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EOS Data Gateway FAQ

FREQUENTLY ASKED QUESTIONS
Version 3.1



General Topics

Q: What is the EOS Data Gateway?
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.

Q: What is a DAAC?
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.

Q: Where can DAAC contact information be obtained?
A: This information is available from the User Support link on the EOS Data Gateway Home page.

Q: I hit my browser's Back button and the page was missing. What happened? What do I do?
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

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?
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.

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?
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.

Q: What do I do if I forget my password?
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

Q: What are the links on the left of each page?
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.

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"?
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.

Q: What are "user-preferences"?
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

Q: What is the difference between a "data set" and a "data granule"?
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 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?
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.

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?
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.

Q: What is a Local Granule ID Search?
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.

Q: What is a Summary Document Search?
A: You can use Summary Document Search to find documents that provide summary information about a data set of interest.

Q: What is a Detailed Document Search?
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.

Q: What are "ordering" and "ordering options" and why do I have to "select order options"?
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".

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.

Search Form

Q: How do you change map coordinate values if you make a mistake?
A: It depends on which way you're selecting the area.

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?
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.

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?
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.

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?
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

Q: Why is map selection so slow?
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.

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?
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

Q: Can data be viewed prior to placing an order?
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.

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?
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, ...

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"?
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.).

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?
A: Yes! We have added new subsetting features to the ordering process.

Browse Screen

Q: After selecting View Browse Image, what are we waiting for?
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.

DAACs can also provide a direct URL link to the image, and we simply show that to you if that's what they provide.

Shopping Cart

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?
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

Q: If I order data, how much will it cost?
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.

Q: I'd just like to see some images. Do I have to go through all this "ordering" and "selecting ordering options" just to see some pictures?
A: Casual users who are simply interested in examining what the data looks like do not need to place an order. They can simply can look at "browse images" - GIF renderings of the data - to see it. If this is what you want to do, you can set options in your search to tell the EOS Data Gateway to make sure that the data granules you get are data granules with images.

Q: Is it obvious that an order has been placed? Could multiple orders result from the user not realizing that they've already placed an order, and placing it again?
A: It's pretty obvious when an order has been placed. On successful placement of an order, the user is shown an "Order Submitted!" page, which includes an order confirmation number with instructions to write this number down for your records.

Also, the web gateway will, by default, empty your shopping cart when you've placed an order. You can choose to have the gateway leave your items in the cart if you want, but having the cart emptied automatically helps keep you from accidentally ordering things multiple times.

Lastly, as a sort of backstop to let you know you've made an order, you receive an e-mail confirmation.