天绘一号卫星为测绘卫星，测绘卫星标称轨道是卫星进行长期轨道维持的目标，对卫星的地面覆盖性能起到决定性的作用。为了分析和提高卫星对地面目标的覆盖性能，根据天绘一号卫星轨道设计和维持的特点，提出了基于条带—纬度覆盖图的分析和优化方法。推导了推扫式成像卫星覆盖经度跨度计算公式，构建了基于条带—纬度覆盖图的分析方法，通过将多颗卫星的条带—纬度覆盖图叠加得到不同区域的覆盖次数，根据每次重访时的卫星星下点条带号计算对地面目标的重访时间间隔。提出了通过调整当前条带号和降交点地方时减小对目标区域的重访间隔的优化方法。通过与网格点方法的计算结果比较，验证了该方法的有效性。

TH01 is a kind of surveying and mapping system with three satellites in orbit. The nominal orbit is the long-term maintaining target, which determines the coverage property of the constellation. This study aims to find a useful method for evaluating and optimizing coverage performance.
In this study, a path-latitude cover-map method is proposed for analysis and optimization. In the path-latitude cover-map, the covered areas are drawn on a map with a path number as the X-axis rather than longitude, where the access number of certain target regions can be read, and the access intervals can be acquired via the access path numbers.
The formula of the longitude span of a certain sweep-imaging satellite is derived to depict the path-latitude cover-map. The procedure is provided for evaluating the access number and intervals. An optimization method is also proposed with the current path number and the local time of a descending node as parameters.
A numerical example of long-term analysis is provided to validate the effectiveness of the proposed method. A certain region with anomalous shape is selected as a target, whose number and intervals of accesses in a repeating period are analyzed through the proposed procedure and the traditional grid point covering method. Results show that the proposed method can achieve similar accuracy through the grid point covering method.
The proposed optimization method is conducted to shorten the access intervals of the constellation by adjusting the current path numbers and local time of a descending node of each satellite, thus resulting in a 30% shorter maximum access interval.
The proposed path-latitude cover-map method is effective for a long-term analysis of the TH01 satellite over an anomalous geometric area, thereby achieving similar accuracy through the traditional grid point method and remarkable saving of resource and time. The optimization method is also effective for limiting the maximum access intervals, which can provide helpful advice for long-term orbit maintenance.