UVIS
OBSERVATION
DESCRIPTION
HANDBOOK
6 January 1994
Revised: 9/97, 1/98, 9/98, 6/99
TABLE OF CONTENTS
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
OBSERVATIONS BY ORBIT PERIOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
OBSERVATION DESCRIPTIONS
HDAC OBSERVATION DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
URSTAR OBSERVATION DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
UCSTAR OBSERVATION DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
UHSTAR OBSERVATION DESCRIPTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
UISTAR OBSERVATION AND DESCRIPTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
USUN OBSERVATION DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
UHIGHSN OBSERVATION DESCRIPTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
ULIMDRFT OBSERVATION DESCRIPTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
USTARE OBSERVATION DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
UMAP OBSERVATION DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
USYSCAN OBSERVATION DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
UFPSCAN OBSERVATION DESCRIPTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
APPENDICES
CASSINI UVIS INVESTIGATION DESCRIPTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
INSTRUMENT CAPABILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
UVIS ANTICIPATED RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
UVIS MAP CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
DATA AND PACKET PRODUCTION RATES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
MINIMUM INTEGRATION PERIODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
COMPRESSION ALGORITHMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
LIST OF FIGURES
HDAC Figure 1. Filament cycling for D/H measurement..............................................................9
HDAC Figure 2. Relative velocity for Titan Flyby #22...............................................................10
HDAC Figure 3. HDAC FOV projected on Titan at 45,000 km range .......................................11
HDAC Figure 4. HDAC FOV projected on Titan at 14,000 km range .......................................12
URSTAR Figure 1. Shadowed ring stellar occultation................................................................14
UISTAR Figure 1. Setup and slit orientation prior to occultation...............................................18
UHIGHSN Figure 1. Iapetus raster...............................................................................................22
ULIMDRFT Figure 1. EUV, FUV slits cross terminator at beginning of drift to obtain
airglow temporal properties. .......................................................................................................24
ULIMDRFT Figure 2. EUV, FUV low resolution slits drift across Titan disk............................25
ULIMDRFT Figure 3. Titan limb scan.........................................................................................26
ULIMDRFT Figure 4. Enceladus limb drift..................................................................................27
ULIMDRFT Figure 5. EUV, FUV low resolution slits drift across Saturn dayside
atmosphere to determine local time structure of dayglow.............................................................28
ULIMDRFT Figure 6. EUV, FUV low resolution slits drift across Saturn terminator to
measure local time decay of dayglow into the darkside. S/C range 7 RS , 0.40 x 106 km. ..........29
ULIMDRFT Figure 7. EUV, FUV low resolution slits drift across Saturn dayside. ..................30
USTARE Figure 1. EUV, FUV high resolution deep exposure of Saturn dayside noon
local time emission. .......................................................................................................................32
USTARE Figure 2. EUV, FUV high resolution deep exposure of Saturn dayside
early evening local time emission..................................................................................................33
USTARE Figure 3. EUV, FUV high resolution deep exposure of Saturn dayside
early evening local time emission. ...............................................................................................34
USTARE Figure 4-A. EUV, FUV high resolution exposures of Saturn
darkside south pole. .....................................................................................................................35
USTARE Figure 4-B. EUV, FUV high resolution exposures of Saturn
dayside south pole..........................................................................................................................36
USTARE Figure 5. EUV, FUV high resolution exposures of Saturn
darkside / dayside north pole. ........................................................................................................37
USTARE Figure 6. EUV, FUV high and low resolution exposures of Titan
darkside emission. ........................................................................................................................38
USYSCAN Figure 1. Raster pattern.............................................................................................41
INTRODUCTION
This handbook describes the planned range of UVIS observations. Each observation
description allows for some variety in targets and objectives by permutation of the symbols within
brackets […] in the observation mnemonic. This flexibility allows a small number of descriptions
(and likewise a similar number of observation lists for the UVIS microprocessor memory) to
cover the majority of orbit observations.
Every observation described here can be called by an appropriate observation description command (ODC). These observations encompass the capabilities of the UVIS experiment.
A particular observation of a particular target is termed a link. These links will be composed of
ODC’s or perhaps distributed sequences (DS) stored in the UVIS program memory; they may
be repeatable. Consequently, the observation descriptions in this handbook (and associated
ODC’s) provide the vocabulary for building distributed sequences and links.
For a table summarizing UVIS observations, see the Observation Description Summary,
(the first table in the printed document; a separate PDF file in the document section of the team
website.)
For more detail on a number of topics concerning flight operability, refer to the UVIS
Flight Code User’s Guide, which can be accessed in the document section of the team website.
GENERAL PERFORMANCE ISSUES
UVIS data are transferred via packets to the CDS, the SSR, and eventually the ground.
The UVIS has two available packet pickup rates. See DATA AND PACKET PRODUCTION
RATES in the Appendices.
Because of limitations on interrupt frequency, initialization, and read-out, the UVIS has
minimum possible integration periods. See MINIMUM INTEGRATION PERIODS in the
Appendices. The buffer memory can store up to 720 packets if the instrument packet production
rate exceeds the packet pickup rate. If this volume is exceeded, the newest data will be lost.
UVIS data will also be limited by the assigned SSR volume between downlinks: this may
be the most severe limit on our data-taking. All UVIS raw data may be compressed to reduce data
volume. The options available are: “no compression,” 8 bit compression, SQRT-9, and SQRT-8.
The default compression for UVIS is SQRT-9. See COMPRESSION ALGORITHMS in the
Appendices.
RETURN TO TABLE OF CONTENTS.
5
OBSERVATIONS BY ORBIT PERIOD
APOAPSIS
• USYSCAN
• USTARE: SATURN, TITAN
• UMAP: INNER MAGNETOSPHERE
• UFPSCAN
TITAN
• UHIGHSN
• UMAP: POLES, EQUATOR, TERMINATOR, DARKSIDE, ETC.
• ULIMDRFT
• UHDAC
• UCSTAR
• UHSTAR
• USUN
PERIAPSE
• UHIGHSN: RINGS, FEATURES, LIMB
• UMAP: SATURN N-S, POLES, ETC.
• URSTAR
• UCSTAR
• UHSTAR
ICY SATELLITE
• UHIGHSN
• UMAP
• ULIMDRFT
• UISTAR
• USUN
SATURN
• UHDAC
• ULIMDRFT
• USUN
• UHIGHSN: PHASE ANGLE COVERAGE
RETURN TO TABLE OF CONTENTS.
