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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B1. Istanbul 2004
Photo 2. Overview of GEONET GPS receiving station
3.4 Along-Path GCP Using Automatic GPS Stations
Using the along-path GCP in Figure 8, there are only three
observations during the 46 day recurrent ALOS orbit because
the along-path GCP is only covered by three paths (RSP 67 —
69). That is not enough to evaluate above items, especially in
the initial calibration phase. Therefore, we examined the
automatic GPS receiving stations for use as GCPs.
In the Japan area, GSI maintains the GPS Earth Observation
Network (GEONET). This network was basically established
to monitor crustal deformation. Currently over 1,200 automatic
GPS receiving stations have been installed and are being
continuously monitored. The average distance between each
station is 10 km, so these stations can be used as GCPs for
addition, this data is available worldwide via the Internet.
Available real time data with image acquisition of PRISM after
launch of the ALOS will be distributed worldwide.
Photo 2 is an overview of the GEONET stations with a height
of about 5 m. Figure 9 depicts the locations of all GEONET
GPS stations in Japan. We tried to identify the 133 stations as
the test data using aerial photographs, although some could not
be clearly identified.
The red dots in Figure 9 indicate the locations of selected the
133 points, which are along ALOS paths i.e, RSP 67-69, 73-75,
and 82-84. From the results, 25% (33 points) could be
identified in aerial photographs, 6896 (91 points) were unclear,
and 7% (9 points) could not be identified. This result is
dependent on the scale of the utilized aerial photographs.
: PRISM. Their absolute accuracy is very high and stable. In
17
Figure 9. Locations of GEONET station and selected points
Figure 10. Example of the identified GEONET in aerial photo
Therefore, the success rate will be increased using high-scale
aerial photographs. Figure 10 is an example of a station
identified in a 1:4,000 scale aerial photograph.
3.5 Along-Path GCP to Evaluate Thermal Conditions
Figure 11 displays ALOS paths RSP 67 to 69, from north to
south latitudes around the East Asia and Oceania regions, and
the locations of the prepared GCPs. An along-path GCP must
be required for over 91 sec to evaluate the effects of variability
of thermal conditions, especially the thermal distortion of CCDs
that is a function of latitude. It would be convenient to use
identical orbits to reduce other factors. Therefore, we estab-
lished a GCP around southwest Australia.
Figure 12 indicates the GCP prepared using a DGPS in
southwest Australia with ALOS paths RSP 67 to 69. Three
GCP areas were established between the cities of Kalgoorlie
and Esperance. Each area was composed of only one line from
west to east with less than a 10 km step. These areas could not
be covered by nadir observation of RSP 67 because they were