Data from the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) suite of instruments on board the NASA Solar TErrestrial RElations Observatory (STEREO) spacecraft, from 2006-12-13 onwards.

The UK Solar System Data Centre (UKSSDC) holds datum from the Sun Earth Connection Coronal and Heliospheric Investigtion (SECCHI). SECCHI is a suite of instruments on board NASA's twin Solar TErrestrial RElations Observatory (STEREO)spacecraft. These spacecraft monitor the Sun from two different points, making a 3D description of solar events possible.

The SECCHI suite consists of 5 cameras:

EUVI
Extreme UltraViolet Imager - Images the full solar disk in 4 different wavelengths [He II 30.4 nm, Fe IX 17.1 nm, Fe XII 19. 5nm, Fe XV 28.4 nm]
COR1
A classic Lyot internally occulting refractive coronagraph, with a field of view is from 1.3 to 4 solar radii. A linear polarizer is used to suppress scattered light, and to extract the polarized brightness signal from the solar corona.
COR2
An externally occulted Lyot coronagraph, with a field of view from 2.5 to 15 solar radii.
HI_1
Heliospheric Imager 1 - white light camera with a 20 degree field of view centred 14 degrees off the Sun in the ecliptic plane.
HI_2
Heliospheric Imager 2 - white light camera with a 70 degree field of view centred 54 degrees off the Sun in the ecliptic plane.

Datum from each of these cameras is available at processing level 0.5 (see below).
Datum from the HI instruments is available at processing levels 1 (see below) and 2 (see below). The primary goal of these instruments is to detect and describe Coronal Mass Ejections (CME's), in particular halo CME's (Earth-bound CME's).

Processing Levels

Level 0.5 :
Data processed to level 0.5 is downloaded from the Naval Research Laboratory, Washington DC.

Level 1:
HI data is then subsequently processed to level 1 by the UKSSDC. This means that the images have been processed by the SECCHI_PREP routine to remove the effects of the the shutterless readout and to apply a flatfield. The treatment can be roughly broken down as follows:
1. Reject corrupted images - a list is maintained of images that were badly corrupted in processing and transmission - these images are not processed to level 1.
2. Extract cosmic ray report - [only present in s4 images]. The pixels are replaced by a duplicate of the line below to allow subsequent processing.
3. Remove columns where saturation has occurred on the CCD - due to there being no shutter on the camera it is not in general possible to recover columns where saturation has occurred. Bright stars and planets often saturate.
4. De-smear the image - by applying a matrix multiplication algorithmically remove the smear caused in clearing and readout of the CCD. This process automatically normalises the exposure time to 1 second and removes the summing effect in the s4 images.
4. Remove pixels marked as having missing telemetry from the image.
5. Apply a calibration factor to the image - currently this allows for the geometric effect in the lenses and for a linear production feature in the CCD.
The pointing information in the header is updated by reference to the observed starfield.

Level 2:
Level 1 images are then processed to remove light scattered from the f and k coronas. These images a dubbed level 2.
Level 2 processing involves:
1. Selecting a running window of 1 or 11 days
2. Selecting the lowest 25% of the data within that window
3. Forming an average of that on a pixel by pixel basis
4. Subtracting this from the original image
This forms the L2_1_25 and L2_11_25 data sets, depending on whether a 1 or 11 day running window has been used.