DESIGN AND CONCEPT OF THE COMPACT INFRARED CAMERA (CIRC)
WITH UNCOOLED INFRARED DETECTOR
Haruyoshi Katayama, Masahiro Suganuma, Yoshihiko Okamura, Masataka Naitoh, Yoshio Tange,and Koji Nakau
Earth Observation Research Center, Japan Aerospace Exploration Agency, Ibaraki, Japan,
E-mail: katayama.haruyoshi@jaxa.jp
327 x 240 array providing good sensitivity (D* ~ 5e9
cmHz1/2/Watt) in the thermal infrared region. Recentmissions to measure the atmosphere vertical profiles like
CALIPSO [4] and EarthCARE [5] also use amicrobolometer as an imaging infrared instrument.
JAXA began research for applying microbolometers toEarth observation in 2000. The Wide-Angle Multi-bandSensor - Thermal Infrared (WAMS-TIR) [6], aboard thestation-keeping test airship (SPF-II) for the stratosphericplatform project, is a thermal infrared multi-band
radiometer using a 320 x 240 microbolometer FPA.
The compact infrared camera (CIRC) was chosen as atechnology demonstration payload for the Small
Demonstration Satellite (SDS) in order to demonstrate thepotential of microbolometers in thermal infrared imagingfrom space. The SDS program is a JAXA activity todemonstrate a variety of new technologies and newmissions. The mission of the SDS/CIRC project is todemonstrate the potential of the microbolometer,
especially for wildfire detection but also for otherapplications. The second purpose of the CIRC project isthe low-cost and early development of the thermalinfrared imager.
This paper introduces the detailed concept of the CIRC.
We also present preliminary results of a feasibility study
on wildfire detection and other applications.

ABSTRACTThe compact infrared camera (CIRC) is atechnology-demonstration payload to be carried on theSmall Demonstration Satellite (SDS). CIRC is an infrared
camera equipped with an uncooled infrared array detector(microbolometer). Microbolometers have an advantage of
not requiring cooling systems such as a mechanicalcooler.
CIRC’s main mission is technology demonstration of
wildfire detection using the microbolometer. This paper
presents the detailed design and concept of CIRC. We
also discuss preliminary results of the feasibility study on
wildfire detection and other applications using thermal
infrared images.
1. INTRODUCTION
Microbolometers are widely used in commercial andmilitary 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 requiringcooling systems such as a mechanical cooler. Eliminating
the detector cooling system can reduce the size, cost andelectrical power consumption of the sensor. Although
microbolometers are less sensitive than HgCdTe-based
photonic infrared detectors, the advantage of not requiring acooling system is suitable for small satellites orresource-limited sensor systems.
For this reason, microbolometers began to be employedfor various space applications. In planetary missions, theThermal Emission Imaging System (THEMIS) [1]
aboard the Mars Odyssey spacecraft used a
microbolometer focal plane array (FPA). The array is 320(cross-track) by 240 (along-track) with 50μm pixels. The
Longwave IR camera (LIR) carried by the Venus Climate
Orbiter (PLANET-C) [2], which is scheduled to belaunched in 2010, also uses a 320 x 240 microbolometer
array.
In Earth-observation missions, the Infrared Spectral Imaging
Radiometer (ISIR) [3] experiment tests the potential of
microbolometers for application to thermal infrared imaging.
The ISIR was flown as a hitchhiker experiment on the space
shuttle in 1997. The instrument was installed in apressurized canister. The microbolometer used in ISIR is a

2. MICROBOLOMETERS
Microbolometers detect infrared energy as minutechanges of the detector temperature. A microbolometerconsists of an array of pixels, each pixel being made up of
several layers. Although there are several different
structures that differ from company to company, theselayers consist of an IR absorbing layer, a reflection layer,
and a readout integrated circuit (ROIC). The key
technologies of the microbolometer are the IR absorber,
the temperature sensor to detect the temperature change of
the IR absorber, and thermal isolation structures of the IRabsorber.
In Japan, two companies provide microbolometers,
Mitsubishi Electric Corporation (MELCO) and NECCorporation. MELCO’s uncooled infrared FPA iscomposed of a series of PN junction diodes fabricated ona Silicon-On-Insulator (SOI) wafer. In contrast, NEC uses
vanadium oxide as IR absorbing material. Both1

companies can provide a 640 x 480 large format arraywith 23.5 or 25μm pixel [7], [8]. We are planning tochoose one of these devices. The 640 x 480
microbolometer array is the largest format ever used inEarth observations from space.

