Google Earth Engine——WWF/HydroSHEDS/15DIR该数据集的分辨率为15弧秒。15角秒的数据集是水文条件下的DEM、排水（流）方向和流量累积。

HydroSHEDS is a mapping product that provides hydrographic information for regional and global-scale applications in a consistent format. It offers a suite of geo-referenced datasets (vector and raster) at various scales, including river networks, watershed boundaries, drainage directions, and flow accumulations. HydroSHEDS is based on elevation data obtained in 2000 by NASA's Shuttle Radar Topography Mission (SRTM).

This drainage direction dataset defines the direction of flow from each cell in the conditioned DEM to its steepest down-slope neighbor. Values of drainage direction vary from 1 to 128. All final outlet cells to the ocean are flagged with a value of 0. All cells that mark the lowest point of an endorheic basin (inland sink) are flagged with a value of -1. The drainage direction values follow the convention adopted by ESRI's flow direction implementation: 1=E, 2=SE, 4=S, 8=SW, 16=W, 32=NW, 64=N, 128=NE.

This dataset is at 15 arc-second resolution. The datasets available at 15 arc-seconds are the Hydrologically Conditioned DEM, Drainage (Flow) Direction, and Flow Accumulation.

Note that the quality of the HydroSHEDS data is significantly lower for regions above 60 degrees northern latitude as there is no underlying SRTM elevation data available and thus a coarser-resolution DEM was (HYDRO1k provided by USGS).

HydroSHEDS was developed by the World Wildlife Fund (WWF) Conservation Science Program in partnership with the U.S. Geological Survey, the International Centre for Tropical Agriculture, The Nature Conservancy, and the Center for Environmental Systems Research of the University of Kassel, Germany.

HydroSHEDS是一个制图产品，以一致的格式为区域和全球范围的应用提供水文信息。它提供了一套不同尺度的地理参考数据集（矢量和栅格），包括河流网络、流域边界、排水方向和流量积累。HydroSHEDS是基于NASA的航天飞机雷达地形任务（SRTM）在2000年获得的高程数据。

这个排水方向数据集定义了从条件DEM中的每个单元到其最陡峭的下坡邻居的流动方向。排水方向的值从1到128不等。所有通向海洋的最终出口单元都标记为0，所有标志着内流盆地（内陆水槽）最低点的单元都标记为-1。 排水方向值遵循ESRI的流向实施惯例。1=e, 2=se, 4=s, 8=sw, 16=w, 32=nw, 64=n, 128=ne.

该数据集的分辨率为15弧秒。15角秒的数据集是水文条件下的DEM、排水（流）方向和流量累积。

请注意，在北纬60度以上的地区，HydroSHEDS数据的质量要低得多，因为没有底层的SRTM高程数据可用，因此要用更粗的分辨率DEM（美国地质调查局提供的HYDRO1k）。

HydroSHEDS是由世界自然基金会（WWF）保护科学项目与美国地质调查局、国际热带农业中心、大自然保护协会和德国卡塞尔大学环境系统研究中心合作开发的。

Dataset Availability

2000-02-11T00:00:00 - 2000-02-22T00:00:00

Dataset Provider

WWF

Collection Snippet

ee.Image("WWF/HydroSHEDS/15DIR")

Resolution

463.83 meters

Bands Table

* = Values are estimated

引用：

Lehner, B., Verdin, K., Jarvis, A. (2008): New global hydrography derived from spaceborne elevation data. Eos, Transactions, AGU, 89(10): 93-94.

代码：

var dataset = ee.Image('WWF/HydroSHEDS/15DIR');
var drainageDirection = dataset.select('b1');
var drainageDirectionVis = {
  min: 1.0,
  max: 128.0,
  palette: [
    '000000', '023858', '006837', '1a9850', '66bd63', 'a6d96a', 'd9ef8b',
    'ffffbf', 'fee08b', 'fdae61', 'f46d43', 'd73027'
  ],
};
Map.setCenter(-121.652, 38.022, 8);
Map.addLayer(drainageDirection, drainageDirectionVis, 'Drainage Direction');