SAR Tomographic imaging of tropical forests: P and L-band

Transcription

1 SAR Tomographic imaging of tropical forests: P and L-band Dinh Ho Tong Minh 1, Thuy Le Toan 1, Stefano Tebaldini 2, Fabio Rocca 2 (1) Centre d Ėtudes Spatiales de la Biosphère (CESBIO), Toulouse, France (2) Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Italy Frascati, PolInSAR st BIOMASS Science workshop, 29 January

2 Airborne tomography TropiSAR campaign in Paracou and Nouragues P-band SAR BIOMASS mission French Guiana Paracou Nouragues P/L-Band 6 tracks Full-Pol 9-1 h, 24/8/29 Data from TropiSAR 29 ESA System Scene Sethi - ONERA Tropical forests forest height : 2-4 m Biomass : 2-6 t/ha P-Band 5 tracks Full-Pol

3 New method TomoSAR (SAR Tomography) o z P-band BIOMASS: TomoSAR x y Gain new knowledge Jointly interferometry - polarimetry to gain vertical (altimetry) information W K kc k 1 k R k C Ground spectrum Volume spectrum 6 g R g C v R v 4 2 Ho Tong Minh et al., TGRS (Tropical forest : Nouragues )

4 SAR Tomography over forested areas SAR Tomography (TomoSAR) 3D imaging of the forest structure P-band TomoSAR yields the forest vertical structure even in the tropical forests. Complex reflectivity along cross-range ( ) direction and signal along image index are related by a Fourier Transform. 4 yn r, x P, r, x exp j bn d r Paracou, French Guiana, HV z r 2b max sin 45 6 Range [m] Nouragues, French Guiana, HV

5 P-band tomographic analysis

6 P-band TomoSAR to understand Scattering Mechanisms Topography Significant scattering contributions are observed at the canopy level in HH polarization, whereas this volume scattering contribution is dominating in HV polarization. Algorithm: Coherent focusing HH channel LiDAR height P-band P-band HV channel LiDAR height Slant range [m] The forest height can be readily determined, and it matches with LiDAR height.

7 Ground range [m] g Ground range [m] TomoSAR to understand how to retrieve biomass SAR resolution cell Intensity (db) Intensity - biomass a Original image Paracou 15 g HV [db] Original image, r P =.37, Slope = t/ha Best fit line in-situ Paracou in-situ Nouragues t/ha - 6 t/ha Height is always measured with respect to 3 m layer terrain elevation. 2 Layer 3m, r P =.75, Slope = 1.84 TomoSAR resolution cell -5 a 3m 15m m Ho Tong Minh et al., TGRS RSE HV [db] t/ha - 6 t/ha The effects of the ground contribution is minimized. Total AGB at large trees is well represented in 2-4 m layer.

8 Airborne data 1 Generation of 6 MHz data Two different processing approaches have been considered : 1. Back projection of airborne tomographic data onto BIOMASS geometry. (6 MHz simulation spaceborne geometry) 3D Tomographic reconstruction BIOMASS data H 4 m B = 125 MHz 2 Simulated Orbits + Impulse Response Function 3 H = 65 Km B = 6 MHz 2. Degrading the resolution of 125 MHz airborne data through linear filtering (ONERA) (6 MHz filtering airborne geometry)

9 Retrieved biomass (t/ha) Retrieved biomass (t/ha) Retrieved biomass (t/ha) Observation 125 MHz r P =.94 R 2 =.89 p <<.1 Implications : 6 MHz Observation 6 MHz airborne geometry r P =.83 R 2 =.69 p =.8 Simulation 6 MHz spaceborne geometry r P =.84 R 2 =.7 p = RMSE = (t/ha) = 5.28 (%) In situ above-ground biomass (t/ha) 1 RMSE = (t/ha) = 9.97 (%) In situ above-ground biomass (t/ha) 1 RMSE = 35.2 (t/ha) = 9.86 (%) In situ above-ground biomass (t/ha) Results at 6 MHz in both the spaceborne geometry and the airborne geometry appear to be well consistent with those observed in the 125-MHz case, indicating that the 3-m layer appears to be the most informative about the AGB. Algorithm: Coherent focusing Paracou forest: Plot size 25 m x 25 m D. Ho Tong Minh, S. Tebaldini, F. Rocca, T. Le Toan, L. Villard, and P. Dubois-Fernandez, "Capabilities of BIOMASS Tomography for Investigating Tropical Forests," Geoscience and Remote Sensing, IEEE Transactions on, vol.53, no.2, pp.965,975, Feb. 215 D. Ho Tong Minh, T. Le Toan, F. Rocca, S. Tebaldini, M. Mariotti d Alessandro, and L. Villard, Relating P-band SAR tomography to tropical forest biomass, IEEE Transactions on Geoscience and Remote Sensing, Vol. 52, No. 2, pp , Feb. 214.

10 L-band tomographic analysis

11 Penetration of L and P-band signal in a tropical forest Optical image at Paracou tropical forest Co-polar phase HH-VV 5 L-band L band 3 2 or P band 5 1 P-band

12 Slant range [m] Tropical forest : Paracou 2D Intensity L-band L and P-band tomographic profiles HV Boreal forest 2D Intensity : Krycklan Tomogram L-band Tomogram L-band 6 6 L-band L-band height [m] Tomogram P-band Tomogram P-band P-band 4 P-band Algorithm: Capon spectrum

13 Imaging the Ground scattering Tree top height [m] Topographic slope [ ] L-band, HH Intensity [db] Original SLC Ground layer Original SLC 1 5 Ground layer 1 5 P-band,HH -5-5 Intensity [db]

14 Co-polar phase [ ] Co-polar phase [ ] Co-pol phase [ ] Co-pol phase [ ] Imaging the Ground scattering Co-polar phase HH-VV or - L-band Original SLC Ground layer Ground slope [ ] Ground slope [ ] 15 1 Original SLC 15 1 Ground layer 1.8 P-band Ground slope [ ] Ground slope [ ].2

15 Conclusions The vertical structure of the forest in a dense tropical forest: At P-band Ground scattering is strongly visible Volume scattering is significantly related to the biomass from 2 t/ha 5t/ha 6 MHz, RMSE 1% at 6.25-ha plots). Forest height can be readily determined, and it matches with LiDAR height. At L-band Ground scattering is partly visible The L-band tomographic profile is quite disturbed as compared to the P-band profile. In this condition, the use of tomographic imaging at L-band in tropical forests appears limited. However, when the forest top height is roughly below 2 m (e.g. in forest regrowth), the tomographic results are expected to be the same as in boreal forests.