GEE——利用Landsat系列数据集进行1984-2023EVI指数趋势分析

简介：

利用Landsat系列数据集进行1984-2023EVI指数趋势分析其主要目的是进行长时序的分析，这里我们选用EVI指数，然后进行了4个月的分析，查看其最后的线性趋势以及分布状况。

EVI指数：

EVI指数（Enhanced Vegetation Index，增强型植被指数）是一种反映植被生长状态的遥感指数，它结合了植被指数的红光波段和近红外波段的信息，可以消除植被覆盖度、土壤背景和大气影响等因素对遥感数据的影响，用于研究植被生长和陆地生态系统的动态变化。EVI指数的计算公式为：EVI=(2.5*(NIR-Red))/(NIR+6*Red-7.5*Blue+1)，其中NIR、Red和Blue分别为近红外、红光和蓝光波段反射率。EVI指数的取值范围在-1到1之间，数值越大表示植被覆盖度越高，反之则越低。

函数：

ee.Filter.calendarRange(start, end, field)这个用来筛选指定年月日特定时间的函数

Returns a filter that passes if the object's timestamp falls within the given range of a calendar field. The month, day_of_year, day_of_month, and day_of_week are 1-based. Times are assumed to be in UTC. Weeks are assumed to begin on Monday as day 1. If end < start then this tests for value >= start OR value <= end, to allow for wrapping.

Arguments:

start (Integer):

The start of the desired calendar field, inclusive.

end (Integer, default: null):

The end of the desired calendar field, inclusive. Defaults to the same value as start.

field (String, default: "day_of_year"):

The calendar field to filter over. Options are: year, month, hour, minute, day_of_year, day_of_month, and day_of_week.

Returns: Filter

ee.ImageCollection.fromImages(images)从列表中讲影像转化为影像集合

Returns the image collection containing the given images.

Arguments:

images (List):

The images to include in the collection.

Returns: ImageCollection

ee.Algorithms.If(condition, trueCase, falseCase)这个是防止数据集中出现没有影像的情况，然后进行条件筛选

Selects one of its inputs based on a condition, similar to an if-then-else construct.

Arguments:

condition (Object, default: null):

The condition that determines which result is returned. If this is not a boolean, it is interpreted as a boolean by the following rules:

• Numbers that are equal to 0 or a NaN are false.

• Empty strings, lists and dictionaries are false.

• Null is false.

• Everything else is true.

trueCase (Object, default: null):

The result to return if the condition is true.

falseCase (Object, default: null):

The result to return if the condition is false.

Returns: Object

ui.Chart.feature.groups(features, xProperty, yProperty, seriesProperty)按照矢量组加载时序图表

Generates a Chart from a set of features. Plots the value of a given property across groups of features. Features with the same value of groupProperty will be grouped and plotted as a single series.

• X-axis = xProperty values.

• Y-axis = yProperty values.

• Series = Feature groups, by seriesProperty.

Returns a chart.

Arguments:

features (Feature|FeatureCollection|List<Feature>):

The features to include in the chart.

xProperty (String):

Property to be used as the label for each feature on the x-axis.

yProperty (String):

Property to be plotted on the y-axis.

seriesProperty (String):

Property used to determine feature groups. Features with the same value of groupProperty will be plotted as a single series on the chart.

Returns: ui.Chart

代码：

var counties = ee.FeatureCollection("TIGER/2018/Counties"),
    elev = ee.Image("USGS/NED"),
    wdpa = ee.FeatureCollection("WCMC/WDPA/current/polygons"),
    slr_high = ee.FeatureCollection("users/caitlittlef/Acadia_SLR"),
    marsh = ee.FeatureCollection("users/caitlittlef/Acadia_marsh"),
    l8 = ee.ImageCollection("LANDSAT/LC08/C02/T1_L2"),
    l5 = ee.ImageCollection("LANDSAT/LT05/C02/T1_L2"),
    margin = ee.FeatureCollection("users/caitlittlef/Acadia_marsh_slr_margin"),
    slr_buff = ee.FeatureCollection("users/caitlittlef/Acadia_SLR_buffer"),
    marsh_buff = ee.FeatureCollection("users/caitlittlef/Acadia_marsh_buffer"),
    bass_harbor = /* color: #90d614 */ee.Geometry.Point([-68.34446051531992, 44.257472150621076]),
    thompson_island = /* color: #90d614 */ee.Geometry.Point([-68.36250246923403, 44.4225955588721]),
    babson_creek = /* color: #90d614 */ee.Geometry.Point([-68.32728158629772, 44.37497962957902]),
    sch