NCKU UCB Tohoku ISUAL / ROCSAT-2 August 2001 Sprites observation by ISUAL on the ROCSAT-2 satellite J. L. Chern, R. R. Hsu, H. T. Su, A. B. Chen, and L

NCKU UCB Tohoku ISUAL / ROCSAT-2 August 2001

Sprites observation by ISUAL on

the ROCSAT-2 satellite

J. L. Chern, R. R. Hsu, H. T. Su, A. B. Chen, and L. C. LeePhysics Department, National Cheng Kung University, Tainan 70101, Taiwan

S. B. MendeSpace Science Laboratory, University of California, Berkeley, CA 94720, USA

H. Fukunishi and Y. Takahashi Geophysics Department, Tohoku University, Sendai 980-8578, Japan


The ROCSAT-2 satellite

• 891km altitude, sun-synchronized, polar-orbit, 9:30 am/pm at 23.5 N

• orbital plane: 98.99• period: 14 rev/day

• dry weight: 700kg (small-sat)

• pointing accuracy: ground error < 100m

• lifetime: 5 years

• payload: RS-camera, ISUAL

• launch day: 31 August, 2003


Major ISUAL science objectives

• To determine the location and timing of luminous

phenomena above thunderclouds and to investigate their

spatial, temporal and spectral properties

• to obtain an global survey of upper atmospheric optical flash

transients (sprites, elves, blue jets etc.).

• To obtain an global survey of aurora and airglow


ISUALImager of Sprites / Upper Atmospheric Lightnings

Instrument:

• a CCD Imager

• 6-channel spectrophotometer (SP)

• two array photometers (AP)


ISUAL operation region

61.3deg

ISUAL operation

range

(Not to scale)

Earth

100km

17.8deg 891km

Sunlight


ISUAL CCD Imager

• Limb-viewing

• Gated intensified CCD camera

• 512 128 pixel resolution

• 20 deg. 5.0 deg FOV(1173km x 150km at the 3373km)

• Burst or continuous modes(1 ms to 30 ms resolution)

• Six selectable filters

w

h

ROCSAT

ISUAL IMAGER


ISUAL Imager’s filters

1: 623 – 750 nm

2: 762 nm

3: 427.8 nm

4: 630 nm

5: 557.3 nm

6: Open (420-780 nm) w

ideband


ISUAL Imager filters

• Filter 1N2 1st positive band filter for observing Sprites. Removes the lightning induced 777.4 nm line and minimizes the airglow 760 nm O2 band

contribution.

• Filter 2

762 nm O2 (0,0) atmospheric band for observing airglow (waves) and aurora

• Filter 3

427.8 nm energetic electron induced emissions (sprites and aurora)

• Filter 4

630 nm auroral and airglow emissions

• Filter 5

557.7 nm auroral and airglow emissions

• Filter 6

Broad band filter (lens, no filter)


ISUAL spectral photometers

– Six photometer modules are identical except for spectral characteristics

– 20 deg. 5.0 deg. FOV

– All boresighted in the same direction as the imager

– All six channels are sampled at a 10 kHz rate


ISUAL Spectrophotometers - bandpass

SP Channels 1&2

C1 - bandpass: 150 - 280 nm• No filter used

• EMR type 541 PMT

• Rubidium Telluridephotocathode

• Sapphire window

C2 - bandpass: 250 - 390 nm• Barr UG-5 glass filter


• Bi-alkali photocathode

• Magnesium Fluoridewindow



SP Channel 3&4

C3 - Center: 337 nm• Barr interference filter



• Sapphire window

C4 - center: 391.8 nm• Barr interference filter



• Sapphire window



SP Channel 5&6

C5 - bandpass: 623 - 750 nm• Barr interference filter


• Tri-alkali photocathode

• Sapphire window

C6 - center: 777.4 nm• Barr interference filter


• Tri-alkali photocathode

• Sapphire window



1. Ultraviolet filter. Looking at N2 LBH long wavelength bands. Upper state lifetime is 0.14 ms resulting in some quenching at lower altitudes. The altitude of unit optical depth is about 40 km in this range perhaps possible to see sprites while attenuating lightning.

2. Ultraviolet filter. It might be possible to see sprites and much attenuated lightning.

3. 337.0 nm N2 2nd positive band requires higher electron energies therefore provides a particle energy “spectrometer” .

4. N2 + 427.8 nm Energetic electron detector in sprites and aurora.

5. N2 1st positive emission “bread and butter” sprite measurement.

6. 777.4 O lightning “perhaps trigger”.


ISUAL Array Photometers

• Two 16-channel array photometers

Red or blue filters

• Total FOV: 20 deg. 3.2 deg

(20 deg. 0.2 deg each)

• Acquisition modes:

– Sprite 1 mode: sampling at 20 kHz

– Sprite 2 mode: sampling at 2 kHz

– Auroral mode: sampling at 200 Hz


ISUAL operation modes

• Sprite Continuous Mode

– Imager is continuously taking images at a 100 frame/sec rate

– Array Photometer is continuously sampled at a 20 or 2 kHz rate

– Spectrophotometer is continuously sampled at a 10 kHz rate

– All data are written into a series of circular memory buffers

– Upon meeting trigger criteria on Spectrophotometer data, a selected block of data are saved in Mass Memory for compression and transfer to T/M

– Selectable trigger parameters include channel, level, rise time, and pre-trigger block size and post-trigger block size

• Sprite Burst Mode

– Same as continuous mode except sample rate is 650 Hz for a limited period

– Price of high sample rate is ~80% dead time

• Auroral Mode

– All instruments operate at a constant rate of 1 sample/second

– All data saved, compressed, and transferred to S/C for downlink


Space/ground coordinated observations


ISUAL contacts

ISUAL Principal Investigater:

Prof. Jyh-Long Chern (physics Dept., NCKU) [email protected]

ISUAL NCKU Team: [email protected] Team: [email protected] Team: [email protected]

ISUAL website: http://sprite.phys.ncku.edu.tw/


ISUAL meetings

• During the 2001 AGU meeting at San Francisco an informal meeting

• Two days before the 2002 AGU meeting at San Francisco

2 days formal meeting at the Space Science Lab., UCB

Additional information will be released on the ISUAL website.

Documents

NCKU UCB Tohoku ISUAL / ROCSAT-2 August 2001 Sprites observation by ISUAL on the ROCSAT-2 satellite J. L. Chern, R. R. Hsu, H. T. Su, A. B. Chen, and L