Leong Keong Kwoh

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.

Tsunami damage assessment using high resolution satellite imagery: a case study of Aceh, Indonesia

We used high resolution SPOT 5 images to perform damage assessment of the regions affected by the December 2004 Indian Ocean tsunami. and to study the effects of the tsunami on coastal features. The study area is located at Banda Aceh, Aceh Besar and the northern part of Aceh Jaya which is the most severely affected region in Aceh province of Sumatra. The before-tsunami images were classified into thematic The tsunami affected areas and the severity of damage were delineated on the after-tsunami images to produce a damage map. Our map shows that much of the low land area, which include fishponds, the Banda Aceh city, some villages, paddy fields, mangrove and peat swamps, were severely damaged and the coastline were significantly eroded and destroyed. This paper illustrates the use of remote sensing imagery for tsunami damage assessment and it shows that remote sensing and GIS provide a means for performing rapid disaster assessment.

Delineating land/forest fire burnt scars with ERS Interferometric Synthetic Aperture Radar

Cloud-penetrating C-band synthetic aperture radar imagery acquired during two ERS-1/2 tandem missions (April 1996 and October 1997) was used in mapping burnt areas in South Kalimantan, Indonesia, during the 1997 Southeast Asia forest fire episode. Vegetated areas were classified by their low interferometric coherence in both the 1996 and 1997 imagery while the burnt areas were delineated by their increased coherence in 1997. A total of 552 kha of land was found to be burnt scars out of the 3.6 Mha area surveyed. The results were validated using a multispectral SPOT image of the area acquired in September 1997.

Ship and ship wake detection in the ERS SAR imagery using computer-based algorithm

A computer-based algorithm for ship and ship wake detection in SAR imagery is being developed to monitor ship traffic near Singapore waters. This paper presents current progress made on the algorithm. In particular, issues on the elimination of false targets are addressed. The morphological filter, half Radon (Hough) transform, and other wake criterion tests are applied to strengthen the detecting capability.

Detection of vegetation fires and burnt areas by remote sensing in insular Southeast Asian conditions: current status of knowledge and future challenges

The humid tropical insular Southeast Asian region is one of the most biologically diverse areas in the world. It contains around 70 Gt of carbon stored in peat deposits susceptible to burning when drained and it has significantly higher population density than any other humid tropical region. This region experiences yearly fire activity of anthropogenic origin with widely varying extent and severity. At the same time, there are several geographic, climatic, and social aspects that complicate fire monitoring in the region. In this review article, we analyse the current knowledge and limitations of active fire detection and burnt area mapping in insular Southeast Asia, highlighting the special characteristics of the region that affect all types of remote-sensing-based regional-level fire monitoring. We conclude that the monitoring methods currently employed have serious limitations that directly affect the reliability of results for fire and burnt area monitoring in this region. With the materials and methods presently available, the regional and global effects of fire activity taking place in insular Southeast Asia are in danger of being underestimated. New approaches utilizing higher spatial and temporal resolution remote-sensing data are needed for more detailed quantification of fire activity and subsequently improved estimation of the effects of fires in this region.

Ocean oil pollution mapping with ERS synthetic aperture radar imagery

Over six thousand of ERS-1/2 SAR images has been used to map the spatial distribution of ocean oil pollution in the Southeast Asian waters. The relative frequency of oil spills is characterised by a normalised oil spill index representing the average number of oil slicks detected in an ERS scene. Most oil spills are found along the major international shipping routes as well as in those areas with intensive large-scale oil exploitation activities. This work can be taken as the first step of an overall future ocean oil spill monitoring campaigns. Compilation of a global ocean oil pollution map is suggested.

3D building reconstruction and visualization for single high resolution satellite image

This paper presents a semi-automated method for 3D building reconstruction and height measurement from a single very high resolution satellite image by using the building top, building base and/or building shadow information. An interactive software system, complete with editing and visualization features has been implemented.

Modeling the reflectance spectra of tropical coastal waters

This work aims to extract optical parameters of coastal sea water with high sediment and chlorophyll content by fitting reflectance spectra to a model. Sea-truth water sampling campaigns were carried out from Dec 1996 to Dec 1999 in coastal waters around Singapore. In-situ reflectance spectra were acquired using a portable spectro radiometer. Laboratory measurements of the total suspended solid (TSS) and chlorophyll-a (Chl-a) were made from the water samples. The Chl-a concentration ranges from 1 to 90 mg/m3, with an average value of about 10 mg/m3. The three component model for sea water was used to model the reflectance spectra. The model also includes chlorophyll fluorescence and surface reflection due to skylight. Each reflectance spectrum is fitted to the model by finding a set of the fitting parameters that best fits the reflectance curve to the mode. The downhill simplex method is employed as the optimization procedure. The chlorophyll absorption coefficient at 440 nm is retrieved and is found to relate to the measured chl-A concentration by a power law relation.

Finding the best-fit bounding-boxes

The bounding-box of a geometric shape in 2D is the rectangle with the smallest area in a given orientation (usually upright) that complete contains the shape. The best-fit bounding-box is the smallest bounding-box among all the possible orientations for the same shape. In the context of document image analysis, the shapes can be characters (individual components) or paragraphs (component groups). This paper presents a search algorithm for the best-fit bounding-boxes of the textual component groups, whose shape are customarily rectangular in almost all languages. One of the applications of the best-fit bounding-boxes is the skew estimation from the text blocks in document images. This approach is capable of multi-skew estimation and location, as well as being able to process documents with sparse text regions. The University of Washington English Document Image Database (UW-I) is used to verify the skew estimation method directly and the proposed best-fit bounding-boxes algorithm indirectly.

Monitoring turbidity and suspended sediment concentration of coastal and inland waters using satellite data

A method for retrieving water turbidity and suspended sediment concentration of inland and near-shore coastal waters using high resolution remote sensing satellite data is described. Backscattering coefficient at the near infrared band is first derived from the satellite images using a quasi-analytical algorithm after applying a simple atmospheric correction routine. A turbidity map is obtained by applying an empirical relation derived from laboratory experiments to convert the backscattering coefficient to nephelometric turbidity units (NTU). This method can be operationalized for global water quality monitoring using currently operating satellite sensors such as those on Landsat, SPOT and Terra / Aqua MODIS.