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Using SAR Images to Locate Gaps
in the Riparian Forests of Colombian Tropical Lowlands |
 Riparian forest acts as a natural buffer against contamination and sedimentation, protects the banks against erosion, and forms a reservoir for plant biodiversity, a habitat for wildlife and biological corridors when it is continuous. The objective of this study is to locate sections where the riparian forest is either discontinuous or excessively narrow, in an area of savannah dominated by livestock agriculture. The study area is located south of the Meta River in the Department of Meta, Colombia. The goal was also to develop a tool that would allow for guiding and monitoring reforestation initiatives in spite of the cloud cover that affects this area during much of the year and the haze caused by the burning of grasslands.  In contrast to optical sensors, radar sensors have the ability to acquire images that are not affected by clouds or haze. The L-band used by the Synthetic Aperture Radar (SAR) aboard the Japanese JERS-1 satellite provides excellent contrast between forest and either natural or improved pasture. Two SAR images from JERS-1 of March 1996 were georeferenced to an ARC/INFO database of the area containing watercourses digitized from 1:25,000 scale topographic maps. Buffers of 87.5 m (7 pixels of a JERS-1 image) along the rivers were derived to examine an area slightly wider than |
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| that required for protection (30 meters on either bank of a river according to the Colombian law). A median filter was applied to reduce speckle (a grainy noise typical of radar imagery); the image was then classified into forest and non-forest. (Pixels of non-forest falling into the study buffer constitute the areas potentially needing reforestation.) Processing was conducted using EASI/PACE version 6.1 on a Sun SparcStation 5. |
 The figures shows an area of 6.4 km x 6.4 km Southwest of Puerto Gaitán. Clusters of red on the extremities of streams are critical, because they allow contamination and sedimentation to directly enter the stream network. In Colombia, farmers can benefit from economic incentives for reforestation. CORPOICA, the national institution in charge of agricultural development, will use the results of this study to focus reforestation and conservation initiatives towards the environmentally most critical areas. | |||||
International Centre for Tropical Agriculture (CIAT), A.A. 6713, Cali, Colombia Phone: +1 572 445 0000 ext. 373 Fax: +1 572 445 0073 E-mail: n.beaulieu@cgnet.com | http://www.ciat.cgiar.org/ |
Right: Areas potentially needing reforestation appear in red on the filtered JERS-1 SAR
image. Areas not included in the study buffers are masked in yellow.
Below: Close-up of the unfiltered JERS-1 SAR image; the riparian forest is bright on the dark
pasture background. Watercourses are displayed in blue.