FAQs

Got a question about the DAAC? Never fear, your answer might be here! If it isn't, feel free to reach out to us at lpdaac@usgs.gov 

ASTER

Is there a fee associated with ordering ASTER data?

No. Effective April 1, 2016, all data products distributed by the LP DAAC are available for public distribution at no charge.

What ASTER data products require an order to be placed?

All ASTER data, aside from the Precision Terrain Corrected (AST_L1T) and expedited data (AST_L1AE and AST_L1BE), require an order to be placed, as the product will be made on-demand. This includes radiance data (AST_09, AST_09T, AST_09XT, AST_L1B, and AST_14OTH), elevation data (AST14DEM, AST14DMO), emissivity data (AST_05), temperature data (AST_08), reflectance data (AST_07 and AST_07XT), and unprocessed data (AST_L1A). In addition, ASTER GDEM (ASTGTM) Version 3 data can be accessed using NASA's Earthdata Search.

Can anyone submit a request to acquire new ASTER data over a specific location?

Requests for ASTER acquisitions can be submitted by approved users through the Data Acquisition Request (DAR) tool. More information on how to apply to be an approved user is available through the NASA JPL ASTER website.

Why are the corners clipped for some AST_L1T VNIR only scenes?

These clipped corners are due to errors, such as band offsets or projection of boundary data outside of the scene frame.

Why is there not an AST_L1T scene for every AST_L1A granule?

ASTER Precision Terrain Corrected scenes are not produced if any of the bands in an AST_L1A granule fail during resampling. This typically occurs due to errors in the AST_L1A geolocation arrays. Additionally, since AST_L1T scenes are processed using AST_L1B processing algorithms, AST_L1T scenes are not available when there are any band failures in an AST_L1B granule. Finally, a band in a AST_L1T scene may not be available if the telescope related to the band was not requested to be turned on during acquisition.

How can I tell if a scene is terrain or precision corrected?

This information can be found in the ASTER Precision Terrain Corrected (AST_L1T) metadata, under the field "CorrectionAchieved". This field will be populated with the level of correction (Terrain+Precision, Terrain+Systematic, Systematic, or Precision) obtained for the scene.

What is the difference between terrain and precision correction?

Terrain correction removes geometric errors associated with observing a ground location from an off-nadir angle. AST_L1T scenes that do not have Digital Elevation Model (DEM) available will not have terrain correction. These scenes are typically over open ocean and small islands. Precision correction removes the geometric errors due to imprecise knowledge of the satellite's location and velocity (or ephemeris), its behavior (yaw, pitch, or roll), and the detector acquisition information. Precision correction is completed when 20 or more ground reference points can be matched to an equivalent region in an ASTER Precision Terrain Corrected (AST_L1T) scene. If these locations cannot be matched, the scene will not be precision corrected. This may be due to clouds in the region, a dark scene (potentially a scene captured at night), the angle of the sun and shadows in the scene, or the scene is a thermal infrared (TIR) scene. If a scene is not precision terrain corrected, it will have systematic correction, similar to a north-up AST_L1B scene. For more information please read the AST_L1T Quick Guide.

What is the difference between ASTER GDEM Versions 1, 2 and 3?

ASTER GDEM Version 1, released in June 2009, was generated using stereo-pair images collected by the ASTER instrument aboard Terra. ASTER GDEM coverage spans from 83 degrees north latitude to 83 degrees south, encompassing 99 percent of Earth's landmass and comprising 16,602 1° by 1° tiles.

Version 2 added 260,000 stereo-pairs, improving coverage and reducing the occurrence of artifacts. The refined production algorithm provided improved spatial resolution, increased horizontal and vertical accuracy, and superior water body coverage and detection. It comprises 16,704 tiles.

Version 3 added another 360,000 stereo-pairs and comprises 22,912 tiles. Compared to Version 2, Version 3 has fewer void areas due to the increase of ASTER stereo image data and new processes, and a decrease in water area anomaly data due to the incorporation of new global water body data. With this release, an additional global product is now available: the ASTER Water Body Database (ASTWBD). This raster product identifies all water bodies as either ocean, river, or lake. Each GDEM tile has a corresponding ASTERWBD tile, which can be used as a water bodies mask.

Does ASTGTM V3 have special policy agreements similar to V2?

ASTGTM V3 does not have restrictions on reuse, sale, or redistribution. Please see proper data citations and policies at https://lpdaac.usgs.gov/data/data-citation-and-policies/.

What files do you get when you request HDF-EOS or GeoTiff?

