational results.
200412 28 A. B. Chen, M. H. Chang, T. H. Huang, C. L. Kuo, S. C. Wang, P. S. Chiang, R. R. Hsu, H. T. Su, Y. S. Chang, T. Y. Liu, S. B. Mende, H. U. Frey, H. Fukunishi, Y. Takahashi, T. Adachi, and L.C. Lee( 200412 ).ISUAL calibration and optimal ground coverage for detecting transient luminous events, American Geophysical Union, Fall Meeting 2004, San Francisco, USA. AE31B-0164 ISUAL, the scientific payload of ROCSAT-2 satellite began its operation since July 1, 2004. ISUAL consists of an intensified imager, a 6-channel spectrometer and a dual-channel/16-anodes array photometer. The mission goals are to acquire spatial, spectral and temporal informations of transient luminous events (TLEs) from an 891 km sun-sync polar orbit. A series of post-launch on-orbit tests were performed to extract crucial instrumental parameters for data processing. We will report some of the results. To maximize the efficiency for global survey, the ground coverage of ISUAL at different spacecraft roll and yaw angles as well as in different seasons was computed. By comparing the computed ground coverage and the global lightning distribution maps obtained from satellites like TRMM, we can determine the best altitude of imaging in order to maximize the chance in capturing TLEs. In this presentation, the salient informations for the groups that wish to perform future ground/space coordinated observations of TLEs will also be provided. *Works performed at National Cheng Kung University were supported in part by grants from NSPO (93-NSPO(B)-ISUAL-FA09-01) and NSC (NSC93-2112-M-006-007, NSC93-2111-M-006-001) in Taiwan.
200412 29 T. Adachi, H. Fukunishi, Y. Takahashi, R. R. Hsu, H. T. Su, A. B. Chen, S. B. Mende, H. U. Frey, and L.C. Lee( 200412 ).Spatial and Temporal Structures of Sprites Observed with the Array Photometer on board the ROCSAT-2 Satellite, American Geophysical Union, Fall Meeting 2004, San Francisco, USA. AE31B-0165 Sprites are transient luminous events at the altitude of the mesosphere mostly induced by positive cloud-to-ground lightning discharges ( CGs). Past theoretical and experimental studies put forward the quasi-electrostatic (QE) model in which energetic electrons accelerated by the QE fields excite and ionize ambient neutral particles such as nitrogen molecules through collision processes. By measuring the spatio-temporal evolution and spectral characteristics of optical emissions, it is possible to investigate the physical and chemical processes occurring in sprites quantitatively. Miyasato et al. [2004] estimated electron energies by analyzing sprite data obtained from ground-based observations with a dual-color photometer, and suggested that strong ionizations occur at the initial stage of sprite halo. Ground spectral information of sprites, however, has large uncertainty due to the attenuation effects by atmospheric molecules and aerosol particles along the light path from the sprite emission region to the ground observation site. For that reason, optical observations from space are essential for the precise estimation of absolute luminosity. The ROCSAT-2 satellite with a scientific payload named ISUAL (Imager of Sprites/Upper Atmospheric Lightning) is the first satellite which observes transient luminous events such as sprites from space. The ISUAL is composed of an imager, a spectrophotometer, and an array photometer (AP). The AP provides us spectral information by measuring two wave length ranges of 360-470 nm and 520-750 nm selected by blue and red filters, respectively. The AP has 16 channels arrayed in vertical and spatial resolution corresponds to ~11 km in the case of sprites occurring at the limb point 3315 km away from the satellite. The time resolution of 50 or 500 TLEs enables us to detect vertical motions of sprites which have an average duration of several to tens of ms. From the middle of July to the end of August in 2004, we observed ~2210 lightning flashes, ~20 sprites, and ~100 elves. The average observation frequency of lightning and sprite flashes are 55 and 0.5 per day, respectively. The AP succeeded in detecting clear upward/downward vertical motions of sprites in both the blue and red channels with quite high signal-to-noise ratios. In this study, we discuss the spatio-temporal evolution and spectral characteristics of sprites in detail.
200412 30 L.C. Lee, R. R. Hsu, H. T. Su, A. B. Chen, S. B. Mende, H. U. Frey, H. Fukunishi, Y. Takahashi, and T. Adachi ( 200412 ).Overview of the FORMOSAT-2 Satellite and ISUAL Instruments, American Geophysical Union, Fall Meeting 2004, San Francisco, USA. AE51A-01 After six years of preparation, ROCSAT-2 - the second satellite from Taiwan was successfully launched on 20 May 2004 from Vandenberg Air Force Base in California. ROCSAT-2 carries two payloads onboard: the Remote Sensing Imager (RSI) to image the ground Earth, and the Imager of Sprites and Upper Atmospheric Lightning (ISUAL) to study the transient luminous phenomena. The ISUAL instruments consist of a low-light level camera, a six-channel spectrophotometer and a red/blue band array photometer. With this set of instruments, ISUAL project seeks to determine the location and timing of upper atmospheric transient events above thunderstorms, to investigate their spatial, temporal and spectral properties, to obtain a global survey of upper atmospheric flashes, and to perform an additional global survey of auroras and airglows. In this talk, the characteristics of the ISUAL payload, the key parameters of ROCSAT-2, the observation strategy of the experiment and some preliminary results will be presented. ISUAL project is an international collaboration supported by the National Space Program Office in Taiwan, with additional contributions from the National Cheng Kung University (NCKU), Taiwan, the Space Science Laboratory of the University of California at Berkeley, and Tohoku University, Japan. The NCKU team is supported in part by research grants from National Space program Office (93-NSPO(B)-ISUAL-FA09-01) and National Science Council (NSC93-2112-M-006-007,, NSC93-2111-M-006-001) in Taiwan.
