Calibration Results of the Compact Infrared Camera (CIRC) Ground Test Model
(9mm)

1)

By Ryoko Nakamura , Haruyoshi Katayama1), Masataka Naitoh1), Masatomo Hadara1),
Masahiro Suganuma1) and Ryota Sato1)
(5mm)
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Japan Aerospace Exploration Agency, Tsukuba, Japan(12mm)

The compact infrared camera (CIRC) is a technology demonstration instrument equipped with an uncooled infrared
array detector (microbolometer). Eliminating the cooling system reduces the size, cost, and electrical power of the sensor.
The CIRC also achieves small size and light weight by employing athermal optics and shutter-less system. The main
mission of the CIRC is the technology demonstration of the wildfire detection. Wildfires are major and chronic disasters
affecting many countries in the Asia-Pacific region. The second purpose is the low-cost and early development of a thermal
infrared imager. The CIRC is designed based on a commercial infrared camera and is employing commercial-off-the-shelf(COTS) parts to reduce cost and time for development. The CIRC ground test model was made to establish a prelaunchcalibration method. The main calibration items are imaging quality (Modulation Transfer Function; MTF), and radiometricquality. We have measured MTFs in a vacuum environment. Nyquist MTF at center positions is from 0.1 to 0.3. We alsomeasured athermal characteristics in the temperature range from -10 to 50 degrees C. We confirmed the athermal
characteristics. In this paper, we show the current status of the CIRC development, and the calibration results of the CIRC
ground test model.
Key Words: remote sensing, thermal infrared imaging, wildfire, uncooled infrared detector

1.

Introduction

been contributing to cartography, regional observation,
disaster monitoring, and resource surveys, since its launch in2006. JAXA is conducting research and development
activities to improve wide and high-resolution observation
technologies developed for ALOS in order to further fulfill
social needs. These social needs include: 1) Disastermonitoring of damage areas, both in considerable detail, andwhen these areas may be large 2) Continuous updating of dataarchives related to national land and infrastructure information
3) Effective monitoring of cultivated areas 4) Global
monitoring of tropical rain forests to identify carbon sinks.
Alos-2 will be launched in 2013.
ALOS-2 succeeds the L-band Synthetic Aperture Radar(SAR) observation of ALOS PALSAR with enhanced
capabilities. Table 1 shows the baseline specifications of
ALOS-2. The mounting location of CIRC is shown in figure 1.
CIRC will take images of the target area during the SAR
pointing to the right at its off-nadir angle of 30 degrees.

Microbolometers are widely used in commercial andmilitary applications, such as night vision. Microbolometers
have the advantage of not requiring a cooling mechanism,
such as a mechanical cooler. Eliminating the detector coolingsystem reduces the size, cost, and electrical power of thesensor. Although the sensitivity of microbolometers is lower
than that of HgCdTe-based photonic infrared detectors, theadvantage of not requiring a cooling mechanism is suitable forsmall satellites or resource-limited sensor systems.
JAXA has researched the application of microbolometers for
Earth observation 1). In order to demonstrate the potential of
microbolometers to thermal infrared imaging from space, theCompact Infrared Camera (CIRC) is developed as atechnology demonstration payload of the Advanced Land
Observing Satellite-2 (ALOS-2), and CALorimetricElectron Telescope (CALET) which will be attached to theJapanese Experiment Module (JEM-EF) of the International
Space Station (ISS).
In this paper, we show the current development status of
CIRC. In §2, we briefly describe ALOS-2 and CALET. The
mission and the details of the CIRC are shown in §3 and §4,
respectively. In §5, we show the initial calibration results of
the CIRC ground test model that has been studied withlaboratory experiments to establish a prelaunch calibration
method. Discussion and Summary are shown in §6.
2. ALOS-2 and CALET
2.1 ALOS-2
ALOS-2 2) is a follow-on mission from ALOS, which has

Fig. 1 Schematic view of ALOS-2 and the mounting location of CIRC

1

CIRCs are carried on various satellites by taking advantagesof small size, light weight and low power consumption. The
other CIRC mission targets are volcanoes or heat island
phenomena in a city. The observations of these targets withthermal infrared imager will become a useful tool to monitor
volcanoes or to solve the heat island problem.