6
OBSERVATION
DESCRIPTIONS
HDAC OBSERVATION DESCRIPTION
1. Title:
Hydrogen Deuterium Cell Measurements
2. Mnemonic:
U[T,S]HDAC
3. Purpose:
Measure D/H ratio, atomic H temperature,
thermospheric wind
4. Set-up:
Point to [Titan, Saturn] 2 hours before closest
approach
5. Observations:
Doppler scan - Cycle through predefined sequence
of filament settings (~5 minutes per cycle). Repeat
this sequence continuously across the full Doppler
range of the flyby. Total duration: 4 hours for
“reference” Titan flyby; 1.5 hours for Titan D/H
measurement only. Optimal Titan closest approach
altitudes: ~10,000 km. See attached figures
6. Data handling:
Read out CEM every 1/8 sec
7. Data product:
Time series of cell transmission
8. Support required:
None
9. Other experiments:
None
10. Raw data rate:
72 bps = 0.55 packets/64 sec
11. TM rate:
ORS: 37 packets/64 sec
12. End of observation status:
All filaments off
13. Special requirements:
None
8
HDAC OPERATION
The HDAC filament voltage is controlled by 3 control bits; these bits create 8 discrete voltage
steps. One lookup table per cell containing codes for 16 filament voltages is uplinked to the
spacecraft. This list is used to sequentially set the voltages, pausing at each voltage level for an
amount of time defined by the dwell period. During the entire sequence, the CEM continuously
integrates at 0.125 second intervals.
HDAC Figure 1. Filament cycling for D/H measurement
H Filament Current
maximum
H filament
Off
D Filament Current
maximum
D filament
time
Off
Dwell Time
16 sec
Typical sequence for Doppler scan: As the spacecraft swings through the Doppler velocities
of the flyby, the HDAC probes the emission line. During this time, a standard filament sequence
(lasting ~5 minutes) is continuously repeated. The H filament is cycled through several settings
during a sequence, while the D filament is cycled through two states only. To achieve significant
Deuterium signal modulation, the D filament is cycled on/off only when the H filament current is
at maximum. The baseline values for maximum optical depth are tmax(H) = 17, tmax(D) = 2.
The optimal Titan flybys are those with a closest approach altitude of around 10,000 km.
These flybys have slower changes in Doppler velocity than the 1000 km flybys; thus the 10,000
km flybys allow the HDAC to spend more time observing near 0 km/s. The more distant Titan flybys underfill the HDAC FOV. Titan fills the HDAC FOV at 90,000 km; this distance typically
occurs around 4 hours before closest approach.
9
HDAC Figure 2. Relative velocity for Titan Flyby #22
10
HDAC Figure 3. HDAC FOV projected on Titan at 45,000 km range
11
HDAC Figure 4. HDAC FOV projected on Titan at 14,000 km range
RETURN TO TABLE OF CONTENTS.
12
URSTAR OBSERVATION DESCRIPTION
1. Title:
Ring Stellar Occultation and Imaging Spectroscopy
2. Mnemonic:
URSTAR
3. Purpose:
Measure ring opacity with HSP; ring background,
reflected spectrum (with lit rings), and diffraction
pattern (with shadowed rings) with FUV.
4. Set-up:
Point to star. HSP, FUV on; EUV off (or on for some
rare stars). FUV slit: 8 mrad (or 2 mrad). EUV slit
(if on): 8 mrad.
5. Observations:
Point to star for duration of occultation, starting 10
minutes before and ending 10 minutes after rings
occult star.
6. Data handling:
HSP readout every 2 msec. FUV readout every
4 sec. FUV binning and windowing: Option A:
Window 1: [0, 63], [1023, 0], XBIN=32, YBIN=1.
Option B: Window 1: [0, 63], [1023, 50], XBIN=32,
YBIN=1. Window 2: [0, 36], [1023, 27], XBIN=32,
YBIN=1. Window 3: [0, 13], [1023, 0], XBIN=32,
YBIN=1. EUV binning and windowing (if on):
Window 1: [0, 63], [1023, 0], XBIN=32, YBIN=1.
7. Data products:
Time series of ring opacity. Spectral-spatial image
cubes.
8. Support required:
Back-up imaging.
9. Other experiments:
VIMS? CIRS?
10. Raw data rate:
HSP: 4.5 kbps = 33.8 packets/64 sec.
FUV Option A: 4.6 kbps = 34.8 packets/64 sec.
Option B: 2.6 kbps = 19.8 packets/64 sec.
EUV: 4.6 kbps = 34.8 packets/64 sec.
11. Telemetry rate:
OCC = 236 packets/64 sec
12. End of observation status:
TBD
13. Special:
Pointing uncertainty and drift over the duration of
the occultation (1 to several hours) must be less than
2 mrad. FUV option B will be used if data rate or
volume is limited or if higher time resolution in the
FUV is desired.
13
URSTAR Figure 1. Shadowed ring stellar occultation
RETURN TO TABLE OF CONTENTS.
14
UCSTAR OBSERVATION DESCRIPTION
1. Title:
Saturn [Titan] atmosphere cool star (A) occultation
2. Mnemonic:
U[S,T]CSTAR
3. Purpose:
Measure absorption by hydrocarbons and aerosols in
Saturn’s [Titan’s] atmosphere
4. Set-up:
Point to star
HSP, EUV off
FUV on
FUV slit: 8 x 64 mrad
5. Observations:
Point to star for duration of occultation (≤120
seconds, starting 2 minutes before occultation and
ending 2 minutes after star is lost behind Saturn
[Titan]
Total duration: ≤6 minutes
6. Data handling:
FUV readout every 1 second
Spatial binning by 2; spatial window: central 16
pixels; binning by 2 (readout 512 elements)
XBIN=2, YBIN=2
7. Data product:
Time series of atmospheric opacity vs. wavelength
8. Support required:
TBD
9. Other experiments observing:
VIMS? CIRS?
10. Raw data rate:
36.9 kbps = 279.8 packets/64 sec
11. Telemetry rate:
OCC = 236 packets/64sec. Excess stored in UVIS
memory, up to 720 packets (about 16 min.)
12. End of observation status:
TBD
13. Special:
Pointing uncertainty and gyro drift over the duration
of occultation must be less than 2 mrad. Point only
at dark limb of Saturn [Titan]
RETURN TO TABLE OF CONTENTS.
