Development of the Compact Infrared Camera (CIRC)
for earth observation
Eri. Kato*a, Haruyoshi. Katayamaa, Masataka. Naitoha, Masatomo. Haradaa, Ryoko. Nakamuraa,
and Ryota. SatoaaJapan Aerospace Exploration Agency, 2-1-1 Sengen, Tsukuba, Ibaraki, 305-8505, Japan
ABSTRACT
We have developed Compact Infrared Camera (CIRC) with an uncooled infrared array detector (microbolometer) for
space applications. The main mission of the CIRC is to demonstrate technology for wildfire detection. Wildfires are amajor and chronic disaster that affects many countries, especially those in the Asia-Pacific region, and the situation may
get worse with global warming and climate change. The CIRC detector has the largest format (640 × 480 pixels) everused for observations of Earth from space. Microbolometers have the advantage of not requiring cooling systems such asa mechanical cooler and are suitable for resource-limited sensor systems or small satellites. In addition, the CIRC
employs athermal optics and a shutter-less system, and hence, it is of a small size, is lightweight, and consumes low
electrical power. The CIRC design was based on a commercial infrared camera and employs commercial-off-the-shelf(COTS) parts to reduce the cost and time for development. The CIRC will be carried as a technology demonstration
payload of ALOS-2 and ISS/JEM, which will be launched in 2013 and 2014. We have developed the CIRC Proto Flight
Model (PFM) and performed experiments for calibration in January 2012. In this paper, we present the verification
results of the athermal characteristics and the calibration of the shutter-less system.
Keywords: remote sensing, thermal infrared imaging, uncooled infrared detector, wildfire

1. INTRODUCTION
Microbolometers are widely used in commercial and military applications. 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,
be lightweight, and consume low power. Although the sensitivity of a microbolometer is lower than that of an HgCdTebased photonic infrared detectors, its advantage of not requiring a cooling mechanism makes it suitable for small
satellites or resource-limited sensor systems.
JAXA has researched the application of microbolometers for observations of Earth1. The Compact Infrared Camera(CIRC) was developed as a technology demonstration payload for thermal infrared imaging from space using a
microbolometer. The main mission of the CIRC is to detect wildfires. Wildfires are a major and chronic disaster that
affects many countries, especially those in the Asia-Pacific region, and early detection is important. An effective meansof early detection is to raise the observation frequency. Therefore, our aim is to realize frequent observations by loading
CIRCs in many satellites in the future to take advantage of its small size, lightweight, and low power consumption. Other
CIRC mission targets are volcanoes or heat island phenomena in a city. The CIRC will be carried as a technology
demonstration payload of the Advanced Land Observing Satellite-2 (ALOS-2), and CALorimetric Electron Telescope(CALET), which will be attached to the Japanese Experiment Module (JEM-EF) of the International Space Station (ISS).
In this paper, we present the verification results of the athermal characteristics and the calibration of the shutter-lesssystem with the CIRC Proto Flight Model (PFM). In §2, we describe ALOS-2 and CALET. The mission and details of
the CIRC are described in §3 and §4, respectively. In §5 and §6, we present the measurements and the initial calibration
results of the CIRC PFM. The discussion and summary are given in §7.

*katoh.eri@jaxa.jp; phone +81-50-3362-3121; fax+81-29-868-2961

Infrared Technology and Applications XXXVIII, edited by Bjørn F. Andresen, Gabor F. Fulop, Paul R. Norton,
Proc. of SPIE Vol. 8353, 83533J · © 2012 SPIE · CCC code: 0277-786X/12/$18 · doi: 10.1117/12.918546

