Basic Notes for using the CLASS (formerly SAA)
[For French speakers] Il y a une version française de langage de ce document fourni
ici. Il a été écrit par Gérard F6BEK.
Beaucoup de grâce à
[For German speakers] Informationen auf Deutsch über das Verwenden des SAA.
Vielen Dank Angela Schwiebus für die Übersetzung.
At www.class.noaa.gov the
first thing you have to do is to register as a user. This is quite easy,
and doesn't bring any junk e-mail or anything like that. Data downloaded
can be read with my Windows HRPT Reader software. Back
to the HRPT Reader page.
The format of the CLASS (formerly SAA) page has changed, so the information
below will be more of a guide than step-by-step instructions. The type of
data you should first select is: Advanced Very High Resolution Radiometer.
Selecting the Data
Once you've registered, you click on:
- Enter as a registered user - you enter your user
name and password
- Select the time region that interests you.
Perhaps you want today's images, so you in Temporal, select the start and end date as 2001 August 06 (for
- You could restrict the area to search if you want by
selecting in Spatial.
Let's assume you know you want a particular NOAA-16 pass (only
certain satellites are recorded). The full resolution passes are called
either LAC (if recorded) or HRPT (if downloaded live over the USA). Using WXtrack,
we find there was a pass at 11:56 just crossing Egypt.
You can see that passes are due to be available at: http://www.cira.colostate.edu/special/wxcal/wxcal.htm#LAC
So now we have chosen all the LAC passes for this particular
day. You could narrow the search further in Satellite.
- Instead, click on Search at the bottom of
- You will now get a list of the results. There are two
things you can do, View the Detail (checks the start and end times etc.) or
Add to Shopping Basket (abbreviated as Shopping Cart).
- As we do not see the 11:56 pass on the first page, click on
- We now see the pass selected. Pressing the button
"4" will give us the details - and we see the pass lasts
until 12:08, just covering to the "top" of Norway. While
viewing the detail page, we can check the Add Selection box (top
left) to order the file.
- When you have made all the selections you want, click on
the Goto Cart button. You should see the pass or passes you
have selected. At this point, you can enter a comment for the whole
order, or for each pass. Note that you can also select which channels
and how many bits per pixel you want, but these are not always honoured for
every type of pass.
- Be sure that the Include Archive Header checkbox is
checked. Without this tiny 122 byte header the HRPT Reader will not be able to
understand the format of the remaining data!
- Unless you have particular reasons for choosing otherwise,
I recommend you leave the default 10 bits/pixel of channels 1 to 5 selected.
- When you have finished entering comments, click on the Place
Order button (top left). You will then get a confirmation number
such as: A1122325. Make a note of this number, so you will know which directory
to get your files from.
If you have chosen to get e-mail confirmation, sometime later
(typically a few minutes) you will get an e-mail confirming that your order has
been "Verified", and then a message telling you that the items are
Back to the HRPT Reader page
Downloading the Data
To download the items, you use FTP.
- With your FTP client, connect to ftp.class.noaa.gov
using anonymous access. You should see a folder named A1122325.
Change directory to that folder. You should see the file you ordered,
but beware, they are symbolic links and some FTP clients don't understand
this. WS_FTP does.
- Ensure that you have BINARY mode selected for
transfers, and download the file or files.
- You will need to rename the files to have a .LAC, L1B or .HRP
suffix for the HRPT Reader to understand them. You may need to set up
a particular association for .HRP files to the HRPT reader so that you can
launch the .HRP file simply by double-clicking on the file.
- Finally, I suggest you rename the file to something more
meaningful such as 2001-08-05-1156-n16.hrp.
But I only have a 56K modem!
If you only have a modem for your Internet connection, files
from the CLASS can seem quite big, but you can use GAC data rather than LAC or
HRPT data. GAC is the format that covers the whole world, but at a reduced
resolution. By selecting carefully both with a time selection (temporal),
and with a geographical selection (spatial), you can get the files down
to 2MB. For example, I recently wanted an image of Brazil (Sao Paulo), so
I used WXtrack to see when NOAA-15 was near there (it was Saturday, March 30 at
09:52). To limit the search to one revolution, I entered 09:30 and 10:30
as the time constraints. Then, to limit the image I used the spatial
search to enter the co-ordinates as: 15S - 30S and 40W to 50W. The
resulting file size was just 2.5MB.
You can see some sample images
derived from CLASS data.
Back to the HRPT Reader page