衛星影像與其他相關資料進行整合時，需進行幾何改正。嚴密之幾何改正包括兩個部份，修正傾斜移位及高差移位。對於大範圍土地利用監測之應用，單張衛星影像可能無法涵蓋目標區域的所有範圍。以多軌道之衛星影像進行影像正射化後，經鑲嵌可得到大範圍之正射化衛星影像。 若不同軌道之衛星影像單獨進行方位重建，每一軌道之衛星影像都是獨立進行幾何改正，有可能造成在重疊區域中相同之地面點在兩張正射影像上不重合，使得鑲嵌後之正射影像在接縫處有錯開的現象。欲減少此現象，在軌道幾何校正時使用區域平差是較佳的方式。 傳統光束法需要較佳之幾何交會條件，但是對於環境監測(正射化處理)為導向之多軌道衛星影像而言較不易達到，因此需要加入高程的約制條件。本研究將提出一個軌道區域平差之模式，其主要工作包括(1)將建立載體參數修正模式進行初步衛星軌道密合，(2)計算航帶連結點之修正向量，(3)以最小二乘過濾進行衛星軌道精密修正，(4)使用逆轉換模式進行衛星影像正射化，最終進行正射影像鑲嵌。 實驗結果顯示，加入航帶連結點進行軌道區域平差，可大幅提升正射影像間之相對精度。且減少鑲嵌影像上重疊區影像錯開之現象。 Satellite images need geometric corrections for combining with other spatial data. The major work of rigorous geometric corrections is to compensate for the tilt displacement and relief displacement. In various applications, areas of interest sometimes cover two or more satellite images, thus mosaicking for those images becomes important. Orthoimages are frequently used in the mosaicking process. While orbit adjustment is a prerequisite in the image orthorectification. Scene-based orbit adjustment could yield geometric discrepancies that could cause image discontinuity along the seam line during mosaicking. Thus, block adjustment is preferable. A traditional block adjustment is performed in three dimensions. The base-to-height ratio of multi-orbit satellite images is, frequently, not large enough. Hence, those tie points need elevation control in the block adjustment procedure. The objective of this investigation is to establish a simple yet effective block adjustment procedure for multi-orbit satellite images. The major works of the proposed scheme are: (1) adjustment of satellite’s orbit accurately, (2) calculation of the error vectors for each tie point using digital terrain model and ray tracing technique, (3) refining the orbit using the Least Squares Filtering technique and (4) generation of the orthophotos. In the process of least squares filtering, we use the error vectors of ground control points and tie points to collocate the orbit. In orthorectification, the indirect method is employed to generate the orthoimage. Test images are from SPOT 5 satellite. Experimental results indicate that, block adjustment can improve the relative accuracy between orthoimages. It is also demonstrated that the mosaicked image is better seamed when tie points are employed in the adjustment.
