Snow cover change detection with laser scanning range and brightness measurements

Laser scanning is a well-established method of topographic measurement, but the intensity data have not been used until very recently, as the first calibration methods have become available. Since the data from airborne or terrestrial laser scanning are sometimes the major or only source of (brightness) information from a particular area, the intensity calibration and applications have become a topic of active research. This has required extensive experimental research, which has been possible with a large variety of laser instruments available for our study.

The snow-forest interaction in the boreal regions is an important and timely topic because of the rapid environmental and climate changes. As the snow-vegetation albedo is an important parameter in climate models, long-term monitoring of snow brightness effects is needed in the investigation of climate trends, especially in boreal regions, where strong effects of the global climate change are expected. Range and brightness measurements from airborne and terrestrial laser scanning would provide an easy-access tool for snow cover monitoring and provide reference and ground truth for airborne and satellite campaigns. We present the first results of the test campaign of snow cover monitoring using the brightness data obtained with a terrestrial laser scanner, and present the ongoing research for laser-based reflectance experiments in snow monitoring. The changes (due to, e.g., snowmelt) are clearly visible in the range and intensity data, and these first results call for more extensive monitoring and measurement campaigns. We also present a newly developed radiometric calibration concept for laser scanners, based on portable reference targets, which have also been applied in snow cover measurements. We have also carried out an extensive study of the challenges in the calibration of backscattered laser signal.

The brightness data combined with the topographic and orientation information obtained from laser scanners will provide an effective in situ and remote snow metamorphism and change detection tool, which has not been applied thus far. The results and new methods will be applied in the validation of airborne and satellite-based snow albedo monitoring campaigns (e.g., in the Finnish Lapland) and in small-scale snow cover change detection of representative sample areas in the boreal forests.