Submitted to: Biannual Workshop in Color Photography and Videography in Resource
Publication Type: Proceedings
Publication Acceptance Date: 9/5/2005
Publication Date: 10/6/2005
Citation: Booth, D.T., Cox, S.E., Berryman, R.D. 2005. Stream width and other resource measurements from vlsa imagery. Biannual Workshop in Color Photography and Videography in Resource. #13 CD-ROM. Interpretive Summary: Managers of public lands containing riparian systems are often faced with measuring stream widths and canopy diameters of over-story shrubs and trees. Accurate assessments of average width, length, or diameter of any of these population groups depends on making many measurements evenly distributed over or among the population of plant communities or stream reaches being monitored. Conventionally, such measurements are made by crews working on the ground with tape measures. This is expensive and measurement-distributions are often biased by ground access. It is now possible to obtain very-large scale aerial (VLSA) photography that clearly shows features land managers need to measure. This paper describes three software applications that capitalize on the potential to obtain accurate measurements from high-resolution digital aerial photography. We also present an example geographic information system data overlay of stream-width measurements for a watershed that was developed from measurements extracted form VLSA imagery. We found that by using the software, we could make one measurement per image and complete four images a minute – that is equivalent to ground crews driving or walking to four separate sites and making a measurement. We believe the software will help reduce the cost and increase the sample adequacy of natural-resource monitoring efforts.
Technical Abstract: Collection of reliable data on riparian condition is critical to sustainable management of riparian resources. However, data on primary indicators like stream and greenline width are difficult and expensive to obtain due to travel times and the limitations of ground access. Because very-large scale aerial (VLSA) imagery has sensor resolutions as fine as 1 mm ground sample distance (GSD), it provides new opportunities for all types of linear feature dimension measurement. Linear dimension measurement can be easily obtained from VLSA imagery using three new, ARS-developed software programs. VLSA images have small fields of view and are used for intermittent sampling. Pixel-coverage among images is influenced by small changes in airplane altitude above ground level (AGL) and orientation relative to the ground. These factors affect the object-to-camera distance used for image-resolution calculations. ‘ImageMeasurement’ offers a user-friendly interface for accounting for pixel-coverage variation among images by utilizing a database to manage image-capture metadata. ‘LaserLOG’ records and displays airplane AGL measured from a high frequency laser rangefinder and displays the vertical velocity. ‘Merge’ sorts through large amounts of data generated by LaserLOG and matches precise airplane altitudes with camera trigger times for input to the ImageMeasurement database. We found measurements from aerial images (5 – 26 mm GSD) using Imagemeasurement, LaserLOG, and Merge, were accurate to centimeters with an error less than 10%. We recommend these software packages as a means for expanding the utility of VLSA data.