With GeoTiff (.tif) as an output file format, there are multiple files associated with one granule; therefore, the file is compressed. The compressed file contains a GeoTiff file for each band as well as GeoTiffs for metadata and ancillary data files. The HDF-EOS file contains all the band information and ancillary data in one file.

What software can be used with ASTER?

A number of applications and software packages can be used to work with ASTER data. A list of potential resources can be found on ASTER Tools and Services.

What ASTER data would be best to use for mineral research?

Some minerals have distinctive shortwave infrared spectral signatures while others have unique thermal infrared emissivity spectral signatures. Therefore, ASTER Level 2 data products (AST_05, AST_07, AST_07XT, AST_08, AST_09, and AST_09XT) are suitable for mineral research. However, it is highly recommended that users perform additional research on their own for their mineral of interest.

MODIS

Why do I get some unexpectedly large or hard to interpret data values when I am working with MODIS data?

Most MODIS Science Data Set (SDS) layers are in 8-bit or 16-bit format. This requires a scaling factor to be applied. For information on the scale factor of a specific band for a specific product, please see the corresponding DOI landing. DOI landing pages can be access via the MODIS Products Table. More information on the scaling factor is available by watching the Part 2s of the MODIS Version 6 Data at NASA's LP DAAC videos on YouTube.

How can I interpret the MODIS Quality data layers?

The majority of the MODIS land products contain quality layers. Each layer contains a lot of information about the quality information associated with each individual pixel in the scene. To aid in file size management, this data has been packed in bit format. The LP DAAC offers several tools to aid in unpacking the bits and interpreting the quality information. The Application for Extracting and Exploring Analysis Ready Samples (AppEEARS) allows users to view and interact with quality information for a variety of products before they download the data. The ArcGIS MODIS Python Toolbox provides users with a simple and intuitive way to decode and interact with quality layers for previously downloaded MODIS products using ArcGIS. More information on interpreting the quality information and using these tools is available by watching the Part 3s of the MODIS Version 6 Data at NASA's LP DAAC on videos YouTube.

Why do some MODIS data not extend beyond March 2017?

Occasionally MODIS data are reprocessed to provide updates to make previous data even more accurate and to create new data products. Recently MODIS data were reprocessed from Version 5 data to Version 6. Version 5 data are now in the process of being retired. Part of this process included the ceasing of forward processing on March 31, 2017. MODIS Version 5 data will be available for download until April 9, 2018. After this date the data will officially be retired and no longer distributed by the LP DAAC. Visit the LP DAAC MODIS Products Table to see the available MODIS Version 6 data products and to access their individual DOI landing pages. Each DOI landing page will describe the improvements to that specific data product and how it differs between Version 5 and Version 6.

ECOSTRESS

Why are there no ECOSTRESS observations over my specific study site?

ECOSTRESS priority data coverage includes the lower (48) continental United States (CONUS), twelve 1,000 x 1,000 km key climate zones, and twelve Fluxnet sites.

Red polygons represent high priority targets for acquisition.  Note instrument is capable of additional coverage and can be commanded to acquire data over additional regions given sufficient downlink.

Why are there Level 1B ECOSTRESS observations over my specific study site, but not matching higher-level observations over my specific site?

There may be ECOSTRESS Level 1B observations that are acquired over your study site, but if the observation lies outside of one of the zones described above, they will not be processed into the L2-L4 products. Also, higher-level products are dependent on a suite of input variables in addition to the Level 1B radiance files. If circumstances such as cloudy observations, missing required input variables, or higher-level product model failures, this will lead to fill values or no data over your study site.

Why are there gaps in the observation record?

ECOSTRESS was launched on June 29, 2018, and moved to autonomous science operations on August 20, 2018, following a successful in-orbit checkout period. On September 29, ECOSTRESS experienced an anomaly with its primary mass storage unit (MSU). ECOSTRESS has a primary and secondary MSU (A and B). On December 5, 2018, the instrument was switched to the secondary MSU and operations resumed with initial acquisitions over Australia and wider coverage resumed on January 9, 2019. The initial anomaly was attributed to exposure to high radiation regions, primarily over the Southern Atlantic Anomaly, and the acquisition strategy was revised to exclude these regions from future acquisitions. On March 14, 2019, the secondary MSU experienced a similar anomaly temporarily halting science acquisitions. On May 15, 2019, a new direct streaming data acquisition approach was implemented, and science acquisitions resumed.