200412 31 S. B. Mende, H. U. Frey, R. R. Hsu, H. T. Su, A. B. Chen, L.C. Lee, H. Fukunishi, and Y. Takahashi( 200412 ).Sprite Imaging Results from the ROCSAT2 ISUAL Instrument, American Geophysical Union, Fall Meeting 2004, San Francisco, USA. AE51A-02(invited) For the systematic observations of Transient Luminous Events (TLE-s, sprites, elve-s, blue jets etc.) and the study of their global distribution, a satellite based camera was launched as part of the "Imager for Sprites and Upper Atmospheric Lightning" (ISUAL) instrument on the Taiwanese ROCSAT 2 satellite. In addition to being a high quality imager of TLE-s the camera is suitable for the observation of aurora and airglow. The imager is bore-sighted with two photometers and the combined instrument package images the atmospheric phenomena and measures their spectral and rapid temporal properties. The imager has a field of view of 20 degrees horizontal and 5 degrees vertical covering a region that is approximately 1000 x 250 km at the earth limb. The view direction is perpendicular to the orbital plane. The imager carries a filter wheel and it can be operated in a number of wavelength regions uninhibited by atmospheric absorption. The spectral ranges are: 427.8 nm for the detection of energetic electron induced phenomena in TLE-s (e.g. blue jets) and aurora, 557.7 nm for the observation of aurora and airglow, 630 nm for the observation of ionospheric irregularities and aurora, wide red/IR N2 1st positive band region for the quantitative observation of sprites and elve-s and 762 nm for the observation of the airglow and especially gravity wave modulated intensity fluctuations. This filter is also effective in suppressing the low altitude part of TLE-s because of the atmospheric O2 absorption. Numerous examples of elve-s were observed both in the N2 1st positive and the 762 nm filter bands. The nicest data on fully developed sprites was obtained in the N2 1st positive band. High intensity gravity waves were seen in the 762 nm band. Examples of various kinds of TLE-s, aurora and airglow that were observed by the imager illustrate its wide variety of application in aeronomy research.
200412 32 H. T. Su, T. H. Huang, C. L. Kuo, A. B. Chen, R. R. Hsu, S. B. Mende, H. U. Frey, H. Fukunishi, Y. Takahashi, and L.C. Lee( 200412 ).Global distribution of TLEs based on the preliminary ISUAL data, American Geophysical Union, Fall Meeting 2004, San Francisco, USA. AE51A-03(invited) The ISUAL payload on the ROCSAT-2 satellite successfully passed the instrument checkout phase, and has started its global survey of upper atmospheric transient luminous events since early July of 2004. As of the mid-September of 2004, ISUAL has captured 140 TLE events in the first 70 days of operation. In this talk, the preliminary global distribution of TLEs will be presented. Also the correlation between TLEs and global lightning distributions will be evaluated. Comparisons of the occurrence rates for different types of TLEs between ground observation data and ISUAL data will also be presented. *Works performed at National Cheng Kung University were supported in part by grants from NSPO (93-NSPO(B)-ISUAL-FA09-01) and NSC (NSC93-2112-M-006-007, NSC93-2111-M-006-001) in Taiwan.
200412 33 H. Fukunishi, Y. Takahashi, T. Adachi, R. R. Hsu, H. T. Su, A. B. Chen, S. B. Mende, H. U. Frey, and L.C. Lee( 200412 ).Observations of Sprites and Elves with the ISUAL Array Photometer, American Geophysical Union, Fall Meeting 2004, San Francisco, USA. AE51A-04(invited) The ROCSAT-2 satellite with a scientific payload named ISUAL and a remote sensing payload was launched on May 20, 2004 from the Vandenberg range in California. The ISUAL (Imager of Sprites/Upper Atmospheric Lightning) instrument is composed of an imager, a spectrophotometer, and an array photometer. The ISUAL project is an international collaboration of National Cheng Kung University and National Space Program Office in Taiwan, University of California in USA, and Tohoku University in Japan. The goals of ISUAL are to complete a global survey of transient luminous events (TLEs: sprites, elves, blue jets, gigantic jets etc.) and also to investigate the global distributions of airglow and aurora and their dynamical processes. The ISUAL instrument observes optical emissions at the limb of the Earth with a range of 3373 km to the limb at the 60 km altitude tangent point. The array photometer developed by the Tohoku University group can capture spatial and temporal evolution of TLEs at the two wavelength ranges of 370-450 and 530-650 nm selected by blue and red filters, ewspectively. Each photometer consists of 16 channels arrayed in vertical with a field of view of 0.23 degrees (vertical) by 22.5 degrees (horizontal). The vertical resolution of 0.23 degrees corresponds to about 11 km at the limb. The array photometer is operated in an event trigger mode for TLE measurement. The length of data for one event is 220 ms, and the sampling frequency is 20 kHz for the first 18 ms and 2 kHz for the following 202 ms. The ISUAL has been operated on a routine basis from the middle of July in 2004. The total number of lightning cloud flashes measured by the ISUAL for 40 days from the middle of July to the end of August is 2210, while the numbers of sprites and elves for the same period are 20 and 100, respectively. A high time resolution (50 microseconds) and a high vertical resolution (11 km) of the array photometer enable us to investigate rapid intensity variations of sprites and elves as a function of altitude. Furthermore, blue/red intensity ratio measurements at 16 channels enable us to estimate the energies of electrons inducing optical emissions as a function of altitude. Typical examples of sprites and elves captured by the array photometer are presented, and their space-time structures and spectral features are discussed.
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