International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004
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Figure 2. Principle of STARIMAGER
1) Photo developing and scanning processes are unnecessary
and there is no image deformation such as damage or
deterioration on a film. Moreover, since the dynamic range
of an output image that is linearly proportional to the
luminance of the image plane is wide, it is possible to
recover easily even an image part that is in the shade of a
building, a cloud, and so on by increasing its image intensity,
which reduces the field survey after data acquisition.
LI
The ground control points (GCPs) for the orientation can be
unnecessary, or fewer due to the existence of a GPS/IMU. It
is therefore suitable for data acquisition at an emergency, on
the sea, and so on, where GCPs are difficult to get.
3) Due to a high-performance stabilizer, the original image is
not waving and has no blurs, thus it is suitable for the image
at an emergency and the burden for post-processing can be
reduced (Figure 3). And, the oblique photography that is
realized by slanting the stabilizer is effective in the texture
acquisition of building walls.
4
—
A helicopter allows low altitude and low speed operation,
leading to a high-resolution image. Since the influence of
field visibility and weather condition is small due to low
altitude, photography can be done more frequently than
conventional aerial photography. And, a helicopter can take
pictures of the linear-shaped objects efficiently by tracking
them over at a low speed.
5)
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With the TLS principle, an image has very little distortion
caused by the height of ground objects in the flight direction
(a line-perspective image as compared with a conventional
central perspective image), and suitable for less-distorted
ortho-image generation. One does not need mosaic
processing in the flight direction and it can get the spatial
data of linear-shaped objects seamlessly, such as roads,
railways, rivers, etc. Moreover, the system can get an image
that 15 redundant and with little loss due to the photography
in three different directions (three different times), leading
to fewer field survey burdens after the data acquisition.
Furthermore, a corresponding point searching in stereo
matching is easy due to the stereo angles being constant, and
measurement precision improves by triplet matching
(Shibasaki, R., 1987). The STARIMAGER sensor system
also allows multispectral data acquisition and allows
generating a multispectral image by integrating RGB three
line sensor images and an NIR image as an index which
shows vegetation and water in the soil more distinctively
than a color image only.
with stabilizer
without stabilizer
Figure 3. Stabilizer’s Effect
2.2 System configuration
The focal length of the TLS camera lens system is 60 mm, and
the stereo angles are 17, 23 and 40 degrees between forward
and nadir, nadir and backward, and forward and backward,
respectively (see Table 1 for the STARIMAGER SI-250
specifications). Each line sensor consists of 14,400 CCD pixels
with 5 um spacing, and acquires 500 line images in a second (2
msec acquisition interval). The image data is recorded in a
controlling and recording device that is installed in the
helicopter cabin. The GPS antenna acquires the camera position
signal at 5 Hz and the IMU acquires the camera attitude signal
at 500 Hz. The camera is calibrated in a laboratory as well as
through a self-calibration process in a test field (Chen, T., 2003).
The TLS sensor model and triangulation are described in
(Gruen, A., 2002).
configuration item | specification
TLS Camera | CCD Elements pixels/line 14.400
pixel pitch sum ed
Number of Sensors 10 (3 directions — with RGB - and NIR)
Intensity dynamic range ——— © obitsormore
Lens focal length 60 mm
Stereo angle : : ERES 17 23 40 etc.
ted
Number of capturing lines 125, 230. and 500 lines/sec
Stabilizer Angle resolution in attitude
Spatial stability
Maximum angle velocity 30 /sec
500 Hz
Data output (acceleration/attitude)
GPS Receiver | 2f kinematics »lanimetric accuracy 2 crn + 2 ppm
LP HEN oe ZH
{post processes! | height accuracy 3 cm +2 ppm
Data output SHz
recording speed
recording capacity
Recorder HDD recording
150 MB/sec or more
320 GB
Table 1. SI-250 Specifications
2.3 Applications
The features of the TLS data are stimulating more demand for
3-D seamless geographical information of linear-shaped man-
made objects and terrain with high resolution and efficiency.
Those objects include roads, bridges, railways, power cables,
pipelines, etc. for investigation before the construction of those,
maintenance and management after the construction, and base
data for a variety of GIS systems (Tsuno, K., 2002).
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