From February 8 to February 16, 2020 an ECOSTRESS instrument issue resulted in a data anomaly that created striping in band 4 (10.5 micron). This anomaly has affected ECOSTRESS Level 1B and Level 2 datasets, which include the attitude, geolocation, radiance, cloud mask, land surface temperature and emissivity data products. These data products have been removed from data access and are no longer available. Masked data are expected to be available by March 16, 2020 for all product levels. Data acquired following the anomaly have not been affected.

Why are some of my Level 1B Radiance observations missing bands 1 and 3?

In order to implement the direct streaming option, the new acquisition approach is to only download TIR data for bands 2, 4, and 5. The data products are as before, except that TIR bands 1 and 3 are not downloaded and contain fill values (in L1 radiance and L2 emissivity). All ECOSTRESS observations from May 15, 2019 to present will contain fill values in bands 1 and 3.

Why do I see striping artifacts in the ECOSTRESS data--even after projecting the swath data to a grid?

There are multiple possible reasons for striping artifacts in ECOSTRESS data acquisitions. (1) Detectors in TIR bands 1 and 5 and the SWIR band were damaged during testing, before launch. This will result in 8 lines of missing data every 128 lines in the across-track direction in those bands, and an error code of -9998 for the missing pixels. These missing pixels are filled using a neural network algorithm, but may appear as striping in cases where the prediction is not accurate. (2) ECOSTRESS is a push-whisk instrument, which means that a scene is made up of 44 scans, stacked in the along-track direction. Each of these scans has an overlap, and so before geolocation, some apparent spatial discrepancies may be observed. This will be visually corrected through geolocation. (3) An overlap between ECOSTRESS scans results in a line overlap and repeating data. Additional information is available in section 3.2 of the User Guide. If using AppEEARS or the swath2grid.py script to reproject the swath data, you still may see artifacts due to nearest neighbor resampling.

Why are there small patches of missing data?

Data are transferred in “packets”, which represent data bundles. Occasionally, a single packet is corrupted as it is transferred from the instrument to the ground data system.

Sometimes there are obstructions in the image, what is this?

Occasionally the ISS must adjust the position of some of its solar panel arrays. These may pass into the ECOSTRESS field of view.

Can I use ECO1BGEO files with corresponding Level 1B - Level 4 files if the build ID and/or product version number differ?

Yes, ECO1BGEO files are not reprocessed unless necessary and thus they may have a build ID and/or product version number different from corresponding Level 1B radiance or higher-level products.

GEDI

Why do GEDI elevation values over my region of interest not match elevation values from another digital elevation model (DEM)?

A known ranging issue affects the absolute elevations of two of the eight beams (Beam0000 and Beam0001). Users are encouraged to read Section 3.7 of the ATBD for GEDI Waveform Geolocation for L1 and L2 products to fully understand the application of geophysical corrections. See Sections 6 and 7 of the Level 1 User Guide for a full description of quality and known issues. Section 6 of the Level 2 User Guide also provides important quality filtering information to ensure the elevation values are not affected by erroneous and/or lower quality returns.

How do I find GEDI orbits intersecting my region of interest?

GEDI Finder is a web service for locating GEDI orbits (files) that intersect an input bounding box. The GEDI Finder web service is available at: https://lpdaacsvc.cr.usgs.gov/services/gedifinder.

How are GEDI beams split and dithered and what do these two terms mean?

Two of the GEDI lasers are full power, and the third is split into two beams, producing a total of four beams. Beam Dithering Units (BDUs) rapidly change the deflection of the outgoing laser beams. This produces eight ground tracks: four power and four cover tracks. Footprints are separated by 60 m along track and 600 m across track.

How should I quality filter GEDI L1B - L2B data?

Although all L2A and L2B algorithm results are available for every shot with a valid waveform, the science team recommends the following guidelines for selecting “best” data:

GEDI coverage beams (beams 0000, 0001, 0010, and 0011) were designed to penetrate canopies of up to 95% canopy cover under “average” conditions. For this reason, it is recommended to preference the GEDI full power beams in cases of dense vegetation. Second, nighttime GEDI data (solar_elevation < 0) is recommended over daytime acquisitions due to the negative impact of background solar illumination. It is then recommended to use the quality_flag dataset to remove erroneous and/or lower quality returns. For example, a quality_flag value of 1 will indicate that the shot meets criteria based on energy, sensitivity, amplitude, and real-time surface tracking quality.

How do I subset GEDI data spatially and by band/layer?

