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Pinpointing the sources and measuring
the lengths of the principal rivers of
the world
S. Liu a , P. Lu b , D. Liu a , P. Jin c & W. Wang d
a Institute of Remote Sensing Applications, Chinese Academy of
Sciences, Datun Road, Chaoyang District, Beijing, 100101, China
b China Association for Science and Technology, 86 Southern
Colleges Road, Haidian District, Beijing, 100081, China
c China Aero-Geophysical Survey & Remote Sensing Centre for
Land and Resources, 31 Colleges Road, Haidian District, Beijing,
100083, China
d School of Environment and Nature Resources, Renmin University
of China, 59 Zhongguancun Street, Beijing, 100872, China
Version of record first published: 17 Mar 2009.
To cite this article: S. Liu , P. Lu , D. Liu , P. Jin & W. Wang (2009): Pinpointing the sources and
measuring the lengths of the principal rivers of the world, International Journal of Digital Earth,
2:1, 80-87
To link to this article: http://dx.doi.org/10.1080/17538940902746082
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Pinpointing the sources and measuring the lengths of the principal rivers
of the world
S. Liu
a
*, P. Lu
b
, D. Liu
a
, P. Jin
c
and W. Wang
d
a
Institute of Remote Sensing Applications, Chinese Academy of Sciences, Datun Road,
Chaoyang District, Beijing 100101, China;
b
China Association for Science and Technology, 86
Southern Colleges Road, Haidian District, Beijing 100081, China;
c
China Aero-Geophysical
Survey & Remote Sensing Centre for Land and Resources, 31 Colleges Road, Haidian District,
Beijing 100083, China;
d
School of Environment and Nature Resources, Renmin University of
China, 59 Zhongguancun Street, Beijing 100872, China
(Received 10 November 2008; final version received 5 January 2009)
Cultures throughout the world are associating with the rivers. People depend
upon the rivers and their tributaries for food, water, transport, and many other
aspects of their daily lives. Unfortunately, human beings have not calculated the
accurate lengths for the great rivers even today. The lengths of the rivers are very
different in popular textbooks, magazines, atlases and encyclopedias, etc. To
accurately determine the lengths of the principal rivers of the world, the
combination of satellite image analysis and field investigations to the source
regions is proposed in this paper. The lengths of the Nile, Amazon, Yangtze,
Mississippi, Yellow, Ob, Yenisey, Amur, Congo and Mekong, with lengths over or
close to 5000 km, were calculated using the proposed method. The results may
represent the most reliable and accurate lengths of the principal rivers of the
world that are currently achievable.
Keywords: principal rivers of the world; sources pinpointing; lengths measuring;
satellite remote sensing; field explorations
Introduction
In 1852, human beings made the first attempt to measure the height of the highest
summit of the world Qumolongma (also known as Everest). Thereafter, geodesists
carried out several geodetic campaigns to determine the Qumolongma’s accurate
height with cutting-edge instruments and announced their measured results on
several occasions. Chinese scientists have made six attempts to determine the
accurate height of the Qumolongma since the Chinese alpinists conquered it in 1965
(Chen et al. 2001, Chen et al. 2006). Human beings began to explore the source of
the Nile and measured the height of the Qumolongma almost at the same time. The
longest river in the world, the Nile or the Amazon, has remained a mystery although
Sir Richard F. Burton and John Hanning Speke began their exploration on the
source of the Nile in 1856 (Ondaatje 1998).
Since the last century, the lengths of the Nile and Amazon have been contesting
for the title of the world’s longest river. From the lengths recorded in encyclopedias,
*Corresponding author. Email: liusc@irsa.ac.cn
ISSN 1753-8947 print/ISSN 1753-8955 online
#2009 Taylor & Francis
DOI: 10.1080/17538940902746082
http://www.informaworld.com
International Journal of Digital Earth,
Vol. 2, No. 1, March 2009, 8087
Downloaded by [Institute of Remote Sensing Application] at 21:20 19 April 2013
textbooks, magazines and atlases with various languages, one could not recognise the
longest river in the world. The Nile in Africa is reported to be anywhere from
5499 km to 6695 km with a maximum difference of 1196 km. And the Amazon in
South America from 6275 km to 7025 km with a maximum difference of 750 km.
