ASTER Global Water Bodies Database2019

Japan’s Ministry of Economy, Trade, and Industry(METI)
National Aeronautics and Space Administration (NASA)
Jet Propulsion Laboratory, California Institute ofTechnology

User Guide
Prepared by Michael Abrams
Version 1June 2019
Copyright 2019 California Institute of Technology. U.S. Government sponsorship acknowledged.

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Table of Contents
1.

Introduction ...................................................................................................................................................32.

How ASTWBD Was Created............................................................................................................................33.

Data Set Container .........................................................................................................................................44.

Data Formats ..................................................................................................................................................45.

Filename Convention .....................................................................................................................................56.

How to Obtain Data........................................................................................................................................5

7.

Comparison with SRTM Water Body Dataset ................................................................................................58.

Key Processing Factors ...................................................................................................................................6

9.

References ......................................................................................................................................................721. Introduction
The ASTER instrument, launched onboard NASA’s Terra spacecraft in December 1999, has an alongtrack stereoscopic capability using its near infrared spectral band to acquire the stereo data. ASTER
has two telescopes, one for nadir-viewing and another for backward-viewing, with a base-toheight ratio of 0.6. The spatial resolution is 15 meter (m) in the horizontal plane. One scene consists of
4,100 samples by 4,200 lines which corresponds to about 60 km by 60 km ground area.
A number of 1,880306 scenes (Level-1A products) that was acquired from March, 2000 toNovember 31, 2013 was used to generate ASTER Global Digital Elevation Model (ASTERGDEM) version 3. ASTER GDEM was created by stacking all cloud-masked scene DEMs andnon-cloud-masked scene DEMs, and statistical selection algorithm to remove abnormal data.
In addition to ASTER GDEM, the ASTER Global Water Body Database (ASTWBD) was generated
as a by-product to correct elevation values of the water body surface like ocean, river, and lake.
The ASTWBD was applied to GDEM such that it has a proper elevation value for water bodysurface. The ocean and lakes have a flattened, constant elevation value. Rivers have a stepped-down
elevation value from their upper reaches to where they join another river or reach the ocean.
The ASTWBD is the only (near-) global raster data set; it delineates water bodies smaller than 0.2 sq.
km. In addition, the data set defines what kind of water body is delineated: ocean, lake or river. Twoother, less complete, data sets are publicly available. The Shuttle SRTM Water Body Dataset wascreated from the Shuttle SRTM SAR mission of 2000, and covers 60 degrees north to 54 degrees
south at 30 m resolution and is available from the Land Processes Distributed Active Archive Center(LP DAAC) at lpdaac.usgs.gov. It is a binary vector, data set: water or no water.
The Landsat Global Surface Water Explorer, developed by the European Commission, is based on 32years of Landsat data, and maps show change from 80 degrees north to 60 degrees south, at 30 mresolution and is available at https://global-surface-water.appspot.com/. The “occurrence” data set isa binary water/no-water raster data set, which does not identify the types of water bodies.

2. How ASTWBD Was Created
The ASTWBD was procured from the Sensor Information Laboratory Corp. (SILC) in Tokyo. SILC
used proprietary software to extract water bodies from the ASTER images used to create the GDEM.
In addition, considerable hand editing was done on each tile to improve the output from the automatic
detection algorithms.
ASTWBD generation consisted of two parts: separation of waterbodies from land areas; andclassification of detected waterbodies into three categories: ocean, river, and lake. The separation
process was carried out during scene-based DEM generation using an algorithm that created theGDEM3. For ocean-waterbodies, the effect of sea ice was manually removed to better delineate ocean
shorelines in high latitude areas, because virtually no ice areas along ocean shorelines are not
identified as a sea-waterbody with zero elevation. This process was enhanced by reference to Google
Earth and GeoCover images. For lake-waterbodies, the elevation for each lake was calculated fromthe perimeter elevation data using the mosaic image that covers the entire area of the lake. All lakes
with an area greater than 0.2 square kilometers were identified. Rivers presented a unique challenge,
because their elevations gradually step down from upstream to downstream. Initially, visual3inspection was required to separate rivers from lakes. A stepwise elevation assignment, with a step of
one meter, was carried out by manual or automated methods, depending on the situation.

3. Data Set Container
The ASTWBD zipped tiles accommodate two files: an attribute (*.att) file and an elevation (*.dem)
file. Both files have a dimension of 3601 samples by 3601 lines, which corresponds to 1 degreeby 1 degree data area at 1 arc-second (~30 m) resolution. The names of individual data tiles referto the latitude and longitude at the geometric center of the lower-left (southwest) corner pixel.
For example, the coordinates of the lower-left corner of the ASTWBD_V001_N00E006 tile are 0degree north latitude and 6 degrees east longitude. ASTWBD_V001_N00E006_dem andASWBDV001_N00E006_att files accommodate DEM and attribute, respectively (Tables 1 and 2).
The rows at the north and south edges as well as the column at the east and west edges of each tile
overlap and are identical to the edge row and column in the adjacent tile. The data are in geographic
latitude/longitude rectangular projection (also called plate carree). The data coverage is north 83
degrees to south 83 degrees. A set of ASTWBD includes 22,886 tiles.
Table 1. ASTWBD and GDEM3 tiles
case1
case2
(subtotal)
case3
total # of tiles#tiles
16,833
6,053
22,88636,874
59,760

