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EOS Data Gateway FAQ
FREQUENTLY ASKED QUESTIONS
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Q: What is the EOS Data Gateway?
Q: What is a DAAC?
Q: Where can DAAC contact information be obtained?
Q: I hit my browser's Back button and the page was missing.
What happened? What do I do?
Q: What is the difference between using the system as a "guest", and
using the system as a "registered user"? Why be a registered user?
Note that beginning in early 2001, user registration will be linked to
EOSDIS so registered users will have access to more services. This page
will be updated with information on services when that link-up is complete
and operational.
Q: How do I become a registered user?
Q: What do I do if I forget my password?
Q: What are the links on the left of each page?
It is strongly recommended that you use these links, rather than the
browser "back button" to navigate through the EDG.
Q: What is a "session"?
Q: What are "user-preferences"?
Q: What is the difference between a "data set" and a "data granule"?
A data granule is the smallest amount of data that can be
independently searched for, described and ordered in the EOS Data
Gateway. These are the actual things you'll use to get the data you
want.
Q: How do I get the data I am interested in?
You then choose the data granules you want and order them through the
EOS Data Gateway to gain access to the data you need.
Q: What is a Data Granule ID Search?
Q: What is a Local Granule ID Search?
Q: What is a Summary Document Search?
Q: What is a Detailed Document Search?
Q: What are "ordering" and "ordering options" and why do I have to
"select order options"?
Most data is available in a number of formats - on tapes of various
type; sometimes on CD-ROM; and many data granules may simply be
accessed via FTP to the DAAC where they reside. You select the way in
which you want the data to be accessible - the "ordering options" -
and the EOS Data Gateway notifies the DAAC (or DAACs) where the data
granules you want reside as to how to deliver them to you.
You then get e-mail from the DAACs to either tell you that the data
granules are available for FTP, or confirming that they should send
the tape/CD/etc. that you chose.
Q: How do you change map coordinate values if you make a mistake?
If you're using one of the clickable maps, just finish making the
selection. The web gateway will let you see the complete selection a
final time before you return to the search screen. You can simply
click on the map which shows you the complete selected region again to
respecify the region. You can do this as many times as you need.
If you're entering latitude/longitude or row/path information, all of
the standard editing methods supported by the browser in use are
available. You can usually just move the text cursor into the field to
be corrected, rubout the erroneous data, and enter the correct
information.
Q: Are search criteria coupled so that for example, if ozone is
selected, all DAACs that have ozone data will be queried?
For example, if you are doing a Granule ID search and selected all of
the data centers, the data centers which don't support data granule ID
search would automatically be excluded, even if you selected them,
when you request the search be done.
Q: Can the search criteria from the search selection screen be
saved?
You can also do a file upload; features have been added to the web
gateway to allow you to upload a saved query.
Internet Explorer at present does not properly support the upload
and download features of the gateway.
Q: Will a different search engine be required to retrieve ASF data sets,
or can they be retrieved using the existing web gateway?
Q: Why is map selection so slow?
Users with Java-enabled browsers can now use a new map selection
applet to make their geographic selection. We advise all users who
are interested in using the applet to read the
Java FAQ; despite claims of "write once,
run anywhere, there are significant differences in Java implementations
in different browsers (and even in different releases of browsers).
The FAQ will let you know what you need to check on your machine,
and what to expect in terms of known Java bugs for your machine.
Q: What other map projections are available?
Q: Can data be viewed prior to placing an order?
Q: Why do you have to select the data sets or data granules in one
operation, and then add them to the cart or order them separately?
The idea is to make it easier to order multiple things than it is to
order just one. We chose not to have both a check box and the
add/remove/order buttons next to each item to keep the interface simpler,
as well.
Q: What is the difference between "data set ordering" and "data granule
ordering"?
The EOS Data Gateway indicates on the "Data set Listing" page if a
data set is eligible for data set ordering by putting a special button
next to such data sets. Only some specific data sets are eligible.
Granules, on the other hand, are always treated as individual
entities. You simply select all of the ones you want and order them.