GEDI data can be spatially subset for specific bands/layers using the services provided in NASA’s Earthdata Search Client. However, spatial querying is not available in Earthdata Search Client. It is recommended to use the GEDI Finder web service to first identify GEDI granules intersecting your region of interest. Once you have the list of GEDI granules that you would like to spatially subset, you can search for those granules using Earthdata Search Client and add them to your project. From there, under Edit Options > Customize you can perform spatial subsetting and band/layer subsetting.

In addition to the GEDI Finder web service, the LP DAAC has developed a data prep script called the GEDI Spatial and Band/layer Subsetting and Export to GeoJSON (GEDI Subsetter) script. The GEDI Subsetter is a command line executable python script that allows users to spatially subset GEDI files by submitting a GeoJSON or bounding box (Upper Left, Lower Right) region of interest. Users can also perform layer subsetting by defining specific GEDI datasets to be included in their subset output. The script will extract the desired layers, clip to the region of interest, and export as a GeoJSON file of points (shots) that can easily be loaded into GIS and/or Remote Sensing software for further visualization and analysis.

To access the GEDI Subsetter and for additional information on how to use it, visit: https://git.earthdata.nasa.gov/projects/LPDUR/repos/gedi-subsetter/browse.

How do I cite the data?

The following citation information is applicable for the GEDI01_B.001, GEDI02_A.001, and GEDI02_B.001 products:

Dubayah, R., Luthcke, S., J. B. Blair, Hofton, M., Armston, J., Tang, H. (2020). GEDI L1B Geolocated Waveform Data Global Footprint Level V001 [Data set]. NASA EOSDIS Land Processes DAAC. Accessed YYYY-MM-DD from https://doi.org/10.5067/GEDI/GEDI01_B.001.

Dubayah, R., Hofton, M., J. B. Blair, Armston, J., Tang, H., Luthcke, S. (2020). GEDI L2A Elevation and Height Metrics Data Global Footprint Level V001 [Data set]. NASA EOSDIS Land Processes DAAC. Accessed YYYY-MM-DD from https://doi.org/10.5067/GEDI/GEDI02_A.001.

Dubayah, R., Tang, H., Armston, J., Luthcke, S., Hofton, M., J. B. Blair (2020). GEDI L2B Canopy Cover and Vertical Profile Metrics Data Global Footprint Level V001 [Data set]. NASA EOSDIS Land Processes DAAC. Accessed YYYY-MM-DD from https://doi.org/10.5067/GEDI/GEDI02_B.001

What science datasets does the GEDI Geolocated Waveforms product contain?

The L1B product provides corrected geolocated waveform returns, including transmit and receive housekeeping and relevant instrument parameters, as well as geolocation parameters and geophysical corrections. The detailed product contents are defined in the GEDI L1B Product Data Dictionary.

What science datasets does the GEDI Level 2A product contain?

The L2A product contains information derived from the geolocated GEDI return waveforms, including ground elevation, highest and lowest surface return elevations, energy quantile heights (“relative height” metrics), and other waveform-derived metrics describing the intercepted surface. The detailed product contents are defined in the GEDI L2A Product Data Dictionary.

What science datasets does the Global Ecosystem Dynamics Investigation Level 2B product contain?

The L2B product contains biophysical information derived from the geolocated GEDI return waveforms, including total and vertical profiles of canopy cover and Plant Area Index (PAI), the vertical Plant Area Volume Density (PAVD) profile, and Foliage Height Diversity (FHD). The detailed product contents are defined in the GEDI L2B Product Data Dictionary.

Why is the uneven spacing between beams across track?

While the design of the instrument and its operational implementation are to provide even cross-track spacing of the beams, several factors cause the beams to have small differences in the cross-track spacing. These factors include slight variations in beam alignment in the instrument frame, changes in altitude of the ISS, and changes in ISS attitude orientation, specifically yaw.

How do I extract elevation and height metrics for alternative algorithm setting groups in L2A?

Only the suggested result for each laser footprint is stored in the root group of the L2A product for each beam. This is currently set to the output of algorithm setting group 1 (see Table 5 of the Level 2 User Guide) and will be updated as post-launch cal/val progresses. Elevation and height metrics outputs for all algorithm setting groups can be found in the geolocation subgroup of the L2A data product. For example, elev_lowestreturn_a is the elevation of lowest return detected using algorithm setting group, relative to reference ellipsoid; and rh_a are the relative height metrics at 1% intervals using algorithm (in cm). See Section 5 of the ATBD for GEDI Waveform Geolocation for L1 and L2 Products for additional details.

How do I extract cover and vertical profile metrics for alternative algorithm setting groups in L2B?