Table 1. Baseline specifications of ALOS-2

Parameter
Size
Mass
Bus power
Communication
Orbit

Specification
9.9m x 16.5m x 3.4m
< 2000 kg> 5200W< 800Mbps
628 km4.

2.2 CALETCALET 3) is an international program for the ISS that will
search for signatures of Dark Mater and provide the highest
energy direct measurements of the cosmic ray electron
spectrum in order to observe discrete sources of high energy
particle acceleration in our local region of the Galaxy. CALET
will address many of the outstanding questions including (1)the nature of the sources of high energy particles and photons,
through the high energy spectrum, (2) the details of particle
transportation in the Galaxy, and (3) signatures of dark matter,in either the high energy electrons or gamma ray spectrum. It
will also be capable of monitoring gamma ray transients andsolar modulation. CALET will be launched in 2013.
The baseline specifications of CALET are shown in table 2.
CIRC will be mounted on the bottom of CALET, shown infigure 2.

Baseline specifications of the CIRC

Baseline specifications of the CIRC are shown in Table 3. We
set the baseline specifications to meet requirements for thewildfire detection. The detector is a large format (640 × 480)
to obtain a wide field of view. The spatial resolution is an
important factor for the wildfire detection. The spatial
resolution is 200 m from the altitude of 600 km (ALOS-2),
and 130 m from the altitude of 400 km (CALET), respectively.
Eliminating the cooling system reduces the size (110mm x
180mm x 230mm) and electrical power (<20 W).
Table 3.

Table. 2 baseline specifications of CALET

Parameter
Mass
Bus power
Communication
Orbit

Baseline specifications of the CIRC

Parameter
Size
Mass
Detector
Wavelength
Number of pixels
Special resolution

Specification< 500 kg
< 500W< 300kbps
407 km (nominal)

Field of View
Exposure
Dynamic range
NEdT
Power

5.

Specification
110mm x 180mm x 230mm~3kg
Uncooled infrared detector
8 - 12 μm
640 × 480
< 200 m @ 600 km (ALOS-2)< 130m @ 400km (CALET)(< 0.33 mrad)
12°× 9°33 ms
180 K - 400 K
0.2 K@300 K< 20W

Calibration of the CIRC ground test model

In this section, we present the calibration results of the
CIRC ground test model. Figure 3 shows the picture of the
CIRC ground test model.

Fig. 2 Schematic view of CALET and the mounting location of CIRC

3.

Mission of the CIRC

The main mission of CIRC is a technology demonstrationof a wildfire detection using the microbolometer. Wildfires are
one of the major and chronic disasters affecting many
countries in Asia-Pacific region, and some suggestions are that
this will get worse with global warming and climate change.
In Sentinel Asia project to share the disaster information innear real-time across the Asia-Pacific region, the wildfire
detection is chosen as one of the important activities. It is
possible to increase observational frequency of wildfires if

200 mmFig. 3 Picture of the CIRC ground test model

In the laboratory experiment at JAXA Tsukuba Space center,
we measured the Modulation Transfer Function (MTF) of the2CIRC ground test model in a vacuum to evaluate the image
capture performance of the sensor system.
5.1 Measurement Setup
The schematic diagram and the configuration of theexperimental setup are shown in Fig. 4 and 5, respectively.

Fig. 4 Schematic diagram of the experimental setup

Fig. 6 (top) 4-bar target mounted on the collimator system. 1/6-, 1/4-, 1/2-,
1-nyquist frequency from the left. (bottom) image of the 4-bar target takenwith CIRC.

