Agricultural and Water Resources Data Pathfinder: Land Data

Land surface reflectance is useful for measuring the greenness of vegetation, which can then be used to determine phenological transition dates including start of season, peak period, and end of season. Two moderate resolution instruments that are primarily used for this measurement include NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) and the Visible Infrared Imaging Radiometer Suite (VIIRS) on the joint NASA/NOAA Suomi National Polar-orbiting Partnership satellite. MODIS reflectance products are available at 250 m and 500 m spatial resolution. VIIRS reflectance products are available at 500 m and 1000 m spatial resolution. MODIS data are acquired every 1-2 days, whereas the wider swath width of VIIRS allows for daily global coverage.

Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)—a cooperative effort between NASA and Japan's Ministry of Economy Trade and Industry—is a high-resolution option that acquires visible and near-infrared (VNIR) reflectance data at 15 m resolution and shortwave-infrared (SWIR) reflectance data at 30 m resolution. Note that ASTER is a tasked sensor, meaning that it only acquires data when it is directed to do so over specific targets, making its temporal resolution variable depending on your target region of interest.

• MODIS Surface Reflectance from Earthdata Search
• VIIRS Surface Reflectance from Earthdata Search
• ASTER Surface Reflectance from Earthdata Search

A high resolution option, the joint NASA/USGS Landsat 8 Operational Land Imager (OLI) instrument, acquires data in the VNIR and SWIR, and is available at 30 m spatial resolution, acquired every 16 days. Landsat data can be discovered using Earthdata Search, however, you will need a USGS EROS Registration System (ERS) login to download the data from the USGS Earth Explorer.

• Landsat 8 Operational Land Imager (OLI) from Earthdata Search
• Landsat 7 Enhanced Thematic Mapper Plus (ETM+) from Earthdata Search

Another high resolution option is the new (but currently PROVISIONAL) Harmonized Landsat and Sentinel-2 (HLS) project, which provides consistent surface reflectance and top of atmosphere brightness data from the OLI aboard the joint NASA/USGS Landsat 8 satellite and the Multi-Spectral Instrument (MSI) aboard Europe’s Copernicus Sentinel-2A and Sentinel-2B satellites. The combined measurement enables global observations of the land every 2–3 days at 30-meter (m) spatial resolution. Explore the Getting Started with Cloud-Native HLS Data in Python Jupyter Notebook for extracting an EVI Time Series from HLS.

• HLS Surface Reflectance from Earthdata Search

NASA's Land Processes Distributed Active Archive Center (LP DAAC) also provides a tool called the Application for Extracting and Exploring Analysis Ready Samples (AppEEARS). AppEEARS offers a simple and efficient way to access, transform, and visualize geospatial data from a variety of federal data archives. MODIS and VIIRS surface reflectance data are available in AppEEARS, as well as the USGS Landsat Analysis Ready Data (ARD) surface reflectance product. Other products useful for agriculture and water applications available in AppEEARS include Daymet daily weather parameters, Soil Moisture Active Passive (SMAP) soil moisture products, and MODIS snow cover products.

NASA's Oak Ridge National Laboratory DAAC (ORNL DAAC) also provides tools for on-demand subsetting MODIS and VIIRS land data. In particular, the Subsets API allows users to retrieve custom subsets of MODIS and VIIRS data products.

Near real-time data can be accessed via Worldview:

• MODIS True Color in Worldview
  Note that Worldview does have a corrected reflectance product but it is not a standard, research quality product. The purpose of this algorithm is to provide natural-looking images by removing gross atmospheric effects, such as Rayleigh scattering, from MODIS visible bands 1-7.
• HLS Surface Reflectance in Worldview

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Land surface temperature is useful for monitoring changes in weather and climate patterns and is used in agriculture and water resource management to allow farmers and decision makers to evaluate water requirements.

