Welcome to the Earthdata Forum! Here, the scientific user community and subject matter experts from NASA Distributed Active Archive Centers (DAACs), and other contributors, discuss research needs, data, and data applications.
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?
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.
Why was radiometric calibration coefficients (RCC) updated from Version 4 to 5 and applied to the entire ASTER line of products?
Since 2000, radiometric corrections derived from onboard calibrator degradation curves have been applied to L1A processing to offset sensor degradation, which can occur naturally as sensors degrade over time while in orbit. Radiometric calibration coefficients (RCC) Versions 1 – 3 relied primarily on the degradation curves from the onboard calibrator. However, studies have found that degradation curves from the onboard calibration were inconsistent against vicarious and cross calibrations. In 2014, the ASTER Science Team combined results of degradation curves from onboard calibration, vicarious calibration and cross calibration approaches to derive radiometric corrections, known as V4; however, inter-band and band traceability inconsistencies have been observed based on other calibration approaches (inter-band and lunar calibrations). The ASTER Science Team decided to rely on vicarious and lunar calibrations to derive degradation curves to generate radiometric corrections, which are known as RCC V5. The recent degradation curves derived from vicarious and lunar calibrations are consistent with inter-band and lunar calibrations and yield same traceability in bands. The degradation curves only affect bands from the VNIR region of the spectrum. Degradation curves for band 1 show minimal difference between RCC V4 and RCC V5 while bands 2 and both forward and backward-looking band 3 showed considerable difference. ASTER expedited products as well as ASTGTM and ASTWTB undergo separate processing route; therefore, they are not impacted by the application of the new RCC V5.
Information on the study can be found in the following document: Tsuchida, S.; Yamamoto, H.; Kouyama, T.; Obata, K.; Sakuma, F.; Tachikawa, T.; Kamei, A.; Arai, K.; Czapla-Myers, J.S.; Biggar, S.F.; Thome, K.J. Radiometric Degradation Curves for the ASTER VNIR Processing Using Vicarious and Lunar Calibrations. Remote Sens. 2020, 12, 427. https://doi.org/10.3390/rs12030427.
What is the difference between ASTER L1T V003 and ASTER L1T V031?
ASTER L1T V003 is generated from forward processing derived directly from the ASTER L1T inventory pre-processed with radiometric calibration coefficient (RCC) Version 4. The intent is to provide quick turnaround of ASTER L1T V003 to users who are interested in generating time series analysis with one consistent RCC version.
ASTER L1T V031 is generated from on-demand processing where Science Scalable Scripts-based Science Processor for Missions (S4PM) processing system is used to generate on-demand products. S4PM generates the user requested ASTER L1T V031 product with RCC V5 applied. The turnaround is dependent on the number of granules the user ordered.
