Sains Malaysiana 44(8)(2015): 1085–1093

Estimating Biomass in Logged Tropical Forest Using L-Band SAR (PALSAR) Data and GIS

(Penganggaran Biojisim dalam Hutan Hujan telah Diteroka menggunakan Data SAR Berjalur L (PALSAR) dan GIS)

HAMDAN OMAR¹*, MOHD HASMADI ISMAIL², KHALI AZIZ HAMZAH¹, HELMI ZULHAIDI MOHD SHAFRI² & NORIZAH KAMARUDIN²

¹Forest Research Institute Malaysia, 52109 FRIM, Kepong, Selangor Darul Ehsan, Malaysia

²Universiti Putra Malaysia, 43400 Serdang, Selangor Darul Ehsan, Malaysia

Diserahkan: 28 Jun 2014/Diterima: 5 Mac 2015

ABSTRACT

The use of remote sensing imagery, to some extends geographic information system (GIS), have been identified as the most recent and effective technologies to assess forest biomass. Depending on the approaches and methods employed, estimating biomass by using these technologies sometimes can lead to uncertainties. The study was conducted to investigate appropriate methods for estimating aboveground biomass (AGB) by using synthetic aperture radar (SAR) data. A total of 60187 ha in Dungun Timber Complex (DTC) were selected as the study area. Thirty seven sample plots, measuring 30×30 m were established in early 2012 covering both natural and logged forests. Phase Array Type L-Band SAR (Palsar) images that were acquired in 2010 were used as primary remote sensing input and shapefile polygons comprised logging records was used as supporting information. By using these data, two estimation methods, which were ‘stratify and multiply’ (SM) and ‘direct remote sensing’ (DR) have been adopted and the results were compared. The estimated total AGB were about 20.1 and 22.3 million Mg, from SM and DR methods, respectively. The study found that the images that incorporated texture measures produced more accurate estimates as compared to the images without texture measures. The study suggests that SM method still a viable and reliable technique for quick assessment of AGB in a large area. The DR method is also relevant provided that an appropriate type and processing techniques of SAR data are utilized.

Keywords: Biomass estimate; GIS; L-band SAR; tropical forest

ABSTRAK

Penggunaan citra penderiaan jauh dan seiringan dengan sistem maklumat geografi (GIS), telah dikenal pasti sebagai teknologi terkini yang paling efektif untuk penilaian biojisim hutan. Penganggaran biojisim menggunakan teknologi ini bergantung kepada pendekatan dan kaedah yang diguna pakai kerana kadangkala ia boleh membawa kepada kesilapan. Kajian ini dijalankan untuk menentukan kaedah yang sesuai untuk menganggar biojisim atas tanah (BAT) menggunakan data bukaan radar sintetik (SAR). Sejumlah 60187 ha di dalam kawasan Kompleks Kayu-Kayan Dungun (DTC) telah dipilih sebagai kawasan kajian. Tiga puluh tujuh plot sampel berukuran 30×30 m telah disediakan di dalam kawasan kajian pada awal tahun 2012 merangkumi kedua-dua hutan asli dan hutan yang telah dibalak. Fasa tatasusunan jenis SAR berjalur L (Palsar) merupakan data penderiaan jauh yang dicerap pada tahun 2010 telah digunakan sebagai input utama, manakala poligon yang mengandungi rekod pembalakan telah digunakan sebagai maklumat sokongan. Dengan menggunakan data-data tersebut, dua kaedah penganggaran iaitu ‘mengelas dan mendarab’ (SM) dan juga ‘penderiaan jauh langsung’ (DR) telah diguna pakai dan hasil daripada kedua-duanya dibandingkan. Kajian menganggarkan BAT yang masing-masing 20.1 dan 22.3 Mg dijalankan melalui kaedah SM dan DR. Kajian juga mendapati bahawa imej yang telah menggunakan ukuran tekstur menghasilkan anggaran yang lebih tepat berbanding imej tanpa ukuran tekstur. Kajian ini menyarankan bahawa kaedah SM masih relevan untuk penilaian segera AGB bagi kawasan yang luas. Kaedah DR juga relevan dengan syarat teknik pemprosesan data SAR yang sesuai digunakan.

Kata kunci: Anggaran biojisim; GIS; hutan tropika; SAR berjalur L

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*Pengarang untuk surat-menyurat; email: hamdanomar@frim.gov.my