15
UHSTAR OBSERVATION DESCRIPTION
1. Title:
Saturn [Titan] atmosphere hot star (O, B)
occultation
2. Mnemonic:
U[S,T]HSTAR
3. Purpose:
Measure absorption by hydrocarbons, molecular
hydrogen, and aerosols in Saturn’s [Titan’s]
atmosphere
4. Set-up:
Point to star
HSP off
FUV, EUV on
FUV, EUV slits: 8 x 64 mrad
5. Observations:
Point to star for duration of occultation (≤120
seconds), starting 3 minutes before occultation and
end 3 minutes after star is lost behind Saturn [Titan].
Total duration: ≤10 minutes
6. Data handling:
FUV readout every 1 second. Spatial binning by 2.
Spatial window: central 16 pixels. Spectral binning
by 2. XBIN=2, YBIN=2. [same as UCSTAR].
EUV readout every 1 sec. Spatial binning by 64.
Spectral binning by 8. XBIN=8, YBIN=64
7. Data product:
Time series of atmospheric opacity versus
wavelength
8. Support required:
TBD
9. Other experiments observing:
VIMS?, CIRS?
10. Raw data rate:
FUV = 36.9 kbps = 279.8 packets/64 sec
EUV = 1.2 kbps = 8.7 packets/64 sec
11. Telemetry rate:
OCC=236 packets/64 sec. Excess stored in UVIS
memory, up to 720 packets (about 14 min.)
12. End of observation status:
TBD
13. Special:
Pointing uncertainty and gyro drift over the duration
of occultation must be less than 2 mrad. Point only
at dark limb of Saturn [Titan]
RETURN TO TABLE OF CONTENTS.
16
UISTAR OBSERVATION AND DESCRIPTION
1. Title:
Saturnian satellite stellar occultation
2. Mnemonic:
UISTAR
3. Purpose:
Search for tenuous or transient atmospheres whose
origin may be due to eruptive activity, seasonal
sublimation, or sputtering. Chord slices may
improve geodesy
4. Setup:
Point to star
HSP, FUV, and EUV on
Slit width = 8 mr
5. Observations:
Point to star starting 1000 km from satellite limb, or
3 minutes prior to limb occulting star (distance and
time depend on which satellite is to be observed).
Allow time for limb occultation of star plus any pad
necessary to allow for timing uncertainties. Do both
ingress and egress (use dark limb to subtract
scattering from bright limb). Use time between
limbs to read out UVIS memor.
6. Data handling:
Define up to 10 spectral windows in FUV and EUV.
Binning in FUV: 2 pixels in spatial window: central
16 elements. Spectral binning in EUV: 8 pixels in
spectral, 64 pixels in spatial. Readout in EUV, FUV
every 1 second. HSP: readout every 2 ms
7. Data product:
Spectra of selected portions of the FUV and EUV
range for time intervals which may be binned post
data receipt
8. Support required:
Backup imaging desirable but not necessary
9. Other experiments observing:
?
10. Raw data rate:
HSP: 33.8 packets/64 sec. FUV, EUV depend on
spectral windows
11. Telemetry rate:
OCC: 236 packets/64 sec. excess may be stored in
UVIS memory and readout partly between ingress
and egress
12. End of observation status:
set up for next observation
13. Special:
None
17
UISTAR Figure 1. Setup and slit orientation prior to occultation.
RETURN TO TABLE OF CONTENTS.
18
USUN OBSERVATION DESCRIPTION
1. Title:
Saturn [Titan] atmosphere solar occultation
2. Mnemonic:
U[S,T]SUN
3. Purpose:
Measure absorption by hydrocarbons and hydrogen
in Saturn’s [Titan’s] atmosphere
4. Setup:
Point solar occultation port to Sun
HSP, FUV off
EUV on
EUV slit: 8 x 64 mrad
5. Observations:
Point to Sun for duration of occultation (≤103
seconds), starting 2 minutes before occultation and
ending 2 minutes after Sun is lost behind Saturn
[Titan].
Sun should be recovered when emerging from
behind Saturn [Titan]
6. Data handling:
EUV read out every 2 seconds.
Spatial binning by 16 (read out 4 elements) spectral
binning by 2 (read out 512 elements.
7. Data product:
Time series of atmospheric opacity versus
wavelength
8. Support required:
TBD
9. Other experiments observing:
VIMS? CIRS?
10. Raw data rate:
18.4 kbps = 139.1 packets/64 sec
11. Telemetry rate:
OCC: 236 packets/64 sec
12. End of observation status:
TBD
13. Special:
Pointing uncertainty and gyro drift over the duration
of occultation must be less than 2 mrad
RETURN TO TABLE OF CONTENTS.
19
UHIGHSN OBSERVATION DESCRIPTION
1. Title:
High S/N FUV and EUV Spectral Imaging
2. Mnemonic:
UHIGHSN
3. Purpose:
Map target body in order to obtain high S/N FUV
spectral image cubes for chemical abundance,
aerosol profiling, and compositional albedo
4. Set-up:
Point to starting location
FUV on
EUV on.
Middle resolution:
Slit width = 150 micron (FUV)
200 micron (EUV)
5. Observations:
Point to start location. Fix pointing during exposure
and step in elevation to build up image cube as
determined by module selected. Integration period =
64 secs, so dwell time in module should be a
multiple of 64 sec. Shorter integration times may be
selected if pointing stability or other scan platform
requirements dictate. Typical observation periods at
10-100 minutes whenever spacecraft is within 100 x
object radius. Candidate targets are Saturn, Saturn’s
rings, Titan, Jupiter, Earth, Venus, asteroid, and the
icy Saturnian satellites
6. Data handling:
FUV read into UVIS data memory at raw data rate.
Data compression not used on icy satellites may or
may not be used on other targets. In the UVIS
planning process software, select windowing and
binning so that signal/noise per bin is at least 10,
number of spectral elements per bin is 2, 4 or 8,
except no spectral binning (spatial binning only) for
icy satellite targets. Expected data product is
LxMxNx9-bit image cube, where N is positions
along the scan direction and may depend on scan
rate and signal level
7. Data product:
Spectra of all or selected portions of the FUV range
for time intervals which may be binned post data
receipt
8. Support required:
Backup imaging desirable
9. Other experiments observing:
ISS, VIMS, CIRS expected
20
10. Raw data rate:
Maximum for icy satellites: no compression, no
spectral binning, no spatial binning:
16 * 1024 * 64/64 = 16.4 kbps
= 123.65 packets/64 sec
11. Telemetry rate:
Maximum for Jupiter, Saturn, Titan:
9 x 1024 x 64/64/2 = 4.6 kbps
= 34.8 packets/64 sec
ORS: 37 packets/64 sec
UVIS memory will fill in 8 minutes at maximum icy
satellite rate or in 23 minutes with SQRT9
compression
12. End of observation status:
TBD
13. Special:
None
21
UHIGHSN Figure 1. Iapetus raster
RETURN TO TABLE OF CONTENTS.
