Optical remote mapping of rivers at sub‐meter resolutions and watershed extents

Abstract

At watershed extents, our understanding of river form, process and function is largely based on locally intensive mapping of river reaches, or on spatially extensive but low density data scattered throughout a watershed (e.g. cross sections). The net effect has been to characterize streams as discontinuous systems. Recent advances in optical remote sensing of rivers indicate that it should now be possible to generate accurate and continuous maps of in‐stream habitats, depths, algae, wood, stream power and other features at sub‐meter resolutions across entire watersheds so long as the water is clear and the aerial view is unobstructed. Such maps would transform river science and management by providing improved data, better models and explanation, and enhanced applications. Obstacles to achieving this vision include variations in optics associated with shadows, water clarity, variable substrates and target–sun angle geometry. Logistical obstacles are primarily due to the reliance of existing ground validation procedures on time‐of‐flight field measurements, which are impossible to accomplish at watershed extents, particularly in large and difficult to access river basins. Philosophical issues must also be addressed that relate to the expectations around accuracy assessment, the need for and utility of physically based models to evaluate remote sensing results and the ethics of revealing information about river resources at fine spatial resolutions. Despite these obstacles and issues, catchment extent remote river mapping is now feasible, as is demonstrated by a proof‐of‐concept example for the Nueces River, Texas, and examples of how different image types (radar, lidar, thermal) could be merged with optical imagery. The greatest obstacle to development and implementation of more remote sensing, catchment scale ‘river observatories’ is the absence of broadly based funding initiatives to support collaborative research by multiple investigators in different river settings. Copyright © 2007 John Wiley & Sons, Ltd.

Seamless Mapping of River Channels at High Resolution Using Mobile LiDAR and UAV-Photography

“…While green LiDAR is not yet used much for measuring river bathymetry [37], river bed topography has been mapped successfully using aerial photography using linear transform [38][39][40][41] or band ratio transform methods [42][43][44][45]. The most commonly used method is the deep-water correction algorithm developed by Lyzenga [9].…”

“…Aerial imagery based bathymetric models rely on the river bed being visible, so that depth can be modelled (e.g., [44]). This means that the water has to be reasonably clear, the water surface has to be calm enough so as to avoid ripples that cause bi-directional reflectance problems, and the view of the river has to be unobstructed by overhanging trees, for instance.…”

Remote Sensing of Channels and Riparian Zones with a Narrow-Beam Aquatic-Terrestrial LIDAR

“…Some recent progress has been made using remote passive optical systems that relate reflected solar radiation to the depth of water [1][2][3][4]. However, this technique must account for spatiotemporal changes in other variables such as substrate reflectivity due to variations in sediment type and patchy periphyton growth, water turbidity, atmospheric transmission of electromagnetic energy, and reflectance and shadowing from overhanging vegetation on stream banks.…”

Towards the sequential assimilation of SAR-derived water stages into hydraulic models using the Particle Filter: proof of concept

“…Optical imagery has been successfully used in the past to extract flooded areas (e.g. Marcus and Fonstad, 2008). However, the rapid flood recession in small-to medium-sized catchments and the typical weather conditions during flood events hamper systematic and global flood detection with visible satellite imagery.…”