sz /science system data
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Atmospheric Chemistry and Dynamics Laboratory (Code 614)

For Our Colleagues
Scientific/Technical Information

/science system data

What?

This is a web interface to the data in our "/science system" . These data include gridded three-dimensional meteorological fields (from NCEP, GSFC DAO, and the UARS UKMO assimilation effort), data from satellite instruments, and model results.

To access these data, you will need to have a user name and password assigned. This user name is valid only for accessing these data and cannot be used for login access to our system. You can use an interactive web browser to download data files, or you can use a batch-mode program that gets files from a web site.

Why?

These data are intended for use by our scientific colleagues. In the past, we would assign login accounts to guest users at other institutions, and those guests would use ftp to transfer data to their home machines. Alternatively, they would telnet in to our machines, run software to read our data, write the data out into their own format, and then ftp the rewritten data to their home machines.

Unfortunately, telnet and ftp transmit user names and passwords in clear text across the Internet. Any eavesdropper could get this information and use it to log on to our machines illegally. Moreover, we found that many of our remote users were sharing account names and passwords, even though we were willing to give each individual an account.

Several break-in incidents have led us to reconsider our guest user practices. Most such guests simply want access to the data, and they do not really need login access to our machines. That being the case, we have set up web-only accounts for them which cannot be used for login access.

How?

Assuming you have a valid user id and password for these pages, you can use any interactive web browser to see what data are available and to retrieve specific items of interest. Alternatively, if you know what files you want and wish to set up an automated procedure to retrieve them from this web site, several programs exist that will allow you to do this.

For non-interactive (batch-mode) data acquisition, you can try the wget package. You will need to obtain the source code and compile it.

For example, to retrieve a DAO data file of EPV, give the command 

wget --timestamp -nd http://myusername:mypassword@acd-ext.gsfc.nasa.gov/Data_services/science/asm/data/GG2%255X2/Y1998/M01/EPV_I98010300_GG2%255X2_X_ESTRATF.ASM

and the file EPV_I98010300_GG2%5X2_X_ESTRATF.ASM will automagically appear on your machine. (Note that the "%" signs in the file name had to be entered as "%25" in the URL, since "%" is an escape character in a URL, and "%" is ASCII 37, 25 hexadecimal. Use this same escape mechanism for any other odd characters you might need.) The "--timestamp" option, by the way, forces the downloaded file ot have the same time stamp as the file on the remote end. And the "-nd" (aka "--no-directories") option means that the file is to be downloaded to the current directory on the local end. Wget has many options--read the info pages that come with the program for a full description.

Note: the usernames and passwords you need for accessing these data are not valid account names on our systems, so intruders cannot use them to break in. Nevertheless, these raw and frequently preliminary data are not supposed to be open to the general public, so please keep your usernames and passwords as secret as possible. If you imbed them in your batch scripts, please set the file permissions so that only you can read them.

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