Infrared Quantitative Image Velocimetry (IR-QIV): Instantaneous River-Wide Water Surface Velocity Measurements at Centimeter Scales

The changing climate and corresponding increased variability in weather events globally have made clear the need for accurate measurements of streamflow, and the ability to respond quickly to conditions as they occur.

We present Infrared Quantitative Image Velocimetry (IR-QIV), a nearfield remote sensing method that uses infrared imagery of the surface of a river or other body of water to accurately calculate the surface flow field at high resolution in space (~10cm resolution) and time (>1Hz), accurately and continuously, over large areas (1,000s of m^2), for extended periods of time.

IR-QIV is similar to LSPIV (Large Scale Particle Image Velocimetry) and other image-based velocity measurement methods, however, it does not require any illumination or tracer particles since it uses thermal infrared images. IR-QIV has the advantages of being able to measure instantaneous velocity, in addition to mean velocity, and hence makes it possible to calculate metrics of turbulence, from which additional hydrodynamic properties of the flow can be found, including estimates of local bathymetry and bed stress, which allow estimation of discharge from a single, non-contact, measurement.

Since IR-QIV can be used to measure a wide range of flows, can operate day or night and in most weather conditions, and can continuously and robustly measure at high spatial resolution over large areas, it is particularly of use where high accuracy and resolution measurements are required, such as for fish management applications, near hydraulic structures or at other locations with complex hydrodynamics, or at locations where physical access to the water is restricted or dangerous. Because measurements can be set up relatively quickly and without requiring contact with the water, we expect IR-QIV to increasingly become an important tool in responding to changing environmental conditions.

IR-QIV was developed in a partnership between Cornell University, the California Department of Water Resources (DWR), and the US Geological Survey (USGS) for applications including monitoring flow and discharge, and high resolution hydrodynamic measurements near fish guidance structures and barriers. In this presentation we will present an overview of the method, and discuss its capabilities and applications, including considerations that are relevant for any image-based velocity measurement methods, regardless of the imaged wavelengths (thermal, or visible-light).

Figure 1. IR-QIV example: Velocity calculated by IR-QIV (black arrows), plotted over an infrared image of the water surface at Sutter Slough, Califiornia, USA, superimposed on an aerial image.  From: Schweitzer, S. A., & Cowen, E. A. (2021). Instantaneous river-wide water surface velocity field measurements at centimeter scales using infrared quantitative image velocimetry. Water Resources Research, 57, e2020WR029279. https://doi.org/10.1029/2020WR029279