Evaluation of current and future Synthetic Aperture Radar (SAR) data to extract forest attributes over various sites is needed. This study focuses on hilly forested man-managed pine plantation for which the estimation of height is of primary importance. Indeed this parameter is a good indicator of the forest productivity i.e. rate of growth. Furthermore it may be used to observe how forests react to their changing environment. ERS (European Remote Sensing Satellite) differential interferogram offers a great potentiality for the retrieval of such parameters. However these data may be affected by different sources of errors. In this study a simple additive model to analyze the error on the estimation of forest height is first proposed. Next, the measured and interferometric-derived height are compared. The results show a low correlation associated with high error. The error analysis shows a good agreement between predicted and observed value especially for the residual relative height. From there, it appears that the main source of error comes from the Digital Elevation Model (DEM) uncertainty and particularly for area under forest cover. A numerical study based on the model of error shows that a low level of coherence – deccorelation effect – may be considerable. Moreover, a systematic error is related to the fact that the scattering center of the layer is not the top of the canopy. Finally, the results indicate that 1) to date, differential interferometry is far from an operational use for forest height retrieval over hilly terrain, 2) even if the total error is a mixture of various sources deccorelation as well as penetration depth effects may be strongly reduced and 3) toward application purpose, a decrease on the DEM uncertainty is needed.
Agricultura 1: 15-23 (2002)

Key words: differential interferometry; SAR; forest; estimation; tree height; error; DEM

CITATED REFERENCES :

1. Askne J, Dammert PBG and Smith G. Interferometric SAR observations of forested areas. 3rd ERS Symposium. Florence, Italy, 1997; 1-8.

2. Beaudoin A, Le Toan T, Goze S, Nezry E, Lopes A, Mougin E, Hsu CC, Han HC, Kong JA and Shin RT. Retrieval of forest biomass from SAR data. Int. J. Remote Sens. 1994;15(14):2777-96.

3. Beaudoin A, Castel T and Rabaute T. Forest monitoring over hilly terrain using ERS INSAR data. Fringe ’96 Workshop. Zurich, Suisse, 1996 a.

4. Beaudoin A, Castel T and Rabaute T. Potential of ERS1/2 Insar Data for forest monitoring over hilly terrain: case study on Austrian pine plantations. PIERS 1996. Innsbruck, Austria, 1996 b.

5. Castel T. Forest biomass retrieval from Synthetic Aperture Radar. Ph. D. Dissertation: ENGREF, Montpellier - France, 1998.

6. Castel T, Martinez JM, Beaudoin A, Wegmüller U and Strozzi T. ERS INSAR data for remote sensing hilly forested area. Remote Sens. Environ. 2000;73(1):73-86.

7. Castel T, Caraglio Y, Beaudoin A and Borne F. Using SIR-C SAR data and the AMAP model for forest attributes retrieval and 3D stand simulation. Remote Sens. Environ. 2001;75(2):279-90.

8. Dobson MC, Pierce L, Sarabandi K, Ulaby FT and Sharik T. Preliminary analysis of ERS-1 SAR for forest ecosystem studies. I.E.E.E.T. Geosci. Remote 1992;30(2):203-11.

9. Dobson MC, Ulaby FT, Pierce LE, Sharik TL, Bergen K, Kellndorfer M, Kendra JR, Li E, Lin YC, Nashashibi A, Sarabandi K and Siqueira P. Estimation of forest biophysical characteristics in northern Michigan with SIR-C/X-SAR. I.E.E.E.T. Geosci. Remote 1995;33(4):877-95.

10. Duren R, Wond E, Breckenridge B and Shaffer S. Metrology, attitude and orbit determination for spaceborne interferometric synthetic aperture radar. In: SPIE, ed. Acquisition, Tracking and Pointing XII, 1998: 1-10.

11. Evans DL, Plaut JJ and Stofan ER. Overview of the Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) missions. Remote Sens. Environ. 1997;59:135-40.

12. Floury N, Le Toan T, Souyris JC and Bruniquel J. A study of SAR interferometry over forests: theory and experiment. Proceedings of IGARSS'97 Symposium. Singapore, 1997; 1868-70.

13. Gens R and van Genderen JL. Review article: SAR interferometry--issues, techniques, applications. Int. J. Remote Sens. 1996;17(10):1803-35.

14. Hagberg JO, Ulander LMH and Askne J. Repeat-pass SAR interferometry over forested terrain. I.E.E.E.T. Geosci. Remote 1995;33(2):331-40.

15. Herland EA. SAR interferometry with ERS-1 in forested areas. Proceedings of IGARSS'95 Symposium. Florence Italy, 1995: 202-4.

16. Holmes MG. Monitoring vegetation in the future: radar. Bot. J. Linn. Soc. 1992;108:93-109.

17. Kasischke ES, Bourgeau-chavez LL, Christensen J, N. L. and Haney E. Observations on the sensitivity of ERS-1 SAR image intensity to changes in aboveground biomass in young loblolly pine forests. Int. J. Remote Sens. 1994;15(1):3-16.

18. Kasischke ES, Melack JM and Dobson MC. The use of imaging radars for ecological applications-A review. Remote Sens. Environ. 1997;59:141-56.

19. Le Toan T, Beaudoin A, Riom J and Guyon D. Relating forest biomass to SAR data. I.E.E.E.T. Geosci. Remote 1992;30(2):403-11.

20. Li FK and Goldstein RM. Studies of multibaseline spaceborne interferometric synthetic aperture radar. I.E.E.E.T. Geosci. Remote 1990;28:88-97.

21. Massonnet D and Rabaute T. Radar interferometry: limits and potential. I.E.E.E.T. Geosci. Remote 1993;31(2):455-64.

22. Massonnet D, Rossi M, Carmona C, Adragna F, Peltzer G, Feigl K and Rabaute T. The displacement field of the landers earthquake mapped by radar interferometry. Nature 1993;364:138-42.

23. Massonnet D. Validation of ERS-1 interferometry at CNES. Second ERS-1 Symposium. Hamburg Germany, 1994; 703-9.

24. Ranson KJ, Saatchi S and Sun G. Boreal forest ecosystem characterization with SIR-C/X-SAR. I.E.E.E.T. Geosci. Remote 1995;33(4):867-76.

25. Schmullius CC and Evans DL. Review article: Synthetic aperture radar (SAR) frequency and polarization requirements for applications in ecology, geology, hydrology, and oceanography: a tabular status quo after SIR-C/S-SAR. Int. J. Remote Sens. 1997;18(13):2713-22.

26. Ulander L, Dammert PBG and Hagberg JO. Measuring tree height with ERS-1 SAR interferometry. Proceedings of IGARSS'95 Symposium. Florence Italy, 1995; 2189-91.

27. Wegmüller U and Werner CL. Farmland monitoring with SAR interferometry. Proceedings IGARSS’95 Symposium. Florence, Italy, 1995; 544-6.

28. Wegmüller U, Werner CL and Strozzi T. SAR interferometric and differential interferometric processing chain. Proceedings IGARSS’98 Symposium. Seattle, 1998; 1106-8.

29. Zebker HA and Goldstein RM. Topographic mapping from interferometric SAR observations. J. Geophys. Res. 1986;91:4993-99.

30. Zebker HA and Villasenor J. Decorrelation in interferometric radar echoes. I.E.E.E.T. Geosci. Remote 1992;30(5): 950-9.