Data Collection and Monitoring

Why UAV Imagery?

Unmanned Aerial Vehicle (UAV), or drone, technology has become increasingly affordable in recent years, opening the door to endless possibilities for its use. One major goal of the Green Drone AZ project is to highlight how UAV data collection can be utilized as a monitoring tool for ongoing restoration projects. While there is a long list of ways natural resource managers can benefit from this technology, we will try to sum it up in three categories.

Temporal Resolution

This refers to the frequency in which imagery data is captured. Depending on the data source such as satellite or aerial imagery, this could be weekly, monthly, or even bi-annually. For resource managers this can often mean analyzing imagery that is weeks or even a year or more old. The benefit in collecting UAV imagery on the LSRRP site is that project managers can obtain a highly accurate view of conditions on the project site on any given day. This data is vital in monitoring the effectiveness of past management actions, identifying new populations of invasive plant species, and planning future management in the most efficient way possible.

Spatial Resolution

Spatial resolution is just like the resolution of a picture or the pixel size on a camera. In satellite or aerial imagery, this is often represented by a measurement such as meters per pixel. Depending on the source, publicly available satellite or aerial imagery provides a spatial resolution ranging from 1-30 meters/pixel. These imagery data sources are invaluable for large scale research and remote sensing, but they lack the spatial resolution to track changes on a local scale, such as the LSRRP project site. UAV technology provides us the ability to record data with a spatial resolution of 1-10 cm/pixel. This fine scale data can be used to track changes in vegetation populations and model metrics such as canopy height and density.

Spectral Resolution

Spectral resolution refers to the size, number, and position of imaging bands being recorded. Red, green, and blue bands of light on the electromagnetic spectrum are those visible to the human eye. What we typically see when viewing an image on a computer screen is a combination of these bands commonly referred to as RGB. Not only does UAV collected imagery allow us to isolate these bands for further analysis, but we can also collect additional bands of light not visible to the human eye. Spectral bands such as Near Infrared (NIR) and Red Edge (RE) capture the light reflected by plants and can be used to generate a series of spectral indices useful in the classification of plant species. This process entails using machine learning to identify and map individual plant species, saving countless hours of on the ground monitoring.

Vegetation Classification

One of the truly exciting pieces of the Green Drone AZ project is the opportunity for collaboration it provides. By partnering with Arizona State University’s Master of Advanced Study in Geographic Information Systems (MASGIS) Program, Green Drone AZ provides a creative space for graduate level GIS students to perform analysis. At the onset of the project, we set out with a goal to achieve an accurate model of vegetation classification on the LSRRP site. This process of machine learning utilizes structural and spectral data in a series of algorithms to identify unique characteristics pertaining to individual plant species. This training model can then be used to map plant populations across the site. Each year MASGIS students are hired as interns and work to fine tune this process. We are excited to share that work completed in the first year of Green Drone AZ was highlighted in the scientific journal Drones, serving as a significant contribution to the world of vegetation mapping using drone technology.

Long Term Data Collection and Monitoring

The Green Drone AZ data collection effort began in the spring of 2020. Each year Green Drone AZ collects aerial imagery in the fall and spring to account for varying characteristics across the project site. Data is collected over areas that are currently being managed, as well as those that will be addressed in the near future. To date we have collected imagery on nearly 600 acres of the Lower Salt River Recreation Area, spanning from Granite Reef Recreation Area to Coon Bluff Recreation Area. These data sets serve as a valuable monitoring tool to track project progress and the effectiveness of management actions. While it is commonly agreed upon that monitoring is an important piece of the adaptive management process, this resource intensive practice is too often overlooked. By implementing a long term UAV monitoring protocol for this area, Green Drone AZ houses a plethora of data that can be used for past, present and future analysis.

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