Development of the Compact Infrared Camera(CIRC) for Earth Observation
Masataka Naitoh1, Haruyoshi Katayama1, Masatomo Harada1, Ryoko Nakamura1, Eri Kato1,
Yoshio Tange1, Ryota Sato1 , Koji Nakau2
1

Earth Observation Research Center, Japan Aerospace Exploration Agency, Japan.
2-1-1, Sengen, Tsukuba, Ibaraki, 305-8505, Japan.
2

Faculty, Graduate School and School of Engineering, Hokkaido University
Kita 13, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
naitoh.masataka@jaxa.jp

Abstract— The Compact Infrared Camera (CIRC) is an
instrument equipped with an uncooled infrared array detector(microbolometer). We adopted the microbolometer, because it
does not require a cooling system such as a mechanical cooler,and athermal optics, which does not require an active thermal
control of optics. This can reduce the size, cost, and electrical
power consumption of the sensor.
The main mission of the CIRC is to demonstrate thetechnology for detecting wildfire, which are major and chronic
disasters affecting many countries in the Asia-Pacific region. It is
possible to increase observational frequency of wildfires, if
CIRCs are carried on a various satellites by taking advantages ofsmall size and light weight.
We have developed two CIRCs. The first will be launched in
JFY 2013 onboard Advanced Land Observing Satellite-2 (ALOS2), and the second will be launched in JFY 2014 onboard
CALorimetric Electron Telescope (CALET) of the JapaneseExperiment Module (JEM) at the International Space
Station(ISS). We have finished the ground Calibration of the first
CIRC onboard ALOS-2. In this paper, we provide an overview of
the CIRC and its results of ground calibration.
Index Terms—CIRC, ALOS-2, CALET, microbolometer,
wildfire

I. INTRODUCTION
Microbolometers are widely used in commercial andmilitary applications. Their advantage is that they do not
require a cooling system, such as a mechanical cooler. Sensors
without a cooling system for a detector are small in size,
lightweight, and consume less power. Although the sensitivityof a microbolometer is lower than that of an HgCdTe-based
photonic infrared detectors, its advantage of not requiring a
cooling mechanism makes it suitable for small satellites or
sensor systems whose resources are limited.
For this reason, microbolometers begin to be applied forvarious space applications. In planetary missions, the Thermal
Emission Imaging System (THEMIS)1 onboard Mars Odyssey

spacecraft used a microbolometer focal plane array (FPA). The
Longwave IR camera (LIR) onboard Venus Climate Orbiter(PLANET-C)2, which was launched in 2010, also uses a
microbolometer array.
In earth observation missions, the Infrared Spectral
Imaging Radiometer (ISIR)3 experiment tests the potential of
microbolometer for applications to thermal infrared imaging.
The ISIR was flown as a hitchhiker experiment on the space
shuttle in 1997. Recent missions to measure the atmospherevertical profiles like CALIPSO4 and EarthCARE5 also use amicrobolometer as an imaging infrared instrument. In 2011,
NIRST6 was launched onboard Aquarius/SAC-D. NIRST is an
infrared radiometer based on uncooled microbolometer
detectors. JAXA began a research for application of
microbolometer to earth observation since 2000. The WideAngle Multi-band Sensor – Thermal Infrared (WAMS-TIR)7,
aboard the station-keeping test airship (SPF-II) for the
stratospheric platform project, is a thermal infrared multi-band
radiometer using a microbolometer FPA.
We have developed the Compact Infrared Camera (CIRC) 8
as a technology demonstration payload for thermal infrared
imaging from space using a microbolometer. The main missionof the CIRC is to detect wildfires, which are a major andchronic disaster that affects many countries, especially those in
the Asia-Pacific region; therefore, their early detection isimportant. An effective means of early detection is to increase
their observation frequency. Our aim is to realize frequent
observations by loading CIRCs in as many satellites as possible
by taking advantage of there small size, low weight, and low
power consumption. Other mission targets of the CIRC are
volcanoes or heat island phenomena in a city. The CIRC will
be carried as a technology demonstration payload of theAdvanced Land Observing Satellite-2 (ALOS-2)11, andCALorimetric Electron Telescope (CALET)12, which will be
attached to the Japanese Experiment Module (JEM-EF) at theInternational Space Station (ISS).
In this paper, we present the verification results of theathermal characteristics and the calibration of the shutter-lesssystem with the CIRC Proto Flight Model (PFM). The mission
and details of the CIRC are described in section 2 and section 3,
respectively. In section 4 and section 5, the measurements andthe initial calibration results of the CIRC PFM are presented. In
section 6, the results of airborne observations is reported, andin section 7, the summary is provided.
II. MISSION OF THE CIRC
The main mission of CIRC is to demonstrate thetechnology for detecting wildfires using a microbolometer. As
mentioned earlier, wildfires are disasters that affects many
countries in the Asia-Pacific region, and there are suggestions
that this situation will get worse with global warming andclimate change. In the Sentinel Asia project, which will sharedisaster information in almost real time across the Asia-Pacificregion, wildfire detection has been chosen as one of theimportant activities to be monitored. The other objectives of
CIRC mission are to monitor volcanoes and heat island
phenomena in a city. Observing these with a thermal infrared
imager will be useful in monitoring volcanoes and solving theheat island problem.
The CIRC has the characteristics of athermal optical andshutter-less systems. The athermal optical system of the CIRC
was designed by combining two infrared materials; germanium
and chalcogenide glass. As the temperature does not have to becontrolled using a heater, we realized a CIRC with its small
size, low weight, and low power consumption. Moreover, theCIRC design was based on a commercial infrared camera, andit employs commercial-off-the-shelf (COTS) parts to reduce
cost and time for development.
It is possible to increase the observational frequency ofwildfires if CIRCs are carried on various satellites by taking
advantage of its small size, low weight, and low power
consumption. Two CIRCs will be launched, one in JFY 2013
and the other in JFY 2014. The first one will be carried on
Advanced Land Observing Satellite-2 (ALOS-2)11 in JFY 2013,
and the second will be in JFY 2014 onboard CALorimetricElectron Telescope (CALET)12 of the Japanese Experiment
Module (JEM) at ISS.
The orbits of ALOS-2 and ISS are shown in Fig. 1. The
green lines represent the ALOS-2 orbit; this is synchronous
sub-recurrent orbit at an altitude of 628km. In contrast, thewhite lines represent the ISS orbit. It has an orbital inclinationof 52.8 degree; it is located at an altitude of about 400km.