22
ULIMDRFT OBSERVATION DESCRIPTION
1. Title:
LIMB DRIFT
2. Mnemonic:
U[S,T,I]LIMDRFT
3. Purpose:
Measure limb brightness over a range of altitudes.
Determine vertical profiles of clouds, hazes,
emitters, absorbers, tenuous atmospheres
4. Set-up:
Point off limb with slit perpendicular to target
radius. FUV and EUV on. Slit width: 0.5 mr. Range
such that 0.5 mr < scale height, i.e., R < 1.E5km for
Titan
5. Observations:
Drift or roll to desired point at limb. At that point,
slit is tangent to limb. Integration period 4 sec.
Duration 2-10 min. (1000 - 2000 km in altitude).
Maximum counts expected: 1000/channel/
integration period
6. Data handling:
Sum all spatial elements along slit (bin by 64);
YBIN=64
7. Data product:
Spectra as a function of altitude
8. Support required:
Back-up imaging
9. Raw data rate:
4.6 kbps (2.3 kbps for each channel) =
0.54 packets/sec =
34.8 packets/64 sec
10. Telemetry rate:
ORS: 37 packets/64 sec
23
ULIMDRFT Figure 1. EUV, FUV slits cross terminator at beginning of drift to obtain
airglow temporal properties.
Slit crosses (tangent) limb near south pole to obtain transition from airglow to aurora. Drift
continues above the limb to obtain emission scale. Slit orientation minimizes off-axis scattering.
Spatial resolution 150 to 200 km in both dimensions of the slit. S/C range 4Rs , 0.2 x 106 km.
Spectrum will be dominated by H2 and H emission. Possible heavy ion capture spectra.
24
ULIMDRFT Figure 2. EUV, FUV low resolution slits drift across Titan disk.
Obtain spectra of darkside and airglow emissions. Slit makes near tangent crossing of terminator
to obtain transition from dark to solar stimulated atmosphere. S/C range 4RT , 0.34 x 106 km.
Spectrum dominated by N2, N, and N+ emissions. Possible detection of argon. Drift must start and
end at impact parameters of at least 2 RT.
25
ULIMDRFT Figure 3. FUV/EUV low-resolution sub-solar Titan limb scan.
Obtains emission distribution in all species from above the exobase across the planet disk. Plot
shows data from Voyager UVS at the sunlit limb in N2 c’4 (0,0) band and H (ls - 2p) emission.
The H emission signal is composed of interplanetary and planetary emissions with opacity effects.
The N2 emission is also affected by opacity. Brightness scale is shown on the plot.
26
ULIMDRFT Figure 4. Enceladus limb drift
27
ULIMDRFT Figure 5. EUV, FUV low resolution slits drift across Saturn dayside
atmosphere to determine local time structure of dayglow.
S/C range 11 RS , 0.65 x 106 km. Rings are edge-on to minimize obscuration and scattering,
allowing measurement close to equator. Obtain H2, H, and solar reflection spectrum defining
upper atmosphere properties.
28
ULIMDRFT Figure 6. EUV, FUV low resolution slits drift across Saturn terminator to
measure local time decay of dayglow into the darkside. S/C range 7 RS , 0.40 x 106 km.
29
ULIMDRFT Figure 7. EUV, FUV low resolution slits drift across Saturn dayside.
S/C range 20 RS , 1.1 x 106 km. Length of slit on planet allows measurement of latitudinal
structure of dayglow. Rings are edge-on to minimize obscuration and scattering.
RETURN TO TABLE OF CONTENTS.
30
USTARE OBSERVATION DESCRIPTION
1. Title:
Long exposure observations. Replaces UPMAGDL,
UPMAGTL, UPMAGRL, UTETERM, UTSTERM,
UTDRKH, UTELL, UTEH, UPMGTITL,
UPPOLEL, UPPOLEH, UPADKNSH, UPEQH
2. Mnemonic:
U[SYS, S, T][LIM, POL, EQT, LYA, DRK,
TRM]STARE[H]
3. Purpose:
Spectroscopy and imaging of emitters at Saturn,
Titan, and in the magnetosphere
4. Set-up:
Orient slit at appropriate target, at appropriate range
to give desired resolution and coverage. FUV
(sometimes EUV) o.
5. Observations:
Integrate for 1024 sec (sometimes 512 sec).
Continue for duration of observation, 1-10 hr
6. Data handling:
Bin by 2-4 spectral (sometimes no binning). Bin by
4-64 spatial. XBIN=2,4; YBIN=4-64
7. Support required:
Backup images useful
8. Raw data rate:
Maximum rate for one channel: 144 bps =
0.02 packets/sec = 1.09 packets/64 sec
9. Special Requirements:
Good pointing (<2 mr) required for some. See
attached originals by Shemansky
31
USTARE Figure 1. EUV, FUV high resolution deep exposure of Saturn dayside noon
local time emission.
S/C range 24 RS , 1.4 x 106 km. Rings are edge-on. This observation is designed to obtain accurate
excitation mechanism, thermal and altitude structure of H2 dayglow emission. The data will
include latitudinal distribution structure.
32
USTARE Figure 2. EUV, FUV high resolution deep exposure of Saturn dayside
early evening local time emission.
S/C range 28 RS , 1.4 x 106 km. Spectrum will include some ring reflection. This observation is
designed to obtain accurate excitation mechanism, thermal and altitude structure of H2 dayglow
emission. The data will include latitudinal distribution structure.
33
USTARE Figure 3. EUV, FUV high resolution deep exposure of Saturn dayside
early evening local time emission.
S/C range 28 RS , 1.7 x 106 km. Spectrum will include some ring reflection. This observation is
designed to obtain accurate excitation mechanism, thermal and altitude structure of H2 dayglow
emission. The data will include latitudinal distribution structure. The ends of the slit will contain
north and south pole auroral emission.
34
USTARE Figure 4-A. EUV, FUV high resolution exposures of Saturn
darkside south pole.
S/C range 3.7 - 4.7 RS , 0.22 - 0.28 x 106 km. This observation is designed to obtain high
resolution auroral spectra over as large a range in longitude as allowed by the fly-by period in
order to characterize longitudinal precipitation structure, penetration depth, and search for heavy
ion emissions.