These significant inconsistencies could be found in other great rivers, e.g. the Yangtze
from 5550 km to 6397 km, the Mississippi from 5970 km to 6415 km, etc. (Hanks
et al. 1979, Arthur et al. 1980, Rand McNally Encyclopaedia of World Rivers 1980,
The Encyclopaedia of American (International Edition) 1980, McWillam 1995,
National Geographic Society 2000, National Geographic World Atlas for Young
Explorers 1998, O’Neill and Yamashita 1993, Osborne, Peissel 1997, Ondaatje 1998),
The New Encyclopaedia Britannica (15th Edition) 1980, William and Levey (eds)
1975, Winchester 2000). It is impossible to distinguish which is correct (or more
accurate) in a series of controversial lengths for each river. Therefore, recalculation of
the lengths with high accuracy using modern technologies is highly desirable.
The calculated length of one river depends on the position of the geographical
source and the mouth, the data sources of the measuring based on and length
measuring techniques. Locating the mouth of a river is pretty straightforward. It is
normally defined as the intersection of the tangential line of two sides of the outlet
and the middle line of the river. Searching the sources in the most inaccessible region
on the Earth is an important event in the field of geography and has intrigued
explorers for centuries. At present, pinpointing the sources of the great rivers can still
arouse the interest of explorers around the world. As the Chinese saying goes, ‘‘When
one drinks water, one should think of the source’’. This Chinese proverb describes
the explorers’ motivations for discovering the source of the great rivers. Most of the
sources of the great rivers have been determined by different explorers according to
various criteria in the past. In our investigations, the source of the river is defined as
the spring corresponding to the longest branch in the drainage basin from which
water runs all year round. It is believed that this definition of the geographical source
is reasonable because the length of the river is more stable than the amount of water
flow, the latter with annual, seasonal and even daily change. Furthermore, the length
of one river defined as the length from the mouth at the sea to the spring farthest
from the sea tallies with the human beings’ convention.
The common data sources for measuring the lengths of the rivers are the
topographic maps with adequate scale. However, the large-scale topographic maps
are classified information to many countries and are not available for purchase from
market sources. In addition, for some regions of the rivers’ traversed, the large scale
topographic maps are not readily available although the small- or medium-scale
maps can be obtained from atlases in different languages. It is well-known that
the measured length of a river depends on the scale of the map on which the
measurement is based on; in general, due to the fractal quality of a river, the smaller
the scale, the shorter the resulting length measurement. This is because some details
of the river’s channels are generalised according to various mapping specifications.
This is the reason for large variation in the lengths of the principal rivers in various
literatures.
In addition, the length measuring techniques also influence the accuracy of
measured length of the rivers. Many decades ago, geographers and cartographers
measured the lengths of the rivers on the topographic maps with special metric scales
that could determine the length of curves, or using digitising tablets after the
International Journal of Digital Earth 81
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appearance of computers. The geographers and cartographers obtained more precise
lengths with computer and digitising tablets than with the use of metric scales.
However, the accuracy of the length by both methods is inferior compared with the
geographical information system (GIS) and/or remote sensing software that have
been widely used by modern geoscientists. Nevertheless, most of the data of the
principal rivers still prevail in encyclopedias, textbooks, magazines and atlases
although computers have appeared.
Based on the maps with inadequate scale and/or incomplete data sources,
inaccurate length measuring techniques and controversial starting points, it is not
surprising that people could not get reliable and accurate lengths for the principal
rivers of the world.
Methodology
Remote sensing imagery is capable of covering large areas with quantitative
observational parameters such as spectral radiance (Rencz 1998, Sabins 1996,
Schowengerdt 1997, Wang 1990). It is therefore a potentially rich data source for
locating the sources and calculating the length of the rivers. Governments and
commercial agencies of many countries support a series of satellites for long-term
global observations of the land surface, biosphere, solid Earth, atmosphere and
oceans. Although there are many remote sensing satellite series in operations, such as
IKONOS, QuickBird, SPOT, ERS, RADARSAT, IRS, CBERS, LANDSAT and
others, not all is suitable for measuring the length of rivers on the Earth. The images
are selected on the basis of converges, resolution, availability and cost. Among all the
remote sensing satellites, Landsat series satellite data are the only record of global
land-surface conditions at the scale of tenths of meters over the last 30 years. Data at
these spatial resolutions can provide acceptable accuracy in measuring the rivers and
are also available in the market. In this paper, the Landsat TM and ETMimage
are chosen as the data source for measuring the length of the principal rivers of the
world.
