Data Latency Terminology
NASA and other Earth science data providers use different terminology to describe data latency. The terms near real-time (NRT), low latency, and expedited are often used interchangeably to refer to data that are made available more quickly than routine processing allows.
In 2016, the Time Sensitive Applications of NASA Data workshop was held at NASA's Langley Research Center in Hampton, VA, to identify, coordinate, and focus attention on low-latency satellite data. At this workshop the terms for latency were defined and agreed to by participants across NASA for all data managed by NASA's Earth Observing System Data and Information System (EOSDIS) on behalf of NASA’s Earth Science Division. The table below summarizes these terms.
Term | Latency | Purpose |
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Real-time | Less than 1 hour | These terms are often used to refer to data that are made available more rapidly than routine processing allows. They are used for a range of applied sciences, decision and tactical support, monitoring, and early warning of events. |
Near real-time (NRT) | 1 to 3 hours |
Low latency | 3 to 24 hours |
Expedited | 1 to 4 days |
Standard routine processing | Generally 8 to 40 hours, but up to 2 months for some higher-level products | Standard products provide an internally consistent, well-calibrated record of Earth’s geophysical properties to support science. |
A new data latency product called ultra real-time (URT) is available through NASA's Fire Information for Resource Management System (FIRMS). URT products from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) thermal anomaly products are available within 60 seconds of acquisition via direct download for display on the FIRMS Fire Map. Note that URT has not been adopted as a formal latency designation by EOSDIS. For more information about URT data in FIRMS, please see FIRMS Adds Ultra Real-Time Data from MODIS and VIIRS.
Low-latency data products are made available more rapidly than standard processing to support users interested in monitoring a wide variety of natural and human-made phenomena. In the context of NASA data, low latency products are distinct from standard data products in that the algorithms for low latency products are modified to expedite data availability.
One key difference between some NRT and standard products is that NRT data use predictive orbit information for geolocation instead of definitive orbit information, which may not be available until after the NRT products are produced.
A second key difference applies to NRT products that make use of ancillary data as part of the processing algorithm from sources other than the satellite. These ancillary data are combined with the satellite data to create higher-level products. Some algorithms for NRT data products use different or less accurate ancillary data than standard products. Standard products are processed using definitive geolocation and instrument calibration, and provide an internally consistent, well-calibrated record of Earth’s geophysical properties to support scientific research.
These science-quality standard data products require routine processing, which takes time. They are typically made available between eight hours to two months from data acquisition. If latency is not a primary concern, users are encouraged to use standard science products.
EOSDIS data products are processed at various levels ranging from Level 0 to Level 4. Level 0 products are raw data at full instrument resolution. At higher levels, the data are converted into more useful parameters and formats. NRT data are often provided at Level 0, 1, and 2; some are Level 3 products.
Level Name | Processing Level |
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Level 0 | Level 0 data products are reconstructed, unprocessed instrument/payload data at full resolution; communications artifacts (e.g., synchronization frames, communications headers, duplicate data) are removed. |
Level 1A | Level 1A data products are reconstructed, unprocessed instrument data at full resolution, time-referenced, and annotated with ancillary information, including radiometric and geometric calibration coefficients and georeferencing parameters. |
Level 1B | Level 1A data that have been processed to sensor units (not all instruments will have a Level 1B equivalent). |
Level 2 | Level 2 data products are derived geophysical variables at the same resolution and location as the Level 1 source data. |
Level 3 | Level 3 data products are variables mapped on uniform space-time grid scales, usually with some completeness and consistency. |
Level 4 | Level 4 data products are model output or results from analyses of lower level data, e.g., variables derived from multiple measurements. |
Explore NRT Imagery and Data
NASA's Land, Atmosphere Near real-time Capability for Earth observation (LANCE) supports users interested in monitoring a wide variety of natural and human-made phenomena.
NASA provides satellite imagery in real-time and NRT on the Worldview interactive data visualization application. For example, NASA’s Global Imagery Browse Services (GIBS) and Worldview provide imagery from geostationary platforms available in 10-minute increments approximately 40 minutes after the imagery is captured by an instrument aboard the platform. Many products are available within three to five hours of being observed.
Resources
Summary of the Workshop on Time-Sensitive Applications of NASA Data. The Earth Observer, 29(2): 19-22.
Davies, D.K., et al. (2017). Workshop on Using NASA Data for Time-Sensitive Applications. IEEE Geoscience and Remote Sensing Magazine, 5(3): 52-58. doi:10.1109/MGRS.2017.2729278