As part of a pilot project Spitfire performed a thermal drone survey of a Fraser Valley Creek to determine the feasibility and accuracy of producing a radiometric orthomosaic to determine water temperatures.  By using recommended flight parameters for radiometric orthomosaic production and recording atmospheric conditions we found that the temperature values from the radiometric orthomosaic agreed to within 2 degrees Celsius of the measured temperature of the stream. With the advent of newer thermal cameras there is no doubt that the resolution and accuracy of thermal imagery will improve.  However, compatibility of the data between certain thermal cameras and processing software is the biggest challenge in the production of georeferenced radiometric orthomosaics.

Advantages of Drone Thermal Mapping vs. Traditional Methods

Traditionally scientists have assessed streams temperatures by using point data loggers.  This involves setting numerous data loggers in often difficult to access areas and considerable field time for crews.  Drones can capture high resolution RGB and thermal imagery non-intrusively in a fraction of the time.
The RGB and thermal imagery collected by drones provides an instant visual of the entire area of interest including those areas that are inaccessible.  In the photogrammetric processing software it is possible to determine temperature values from each pixel in the radiometric orthomosaic and to compare RGB and thermal imagery side by side allowing for easy interpretation.

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Drone Thermal Mapping and Water License Applications

‍In this case the client was exploring the idea of using thermal imaging drones to map groundwater inputs and dry reaches within the creek to provide more information when reviewing water license applications.  Groundwater extraction can cause lowering or raising of the head of an aquifer releasing groundwater into the stream.  Groundwater has poor water quality in terms of diluted oxygen, which is bad for fish, but it also has low water temperature which is good for fish.  By mapping these areas, it facilitates the design of habitat improvements such as increasing diluted oxygen through riffle construction or with changes in flow dynamics. (C.S.)

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Dry reaches of a stream can easily be monitored over time through the high-resolution imagery and LiDAR data which is used to create digital terrain models.  Often dry reaches can be obscured by vegetation which can make identifying these areas by photogrammetry difficult.  LiDAR can penetrate through the gaps in vegetation mapping bare earth and those dry reaches.

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The changing landscape, industrialization, and development have an impact on our water resources. Climate change with its reduced precipitation, increased solar exposure and higher temperatures also have an impact.  Drone mapping aids the authorities in decision making and management of our very important water resources. (C.S.)