Measuring rangeland vegetation with high resolution airborne videography in the blue-near infrared spectral region

An airborne video system was used to investigate the visible and near-infra red (NIR) spectral properties of soil and vegetation features across a rang e of common arid landscape types. The four-camera system eras equipped with filters of 25 mm bandwidth centred on 450 nm ('blue'), 550 nm ('green'), 6 50 nm ('red') and 770 nm ('NIR'). The aim was to determine what vegetation properties could be detected by combining data from the blue part of the sp ectrum with the green,red and NIR range, thereby utilizing information cont ained in the first channel of Landsat Thematic Mapper (TM) (450-520 nm). Ad ding information from the blue end of the spectrum did not assist in discri minating between green vegetation and dry vegetation or green vegetation an d bare soil. This separation is best done with a red/NIR ratio. Neither was the blue band an improvement over the PD54 red-green perpendicular distanc e index in distinguishing between soil and vegetation, irrespective of phen ological condition. The blue band can help separate soil from dry vegetatio n when combined with the sum of brightness values in the red and green band s in a perpendicular distance index. These properties of the spectral datas pace lead to a sequential classification procedure by which airborne videog raphy data can be used to measure vegetation components which are much slow er to assess with conventional ground-based methods. Videography has great potential for rapidly verifying or calibrating vegeta tion cover indices derived from satellite data. Vegetation cover derived fr om classifying high resolution video data acquired from a heterogeneous flo odplain area correlated well with vegetation indices computed from contempo rary and co-registered TM data. The most effective indices for measuring ve getation cover with TM data are the PD54 index, brightness in the red band and a perpendicular index based on the sum of the red-green bands and the b lue band. However, multiple regression indicates that the addition of a red /NIR ratio as an additional predictor of cover does not greatly improve the performance of these indices.