Satellite image rectification was made for all images used in this study. For
measuring the exact lengths of the principal rivers of the world, it is necessary to
choose one coordinate and projection system that is suitable for high-accuracy
application. NASA has sponsored the creation of an orthorectified and geodetically
accurate global data set of Landsat MSS, TM and ETMto support a variety of
scientific studies and educational purpose (Tucker 2004). These images are precision
orthorectified Landsat scenes delivered in the standard Landsat individual scene
coverage (approximately 180 km 180 km) and are available for the whole globe in
either the two epochs of circa 2000 or earlier base-line coverage of circa 1990. In this
project, orthorectified Landsat ETMscenes of circa 2000 are selected as the main
data source for measuring the length of the rivers. Precision orthorectified Landsat
ETMscenes were acquired from 1999 to 2002 with a spatial pixel resolution of
14.25, 28.5, and 57.0 meters for the panchromatic, reflective and thermal bands
respectively. Nearest neighbour resampling method was used in the orthorectifica-
tion. These data sets are comprised of all nine Landsat ETMspectral bands and
are in a UTM (Universal Transverse Mercator) map projection and WGS-84
coordinate system with a geodetic accuracy of better than 50 meters RMSE (Root
Means Square Error). For some regions that ETMimages are not available, the
82 S. Liu et al.
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orthorectified Landsat TM images acquired in circa 1990 are used. Landsat ETM
and TM bands are generally made into colour images for the interpretation purpose.
In principle, any three of the visible and reflected IR bands may be combined in blue,
green and red channels to produce a colour image. Band assignments are often
expressed in R, G and B order. For example, the assignment 4, 2, 1 means that band
4 was assigned to red, band 2 to green and band one to blue. There are over one
hundred possible colour combinations, which is an excessive number for practical
use. Theory and experience show that a small number of colour combinations are
suitable for most applications. The optimum band combination is determined by
terrain, climate and nature of the interpretation projects. In this project, the water
has the spectral characteristics significantly different from the other objects of the
Earth surfaces and is very easily recognised by the interpreters. The band assignment
is 5 (R), 4 (G), 3 (B) for all the scenes of the Landsat scenes.
The length was measured along the central line of the river’s mainstream, from its
geographical source to the mouth. Prior to or during measurement, the channels can
be recognised from images by processing the satellite images, e.g. contrast
enhancement, intensity, hue and saturation transformation, filtering of random
noise, atmospheric correction and others. Based on the orthorectified satellite images
mentioned above, the measured length of river with accuracy between 3:1000 and
5:1000 of the length can be achieved.
To verify if the springs with water run year-around, late autumn is the ideal
season for field explorations to the source region especially for the rivers with sources
far away from the equator. In winter, the water is frozen or the channels are covered
with snow. In spring the snow and ice is melting. Summer is rainy and the channels in
river source region will be filled with water. In late autumn, the rainy season passed
and winter is not coming. If water is flowing in the creeks in late autumn, we are sure
the springs with water run year-around. We have investigated the source of Mekong
in 1999 and 2002, Yangtze in 2000, Ob-Irtysh in 2003, Yellow, Amur, Yenisey and
Mississippi-Missouri in 2004 and Amazon, Nile and Congo in 2005. The distribution
of the sources of the investigated rivers on the global has been shown in Figure 1.
Figure 1. Global distribution of the sources of the principal rivers.
International Journal of Digital Earth 83
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Table 1. The lengths, geographic sources and the outflow of the top 10 longest rivers of the
world.
River Geographic position
of the source
Outflow Length (km)
Nile Long. 29821?30ƒE Mediterranean
Sea
7088
Lat. 2819?35ƒS
Elev. 2539 m
Nyungwe National Park,
Rwanda
Amazon Long. 71841?36ƒW Atlantic Ocean 6575
Lat. 15830?13ƒ
Elev. 5189 m
Mt. Nevado Mismi,
Peru
Yangtze (Changjiang) Long. 94835?54ƒE Pacific Ocean 6236
Lat. 32843?54ƒN
Elev. 5042 m
Mt. Tangula, Qinghai, China
Mississippi-Missouri Long. 111832?54ƒW Gulf of Mexico 6084
Lat. 44832?18ƒN
Elev. 2692 m
Hell Roaring Creek, Idaho USA
Yenisy Long. 97858?25ƒE Arctic Ocean 5816
Lat. 47854?38ƒN
Elev. 2711 m
West of Mongolia
Yellow (Huanghe) Long. 96820?23ƒE Gulf of Bohai 5778
Lat. 34829?37ƒN
Elev. 4852 m
Lalangqing Qu, Qinghai, China
Ob-Irtysh Long. 89858?17ƒE Gulf of Ob 5525
Lat. 47852?32ƒN
Elev. 2916 m
Mt. Mangdaiqia,
Xinjiang, China
Amur (Heilongjiang) Long. 109810?30ƒE Tatar Strait 5498
Lat. 48847?07ƒN
Elev. 2016 m
East of Mongolia
Congo (Zaire) Long. 31807?58ƒE Atlantic Ocean 5118
Lat. 9822?04ƒS
Elev. 1580 m
East of Zambia
Mekong
(Lancangjiang)
Long. 94840?52ƒE South China Sea 4909
Lat. 33845?48ƒN
Elev. 5200 m
Mt. Jifu, Qinghai, China
84 S. Liu et al.
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By the interpretation of the satellite images with adequate resolutions, the longest
branch in drainage basin can be identified in sources regions. One river may have
several potential sources. The objective of field investigation is to visit all the
potential sources and find out the one fit all the criteria for the geographic source.
