The comprehensive inventory
and monitoring of forest and other renewable natural resources by means of
Remote Sensing data in the
'Three Norths' shelter forest region*
Xu Guanhua
The Research
Institute of Forest Resource Information Technique
The Chinese Academy
of Forestry
Introduction
The 'Three Norths'
shelter forest region is situated in the northern part of China, 'Three
Norths' is the abbreviation of the northwestern, northern and northeastern
part of China, with a total area of 4,069,000 square kilometers, covering
42.4% of land area of China. The 'Three North's' area is the birthplace of
the Chinese nation, with rich natural resources, and has experienced
prosperities several times in the history of mankind. The area is pregnant
with extremely great production potentials. In recent centuries, however,
because of vicissitude in natural conditions and destruction by human
activities, there has been extensive lack of the natural vegetation
coverage. The forest coverage (including brushwood) is only 3.8%. It is
the main forest-lacking and forestless area in China. The lack of
vegetation coverage has caused droughts, sand blown by the wind, soil
erosion and other natural calamities. The area of farmland and pastures
that suffered from wind and sand damages amounts to 6,700,000 ha., and the
desertized land has increased by 32,800,000 ha. In the past 30 years. Soil
erosion has been extremely serious in the middle and lower reaches of the
Yellow River, which causes the landform to be fragmented with crisscross
gullies and ravines. Of the 1,600,000,000 tons of sand poured each year
into the yellow Rover 80% derives from this region. The Yellow River bed
is elevated 10cm each year, and so it has become the river above the
ground. Natural calamities and destruction of ecological environment have
seriously hindered the economic development of the area, and it is known
as one of the backward regions of China..
In order to improve the
ecological environment and to promote the economic development, the
Chinese government began to establish shelter forest in this area in
1950s, and decided to construct the 'Three Norths' shelter forest system,
known as the Green Great Wall, in 1970s. The orientation is to rationalize
land utilization, to increase forest and pasture coverage, to develop
shelter forest, to construct livestock bases and to realize self
sufficiency in grain supply. The forest coverage is to be raised from 3.8%
to 9.5%. The proportion of animal husbandry in productive value of
agriculture is to be elevated from 16.9% to more than 30%. From the year
1978 till 1985, the investments made by the central and local governments
in the project have surpassed 460 million US dollars, and the afforested
area reported to the central government has amounted to 6 million ha. At
present, the economic managerial administration in urgent need of
evaluating the practical economic and ecological benefits resulted from
the huge investment, in the 'Three Norths' project, such as the actual
survival rate of afforestation, the rebuilt pasture area, the improvement
of soil erosion and desertification. At the same time, it also desire to
make clear the results of the economic policies and technical measures
adopted in recent years, so as to provide a reliable base for the drawing
up and completion of further construction plans of the 'Three Norths'
shelter forest system.
The Comprehensive Inventory and Monitoring
of Forest and Other Renewable Natural Resources by Means of Remote Sensing
Data in the 'Three Norths' Shelter Forest Region is one of the key
national projects for scientific development during the Seventh Five-year
Economic Plan ( 1986 - 1990). Its goal is to answer the above questions
put forward by the central economic administration, and to develop the
remote sensing techniques in the process, thus to achieve the practical
application of space-born remote sensing techniques.
Objective
and working procedures
The objective of the project is to
investigate the categories, distribution area and survival rate of the
shelter forest; the quantity, quality and distribution of pasture land; as
well as the types, distribution, quantity, quality and the current
utilization status of the land resources by employing space-born remote
sensing techniques in the 'Three Norths' region. On this basis, a resource
and environment information system is to be established.
To
realize the objective, the project includes the following contents:
- The serial thematic maps on the scale of 1:100,000 should be
compiled with country as mapping unit by space-born remote sensing
images. The serial thematic maps consist of forest distribution map,
forest dynamic distribution map, forest site map, grassland type map,
grassland classification map, land use map and land resources evaluation
map. On this basis, maps on the scale of 1:500,000 should be compiled
with province as mapping unit. These maps include forest distribution
map, forest site map, grassland resource map, land use map and land
resources evaluation map. At the same time, the above mentioned maps on
the scale of 1:1,500,000 should be also compiled for the whole 'Three
Nroths' region.
