外文翻譯---gps的精密單點(diǎn)定位技術(shù)在空中三角測量的應(yīng)用-文庫吧資料
2025-01-23 23:07本頁面
【正文】 in algorithms and correction models for the GPS PPP have been discussed in many papers (Han et al., 2001。 Heipke et al., 2001), but there will be larger vertical parallax when stereo models are reconstructed using these image orientation parameters and the height accuracy cannot satisfy the requirement of large scale topographic mapping. Therefore, a bundle block adjustment should be made, bined image orientation parameters obtained via the POS and photogrammetric observations (Greening et al., 2000). Whether exploiting GPS data or POS data in AT, DGPS positioning is necessary to provide the GPS camera stations at present. In the DGPS mode, one or more GPS reference stations should be emplaced on the ground and observed synchronously and continuously together with the airborne GPS receiver during the entire flight mission. Additionally, signals from GPS satellites should be received as few transmission interruptions as possible. Initialization surveying is also required before aircraft takes off and static surveying should be performed after landing. In the processing of GPS observations, carrier phase differential technique is used to eliminate or reduce GPS positioning errors, including satellite clock error, satellite orbit error, atmospheric delay error, and so on. Generally speaking, it is difficult to emplace proper GPS reference stations when the aerial photographic region is with large scope or difficult to access and municate. In order to guarantee the quality of aerial images, a survey area must be photographed for a long period, which is result from the shortage of weather suitable for photography. GPS reference stations must therefore remain in place for a long time. Moreover, the accuracy of DGPS positioning is relevant to the length of baseline. The longer the baseline, the weaker the correlation between ionospheric refraction error and tropospheric delay error. Due to the need for spatial correlation of atmospheric delay errors, the lengths of GPS differential baselines are typically limited to within 20 km if centimeter level accuracy is required with high reliability (Sun, 2004). When it es to aerial photogrammetry, this is difficult because the length of survey areas is typically more than 200 km and the distance between the survey area and the airport may be greater. For baselines with long length, the atmospheric delay mainly posed of ionospheric delay and tropospheric delay will degrade positioning accuracy significantly. In such cases, even the ionospheric delay can be almost removed by using dual frequency GPS receivers. However, there can still be a tropospheric delay within a few decimeters, meaning that for long baselines, the positioning accuracy is typically in the level of decimeters. At the same time, the establishment of GPS reference stations sometimes makes the implementation of a survey plan difficult due to traffic, munication and cost considerations. As a result, the method of replacing GPS reference stations by Continuous Operating Reference Stations (CORS) was proposed and obtained an accuracy in decimeter level pared with the results obtained by GPS reference stations (Bruton et al., 2001。 Lucas, 1987). After about 20 years of these efforts, GPSsupported AT was extensively applied in aerial triangulation at many scales and in all types of terrain. It is particularly beneficial in areas where they are difficult to establish ground control (Ackermann, 1994). In the late 1990s, with the development of sensor technology, an
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