Development of the Compact InfraRed Camera (CIRC)
for wildfire detection
Haruyoshi Katayamaa*, Masataka Naitoha, Masahiro Suganumaa, Masatomo Haradaa,
Yoshihiko Okamuraa, Yoshio Tangea, and Koji NakauaaEarth Observation Research Center, Japan Aerospace Exploration Agency, Tsukuba, Ibaraki,
Japan 305-8505
ABSTRACTThe Compact InfraRed Camera (CIRC) is a technology-demonstration payload to be carried on the Small Demonstration
Satellite type-2 (SDS-2). The SDS program is a JAXA activity to demonstrate a variety of new technologies and new
missions. The CIRC is an infrared camera equipped with an uncooled infrared array detector (microbolometer). The
mission of the SDS-2/CIRC project is to demonstrate the potential of the microbolometer, especially for wildfire
detection but also for other applications. This paper introduces the detailed design and concept of CIRC. We also discuss
preliminary results of the feasibility study on wildfire detection using thermal infrared images.
Keywords: remote sensing, thermal infrared imaging, wildfire, uncooled infrared detector

1. INTRODUCTION
Microbolometers are widely used in commercial and military applications such as night vision. Because of recent
progress of microelectromechanical system (MEMS) technology, high-resolution, large-format devices are being
developed by many companies.
Microbolometers have an advantage of not requiring cooling systems such as a mechanical cooler. Eliminating thedetector cooling system can reduce the size, cost and electrical power consumption of the sensor. Although
microbolometers are less sensitive than HgCdTe-based photonic infrared detectors, the advantage of not requiring a
cooling system is suitable for small satellites or resource-limited sensor systems.
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 is scheduled to belaunched 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 application to thermal infrared imaging. The ISIR was flown as a hitchhiker experiment on the space
shuttle in 1997. Recent missions to measure the atmosphere vertical profiles like CALIPSO 4 and EarthCARE5 also use amicrobolometer as an imaging infrared instrument. JAXA began a research for application of microbolometer to earth
observation since 2000. The Wide-Angle Multi-band Sensor - Thermal Infrared (WAMS-TIR)6, aboard the stationkeeping test airship (SPF-II) for the stratospheric platform project, is a thermal infrared multi-band radiometer using a
microbolometer FPA.
In order to demonstrate the potential of microbolometer to the thermal infrared imaging from space, the compact infrared
camera (CIRC) is chosen as one of the technology demonstration payloads of Small Demonstration Satellite (SDS). The
SDS program is one of activities of JAXA, to demonstrate a variety of new technologies and new missions.
This paper introduces the details of the design and concept of the CIRC. We also discuss preliminary results of thefeasibility study on wildfire detection using thermal infrared images.

Remote Sensing System Engineering II, edited by Philip E. Ardanuy, Jeffery J. Puschell,
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2. SMALL DEMONSTRATION SATELLITE TYPE-2
The SDS program aims to improve the reliability of practical artificial satellites by demonstrating a wide range of new
space technologies covering everything from equipment and element to system engineering. The SDS-1, the first satellite
in the SDS program, was launched in 2009 as a piggybag satellite of the Greenhouse Gases Observing Satellite “IBUKI”(GOSAT). The mission payloads of the SDS-1 are Multi-mode integrated Transponder (MTP), Space Wiredemonstration Module (SWIM), and Advanced Micro processing In-orbit experiment equipment (AMI).
The SDS-2 is scheduled to be launched as a piggybag satellite in 2013 or later. Table 1 shows a baseline specification of
the SDS-2. The specifications of the SDS-2 are similar to those of the SDS-1 except for the attitude control. The attitudecontrol of the satellite is based on a three axis stabilized attitude control, though that of the SDS-1 is a spin stabilized
attitude control. The SDS-2 is a sun-pointing attitude control in a nominal operation. However, it is possible to change anearth-pointing attitude control during an experiment.
The CIRC is selected as one of mission payloads of the SDS-2. Other mission payloads are next generation star tracker,
contamination monitor using quartz crystal microbalance.

Table 1. Baseline specifications of the SDS-2.
Size
Mass
Bus power
Communication
Orbit
Mission resource

700mm x 700mm x 600mm< 90 kg> 110 WS-bandSun-synchronous Orbit
600 km (TBD)
Size 600mm x550mm x 250mm
Mass ~ 30kg
Power ~30W (nominal)

3. MISSION OF THE CIRC
The main mission of the CIRC is the technology demonstration of the wildfire detection using the microbolometer.
Wildfires are one of the major and chronic disasters affecting many countries in Asia-Pacific region, and somesuggestions are that this will get worse with global warming and climate change. In Sentinel Asia project7 to share thedisaster information in near real-time across the Asia-Pacific region, the wildfire detection is chosen as one of theimportant activities. 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. The other CIRC mission targets are volcanoes or heatisland phenomena in a city. The observations of these targets with thermal infrared imager will become a useful tool tomonitor volcanoes or to solve the heat island problem.