Research quality surface reflectance data products can be accessed directly from Earthdata Search or LP DAAC's Data Pool; MODIS and VIIRS datasets are available as HDF files, but are also customizable to GeoTIFF:

• MODIS Land Surface Temperature from Earthdata Search
  Choose Aqua versus Terra and select daily, 8-day, or monthly at 1 km or 5.6 km resolution. Note: Terra acquires data ~10:30 AM local time and Aqua is at 1:30 PM local time.
• VIIRS Land Surface Temperature from Earthdata Search
• ASTER Surface Kinetic Temperature from Earthdata Search

To quickly extract a subset of MODIS or VIIRS data for your region of interest, use LP DAAC's AppEEARS tool or ORNL DAAC's subsetting tools.

Landsat data from the USGS Earth Explorer are available via Earthdata Search. Note that you will need a USGS login to download the data.

• Landsat 8 Thermal Infrared Sensor (TIRS) from Earthdata Search
  Measures land surface temperature in two thermal bands with a new technology that applies quantum physics to detect heat.

Near real-time data can be accessed via Worldview:

• MODIS Land Surface Temperature in Worldview

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Knowing local topography is essential for professionals seeking to assess an area's runoff potential and the availability of water in lower-lying areas.

A method for delineating topography is the Shuttle Radar Topography Mission (SRTM). SRTM provides a digital elevation model of all land between 60 degrees north and 56 degrees south, about 80% of Earth's landmass. The spatial resolution is 30 m in the horizontal plane. The ASTER Global Digital Elevation Model (GDEM) coverage spans from 83 degrees north latitude to 83 degrees south, encompassing 99% of Earth's landmass. The spatial resolution is 30 m in the horizontal plane.

On average, compared to geodetic points over the U.S., SRTM data has a lower root mean square error (RMSE); RMSE is a commonly used method to express vertical accuracy of elevation datasets. Digital elevation model data accuracy is typically very sensitive to vegetation cover, however. ASTER tends to perform better over certain landcover types.

February 2020, LP DAAC released a new data product, NASADEM, available at 1 arc-second resolution. NASADEM extends the legacy of the SRTM by improving the DEM height accuracy and data coverage as well as providing additional SRTM radar-related data products. The improvements were achieved by reprocessing the original SRTM radar signal data and telemetry data with updated algorithms and auxiliary data not available at the time of the original SRTM processing.

• AppEEARS offers a simple and efficient way to access SRTM and ASTER data.
• SRTM from Earthdata Search
  These data were acquired in 2000 and are in raw format (with the ".hgt" file extension), which can be opened in most Geographic Information Systems (GIS), such as ArcGIS or QGIS. Data are also customizable to GeoTIFF.
• ASTER GDEM from Earthdata Search
  Version 3, released August 2019, has a decrease in elevation void area due to the increase of ASTER stereo image data and an improved process as well as a decrease in water area anomaly data (due to using new global water body data). For more information on the new release, read this LP DAAC news release.
• NASADEM from Earthdata Search
• SRTM and ASTER DEMs in Worldview

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Runoff potential is very important data for water resources and agricultural management, especially after storm events and wildfires. Runoff can impact water quality as chemicals from fertilizers and stormwater runoff, debris, and waste products enter water bodies. Satellites cannot measure runoff directly; however, information that can be used to predict runoff can be measured using remote sensing. These data are then input, along with ground-based data, into land surface models to estimate runoff. NASA's Land Data Assimilation System (LDAS), of which there is a global collection (GLDAS) and a North American collection (NLDAS), takes inputs of measurements like precipitation, soil texture, topography, and leaf area index and then uses those inputs to model output estimates of runoff and evapotranspiration.

• NLDAS (North American) Runoff Data in Giovanni
  Select a map plot (you can generate a time-averaged map, an animation, or seasonal maps), date range and region, select your variable and then plot the data. Data can be downloaded as GeoTIFF.
• GLDAS (Global) Runoff Data in Giovanni
  Select a map plot (you can generate a time-averaged map, an animation, or seasonal maps), date range, select your variable and then plot the data (data are in multiple temporal resolutions and multiple temporal coverages, so be sure to note the starting and end date to ensure you access the desired dataset). Data can be downloaded as GeoTIFF.
  

