SPRITE-SAT Project mission for sprites and TGFs studies

*Yukihiro Takahashi1, Mitsuteru Sato2, Umran Inan3, David Smith4, Sparite-Sat team

1 Tohoku University, Japan2 Hokkaido University, Japan3 Stanford University, U.S.A.4 University of California, Santa Cruz, U.S.A

2008 TLE Workshop, Corte, 26 Jun. 2008

0. Scientific background -- sprites

Sprite↑

QE Model

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 500 1000 1500 2000 2500 3000

Charge moment [Ckm]

Optical energy [MJ]

Y=5.0*10-4X - 0.32R = 0.93

Optical energy of sprites and CMC

Takahashi et al. 2008 (this workshop)

QuickTime˛ Ç∆TIFF (LZW) êLí£ÉvÉçÉOÉâÉÄ

ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB

CMC

Occ

urre

nce

ratio

Occurrence probability of sprites

QuickTime˛ Ç∆TIFF (LZW) êLí£ÉvÉçÉOÉâÉÄ

ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB

Hu et al. 2002

Adachi et al., 2003 (GRL)

QuickTime˛ Ç∆TIFFÅiLZWÅj êLí£ÉvÉçÉOÉâÉÄ

ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB

Ohkubo et al., 2005 (GRL)

CG

suggesting the important roles of:- EMP- intra-cloud (including horizontal) currentsin sprites generation/formation processes

# of columns is determined not by CMC, but by EMP.

Sprites appear in the period of sferics cluster, not at CG.

ELF

VLF

1. TLEs (Transient Luminous Events)

Figs. Horizontal lightning current plays crucial role. [Valdivia et al., 1997]

TLEs・・・ transient optical emission in the stratosphere, mesosphere and lower thermosphere caused by lightning discharges.

Nadir Obs. from Space!

Issues to be answered-time delay and horizontaldisplacement from parent lightning

- CM deviations from QE-model predictions

- what determines number of columns and locations

2. TGFs (Terrestrial Gamma-ray Flashes)

• Observational results from CGRO satellite and RHESSI satellite.

• Discovery of terrestrial gamma-ray flash • High occurrence rate (1 event/2 day)• Associated with lightning discharges?• Timing between TGF and lightning is im

portant

Smith et al. [2005]

TGF and Lightning

Runaway Electron

• Which lightning process generates TGFs?• Relationship between TLEs and TGFs?

Energy (MeV)

Co

un

ts /

(s

Me

V)

Simultaneous Obs. from a Satellite!

The first university satellite in Japan dedicated to the geoscience under collaboration of Science and Eng. faculties

History:

2003 Oct. applied for grant-in-aid for 7 kg satellite with 1 camera and 1 (MeV) electron sensor (failed)

2004 Oct. applied for grant-in-aid again2004 RHESSI results presented in AGU fall meeting2005 Apr. 0.35 M USD for 4 years adopted (0.24M USD used)

modified to 10-kg satellite with 1 camera and 1 TGF counter (TGC)2006 Apr. modified to 40-kg satellite with 4 cameras, 1 TGC2006 Dec. chosen as one of the candidates for piggyback launch of JAXA2007 May chosen as a piggyback satellite2007 Jun. funded by grant-in-aid (~3.5 M USD/4years) for scientific

research in the highest category for individual groups, not by space agency, JAXA.

Outline of the SPRITE-SAT project

Total cost: ~3.8 M USD - including fundamental development and ground measurements/facilities - ~1 M USD for satellite manufacturing

Launch: Jan. 2009Lifetime: 5 years expectedTelemetry: UHF(up), S-band at 9600bps (down) Ground facilities: 2.4 m S-band dishes at Sendai (Japan) and Kiruna

=> 5 MB/day … 5-10 events/day

3. Objects of SPRITE-SAT• Achievement of the first synthetic observation of lightning, TLEs and

TGFs from a satellite

To investigate,• Global distribution of TLEs and TGFs• Horizontal distribution of sprites and their relation to lightning discharges• Relationship between lightning, TLEs and TGFs

SPRITE-SAT Science InstrumentsImaging of TLEs, detection of Gamma-ray, obs

ervation of VLF waves

(a) CMOS Camera (LSI): 2 sets(b) CCD Camera (WFC): 2 sets(c) Gamma-ray detector (TGC): 1 set(d) VLF antenna (VLF): 1 set

4. SPRITE-SAT

Fig. SPRITE-SAT when in orbit

Fig. Top view Fig. Side view

Specification• Size: 480×480×482 mm• Mass: 41 kg• Power:17 W (max)• Stabilization: gravity gladient• Orbit: SSO (13-01 LT)• Altitude: 660 km• Inclination: 98 deg.• Period:98 min.