GDEM3
tile
tile
no tileASTWBD status
tile
Water present (ocean,lake,river) in tile
tile
no waterbody (=land) in tilenumber of ASTWBD or GDEM tiles
no tile ocean in entire tile
# of tiles in latitude 83 [(83*2)*360=59,760]

4. Data Formats
The attribute file has four values: 0 for land, 1 for ocean, 2 for river, and 3 for lakes, in GeoTIFF format.
The accompanying *.dem file has elevation values for all non-land pixels, and is also in GeoTIFF
format. The data tiles cover 1 x 1 degree areas, and are in rectangular, geographic latitude/longitude
projection.
Data formats are summarized in Table 2.
Table 2. Data formats
Tile Size

3601 x 3601 (1 degree by 1 degree)

Posting interval

1 arc-second (~30 m)

Geographic coordinates

Geographic latitude and longitude

Output format

ATT (attribute) file GeoTiff, 8 bits; DN values : 1 forocean, 2 for river, 3 for lake, and 0 for land
DEM (elevation) file: GeoTiff, signed 16 bits, 1m/DN, -9999for land
DEM referenced to the WGS84/EGM96 geoid
4Coverage

North 83 degrees to south 83 degrees,
22,886 tiles for ASTWBD

5. Filename Convention
The ASTWBD product is a zipped file of the ATT file and corresponding DEM file.
Filename example: ASTWBDV001_N40W100_XXX.tif
ASTWBD = Product short name2019 = Publication year
N or S = Northern hemisphere or Southern hemisphere
40 = Latitude of lower left corner
W or E = Western hemisphere or Eastern hemisphere
100 = Longitude of lower left corner
XXX = DEM or ATT for data file type
tif= GeoTIFF

6. How to Obtain Data
The following tools offer options to search the LP DAAC data holdings and provide access tothe data:
Bulk download: LP DAAC Data Pool and DAAC2DiskSearch and browse: NASA Earthdata Search
The Digital Object Identifier (DOI) for the dataset is given below to provide a persistent link to theproduct information.
ASTWBD: ASTER Global Water Body Dataset – ASTWBD.001
DOI: 10.5067/ASTER/ASTWBD.001

7. Comparison with SRTM Water Body Dataset
As described earlier, the SRTM WBD covers the Earth’s surface from 60 degrees north to 54 degrees southlatitudes. It is distributed as 1 by 1 degree tiles, with 30 m postings, so direct comparison with the ASTWBD isstraightforward. We examined tile N41W72 over Rhode Island. The tile contains lakes and ocean (Figure 1).
SWBD is depicted in red; ASTWBD is white for lakes, and gray for ocean. Both data sets do well with lakes:
ASTWBD identifies the lakes and ocean, and the corresponding *.dem file gives the water elevation. TheSWBD data set outlines the lakes. Both miss a few lakes that the other finds. The coastline matches for thewestern half of the tile, but the SWBD has a glaring error starting at the point of land about midway along thecoast, where the boundary takes off in a straight line heading southeast.

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Figure 1. ASTWBD and SWBD for tile N41W72 over part of Rhode Island.

8. Key Processing Factors
The changes in the key processing factors for GDEM and ASTWBD from Version 1 to Version 2 toVersion 3 are listed in Table 3.

Table 3 Key processing factors
Key processing factor

Version 1

6Version 2Version 3

Number of input scene DEMS
Posting intervalCorrelation kernel size
Minimum water body detection size
Water body post-processing
Filtering threshold value
OffsetRelease data

1,264,118
1 arc-second
9 x 9 pixels
12 sq. km
Not applied

1,514,350
1 arc-second
5 x 5 pixels
1 sq. km
Applied

40 m-5 m offset observed
June 200940 m
V1 offset removed
October 2011

1,880,306
1 arc-second
5 x 5 pixels
0.2 sq. km
Separation of rivers
from lakes
40 m--July 2018

9. References[1] Jean-François Pekel, Andrew Cottam, Noel Gorelick, Alan S. Belward (2016). "High-resolution
mapping of global surface water and its long-term changes." Nature, DOI: 10.1038/nature20584.
[2] NASA JPL. NASA Shuttle Radar Topography Mission Water Body Data Shapefiles & Raster
Files. 2013, distributed by NASA EOSDIS Land Processes DAAC,
https://doi.org/10.5067/MEaSUREs/SRTM/SRTMSWBD.003[3] Fujisada, H. Urai, M. and A. Iwasaki, Advanced methodology for ASTER DEM generation, 2011,
IEEE TGARS, vol.49, no.12, pp.5080-5091.
[4] Fujisada, H., Urai, M., Iwasaki, A., Technical methodology for ASTER Water Body Data Base,Remote Sens. 2018, 10, 1860.
https://www.mdpi.com/2072-4292/10/12/1860/xml

10.Acknowledgment
Work by Abrams was performed at the Jet Propulsion Laboratory, California Institute of Technology
under contract with the National Aeronautics and Space Administration.

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