Compact Infrared Camera (CIRC) for Earth Observation
By Masataka NAITOH1), Haruyoshi KATAYAMA1), Masatomo HARADA1), Ryoko NAKAMURA1), Eri KATO1),
Yoshio TANGE1), Ryota SATO1) , Koji NAKAU2)
1)

Japan Aerospace Exploration Agency,Earth Observation Research Center, Tsukuba, Japan
2)
Graduate School of Science, Hokkaido University, Sapporo, Japan

This 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 mechanicalcooler, and athermal optics, which does not require an active thermal control of optics. This can reduce the size, cost, andelectrical power consumption of the sensor.
The main mission of the CIRC is to demonstrate the technology 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 of small size and light weight.
We have developed two CIRCs. The first will be launched in JFY 2013 onboard Advanced Land Observing Satellite-2(ALOS-2), and the second will be launched in JFY 2014 onboard CALorimetric Electron Telescope (CALET) of theJapanese Experiment Module (JEM) at the International Space Station(ISS). We have finished the ground Calibration of the
CIRCs. In this paper, we provide an overview of the CIRC and its results of ground calibration.
Key Words: CIRC, ALOS-2, CALET, microbolometer, wildfire

1.

Introduction

In this paper, we present the verification results of the athermal
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 and the calibration
results of the CIRC PFM are presented. In section 6, the results ofairborne observations is reported, and in section 7, the summary isprovided.

Microbolometers are widely used in commercial and military
applications. Their advantage is that they do not require a coolingsystem, such as a mechanical cooler. Sensors without a coolingsystem for a detector are small in size, lightweight, and consumeless power. Although the sensitivity of 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 for various
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.
We have developed the Compact Infrared Camera (CIRC) 3,4,5
as a technology demonstration payload for thermal infrared
imaging from space using a microbolometer. The main mission of
the CIRC is to detect wildfires, which are a major and chronic
disaster that affects many countries, especially those in the
Asia-Pacific region; therefore, their early detection is important.
An effective means of early detection is to increase theirobservation 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 orheat island phenomena in a city. The CIRC will be carried as atechnology demonstration payload of the Advanced Land
Observing Satellite-2 (ALOS-2)6, and CALorimetric Electron
Telescope (CALET)7, which will be attached to the JapaneseExperiment Module (JEM-EF) at the International Space Station(ISS).

2.

Mission Of The CIRC

The main mission of CIRC is to demonstrate the technology
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 thissituation will get worse with global warming and climatechange. In the Sentinel Asia project, which will share disaster
information in almost real time across the Asia-Pacific region,
wildfire detection has been chosen as one of the important
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 the heat island
problem.
The CIRC has the characteristics of athermal optical andshutter-less systems. 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
1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)6 in JFY 2013,
and the second will be in JFY 2014 onboard CALorimetricElectron Telescope (CALET)7 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.

Fig. 3Fig. 1

Orbits of ALOS-2 and ISS

3.

The schematic views of ALOS-2 and ISS/CALET equippedwith CIRC are shown in Fig.2 and Fig3. ALOS-2 is afollow-up 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) , whichis called PALSAR-2. CALET is an international program of
the ISS that will search for signatures of dark matter andprovide direct measurements of the highest energy of thecosmic ray electron spectrum to observe discrete sources ofhigh-energy particle acceleration in our local region of thegalaxy.

Fig. 2

Schematic view of

Schematic views of ISS (top) and CALET (bottom)

Design of the CIRC

3.1. Specification of the CIRC
The baseline specifications of the CIRC3,4,5 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. 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, forachieving small size, low weight, and low power consumption.
These are described in the subsequent paragraphs.
Table 1. Specification Of the CIRC
Parameter
Specification
Size
110mm × 180mm × 230mm
Mass
3kg
Detector
Uncooled infrared detector
Wavelength
8 - 12 m
Number of pixels
640 × 480
Spatial resolution< 200 m @600 km (ALOS-2)< 130 m @400 km (CALET)
Field of View
12° × 9°Exposure
33 ms
Dynamic range
180-400 K
NEDT
0.2 K @300 K

ALOS-22

3.4. 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 andstray-light correction from the inside the CIRC. We obtained
images of various temperature blackbody with different CIRC
temperatures in order to perform stray-light correction bytemperature of the CIRC. The details are show in section 5.
3.5

Fig. 4

3.2.

An overview of the CIRC ground system is shown in Fig.5.
The ALOS-2/CIRC Ground System (ACGS) consists of threecomponents: a CIRC observation planning system, a dataprocessing system, and a data archive system.

CIRC PFM onboard ALOS-2

Microbolometer

We adopted microbolometers as an infrared (IR) focal planearray (FPA) of the CIRC. Microbolometers are based on theprinciple 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
cooling system can be made to have a small size, low weight,
and consuming 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 same as those of the commercial IR camera. For a space
application, we performed a radiation damage test, and ascreening of commercial devices.
3.4.

Ground System

Fig. 5

Overview of ALOS-2/CIRC Ground System (ACGS)

Generally, observation plans are constructed in response torequests from users by the CIRC observation planning system,
utilizing satellite operation information. After observation, thedata processing system obtains Level0 data from the ALOS-2
ground system and performs geometric and radiometriccorrection to produce Level1 data. Then, the detection of
wildfires, for examples, is conducted to produce Level2 data.
Subsequently, the Level1 and Level2 data are released online
through the data archive system, making them available tousers.
We have developed the ACGS and scheduled the integration
test between ACGS and the ALOS-2 ground system before
launch.

