The document summarizes an experiment to detect wind-thrown trees in VHF and UHF SAR images. It finds that VHF SAR (CARABAS-II) could detect trees over 15cm in diameter if the trunk direction deviated less than 22 degrees from the flight heading, while UHF SAR (LORA) could detect all trees with a deviation under 22 degrees, regardless of size. LORA images provided more distinct detections of trees due to higher resolution. Comparing pre-and post-storm SAR images could likely improve detection of wind-thrown forests using change detection algorithms.

1. Detection of Wind-Thrown Trees in VHF/UHF SAR Images Johan Fransson, Andreas Pantze Swedish University of Agricultural Sciences (SLU) Anders Gustavsson, Lars Ulander Swedish Defence Research Agency (FOI) IGARSS – Beyond the Frontiers: Expanding our Know-ledge of the World, Vancouver, Canada, 25-29 July 2011

6. Test site – Remningstorp IGARSS 2011 ALOS PALSAR image: Copyright JAXA

8. Example of wind-thrown single tree IGARSS 2011 Simulated wind-thrown single tree positioned on an open field with the root end uplifted (here with a breast height diameter of 25 cm and a trunk direction of 80°)

9. Layout on the open field IGARSS 2011 Diameter in breast height (cm) Area: 200×300 m 2 Tree direction (degree) Area: 200×300 m 2

12. Flight program to map experiment set-up IGARSS 2011 CARABAS-II (ping-pong mode) Radar aim point @ p2 Labels at start of registration LORA

13. Layout on the open field IGARSS 2011 Diameter in breast height (cm) Area: 200×300 m 2 Tree direction (degree) Area: 200×300 m 2

14. CARABAS-II 2006 - Image chips r06_2_10 r06_2_1 r06_2_ 3 r06_2_ 8 r06_2_ 4 r06_2_ 9 r06_2_ 7 r06_2_ 2 r06_2_1 1 35° / 125° 215° / 305° 80° / 170° 260° / 350° 125° / 215° 170° / 260° 350° / 80° 305° / 35° 102° / 192° 200 m 300 m IGARSS 2011 xxx° = Flight heading yyy° = Illumination direction

15. LORA 2006 - Image chips r06_ 3 _ 5 r06_ 3 _ 9 r06_ 3 _ 4 r06_ 3 _ 6 r06_ 3 _ 7 r06_ 3_11 r06_ 3 _ 12 r06_ 3 _ 8 215° / 125° 35° / 305° 260° / 170° 80° / 350° 305° / 215° 350° / 260° 170° / 80° 125° / 35° r06_ 3 _ 3 282° / 192° 200 m 300 m xxx° = Flight heading yyy° = Illumination direction IGARSS 2011

16. Results – single trees IGARSS 2011 Breast Height Diameter (cm) CARABAS-II Images Acquired in 2006 (12 passes including repeated headings) Difference between trunk direction and flight heading (°) Number of trees Number of trees visible in imagery Proportion of trees visible in imagery (%) 15 0 20 0 0 22 5 0 0 45 20 0 0 90 15 0 0 20 0 20 16 80 22 5 4 80 45 20 0 0 90 15 0 0 25 0 25 25 100 11 25 24 96 22-23 35 14 40 34 10 2 20 45 20 0 0 56 10 0 0 67-68 25 0 0 79 15 0 0 90 15 0 0

17. Results – single trees IGARSS 2011 Breast Height Diameter (cm) LORA Images Acquired in 2007 (12 passes including repeated headings) Difference between trunk direction and flight heading (°) Number of trees Number of trees visible in imagery Proportion of trees visible in imagery (%) 15 0 15 15 100 22 5 5 100 45 30 0 0 90 10 0 0 20 0 15 15 100 22 5 5 100 45 30 0 0 90 10 0 0 25 0 20 20 100 11 20 20 100 22-23 35 35 100 34 15 13 87 45 30 0 0 56 15 0 0 67-68 25 0 0 79 10 0 0 90 10 0 0