ITSLIVE global glacier velocity data in near-real time

Abstract. Glaciers and ice sheets cover some 15 million square kilometers of the Earth's surface, shaping continental landscapes and modifying climate on a global scale. Recent decades of atmospheric and oceanic warming have induced rapid glacier loss worldwide that has caused sea level rise, flooding, changes to Earth's overall energy balance, and changes in water resources. Accounting for the total impact of glacier change requires observations on a global scale, and planning for future change will require improved understanding of the physical controls that govern glacier change. One key factor that dictates glacier and ice sheet loss is changes in rates of ice flow, the physics of which remain poorly constrained. Our physical understanding of ice flow can be advanced with high-resolution monitoring of glacier flow in near-real time. Automated tracking of glacier flow from space became possible with the launch of Landsat 4 in 1982. Since then, an increasing number of optical and radar satellite sensors have provided a full decade of year-round, global data coverage. This recent plethora of data has introduced new challenges for efficiently processing such large and myriad data streams in a standardized manner with low latency. Here we present the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) Inter-mission Time Series of Land Ice Velocity and Elevation (ITSLIVE) global glacier velocity dataset, which is freely available to the public and is currently on major release version 2. 0. ITSLIVE has computed surface velocities using every, excluding those with high cloud cover, available image from Landsat 4 through Landsat 9 as well as Sentinel-1 and Sentinel-2, creating a global glacier velocity record of over 36 million image pairs dating back to 1982. The ITSLIVE processing chain automatically performs feature tracking on more than 20 000 image pairs per day, within minutes of image availability, and will soon include data from Sentinel-1C and NASA-ISRO SAR Mission (NISAR) satellites. This paper describes the ITSLIVE processing chain and provides guidance for working with the cloud-optimized velocity data it produces.