·

Note for Solarwatchers: SOHO EIT is in “the keyhole”

note-for-solarwatchers-soho-eit-is-in-the-keyhole

We recieve lots of questions from our readers considering SOHO EIT data. SOHO’s near-real time images from EIT instruments stop uploading in January 6, however there is nothing wrong with SOHO instruments  because EIT is in a telemetry keyhole. The lack of fresh images came as no surprise to the SOHO science community. And they may have stumbled across the rather cryptic terms “keyhole”, as in “keyhole period” or “keyhole operations”. (You can observe similar images via SDO AIA)

The term “keyhole”, in antenna terminology, stems from a characteristic feature of aerial navigation maps showing the coverage of e.g. a radar antenna: A circular area near the antenna is shaded due to too-short range. In addition, any obstructions (hilltops, buildings) near the antenna will cause wedges to be shaded due to lack of coverage. Taken together, the appearance of the shaded area is often that of a keyhole. The term has since been generalised to refer to any area not covered by an antenna.

In order to get a good downlink signal, SOHO’s High Gain Antenna (HGA) needs to be pointed correctly as the spacecraft traverses its highly elliptical orbit around the L1 Lagrangian point, some 1.5 million kilometres sunward of the Earth. SOHO has “keyhole periods”, occurring twice per orbit. Each orbit around L1 takes about half a year, so keyholes affect SOHO operations roughly every 3 months.

 

ESTIMATED DATES OF FUTURE SOHO KEYHOLES

2011 11-Jan-11 15-Jan-11 26-Jan-11 30-Jan-11
12-Apr-11 15-Apr-11 23-Apr-11 25-Apr-11
08-Jul-11 12-Jul-11 24-Jul-11 28-Jul-11
10-Oct-11 13-Oct-11 20-Oct-11 23-Oct-11
--------------------------------------------------------------------------
2012 02-Jan-12 06-Jan-12 17-Jan-12 21-Jan-12
02-Apr-12 04-Apr-12 12-Apr-12 15-Apr-12
27-Jun-12 01-Jul-12 13-Jul-12 18-Jul-12
30-Sep-12 02-Oct-12 10-Oct-12 13-Oct-12
23-Dec-12 27-Dec-12 07-Jan-13 11-Jan-13
--------------------------------------------------------------------------
2013 23-Mar-13 26-Mar-13 04-Apr-13 06-Apr-13
18-Jun-13 22-Jun-13 04-Jul-13 08-Jul-13
20-Sep-13 23-Sep-13 01-Oct-13 04-Oct-13
13-Dec-13 17-Dec-13 29-Dec-13 02-Jan-14
--------------------------------------------------------------------------
2014 11-Mar-14 15-Mar-14 26-Mar-14 30-Mar-14
02-Jun-14 09-Jun-14 26-Jun-14 04-Jul-14
08-Sep-14 12-Sep-14 23-Sep-14 27-Sep-14
30-Nov-14 07-Dec-14 23-Dec-14 30-Dec-14
--------------------------------------------------------------------------
2015 02-Mar-15 06-Mar-15 17-Mar-15 21-Mar-15
24-May-15 31-May-15 16-Jun-15 24-Jun-15
--------------------------------------------------------------------------


 

SOHO website

All images credits:  “Courtesy of SOHO/ consortium. SOHO is a project of international cooperation between ESA and NASA.”

If you value what we do here, create your ad-free account and support our journalism.

Share:

Producing content you read on this website takes a lot of time, effort, and hard work. If you value what we do here, select the level of your support and register your account.

Your support makes this project fully self-sustainable and keeps us independent and focused on the content we love to create and share.

All our supporters can browse the website without ads, allowing much faster speeds and a clean interface. Your comments will be instantly approved and you’ll have a direct line of communication with us from within your account dashboard. You can suggest new features and apps and you’ll be able to use them before they go live.

You can choose the level of your support.

Stay kind, vigilant and ready!

$5 /month

  • Ad-free account
  • Instant comments
  • Direct communication
  • New features and apps suggestions
  • Early access to new apps and features

$50 /year

$10 /month

  • Ad-free account
  • Instant comments
  • Direct communication
  • New features and apps suggestions
  • Early access to new apps and features

$100 /year

$25 /month

  • Ad-free account
  • Instant comments
  • Direct communication
  • New features and apps suggestions
  • Early access to new apps and features

$200 /year

You can also support us by sending us a one-off payment using PayPal:

2 Comments

Leave a Reply to The Watchers - Solar monitors offline?! Cancel reply

Your email address will not be published.