The Scripps-Earth Polychromatic Imaging Camera (Scripps-EPIC) provides high resolution images of the Earth from the L-1 orbit. The camera consists of a Cassegrain telescope with a 12-inch aperture and a 0.62° field of view, mated to a 10-color filter-wheel assembly and shutter, followed by a 4 mega-pixel, UV-sensitive charge coupled device (CCD). Performance characteristics of EPIC are provided in Table A-1.
The 10 filters are contained in two filter wheels. The three shutter apertures provide nominal exposure times of 2 ms, 10 ms, and 40 ms or greater. Exposures of 40 ms or greater are obtained by varying the motor speed. Intermediate exposures (between 2 ms and 40 ms) are obtained by up to 8 multiple exposures of the 2- and 10-ms apertures. These multiple exposures can be made on a 100 ms cadence.
The focal plane is a 2048 x 2048 CCD, backside-thinned and backside-illuminated to optimize quantum efficiency down to 300 nm (modified LMFS-type CCD 442A). The CCD is passively cooled to -40°C on orbit to reduce dark current and other noise effects. Commands from the ground or as a result of on-board pre-planned sequences are sent to the EC to request images, initiate on-board image processing, or collect EPIC instrument status and housekeeping data. The EC includes sufficient on-board memory (320 MB) to store a large number of images in various stages of processing or compression. The flight software includes CCD flat-fielding, thresholding, region-of- interest selection, and the ISO-standard 12-bit JPEG compression algorithm as image processing options. Unprocessed raw CCD frames can also be provided for downlink. The number and type of images that can be sent to the ground are only limited for practical purposes by the Triana telemetry capacity and the amount of on-board image processing or compression.
Telescope: Cassegrain, with adjustable secondary for on-orbit focus
| Aperture | 12.00 inches |
| Effective focal length | 111.1 inches |
| Field of view | 0.62 degrees |
| 0.62 degrees | 0.054 waves RMS at 633 nm on-axis |
| A 3-element field lens | group provides off-axis corrections |
Filters:
| Wavelength (nm) | Full Width (nm) | Purpose |
| 317 | 1 | Ozone, SO2 |
| 325 | 1 | Ozone |
| 340 | 3 | Aerosols |
| 388 | 3 | Aerosols, Clouds |
| 393.5 | 1 | Cloud Height |
| 4435 | 10 | Blue, Aerosols |
| 551 | 10 | Green, Aerosols |
| 645 | 10 | Red, Aerosols |
| 870 | 15 | Clouds, Aerosols |
| 905 | 30 | Water Vapor |
Shutter:
Individual exposure times of 2 ms, 10 ms, and 40 ms to >1 minute
Multiple exposures for timings between 2 ms and 40 ms, at 2 ms resolution
Focal plane:
| CCD format | 2048 x 2048 pixels |
| Pixel size | 15 microns x 15 microns, 100% fill factor |
| CCD type | Thinned, backside illuminated |
| Spectral range | 200 - 950 nm (QE > 25%) |
| Pixel full well depth | >80,000 electrons |
| Digital intensity conversion | 0 - 4095, 12 bits at 20 electrons per bit |
| Readout | Single or dual (opposite corners) |
| Pixel readout rate | 500 kHz |
| CCD operating temperature | -40°C, by passive cooling |
| Dark current | <5 electrons per second per pixel |
| Readout noise | <20 electrons RMS |
Minimum image cadence >15 seconds
Image output formats: Raw (bit map) and 12-bit JPEG/JGIF
Instrument power (normal operations):
| Electronics | 32 W |
| Operational heaters | 30 W |
| Total | 62 W |
Instrument mass:
| CTA | 6.8 kg |
| MEB | 3.2 kg |
| EC | 55.0 kg |
| Total | 65.0 kg |