USING AERIAL PHOTOGRAPHY AND VIDEOGRAPHY FOR DISTINGUISHING GIANT SALVINIA AND WATERLETTUCE INFESTATIONS IN SOUTHEAST TEXAS

Authors: Everitt, James; YANG, CHENGHAI - TX AG EXP STN-WESLACO; FLORES, D - USDA-APHIS-TPQ-EDINBURG

Submitted to: Forest Service Remote Sensing Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/2/2002
Publication Date: 10/15/2003
Citation: Everitt, J.H., Yang, C., Flores, D. 2003. Using aerial photography and videography for distinguishing giant salvinia and waterlettuce infestations in southeast Texas. Forest Service Remote Sensing Conference Proceedings. CD-ROM.

Interpretive Summary: Giant salvinia and waterlettuce are exotic weeds that often invade and clog waterways. Both species are native to South America, but are found in many tropical and subtropical areas of the world. A study was conducted in southeast Texas to evaluate remote sensing techniques to detect giant salvinia and waterlettuce infestations. Field reflectance measurements made on these two weeds showed that they had unique spectral characteristics that facilitated their detection. Color-infrared (CIR) aerial photography was used successfully to distinguish giant salvinia infestations. Waterlettuce could be distinguished on both CIR photography and videography. These results should be of interest to aquatic weed specialists and wetland resource managers who are interested in locating infestations and controlling these two troublesome plants.

Technical Abstract: Giant salvinia (Salvinia molesta Mitchell) and waterlettuce (Pistia stratiotes. L.) are two free-floating aquatic plants (weeds) that often invade and clog waterways. Both waterlettuce and giant salvinia are native to South America, but are found in many tropical and subtropical areas of the world, including parts of the southeast U. S. This paper presents data on the light reflectance characteristics of these two weeds and the application of aerial photography and videography for their detection in southeast Texas. Reflectance measurements made on these weeds showed that they had unique spectral characteristics that facilitated their detection on aerial imagery. Giant salvinia occurs in two classes: green giant salvinia (green foliage) and senesced giant salvinia (mixture of green and brown foliage). Both classes had distinct reflectance characteristics. Green giant salvinia and senesced giant salvinia could be distinguished on color-infrared (CIR) aerial photographs where they had pink and grayish-pink or olive-green image responses, respectively. Waterlettuce could be distinguished on both aerial CIR photography and videography where it had light pink to whitish-pink image responses. Computer analysis of a CIR photograph showed that both green giant salvinia and senesced giant salvinia populations could be quantified and that an accuracy assessment performed on the image had an overall accuracy of 87%. Computer analysis of CIR photographic and videographic images of waterlettuce showed that infestations could be quantified and that overall accuracy assessments performed on both images were greater than 83%.