Large-scale aerial images capture details of invasive plant populations

Authors: Blumenthal, Dana; Booth, D; Cox, Samuel; Ferrier, Cara

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2007
Publication Date: 9/15/2007
Citation: Blumenthal, D.M., Booth, D.T., Cox, S.E., Ferrier, C.E. 2007. Large-scale aerial images capture details of invasive plant populations. Rangeland Ecology and Management 60:532-528.

Interpretive Summary: Satellite and aerial remote sensing have been successfully used to measure invasive weed infestations over very large areas, but have limited resolution, and therefore miss the details of weed infestations. Ground-based methods allow for detailed measurements of invasive weeds, but can measure only limited areas. Here we test a new approach that uses a lightweight airplane to combine high resolution imagery with the ability to sample larger areas than would be possible using ground-based methods. We obtained 1,987 images, each representing 48.5 m2 of mixed-grass prairie with 2 mm resolution (the ground area represented by 1 pixel). From these images we were able to reliably measure small patches and even individual plants of the invasive weed Dalmatian toadflax. The time required to analyze images ranged from 4 to 45 seconds for presence/absence data and from 1 to 6 minutes for plant cover data. Toadflax was present in 795 of 1,987 images, but exceeded 1% cover in only 99 images. Given the observed variation among images in toadflax cover, at least 400 images were needed to precisely estimate the mean toadflax cover of 0.2%. These results suggest that such high-resolution aerial imagery could be used to obtain detailed measurements of many invasive weed populations. It may be most useful for identifying incipient weed infestations and measuring population level attributes of weed populations over large areas or rough terrain. Abstract Satellite and aerial remote sensing have been successfully used to measure invasive weed infestations over very large areas, but have limited resolution. Ground-based methods have provided detailed measurements of invasive weeds, but can measure only limited areas. Here we test a novel approach that uses a lightweight airplane, flying at 72 km/hr and 100m altitude, to combine high resolution imagery with the ability to sample at larger scales than would be possible using ground-based methods. We obtained 1,987 images, each representing 48.5 m2 of mixed-grass prairie with 2 mm resolution (ground sample distance). From these images we were able to reliably measure small patches and even individual plants of the invasive forb Linaria dalmatica (Dalmatian toadflax). Ground-based measurements of above-ground toadflax biomass were highly correlated (R2 > 0.93) with point intercept and visual estimate cover measurements from aerial images. The time required to analyze images ranged from 4 to 45 seconds for presence/absence data and from 1 to 6 minutes for cover data. Toadflax was present in 795 of 1,987 images, but exceeded 1% cover in only 99 images. Given the observed variation among images in toadflax cover, at least 400 images were needed to precisely estimate the mean toadflax cover of 0.2%. These results suggest that such high-resolution aerial imagery could be used to obtain detailed measurements of many invasive weed populations. It may be most useful for identifying incipient weed infestations and measuring population level attributes of weed populations over large areas or rough terrain.

Technical Abstract: Satellite and aerial remote sensing have been successfully used to measure invasive weed infestations over very large areas, but have limited resolution. Ground-based methods have provided detailed measurements of invasive weeds, but can measure only limited areas. Here we test a novel approach that uses a lightweight airplane, flying at 72 km/hr and 100m altitude, to combine high resolution imagery with the ability to sample at larger scales than would be possible using ground-based methods. We obtained 1,987 images, each representing 48.5 m2 of mixed-grass prairie with 2 mm resolution (ground sample distance). From these images we were able to reliably measure small patches and even individual plants of the invasive forb Linaria dalmatica (Dalmatian toadflax). Ground-based measurements of above-ground toadflax biomass were highly correlated (R2 > 0.93) with point intercept and visual estimate cover measurements from aerial images. The time required to analyze images ranged from 4 to 45 seconds for presence/absence data and from 1 to 6 minutes for cover data. Toadflax was present in 795 of 1,987 images, but exceeded 1% cover in only 99 images. Given the observed variation among images in toadflax cover, at least 400 images were needed to precisely estimate the mean toadflax cover of 0.2%. These results suggest that such high-resolution aerial imagery could be used to obtain detailed measurements of many invasive weed populations. It may be most useful for identifying incipient weed infestations and measuring population level attributes of weed populations over large areas or rough terrain.