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 Gérard.

[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 example).
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

In Datatype, select 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 the screen.
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 Next Page.
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 available.

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.

Sample Images

You can see some sample images derived from CLASS data.

Back to the HRPT Reader page