The schematic views of ALOS-2 and ISS/CALET equippedwith CIRC are shown in Fig.2 and Fig3. ALOS-2 is a followup mission to ALOS, which has been contributing tocartography, regional observation, disaster monitoring, andresource surveys since its launch in 2006. ALOS-2 has a
Phased Array L-band synthetic aperture radar (SAR) , which iscalled PALSAR-2. CALET is an international program of the
ISS that will search for signatures of dark matter and provide
direct measurements of the highest energy of the cosmic ray
electron spectrum to observe discrete sources of high-energy
particle acceleration in our local region of the galaxy.

CIRC

Field of View
(9ﾟ×12 ﾟ)Off-nadir Angleof 30ﾟ

Fig. 2. Schematic view of ALOS-2

Fig. 3. Schematic views of ISS (top) and CALET (bottom)
Fig. 1. Orbits of ALOS-2 and ISS

III. DESIGN OF THE CIRC
The baseline specifications of the CIRC8,9,10 are listed inTable 1. We set the baseline specifications to meet therequirements for wildfire detection. The detector has a large
format (640 × 480 pixels) to capture a wide field of view.
Spatial resolution is an important factor for wildfire detection;
it is 200 m from an altitude of 600 km (ALOS-2) and 130 m
from an altitude of 400 km (CALET). Eliminating the coolingsystem reduces the size (110 mm × 180 mm × 230 mm) andthe consumption power (<20 W) of the CIRC.
The CIRC PFM onboard ALOS-2 is shown in Fig.4. The
CIRC is based on a commercial infrared camera developed by
Mitsubishi Electric Corporation (MELCO). We modified the
hardware design so that it can be applicable for a space
application. CIRCs have key technologies, i.e., microbolometer,
athermal optics, and shutter-less system, for achieving small
size, low weight, and low power consumption. These aredescribed in the subsequent paragraphs.

