Soo Chin Liew

Remotely sensed evidence of tropical peatland conversion to oil palm

Rising global demands for food and biofuels are driving forest clearance in the tropics. Oil-palm expansion contributes to biodiversity declines and carbon emissions in Southeast Asia. However, the magnitudes of these impacts remain largely unquantified until now. We produce a 250-m spatial resolution map of closed canopy oil-palm plantations in the lowlands of Peninsular Malaysia (2 million ha), Borneo (2.4 million ha), and Sumatra (3.9 million ha). We demonstrate that 6% (or ≈880,000 ha) of tropical peatlands in the region had been converted to oil-palm plantations by the early 2000s. Conversion of peatswamp forests to oil palm led to biodiversity declines of 1% in Borneo (equivalent to four species of forest-dwelling birds), 3.4% in Sumatra (16 species), and 12.1% in Peninsular Malaysia (46 species). This land-use change also contributed to the loss of ≈140 million Mg of aboveground biomass carbon, and annual emissions of ≈4.6 million Mg of belowground carbon from peat oxidation. Additionally, the loss of peatswamp forests implies the loss of carbon sequestration service through peat accumulation, which amounts to ≈660,000 Mg of carbon annually. By 2010, 2.3 million ha of peatswamp forests were clear-felled, and currently occur as degraded lands. Reforestation of these clearings could enhance biodiversity by up to ≈20%, whereas oil-palm establishment would exacerbate species losses by up to ≈12%. To safeguard the regions biodiversity and carbon stocks, conservation and reforestation efforts should target Central Kalimantan, Riau, and West Kalimantan, which retain three-quarters (3.9 million ha) of the remaining peatswamp forests in Southeast Asia.

2010 land cover map of insular Southeast Asia in 250-m spatial resolution

In this letter, we present the methodology and accuracy assessment of a new regional 250-m spatial resolution land cover map of insular Southeast Asia. Nearly 500 daily Moderate Resolution Imaging Spectroradiometer images (acquired 2 January–3 July 2010) were used in the production of the map. Additionally, peatland maps, elevation information and Daichi-Advanced Land Observing Satellite mosaic data were utilized in the mapping process. The map covers the Malaysian Peninsula and the major islands of Sumatra, Java, Borneo, Sulawesi and Mindanao, in addition to the western part of New Guinea and numerous smaller islands. The classification scheme of 13 classes reflects the special characteristics of land cover of insular Southeast Asia, including, for example, peatswamp forests and large-scale palm plantations. The map was assessed to have 85% overall accuracy using high-resolution (10–30 m) satellite data as reference material. It can therefore be considered to provide reliable information on the current status of land cover in this region experiencing rapid land cover changes.

Extent of industrial plantations on Southeast Asian peatlands in 2010 with analysis of historical expansion and future projections

Tropical peatlands cover over 25 Mha in Southeast Asia and are estimated to contain around 70 Gt of carbon. Peat swamp forest ecosystems are an important part of the regions natural resources supporting unique flora and fauna endemic to Southeast Asia. Over recent years, industrial plantation development on peatland, especially for oil palm cultivation, has created intense debate due to its potentially adverse social and environmental effects. The lack of objective up‐to‐date information on the extent of industrial plantations has complicated quantification of their regional and global environmental consequences, both in terms of loss of forest and biodiversity as well as increases in carbon emissions. Based on visual interpretation of high‐resolution (30 m) satellite images, we find that industrial plantations covered over 3.1 Mha (20%) of the peatlands of Peninsular Malaysia, Sumatra and Borneo in 2010, surpassing the area of Belgium and causing an annual carbon emission from peat decomposition of 230–310 Mt CO2e. The majority (62%) of the plantations were located on the island of Sumatra, and over two‐thirds (69%) of all industrial plantations were developed for oil palm cultivation, with the remainder mostly being Acacia plantations for paper pulp production. Historical analysis shows strong acceleration of plantation development in recent years: 70% of all industrial plantations have been established since 2000 and only 4% of the current plantation area existed in 1990. ‘Business‐as‐usual’ projections of future conversion rates, based on historical rates over the past two decades, indicate that 6–9 Mha of peatland in insular Southeast Asia may be converted to plantations by the year 2020, unless land use planning policies or markets for products change. This would increase the annual carbon emission to somewhere between 380 and 920 Mt CO2e by 2020 depending on water management practices and the extent of plantations.

Two decades of destruction in Southeast Asia's peat swamp forests

We used land-cover maps and active fire detection based on satellite imagery to evaluate the rates and spatial distribution of peatland deforestation in Southeast Asia from 1990 to 2010. Over this time period, the proportion of forest cover in the peatlands of Peninsular Malaysia, Sumatra, and Borneo fell from 77% to 36%. After two decades of extensive deforestation (31 000 km2; 4.9% yr−1) strongly associated with fire activity, Sumatra has been left with just 28% of its historical forested peatlands. If peatland deforestation is allowed to continue at current rates, the Southeast Asian peat swamp forests will disappear by around 2030. This will have serious consequences for the local communities that rely on the environmental services provided by peat swamp forests, will lead to the extinction of peat swamp forest species endemic to this region, and will contribute to global carbon emissions.

The National University of Singapore nuclear microscope facility

Abstract The National University of Singapore nuclear microscope facility is based around a HVEC AN2500 single ended Van de Graaff accelerator and an Oxford Microbeams coupled quadrupole triplet focusing system. Particle induced X-ray emission (PIXE), nuclear or Rutherford backscattering spectrometry (RBS) and scanning transmission ion microscopy (STIM) can be carried out simultaneously. Data acquisition is carried out using a simple but flexible PC based system (Oxford Microbeams DAQ) and the data is analysed using a combined RUMP and GUPIX PC based interactive package (NUSDAN) acting under WINDOWS. Resolution tests using a calibration grid and a multi layer integrated circuit have shown the facility to be capable of 600 nm spot sizes for 2 MeV protons at currents suitable for microanalysis.

