Every one to two days, the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard NASA’s Terra and Aqua satellites orbit the globe and collect data on Earth’s atmosphere, cryosphere, land, and ocean in 36 spectral bands. The Visible Infrared Imaging Radiometer Suite (VIIRS) instruments aboard the joint NASA/NOAA Suomi National Polar-orbiting Partnership (Suomi NPP) and the Joint Polar Satellite System’s NOAA-20 and -21 satellites do the same in 22 spectral bands. That’s a lot of data, and sifting through them all to find data pertaining to a particular location or region can be a challenge, especially for those new to working with remotely sensed Earth science data.
Fortunately, NASA's Distributed Active Archive Centers (DAACs) have a variety of tools to help users find the data they need. One such tool is View Data from NASA's Level-1 and Atmosphere Archive and Distribution System DAAC (LAADS DAAC).
In the words of Greg Ederer, LAADS DAAC senior application developer, View Data is a visual search tool that lets users “find and preview full-resolution Level 1, Level 2, and Level 3 datasets from MODIS and VIIRS prior to download,” thereby ensuring users get the data that best meet their needs. “[View Data] benefits researchers by letting them narrow their search to just the data they're interested in and filters out the data that are irrelevant to their research,” he said.
The View Data interface consists of a basemap, a menu box (located in the upper right portion of the screen), several buttons along the bottom of the screen (i.e., measure, select, location, etc.), and a timeline below the buttons. Users can move the map by clicking and dragging it with their mouse and change how they’re viewing it by zooming in and out (via the plus [+] and minus [-] buttons in the upper left corner of the screen, the thumbwheel on their mouse, or by pinching or expanding their touchscreen).
Using View Data
Finding Data
To search for and view data, users should begin by choosing a timeframe via the timeline. Clicking on the date (e.g., February 16, 2024) will open a calendar that lets users select the start date of their timeframe. Then, they can pull the end of the blue slider on the timeline to determine their desired date range. Conversely, users can click the button labeled 1 Day in the lower right corner of the View Data screen, which allows them to choose timeframes ranging from 1 day to 31 days.
Next, users can select the appropriate data layers by clicking the green Add Layers button in the box in the top-right of the screen. Doing so opens a larger window with tabs that let users search for data by mission, processing level (Level 0 or 1), and discipline (atmosphere or land). Selecting or deselecting these tabs will change the options in the column on the left side of the window. These options allow users to further refine their search filters, as does the green "Show products with imagery only” check box on the top of the right column. When users have finished choosing the filters they wish to apply, a list of data products that meet their criteria will appear in the bottom of the right column. These data products can then be viewed as layers on the map by clicking the boxes in front of each dataset on the list and then closing the pop-up window.
Viewing Selected Data
Once the pop-up window is closed, all of the user-selected data products will appear as individual layers on the map in the View Data interface. Users can show or hide each layer by clicking on the eye icon next to the layer in the box on the right side of the screen. In addition, clicking the letter “i” in the gray circle will open a window containing more information about each dataset. Users can change the opacity of the data displayed on the map by clicking on the half-filled circle icon and then moving the slider to whatever level of opacity they deem appropriate.
Along with the data, users can also add additional layers to the map, including:
- Orbit tracks and overpass times for the Aqua, Terra, Suomi NPP, NOAA-20, Landsat 8, and Sentinel 2A and 2B satellites (Note: Data from NOAA-21 will be added in the near future)
- Overlays, such as latitude and longitude lines, coastlines and borders, and roads
- Static backgrounds (i.e., different variations of the interface’s basemap, such as the Blue Marble, topographic maps, or a detailed map with place names, streets, and select locations of interest)
- Dynamic backgrounds, which allows users to apply a number of MODIS or VIIRS products (e.g., MODIS/Terra Corrected Reflectance)
Selecting an Area of Interest
To select a specific area of interest, users can click the Select button at the bottom of the screen. Doing so will open a window in the top-left corner of the screen with the “World” view setting as the default. Users have the option of changing that and viewing data by:
- Country, which allows users to click on the country of their choice
- Tile, which allows users to click on the tile that pertains to their area of interest
- Site, which allows users to search by validation site location(s)
- Polygon, which allows users to define their areas of interest by drawing a polygon on the map
- Classic, which allows users to draw a square or rectangle associated with a particular set of coordinates
Downloading the Data
Once users have defined their area of interest, defined the timeframe for the data they want, and defined the data product types in which they’re interested, they can then click the Data Search tab (next to Layers) in the box on the right side of the screen. Doing so reveals the available data products corresponding to the timeframe and location selected. Users have the option of selecting Day, Night, or Day/Night Boundary, further refining their desired data.
Once the data product and type of coverage have been selected, users can click the Search button at the bottom of the box. This will produce a file summary highlighting the number of data records available for download. Clicking on the data product and number of records opens a window showing the details of each individual file. Users then have the option of selecting all the files shown (by clicking the box next to Name at the top of the window) or selecting individual files by clicking the box next to each filename. Further, users can select the file format in which they’d like to receive their selected data by clicking the JSON or CSV tabs at the top of the window. (Note: There is also a tab for wget access, but this capability is not available at this time.)
Useful Widgets
In addition to the features described above, View Data also offers a number of widgets (located above the timeline on the bottom of the screen) that users can employ to share and enhance their visualizations. These include:
- A Share button that lets users share their data visualizations via social media or email; similarly, users can click the copy button to get a URL of the data visualization they’ve created, allowing them to include it in documents
- A Capture button that allows users to produce an image of their visualization that includes a header, a timestamp, and a scale bar (these images can be downloaded in PNG, JPEG, or GIF format)
- A Measure button that enables users to measure distances within their area of interest
- A Location button that allows users to mark a specific location in the map, search for a location, and save previously identified locations
- A Help button that provides users with information about the View Data tool, citation and acknowledgements, a means of offering feedback about the tool to LAADS DAAC, a list of Frequently Asked Questions, and tutorials (users also can get advice on using View Data from the Earthdata Forum and by contacting the LAADS DAAC directly via the Contact Us link under the About LAADS dropdown menu on the DAAC’s website)
Yet, explaining the features and functionality of the View Data tool in an article like this only takes a user so far. Ederer notes that the best way for people to familiarize themselves with and benefit from this tool is just to jump in and start using it.
“The Find Data page on the LAADS DAAC website can be a little intimidating because there's a lot of information there, but the View Data tool was designed to walk users through the process of helping them get the data that they need,” Ederer said. “Don't let the huge list of products available from the DAAC scare you away. Play around with View Data a little bit and before long you'll find out that it’s a very easy tool to use.”
About NASA's LAADS DAAC
As one of 12 DAACs within NASA's Earth Observing System Data and Information System (EOSDIS), LAADS DAAC archives and distributes data on clouds, water vapor, and aerosols in Earth’s atmosphere as well as key instrument data for NASA, NOAA, and ESA (European Space Agency) missions. The primary mission of LAADS DAAC is to archive and distribute MODIS science data products and NASA versions of VIIRS science data products to the global Earth science research and applications community. Its focus is on Level 1 calibrated and geolocated moderate resolution instrument data and Level 2 and 3 atmosphere products. In addition, the DAAC serves as a backup source for MODIS and VIIRS land products.
