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Background

Decreasing the data latency of the widely-used Harmonized Landsat and Sentinel-2 (HLS) product will provide significant benefit across Satellite Needs Working Group (SNWG) agencies. HLS is an SNWG-2016 solution that provides a global dataset of surface reflectance with a temporal resolution of two days while retaining the geometry and 30-m spatial resolution of Landsat data. The current data latency is 3-4 days and is constrained by Moderate Resolution Imaging Spectroradiometer (MODIS) atmospheric correction data. This multi-day data latency makes the HLS data less useful to many agencies that utilize satellite data for rapidly changing phenomena (i.e., fires, floods, crops, etc.) and for operational needs. To meet this need, NASA is exploring the ability to decrease the latency by using an alternative auxiliary data source required for atmospheric correction. Currently, the HLS processing pipeline uses the Visible Infrared Imaging Radiometer Suite (VIIRS) data products for atmospheric correction. This solution will explore alternate auxiliary products for atmospheric correction that are published at lower latency compared to VIIRS data products to produce HLS data with a median latency of 6 hours. 

Status

NASA is currently investigating how to develop the low-latency products in the most technologically feasible way. Investigations into the feasibility of National Centers for Environmental Prediction (NCEP) water vapor and ozone products for atmospheric correction and their effects on HLS data quality are currently ongoing. Two options for these solutions that are being evaluated are: 

  1. The creation of a provisional low-latency product that would be replaced when the science quality product is released
  2. A new processing approach that would retain the overall science quality of the data but decrease the overall HLS processing times 

The results from these studies are anticipated to be completed by the end of 2025. 

Solution Characteristics

PlatformsTemporal FrequencyHorizontal ResolutionGeographic DomainLatencySpectral BandsThematic Areas
Landsat-8, Landsat-9, Sentinel-2A, Sentinel-2B, Sentinel-2C2-3 days30 mGlobal6 hoursVisible (VIS), Near Infrared (NIR), Short-Wave Infrared (SWIR)Carbon Cycle and Ecosystems, Disaster Response, Earth Surface and Interior, Land Cover and Land Use Change, Water and Energy Cycle

Societal Impact

The HLS dataset is compatible with the 40-year Landsat record but with a higher temporal resolution of two days. These features have made HLS popular across disciplines and institutions. Considering the widespread usage of HLS among Federal agencies, a low latency version of HLS -- here defined as a 6-hour latency -- will enhance Agencies' ability to respond to wildfires, earthquakes, droughts, oil spills, etc.​