Finding and Requesting LAADS Data
This document describes steps for finding and requesting data from the LAADS DAAC web site.
In some cases, you might want to do more than just download a directory full of files from the LAADS data archive. You might want to refine your search to only include files from a certain time range or from a certain geographic area of interest. You might want to filter out data sets that are not of interest. Your analysis tools might prefer a file format different from the standard HDF4 file format. All of these operations are supported by the LAADS Find Data tool. The following section describes how to use this tool.
Using the LAADS "Find Data" Tool
Begin by selecting "Find Data" on the top navigation bar of any LAADS DAAC page. This will navigate you to the Find Data page. Then follow the five steps in the blue bar across the top of the page. These five steps are also described as follows.
select "(1) Products"
- The easiest way to find a list of products is to type a keyword into the "Keyword" field on the right-hand side of the grey selection bar (to the right of the "Select a Sensor" button). You can use the LAADS product name if you know it (for example, MYD11A2 or VNP02IMG), but you can also use measurement names (for example, Aerosol, Surface Reflectance, EVI, etc). If this results in a list of products that interest you, select the product(s) you want by clicking on the bold product name and proceed to step 2. Otherwise...
If you already know the instrument that measured the data you want, use the "Sensor" pull-down to select it, and use the "Collection" pull-down to select the appropriate data collection. If you do not select a collection, then the collection field defaults to the most recent science collection available. If you do not know the instrument or sensor, then ...
- use the site "Search" field at the very top center of the page, to the right of the "LAADS DAAC" title. Type a keyword or phrase about the data you want into the field and click the magnifying glass icon. This will result in a new page that lists all the LAADS pages that contain your keyword or phrase. You can explore these pages for more information that will help you refine your search for LAADS products. Look for information about the satellite, instrument, and collection. This will help you make the right choice for the "Sensor" and "Collection" fields.
- After selecting a collection, you will see a list of science areas displayed in a box to the left and a list of products displayed in a list to the right. By clicking on a science area, you can filter (shorten) the list on the right to make it easier to find what you want. When you find the product(s) you want, select them by clicking on their bold product name and proceed to step 2.
- select "(2) Time"
- There are many different ways to specify the Time, including date ranges, single dates, and custom times (click the "+Advanced" link under the "Add Date" button to add custom times). If you are interested in Day only or Night only measurements, you can select that as well. We suggest a short duration (1 day) for your first request to make sure your settings give you what you need.
select "(3) Location"
- Like the "Time" selection, there are many ways to select a location or region of interest. If you specify nothing, your search will include the entire globe.
- select "(4) Files"
- You should now see a list of files that correspond to your parameters specified in steps (1)..(3). You can click on the "Image" column (if there is an image icon there) or "Images" tab to see jpegs of layers that have images (NOTE: we only produce images for a select set of products. Not all products have associated images).
- You can download files directly from this page if they are available online (otherwise we will re-create them for you if they are not immediately available). Click on the link in the "Download" column. Or...
- select the files you want by clicking on each one (or use the "Select All" link at the top of the list, you can then click on any files you do NOT want). If, after selecting your files, you want to search for and add more files to this particular request, you can go back and repeat steps (1)..(4) and search for more files. This page will remember the files that you have already added.
- select "(5) Review and Order"
If you haven't registered with Earthdata, you will need to do so before you can complete your request. The browser will automatically take you to the Earthdata login site to register or login if you have not already done so. Once you have an Earthdata login account and are logged in you will be able to continue with your request.
- Choose Post Processing
Click the "Post Processing Parameters" button. Post Processing allows you to further customize your files before they are sent to you. Post Processing can shrink the size or number of files you need to download, and can change their storage format. We support the following Post Processing operations for many of our products.
- select only the data sets that you want from a file. Most LAADS products contain many data sets (some contain thousands of data sets). If you will not need most of them, choose only the ones you will use. This can reduce the size and number of files you will need to download.
- select only the data from the geographic region you specify. Even if you searched for data from only a specific region in step (3), the files can contain more data, with only some of it actually intersecting the region you specified. By selecting this option, we will slice out all data that are not in your specified region. This can further reduce the size of files you will need to download, and will also reduce the amount of data you need to process.
this option can combine the data from multiple files into one file, with all the data correctly geolocated. Some caveats:
- all combined files will be from the same date (for lists of files from multiple dates, there will be a result file for each separate date)
- data sets remain separate -- our tool does not combine data from different data sets together
- where files overlap geographically, we will favor pixels based on whether the pixel contains a measurement value or not, and then favor the pixel nearest to the satellite's nadir position
- change the format of the file. Currently, we offer the GeoTIFF file format, commonly used in Geographic Information System (GIS) tools.
- change the Map Projection or Sample Size. Many maps and data sets from other instruments do not use the Geographic, or Cartesian, coordinate system. When overlaying data sets, they will line up better if they use the same coordinate system. The Reproject option allows one to specify parameters that govern the reproject operation. Refer to the U.S.Geological Survey Professional Paper 1395, "Map Projections -- A Working Manual", U.S. Government Printing Office, Washington: (C)1987, for detailed information on map projections.
- Include process log files with the output. Most users will not find this option particularly useful.
- Choose Delivery Method
- for most users, this will always be "Pull". This means that we will copy your data to a staging area on our disks, send you an email when your data are available, and you can then "pull" (download) them at your convenience (your files will remain in your staging area for up to 5 days).
- We do offer an option where we "Push" the files directly to you, but this requires you to be running an FTP server to receive them, something which most people are prohibited from doing because of security issues. Consult your IT department if this is still the desired option.