4. SPRITE-SAT

SPRITE-SAT

Science Instruments(Dept. of Geophysics, Tohoku Univ.)

Bus System(Dept. of Aerospace Engineering, Tohoku Univ.)

CMOS, CCD Cameras• H/W logic• S/W development• Optics development(Dept. of Geophysics, Tohoku Univ.)

Gamma-ray Detector(IASA/JAXA, UCSC)

VLF-ANT(Stanford Univ.)

H/W Development(AD. Co., Ltd.)

Development Team

5. SPRITE-SAT Bus SystemMTM (Mechanical Test Model) of the satellite

Fig. MEM without shield panel.

Fig. MEM with shield panel.

In-house assembling with supports by small companies…

Making of flight model

6. Observation Modes

Fig. : Obs. geometry

SPRITE MODESPRITE MODE

TGF MODETGF MODE

- detection of TGFs and imaging detection of TGFs and imaging of their parent lightning (30/60 fps) of their parent lightning (30/60 fps)- TGF and VLF timing with accuracy of 0.5 ms.

At SPRITE and TGF modes, event trigger scheme will be used.

imaging of lightning/sprite horizontal distribution (29 fps)

• Nadir obs. using LSI-1,2 (FOV/35 deg)

• VLF is also operated

• TGC, WFC(FOV/140 deg), VLF-ANT

Sprite Obs. ModeSprite Obs. Mode

Using two CMOS cameras with band-pass filters （ 740-830 nm, 762nm ） , we will identify the horizontal distribution of sprite columns.

TGF Obs. ModeTGF Obs. Mode

Using TGC and CCD camera with fish-eye lens, we will identify the spatial relationship between TGFs and lightning.

Cloud-to-Ground Discharge

Scattered Lightning Flashes

Sprite

762nm 740-830 nm

Gamma-Ray

FOV=30 degFOV=140 deg

7. Science Instruments

7. Imager (LSI-1, -2)

• low alt. lightning emission → absorption• high alt. sprite emission (100J) → very weak absorption

Fig. : (top) Sprite emission spectrum calculated by numerical simulation [Milikh et al., 1997]. (bottom) Lightning emission derived from optical observation [Christian et al., 1996].

LSI-2 LSI-2 (for sprite detection)

: Most strong emission line of sprites severe O2 absorption

762 nm

730-830 nm

Lightning and Sprite Imager (LSI)

LSI-1 LSI-1 (for lightning detection)

: Strong emission line of lightning• >90% lightning has energy of >20J

LSI-1 & 2

- CMOS image sensors: “STAR250”, product of Cypress Semiconductor Co. are sued - FOV: ~30°

WFC

- CCD image sensor: “ES2” by WATEC Co., Ltd. is used. - Equipped with fish eye lens. - FOV: ~140°.

HSS.

- CCD image sensor: “ES2”, by WATEC Co., Ltd. is used.- FOV: ~40° 　　

7. Imager (LSI-1, -2, WFC)

Lightning

City light

Noisecalcuration of calcuration of differencialdifferencial

trigger if the value exceed the threshold

Differential of same pixelDifferential of same pixel (Cn-Cn-1)

・・・

・・・

> threshold ? (Cn-Cn-1 > TP)

Integration of (Cn-Cn-1) (Fn=Fn+ (Cn-Cn-1))

> threshold ? (Fn-Fn-1> TF)

Transient Emission（ Lightning, TLEs）

dark imagex4 gain

LS

B

Fig.: sample dark image of CMOS camera

29 frames/sec for LSI30 or 60 frames/sec for WFC

7.1　 Verification of the trigger logic

PC CMOS(LSI)

Time data

Clock counting in FPGA

dT = 100 μsec

1PPS (Pulse Per Second)

Image header = 16 Byte

Time data Camera parameters

Image data

PCImaging of display

Lightning Lightning simulatorsimulator 　　

GPS time counting systemGPS time counting system

7.1　 Verification of the trigger logic

Fig. : Lightning emission with city light.

Lightning flash with city light contamination

All the lightning events are triggered

comparison of LSI-1 (lightning) and LSI-2 (sprites) intensities

7.2　 Sprite judgment logic by CPU

Lightning

Lightning

Sprite

Sprite

Lightning

Lightning

without sprite

with sprite

differential of two images is used in sprite judgment

8. VLF receiver

Fig. SPRITE-SAT with extended boom

• BeCa boom for gravity gradient stabilization also works as VLF antenna.

• Analog circuit for the VLF receiver provided by Stanford Univ.