- Statistical analysis on renewable resources of major afforestation
counties should be submitted. The statistical data should be calculated
and obtained from thematic maps one the scale of 1: 100,000. The
emphasis of resources analysis is to scientifically evaluate the
suitability of afforestation and status of administration of various
districts through comparison and analysis of survival rates of
afforestation and grass-planting, and in the mean time, to deliver
analysed results about the ecological benefits of the shelter
forest.
- The resources and environment information and its dynamic monitoring
system are to be established for the whole 'Three Nroths, region as well
as for typical counties, for the realization of scientific management,
dynamic monitoring and predictive analysis of forest and other renewable
resources.
- Basic research and advanced research of remote sensing techniques
are to be exploited, which includes the researches of spectral
characteristics of objects, image processing, information system, expert
system, analysis model and computer-aided cartography,. Such work would
create conditions for setting remote sensing projects on a new level.
The project has been practiced according to the following steps:
- The first stage ( 1986). For the successful implementation of the
comprehensive remote sensing inventory in the whole 'Three Norths'
region, a typical experimental area was selected, so that the key
problems concerning technical schemes and technical regulations for the
project were studied and solved.
- The second stage ( 1987). The 'Three Norths' areas was divided into
6 category region according to their natural and economic conditions.
Within each category region, 1-3 typical counties were selected to carry
out remote sensing inventory experiments. The details of the technical
scheme and regulations were drawn up on the basis of the characteristics
of category region, thus to create conditions for the overall
implementation of comprehensive remote sensing inventory.
- The third stage ( 1988-1989). Field investigation and serial mapping
were to carry out in the whole 'Three Norths' region.
- The fourth stage (1990) . The serial mapping has been completed. The
resource and environment information system for the 'Three Norths'
region is being constructed.
More than 60 institutions took part
in the project including Chinese Academy of Forestry, 9 research institute
of Chinese Academy of Sinica, more than 20 colleges and universities,
Chinese Academy of Agriculture, Forest Planning and Design institute,
National Mapping Bureau, and local remote sensing research depths. The
number of scientists concerned exceeds 300. At present ,the whole project
has been basically completed, and will pass the state appraisal at the end
of this year.
The technical achievements made during the
project
- Breakthroughs have been Achieved in Both The Comprehensive
Evaluation Techniques of Remote Sensing Data and The Satellite Image
Processing Techniques.
In the first stage of the comprehensive
remote sensing inventory, Ping Quan county of Hebei province was
selected as the typical experimental area. In Ping Quan experiment,
Mulitple images of the same period were obtained from different space
platforms and from aerial platforms of different heights, covering an
area of 3,300 square kms. The images and photos obtained include Landsat
MSS and TM images, SPOT HRV images, images taken by China Territory
Satellite, as well as color 1R air photos on the scales of 1:130,000,
1:75,000 and 1:30,000. During the study, these images and photos were
respectively evaluated according to multiple quantitative and
qualitative factors, i.e. the geographic precision of the images, the
precision of area measurement, the actual area of interpretable smallest
objects, the visual interpretation results of boundary between different
categories, the proportion of correct interpretation of patches for
various categories, the area accuracy of patches for various categories,
the cost and usability of images and photos, etc. In the meantime, a
model was designed to make an integrated evaluation on the images and
photos, and an integrated index was used to quantitatively describe the
general effect of visual interpretation. Thus theoretical foundation was
laid down for the evaluation of application potentials of various remote
sensing images in the Landsat TM images as the backborn, with the
Chinese satellite images and color IR air photos on the scale of
1:130,000 as auxiliary data in partial area was optimal combination of
information source, both technically and economically, for the project.
The SPOT images also possess its own technical advantages, however its
was a pity that the problem to receive the SPOT data in China has not
been solved and the images were not widely used .
The project
were carried out overall researches on processing techniques of a new
generation of remote sensing images. According to the characteristics
and needs of remote sensing inventory of renewable resources, peculiar
information extraction techniques and the scheme about images scale,
images seasons and bands combinations were proposed. For example, a
method of superiority index factor was proposed for the evaluation of
color composition of radioed images, which could quantitatively
determine the optimal combination and thus avoid a host of experiments.
Such work laid a foundation for the image processing techniques to
transfer from optical processing to a stage of computer-optical one in
large area remote sensing inventory.