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2. ALOS-2 AND CALET
2.1 ALOS-2
ALOS-22 is a follow-up mission to ALOS, which has been contributing to cartography, regional observation, disastermonitoring, and resource surveys since its launch in 2006. JAXA is conducting research and carrying out development
activities to improve the wide and high-resolution observation technologies developed for ALOS to further fulfill social
needs. These social needs include (1) disaster monitoring of damage areas, both in considerable detail and when theseareas may be large; (2) continuous updating of data archives related to national land and infrastructure information; (3)effective monitoring of cultivated areas; and (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 lists the baseline specifications of ALOS-2. The mounting location of CIRC is shown in Figure 1. Basically,
CIRC will take images of the target area when the SAR is pointing to the right at an off-nadir angle of 30°.
Table 1. Baseline specifications of ALOS-2.
Parameter
Size
Mass
Bus power
Communication
Orbit

Specification
9.9 m×16.5 m×3.4 m<2000 kg
>5200 W
<800 Mbps
628 kmCIRC

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

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

2.2 CALETCALET3 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. CALET will address many outstanding questions, including (1) thenature 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 the gamma ray
spectrum. It will also be capable of monitoring gamma ray transients and solar modulation. CALET will be launched in2013.

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The baseline specifications of CALET are listed in Table 2. CIRC will be mounted on the bottom of CALET, which isshown in Figure 2.

Table 2. Baseline specifications of CALET.
Parameter
Mass
Bus power
Communication
Orbit

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

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

3. MISSION OF CIRC
The main mission of CIRC is to demonstrate technology for wildfire detection using a microbolometer. Wildfires are amajor and chronic disaster that affects many countries in the Asia-Pacific region (see Figure 3), and there aresuggestions that this will get worse with global warming and climate change. In the Sentinel Asia project, which will
share disaster information in near real-time across the Asia-Pacific region, wildfire detection has been chosen as one of
the important activities to be monitored. The other CIRC mission targets are volcanoes or heat island phenomena in acity. Observing these targets with a thermal infrared imager will be useful at monitoring volcanoes or solving the heatisland problem.
The CIRC has the characteristics of athermal optical and shutter-less systems. The athermal optical system of the CIRC
was designed by combining two infrared materials: germanium and chalcogenide. The temperature does not need to becontrolled using a heater. Thus, we realized a CIRC with a small size, light weight, and low power consumption.
Moreover, the CIRC design was based on a commercial infrared camera and employs commercial-off-the-shelf (COTS)
parts to reduce cost and time for development.
It is possible to increase the observational frequency of wildfires if CIRCs are carried on various satellites, which cantake advantage of its small size, lightweight, and low power consumption. If CIRCs are carried on ALOS-2 andISS/CALET, the average observation interval becomes 39, 97, and 196 h in Russia, Japan (Tokyo), and Brunei,
respectively (Figure 4).

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Figure 3. ASTER/TIR image of a forest fire in California.

Figure 4. Average observing interval.

4. BASELINE SPECIFICATIONS OF THE CIRC
The baseline specifications of the CIRC are listed in Table 3. We set the baseline specifications to meet requirements forwildfire detection. The detector has a large format (640 × 480 pixels) to obtain a wide field of view. The spatial
resolution is an important factor for wildfire detection. The spatial resolution is 200 m from an altitude of 600 km(ALOS-2) and 130 m from an altitude of 400 km (CALET). Eliminating the cooling system reduces the size (110 mm ×
180 mm × 230 mm) and electrical power (<20 W).
Table 3. Baseline specifications of the CIRC.
Parameter
Size
Mass
Detector
Wavelength
Number of pixels
Special resolution
Field of view
Exposure
Dynamic range
NEdT
FPN
Power

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

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5. CALIBRATION OF THE CIRC PFM
In this section, we present the calibration results of the CIRC PFM. Figure 5 shows a picture of the CIRC PFM.

