Mengxu Gao

Change detection of an earthquake-induced barrier lake based on remote sensing image classification

The earthquake-induced barrier lakes that are caused by landslides are at risk of bursting after excessive rainfall, and they are a serious threat to the surrounding residents. This paper proposes a change detection approach of the barrier lake using the method of post-classification comparison combined with background subtraction. The case studied in the paper is the detection of the Tangjiashan barrier lake, which is one of the largest lakes induced by the Wenchuan Earthquake on 12 May 2008. Both the pre- (31 March 2007) and post-earthquake (16 May 2008) images of the Advanced Land Observing Satellite (ALOS) Advanced Visible and Near Infrared Radiometer type 2 (AVINER-2) were collected in the paper. The results show that the river widened through the Zhangping area, increasing from 90 m pre-earthquake to 545 m post-earthquake, and the surface area of the barrier lake increased from 0.945 km2 to 1.471 km2.

Risk analysis for the highly pathogenic avian influenza in Mainland China using meta-modeling

A logistic model was employed to correlate the outbreak of highly pathogenic avian influenza (HPAI) with related environmental factors and the migration of birds. Based on MODIS data of the normalized difference vegetation index, environmental factors were considered in generating a probability map with the aid of logistic regression. A Bayesian maximum entropy model was employed to explore the spatial and temporal correlations of HPAI incidence. The results show that proximity to water bodies and national highways was statistically relevant to the occurrence of HPAI. Migratory birds, mainly waterfowl, were important infection sources in HPAI transmission. In addition, the HPAI outbreaks had high spatiotemporal autocorrelation. This epidemic spatial range fluctuated 45 km owing to different distribution patterns of cities and water bodies. Furthermore, two outbreaks were likely to occur with a period of 22 d. The potential risk of occurrence of HPAI in Mainland China for the period from January 23 to February 17, 2004 was simulated based on these findings, providing a useful meta-model framework for the application of environmental factors in the prediction of HPAI risk.

Epidemic risk analysis after the Wenchuan Earthquake using remote sensing

On 12 May 2008, Wenchuan Earthquake, magnitude 8.0, destroyed thousands of buildings, and resulted in thousands of people being buried in the collapsed buildings. In order to investigate the potential epidemic disease risk after earthquake, a Backward Propagation Neural Network (BPNN) was constructed to assess the potential epidemic risks by applying remote sensing technology to obtain Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) values, as well as by using a geographic information system (GIS) to gain ambient epidemic-related spatial factors over the earthquake region. In this study, a relationship was established between the change in environmental factors after earthquake and potential epidemic risks, which was found to be statistically significant. The result might be explained for three change perspectives, namely environmental risks, medical risks and psychological risks. The corresponding strategies for preparedness in case of epidemic disease were given.

The novel H1N1 Influenza A global airline transmission and early warning without travel containments

A novel influenza A (H1N1) has been spreading worldwide. Early studies implied that international air travels might be key cause of a severe potential pandemic without appropriate containments. In this study, early outbreaks in Mexico and some cities of United States were used to estimate the preliminary epidemic parameters by applying adjusted SEIR epidemiological model, indicating transmissibility infectivity of the virus. According to the findings, a new spatial allocation model totally based on the real-time airline data was established to assess the potential spreading of H1N1 from Mexico to the world. Our estimates find the basic reproductive number R0 of H1N1 is around 3.4, and the effective reproductive number fall sharply by effective containment strategies. The finding also implies Spain, Canada, France, Panama, Peru are the most possible country to be involved in severe endemic H1N1 spreading.

Wetland changes and droughts in southwestern China

The five provinces of southwestern China, Sichuan, Chongqing, Guizhou, Yunnan and Guangxi, frequently suffer from droughts, especially the recent severe drought of five consecutive months from autumn 2009 to spring 2010, which caused serious water shortages, huge economic losses and adverse social consequences. With increasing human activity in the last 200 years, the wetland areas have decreased and their ecological functions such as water conservation, climate regulation have declined, which has a direct impact on climate and the ecological environment. Using satellite images, changes in wetland areas of the five provinces of southwestern China have been mapped from 1970 to 2008. Our detailed analysis shows that the wetland area in the 1970s, 1990, 2000 and 2008 occupy an area of 20822.9, 18386.16, 19904.22 and 17269.72 km2, respectively, which indicate that the wetland areas have a downtrend, at an accelerating rate, from 2000 to 2008. Considering the complexity between wetland change and drought, the correlation between spatial and temporal wetland change and drought have been analysed using monthly ground meteorological data from 1971 to 2009, obtained from the China Meteorological Data Sharing Service Network. The analysed results show that the decrease of the wetland area, damage to biological resources and decline in climate regulation function are closely related to serious drought problems in the five provinces of southwestern China. Finally the corresponding solutions are discussed by analysing the problems faced by the wetland ecological system.