35
USTARE Figure 4-B. EUV, FUV high resolution exposures of Saturn
dayside south pole.
S/C range 3.7 - 4.7 RS , 0.22 - 0.28 x 106 km. This observation is designed to obtain high
resolution auroral spectra over as large a range in longitude as allowed by the fly-by period in
order to characterize longitudinal precipitation structure, penetration depth, and search for heavy
ion emissions.
36
USTARE Figure 5. EUV, FUV high resolution exposures of Saturn
darkside / dayside north pole.
S/C range 6.4 RS , 0.39 x 106 km. This observation is designed to obtain high resolution auroral
spectra over as large a range in longitude as allowed by the fly-by period in order to characterize
longitudinal precipitation structure, penetration depth, and search for heavy ion emissions.
37
USTARE Figure 6. EUV, FUV high and low resolution exposures of Titan
darkside emission.
S/C range 31 RT , 0.08 x 106 km. This observation is designed to obtain as large a range in
longitude as allowed by the fly-by period in order to characterize longitudinal precipitation
structure. The projected slit is the diameter of the body, providing latitudinal distribution in a
single exposure.
RETURN TO TABLE OF CONTENTS.
38
UMAP OBSERVATION DESCRIPTION
1. Title:
Map emissions from a variety of targets. Some
similarities to UHIGHSN
2. Mnemonic:
U[SYS, S, T][NS, EW, LYA, MAG]MAP.
Replaces UTNSMAP, UTDRKLM, UPHLAM
3. Purpose:
Imaging of system, Saturn, Titan emissions
4. Set-up:
Slit = ?
Orient slit offset from appropriate target at
appropriate distance for desired resolution. FUV
(EUV sometimes) on
5. Observations:
Integrate for 512 sec. Scan or drift or step
perpendicular to slit. Repeat until coverage complete
6. Data handling:
Bin by 8 spectral and spatial (XBIN=8; YBIN=8)
7. Support required:
Backup images useful
8. Raw data rate:
18 bps/channel = 0.002 packets/sec = 0.14 packets/
64 sec
9. End of observation:
No requirements
10. Figures
Figures can be obtained from Shemansky.
RETURN TO TABLE OF CONTENTS.
39
USYSCAN OBSERVATION DESCRIPTION
1. Title:
Systematic scans of Saturn and its environment
2. Mnemonic:
USYSCAN
3. Purpose:
Search for and measure emissions while scanning
the Saturn system repeatedly west-to-east. First slew
North of Saturn; Second slew centered on Saturn;
Final slew south of Saturn
4. Set-up:
Point off Saturn with slit oriented North-South.
EUV, FUV on.
HDAC photometry mode (filaments off).
Slits: narrow early in tour (discovery mode). Wide
later (higher SNR)
5. Observations:
Slew at 32 mrad/sec for 20,000 sec (640 mr = 20 Rs
for range 31 Rs) W to E. Offset slit southward one
slit length, repeat E to W. Offset again one slitlength south, repeat W to E. Duration: approx 16 hr
6. Data handling:
No binning. Integrate for 256 sec, i.e., every 8 mr of
slew
7. Data product:
Full spectral resolution image cubes with
rectangular pixels 1 mr (N-S) by 8 mr (E-W)
8. Support required:
None
9. Other experiments:
MAPS?
10. Raw data rate:
2.3 kbps/channel = 4.6 kbps = 0.54 packets/sec
= 34.8 packets/64 sec
11. Telemetry rate:
ORS: 37 packets/64 sec
12. End of observation status:
Switch to UFPSCAN for downlink
13. Special
None
40
USYSCAN Figure 1. Raster pattern
RETURN TO TABLE OF CONTENTS.
41
UFPSCAN OBSERVATION DESCRIPTION
1. Title:
All sky observations while S/C spins during downlink
2. Mnemonic:
UFPSCAN
3. Purpose:
Measure Lyman Alpha and other emissions during fields and particles slow
rotation
4. Set-up:
HDAC photometry mode (filaments off). FUV on. EUV on. Low resolution
slits
5. Observations:
Integrate FUV EUV for 2 degree of rotation = 8 sec @ 0.26 deg/sec. HDAC
1/8 second IP. Continue for duration of DSN pass
6. Data handling:
Sum entire slit: Bin by 64 spatial (YBIN = 64)
7. Support required: None
8. Raw data rate:
72 bps (HDAC)+1152 bps (FUV)+1152 bps (EUV)=2.3 kbps =
0.01 + 0.14
+ 0.14
= 0.28 bps
.55 + 8.7
+ 8.7
= 17.94
packets/64 sec
9. TM rate to ground: DFPW = 37 packets/64 sec
10. End of observation: No requirements
11. Special requirements: None
RETURN TO TABLE OF CONTENTS.
42
APPENDICES
CASSINI UVIS INVESTIGATION DESCRIPTION
INSTRUMENT
Two channel spectrometer + High Speed Photometer + Hydrogen-Deuterium Cell
DATA PRODUCTS
Spectra, Images, Stellar and Solar Occultations, D/H
OPERATIONS
•
Stored sequences initiated by CDS command
•
Spacecraft pointing to stars, Sun, features, limbs
•
Slew, step, or drift
•
Data buffered to two rates:
1. 32 kbps (occultation)
2. 5 kbps (spectra, imaging, FPSCAN and all others)
SCIENCE OBJECTIVES
Titan abundance and chemistry:
CH4, C2H6, C2H2, H, H2, N, N2, Ar, CO,
C2N2. D/H
Titan aerosols:
Spectra 160-190 nm, vertical profiles
Thermospheric composition and energy sources
Saturn composition, chemistry, aerosols, winds
Magnetosphere remote sensing:
Neutrals and ions, sources and sinks
NI, NII, NIII, OI, OII, OIII, H, D.
Rings:
Structure, dynamics, evolution
Composition
Satellite and meteoroid
Interactions
Dust and spokes
RETURN TO TABLE OF CONTENTS.