- New Developments have been Achieved in the Techniques of the
Comprehensive Remote Sensing Inventory and Serial Thematic Mapping.
In the comprehensive remote sensing inventory. The different
specialties could share the information sources and field work data thus
saving human and material resources .The mutual comparison and
coordination among the thematic , maps serial mapping have improved the
mapping quality obviously but the comprehensive inventory and serial
mapping is different from traditional technique .Especially the natural
conditions of the vast 'Three North's region are complicated and the
social and economic conditions are in great disparity. Therefore it is
really an important task for this research to draw up a unified
technical scheme to coordinate investigation contents classification
systems and mapping methods of various specialties to guarantee the
quality of the comprehensive remote sensing inventory and serial mapping
the technical scheme formulated on the basis of the results of Ping Quan
remote sensing Experiment by has brought about a important progress both
scientifically and practically.
- The classification system of the comprehensive remote sensing
inventory in the three North's region has been established.
The characteristics of the classification system are:
- to coordinate with existent thematic classification systems
china ;
- to present the characteristics of comprehensive remote sensing
inventory by using image features as the main classification factor.
- to emphasize consistency among thematic classification systems
the macroscopic controlling concepts of type classifications among
the thematic maps have been unified and then the contents of various
thematical classification systems have been coordinated thus to
avoid classification overlap.
- The rational scale of mapping and area measurements have been
determined.
The results of evaluation of aerospace remote
sensing images on the scale of 1:500,00 1:200,00 anfd1:100,000 show
that it is optimum to implement thematic mapping on the scale of
1:100,000 by using the generations of satellite images after computer
optical processing such images could fully satisfy the requirements of
the second level classification of various thematic mapping for
example the following categories could be distinguished forested land
shrub forest thin forest land cutover natural grassland man made
grassland irrigates farmland no irrigated farmland vegetable plot
orchard as well as railway high way river lake, flood land waste land
salinised land marshland sandy beach etc. In the mean time some
categories could be distinguished at the third level classification
eg. Species or group of species could be delineated from forecasted
land and rice land could be delineated from irrigated farmland etc.
Therefore, the area measurement and mapping for the whole 'Three
Norths' region have been basically completed by the images on the
images on the scale of 1:100,000, and a number of the maps has
submitted for publication.
- A new field was expended for mapping with remote sensing
It was the first time in China to realize the compiling of serial
thematic mapping on the scale of 1:100,000 at a large area for
renewable resources with satellite images in the project. They are of
originality and an important practical value.
The forest
dynamic distribution maps, compiled by relying on the superiority of
availability of multi-temporal satellite images, and through the
analysis and comparison, show forest changes from the 1970s to 1980s,
and thus provide a foundation for the evaluation of afforestation
results in the area.
The forest site map is a map showing the
position and classes of the land suitable to different species of
trees for afforestation. The forest site map was compiled with
satellite images as the major information source, and the site
condition areas were delineated according to landscape types. Within
site condition areas, The leading factors of site conditions were
first determined according to statistical analysis of the relationship
between site conditions and growth situation of forest trees, which
was acquired through field investigation, and then site condition
groups were delineated through interpretation of leading factors. Some
of the leading factors ( for example, the soil thickness) could not be
directly interpreted from remote sensing images, but they could be
indirectly interpreted through correlative analysis of remote sensing
information and knowledge of geography. The forest site map would play
an important role in carrying out the principle of planting trees in
the suitable places, and in drawing up to future afforestation
planning for the 'Three Norths' region.
The grassland
classification map is a map reflecting grassland conditions
quantitatively and qualitatively. In the compilation of the grassland
classification map, ecological types, living types and vegetation
coverage were interpreted, according to the differences in spectral
reflectance of grass types and by combining geographical analysis of
related regions. However, for the estimation of grass yield, besides
satellite images, appropriate yield data, measured by ground
investigation, should be applied, as well as precipitation data and
sample yield data of many years in fixed position. All these data
should undergo checking, correction and interbalance to finally obtain
the grass yield. The compiling of the grassland classification map was
also a new attempt in mapping by using space-born remote sensing data.