It is possible that the ordering options you select (for example, a
CD-ROM) might actually make it so that you are receiving all of the
other data granules in the data set along with the ones you're
specifically ordering, but from the standpoint of how orders are
processed, you're still only ordering the data granules you selected;
the actual contents of the medium you receive them on may or may not
include other data granules. Examining the ordering options will tell
you what you will get.
Q: Can data subsetting be performed on data sets found through the
web gateway?
Q: After selecting View Browse Image, what are we waiting for?
DAACs can also provide a direct URL link to the image, and we simply
show that to you if that's what they provide.
Q: What happens if you add something to the shopping cart and then
decide that you don't want it? How should the product be
deleted?
Q: If I order data, how much will it cost?
A:
The EOS Data Gateway (EDG) is the primary interface to all data
available in NASA's Earth Observation System Data Information System, and
related data centers. With EDG, a user can search for and acquire a large
variety of earth, ocean, and atmospheric science data obtained from EOS
instruments such as MODIS and MISR, as well as other satellites such as
Landsat and TRMM.
A:
The acronym "DAAC" stands for "Distributed Active Archive Center". As
components of the EOS Data Information System (EOSDIS), DAACs are
institutions that generate EOS standard data products and carry out
NASA's responsibilities for data archival, distribution, and management.
Many of these sites also carry related data products that pre-date EOS.
Each DAAC has a home page and an FTP site for transfer of insormation
and data.
A:
This information is available from the User Support link on the EOS
Data Gateway Home page.
A:
When you hit a browser's Back button, the browser tries to display
the page from its local storage, called cache. Many pages on the Web
are generated by a process called POST, and can't be retrieved from
the browser's cache. Also, your browser may be set up to not have any
or enough cache. You probably got a page saying "Missing Data".
Actually, this is a good thing because in a system like the EOS Data
Gateway, when you go from one page to another, the system state
changes and if you view an old page it may not reflect the true state
of the system. Sometimes you can regenerate the page you wanted by
using your browser's "Reload" button to reload the page (some browsers
call this "Refresh"). If you get an error, use your browser's Forward
button to get back to the EOS Data Gateway and then use the navigator
tabs on the left side of the screen.
If a web page has navigation tabs or links on it, you should use those
instead of the browser's Back button.
Accessing the EDG
A:
As of September 2000, a user accessing the EDG as a guest and a
user accessing EDG as a registered user encounter no differences in the
types of data services available. A guest user can search for and order
data in the same manner as does a registered user. However, using the EDG
as a registered user allows your user preference information as well as
your most recent search to be saved by the system for 14 days. This
convenience feature can be a time-saver for a user in that he/she can
re-enter the EDG at a later date and not need to type in certain
information again.
A:
Click the "Become a Registered User" link on the EDG welcome page.
Then fill in the information required and choose a personal password. The
system will generate a "username" for you, but you can change this name if
you so desire. After you complete these actions, you will be able to
enter the EDG by clicking on the "Enter as a Registered User" link on the
welcome page.
A:
Use the "Forgot My Password" link on the welcome page. This tool
will quickly generate a new password for you and email that password to
you.
General Interface Questions
A:
The most common activities are available as links at the left of
each page. Use these links to move to different pages of the EDG
system.
A:
Every time you run the EOS Data Gateway interface, a new
"session" is created for you with its own temporary disk space
on the machine you're accessing the interface from.
This disk space holds your user profile, search results, etc.
If your session remains idle for more than a couple of hours, the
temporary space is deleted, and the session is ended.
A:
Netscape 2.0 and later only:
If you plan to run the interface more than once (and you don't
want to keep filling in the same on-screen forms), you can save
certain information to a "preferences" file.
This is a simple text file that you can download from the current session
and keep anywhere on the WWW. You can edit it
(if you like), and upload it into any future EOS Data Gateway
session.
Types of Searches/Terminology
A:
A data set is a logically-meaningful grouping of similar or related
data. This data will usually have mostly similar characteristics in terms
of source, processing level, etc. Data sets contain one or (usually) more
data granules, which actually contain the specific data.