Application of multitemporal ERS-2 synthetic aperture radar in delineating rice cropping systems in the Mekong River Delta, Vietnam

The authors report the use of multitemporal ERS-2 satellite synthetic aperture radar (SAR) images in delineating and mapping areas under different rice cropping systems in the Mekong River Delta, Vietnam. Change index maps were generated from seven images acquired between May and December 1996. Using a 3-dB threshold, the pixels in each change index (CI) map were classified into one of three classes: Increasing, decreasing, or constant backscattering. Five of the CI maps were used to generate a composite map with 243 possible change classes. These change classes were grouped into thematic categories of rice cropping systems using two methods: human visual inspection and a semiautomatic hierarchical clustering algorithm. The derived thematic maps were compared with SPOT scenes acquired during the same rice seasons.

Description of a simultaneous emission-transmission CT system

We are designing an instrument which will perform correlated emission-transmission image acquisition, but which departs from previous systems by incorporating a low-power x-ray tube and generator, rather than a radionuclide source, for the transmission image. The system uses an array of high-purity germanium (HPGe) detectors and detector electronics with energy discrimination circuitry to separate x-rays (at 100 or 120 kVp) from higher energy gamma rays from the 99mTc or 123j radiopharmaceutical injected into the patient. The data acquisition electronics have time constants matching the charge collection time (50 ns) of the HPGe detectors to maximize count-rate capabilities (up to 1 million cps per detector element), while maintaining adequate energy resolution (approximately 10% FWHM). Each detector channel has two energy windows for simultaneous transmission-emission imaging or for dual-energy x-ray studies. A host computer provides system control as well as data acquisition, data correction, tomographic image reconstruction, image display, and data analysis. As a radionuclide imaging system, this instrument will function as a single-slice SPECT scanner with high-count rate capabilities and excellent energy resolution for imaging short-lived radionuclides, improved photopeak discrimination and scatter rejection, and simultaneous imaging of multiple radionuclides. The system also will generate radiographic images in either a tomographic or projection scanning mode, while dual-energy x-ray CT will provide material specific imaging. However, the novel and potentially powerful capabilities of this instrument would derive from its inherent correlation of functional information from SPECT with precise anatomic information from CT or the material-specific morphologic information from dual-energy x-ray CT. The simultaneously acquired radiographic images should relieve the deficiencies of poor statistics and limited spatial resolution commonly associated with SPECT systems. Dual-energy xray CT also can provide an energy-corrected and anatomically-correlated map of attenuation coefficients for more accurate quantitation of emission radionuclide data.

Noise propagation in SPECT images reconstructed using an iterative maximum-likelihood algorithm.

The effects of photon noise in the emission projection data and uncertainty in the attenuation map on the image noise in attenuation-corrected SPECT images reconstructed using a maximum-likelihood expectation-maximization algorithm were investigated. Emission projection data of a physical Hoffman brain phantom and a thorax-like phantom were acquired from a prototype emission-transmission computed tomography (ETCT) scanner being developed at UCSF. Computer-simulated emission projection data from a head-like phantom and a thorax-like phantom were also obtained using a fan-beam geometry consistent with the ETCT system. The simulation assumed a 99Tcm source, included collimator blurring but ignored photon scatter. For each phantom, a region of interest (ROI) at the centre of the reconstructed image was chosen for the purpose of noise analysis. In all cases, the mean value (m) in the ROI approached a constant value after approximately 20 iterations. The standard deviation (sigma) generally increased with the number of iterations. The ratio (sigma/m) was found to be inversely proportional to the square root of the total detected counts and proportional to the relative uncertainty in the attenuation maps. These two noise components contributed independently towards the noise in the reconstructed image. In the ETCT system employing an x-ray tube for attenuation map acquisition, the uncertainty in the reconstructed radionuclide distribution is limited mainly by photon noise in the emission projection data. Our results are expected to be generally applicable to other emission-transmission systems, including those using external radionuclide sources for the acquisition of attenuation maps.

A study of the 1997 forest fires in south east Asia using SPOT quicklook mosaics

The ground station at the Centre for Remote Imaging, Sensing and Processing (CRISP), Singapore has acquired numerous SPOT images of the region during the 1997 forest fire episode in South Asia with almost complete coverage of Sumatra and Borneo. Mosaics of the SPOT quicklook images have been generated to provide a synoptic view of the areal extent of the fires affected areas. The total area of burnt scars was estimated to be 1.50/spl times/10/sup 6/ ha in Sumatra and 3.06/spl times/10/sup 6/ ha in Kalimantan.

Separability of insular Southeast Asian woody plantation species in the 50 m resolution ALOS PALSAR mosaic product

Four types of woody plantations dominate in insular Southeast Asia: oil palm (Elaeis guineensis), rubber (Hevea brasiliensis), wattles (Acacia spp.) and coconut (Cocos nucifera). Because of the economic importance and socio-environmental controversies related particularly to oil palm cultivation, capability to perform large-scale plantation monitoring is urgently needed in this region. In this letter we report initial findings on the potential of Daichi-Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) data for regional level woody plantation monitoring. We found very high separability between rubber, wattles and palms (oil palm and coconut combined) in known closed canopy plantation areas using the annually created 50 m resolution orthorectified mosaic products. Further investigation is needed to find the best ways to implement this ability in practice. Nevertheless, the findings may enable regional plantation monitoring in insular Southeast Asia at an unprecedented level of accuracy and detail.