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.