44
INSTRUMENT CAPABILITIES
•
RING STELLAR OCCULTATIONS
•
ATMOSPHERE STELLAR OCCULTATIONS
•
ATMOSPHERE SOLAR OCCULTATIONS
•
ATMOSPHERE BRIGHT LIMB DRIFT
•
SYSTEM SCANS, F/P SCANS
•
INNER MAGNETOSPHERE EMISSIONS
•
LYMAN ALPHA ALL-SKY PHOTOMETRY
•
UPPER ATMOSPHERE EMISSIONS FROM SATURN AND TITAN
•
D/H IN TITAN, SATURN, RINGS
•
ICY SATELLITE STELLAR, SOLAR OCCULTATIONS
•
SATURN, TITAN LAT-LONG MAPS
•
PHASE COVERAGE ON SATURN, TITAN*
•
FEATURE OBSERVATIONS*
•
SPECTRAL MAPS OF ICY SATELLITES*
*
Coordinate with other remote sensing instruments
RETURN TO TABLE OF CONTENTS.
45
UVIS ANTICIPATED RESULTS
TITAN
1. Atmospheric abundances
UVIS will determine the altitudinal and latitudinal distribution and mixing ratios of CH4,
C2H6, and C2H2 via the detection of well-defined absorption features. Vertical profiles of these
molecules will be determined from limb observations and solar and stellar occultations. Solar and
stellar occultations will yield measurements of H, and H2, as well as N, N2, C 2H4, C 4H2, Ar, CO,
and C2N2. The deuterium/hydrogen ratio will be determined. It may be possible to differentiate
argon from nitrogen with UVIS in a high spectral resolution mode.
2. Atmospheric Chemistry and distribution of species; Aerosols
Horizontal and vertical distribution of active species will be detected. The photochemistry of
the atmosphere of Titan displays a rich interaction between hydrocarbons, oxygen, and nitrogen
species. The overall chemical composition can be understood in terms of a small number of chemical cycles that generate more complex compounds from the simple parent molecules (N2, CH 4,
and H2). The UVIS will make a systematic survey of all the hydrocarbon species from which
sources and sinks may be deduced.
The UVIS instrument will map the global distribution of UV-absorbing aerosols in Titan’s
atmosphere in the spectral range 160 to 190 nm. Vertical profiles of high-altitude aerosols were
seen in Titan’s atmosphere by the Voyager UVS while observing a solar occultation. This type of
measurement, as well as stellar occultations, will allow detailed vertical profiling of Titan’s high
altitude aerosols at a variety of latitudes by the Cassini UVIS.
3. Atmospheric circulation and physics
Atmospheric transport processes may be inferred from the spatial distribution of chemical
species. UVIS will search for polar vortices via the observed gradients of chemical species. The
exact variation of species abundances between the tropopause and the mesosphere depends sensitively on the nature of the vertical transport (advection and diffusion), so a precise determination
of the vertical distribution of the photochemically produced species will greatly constrain models.
UVIS mapping of the distribution of hydrocarbons will reveal the dynamics of the curious seasonal behavior of Titan’s atmosphere—the asymmetry between the northern and the southern
hemisphere at the time of the Voyager encounter, and the polar hood.
4. Upper atmosphere and relation to magnetosphere
Spectral images of UV thermospheric emission of the major nitrogen and hydrogen atmospheric species on Titan on Saturn will allow partitioning of excitation processes, determination
of energy deposition (heating) rates, and ionospheric structure. The peak in emission brightness at
the exobase may or may not be due to interaction with the magnetosphere, and the high spectral
resolution of UVIS’ EUV channel will help to answer this question: the spectral resolution of the
UVIS can provide a definitive separation of H 2C4 bands and N + emissions, giving direct diagnostic information on excitation processes.
46
SATURN
1. Atmospheric and cloud properties and composition
The UVIS will map the global distribution of UV-absorbing aerosols in Saturn’s atmosphere
in the spectral range 160 to 190 nm. The UVIS will determine the altitude-latitude distribution of
the chemical species H, H2, CH4, C2H6, C2H4, and C2H2.
2. Synoptic features and processes; winds and eddies
UVIS mapping of the hydrocarbon species will provide a basis for constructing two-dimensional models of the photochemistry, radiation and dynamics of Saturn’s atmosphere. Upwelling
brings the parent molecule CH4 from the troposphere into the upper atmosphere, where it undergoes photolytic decomposition. The products will descend into the lower stratosphere, and may be
partially converted into photochemical aerosols. The distribution of aerosols will be affected by
the meridional circulation, which in turn is caused by radiative heating due to the hydrocarbons
and the aerosols.
3. Ionospheric diurnal variations and magnetic control
The aurora on Saturn shows two distinctly different morphological characteristics. Most of the
Voyager observations show a high altitude emission from 80 deg latitude in the north and south
polar regions with an H2 band spectrum that is remarkably similar to the emission for the sunlit
equatorial region. The spectra appear to contain additional features that are compatible with transitions in N+. Much brighter spectra from deep in the thermosphere are also observed, showing the
same periodicity in apparition as the planetary rotation period. These spectra show the effects of
CH4 absorption, strong self absorption and a very weak H Lyman-alpha line, characteristic of
excitation of H2 with a very low [H]/[H2] mixing ratio. This behavior and the connection to the
magnetosphere is not clear, and the better resolution of the Cassini UVIS (as compared to Voyager’s UVS) will yield more insight into the primary processes.
4. Physical and compositional properties and evolution
In bulk composition, Saturn is a typical Jovian planet with reducing chemistry. The dominant
chemistry in the upper atmosphere is the hydrocarbon chemistry initiated by the photolysis of
CH4 and leading to the production of C2H6, C 2H4, and C2H2. The UVIS will make a systematic
survey of these major carbon species as well as H atoms. Limb observations and solar stellar
occultations will yield vertical profiles. Sources, sinks and atmospheric transport processes may
also be inferred from the spatial distribution of these chemical species.
5. Lightning (SED, whistlers)
Optical searches will be made for lightning in the FUV, in concert with other remote sensing
instruments.
47
RINGS
1. Configuration and processes
UVIS will provide high spatial resolution, low noise stellar occultations, spectroscopy, photometry, and limited imaging of the rings. Several high resolution (10 to 32 m), low noise occultation opportunities at multiple azimuths will be available during each Cassini orbit. Measurement
of these occultations will reveal ring structures with spatial variability on the scale of the larger
abundant ring particles. The true sharpness, shape, and azimuthal variability of the many sharp
edges in Saturn’s rings will be measured with a spatial resolution of approximately 20 m. Ring
thickness will be measured directly from oblique occultations of sharp edges. Closely spaced
occultations will show the time development of spiral waves, wakes, and edge waves.
2. Composition and particle size
With the UVIS operating as a spectrograph, scans and drifts will yield the aerial variation of
UV brightness across the rings showing compositional or age differences and the presence of submicron particles as postulated to form the spokes. Variations in reflectance can be interpreted in
terms of the individual particle properties like albedo and phase function because the radial profile
of extinction optical depth will be known from the occultations.