4. BASELINE SPECIFICATIONS OF THE CIRC
A baseline specification of the CIRC is shown in Table 2. We set the baseline specification to meet requirements forthe wildfire detection8,9. 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 baseline specification of the spatial resolution is 200 m from thealtitude of 600 km.
Fig. 1 shows a system block diagram of the CIRC. In order to reduce the size, weight, and cost, we minimized thefunction of the CIRC. The optics unit of the CIRC is f/1.2 optics. We employ an athermal optics to keep the optical
performance in a wide range of temperature. This will be an advantage of the CIRC for small satellites, because we don’t
need an active thermal control or a focus mechanism to the optics.

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Table 2. Baseline specifications of the CIRC.
Item
Size
Mass
Detector
Wavelength
Number of pixels
Spatial resolution
Field of View
Exposure
Dynamic range
NEDT

Characteristics< 150mm × 100mm × 200mm< 3kg
Uncooled infrared detector
8 - 12 μm
640 × 480
< 200 mobserved from 600 km (< 0.33 mrad)
12°× 9° (128 ×96 km)
33 ms
180 K - 400 K
0.2 K@300 K

Compact Infrared Camera (CIRC)
Temperature
sensors

Optics Unit

Detector
Unit

Signal
Processor
Unit

Power
SupplyUnit

Satellite Bus
SystemCommandImage data
HK telemetry

Bus power

Signal I/FPower I/F
Fig. 1. System block diagram of the CIRC.

5. FEASIBILITY STUDY OF WILDFIRE DETECTION
For feasibility study of the wildfire detection and other possible application, we used Advanced Spaceborne Thermal
Emission and Reflection Radiometer (ASTER) / thermal infrared (TIR)10 data. ASTER has a significant advantage overprevious datasets because of the combination of high spatial resolutions (15–90 m) and enhanced multispectral
capabilities, particularly in the TIR. The spatial resolution and swath of the ASTER/TIR are 90m and 60km,
respectively. The 90m spatial resolution in the thermal infrared band is useful to simulate various case of a spatial
resolution.
In order to check the delectability of wildfire, we obtained the wildfire data taken by ASTER. Table 3 shows the list of
wildfire data we checked. These are typical wildfire data including forest fires, tundra fires, and peat fires.
In order to investigate the difference of the wildfire detectability depending on the spatial resolution, we made simulated
images of which spatial resolutions are 180m and 270m from the original ASTER/TIR image.

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Table 3. Analyzed wildfire data of the ASTER/TIR.
Location

Date

Type

Alaska2004-07-17

Forest fire

Alaska2007-09-08

Tundra fire

California

2003-10-26

Forest fireIndonesia

2006-10-12

Peat fire

Fig. 2. ASTER/TIR images of forest fire in California on October 26, 2003 (left) and peat fire in Indonesia on October 12, 2006
(right). The spatial resolutions are 90m (top), 180m (middle), and 270m (bottom). Red filled squares are the results of wildfire
detection using thermal infrared data only. Yellow open squares are the results using MOD14.

Fig. 2 show simulated images of the forest fire in California and the peat fire in Indonesia. We searched the image forregions of anomalously high brightness to detect wildfires. In general, the wildfire detection using satellite data uses
short or medium infrared images in addition to the TIR image. However, by optimizing a threshold level, we can detect awildfire only from the thermal infrared image. Hotspots are detected by contextual threshold method. A pixel is defined
as hotspot if the anomaly in 11μm brightness is higher than 3σ, where σ is standard deviation of brightness in pixels
within 1km radius.

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In order to check the detectability, we used the MODerate-resolution Imaging Spectroradiometer (MODIS) Thermal
Anomalies/Fire products (MOD14v4). MOD14 algorithm detects fire locations using 4μm and 11μm brightness
temperatures with the spatial resolution of 1km.
From this simulation, we found that the detectability of forest fire or tundra fire using thermal infrared images of which
spatial resolution of 180m is comparable to that of MOD14 algorithm. On the other hand, the detection of the peat fireneeds higher spatial resolution. Because the burning temperature of peat fires is lower than that of other wildfires.
Although further improvements of the detection algorithm are needed especially for peat fires, we find that 200m spatial
resolution is almost appropriate for the wildfire detection. The detectability of wildfires should have a dependency to theburning area. In addition to that, there is a possibility to detect a “false alarm” wildfire in a city due to various heatsources like heat power plants. So we are planning to apply this algorithm to other various dataset and check thedetectability.

6. HARDWARE DESIGNS OF THE CIRC
Fig. 3 shows a schematic view of the CIRC. The CIRC is based on a commercial infrared camera developed by
Mitsubishi Electric Corporation (MELCO). However, in order to apply it for a space application, we add somemodifications to the hardware design. In this section, we introduce the hardware design of the CIRC

198mm

149.5mm

95mm

Fig. 3. Schematic view of the CIRC.

