很多时候我们大部分人想知道如何使用功能，但是不知道具体的函数该如何使用，今天我们就以影像集合为研究对象，分别研究我们常用的功能，以及再GEE中的函数内容。本次研究的内容涵盖了影像数量统计、影像筛选、影像属性获取，单波段影像合成等等功能。
函数：
distinct(properties)
Removes duplicates from a collection. Note that duplicates are determined using a strong hash over the serialized form of the selected properties.
Arguments:
this:collection (FeatureCollection):
The input collection from which objects will be selected.
properties (Object):
A property name or a list of property names to use for comparison. The '.geo' property can be included to compare object geometries.
Returns: FeatureCollection
count()
Reduces an image collection by calculating the number of images with a valid mask at each pixel across the stack of all matching bands. Bands are matched by name.
Arguments:
this:collection (ImageCollection):
The image col