A Direct Approach for Quantifying Stream Shading

Abstract

Management and regulatory standards for stream shading have been established to mitigate excessive stream temperature. Existing shade assessment tools, however, are inadequate for monitoring extensive stream networks. Our objectives were to develop and evaluate an efficient, low-cost field technique for sampling stream-surface shading using digital images and to evaluate the efficiencies and effectiveness of eight different digital image analysis techniques for shade assessments. We developed a quadrat-based technique and associated field equipment to directly photograph stream-surface shading. Sampling at random points (pixels) within the resultant digital images was the most accurate, efficient, and robust image analysis technique. An approach pairing the photographic field technique and the random point-sampling image analysis technique should enable managers to conduct ground-based assessments of stream shading over extensive stream networks. This approach may also provide an efficient means of collecting ground truth samples for even broader scale, remote sensing-based streamshade assessments. Resumen Estándares para el manejo y regulación de sombras sobre corrientes de agua han sido establecidos para mitigar las temperaturas excesivas en las mismas. Las herramientas existentes para la evaluación de sombras son, sin embargo inadecuadas para el monitoreo extensivo de las redes de drenaje. Nuestros objetivos fueron desarrollar y evaluar una te´cnica de campo eficiente y de bajo costo para muestrear la sombra sobre la superficie de las corrientes de agua usando imágenes digitales, y evaluar las eficacias y eficiencias de ocho diferentes te´cnicas de análisis de imágenes digitales para las evaluaciones de sombra. Hemos desarrollado una técnica basada en cuadrantes y asociada al equipo de campo para fotografiar directamente la sombra en la superficie de la corriente de agua. Un muestreo de puntos al azar (pixeles) dentro de las imágenes digitales resultantes fue la te´cnica de análisis de imagen más precisa, eficiente, y robusta. Una estrategia combinando la te´cnica fotográfica de campo y la te´cnica robusta de muestreo de puntos al azar con imagines digitales podría permitir a los usuarios llevar a cabo evaluaciones de campo extensivas de las sombras existentes sobre las corrientes de agua. Esta estrategia podría tambie´n proporcionar medios eficientes para recolectar muestras de campo incluso para evaluaciones de sombra a escalas más amplias usando metodologías basadas en sensores remotos.

Eye in the Sky: Using UAV Imagery of Seasonal Riverine Canopy Growth to Model Water Temperature

“…Prior to the use of UAVs for canopy cover monitoring, methods were limited by the spatial extent that could be covered due to most survey elevations, as well as the cost and time needed to perform the surveys. As recently as 2017, imagery taken from a height of 2-5 m above a stream's water surface was considered aerial imagery [36,37]. Those survey altitude limits further constrained the size of stream that could be surveyed; at the upper bound of those aerial surveys, study sites were limited to streams up to 10 m wide [36].…”

Using LiDAR Data Analysis to Estimate Changes in Insolation Under Large‐Scale Riparian Deforestation1

“…, 1998b), vegetation cover is represented by large‐scale polygons that are characterized in terms of width, average height, and average density. Thus, these approaches provide an average shade estimate for a selected transect of vegetation that is similar to field‐based methods, which provide a channel‐scale estimate of shade cast by vegetation rather than directly assessing shading on the river surface (Clark et al. , 2008).…”