The land resources evaluation map, which focuses on biomass
production potentials of land, is used to make qualitative assessment
on land unit, to make clear the quantity, quality and distribution of
land resources, to determine the optimal direction of land use
according to its suitability, to plan measures for land controlling
and transformation in line with local conditions and in accordance
with types and intensity of restrictive factors of a land. The land
resources evaluation map was compiled based on the analysis of the
shape, colour, spatial structure and dynamic evolution pattern of land
units shown in satellite images. After such analyses , land
suitability types and the quality classes were identified, and
information of restrictive types were also abstracted. The land
resources evaluation map would play an important role in the planning
of an integrated land utilization program.
- The research on the ecological benefits of the 'Three Norths'
shelter forest system by means of remote sensing data.
The
ecological benefits of the 'Three Norths' shelter forest system are
centrally represented in the results of preventing soil erosion and
desertification. In the / Three Norths' region, the factors that
effect the intensity of soil erosion include gully density, land
cultivation degree, slope and length of water collecting area,
vegetative coverage etc. A mathematic model for the evaluation of soil
erosion was established on the basis of estimating these factors by
using remote sensing data. In the studies of the project, the
expending and Shrinking of desert were also monitored in some typical
areas of the 'Three Norths' region, through comparative analysis of
multi-temporal satellite images. And mathematical models were
established to analyze the relation between desert change and
vegetative cover. For the northwestern part of China, the map of land
desertification condition was also compiled. Up to data, the research
results in typical areas preliminarily show that the increase of
forest coverage played a positive role in preventing soil erosion and
land desertification. However, the last conclusion still needs the
verification of the results of long term remote sensing monitoring.
- The Establishment of the Resources and Environment Information
System
The purpose of establishing of the resources and
environment information system is to put the results of the project into
a data base and a spatial information system, and to renew these data
through image processing of remote sensing data. On this basis,
scientific management, integrated analysis and development prediction of
multiple data have been realized. Such work made the comprehensive
remote sensing inventory in the 'Three Norths, region break through the
frame of previous resource investigations, and put it on a completely
new level, The system was designed independently and all softwares of
the system have been developed by ourselves, which possesses the
following characteristics:
- Flexible in use and small in size:
The system is
installed on a micro-computer, equipped with a high resolution color
display, a digitizer, a plotter, a CCT tape driver and other
peripherals. Therefore it is small and flexible, easy to replant and
cost effective, which makes it of high competitive capability.
- With complete functions:
The system is composed of a
geographical information management subsystem, a remote sensing image
processing subsystem, and a statistical administration and analysis
subsystem of forest resources. The main function of the geographical
information management subsystem is similar to that of PC - ARC/INFO
system, while the remote sensing image processing subsystem possesses
the functions of general image processing system that fits in with
needs of the resources inventory. The statistical administration and
analysis subsystem of forest resources could realize the analysis and
prediction of forest resources. Thus the practical function modules of
the system could fully satisfy the requirements of resources
information in acquisition, processing and analysis.
- Rational in structure:
The system involves both the
raster and vector data structure, and could carry out systematic
administration of map data, thematic attribute data, spatial graphic
data and satellite image data. The system combines the advantages of
both raster and vector data structures, to save storage space and
ensure the accuracy and reliability of the input data. In the means
time, The system builds up the connection between the spatial data
administration and the relational database management system ORACLE,
thus expending the connection as well as the capability of system
inquiring operation. The system, integrating a geographical
information management subsystem and a remote sensing image processing
subsystem into a universal information system, realizes the dynamic
monitoring of the natural resources.
- Flexible in operation and manipulation:
- Multiple functioning: It has the functions of map windowing,
clipping, joining, overlapping, inquiring and drawing, and therefore
brings great flexibility to the user.
- The men-machine interactive processing of graphs brings about a
friendly interface to select the objects and forms of display and
regeneration by an intuitive way.
- The Chinese character display is realized with user interface on
the high resolution graphic display.
- The mutual conversion of raster and vector data structures is
realized, which brings about further adaptability.
- Easy to expend. The system provides double user interfaces of
both system application and system expansion. The user could utilize
function module directly or further explore system functions through
using the function base provided by the system, both for
accomplishing the tasks of application analysis and administration.
Thus it offers the user a possibility to exploit system potentials.
- Application analysis. At present, the system provides multiple
application functions under the two data structures, such as forest
dynamic analysis, multiple elements analysis, tendency analysis,
analysis on the development conditions of local
situation.