Fig. 4. CIRC PFM onboard ALOS-2

TABLE I. SPECIFICATIONS OF CIRC
ParameterSize

110 mm × 180 mm × 230 mm

Specifications

Mass

3 kg

Detector

Uncooled infrared detector

Wavelength8-12 m

Number of
pixelsSpatialresolution
Field of view

640 × 480
<200 m @600 km (ALOS-2)<130 m @400 km (CALET)
12° × 9°Exposure

33 ms

Dynamic range

180-400 K

NEDT

0.2 K @300 K

A. Microbolometer
We adopted microbolometers as an infrared (IR) focal
plane array (FPA) of the CIRC. Microbolometers are based on
the principle of detecting infrared energy as minute changes of
the IR absorber temperature when an infrared enter it.
Their advantage is that they do not require a cooling system,
such as a mechanical cooler. Sensors without a detector coolingsystem can be made to have a small size, low weight, andconsuming less power.
The CIRCs have a 640 × 480 pixel silicon-on-insulator(SOI) diode uncooled IR FPA developed by MELCO. Its pixel
size is 25μm square. The SOI diode uncooled IR FPA uses asingle-crystal silicon pn-junction diode as a temperature sensor.
The single-crystal sensor based on silicon large-scale
integration (LSI) technology gives it a low-noise characteristic.
The noise equivalent differential temperature (NEDT) is 40mK
with f/1 optics. Drive and readout circuits are almost the sameas those of the commercial IR camera. For a space application,
we performed a radiation damage test, and a screening ofcommercial devices.
B. Athermal Optics
The optics of the CIRC is an f/1.2 refractive infrared optics.
The focal length of the optics is 78mm. The temperature of the
CIRC changes on orbit. The temperature change of the optics
causes a defocus because refractive indices of lens materials
are highly dependent on temperature. In order to compensate
for this defocus, we need to employ a focus mechanism or aheater to maintain a constant optics temperature. However,such mechanisms increase sensor resources. An athermal
optics can compensate for the defocus due to the temperaturechange without requiring such mechanisms.
Fig. 5 shows the optical design of the CIRC. The athermal
optics of the CIRC compensates for the defocus by using a
combination of different lens materials and diffractive lenses.
The optics of the CIRC uses a germanium and a chalcogenide
glasses (GASIR®1) and is designed in such a way that its
modulation transfer function (MTF) changes only slightly
when the ambient temperature changes from -15ºC to 50ºC.

enabled it to capture the four-bar target images at any positions
on the image of the CIRC.

Fig. 5. Optical design of the CIRC

C. Shutterless System
We eliminated the mechanical shutter from the CIRC. This
enables us to downsize the CIRC. A mechanical shutter ismore commonly used as a calibration source. Therefore, we
devised a way to achieve temperature calibration and straylight correction from the inside the CIRC. We obtained imagesof various temperature blackbody with different CIRC
temperatures in order to perform stray-light correction bytemperature of the CIRC. The details are show in section 4.

Fig. 6. Schematic view of MTF measurement

真空チャンバVacuumchamber
Ge window
Ge窓
Collimatedコリメート赤外光
infrared-ray

IV. CALIBRATION INSTRUMENTS OF THE CIRC PFM
We carried out the ground calibration test9,10 of the first
CIRC onboard ALOS-2. Here, we report the result of thecalibration test.
We measured the modulation transfer function (MTF) in
order to evaluate the optical performance of CIRC at various
operating temperatures of the CIRC. Further, we evaluated thenoise equivalent differential temperature (NEDT) and flat
pattern noise (FPN) in radiometric tests.
We carried out ground calibration tests of CIRC at thefacility in Tsukuba Space Center in JAXA.
A. Esperimental setup for MTF meaurements
The schematic view and experimental setup for MTF
measurement are shown in Figs. 6 and 7, respectively. The
CIRC was installed in a vacuum chamber and enclosed a
shroud to control its ambient temperature with a heater andcooler. During the experiment, the pressure in the vacuum
chamber was ~10-5 Torr. Infrared rays were emitted by ablackbody (CI Systems SR800) and passed through the fourbar targets (as shown in Fig. 8) installed in the reflective
collimator system (CI Systems ILET-5-1.1). The collimatedinfrared rays passed through a germanium window on the sideof the vacuum chamber. The CIRC was able to capture imagesof the four-bar target. A image of four-bar target captured by
CIRC is shown in Fig.9. And a rotating stage under the CIRC

黒体 Blackbody(CISystems
Systems SR800)(CI
SR800)

コリメータ
Collimator

Fig. 7. Experimental setup of MTF measurement

1/6 Nyquist
1/4 Nyquist
1/2 Nyquist
1 Nyquist
Fig. 8. Four-bar targets mounted on the collimator system

B. Radiometric calibration tests
Fig. 11 shows the schematic view of the experimental setup
for radiometric calibration tests. It was the same as that for the
MTF experiments except for the blackbody was placed in frontof the CIRC.
shroudblackbodyFig. 9. Image of four-bar target as captured by CIRC for evaluation MTF
Fig. 11. Schematic view of experimental setup for radiometric measurements