Specification• freq. range: <25 kHz• sampling freq.:100 kHz

QuickTime˛ Ç∆TIFFÅiîÒà≥èkÅj êLí£ÉvÉçÉOÉâÉÄ

ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB

SPRITE-SAT will provide important practical information to following missions, such as, TARANIS, ASIM and GLIMS/ISS

- Brightness and spectrum of lightning flashes /sprites measured with nadir looking cameras

- Detection frequency of sprite /TGF events using same time of instruments

- will contribute to improve the triggering method/criteria

10. Summary

• SPRITE-SAT equipped with 3 cameras, VLF receiver and TGF detector,

will be launched in January 2009.

• Manufacturing of flight model of BUS and SI is almost completed. Now final asse

mbling of satellite. The delivery to JAXA will be in November.

• SPRITE-SAT must be a good precursor mission for TARANIS, ASIM and GLIMS, pro

viding important practical information.

• Collaborative proposal with ground-based / space observations are very welcom

e.

Abstract

SPRITE-SAT is now being developed in-house by the Tohoku University team, which will be launched in summer, 2008. The total weight of the satellite would be less than 50 kg, including 4-5 kg science mission payload. There are two scientific objectives in this micro-satellite mission:

(1) to identify the generation mechanisms of sprites by investigating their horizontal structures, (2) to identify the generation mechanisms of TGFs by investigating their source location and relationship to lightning discharges.

Lightning and Sprite Imager-1 and -2 (LSI-1 and 2) are CMOS cameras with 512 x 512 pixels and the pixel size of 25 m, which pointed at nadir to take images of the horizontal structures of lightning and sprites. In order to detect lightning emissions, we equip LSI-1 with a broadband filter between 740 and 830 nm. We also equip LSI-2 with a rather narrow band-pass filter centered at 762 nm. The optics and the detector array altogether yield an effective field of view (FOV) of 35 deg, giving the pixel resolution of less than 660 m from the altitude of 660 km. Wide Field CCD imager (WFC) is a CCD camera with 659 x 494 pixels and the pixel size of 7.4 um, which takes images of lightning discharges inducing TGFs. WFC is also pointed at nadir and is equipped fish-eye lens (FOV is larger than180 deg). The outputs of all cameras are digitized by 10 bit A/D conversion. One instrumental case contains LSIs and WFC and the total weights is 630 g.

In order to detect TGFs, terrestrial gamma-ray counter (TGC) which consists of CsI scintillator is installed at the satellite. TGC can detect gamma-rays in the energy range from 30keV to a few MeV. This satellite also equips a VLF antenna which receives VLF radiations from lightning discharges. At the presentation, we will show the specifications of the instruments and the status of the satellite development more in detail.

7. Imager (LSI-1, -2, WFC)

LSI-1 LSI-2 WFC

LSI-1LSI-1、、22

WFCWFC

Mass： 630 g Power： 1.94 W

• CMOS 、 512x512 pix440x440pix

• 1/38 s1/38 s, 10bit output

• FOV=24.8 x 24.8 degSpatial Res. : <660 m<660 mDetection Rate: 1.23 /day1.23 /day

• 2020μμJ = 3LSB (SN=12)J = 3LSB (SN=12)

• CCD 、 659x494 pix• 1/60 s1/60 s, 10bit output• FOV > 140 degFOV > 140 deg• 2020μμJ = 230LSB (SN=81)J = 230LSB (SN=81)

7.1　 Verification of the trigger logic

10km

10km

Possible to detect Possible to detect <3 LSB emission<3 LSB emission

Fig. : Typical lightning image

Possible to Possible to detect >90% detect >90% lightning lightning eventsevents

All the lightning events are triggered

Lightning emission without city lights

7. Imager (LSI-1, -2, WFC)

SRAM (8M)

SRAM (8M)

DSP(TMS320VC5510)

ROM

data compression

Control of SI

FPGA (Virtex-2)

ROM1st trigger(lightning detection)

2nd trigger(TLEs detection)

Temporal data save memory

SHUSHU

ScienceInstruments

Satellite BUS

data

CMD

7. Imager (LSI-1, -2, WFC)

FOVFOV 28.7×28.7 deg28.7×28.7 deg @512×512 pix.

Spatial Res.Spatial Res. 0.6 km0.6 km to detect columniform sprites

Frame Rate 29 fps to reduce background noise

Pixel SizePixel Size 512×512512×512 max value (variable)

Detection RateDetection Rate > 1 event/day> 1 event/day global survey

FOVFOV 134×180 deg134×180 deg

Frame Rate 30 or 60 fps to reduce background noise

Pixel Size 659×494 detect >90% lightning events

LSI-1, 2

WFC (Wide Field CCD Camera)

Specification