- The Application Research of Forward Position Techniques of Remote
Sensing were developed
The project has made new advances in
the forward position techniques of remote sensing application, which
include:
- The application of expert system in interpretation and analysis
of remote sensing images
The expert system is a computer system
to imitate the ability of human experts, and it is composed of two
basic parts: a knowledge base and a inference engine. It has the
ability to reduce conclusion from known information by applying logic
inference rules. It has the project, two rule based expert systems for
the interpretation of remote sensing images have been developed. One
of them was based on the Bayes method, adopting mixed of forward
reasoning and backward reasoning and the strategies of uncertainty
inference. Whereas the other was constructed with LISP language, based
on the method of integrating information, and proposed by Shafer. The
common goal of these two methods is to comprehensively analysis with
expert knowledge, the spectral data of images, and the topographic
map, as well as well as the data of original thematic maps, to raise
the interpretation accuracy. In the mean time, during the experiment,
an expert system for analysis of the dynamic change of forest
resources by LISP language has been also established, to determine the
area and position of the change of forest resources.
- The application of mathematical models in the analysis and
prediction of renewable natural resources.
In the experiment,
the research of the establishment of mathematical models has been
carried out. The related ones are the model for land resources
evaluation, the model for evaluation of site condition for
afforestation and for site quality evaluation, the model for
monitoring and prediction of changes of forest resources etc. For
example, the mathematical model for forest timber volume estimation by
remote sensing is based on a non-linear score model, in which the
matching of satellite remote sensing data with ground sample plots has
been realized, to estimate forest timber volume and to draw the
distribution map of forest timber volume. Practices showed that these
models were of important significance for the effective utilization of
the multi-layer data of the resources and environment information
system, and for the realization of qualification and automation of
resources analysis, prediction and administration.
- The application of computer graphics in the resources and
environment information system.
In the process of establishing
the resources and environment information system for Ping Quan county,
the application research on related fields of computer graphics
achieved development. The related papers published after the
experiment discussed on many aspects of the problem, such as
administrative system of spatial data, graphic data base, the
expression of graphic information and its processing algorithms, the
integrated analysis method of multi-layer data. All these have their
theoretical significance and practical value.
- The application of research of extra-small scale color IR
aerial photos in resources investigation.
Color IR aerial
photos of three scales have been taken In Ping Quan remote sensing
experiment, including the extra-small scale color IR aerial photos on
the scale of 1:130,000. In the experiment, the processing ,
enlargement, interpretation and measurement techniques have been
studied. The study indicates that, owing to its high spatial
resolution, spectral resolution and fairly low cost, the photos
matching with satellite images has broad application in the
investigation of forest and other resources, and is an information
source of bright prospect.. Conclusion
- The Satellite Remote Sensing Data Possess the Advantages of High
Speed and Low Cost in the Macroscopic Inventory and Monitoring of Forest
and Other Renewable Natural Resources on Large Area. Its Accuracy Could
also Satisfy the Requirement of Production, and thus They have a Great
Application Potential.
- At Present, Visual Interpretation is Still the Major Way to Use the
Satellite Images in the Macroscopic Inventory of Forest and Other
Renewable Resources at Large Area. However, the Image Processing Differs
from the Previous Methods Based on Optical Composition of Different
Bands, but Stresses the Computer Enhancement of Digital Images, for
Extracting Information about Multiple Renewable Resources, and for
Improving the Results of Visual interpretation.
- The Integration and Cooperation of Inventory of Various Natural
Resources May Help to Improve Mapping Quality, and to Raise Mapping, and
Thus the Inventory Cost Could be Reduced in a Wide Margin. This is the
Development Direction of Resources Inventory.
- The Integration of Remote Sensing Image Processing System, GIS, and
Resources Analysis and Prediction System Would Benefit the Realization
of Automation of Resources Management and Monitoring, and It is the
Direction of Remote Sensing Development.
References
- Xu Guanhua, Xu Jiian, The Study on Renewable Natural Resources by
Remote Sensing Data, China Science Press, 1988.
- Xu guanhua, Xu Jiian et., The Technical Scheme of Comprehensive
Remote Sensing inventory and Monitoring in the ' Three Norths' Shelter
Forest Region, China Forestry Press,
1987.
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* Xu Guanhua and Xu Jiyan are
jointly in charge of the project
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