We evaluated the MTF of the CIRC from images of the
four-bar target. We measured the MTF in a vacuum at a
Nyquist frequency, which is 20 line pairs par mm in the case of
the CIRC, at the whole image of the CIRC, and we measured
the MTF of the CIRC at temperatures ranging from -15°C to+50 °C under changing ambient temperature of the CIRC.
Ambient temperature was controlled by controlling thetemperature of the shroud enclosing the CIRC. This ambient
temperature range is the operational temperature range of the
CIRC. We monitored the temperature of the lens barrel and thedetector package of the CIRC.
Fig. 10 shows the measurement points of the four-bar target
for MTF were at the center, ±5° in the cross-track (CT)direction, and ±3.5° in the along-track (AT) direction. The
MTF in the CT/AT directions was measured by rotating thefour-bar target.
(0, 0)
No.1

No.2+3.5° No.3

No.4

No.5

No.6

-5°

No.7

0°

No.8

+5° Cross
Track
(CT)

-3.5° No.9

Along Track(AT)(639, 479)

Fig. 10. Measurement points of MTF on image acquired by CIRC

We measured the radiometric performance of the CIRC in a
vacuum environment and captured images of the blackbody attemperatures ranging from -10°C to +50 °C under changing
ambient temperature of the CIRC, which ranged from -15°C to
50°C. We performed sensitivity and stray-light corrections
from the images of various temperature blackbody at different
ambient temperature. It is important to correct stray-light frominside the CIRC because it does not have a mechanical shutter.

V. CALIBRATION RESULTS OF THE CIRC PFM
A. Results of MTF measurements
The measurement results of the MTF at Nyquist frequency
are show in Fig. 12. Each line in the figure represents amesurement point in Fig.10.
The MTF in the CT direction (Fig. 12. top) was constantregardless of the environmental temperatures. In contrast, MTF
in the AT direction was slightly lower in low-temperatureenvironments. However, this results is no problem to capture
clear images in the entire range of the operating temperaturesof the CIRC. This confirm the athermal optical performance of
the CIRC.

Next, we performed background correction along withstray-light correction and sensitivity correction. Fig. 13 showsa blackbody image before background correction. And Fig.14.
shows the image of the same blackbody after backgroundcorrection. Background correction10 is performed in thefollowing steps.
1) Subtract the electrical background by using dummy
pixels, which has no sensitivity to incident infrared rays. CIRC
has 20 × 480 dummy pixels besides 640 × 480 effective pixels.
The left twenty pixels in Fig.13 are dummy pixels.
2) Perform stray-light correction for each pixel by using
the same temperature blackbody data at different ambient
temperatures.
3) Perform sensitivity correction for each pixel by using
detector gain devised by different temperature blackbody
images.
The corrected image (Fig. 14) is smooth for all the effective
pixels; we confirmed that the temperature accuracy is below
2K as compared to the brightness temperature of the corrected
image and actual blackbody temperature.
Performing background correction by using the blackbody
data corresponding to the ambient temperature of the CIRC
enables capture of smooth images. We confirmed that it ispossible to correct the background without using a shutter
system. We will continue to search ways to correct images thatwould improve the correction accuracy.

Fig. 12. Measurement results of MTF. MTF in the CT direction (top). MTF
in the AT direction (bottom)

B. Results of radiometric calibration tests
We also verified the radiometric performance of the CIRC
with shutter-less system. First, we estimated the noise
equivalent differential temperature (NEDT) and flat patternnoise (FPN). We performed stray-light correction from the dataof the same temperature blackbody images at different ambient
temperatures, ranging from -15°C to 50°C. We defined themean temperature of the lens barrel and detector package as theambient temperature. In addition, we performed sensitivity
correction using the data on different temperature blackbody
images. Analysis of the data revealed the NEDT and FPN to be
0.19K and 0.27K,respectively9. This is the expected result fromthe design of the CIRC, and satisfied with the specifications of
the CIRC.

Fig. 13. Raw image of blackbody of CIRC

Fig. 14. Corrected image of blackbody of CIRC

VI. AIRBORNE OBSERVATION WITH THE CIRC GROUND TESTMODEL
We carried out airborne observations with the ground test
model (GTM) of CIRC. Fig. 15 shows the CIRC GTM, which
has optical and radiometric performances equivalent to thecorresponding PFM8. The model was constructed forestablishing a way to perform ground calibration and carry out
field observations before fabrication of the PFM.
Observational flight was carried out on March, 22 and 28,
2012. The aircraft was a “Cessna172 Sky hawk” made by the
Cessna Aircraft Company (see Fig.16). It is one of the bestselling single engine aircraft in the world and can carry four
passengers, including the pilot. The observation area was
Tsukuba City, Tsuchiura City in the south of Ibaraki Prefecture,
and Narita City in Chiba Prefecture, all in Japan. The flight
altitude ranged from 300m to 750m. The Ground sample
distance(GSD) in this altitude was about from 10cm to 25cm.

