L-Band SAR Polarimetrie für die Ableitung von Waldparametern
Zusammenfassung der Projektergebnisse
There is an in increasing need for forest information related to its importance for the environment and global climate (e.g., monitoring for the Kyoto protocol) as well as forest management aspects. One possible way is to use longer wavelength of synthetic aperture radar (SAR) remote sensing technique, in particular by combining polarimetric technique. The SAR on the L-band ALOS PALSAR provides not only the acquisitions independent of clouds but also polarimetric SAR (POLSAR) observations throughout the globe. This study reported an investigation of the use of POLSAR data for growing stock volume retrieval. Based on the availability of ground-truth data and SAR data the work was limited to the study of Thüringer Wald and Siberian forests. Thirteen and Fourteen ALOS PALSAR L-band quadpol data over forest areas in Thüringer Wald and Siberia respectively have been considered here for the assessment. In order to evaluate the potentiality of ALOS PALSAR L-band full polarimetric radar for estimation of GSV, a number of polarimetric parameters were investigated to characterise the polarisation response of forest cover. Regardless of the weather conditions, a high correlation (R=-0.87) was achieved between polarimetric coherence and GSV. The coherence in sparse forest was always higher than in dense forest. The coherence level and the dynamic range strongly depended on the weather conditions. The four-component power decomposition method has been applied to the ALOS PALSAR L-band fully polarimetric data to compare the decomposition powers with GSV. Double-bounce and volume scattering powers showed significant correlation with GSV. The correlation between GSV and surface scattering power was found to be inconsistent. The correlation between polarimetric decomposition parameters and GSV was enhanced if the ratio of ground-to-volume scattering, which was the ratio of volume scattering times double-bounce and surface scattering, was used instead of considering polarimetric decomposition powers separately. Two empirical models have been developed that describe the ALOS PALSAR L-band polarimetric coherence and ground-to-volume scattering ratio as a function of GSV. The models were inverted to retrieve the GSV for Siberian forests. The best RMSE of 38 m³/ha and R²=0.73 was obtained based on polarimetric coherence. On the other hand, using the ratio of ground-to-volume scattering the best retrieval accuracy of 44 m³/ha and R²=0.62 was achieved. The best retrieval results for both cases were observed under unfrozen condition. Saturation effects for estimated GSV versus ground-truth GSV were not observed up to 250 m³/ha. Therefore, ALOS PALSAR L-band quadpol data can be used to quantify the growing stock volume at stand level with a reasonable accuracy in Siberian forests, although the forest site conditions play a fundamental role for the final accuracy.
Projektbezogene Publikationen (Auswahl)
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"Assessment of the potentiality of L-band quadpol radar for the retrieval of forest structural parameters by means of polarimetric information in central Siberia". Proceedings of ESA living planet symposium, Bergen, Norway, 28 June – 2nd July, 2010
Chowdhury, T. A., Thiel, C. J., & Schmullius, C.
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"Forest structural parameters and growing stock volume retrieval in Thuringian forest using L-band polarimetric radar". Proceedings of POLINSAR 2011, ESA-ESRIN, Frascati, Italy, 24 – 28 January, 2011
Chowdhury, T. A., Thiel, C. J., & Schmullius, C.
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"Growing stock volume retrieval in boreal forest from ALOS L-band polarimetric coherence". Proceedings of IEEE International Geoscience and Remote Sensing Symposium IGARSS 2012, Munich, Germany, 22 – 27 July, 2012
Chowdhury, T. A., Thiel, C. J., & Schmullius, C.
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"Investigating ALOS PALSAR interferometric coherence in central Siberia at unfrozen and frozen conditions: implications for forest growing stock volume estimation. In: Canadian Journal of Remote Sensing 39 (3), pp. 232-250, 2013
Thiel, C. J., & Schmullius, C.
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"Investigating the impact of freezing on the ALOS PALSAR InSAR phase over Siberian forests.-In: Remote Sensing Letters 4 (9), pp. 900-909, 2013
Thiel, C. J., & Schmullius, C.
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"Polarimetric Parameters for Growing Stock Volume Estimation Using ALOS PALSAR L-band Data over Siberian Forests". Remote Sensing, 5, 5725-5756, 2013
Chowdhury, T. A., Thiel, C. J., Schmullius, C., & Stelmaszczuk-Gorsky, M.
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(2013). "Evaluation of the Potential of ALOS PALSAR L-band Quadpol Radar Data for the Retrieval of Growing Stock Volume in Siberia". Ph.D. thesis, Friedrich-Schiller-University, Jena, Germany
Chowdhury, T.A.
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"Growing stock volume estimation from L-band ALOS PALSAR polarimetric coherence in Siberian forest". Remote Sensing of Environment, Volume 155, December 2014, Pages 129-144
Chowdhury, T. A., Thiel, C. J., & Schmullius, C.