3. Interrelation with satellites
The presence or absence of phase shifts in edge waves will be determined from closely spaced
occultations. The effects of imbedded or nearby moonlets will be detected in the F ring and in the
similar rings in the gaps and the C ring region.
4. Dust and meteoroid distribution
Photometric and spectroscopic studies will identify the emissions of H and O near the rings.
Since the rings are mostly water ice, this provides a constraint on ring erosion rates. Submicron
dust will be visible in the UV: the spectral variation of reflected sunlight will establish the number
and size of dust particles near the rings.
5. Interactions with Saturn magnetosphere, ionosphere, and atmosphere
Saturn receives oxygen and nitrogen species from the magnetosphere and the rings; thus, CO
and HCN are predicted to exist in the upper atmosphere.
ICY SATELLITES
1. Characteristics and geological histories.
Regional units may be differentiated by their UV reflectance. Darkening in the UV may be an
indicator of surface age and exposure to radiation.
2. Mechanisms of modification
UVIS limb drifts and stellar occultations will be used to detect the existence of tenuous, possibly transient atmosphere, whose source may be surface activity, sputtering, or seasonal sublimation.
48
3. Composition and distribution of surface materials, especially dark, organic-rich
condensates
UV reflectivity will be used to identify and/or constrain possible composition of surface
materials. The overall phase function of surface materials including the UV is important in determining the fine structure and degree of compaction of surface materials.
4. Interactions with magnetosphere and rings
UVIS will map H Lyman-alpha throughout the Saturnian system as well as emissions from
neutrals and ions, by acquiring data during F&P rolls. A full sky map will identify the sources of
particles being detected in situ by the F&P instruments. Heavy atomic species are known to be
present in the magnetosphere. It has been argued that the heavy ions are mainly O+, derived from
sputtering of the icy satellite surfaces and subsequent H2O chemistry.
MAGNETOSPHERE
General statement: The mass content of the Saturn magnetosphere is determined almost
entirely by sources internal to the Saturn system. The magnetosphere reflects the dynamic processes in the atmospheres and surfaces of the planet and satellites, which in turn are influenced by
interaction with the magnetosphere in a partially closed system. Measurement of the content of
neutrals and ions in the magnetosphere can provide critical information on basic atmospheric
(evolutionary) processes as well as definition of magnetospheric structure. An understanding of
this complex interactive system will clearly require knowledge of the composition, distribution,
and dynamics of the magnetospheric particles. Because of the sensitivity to very weak emissions
and ability to observe the entire magnetosphere remotely, the UVIS will make a unique contribution to this understanding.
1. Configuration of magnetic field and relation to SKR
The UVIS will map H Lyman-alpha throughout the Saturnian system as well as emissions
from neutrals and ions, by acquiring data during F&P rolls. A full sky map will identify the
sources of particles being detected in situ by the F&P instruments.
2. Charged particle currents, compositions, sources and sinks
Atomic H is present in significant quantities in Saturn’s magnetosphere and has a complex
three-dimensional distribution. Lyman-alpha mapping by the UVIS will establish the relative
dominance of the hydrogen sources (e.g., Saturn exosphere, Titan, satellites, rings). The UVIS
will be able to detect emissions from N+, N++, O+ and O++.
3. Wave-particle interactions and dynamics
N/A
4. Interactions of Titan’s atmosphere and exosphere with surrounding plasmas
Spectral images of UV thermospheric emission of the major nitrogen and hydrogen atmospheric species on Titan and Saturn will allow partitioning of excitation processes, determination
49
of energy deposition (heating) rates, and ionospheric structure. The peak in emission brightness at
the exobase may or may not be due to interaction with the magnetosphere, and the high spectral
resolution of the UVIS EUV channel will help to answer this question: the spectral resolution of
the UVIS can provide a definitive separation of H2C4 bands and N + emissions, giving direct diagnostic information on excitation processes.
RETURN TO TABLE OF CONTENTS.
50
UVIS MAP CONSIDERATIONS
•
The magnetosphere is now known to be dominated by neutral gas.
•
Atomic hydrogen fills the system with radial extent of ~ 20 Rs, latitude half width of ± 8
Rs, peak density of 100 cm-3. The distribution contains structure in local time, and merges
with the top of the Saturn atmosphere.
•
OH has been observed with HST in August 1992 and again in December 1994 in observations at 4.5 and 6. Rs; no detection in an exposure at 8. Rs. All measurements were made
far from satellite positions. The latitudinal extent has not been measured, but is assumed to
be within ±.25 Rs of the orbital plane. Estimated density in the plasma sheet: [OH] = 200
cm-3 at 4.5 Rs.
•
According to model calculations, atomic oxygen is expected to be comparable in density
to OH, giving a total estimated neutral density in the plasma sheet at 4.5 Rs of ~500 cm-3.
The neutral/ion mixing ratio is then ~20, indicating that the neutral gas controls the local
electron temperature, limiting the development of the plasma sheet.
•
It is likely that UVIS will be the only facility to detect and map the distribution of atomic
oxygen, given the present estimate of abundance.
•
Given the large abundance of water products in the magnetosphere, it is likely that other
species from sputtering, desorption, and impact phenomena, such as alkali metals, will be
detected with the sub-Rayleigh capability of the UVIS, given sufficient exposure time.
RETURN TO TABLE OF CONTENTS.
51
DATA AND PACKET PRODUCTION RATES
1. DATA PRODUCTION
The rate that data are produced from a given observation is calculated as follows:
A. No Window
For each channel, the data production rate (DPR) is:
Compression
Channel
[16 (no compression)]
[1 (HDAC]
or
or
[9 (SQRT9)]
* [1024 * 64 (EUV, FUV)]
or
or
[8 (8BIT, SQRT8)]
[1 (HSP)]
IP:
Integration
* [IP]-1
Binning
* [XBIN * YBIN]-1
Integration period in seconds
0.125 for HDAC
0.002 for HSP
XBIN:
spectral binning
YBIN:
spatial binning
This yields data production rate in bits/sec.
B. Window
For windowing in EUV and FUV, replace 1024 * 64 by the total window area in CODACON
pixels.
2. PACKET PRODUCTION
The packet production rate for each channel is the data production rate divided by the packet
data volume, PDV.
