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--- science_cases:aop_science_case [2020/11/27 09:25] – admin
+++ science_cases:aop_science_case [2020/11/27 09:39] (current) – admin
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 The scientific risk is that the search does not place a meaningful constraint on the existence of these asteroids.
+===== Information on the spacecraft, instruments and data =====
+**Which spacecraft? STEREO A(head), STEREO B(ehind)**
+The twin STEREO spacecraft were launched aboard a single Delta II rocket from Cape Canaveral Air Force Base at 01:52 UT on 26 October 2007 (8:52 pm EDT on 25 October). Contact with STEREO-B was lost in 2014, but STEREO-A is still operational.
+**Which insturments? SECCHI Heliospheric Imagers (HI-1, HI-2)**
+SECCHI is a set of remote sensing instruments designed to follow Coronal Mass Ejections (CMEs) from their origins on the Sun, out through the corona and the interplanetary medium and to possible impact with the Earth. HI1 and HI2 are externally occulted coronagraphs that image the inner heliosphere between the Sun and the Earth between 12-215 solar radii.
+One of the scientific goals of the instrument is to observe asteroids. Papers on asteroid observations by SECCHI HI:
+  * Phaethon: Jewitt & Li 2010; Jewitt et al. 2013; Li & Jewitt 2013; Hui & Li 2016
+  * Vulcanoids: Steffl et al, 2013
+The HI detectors are CCDs with 2048 x 2048 pixels, where each pixel has a size of 13.5 x 13.5 μm. These are usually binned on board to 1024 x 1024 bins, resulting in image bin angular sizes of 70 arcsec and 4 arcmin, for HI-1 and HI-2 , respectively. Short exposures are taken and cleaned of cosmic rays on board, and a number of such exposures are then summed to produce an image to be down-linked.
+HI-1 images are recorded in sequences of 30 exposures of 40 sec each. These are summed to produce a single image with 40 min cadence. HI-2 images are recorded in sequences of 99 exposures of 50 sec each. These are summed to produce a single image with 2 hr cadence. Exposure cadence is 60 sec. A total of 36 summed images for HI-1, and 12 for HI-2, are taken every 24 hr.
+**Cosmic ray rejection**
+The individual exposures are scrubbed to remove cosmic ray events. The algorithm used compares each new image with the previous image on a pixel-by- pixel basis – if the signal in a given pixel exceeds that in the previous image by more than a defined threshold, then the value for that pixel is replaced by the previous value. The threshold normally used is 5σ, where σ is the predicted noise standard deviation based on the number of photoelectrons detected.
+In addition to the image processing described above for HI science operations, the SEB software also permits other types of images to be down-linked for calibration and engineering purposes, including (i) single full-resolution CCD exposures with 2048 x 2048 pixels, (ii) single 2 x 2 binned exposures, and (iii) exposures which still include the under-scan and over-scan regions. The SEB also produces more highly compressed and binned versions of the summed images which are downlinked in real-time via the STEREO Space Weather Beacon (see Section 9.4).
+The HI-A door was opened on 13 December 2006, two days before STEREO-A lunar swing-by. The HI-B door was deployed on 11 January 2007. The science operations phase for HI commenced at the beginning of April 2007, although observations of scientific importance were made before this time
+Technical Description of SECCHI HI-1 and HI-2: [[http://www.stereo.rl.ac.uk/Documents/firstHI_Instrument_Paper_Revised_v2.pdf|http://www.stereo.rl.ac.uk/Documents/firstHI_Instrument_Paper_Revised_v2.pdf]]
+HI data analysis User Guide: [[https://www.stereo.rl.ac.uk/Documents/HI_user_guidejuly.pdf|https://www.stereo.rl.ac.uk/Documents/HI_user_guidejuly.pdf]]
+How to browse data: [[https://stereo.nascom.nasa.gov/cgi-bin/images|https://stereo.nascom.nasa.gov/cgi-bin/images]] (browse images in jpg format, can choose the resolution from 128×128 to 2048×2048)
+Retrieve data: [[https://stereo.nascom.nasa.gov/data/ins_data/secchi/L0/b/img/hi_2/|https://stereo.nascom.nasa.gov/data/ins_data/secchi/L0/b/img/hi_2/]] \\
+(example above for STEREO Behind Level 0 data from HI-2; data is sorted by date,so directory 20071105 \\
+contains data obtained on that date)
+The data may also be retrieved from the JHU APL mirror site, e.g. [[http://sd-www.jhuapl.edu/secchi/lz/L0/b/img/hi_2|http://sd-www.jhuapl.edu/secchi/lz/L0/b/img/hi_2]]
+**Other ways of retrieving the data **
+  * Using wget and curl:
+[[https://stereo-ssc.nascom.nasa.gov/ftp_deactivation.shtml|https://stereo-ssc.nascom.nasa.gov/ftp_deactivation.shtml]]
+[[https://stereo.gsfc.nasa.gov/curl.shtml|https://stereo.gsfc.nasa.gov/curl.shtml]]
+  * Through IDL, Using the SolarSoft (SSW) package
+<code>
+Example script:
+files =VSO_SEARCH('YYYY-MM-DD hh:mm:ss','YYYY-MM-DD
+hh:mm:ss',source='STEREO_A',instrument='SECCHI',detector='COR2')
+(where the first date string is the start of the period of interest, and the second one is the end of the period of interest)
+datafiles = VSO_GET(files, /FORCE, /QUIET)
+</code>