Only the suggested result for each laser footprint is stored in the root group of the L2B product for each beam. The suggested result corresponds to the L2A algorithm setting group set in /BEAMXXX/selected_l2a_algorithm and will be updated as post-launch cal/val progresses. In contrast to the L2A data, only a select set of L2B algorithm outputs is stored for each L2A algorithm setting group. These outputs can be found in the /BEAMXXXX/rx_processing subgroup and include the directional gap probability (pgap_theta_a<n>), canopy (rv_a<n>) and ground (rg_a<n>) waveform integrals, and the results of the extended Gaussian fit, fit to the ground waveform (rg_eg_*_a<n>), where <n> is the algorithm setting group <n> (see Table 5 of the Level 2 User Guide). These outputs enable rapid recalculation of L2B vertical profiles for different L2A algorithm setting groups. Examples of this recalculation are being prepared by the GEDI Science Team as Python Jupyter Notebooks.

NASADEM

How is NASADEM different from SRTM?

Although NASADEM is derived from Shuttle Radar Topography Mission (SRTM) raw data, one of the primary differences is the use of the latest unwrapping technique and the reliance of auxiliary data to process the raw data, which were not available during the original SRTM processing. Due to an updated unwrapping technique, the results yield fewer voids in the mountainous regions as well as near the peripheral region of the spatial extent. Additional differences can be found on the DEM Comparison Guide.

What is the NASADEM Filename convention?

Each tile covers 1° latitude by 1° longitude of Earth’s surface. Let’s use NASADEM_HGT_n36w112 as an example. The first and second letters, in this case n and w respectively, cover the four corners of Earth’s surface (North, South, East, West). Therefore, n36 covers latitude 36 to 37 North and w112 covers longitude 112 to 113 West. The HGT extension stands for height or elevation.

Does NASADEM have restrictions on reuse, sale, or redistribution?

NASADEM does not have restrictions on reuse, sale, or redistribution. However, users of NASADEM products are encouraged to cite the product. A Citation Generator is available on each NASADEM DOI Landing Page.

Is there a method to download NASADEM data in bulk?

There are multiple methods to download NASADEM in bulk, such as Data Pool, OPeNDAP, and DAAC2Disk, which are all available at the LP DAAC Tools page.

Why can’t I view some NASADEM layers?

NASADEM has five data products, each with a different number of science data layers. The primary data product is the NASADEM_HGT, an elevation data product, which can be displayed in open source as well as commercial geospatial or visualization software. However, some of the auxiliary data layers are binary files; therefore, they must be imported manually to the software.

Data Access

How can I bulk download data distributed by the LP DAAC?

Bulk download options are available from DAAC2Disk as a script that can be downloaded and executed from the command line. Also, data are available from the LP DAAC Data Pool via HTTPS. Please ensure you have authorized your download method for your Earthdata login account. To accomplish this, log in to your account from the Earthdata Login page, and click on “ Authorized Apps” under "Applications" in the title bar. You will be presented with a list of approved applications. At the bottom of the list click the “Approve More Applications” button. Type in “LP DAAC Data Pool” in the text box and hit enter. In the application search results click the checkbox next to “LP DAAC Data Pool” and then click the “Approve” button. You should be returned to the approved applications page with a green confirmation bar acknowledging your request. Be sure to update your scripts to allow for logging in to your Earthdata login account.

Where is my data order notification?

Typically you will receive a notification that your order was submitted within a few minutes. However, if your order was placed more than 3 days ago and you still have not received a notification from us, please check your spam folder. Also, please add "lpdaac@usgs.gov" to your list of trusted senders to prevent notifications from going to Spam folder in the future. If you have checked your Spam folder and did not receive a notification, please contact LP DAAC User Services at lpdaac@usgs.gov.

What is an Earthdata account and how can I create one?

An Earthdata Login account provides a single access point for user registration and profile to manage all EOSDIS system components (DAACs, Tools, and Services). Your Earthdata Login account helps the EOSDIS program understand how users are using EOSDIS services and this aids in helping improve the user experience through improvements to tool customization and services. The Earthdata Login account is available at no charge to the user and provides open access to EOSDIS data free of charge

Data Citation and Reuse

How do I cite my data?

Each DOI Landing Page provides a citation generator that will automatically create a citation for you based on the data product you are using. The DOI Landing Pages can be found under the search data catalog.

Am I allowed to reuse LP DAAC data?

All data distributed by the LP DAAC contain no restrictions on the data reuse.