Detection of salmonid thermal refugia from airborne thermal infrared (TIR) imagery
Abstract
During elevated summer temperatures, salmonid species seek out areas of cool, well-oxygenated river water to alleviate thermal stress. Collectively known as ‘thermal refugia’, these are of great significance to the ability of salmonids to survive increased water temperatures, and a better understanding of their spatial and temporal characteristics may aid mitigation strategies against the possible effects of climate change on rivers. However, thermal refugia are traditionally hard to detect, and their in-river abundance and spatial patterns are largely unknown. Although previous research has examined TIR imaging as a means to sense river temperatures, few have achieved a resolution amenable to the detection of small thermal anomalies typically used by salmonids, with the majority of literature focusing on the general application of thermal imaging to river temperature detection and analysis. From preliminary research, we note that riverine thermal anomalies (as viewed from TIR imagery) can comprise a number of different forms resulting from a diverse range of sources. Given that the structural, spatial and temporal dynamics of thermal refugia in gravel bed rivers are a presumably a function of the complex geomorphological processes within a catchment, the ability to discriminate multi-scale thermal refugia may aid our comprehension not only of the behaviour of salmonids during high temperature events, but also of the geomorphological phenomena that are fundamental in governing river temperature heterogeneity. Initial thermal infrared imagery acquired in August 2009 suggested that while it is possible to manually detect riverine temperature anomalies, the creation of a dedicated remote sensing platform capable of obtaining both TIR and RGB photography easily and with a resolution amenable to refugia detection would greatly aid our ability to discriminate true refugia from other thermal anomalies (false positives). To this end, we have developed a system able to simultaneously acquire high resolution thermal (c. 20cm GSD) and optical (c. 3cm GSD) imagery with a view towards automatically detecting and classifying refugia. This paper presents the preliminary results of several thermal image acquisition flights undertaken in Quebec, Canada, both before and after the development of the new photography system (Summer 2009 and 2010 respectively), with the intention of exploring the various types of different refugia visible to thermal images. Early indications (both from imagery and ground validation) suggest that while the streamwise location of thermal refugias appears to be temporally stable, their form, extent and temperature are highly dynamic.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.H42B..02D
- Keywords:
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- 1825 HYDROLOGY / Geomorphology: fluvial;
- 1855 HYDROLOGY / Remote sensing;
- 1856 HYDROLOGY / River channels;
- 1895 HYDROLOGY / Instruments and techniques: monitoring