The retrieval of shrub fractional cover based on a geometric-optical model in combination with linear spectral mixture analysis

Vegetation fractional cover, which defines the amount of vegetation on the surface of the land, is a key parameter in land surface models. Based on a geometric-optical model in combination with a linear spectral mixture analysis, the retrieval of shrub fractional cover in Wushen Banner of Inner Mongolia in the Mu Us Sandland using HJ-1B multispectral images is discussed. We acquired the surface reflectance based on geometric correction and atmospheric correction of the HJ-1B image. Then we assumed that the reflectance of a mixed pixel is a simple linear combination of two components, namely illuminated background and illuminated canopy, and further calculated the areal proportion of the illuminated background within each pixel based on the linear spectral mixture analysis. Then, combined with the measured shrub structural parameters, the shrub fractional cover was estimated using an inverted geometric-optical model. Finally, the result was validated through the measured shrub cover of 13 sample plots and a comparison study was done with the NDVI regression method and simple linear spectral mixture analysis. The R 2 of the three methods are 0.898, 0.614, and 0.659, with corresponding root-mean-squared errors of 0.136, 0.154, and 0.175, which indicate the reliability of the combined method.

Change detection of the Tangjiashan barrier lake based on multi-source remote sensing data

The paper uses the approach of NDWI model to extract the water bodies of the Tangjiashan barrier lake from the multi-source satellite images of ALOS AVNIR-2 and CBERS-02B CCD and detects the changes of the barrier lake pre- and post-earthquake. The result shows that the river widen through Zhangping area increased from 92 m on Mar. 31, 2007 for per-earthquake to 420 m on May 16, 2008 and 474 m on May 18, 2008 for post-earthquake. And the area of barrier lake in the study area increased from an surface area of 0.6938 km2 on Mar. 31, 2007 for pre-earthquake to 1.2842 km2 on May 16, 2008 and 1.3658 km2 on May 18, 2008 for post-earthquake.

Application of CCD data of HJ-1 satellite in PM 10 evaluation in Shenzhen, China

The main missions of HJ-1 satellite are to monitor pollution, ecosystem destruction and natural disasters. In recent years, Inhalable particle (PM10) has become the primary pollutant of major cities in China, which seriously affects the living environment of its residents. In this paper, we made use of high-resolution CCD data of HJ-1 satellite to monitor atmospheric inhalable particle (PM10) in Shenzhen. Firstly, we inversed the aerosol optical depth (AOD) of CCD data of HJ-1 satellite. Then we analyzed the correlation between AOD and PM10 using PM10 data in six districts of Shenzhen and the AOD data. The conclusions are as follows. 1) The AOD and PM10 are significantly related in spring-summer. 2) The correlation between AOD and PM10 has been improved greatly after considering the variation of aerosol scale height.

Assessment of the degree of building damage caused by the 2010 Yushu, China earthquake using satellite and airborne data

Until now, prevention of earthquakes is rarely achieved and earthquakes continue to pose an increasing threat to life and property. For search and rescue operations, rapid, accurate and reliable information about the building damage and damage distribution is in great need in the critical post-event hours. Fortunately, remote sensing data from satellites and airborne platforms can provide valuable information for detecting the building damage due to earthquakes. In this study, satellite and airborne images were processed to assess the degree of building damage caused by the Yushu, China earthquake on 14 April 2010. The selected study area enclosed part of Jiegu town, which was one of the areas most strongly hit by the earthquake. Combining with the pre-earthquake data of Yushu County from a Google Earth screenshot, we visually interpreted post-earthquake and pre-earthquake buildings in every region, and acquired the degree of building damage. The result shows that in every region of the study area, buildings with brick-clay or brick-wood structures showed characteristics of complete damage over a large area. The alluvial cone has a flat and solid surface but the lower soil is soft, so its structure is not stable enough to withstand a serious earthquake.

Spatial distribution and ecological environment analysis of great gerbil in Xinjiang Plague epidemic foci based on remote sensing

Yersinia pestis (Plague bacterium) from great gerbil was isolated in 2005 in Xinjiang Dzungarian Basin, which confirmed the presence of the plague epidemic foci. This study analysed the spatial distribution and suitable habitat of great gerbil based on the monitoring data of great gerbil from Chinese Center for Disease Control and Prevention, as well as the ecological environment elements obtained from remote sensing products. The results showed that: (1) 88.5% (277/313) of great gerbil distributed in the area of elevation between 200 and 600 meters. (2) All the positive points located in the area with a slope of 0–3 degree, and the sunny tendency on aspect was not obvious. (3) All 313 positive points of great gerbil distributed in the area with an average annual temperature from 5 to 11 °C, and 165 points with an average annual temperature from 7 to 9 °C. (4) 72.8% (228/313) of great gerbil survived in the area with an annual precipitation of 120–200mm. (5) The positive points of great gerbil increased correspondingly with the increasing of NDVI value, but there is no positive point when NDVI is higher than 0.521, indicating the suitability of vegetation for great gerbil. This study explored a broad and important application for the monitoring and prevention of plague using remote sensing and geographic information system.