Harmonized Landsat sentinel 2 data can unveil more nuanced dynamics in lacustrine ephemeral algal blooms

The Landsat series, with its nearly 40-year record and 30 m resolution, was foundational for quantifying lacustrine algal blooms. However, its 16-day revisit cycle, often exacerbated by cloud cover, resulted in prolonged and irregular data gaps. NASA's Harmonized Landsat Sentinel-2 (HLS) product alleviated this limitation by integrating Landsat-8 and Sentinel-2 observations, enabling global monitoring every 2-3 days at a medium spatial resolution. This study evaluated the capability of HLS to capture more detailed statistical trends, temporal patterns, and spatial distributions of algal blooms compared to Landsat-8 alone. Using data from four typical eutrophic inland lakes (2016-2023) and validating with high-temporal-resolution MODIS Aqua (1-day) imagery, we generated surface algal bloom area datasets. Results showed that HLS can detect more stable and frequent variations, including but not limited to reducing omissions in peak date recording, capturing finer seasonal trends, increasing available imagery (about 67.27 %), and enhancing record continuity. And HLS also identified ephemeral bloom events that L8 missed. We also validated the consistency of HLS products in inland lakes, finding a strong correlation (R² = 0.93, RSS = 7.74). Our findings underscored that HLS significantly improved monitoring accuracy and efficiency by mitigating the errors inherent to single-sensor reliance, highlighting the critical need for harmonized data constellations in comprehensive aquatic environment mapping.