本案例主要的目的是利用30天为时间窗口作为平滑的间隔的一个时间间隔，然后按照连接将影像连接起来（这里可以有两个影像集合或者不同Landsat 系列影像，只要有对应的属性即可），因为再join连接的时候需要有共同的属性确保可以连接上。
ee.Join.saveAll(matchesKey, ordering, ascending, measureKey, outer)
Returns a join that pairs each element from the first collection with a group of matching elements from the second collection. The list of matches is added to each result as an additional property. If measureKey is specified, each match has the value of its join measure attached. Join measures are produced when withinDistance or maxDifference filters are used as the join condition.
matchesKey (String):
The property name used to save the matches list.
ordering (String, default: null):
The property on which to sort the matches list.
ascending (Boolean, default: true):
Whether the ordering is ascend