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.
The athermal optics of the CIRC compensates for the
defocus by using a combination of different lens materials anddiffractive lenses. The optics of the CIRC uses a germanium
and a chalcogenide glasses (GASIR®1) and is designed insuch a way that its modulation transfer function (MTF)
changes only slightly when the ambient temperature changes
from -15ºC to 50ºC.

4.

Calibration Instruments of the CIRC PFM

We carried out the ground calibration test4,5 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.

3

4.1.

Experimental setup for MTF measurements(0, 0)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. The collimated infrared rays passed through agermanium window on the side of the vacuum chamber. The
CIRC was able to capture images of the four-bar target. And arotating stage under the CIRC enabled it to capture thefour-bar target images at any positions on the image of the
CIRC.

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)
Fig. 8(639, 479)

Measurement points of MTF on image acquired by CIRCs

4.2. Radiometric calibration tests

Fig. 6

Schematic view of MTF measurement

Fig. 7

Experimental setup of MTF measurement

Fig. 9 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
front of the 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 mechanicalshutter.

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 caseof the CIRC, at the whole image of the CIRC, and wemeasured 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 andthe detector package of the CIRC.
Fig. 8 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.

Fig. 9Experimental setup forradiometric measurements

5.

Calibration Results Of The CIRC PFM

5.1.

Results of The MTF measurements

The measurement results of the MTF at Nyquist frequency
are show in Fig. 10. Each line in the figure represents a
measurement point in Fig. 8.
The MTF in the CT direction (Fig. 10. top) was constantregardless of the environmental temperatures. In contrast,
MTF in the AT direction was slightly lower in
low-temperature environments. However, this results is no
problem to capture clear images in the entire range of theoperating temperatures of the CIRC. This confirm theathermal optical performance of the CIRC.

43) Perform sensitivity correction for each pixel by using
detector gain devised by different temperature blackbody
images.
The corrected image (Right of Fig. 11) is smooth for all theeffective pixels; we confirmed that the temperature accuracy
is below 2K as compared to the brightness temperature of thecorrected 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
that would improve the correction accuracy.

Fig. 11 Left image is a raw image of blackbody of CIRC. Right
one is a corrected image of left one.
Fig. 10 Measurement results of MTF.

MTF in the CT direction (top).

6. Airborne Observation With The CIRC Ground Test
Model

MTF in the AT direction (bottom)

5.2.

Results of radiometric calibration tests
We carried out airborne observations with the ground test
model (GTM) of CIRC. Fig. 11 shows the CIRC GTM, which
has optical and radiometric performances equivalent to thecorresponding PFM. The model was constructed forestablishing a way to perform ground calibration and carry out
field observations before fabrication of the PFM.

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 thedata of the same temperature blackbody images at different
ambient temperatures, ranging from -15°C to 50°C. We
defined the mean temperature of the lens barrel and detector
package as the ambient 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, respectively4.
This is the expected result from the design of the CIRC, andsatisfied with the specifications of the CIRC.
Next, we performed background correction along withstray-light correction and sensitivity correction. Fig. 11 showsa blackbody image before background correction and theimage of the same blackbody after background correction.
Background correction4 is performed in the following steps.

Fig. 11 CIRC Ground Test Model (GTM)

Observational flight was carried out on March, 22 and 28,
2012. The aircraft was a “Cessna172 Sky hawk” made by the
Cessna Aircraft Company. The observation area was Tsukuba
City, Tsuchiura City in the south of Ibaraki Prefecture, andNarita 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.12 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 field

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 thesame temperature blackbody data at different ambient
temperatures.

5

of view of the CIRC, and Fig.13 shows the raw infrared image
captured with the CIRC GTM at the location shown in Fig.12.

Fig. 15

8.
Fig. 12

Image subtracted dark image from Fig.13

SUMMARY

Aerial image of Tsukuba Space center from 750m above.

We 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
be launched in JFY 2014 onboard CALET at ISS. We havefinished the ground calibration of the two CIRCs, and haveconfirmed that the performance of the CIRC is as expected
and sufficient for launch. We have also performed backgroundcorrection using a shutter-less system by analyzing the dataobtained through airborne observations.
References

Fig. 13 Raw image of CIRC captured by Airborne observation.
1)(Tsukuba Space Center from 750m above)

Schueler, C. F, et al.

“Thermal Emission System (THEMIS)“, Proc.

International Thermal Detectors Workshop, (2003)
2)

We performed a background correction of the images aspreviously mentioned in section 5. The result of backgroundcorrection is shown in Fig.14. 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.13) to compare it with thebackground corrected image (Fig.14). The image subtracted
dark image is shown in Fig.15. Both Fig.14 and Fig.15 was asimilar clear images. We confirmed that the background wascorrected in shutter-less system and that the actual images
were able to be corrected by using the ground calibration data.

Fukuhara, T. et al., “Development of the longwave infrared imager(LIR) onboard PLANET-C”, Proc. SPIE, 6940, 694030 (2008)

3)

H. Katayama., et al. " Development of the Compact Infrared Camera(CIRC) for Wildfire Detection, " Proc. SPIE 7458, (2009).

4)

E. Kato, et al. “Development of the Compact Infrared Camera(CIRC) for earth observation”, Proc. SPIE 8353, 8353J1

5)

M. Naitoh, H. Katayama, M. Harada, R. Nakamura, E. Kato, Y.
Tange, R. Satoh, K. Nakau “Development Of The Compact Infrared
Camera (CIRC) For Earth Observation”, ICSO, (2012)

6)

S. Suzuki., Y. Osawa., et al. "Overview of Japan’s Advanced Land
Observing Satellite-2 Mission," Proc. SPIE 7474, (2009).

7)

Fig. 14 Background correction for Fig. 13 with shutter-less system

6

S. Torii et al.," CALET mission on ISS," Proc. SPIE 7021, (2008)