| Budget Amount *help |
¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 1998: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1997: ¥2,200,000 (Direct Cost: ¥2,200,000)
|
|---|
| Research Abstract |
GPS positioning is difficult in forest area compared to agricultural field or ocean. The main reason for this supposed to be cut-off of GPS signal by terrain and tree canopies. So, it is needed to make GPS survey plan, by knowing when GPS satellites will pass through tree canopy gap of particular positioning point, to find out when GPS positioning is possible at that point. This research aims to develop GPS orbit forecasting system for differential positioning in forest area, by combining photograph of the point and GPS orbital information. Research fields were set at Tokyo University Forest in Hokkaido and Tokyo University Forest in Chiba. In each positioning point in the forest, a high-resolution fish-eye digital photograph of the sky and GPS signal of more than one hour were taken. Digital fish-eye photograph was analyzed by digital image analysis technic, to classify the elements of the photograph, such as sky, leaves, branches, and ground. Then those elements were converted into "
… More
openness", which denotes degree of penetration of GPS signal, to generate "openness" image. GPS orbits of the observed satellites were calculated from almanac data, and they were plotted on the "openness" image to extract every 10 seconds' "openness" data. Each GPS satellites' signal were analyzed to calculate signal strength of every 10 seconds. Then "openness" data and signal strength data were combined by using "time" as the key, and relationship of these two data were analyzed. The result showed correlation of "openness" and signal strength on the whole, but does not explain all of fluctuation of signal strength. This owes to uncorrespondance of fish-eye photo and GPS orbit, which caused by bad photographing condition such as unhorizontalness of lens and north position error. But these error may happen usually when taking photographs in forest. So, the program was developed for forecasting number of GPS satellites under user-defined "openness" value and time interval. By using this program, the user can forecast when he (or she) can do GPS positioning at particular point, if he (or she) takes fish-eye photo of that point. This will help greatly to promote use of GPS in the forest area. Less
|