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Earthdata Search | Panoply | Giovanni | Worldview | AρρEEARS | Soil Moisture Visualizer | MODIS/VIIRS Subsetting Tools Suite

Earthdata Search

Earthdata Search is a tool for data discovery of Earth Observation data collections from NASA's Earth Observing System Data and Information System (EOSDIS), as well as U.S and international agencies across the Earth science disciplines. Users (including those without specific knowledge of the data) can search for and read about data collections, search for data files by date and spatial area, preview browse images, and download or submit requests for data files, with customization for select data collections.

In the project area, you can customize your granule. You can reformat the data and output as HDF, NetCDF, ASCII, KML, or a GeoTIFF. You can also choose from a variety of projection options. Lastly you can subset the data, obtaining only the bands that are needed.

Panoply

HDF and NetCDF files can be viewed in Panoply, a cross-platform application that plots geo-referenced and other arrays. Panoply offers additional functionality, such as slicing and plotting arrays, combining arrays, and exporting plots and animations.

• Panoply Orientation on NASA's Earthdata YouTube channel
• Tutorial on Creating Plots in Panoply

HEG

NASA's National Snow and Ice Data Center DAAC (NSIDC DAAC) has an HDF to GeoTIFF conversion tool (HEG), which allows you to geolocate, subset, stitch, and re-grid certain HDF-EOS datasets.

• HDF-EOS to GeoTIFF (HEG)

Giovanni

Giovanni is an online environment for the display and analysis of geophysical parameters. There are many options for analysis. The following are the more popular ones.

• Time-averaged maps are a simple way to observe the variability of data values over a region of interest.
• Map animations are a means to observe spatial patterns and detect unusual events over time.
• Area-averaged time series are used to display the value of a data variable that has been averaged from all the data values acquired for a selected region for each time step.
• Histogram plots are used to display the distribution of values of a data variable in a selected region and time interval.

For more detailed tutorials:

• Giovanni How-To's on GES DISC's YouTube channel.
• Data recipe for downloading a Giovanni map, as NetCDF, and converting its data to quantifiable map data in the form of latitude-longitude-data value ASCII text.

Worldview

NASA's EOSDIS Worldview visualization application provides the capability to interactively browse over 900 global, full-resolution satellite imagery layers and then download the underlying data. Many of the available imagery layers are updated within three hours of observation, essentially showing the entire Earth as it looks "right now." This supports time-critical application areas such as wildfire management, air quality measurements, and flood monitoring. Imagery in Worldview is provided by NASA's Global Imagery Browse Services (GIBS). Worldview now includes nine geostationary imagery layers from GOES-East, GOES-West and Himawari-8 available at ten minute increments for the last 30 days. These layers include Red Visible, which can be used for analyzing daytime clouds, fog, insolation, and winds; Clean Infrared, which provides cloud top temperature and information about precipitation; and Air Mass RGB, which enables the visualization of the differentiation between air mass types (e.g., dry air, moist air, etc.). These full disk hemispheric views allow for almost real-time viewing of changes occurring around most of the world.

AppEEARS

AppEEARS, from LP DAAC, offers a simple and efficient way to access and transform geospatial data from a variety of federal data archives. AppEEARS enables users to subset geospatial datasets using spatial, temporal, and band/layer parameters. Two types of sample requests are available: point samples for geographic coordinates and area samples for spatial areas via vector polygons.

Performing Area Extractions

After choosing to request an area extraction, you will be taken to the Extract Area Sample page where you will specify a series of parameters that are used to extract data for your area(s) of interest.