Fig.17 shows the aerial image of Tsukuba Space Center,
which is a facility in JAXA, captured from an altitude 750m
with a compact digital camera. The yellow rectangle is a fieldof view of the CIRC, and Fig.18 shows the raw infrared image
captured with the CIRC GTM at the location shown in Fig.17.
We performed a background correction of the images aspreviously mentioned in section 5. The result of backgroundcorrection is shown in Fig.19. We were able to get a clear
image. On the other hand, we obtained dark images before
capturing images with a shutter, and we subtracted this dark
image from raw image (Fig.18) to compare it with thebackground corrected image (Fig.19). The image subtracted
dark image is shown in Fig.20. Both Fig.19 and Fig.20 was asimilar clear images. We confirmed that the background wascorrected in shutter-less system and that the actual images wereable to be corrected by using the ground calibration data.

Fig. 17. Aerial image of Tsukuba Space center from 750m above

Fig. 15. CIRC Ground Test Model (GTM)

Fig. 18. Raw image of CIRC captured by Airborne observation(Tsukuba Space Center from 750m above)
Fig. 16. “Cessna172 Sky hawk” used for airborne observations

finished the ground calibration of the first CIRC onboard
ALOS-2, and have confirmed that the performance of the
CIRC is as expected and sufficient for launch. We have also
performed background correction using a shutter-less system
by analyzing the data obtained through airborne observations.

REFERENCES

Fig. 19. Background correction for Fig.18(with shutter-less system)

Fig. 20. Image subtracted dark image from Fig.18(with a shutter)

VII. SUMMARY
We have developed two CIRCs, both of which are thermal
infrared imagers equipped with an uncooled infrared array
detector (called microbolometer). The first one will belaunched in JFY 2013 onboard ALOS-2, and the second will belaunched in JFY 2014 onboard CALET at ISS. We have[1] Schueler, C. F, Silverman, S. H., and Christensen, P. R.,“Thermal Emission System (THEMIS)“, Proc. International
Thermal Detectors Workshop, (2003)[2] Fukuhara, T. et al., “Development of the longwave infrared
imager (LIR) onboard PLANET-C”, Proc. SPIE, 6940, 694030(2008)[3] Spinhirne, J. D., Scott, V. S., Cavanaugh, J.F., Palm, S.,
Manizade, K., Hoffman, J, W., and Grush, R. C., “Preliminary
spaceflight results from the uncooled infrared spectral imaging
radiometer (ISIR) on shuttle mission STS-85”, Proc. SPIE3379,
14-21 (1998)[4] http://smsc.cnes.fr/CALIPSO/GP_iir.htm[5] http://esamultimedia.esa.int/docs/EEUCM/EarthCARE_TPA.pd
f[6] Patrice C., Melanie L., Francois C., Hugo M., “Lens barrel
design of the NIRST IR Camera” Proc.SPIE 7424, 74240E-1[7] Okamura, Y., Matsuyama, H., Kasahara. M., Yoshida, S., andTange, Y., “Development of the WAMS-TIR instrument for
SPF-II”, Proc. SPIE 5659, 105-114 (2005)[8] H. Katayama., M. Naitoh., M. Suganuma., M. Harada., Y.
Okamura., Y. Tange., and K. Nakau.," Development of theCompact Infrared Camera (CIRC) for Wildfire Detection, " Proc.
SPIE 7458, 745806-1-745806-8 (2009).
[9] M. Harada, H. Katayama, M. Naitoh, M. Suganuma, R.
Nakamura, Y. Tange, T. Sato, “Development Of The Compact
Infrared Camera (CIRC) For Earth Observation”, ICSO, (2010)[10] E. Kato, H. Katayama, M. Naitoh, M. Harada, R. Nakamura,and R. Sato. “Development of the Compact Infrared Camera(CIRC) for earth observation”, Proc. SPIE 8353, 8353J1[11] S. Suzuki., Y. Osawa., Y. Hatooka., Y. Kankaku., and T.
Watanabe.," Overview of Japan’s Advanced Land
Observing Satellite-2 Mission," Proc. SPIE 7474,
74740Q-1-10 (2009).
[12] S. Torii et al.," CALET mission on ISS," Proc. SPIE 7021,
702114-1-11 (2008).