Figure 5. Picture of the CIRC PFM

In the laboratory experiment at the JAXA Tsukuba Space Center, we measured the Modulation Transfer Function (MTF)of the CIRC PFM in a vacuum to evaluate the image capture performance of the sensor system. We also carried out
radiometric experiments.
5.1 Measurement setup of MTF experiments
The schematic diagram and configuration of the experimental setup are shown in Figures 6 and 7, respectively. The
CIRC was placed inside the vacuum chamber in the laboratory and surrounded by a shroud to control its ambient
temperature with a heater and cooler. The pressure in the vacuum chamber was ~10-5 Torr during the experiment.
Infrared rays were emitted by a blackbody (CI Systems SR800) and passed through the four-bar targets (shown in Figure8) mounted inside the reflective collimator system (CI Systems ILET-5-1.1). The intervals of the slits of the four-bar
targets were equivalent to 1-, 1/2-, 1/4-, and 1/6-Nyquist frequencies. The collimated infrared rays passed through agermanium window mounted on to the side of the vacuum chamber that transmitted the infrared rays from outside thevacuum chamber to be detected by the CIRC.

Figure 6. Schematic diagram of the MTF experimental setup.

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

黒体 Blackbody(CI Systems(CI
Systems SR800)
SR800)

Collimator
コリメータ

Figure 7. Experimental configuration

1/6 Nyquist
1/4 Nyquist
1/2 Nyquist
1 Nyquist
Figure 8. (left) Four-bar target mounted on the collimator system and (right) image of the four-bar target taken with CIRC.

5.2 Data of MTF measurement
We measured MTF in a vacuum environment. The detector positions for measurement were at the center, ±5° in the
cross-track (CT) direction, and ±3.5° in the along-track (AT) direction, as shown in Figure 9. MTF for the CT/AT
directions was measured by rotating the four-bar target. The temperature of the shroud was set to -15–50 °C. The
procedure for MTF analysis was the same as that used by Nakamura et al. (2011)4.

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No.1

No.2

No.3

No.4

No.5

No.6

No.7

No.8

No.9

Dummy pixels(20 × 480)

Figure 9. Positions of MTF measurement on the screen. The nine positions are marked as Nos. 1–9. Dummy pixels are optical black
pixels, which mean non-photosensitivity and have the same electrical property as standard effective pixels.

5.3 Measurement setup of radiometric experiments
Figure 10 shows the schematic diagram of the radiometric experimental setup. The experimental configuration was thesame as that for the MTF experiments. The blackbody was placed before the CIRC inside the vacuum chamber.

Shroudshroudblackbody

Blackbody

Figure 10. Schematic diagram of the radiometric experimental setup.

5.4 Data of radiometric measurement
We measured the radiometric performance of the CIRC in a vacuum environment. Table 4 lists the measurement
conditions. For sensitivity correction, we measured data at blackbody temperatures of -10–50 °C when environmental
temperature of the CIRC is -15, 5, 15, 30, and 45 °C. Moreover, the environmental temperature was changed from -15 to
50 °C under blackbody temperatures of 50, 30, 10, and -10 °C for stray-light correction.

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Table 4. Measurement conditions for radiometric measurement.
Environmental temperature of the CIRC

Temperature of blackbody

[°C]

[°C]

-15, 5, 15, 30, 45-15–50-10–50(basically every 5 °C)-10, 10, 30, 50(every 1 °C)

6. RESULTS
6.1 Results of MTF measurement
We measured MTF for the CT/AT directions at nine detector positions. Athermal characteristics when measuring the
Nyquist frequencies are shown in Figure 11. MTF for the CT direction was constant regardless of the environmental
temperatures on the whole. In contrast, MTF for the AT direction had a gradient and was lower in low-temperatureenvironments.

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Figure 11. Athermal characteristics at Nyquist frequency for the CT/AT directions. Horizontal and vertical axes represent theenvironmental temperature and MTF, respectively. The upper and lower panels are for the CT and AT directions, respectively.
Differences in color show the detector positions.

