NOAA satellite images for SSO observers

The images received from the low-earth-orbit NOAA satellites are similar to those from the Japanese geostationary satellite, GMS-5.  GMS-5 is the source of most Australian weather sat imagery, such as that presented on TV, and on the Bureau of Met ,  James Cook Uni satellite image web sites.  There are other NOAA receiving stations in Australia, but images presented on this web site are generated by a seriously clever computer program known as WXtoImg, and are different from GMS-5 images in a few key ways:


As with the IR images produced from GMS-5, clouds are easiest to spot when at higher altitudes, when they are cold relative to the ground.  Low level cloud does not show up well on the nighttime MCIR images.

The NOAA satellites orbit at just over 800km altitude, and along their orbital track they scan a swath of Earth about 2800km wide.  Many orbital passes received at SSO are so distant that SSO is left off-the-map, but images posted on these web pages are selected so that SSO always appears on the image, even if at an extreme edge.

At present there are four active NOAA satellites generating images displayed at this site, namely NOAAs 12, 15, 17 and 18.  All four are in sun-synchronous polar orbits, meaning that the planes of their orbits remain approximately the same relative to that of the Earth's day/night terminator.  As the Earth rotates, SSO passes through the plane of NOAA-12's orbit at 4:24am, and again 12.9 hours later at 5:19pm.  Likewise for NOAAs 15, 17, and 18, passage through the orbital planes will occur at 5:21am/18:15pm, 9:52am/10:46pm, and 1:14am/2:12pm respectively.  So an SSO observer will see NOAA passes centred on the times 01:15, 04:24, 05:21, 9:52, 14:12, 17:19, 18:15 and 22:46 AEST.  1-2 passes of a NOAA satellite will occur within ±1 hour of these times.

The present receiving antenna, located approximately 50m uphill of the APT building, is known as a Lindenblad type.  It is designed for the reception of the right-hand-circularly-polarised (RHCP) radio waves transmitted by NOAA satellites, a job it does superbly.  But its one big drawback is a reception 'dead zone' located toward the zenith.  Occasionally high-elevation satellite passes (with a maximum elevation ~ >80°) pass though this 'cone-of-silence', and a 'salt-and-pepper' pattern of interference appears across the image, usually passing right though the location of SSO.  Since SSO observers are particulary interested in local cloud conditions, this interference stripe is particularly inconvenient.  Consequently, during April 2004 I reoriented the receiving antenna to make it more sensitive to satellite signals from near the zenith.  This means that the image quality is now likely to be poorer over Tasmania and Queensland, but locally to SSO it's now pretty good.  On rare occasions, interfering radio signals from junk satellites may place noise stripes across otherwise good images.


A thumbnail image of today's latest downloaded image is shown at the left, and it has a generic URL of http://www.phys.unsw.edu.au/~map/weather/latest-thumb.jpg .  One application of this thumbnail, for webpage designers, is as an attractive link to our main satellite image page.  For example, latest-thumb.jpg icons are a feature of the AAO weather page, and the Coonabarabran.com.  Just for fun, occasionally I like to check who's linked to our homepage.


For comments and suggestions concerning these web pages, please contact Andre at the

UNSW Automated Patrol Telescope
Siding Spring Observatory
Coonabarabran, NSW 2357

2005-06-07