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24 Sep 2015 | News

Improved methods to measure forest above-ground biomass in the Hindu Kush Himalayan region through satellites

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The study of forest above-ground biomass (AGB) for estimating the carbon stock in each tree is important, as it is well established that the emission of carbon is the largest factor affecting today’s climate. The research undertaken by the Institute of Space Technology in Pakistan and supported by ICIMOD under its SERVIR-Himalaya Small Grants Programme has developed methods for forest AGB measurement using remote sensing in Pakistan and the surrounding regions. AGB is traditionally measured by destructive sampling, which is labour-intensive and damages the forest. Satellite remote sensing is a great alternative for AGB assessment. Optical satellite images are restricted in their ability to assess the AGB of trees, which is mostly contained in the woody part, as they are unable to penetrate the forest canopy or cloud cover. Signals from the space-borne SAR (Synthetic Aperture Radar), with its nearly all-weather and day-night functionality, can penetrate the canopy and obtain signal returns from tree stems and branches to give better estimates of forest AGB. However, the extraction of biophysical information from SAR datasets is not a simple task.

This research study developed methodologies for forest AGB estimation in the Hindu Kush Himalayan region using optical high-resolution (WorldView, GeoEye) and SAR (ALOS-1/2 PALSAR) remote-sensing data coupled with field measurements (tree height, stem diameter at breast height) and allometric equations. With a special focus on SAR, these datasets were processed for terrain correction, calibration, speckle noise suppression, and upscaling to 1 hectare resolution. SAR backscatter was related to ground measurements through regression modelling and AGB estimates were made for the whole area. The resulting maps provide a new way of assessing forest AGB resources in the study sites, with the possibility of repeating measurements under all weather conditions. Furthermore, as this pilot methodology may be expanded to more samples and sites, improved regression models will allow for better and more accurate measurement of AGB through SAR.

The study was carried out in the Khayar Khola watershed, Chitwan district, Nepal, and Chichawatni Irrigated Plantation, Sahiwal district, Pakistan. Ground survey and remote sensing data was collected within a few months in each of the study sites, which helped to control the overall accuracy of the results. A three-day field survey campaign was conducted in Chichawatni Irrigated Plantation by the project research team, with the help of collaborating partner organizations and stakeholders, the Punjab Forest Research Institute (PFRI) and University of the Punjab, Lahore.

The methodology developed by this study for forest AGB estimation received positive feedback during the two-day workshop organized to disseminate the approach. Professionals and academics from different departments and organizations in Pakistan attended the workshop. The results presented during the workshop triggered a healthy discussion among participants, who noted the salient points and made suggestions for implementing the methodology on a larger scale. One of the participants said that: “Improved AGB estimation is needed in today’s world and for today’s issues, especially to address climate change. The methodology can be refined so that it can be shared with the technical staff of implementing agencies to make this the standard for REDD+ activities in Pakistan.”

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