(Left) Near infrared photo, used to determine NDVI (Right) Same photo now calculated for NDVI, white reflects areas with high NDVI while black shows low NDVI. Source: UC Davis Center for Watershed Sciences

By Devon Lambert

Remote sensing is all the rage as we start the New Year, largely due to its ability to exponentially increase our areas of analysis for research. What used to take us weeks to survey with traditional field methods can be done in as little as a few hours, sometimes without even leaving our desks. As a result, we’re gaining insight to areas where we used to have little more than questions.

Remote sensing can be done with anything from a drone to a satellite, all producing images that you can then analyze to help answer your question of interest. As new technologies develop and image resolution improves, we are beginning to learn just how many possibilities there are for using imagery data within our research. One new and exciting use for this data is in vegetation classification.

Vegetation is often an important component in our research projects, one great example of this is on the Shasta River.

A salmon swimming among vegetation. Photo by Carson Jeffres, UC Davis

The Shasta River plays a key role for spawning salmon in the Klamath Basin, and one important tributary to the river is Big Springs Creek. Big Springs Creek is a spring-fed creek with water originating from the high slopes of Mount Shasta. A consistent flow of water emerges at the headwaters of the creek at a temperature of about 55 degrees F (12 degrees C).

In addition to being consistently cool, the spring water is also nutrient-rich. As the water flows underground, it picks up nitrogen and phosphorus that allow for emergent aquatic plants to grow in abundance. These plants play an important role in keeping water temperatures cool through the hot summer months. They increase water depth, decrease travel time, and shade the stream from the sun.  During this time, Big Springs provides a majority of downstream flows in the Shasta River, and thus is crucial for reducing daily maximum water temperatures in the Shasta River.

Streamlapse video showing vegetation growth over the summer, with temperature (red) and stage (blue) plotted at upper left. Note the decrease in temperature in the later months of the summer as the vegetation density grows.
Video by Devon Lambert, UC Davis

We have known about this phenomenon for years, but rapid changes in vegetation growth patterns from year to year and within each season made it difficult to measure. Traditional survey methods are often too labor-intensive and expensive to capture those changes. With the use of remote sensing, we are able to more easily quantify the rapid growth changes that occur each season.

By recording aerial imagery over this creek, we are able to create a mosaic image used to map and quantify the amount of vegetation instream. By estimating the amount of vegetation cover, we can more easily model what aquatic conditions should be like throughout the year, which allows us to quantify the effect of emergent vegetation on reducing instream temperatures.  By developing a better understanding of how vegetation can improve conditions for salmon, we can more effectively manage our streams and rivers for salmon habitat.

Yosemite toad at Shorthair Meadow in the Southern Sierra Photo by Teddy Eyster, UC Davis

Remote sensing of vegetation is not only useful in rivers. We can also use the same techniques to create habitat maps for a variety of semi-aquatic species.

The endangered Yosemite Toad exists in a very small subset of meadows across the Sierra Nevada. This species requires specific temperature and surface water habitat conditions in its breeding areas. Mapping those areas is often quite challenging and time consuming.

With the use of high resolution aerial imagery, we are able to create a map of possible areas where the toads may persist by identifying different vegetation types that may correlate with varying surface water conditions.

This map shows the two locations used for remote sensing. Source: UC Davis Center for Watershed Sciences

Within meadows, there is often a gradient of moisture, from wet bogs to dry meadow. The various vegetation communities that grow along this gradient often have unique water tolerances, limiting the places where they occur. By using analytic metrics like NDVI (Normalized Difference Vegetation Index), which quantifies the amount of green vegetation in an area, we are able to create maps of the various meadow habitats that may be suitable for toads or other amphibian species dependent on particular vegetation and surface water conditions.

Aerially-based habitat maps of these meadows help us efficiently survey the areas where the toads are more likely to be, increasing the number of surveys we can complete within a season.  Additional survey data allows us to develop a better understanding of where toads are present and assess what factors may be contributing to the presence or absence of toads in a particular meadow.   With increased understanding of the species’ ecology and their habitat requirements, we can help resource managers in their conservation efforts.

We have only touched the surface when it comes to exploring the potential of remote sensing. These new technologies and their countless applications have and will continue to broaden and enhance our research and understanding. These systems are accomplishing tasks that were once unimaginable and helping us discover seemingly unobtainable answers. We are looking forward to witnessing this technology’s future and the opportunities it affords to science.

Devon Lambert is a field technician at the Center for Watershed Sciences. His field work takes him to remote locations throughout northern and central California, preferably via boat.

Further reading

Jeffres CA, et al. 2009. Baseline Assessment of Physical and Biological Conditions Within Waterways on Big Springs Ranch, Siskiyou County, California. Center for Watershed Sciences, UC Davis

Lusardi RA and Willis AD. 2014. Aquatic plants: unsung but prime salmon habitat. California WaterBlog

Nichols AL, et al. 2014. Water Temperature Patterns Below Large Groundwater Springs: Management Implications for Coho Salmon in the Shasta River, California. River Research and Applications, vol. 30 (4)

Brown, C, et al. 2014. Comparing the Status of Two Sympatric Amphibians in the Sierra Nevada, California: Insights on Ecological Risk and Monitoring Common Species. Journal of Herpetology 48(1): 74-83.

Brown, C, et al. 2015 Yosemite Toad Conservation Assessment Gen. Tech. Rep. R5-TP-040. Vallejo, CA. U.S. Department of Agriculture, Forest Service, Pacific Southwest Region

Weixelman, D. A., et al. 2011. A Field Key to Meadow Hydrogeomorphic Types for the Sierra Nevada and Southern Cascade Ranges in California. Gen. Tech. Rep. R5-TP-034. Vallejo, CA. U.S. Department of Agriculture, Forest Service, Pacific Southwest Region, 34 pp.