Volume 2 Issue 1
Authors: L. Samarakoon; T Tipdecho; M Parnichkun; C. H Wickramasinghe
Abstract: Quasi-Zenith Satellite System (QZSS) is a Japanese GPS augmentation system that provides real-time Precise Point Positioning (PPP) correction through an experimental signal (LEX) established in June 2011. LEX signal provides real-time GPS satellite ephemeris and clock correction. The accuracy of these corrections directly affects the positioning accuracy. This paper compares the LEX PPP data with the IGS Ultra rapid data products to analyze the accuracy of LEX data. The analysis showed that LEX data has systematic errors that can be corrected. A new algorithm was developed to correct clock error and ephemeris errors using a liner model and wavelet transformation. This method improved LEX ephemeris accuracy to decimeter level and the clock correction accuracy to 0.01 microseconds. As a result, LEX based real-time positioning accuracy was improved by 37%.
Keywords: GPS; PPP; QZSS; LEX
Authors: Marco Allain
Abstract: Central California is undergoing sustained periods of drought. Dry conditions are facilitating wildfires and other ecological disturbances. Croplands are also at risk from the drying weather. These recent climatic patterns are well known but require a multi-temporal approach to fully realize the pattern. To accomplish this, normalized difference vegetation indices (NDVI) were run on a series of Landsat Thematic Mapper and Multi Spectral Scanner images. Such an approach was taken to help quantify the loss to cropland and natural habitat. The images were statistically compared and checked against field work of the study area. Results showed that vegetation levels in the 2000s were significantly more stressed than those of the 1980s and 1990s. However, trends in the data gathered suggest that USDA water conservation and similar practices can help alleviate the problem.
Keywords: Landsat; Desertification; GIS; NDVI; Point-Center Quarter Method
Authors: Akajiaku C. Chukwuocha; Joel I. Igbokwe
Abstract: Demarcation of runoff natural flow routes is inestimable in mitigating flooding and erosion. It is useful also in planning urban areas and designing drainage networks. Devastating flooding and erosion are being recorded across the globe as a result of increases in the intensity and duration of storm water precipitation due to global warming. In the developing parts of the world state of the art topographical data is not always available, but it should not be necessary to stop state of the art geospatial topographical analyses especially if there are sources of old topographic data that may be authenticated. In this study, Geographic Information Systems (GIS) were used to create a Digital Elevation Model (DEM) of Owerri in Southeast Nigeria, using data from topographical maps of the city of 1977. The data was authenticated using three dimensional (3D) coordinates of sample points derived from Global Navigational Satellite Systems (GNSS) surveys. The DEM was processed using the ArcGIS and ArcHydro software to determine heavily accumulating flow routes. The accuracy of the result was confirmed by using the coordinates of the delineated flow routes to locate their ground positions with handheld GPS receivers after some heavy storm event.
Keywords: Digital Elevation Model (DEM); Flow Routes; Flow Direction Grid; Flow Accumulation Grid; Stream Definition Threshold