Fig. 5 Configuration of the experimental setup

CIRC is placed inside of the vacuum chamber in thelaboratory and surrounded by a shroud which controls theambient temperature of CIRC by using a heater and a cooler.
The infrared-ray is emitted by the black body (CI Systems
SR800) and passes through the 4-bar targets (shown in Fig.6)
mounted inside of the reflective collimator system (CISystems ILET-5-1.1). The intervals of the slits of the 4-bar
targets are equivalent to 1-, 1/2-, 1/4- and 1/6-nyquist
frequency. The collimated infrared-ray pass through agermanium window, which is mounted on to the side of thevacuum chamber and transmits the infrared-ray from outsideof the vacuum chamber, and is detected by CIRC.

Fig. 7 The positions of MTF measurement
Table 4. The environments of the measurement-10 degrees C

22 degrees C

40 degrees C

50 degrees C± 5 degrees
0 degree *

○

○

○

○

± 3.5 degrees
0 degree #

○

○

---

○

* CIRC is on the bottom panel of the shroud# CIRC is on the side panel of the shroud

5.2 Data
We have measured MTF under a vacuum environment. The
detector positions of measurements are at the center, ±5degrees in the Cross-Track (CT) direction, and ±3.5 degrees
in the Along-Track (AT) direction, shown in figure 7. In order
to measure the MTF at ±3.5 degrees, the CIRC is able to be
replaced to the side panel of the shroud, because only one
rotating stage is set in the vacuum chamber (see figure 4).
MTF for CT/ AT direction were measured by rotating the
4-bar target. The environments of measurement are shown intable 4. The temperatures of the shroud are set to -10 to 50
degrees C.

5.3 Measurement environment
The pressure in the vacuum chamber is ~ 10-5 Torr. We havemonitored the temperature of the CIRC and shroud withplatinum-resistant. The position of resisters are shown infigure 8
Figure 9 shows the temperatures during the experiment. In
the room temperature case, the temperature of CIRC increases
from 22 to 35 degrees C due to the heat from electricalcircuit . The temperature variation between each position is~ 5 degrees C. The temperature of channel 5, 6 and 8, which
are mounted on the lens and body of the CIRC, are higher than3

5.4. Procedure of measurement and analysis
The procedures of measurement are;
1. Obtain a dark image by covering the Ge window withaluminum cover.
2. Target images (1-, 1/2-, 1/4-, 1/6-nyquist frequency) aretaken.
One cycle of this procedure take about 7 minutes.
We analyzed the data with target and dark images. The flow
chart of the MTF analysis is shown in figure 10. Figure 11 isadditional figure to explain the analysis. First of all, we
subtract a dark image from a target image to correct an offset.
As a second step, 4-bar-target area of an image is chosen. We
sum digital number (DN) of each pixel along y-direction infigure 11 (top), and calculate standard deviation as shown infigure 11 (middle). The image is chosen with the area above
one third of maximum standard deviation. Next we integrate
DN of pixels along x-direction in figure 11 (top) in order toreduce random noise. We correct offset again to remove
remaining dark level, by using the target image with no 4-bar
area. Finally, we calculate MTF. A peak and a bottom of DN(Vmax, Vmin) are detected, shown in figure 11 (bottom). MTF is
derived with Vmax and Vmin as shown below;
MTF = ( Vmax +Vmin) / (Vmax－Vmin) .
We can calculate 6 MTFs from 4-bar image, and derive theaverage (MTFaverage), the maximum (MTFmax), and theminimum (MTFmin) of 6 MTFs. The errors of the MTF aredefined as differences between MTFmax (MTFmin) and
MTFaverage.

Fig.8. Position of the platinum-resistant. (right) For the case that CIRC
is on the bottom panel of the shroud. (left) For the case that CIRC ison the side panel of the shroud.

that of others. Although the temperature variation is larger
than the room temperature case, same trend is seen in low andhigh temperature environment. In order to keep thetemperature, we turned off and on again in the hightemperature case.
CIRC have other own thermometers near the lens and thedetector. The difference between lens and channel5
temperature is less than 1 degrees C.