The precise positions of the geographical sources were checked with GPS (global
positioning system) in field explorations. Hand-held GPS provides the position of
the geographic source with an accuracy of 10 to 20 m. The geographic positions of
the sources of the principal rivers with their calculated lengths are listed in Table 1.
Results and conclusions
In 1999, we have the first attempt to measure the lengths of the principal rivers of the
world. Up to now, we have completed the length measuring and sources’ region
explorations for 10 rivers with lengths over or close to 5000 km. The calculated
lengths of the top 10 rivers are the Nile 7088 km (4405 miles), Amazon 6575 km
(4086 miles), Yangtze 6236 km (3876 miles), Mississippi 6084 km (3781 miles),
Yenisey 5816 km (3615 miles), Yellow 5778 km (3591 miles), Ob 5525 km
(3434 miles), Amur 5498 km (3417 miles), Congo 5118 km (3181 miles) and Mekong
4909 km (3051 miles). The lengths with the geographic positions of their sources are
listed in Table I. The distribution of the geographic sources of the great rivers on the
Earth can be found in Figure 1.
In the next stage, some rivers in the world which play an important economic,
social, natural and cultural roles in the lives of more people will also be considered.
We expect to report the new measuring results of those rivers in the near future.
Acknowledgements
The authors would like to thank the following people: Professor Guo Huadong, Professor
Chen Shupeng, Professor Huang Binwei, Professor Wang Zhizhuo, Professor Li Deren,
Professor Lin Zongjian, Professor Li Jiancheng, Dr. Wu Xiaoliang, Professor Qin Dahe,
Professor Liu Xiaohan, Professor Li Xiaowen, Professor Tong Qingxi, Professor Niu Zheng,
Mr Guo Shan, Professor Wu Yirong, Professor Xiang Maosheng, Professor Li Rongxing,
Professor Di Kaichang, Mr. Xiawu Duojie, Mr Zheng Ming, Mr Ye Yan and Mr Fang Zhimin
for their generosity assistances and encouragements. This work was jointly supported by China
High-Tech Research and Development Project (863 Project), the Innovation Project of
Chinese Academy of Sciences, the Special Funds of Director General of Institute of Remote
Sensing Applications, Chinese Academy of Sciences, the Funds of the State Key Laboratory of
Remote Sensing Sciences of China and the Funds of the State Key Laboratory of Information
Engineering in Surveying, Mapping and Remote Sensing of China and Earth & Space Awards
of the Earth and Space Foundation.
Notes on contributors
Shaochuang Liu received a BS degree of Geodesy in 1985 and MS degree and PhD of
Photogrammetry and Remote Sensing in 1991 and 1997 from Wuhan Technical University of
Surveying and Mapping, China. He is a professor of Institute of Remote Sensing Applications,
Chinese Academy of Sciences. His research interests include airborne integrated mapping
system, lunar rover localisation, navigation and mapping technology and remote sensing of the
Earth’s polar region.
International Journal of Digital Earth 85
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Pingli Lu received her MS degree of Remote Sensing and GIS from China University of
Geosciences in 2006. She is an engineer of the China Association for Science and Technology.
Her research interests include image processing and spatial analysis.
Donghui Liu got a MS degree in Geography from Beijing University in 1997. He is an assistant
professor of Institute of Remote Sensing Applications, Chinese Academy of Sciences. His
research interests include images processing and GIS.
Peidong Jin is a principal research scientist of China Aero-Geophysical Survey & Remote
Sensing Centre for Land and Resources. He got his B.S degree from Changchun University of
Science and Technology in 1985. He is specialising in the image processing and GIS.
Wen Wang received his PhD in Cartography and Geographical Information System from
Institute of Remote Sensing Applications, Chinese Academy of Sciences in 1997. He is an
associate professor of the School of Environment and Nature Resources, Renmin University of
China. His research interests include geostatistics and remote sensing for agriculture.
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