Colin J. Gleason (University of Massachusetts Amherst, United States); Brent A. Williams (Jet Propulsion Laboratory, California Institute of Technology, United States); Craig B. Brinkerhoff (Yale University, United States); Tamlin M. Pavelsky (University of North Carolina, United States); Cassie Stuurman (Jet Propulsion Laboratory, California Institute of Technology, United States); Jonathan A. Flores (University of Massachusetts Amherst, United States); Elisa Friedmann (University of Massachusetts Amherst, United States); Travis T. Simmons (University of Massachusetts Amherst, United States)

The SWOT mission is required to measure rivers > 50 m wide—however, much narrower rivers are visible in Level 1 SWOT Single-Look Complex (SLC) imagery. These narrow rivers comprise almost 90% of global river length, and having SWOT RiverSP products for these would be a boon for greenhouse gas exchange and discharge studies. While detection of narrow rivers in the SLC remains a viable path, we seek to first characterize the performance of higher-level SWOT products. We present here an evaluation of the Level 2 SWOT Pixel Cloud (PIXC) product over the four distinct regions of CONUS: specifically, the 2-digit hydrologic units (HUC2) 01, 08, 15, and 17. We use the National Hydrography Database Plus High Resolution river database to mask filtered PIXC data from July 2023 to May 2025 and generate coverage statistics and estimate water surface elevation for more than 4.2 million reaches. To understand what the narrowest river SWOT can detect is, we ask: what does detected mean? Preliminary results suggest that rivers down to 30 m are detected as reliably as rivers 50 m wide, but a smaller number of these narrow reaches yield quality heights. This conclusion is highly sensitive to the definition of ‘detection,’ and we will explore these sensitivities in this presentation.