Fig. 10 Flow chart of the MTF analysis

5.5. Results
We have measured MTF for CT/AT direction at 5 detector
positions. Results are shown in figure 12. Color means
temperature difference; blue, black, magenta, and red
represent results -10, 22, 40, and 50 degrees C, respectively.
CT- and AT-direction MTF are shown in left and right panel.
Top panels show the results at the detector center. Solid anddash lines mean MTF with different configuration that CIRC
is on the bottom and side panel, respectively. MTF for

Fig. 9 Obtained temperatures of each position withplatinum-resistant. (top) In the room temperature. (middle) In
the low temperature. (bottom) In the high temperature.

4CT-direction has same trend with several temperature andconfigurations. Middle and bottom panels show the results at
the edge of the detector, ±5 degrees for CT and ±3.5
degrees for AT direction, respectively. Except for low
temperature case at -5 degrees position, CT-direction MTFs
are same within error. On the other hand, AT-direction MTFs
vary with different temperature and positions. Nyquist MTFs
of low temperature environments are lower than that of roomand high temperature case for CT/AT-direction and all
detector positions.
Figure 13 shows athermal characteristics at nyquist
frequency measurement. Difference in color means thedetector position; black, red, blue, magenta, and cyan
represent at the center, +5, -5, +3.5, and -3.5 degrees,
respectively. Top and bottom panels show the results at CT
and AT direction. CT direction MTF at the detector center and±5 degrees are constant regardless of temperatures. CT at ±3.5 degrees and AT direction MTF has gradient, lower in low
temperature environment.
6. Discussion and Conclusion
Results of MTF measurement are summarized as follows; MTF is lower at low temperature environment
 The variation of AT-direction MTF is large
Possible reason for small MTF at low temperature case is dueto the gap of focal length. Although an alignment of focal
length of CIRC ground test model was adjusted in atmosphere,
focal length changes due to the variation of reflective index in
the vacuum environment. We are planning to adjust focal
length of CIRC PFM for vacuum environment. We could not
find out the reason that the variation of AT-direction MTF. It
seems that misalignment of measurement setup is not a reason.
We need a future work for this problem.
We measured the MTF characteristic of CIRC, which is oneof the important image capture performance parameters of the
optical sensor systems, and confirmed the athermal
characteristics of the CIRC. We input the results todevelopment process of CIRC PFM. In a future experiment,
we will measure the radiometric performance of the CIRC
ground test model. Through these experiments, we establish aprelaunch calibration method for the CIRC PFM onboard
ALOS-2 and CALET.
.

Fig. 11 Additional figure to explain the MTF analysis.
(Top) Image of 4-bar target at the detector center.
(Middle) Standard deviation of integrated image for Y(AT) direction. We set the threshold (red line) andchoose the 4-bar target area. (Bottom) DN of 4-bar
target. We correct the offset (red line), and calculate
MTF with Vmax and Vmin shown in blue line.

5Fig. 12 Results of MTF measurement. In the room temperature (black), low temperature (blue) and high temperature (magenta or red) environment results
are shown. Left panels are CT-direction, and right panels are AT-direction MTF. (Top) Results at the detector center. Solid line shows under theconfiguration that CIRC is on the bottom panel. Dash line is corresponds to the result with CIRC on the side panel. (Middle) Results at ± 5 degrees
positions. Solid and dash line are correspond to the results at + 5 and -5 degrees, respectively. (Bottom) Results at ± 3.5degrees positions. Solid anddash line are correspond to the results at + 3.5 and -3.5 degrees, respectively.

6

References
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2)

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Fig. 13 Athermal characteristics at nyquist frequency. Difference incolor shows the detector position; center is in black (solid and dashlines are correspond to the CIRC installed conditions of bottom andside panel), +5 degrees is in red, -5 degrees is in blue, +3.5 degrees
is in cyan, and -3.5 degrees is in magenta, respectively. (Top)CT-direction. (Bottom) AT-direction.

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