6.2 Results of radiometric measurement
We have verified the calibration in the case of shutter-less system. First, we analyzed noise equivalent differential
temperature (NEdT) and flat pattern noise (FPN) with stray-light correction and thermal sensitivity by using the data at
blackbody temperatures of 15/30/40 °C (TBB15, TBB30, TBB40). Table 5 lists the averages for NEdT and FPN. The
procedures to calculate NEdT and FPN are given below:

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Procedures of NEdT and FPN
0. Perform dummy correction for all frames. Dummy correction is a process of subtracting the average ofdummy pixels (20 × 480 pixels) from each effective pixel.
1. Correct amount of stray light by stray-light correction for all frames.

¾

NEdT
2. Estimate standard deviation (σ1 [DN]) of brightness variation using data at TBB30.
3. Calculate thermal sensitivity [DN/K] from data of TBB40 and TBB15.
Thermal sensitivity =DataTBB 40 − DataTBB15
40 − 15(1)

4. Determine NEdT [K] as shown in the following equation.
NEdT = σ 1 ÷ (thermal sensitivity)
¾

(2)

FPN
2′. Calculate sensitivity correction factor (α) using data of TBB40 and TBB15.

1 N∑ (DataTBB 40 − DataTBB15 )N n=1α=DataTBB 40 − DataTBB15(3)3′. Subtract average of data at TBB15 from data at TBB30 as offset correction ( DataTBB 30,OC ).
4′. Perform sensitivity correction for the offset-corrected data at TBB30 ( DataTBB 30 ,OC ,SC ).

DataTBB 30,OC ,SC = DataTBB 30,OC × α(4)5′. Estimate standard deviation (σ2 [DN]) of brightness using DataTBB 30 ,OC ,SC .
6′. Determine FPN [K] as shown in the following equation:
FPN = σ 2 ÷ (thermal sensitivity)

Table 5. Average for NEdT and FPN.
Average NEdT [K]Average FPN [K]

0.19

0.27

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example images before and after the background correction. The corrected image (right in Figure 12) is smooth for all of
the effective pixels. The procedure for background correction is given below:
Procedure of background correction
0. Perform dummy correction to all frames before background correction.
1. Correct the amount of stray light corresponding to standard data by stray-light correction.
2. Perform background correction by carrying out offset and sensitivity correction.

Figure 12. (left) Image before background correction. This is a stray-light corrected image of step 1. (right) Image after the
background correction. The size of these images is 660 × 480 pixels.

7. DISCUSSION AND CONCLUSION
7.1 MTF
The results of the MTF measurement are summarized as follows:¾

The MTF in the CT direction is constant regardless of environmental temperatures on the whole.

¾

The variation in the MTF in the AT direction was larger than that in the CT direction.

We measured the MTF characteristics of the CIRC as they are an important image capture performance parameter for
optical sensor systems and confirmed the athermal characteristics of the CIRC.
7.2 Radiometry
From the analysis results, NEdT and FPN were estimated to be 0.19 and 0.27 K, respectively. These results satisfy the
specifications for the CIRC. Using background correction with the shutter-less system, we can also get smooth images
by stray-light correction and sensitivity correction. It is possible to correct background noise without using a shutter
system. We will continue to search ways to correct images that would improve the correction accuracy.

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REFERENCES[1] H. Katayama., M. Naitoh., M. Suganuma., M. Harada., Y. Okamura., Y. Tange., and K. Nakau.," Developmentof the Compact Infrared Camera (CIRC) for Wildfire Detection, " Proc. SPIE 7458, 745806-1-745806-8 (2009).
[2] 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).
[3] S. Torii et al.," CALET mission on ISS," Proc. SPIE 7021, 702114-1-11 (2008).
[4] R. Nakamura., H. Katayama., M. Naitoh., M. Harada., E. Kato., M. Suganuma., K. Nakau., and R. Sato.,"Calibration Results of the Compact Infrared Camera (CIRC) Ground test Model," Proc. SANE 111, 243-248(2011).

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