Color Picture of SSI
Camera
| General | |
|---|---|
| Mass | 28 kg |
| Peak power | 23 W |
| Dimensions | 90 x 25 x 30 cm³ |
| Optical | |
| Focal length | 1500 mm |
| Field-of-view | 8.1 mrad |
| Angular resolution | 10.16 µrad/pixel |
| Camera speed | F/8.5 T/10.8 at 576 nm |
| Filter positions | 8 |
| Minimum exposure time | 4.167 ms |
| Maximum exposure time | 51.2 s |
| Detector | |
| Type | Silicon Virtual Phase CCD |
| Dimensions | 12.19 x 12.19 mm |
| Pixel density | 65.6 pixels/mm |
| Pixel format | 800 x 800 |
| Pixel full-well capacity | 108,000 e¯ (normal modes) 432,000 e¯ (summation mode) |
| Noise floor | ±30 e¯ |
| Signal digitization | 8 bits, 256 DN |
| 1 DN (low gain state) | 379 e¯ |
| Gain state factors | 1:4.8:9.8 |
| Nonlinearity | 0.2 DN (normal modes) 0.45 DN (summation mode) |
| Charge transfer efficiency | 0.99997 |
| Dark counts | <10 e¯/s·pixel |
| Frame times for operating modes | |
| Summation mode (2 x 2 pixel) | 2.333 s 15.1667 s |
| Normal modes* | 60.667 s 30.333 s |
| Full-resolution record mode | 8.667 s |
| Tape recorder characteristics for SSI data | |
| Transfer rate | 8.064x10^5 bits/s |
| Maximum storage (images): | |
| Summation mode | 478 |
| 60 2/3 | 128 |
| 30 1/3 compressed | 257 |
| 8 2/3 | 128 |
| 8 2/3 compressed | 257 |
*Normal modes can either be recorded or channelled directly for real-time transmission. The summation mode must be recorded. In the normal modes the data can, if necessary, be compressed by a factor of approximately 2.5 in either an information preserving fassion (lines may be truncated), or in a non-information preserving (lines are complete but pixel values may lose accuracy).
* FOR LEFT HALF OF FRAME ONLY, RIGHT SIDE HAS NON-LINEARITY OF UP TO 4.6%
| Exposure Number | Exposure Time (ms) Phase 1 |
Exposure Time (ms) Phase 2 |
Exposure Limit |
|---|---|---|---|
| 0 | 0 | 0 | |
| 1 | 4-1/6 | 4-1/6 | |
| 2 | 6-1/4 | 6-1/4 | |
| 3 | 8-1/3 | 4-1/6 | |
| 4 | 12-1/2 | 12-1/2 | |
| 5 | 16-2/3 | 12-1/2 | |
| 6 | 25 | 20-5/6 | |
| 7 | 33-1/3 | 29-1/6 | |
| 8 | 50 | 45-5/6 | |
| 9 | 66-2/3 | 62-1/2 | |
| 10 | 100 | 95-5/6 | |
| 11 | 133-1/3 | 129-1/6 | |
| 12 | 200 | 195-5/6 | |
| 13 | 266-2/3 | 262-1/2 | |
| 14 | 400 | 395-5/6 | Longest normal exposure for 2-1/3 s mode |
| 15 | 533-1/3 | 529-1/6 | Longest normal exposure for 15-1/6 s mode |
| 16 | 800 | 795-5/6 | Longest normal exposure in 8-2/3 s, 30-1/3 s and 60-2/3 s mode |
| 17 | 1,066-2/3 | 1,062-1/2 | |
| 18 | 1,600 | 1,595-5/6 | Longest extended exposure, 2-1/3 s mode |
| 19 | 2,133-1/3 | 2,129-1/6 | |
| 20 | 3,200 | 3,195-5/6 | |
| 21 | 4,266-2/3 | 4,262-1/2 | |
| 22 | 6,400 | 6,395-5/6 | Longest extended exposure, 8-2/3 s mode |
| 23 | 8,533-1/3 | 8,529-1/6 | |
| 24 | 12,800 | 12,795-5/6 | Longest extended exposure, 15-1/6 s mode |
| 25 | 17,066-2/3 | 17,062-1/2 | |
| 26 | 25,600 | 25,595-5/6 | Longest extended exposure, 30-1/3 s mode |
| 27 | 34,133-1/3 | 34,129-1/6 | |
| 28 | 51,200 | 51,195-5/6 | Longest extended exposure, 60-2/3 s mode |
| 29 | 0 | 0 | Exposure number 29 occurring in image parameter telemetry is used to identify dark current calibration frames. This exposure number also causes picture count to increment. |
| 30 | 0 | 0 | |
| 31 | 0 | 0 |
| Filter Name | Filter Number | Effective Wavelength (nm)** | Passband (nm) *** | +Sensitivity (w cm¯² ster¯¹ nm¯¹) | *Sensitivity (DN ms¯¹) |