6.1 Detector Unit

A Focal Plane Array (FPA) of the CIRC is a Silicon-On-Insulator (SOI) diode uncooled infrared (IR) FPA developed by
MELCO11,12. The characteristic of the SOI diode uncooled IR FPA is to use a single-crystal silicon pn-junction diodes asa temperature sensor. The single-crystal sensor based on silicon LSI technology offers a low-noise characteristic.
We use a 640 × 480 pixel SOI diode uncooled IR FPA of which a pixel size is 25 μm square. The Noise Equivalent
Differential Temperature (NEDT) is 40mK with f/1 optics. Drive and readout circuits are almost the same as those of thecommercial IR camera. For a space application, we are planning to perform a radiation damage test, and a screening ofcommercial devices.
6.2 Optics Unit

The optics of the CIRC is a f/1.2 refractive optics. A focal length of the optics is 78 mm. The temperature of the CIRC
is changed on orbit. The temperature change of the optics will cause a defocus because refractive indices of lensmaterials are highly dependent on temperature. In order to compensate this defocus, we have to employ a focus

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mechanism or a heater to keep the optics temperature constant. However, such mechanisms increase sensor resources.
An athermal optics 12 can compensate the defocus due to the temperature change without such mechanisms.
Fig. 4 shows the optical design of the CIRC. The athermal optics of the CIRC compensates the defocus by combinationof different lens materials and diffractive lenses. The optics of the CIRC uses a germanium and a chalcogenide glass(GASIR®1). Fig. 5 shows the calculated MTF of the CIRC optics versus the ambient temperature from -15 °C to 50 °C.
The MTF is constant over the wide range of temperature.

Fig. 4. Optical design of the CIRC.

1
0.9
O n-axis C T

M TF(@ 20lp/m m )0.8

O n-axis A T

0.7

V erticalC T

0.6

V erticalA T

0.5

H orizontalC T
H orizontalA T

0.4

C ornerC T

0.3

C ornerA T

0.2

Specification

0.1
0
-20

0

20
Tem perature(℃）

40

Fig. 5. Calculated MTF of the CIRC optics in the ambient temperature from -15 °C to 50 °C.

6.3 Signal Processor Unit

The CIRC has no calibration equipments like a shutter or an onboard blackbody to avoid mechanical equipments. The
commercial IR camera corrects a nonuniformity of the image using data while a shutter is closed. The onboard data
correction of the CIRC is a coarse correction of the analog offset level of the detector and a DC level correction to avoid
a deviation from an ADC input range. Thus, the CIRC data is downlinked without compression and corrected on the
ground using the data taken during a ground calibration. In order to correct effects of a stray light or an analog drift of
the CIRC electronics, we also monitor the temperatures of the optics, the detector, and the electrical circuit of the CIRC.
Image data of the CIRC are 14-bit image. The size of one frame data is 4.3M bits. The frame data is transferred to thesatellite bus system with RS-422. The CIRC can also store 16 frame data in a frame memory.

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7. ON-ORBIT OPERATION PLAN OF THE CIRC
The CIRC is a mission to demonstrate the potential of microbolometer to the thermal infrared imaging from space. We
thus are planning to observe various targets such as wildfires, volcanoes, heat island phenomena. We are also planning toobserve calibration targets like deep space, the moon, and the ocean to demonstrate the on-orbit performance of the
CIRC. Although there is a restriction of a downlink resource of the SDS-2, we will be able to observe one target per day
from these targets.
Fig. 6 shows an observational sequence of the CIRC. In order to stabilize the temperature of the CIRC, the CIRC isturned on 30 minutes prior to the observation. After the heat run, we observe a calibration target which has a uniform
temperature distribution like deep space or the ocean. The satellite maneuvers form the sun-pointing to the earth-pointing
to observe the target area. The CIRC can take the image of the target area up to 16 frames in one observation. The
exposure time of one frame is 33ms. The time between exposures (exposure interval) can be changed from 33ms to
8.45s. If the exposure interval is 33ms, the CIRC observe almost the same area overlapped about 200m each exposure.
By combining these data on the ground, the signal-to-noise ratio of the image can be increased. This is an experiment of
the Time Delay and Integration (TDI). If the exposure interval is longer, we can observe a wider area. The maximum
area the CIRC can observe is about 128km (cross track) × 1000km (along track) in one observation.

Time

CIRC ONHeat run[30min TBD]

Calibration target（16 frame）[20s TBD]

Target area
（16 frame）[20s TBD]

maneuver(sun→earth pointing)[TBD]

maneuver(earth→sun pointing)[TBD]

Calibration target（16 frame）[20s TBD]CIRC OFF

Fig. 6. Observational sequence of the CIRC.

8. SUMMARY
The Compact InfraRed Camera (CIRC) onboard the Small Demonstration Satellite type-2 (SDS-2) is a thermal infrared
imager using microbolometer. The main mission of the CIRC is the technology demonstration of the wildfire detection.
The feasibility study of the wildfire detection shows the CIRC’s specification of the spatial resolution of 200m is almost
appropriate for the wildfire detection.
The hardware design of the CIRC is ongoing. The feature of the CIRC is a small, light-weight, and low-cost thermal
infrared imager for space application. We employ the athermal optics and the shutter-less image correction to reduce thesize and weight of the CIRC. The athermal optics of the CIRC can keep the optical performance in the wide range oftemperature from -15 °C to 50 °C.
We will finish the design of the CIRC and start the fabrication of the ground test model (engineering model) of the CIRC
by the end of FY 2009

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