PARENT SESSION
Poster Session #44: Remote Sensing and GIS.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Comparison of four techniques for estimation of Green Area Index (GAI) on the shortgrass prairie.

Przeszlowska, Agnes^*,1, Trlica, Milton¹, Weltz, Mark², ¹ Colorado State University, Fort Collins, CO² USDA - Agricultural Research Service, Great Plains Systems Research Unit, Fort Collins, CO

ABSTRACT- Although leaf area measurements are frequently collected in shortgrass prairie studies, accurate and efficient measurements are difficult to obtain. Green area index (GAI), an estimate of the total area of photosynthetically active tissue per unit of ground area, is an important variable of vegetation canopy structure and aboveground net primary productivity. The objectives of this study were to (1) determine the feasibility of using high resolution digital camera images, processed with ERDAS Imagine 8.5, to estimate GAI; (2) correlate GAI estimates from digital camera imagery with normalized difference vegetation index (NDVI) from canopy measurements made with a mulitspectral radiometer; (3) compare the digital imagery and NDVI techniques with laser point frame and standard leaf area meter data for accuracy, precision, and time and cost efficiency. Data were collected from 27, 1-m² plots on the Central Plains Experimental Range shortgrass prairie 60 km northeast of Fort Collins, Colorado in May, July, and October 2001. Data collection included digital images of plots and radiometer measurements taken at nadir from a 2-m elevation, point frame measurements, and harvesting of vegetation from plots for analysis with a leaf area meter. Preliminary data analyses suggest that near-ground digital camera imagery is an efficient estimator of GAI in terms of accuracy (90% confidence), precision, and time as compared with the standard area meter and point frame methods. The digital camera imagery technique for estimation of GAI promises to be a valuable and efficient tool for monitoring green area vegetation changes in the shortgrass prairie.

KEY WORDS: GAI, shortgrass prairie, digital camera, laser point frame