Recent studies have established quantitative relationships between MODIS derived AOT and PM2.5 using linear regression models. Wang and Christopher [27] achieved a correlation coefficient of 0.7 between satellite-derived AOT at 550 nm and PM2.5 measured at seven locations in Alabama, United States. Wong et al. [28] showed a good correlation Axitinib VEGFR1 between MODIS derived 500 m AOT and PM2.5 (r2 = 0.67), which demonstrated great potential for MODIS derived 500 m AOT as a good surrogate for PM2.5 monitoring. In this study, we attempted to model the 2D (image) and vertical distributions of PM2.5 which has not been done in any other study. The resulting 3D database of PM2.5 concentrations can be used for daily air quality monitoring in environmental authority.
First, the aerosol extinction profile (��a(z)) was modeled and the columnar AOT was divided into AOT��z at different elevations [29,30]. Then by utilizing the equation (PM2.5 = 63.66 �� AOT + 26.56) developed by Wong et al. [28], the PM2.5��z at different elevations can be derived.By integrating the ex
GPS-NAVSTAR (Global Positioning System-NAVigation Signal Timing And Ranging), popularly known as the GPS system, has considerably gained in civilian interests, since May 2000. Earlier, the system was practically reserved for military purposes. The positioning accuracy for the civilian sector was ca. 100 m due to an intentional error, called Selective Availability. According to report [1], the horizontal positioning error is less than 17 m for 99% of the time in average conditions or 17 m for 90% of the time in worse outdoor conditions.
The error depends on many factors, like atmospheric conditions, sun activity, geographical location, terrain type, satellites’ constellation, etc. In an open space, positioning errors are of ca. 2�C3 m. However, in dense built-up areas, the location error may reach 100 m [2,3] or even more [4]. The error is introduced due to multipath propagation of signals transmitted by the satellites when there is no line-of-sight. A satellite signal is bounced off the walls of a building before finding its way to a GPS receiver. The propagation time of the signal is delayed and the GPS receiver Brefeldin_A miscalculates its location with a reference to the satellites.There are many techniques to improve the location accuracy.
Along coasts, for marine purposes, Trichostatin A supplier special ground DGPS (Differential GPS) reference stations broadcast differential corrections that allow a GPS receiver to eliminate tropospheric, ionospheric, ephemeris and clock errors. The overall error is reduced to 10 m with accuracy decreasing by 1 m with each 150 km increase in distance from the reference station. The corrections are transmitted on a ca. 300 kHz carrier frequency. A receiver must be, however, equipped with an additional antenna [5].A-GPS (Assisted GPS) is a technique that downloads from the Internet the data concerning GPS satellite constellation [6].