International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
be detected and extracted automatically with the algorithm of
feature variance. An obvious shortcoming of this scheme is that
the missed change spots should be more than those detected
with scheme one. So. DGPS will be used on the fields to survey
the missed change data. The advantage of this scheme is that
change information can be extracted. by computer
automatically.
SchemeJ-Having Current Middle Resolution Images and
History High Resolution Images: The order of rectifying
these two kinds of images is the same with that of scheme 3.
Fhe two images will be merged together. Change information
will be detected automatically with the method of feature
variance. But the shortcoming is that the extracted data can not
satisfy with the accuracy need of scale 1:10000 land use maps.
Because current year images have lower resolution. DGPS
technology will be used on the fields to obtain the spots border
points” coordinate with better precision.
SchemeS-Having Current High Resolution Images Only:
Land use maps will be gathered as history reference materials
in this scheme. In order to improve matching precision between
land use maps and images. maps must be rectified firstly and
images will be rectified referencing to these maps. Change area
will be extracted by overlaying these two kinds of data together.
With this scheme, the problem is that change information is
extracted not so completely. DGPS can make up this
shortcoming. The most advantage of this scheme is
consume-saving.
2.2 Investigation on the Fields with GPS
Although most of land use change information have been
detected with GIS and RS technology. but there is still some
information which has not been identified or their precision can
not reach the accuracy demand. The other problem is that it is
difficult to make certain about each land use class right or not
even assisted by other reference materials in. doors. So.
surveying on the fields with GPS is a very necessary work.
Generally. tasks of land use investigation on the fields are to
check and collect information about cach spot’s attributes
which include whether the building is new or not, which
administrative attachment it belongs to. and the reason about
infield land change. and etc.
Land use change detected with RS and GIS can be defined into
two types: certain spots and uncertain spots. Both certain spots
and uncertain spots are defined into two kinds as well: one
comes from high resolution image and one comes from middle
resolution image respectively. Different surveying methods
aided by GPS will be sclected for different kinds of spots.
Those are navigation GPS and DGPS.
2.2.1 Investigation by Navigation GPS: Uncertain spots
detected from high resolution image have good geometric
accuracy enough to reach the precision need of mapping. But
the category identification precision is not so satisfied. Change
spots layer and images or land use maps are put into notebook
PC or PDA which connected with navigation GPS. GPS
provides current point position and directs people adjust his
direction to the object place. This method can prevent people
from losing his way and make investigation job more efficient
and convenient.
2.2.2 Investigation by DGPS: Change spots which have lower
geometric precision or have not been extracted by RS images
must be surveyed with DGPS technology. Hard ware system
should include more than two sets of GPS. One is used as base
station. the others as moving reference stations. The
post-processing accuracy can be reach less than Im.
2.2.3 Coordinate System Exchange: ach country has its
suitable geodetic datum which includes ellipsoid. geodetic
coordinate system and altitude datum. Because coordinates
obtained by GPS are based on WGS 84 system. while our
country's coordinate system is 1954 Beijing or 1980 Xr'an. it is
necessary to exchange them from one to the other in order to
make images matched by the coordinates well.
2.3. Updating
Data collected from investigation on the fields are put into land
use GIS and overlayed with history LUDRG (Land Use Digital
Raster Graph) or land use database. Change area between these
two kinds of data is very clearly. Data is edited firstly. and then
the attributes will be modified by input new information into
the attribute tables. Some spot attribute of land use class before.
land use class current. and the area can be obtained
automatically by GIS software. The other change information
should be input manually. After all of the data have been
updated and checked. statistic works start up. With land use
GIS software, all of the statistic and collect reports can be
finished automatically.
3. EXPERIMENT
Jinnan county was selected as an experiment area. There are
several questions to be answered during this experiment. First
of all is how to select the most suitable images. the second one
is how to extract change information and how well its precision
can reach. the last one is how to use GPS surveving on the
fields.
3.] Experiment Area Introduction
Jinnan was selected as an experiment county representing north
of Chinese county. which lies in north of Tianjin city. Its major
physiognomy feature is plane. The main land use category is
infield and breed aquatics besides resident.
Figure 1. Jinnan county image (Spot 10m + TM 30m)
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