This project will provide measurements of snow depth and vegetation characteristics of Boulder Creek watershed in Colorado that will be used to calibrate and validate airborne LiDAR (Light Detection And Ranging) data acquisition for the Critical Zone Observatories that will take place in May and August. The research team will measure snow conditions on the ground at the time of the LiDAR data acquisition in April-May, since snow conditions change rapidly. In addition, the team will collect control point data so that the two LiDAR flights can be carefully georeferenced, reducing errors in snow pack due to location errors. The team will also measure vegetation characteristics for the full leaf-on flights in late August-early September. The measurements made during the "bare-ground" season will also be used to calculate the snow depths that existed across the watershed during the earlier LiDAR flight.
LiDAR is a powerful tool that provides detailed information concerning topography and landform characteristics at high resolution. Having such data available is crucial to the mission of the Critical Zone Observatories, which are exploring the processes in the region of the Earth's surface that important to sustaining life. This project will enable the LiDAR data to be used with extreme accuracy so that processes within the Boulder Creek watershed can be analyzed more effectively. The effort will help train a graduate student in spatial data acquisition, and several undergraduate students in the details of LiDAR processing and surveying.
Water is a precious resource in the American West, and much of the West’s water comes from melting snow in the mountains. Every winter, snowfall on the mountains replenishes the supply for the summer and fall to come. As the earth’s climate continues to change, it is more important than ever that we have a good inventory of the amount of water stored as snow in the nation’s mountain ranges. Among other things, good estimates of snow pack help water managers determine how much water is available for the coming year, and how much storage capacity the reservoirs should maintain as the spring melt begins. In addition, such estimates are critical for developing, testing, and improving mathematical models that help scientists understand and forecast the water cycle. But measuring the amount of water locked up in the winter snow pack is not an easy task. Mountain snowpack in places like the Rockies and Sierra Nevada Mountains is extremely variable in time and space and extends over enormous areas that are difficult to access. This project was designed to test the potential of an exciting new technology called airborne laser swath mapping (ALSM). Essentially, the technology involves flying a high-precision laser over an area of ground, and using the return signal from the laser to measure the distance to the ground. By taking many measurements – as many as a dozen per square meter of ground – it is possible to create very high resolution maps of either the snow surface (in winter and spring) or the ground surface (in summer). By subtracting maps created in summer versus winter or spring, the technology allows scientists to create high-resolution maps of snow-pack thickness across an entire drainage basin. In addition, an exciting element of the technology is its ability to detect vegetation. In a forested landscape, for example, some portion of most laser shots will bounce off of leaves and branches. The laser system can record these "echoes" and, when the data are processed, it is often possible to reconstruct the height and density of the forest. Thus, when collecting laser scan data over a forested mountain landscape, scientists get two for the price of one: data on snow, and data on the trees. In this project, the team collected laser scan data over the Boulder Creek drainage basin in the Rocky Mountains of Colorado. The aim has been to test the ability of the technology to produce accurate data on snowpack and vegetation, and to use the resulting data to develop a better understanding of the water cycle in this alpine landscape as well as of the forest ecosystem. Two missions were flown: one in spring 2010 when the snowpack was deep, and another in late summer 2010 when the annual snowpack had melted. Fortuitously, these two missions also provided views of the forest canopy at two distinct stages: the spring early-growth season, and the late summer "full leaf" season. During both missions, teams on the ground collected detailed measurements of both the snowpack and the forest canopy in order to test the ability of the laser scans to measure what was happening on the ground. The two missions were successful, and together they resulted in gigabytes’ worth of valuable new data. These airborne data compliment other ALSM data collected at other NSF Critical Zone Observatories (CZO’s). The ground-based surveys were coordinated with scientists from other CZO’s to ensure transferability from site to site. In addition, hyperspectral data from NASA’s Airborne Visible / InfraRed Imaging Spectroradiometer (AVIRIS) were acquired over the same locations as the ALSM flights. Together these measurements provide information of snow properties, vegetation structure, and species type and distribution. As of this writing, the project team is still analyzing the results. More information about the project, as well as about the study site (the Boulder Creek Critical Zone Observatory), can be found at http://czo.colorado.edu.