For HDAC
8432
For HSP
8512
For EUV, FUV
8480 - (Windows - 1) * 48
52
(up to 10 windows)
The total instrument packet production rate is the sum from all the channels:
PPR =
∑
DPR/PDV
3. EXAMPLES
a) HDAC, SQRT9
DPR = 9 * 1 * 8 = 72 bps
PPR = DPR/PDV = 72 / 8432 = 8.54 x 10-3 packets / sec
= 0.55 packets / 64 sec
b) HSP, SQRT9, IP = 2ms
DPR = 9 * 1 * 500 = 4500 bps
PPR = DPR / PDV = 4500 / 8512 = 5.29 x 10-1 packets / sec
= 33.8 packets / 64 sec
c) EUV, SQRT9, IP = 1 sec, no windows, no binning
DPR = 9 * 1024 * 64 * 1 * 1 = 589,824 bps
PPR = 589,824 / 8480 = 69.55 packets / sec = 4451.5 packets / 64 sec
d) Sum of HDAC, HSP, EUV as in a) b) c):
0.55 + 33.8 + 4451.5 = 4485.9 packets / 64 sec
4. INTERNAL MEMORY AND TELEMETRY RATES
UVIS can store up to 720 packets in its internal memory.
The planned packet pickup rates for UVIS are:
Operation Mode
Telemetry Mode
UVIS TM Rate1
ORS
S&ER-1 (OCC)
236 packets every 64 seconds
ORS
S&ER-2 (Titan)
236 packets every 64 seconds
ORS
S&ER-3 (Saturn-1)
236 packets every 64 seconds
ORS
S&ER-4 (Saturn-2)
37 packets every 64 seconds
ORS
S&ER-5 (IcySat-1)
37 packets every 64 seconds
53
1
ORS
S&ER-6 (IcySat-2)
37 packets every 64 seconds
ORS
Alt-5 (Radar Alt)
37 packets every 64 seconds
DFPW
-----
37 packets every 64 seconds
These rates correspond to 32 kbps and 5 kbps.
RETURN TO TABLE OF CONTENTS.
54
MINIMUM INTEGRATION PERIODS
The UVIS CODACONs use a double buffering mechanism. Each CODACON has two 64Kword memory banks, and the software alternates filling and emptying these banks. Thus, while
one bank is being used to integrate, the flight software empties the other memory bank. Since the
software toggles between memory banks after each integration period, the integration period must
be long enough to empty the filled data memory bank, or data will be lost.
Further, when both EUV and FUV channels are producing data, the processor alternates
between the channels. Thus, the active memory banks for each channel must both be emptied
during the defined integration period. In this case, the integration period must exceed a value
twice that for a single channel observation.
Allowed integration periods are in increments of 0.125 seconds, starting at 0.25 seconds.
Because of the speed limitations of our processor, some of these commandable integration periods
may be too short for the actual processor performance, and data will be lost.
To calculate the minimum time to empty the memory banks, and thus the minimum integration period for any particular observation, use the following formula for ∆T (msec).
∆T = [7.85 *CTF +
NPIXELS
0.5 * CCN + 0.32 * CF] ------------------------ * OHF
64
CTF:
compression time factor (1.0 for no compression or 8-Bit; 1.5 for SQRT-9).
CCN:
1.0 for only one CODACON;
0.5
for two CODACONs integrating.
CF:
compression factor (1.0 for no compression, 0.56 for SQRT-9, 0.5 for 8-Bit).
NPIXELS: total number of pixels produced per integration, given windowing and binning,
per CODACON.
OHF:
overhead factor to service downlink and accommodate HSP interrupts. Use
1.01 for no HSP; 1.17 for HSP.
The first term in brackets represents the time to loop through one column in the
integrationbank.
The second term in brackets gives the overhead for looping.
The last term gives the packet production overhead.
NPIXELS / 64: number of columns in the integration bank filled during one integration.
For both channels operating, multiply ∆T * 2.
EXAMPLES
1. FUV channel only, XBIN=1, YBIN=1 (full resolution, no binning). No compression (16 bitwords).
∆T = [7.85 * 1.0 +
0.5 * 1.0
64 × 1024
+ 1.0 * 0.32] ------------------------ * 1.0
64
= [8.67] * 1024 * 1.01 = 8967 ms
Check: measured ∆T (from EMU) : 9.0 sec.
2. FUV: XBIN=1, YBIN=1 (full resolution, no binning)
EUV: XBIN=1, YBIN=1 (full resolution, no binning)
HSP: on , IP=0.002 sec
∆T = 2 * [ 7.85 * 1.0 +
0.5 * 0.5
64 × 1024
+ 1.0 * 0.32] ------------------------ *1.17
64
= 20,775 ms
Check: measured ∆Τ (from EMU): 19.125 sec.
MAXIMUM DATA TAKING RATES FOR FUV AND/OR EUV
With SQRT-9 compression and HSP on, the maximum data rate is given by:
NPIXELS
64
------------------------ = ------------ [7.85 * ctf +
∆T
OHF
0.5 * CCN +
0.32 * cf] -1
64
= ---------- [12.7 ms] -1
1.17
= 4307 pixels / sec
= 292 packets / 64 sec (CODACONS)
= 326 packets / 64 sec (including HSP).
Note that this rate only moderately exceeds our maximum assigned pickup rate of 236 packets /
64 seconds: the processor speed does not allow us to take data at rates much exceeding the
pickup rate.
SETUP TIME
10 seconds per CODACON.
RETURN TO TABLE OF CONTENTS.
COMPRESSION ALGORITHMS
Four compression algorithms are currently defined in the RAM code:
Compression Algorithm
Purpose
No Compression
All 16 bits are returned
8-Bit
Only the low 8 bits are returned
SQRT-9
The compressed value is returned using 9 bits
and is computed using the following algorithm:
If value > 128
Comp. Value = SQRT (value * 2) + 128
Else
Comp. Value = Value
End if
SQRT-8
Same as SQRT-9, but only the low 8 bits are
returned
Note: Each EUV and FUV window is defined using four parameters: (1) the upper left corner
coordinates of the window, (2) the lower right corner coordinates of the window, (3) the spatial
binning to used, and (4) the spectral binning to be used. The window corners are defined in a 0 to
1023 (spectral dimension) * 0 to 63 (spatial dimension) space. In the spectral dimension, the
wavelength increases with the position. Binning in the spectral dimension can be from 0 (no binning) to 1023 (all spectral information is compressed into one measurement). Binning in the spatial dimension can be from 0 (no binning) to 63 (all spatial information is compressed into one
measurement).
RETURN TO TABLE OF CONTENTS.