SECCHI is a suite of five telescopes, with two identical SECCHI suites operating on both NASA STEREO satellites (and only operational on STEREO-A since 2014). The five telescopes are as follows:
- Heliospheric Imager-2 ("HI-2")
- Heliospheric Imager-1 ("HI-1")
- Coronagraph 2 ("COR-2")
- Coronagraph 1 ("COR-1")
- Extreme Ultraviolet Imager ("EUVI")
Each of these telescopes returns a number of different data products, with both the data volume and type variable throughout the entire mission. When searching for SECCHI data from the online database, the following parameters/terms may be encountered.
- Spacecraft: Ahead or Behind
- Telescope/Instrument: EUVI, COR1, COR2, HI1, HI2
- Destination: SSR1 (synoptic program), SSR2 (event partition), Spaceweather/Beacon (low resolution), Realtime Downlink (early ops only). NOTE: During Sidelobe operations, all images come down the Beacon channel.
- Data Source: Usually LZ
- Data Type:
- Intensity (img): EUVI, HI, and COR2 DOUBLE (two polarizer positions)
- Polarized (seq): COR1 and COR2 single polarizer position images
- Calibration (cal): LED, DARK, etc.
- Intensity+Polarized: both img and seq (COR2 only)
- TBPP: Total Brightness and Percent Polarized images in $SECCHI_P0 at NRL
- EUVI Quadrant: 171A, 195A, 284A, 304A
- COR Polar: Usually 0, 120, or 240
For the heliospheric imagers, HI-1 and HI-2, most observations are recorded as an on-board summed exposure of approximately 40-minutes in total duration, and at half resolution (1024x1024). However, the first image of the day is typically a full-resolution (2048x2048) single exposure image.
For the coronagraphs, data can appear as either polarization sequences or double exposures, with the weaving together of these observations dictated primarily by available telemetry (which itself varied throughout the mission). Likewise, image sizes have varied throughout, with full-resolution (2048x2048) observations at high cadence available when the spacecraft were close to Earth, and only a limited number or reduced resolution data available as the spacecraft approached conjunction in 2014/2015.
The EUVI observations are available in the four channels stated, with telemetry priority given to the 171A and 304A channels. Again, the returned data volume has varied throughout the mission as a function of available telemetry.