|---|---|---|---|---|---|
| Clear | 0 | 625 | 440 | 5.84 X 10-8 | 30.9 |
| Violet | 3 | 414 | 45 | 2.06 X 10-6 | 0.900 |
| Green | 1 | 559 | 65 | 4.89 X 10-7 | 4.45 |
| Red | 2 | 664 | 60 | 3.74 X 10-7 | 4.86 |
| "Methane" (7270) | 6 | 731 | 10 | 3.79 X 10-6 | 0.411 |
| "Continuum" | 4 | 757 | 19 | 1.88 X 10-6 | 0.780 |
| "Methane" (8890) | 7 | 888 | 16 | 6.91 X 10-6 | 0.165 |
| "Infrared" | 5 | 990 | 50 | 5.99 X 10-6 | 0.152 |
+ Radiance needed to produce a signal of 1 DN ms-1 in the low gain state
assuming constant spectral radiance across the filter bandpass.
*
Sensitivity at 5.2 AU for a scene of unit reflectivity illuminated by sunlight.
** Assumes a solar spectrum.
*** Full-width at half maximum.
For the Science paper, the effective wavelengths of the SSI system response through various filters are quoted numerous times. The values quoted are in many cases not consistent with the latest SSI calibration results and are often inconsistent with each other.
Here are the latest best estimates of the SSI effective wavelengths in nm for several target bodies:
| Clear | Violet | Green | Red | 727 | 756 | 889 | 1um | |
|---|---|---|---|---|---|---|---|---|
| Solar | 626 | 414 | 559 | 664 | 731 | 757 | 888 | 990 |
| Avg Europa | 636 | 416 | 559 | 664 | 731 | 757 | 888 | 989 |
| Avg Gany | 637 | 415 | 560 | 664 | 731 | 757 | 888 | 989 |
| Avg Io | 644 | 418 | 560 | 664 | 731 | 757 | 888 | 990 |
| GRS | 621 | 415 | 559 | 664 | 732 | 757 | 886 | 991 |
Also, the width of the red bandpass, quoted in the Io section of the paper, is +/-30 nm (FWHM) or +/-40 nm at the 10% of max response level or +/-45 nm at the 1% of max level, but not +/-60 nm.
The effective wavelengths are probably not known to better than 2 or 3 nm I would guess. I recommend that we either consistently use the above values for the solar spectrum everywhere in the paper or that the above wavelengths for each target body be used when discussing the individual targets in their respective sections, and that we not use any obsolete values.
SSI spectral response to a constant source of radiance of (pi)¯¹ watts m¯² ster¯¹ nm¯¹ through each of its eight filters.
Limiting Stellar Magnitudes Through Clear Filter
| Frame No. | Exposure (sec) | Gain | Filter | Lim. Mag. |
|---|---|---|---|---|
| 1 | 0.200 | 10K | Clear | 10.2 |
| 2 | 0.133 | 10K | Clear | 9.8 |
| 3 | 0.100 | 10K | Clear | 9.4 |
| 4 | 0.050 | 10K | Clear | 8.7 |
| 5 | 0.100 | 100K | Clear | 7.4 |
Plot of the point spread functions for two SSI filters (990 and GRN). In the SSI lunar data, the largest ammount of attenuation due to scattered light is observed in the 990-filter data and the least ammount is observed in the GRN-filter data. For a given wavelength, this function describes attenuation of illumination on a single-source pixel due to scattered light (shown as the logarithm, or 10^-n, of the attenuation factor n in inverse steradians) in the 990-nm and 560-nm Galileo SSI filters. To determine the scattered light expected for a single pixel, multiply the attenuation factor for the pixel (at a desired distance) by the illumination at that pixel. For evaluation of scattered light for an entire image, contributions from individual source pixels are summed over the whole image.
Contact for Content: Kenneth P. Klaasen
Homepage creator: Matthew Fishburn
Last updated: February 09, 2000
Schematic of SSI
Camera