A:
When you do a data search using the EOS Data Gateway, it asks the
appropriate DAACs (i.e., DAACs that hold in their data inventories the data
sets that you are interested in) what data sets match your criteria, and
what data granules within those data sets also match your criteria.
A:
This search is used to find a specific data granule having a
specific granule identification number. A data granule ID search
is done typically by an advanced user who knows exactly what
granule he/she is interested in.
A:
This search is applicable only to data from EOS satellites. As
with data granule ID search, a local granule ID search is done typically by
an advanced user who knows the exact granule of interest. Local granule
IDs have specific formats that provide information about the granule to the
user. Note that local granule IDs and data granule IDs are two separate
and distinct identifiers.
A:
You can use Summary Document Search to find documents that provide
summary information about a data set of interest.
A:
A Detailed Document Search lets you get uniform detailed descriptions
of data sets, allowing you to more easily choose which data sets would
be useful to you. These documents are written by DAAC science staff
and contain much more information than do summary documents.
A:
The EOS Data Gateway treats data granules as logical entries,
ignoring their physical storage up to the point that you say, "Yes, I
want these data granules." This is what the EOS Data Gateway calls an
"order". Since data granules are available in a number of ways, you
must tell the EOS Data Gateway the manner in which you wish to receive
them. This is called "selecting ordering options".
Search Form
A:
It depends on which way you're selecting the area.
A:
Yes, this and several other similar types of operations are
performed automatically by the web gateway. If you have selected items
which are incompatible, the most recently selected ones override older
ones.
A:
Users of Netscape 2.0 and later, and Internet Explorer 4.0 and
later only:
Search criteria can be saved to an EOS Data Gateway query file
by clicking on the "download this query to your machine" link at
the bottom of both the "Data Set Listing" page and the main search
pages.
A:
The current version of the gateway can search the ASF DAAC, and
allows you to order any of the free-of-charge, unrestricted products
available at this site. ASF requires an authenticator which the user
supplies in their user preferences. If you are interested in obtaining
restricted-access ASF data, contact the ASF User Services Office.
Search Screen - Map Selection
A:
This in inherent in the way that the maps are generated and
displayed. Every time that a new map is required, a request is
sent to the gateway, where the new map is generated, compressed,
transferred, uncompressed, and rendered. This same sequence of
steps is required even for a simple change, such as adding the
red lat/lon boundary lines to an existing map.
A:
In addition to the various Plate-Carree projections, north-polar and
south-polar projections and orthographic projections are also available.
Granule/Data Set Listing
A:
If browse data is available for a data set, this browse product
can be viewed from the data granule list page. However, browse
products are not universally available, and in particular, very
few of the overseas CINTEX sites offer browse products. The user
does have the ability to restrict a search to only return
information about data sets for which browse products are
available. Additionally, the spatial and temporal coverage of a
data set is always available.
A:
We chose to do it this way because processing each item separately
takes a lot more time
to do if you're working with more than a single item. If you're
buying groceries, you don't go to the store, buy eggs, go home, put them
in the refrigerator, decide you need milk, go back to the store, buy milk,
come home, decide you need tea, ...
A:
Data set ordering allows you to order a selected subset of data
granules from a data set without having to go through the process of
looking at every single data granule and deciding whether or not it
fits your criteria (such as time range, location, etc.).
A:
Yes! We have added new subsetting features to the ordering process.
Browse Screen
A:
A browse product. These can take a significant time to transfer.
We've updated the interface to show you the progress of the FTP
browse.
Shopping Cart
A:
From the "Shopping Cart" page, you can either press the "Remove
all items from shopping cart" button, or you can select one
item for removal and press the button in the Delete column.
Order Form
A:
An order does not imply that the data will cost you anything - by
and large, most data is provided without charge. If there is a charge
for any of the data granules you want, this will be shown explicitly
on the order page, and you will have the option of deleting any items
that aren't free from your order.