Huaining Yang

Unequal Dual-Band Rat-Race Coupler based on Dual-Frequency 180 Degree Phase Shifter

This paper presents a dual-band rat-race coupler with arbitrary power dividing ratio. The dual-band and unequal power dividing characteristics are obtained by using a dual-frequency 180 degree phase shifter with the conventional coupler. Closed-form design equations are derived. The proposed structure can support large power dividing ratio with a wide frequency ratio range. The measured results show that good matching, isolation, power transmission and phase balance can be achieved at two operating frequency bands.

Monitoring Recent Urban Expansion and Urban Subsidence of Beijing Using ENVISAT/ASAR Time Series Datasets

With worldwide economic development and population increases, urban areas create significant stresses on the local, regional and global environment. Information about the spatial and temporal dynamics of the characteristics of urban areas is therefore needed to support sustainable urban development. Time series earth observation data obtained using radar satellites have provided effective data sources for monitoring urban areas. This chapter first describes the development of synthetic aperture radar as well as its important role in the detection and monitoring of urban areas. Then, the fundamental principle of time series radar data in monitoring urban areas is introduced and discussed. Next, to demonstrate the capacity of time series SAR (Synthetic Aperture Radar) imagery for monitoring urban areas using ENVISAT/ASAR (Environmental Satellite /Advanced Synthetic Aperture Radar) time series radar data, Beijing city in China was selected as a test site. Beijing has all of the typical problems of a megacity such as resource, environment and population problems arising from rapid urban expansion during recent decades. A C5.0 rulesets classifier and the Multi Temporal Interferometric Synthetic Aperture Radar (MTInSAR) method were used to map the urban expansion and the millimeter level urban subsidence, respectively and the results were validated via high resolution WorldView optical datasets and leveling benchmark measurement, respectively. The results demonstrate the effectiveness and high accuracy of the time series radar data for monitoring urban areas. Furthermore, the spatial-temporal characteristic of urban expansion and urban subsidence of Beijing city were analyzed. Finally, the mechanisms or driving factors for urban expansion and subsidence are addressed based on economic development, population growth and the impacts of recent Beijing government policy.

Estimating impervious surface of Bohai ring megalopolis from Landsat imagery using SVM method

The objective of this paper is to map large-area impervious surfaces in bohai ring megalopolis areas from Landsat imagery using SVM method. Then, combined with the sixth population census data, the map of the impervious surface area (ISA) per person is derived. Finally, this paper analyses the relationship between the impervious surfaces and population census data, and gross domestic product (GDP) data. Our results indicated that the density of ISA in Beijing and Tianjin were great higher than in other administrative regions. By comparing the ISA with population census and GDP data, our results also indicated that the ISA was highly correlated with population census and GDP data. A strong relationship (R2= 0.879) was observed between the ISA and the population census data in the whole study area. In addition, a strong and positive relationship was observed between the ISA and GDP data (correlation coefficient R2= 0.779 for the whole study area). This research can provide a simple method for policy makers to assess potential urbanization impacts of future urban planning and development activities.

Quaternion-base direct geo-referencing algorithm for ISSAC

The International Space Station Agriculture Camera (ISSAC), Sponsored by the National Aeronautics and Space Administrations (NASA) Education Office and developed by University of North Dakota, aims to demonstrate the applications of precision farming and natural resource management from the International Space Station (ISS). With a designed Ground Sampling Distance (GSP) of ~20 meters, an accurate geo-referencing algorithm is important for near-real time delivery of images that can be used immediately. One outstanding feature of ISSAC is its tilting capability in cross-track direction so that a wide area can be covered. At a relatively low altitude, the ISS, where the ISSAC will be hosted, experiences a large variation in attitude. Additionally, the optics window on ISS where the ISSAC sees through is not at the center of mass of the ISS. All these factors need to be taken care of in the algorithm. Evaluated by the commercial navigation software, Satellite Tool Kit (STK, Analytical Graphics, Inc.), the proposed algorithm can achieve theoretical accuracy within 0.5 meters.

Improved method of Land Surface Emissivity retrieval from Landsat TM/ETM+ data

A comparative study has been carried out on the most recent methods for Land Surface Emissivity (LSE) estimation using Landsat TM/ETM+ data. The popularly used method, the integrating NDVI and classification is chosen and analyzed further. The result shows that the estimation model is not accurate enough for LSE is underestimated at either end of the fractional vegetation cover (Pv) range which would lead to overestimating of corresponding Land Surface Temperature (LST). The drawback is modified based on the threshold method, that is, for natural surface and when Pv <; 0.165, ε= εsoil; for town surface and when Pv <; 0.1375, ε= εm; and for Pv >; 0.5, ε= εv. Finally, a processing way adapting for the improved model in large area is presented and the emissivity model before modification and after improvement is applied to Beijing, China to identify emissivity and further to retrieve LST using image based method. The results show that the large difference between LSE and corresponding LST is located in the town surface and soil with low Pv and that a decrease of emissivity by 0.011058 at 318K will increase LST by about 1K. Thus a promising improvement of comparative accuracy can be expected.