Spatial Subsetting

You can define your region of interest in three ways:

• Upload a vector polygon file in shapefile format (you can upload a single file with multiple features or multipart single features). The .shp, .shx, .dbf, or .prj files must be zipped into a file folder to upload.
• Upload a vector polygon file in Geographic JavaScript Object Notation (GeoJSON) format (can upload a single file with multiple features or multipart single features).
• Draw a polygon on the map by clicking on the Bounding box or Polygon icons (single feature only).

Select the date range for your time period of interest.

Specify the range of dates for which you wish to extract data by entering a start and end date (MM-DD-YYYY) or by clicking on the Calendar icon and selecting dates a start and end date in the calendar.

Adding Data Layers

Enter the product short name (e.g., MOD09A1, WELDUSMO), keywords from the product long name, a spatial resolution, a temporal extent, or a temporal resolution into the search bar. A list of available products matching your query will be generated. Select the layer(s) of interest to add to the Selected layers list. Layers from multiple products can be added to a single request. Be sure to read the list of available products available through AppEEARS.

Selecting Output Options

Two output file formats are available:

• GeoTIFF
• NetCDF-4

If GeoTIFF is selected, one GeoTIFF will be created for each feature in the input vector polygon file for each layer by observation. If NetCDF-4 is selected, outputs will be grouped into .nc files by product and by feature.

Interacting with Results

Once your request is completed, from the Explore Requests page, click the View icon in order to view and interact with your results. This will take you to the View Area Sample page.

The Layer Stats plot provides time series boxplots for all of the sample data for a given feature, data layer, and observation. Each input feature is renamed with a unique AppEEARS ID (AID). If your feature contains attribute table information, you can view the feature attribute table data by clicking on the Information icon to the right of the Feature dropdown. To view statistics from different features or layers, select a different AID from the Feature dropdown and/or a different layer of interest from the Layer dropdown.

Be sure to check out the AppEEARS documentation to learn more about downloading the output GeoTIFF or NetCDF-4 files.

Soil Moisture Visualizer

ORNL DAAC has developed a Soil Moisture Visualizer tool (read about it at Soil Moisture Data Sets Become Fertile Ground for Applications) that integrates a variety of different soil moisture datasets over North America. The visualization tool incorporates in-situ, airborne, and remote sensing data into one easy-to-use platform. This integration helps to validate and calibrate the data, and provides spatial and temporal data continuity. It also facilitates exploratory analysis and data discovery for different groups of users. The Soil Moisture Visualizer offers the capability to geographically subset and download time series data in .csv format. For more information on the available datasets and use of the visualizer, view the Soil Moisture Visualizer Guide.

To use the visualizer, select a dataset of interest under Data. Depending on the dataset chosen, the visualizer provides the included latitude/longitude or an actual site location name and relative time frames of data collection. Upon selection of the parameter, the tool displays a time series with available datasets. All measurements are volumetric soil moisture. Surface soil moisture is the daily average of measurements at 0-5 cm depth, and root zone soil moisture (RZSM) is the daily average of measurements at 0-100 cm depth. Lastly it provides data sources for download.

MODIS/VIIRS Subsetting Tools Suite

ORNL DAAC also has several MODIS and VIIRS Subset Tools for subsetting data.

• With the Global Subset Tool, you can request a subset for any location on earth, provided as GeoTIFF and in text format, including interactive time-series plots and more. Users specify a site by entering the site's geographic coordinates and the area surrounding that site, from one pixel up to 201 x 201 km. From the available datasets, you can specify a date and then select from MODIS Sinusoidal Projection or Geographic Lat/Long. You will need an Earthdata Login to request data.
• With the Fixed Subsets Tool, you can download pre-processed subsets for 2000+ field and flux tower sites for validation of models and remote sensing products. The goal of the Fixed Sites Subsets Tool is to prepare summaries of selected data products for the community to characterize field sites.
• With the Web Service, you can retrieve subset data (in real-time) for any location(s), time period and area programmatically using a REST web service. Web service client and libraries are available in multiple programming languages, allowing integration of subsets into users' workflow.

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