Table 2. CIRC baseline specifications
Parameter
Specification
Size

3. SMALL DEMONSTRATION SATELLITESThe Small Demonstration Satellite (SDS) program is aseries of 100kg-class small satellites to demonstrate a rangeof new space technologies, from elemental to system-wide.
The SDS is a piggyback satellite carried by the HIIA launchvehicle. The first satellite of the SDS series (SDS-1) will belaunched in fiscal 2008 as a piggyback payload with theGreenhouse Gas Observing Satellite (GOSAT).
CIRC is a payload for the second satellite of the SDS series(SDS-2). Although the launch date of the SDS-2 is notdetermined yet, we have started the conceptual design of thesystem. Table 1 lists the baseline specifications of theSDS-2.

< 100mm x 150mm x 200mmMass< 3kgDetector

Uncooled infrared detectorWavelength

8 to 12μm

Number of pixels

640 x 480

Spatial resolution< 200m @600km (< 0.33 mrad)

Field of View

12° x 9°Frame rate

30HzHigh gain: 180K to 340K

Dynamic range

Low gain: 180K to 400K

NEdT

0.2 K@300K

Compact Infrared Camera (CIRC)

Temperature
sensors

Optics Unit

Detector
Unit

Table 1. Baseline specifications of the SDS-2.
Size
700mm x 700mm x 600mm
Mass

100kg

Bus power

130W

Communication

S-band (1Mbps, 16kbps)

Attitude control

Three-axis attitude controlOrbit

Sun–synchronous orbit

Calibration
Unit (TBD)

Satellite BusSystemSignalProcessor
Unit

Power
SupplyUnit

CommandImage data
HK telemetry

Bus power

Heater()Signal I/FPower I/FFig. 1. System block diagram of the CIRC.

Figure 1 presents the CIRC system block diagram. Inorder to reduce the size, weight, and cost, we minimized
CIRC’s functions. CIRC’s optics unit is f/1-f/1.5 optics.
We are discussing using athermal optics to maintain
optical performance over a wide range of temperatures.
This will be an advantage of CIRC for small satellites
because we do not need active thermal control for theoptics.

4. CIRC MISSION AND SPECIFICATIONSCIRC’s main mission is the technology demonstration ofwildfire detection using a microbolometer. Wildfires aremajor and chronic disasters affecting many countries inthe Asia-Pacific region, and the situation may get worsewith global warming and climate change. In the Sentinel
Asia1 project to share disaster information in near realtime across the Asia-Pacific region, wildfire detection ischosen as one of the most important activities.
Table 2 lists CIRC’s baseline specifications. We set thebaseline specifications to meet the requirements for wildfire
detection. The detector has a large format (640 x 480) toobtain a wide field of view. The spatial resolution is an
important factor for wildfire detection. The baseline
specification of the spatial resolution is 200m from analtitude of 600km.

15.
FEASIBILITY
DETECTION

STUDY

OF

WILDFIRE

We used Advanced Spaceborne Thermal Emission andReflection Radiometer (ASTER) / thermal infrared (TIR)[9] data to conduct a feasibility study of wildfire detection
and other possible applications. ASTER has a significant
advantage over previous datasets because it combineshigh spatial resolution (15 to 90m) and enhanced
multispectral capability, particularly in the TIR. TheASTER/TIR spatial resolution is 90m, and its swath is60km. The 90m spatial resolution in the thermal infrared
band is useful for simulating various cases of spatialresolution.
In order to check the ability to detect wildfires, weobtained the wildfire data taken by ASTER. Table 3 lists
the wildfire data we checked. These are typical wildfire
data including forest fires, tundra fires, and peat fires.

http://dmss.tksc.jaxa.jp/sentinel/2

Table 3. ASTER/TIR wildfire data analyzedLocation
Date
TypeAlaska

5.1

2004-07-17

Forest fire

Alaska2007-09-08

Tundra fire

California

2003-10-26

Forest fireIndonesia

2006-10-12

Peat fire

Spatial resolution

We made simulated images with spatial resolutions of
180m and 270m from the original ASTER/TIR image inorder to investigate the dependence of wildfire
detectability on the spatial resolution.
Figures 2 and 3 present simulated images of a forest fire in
California and a peat fire in Indonesia. We searched theimages for regions of anomalously high brightness to detect
wildfires. In general, wildfire detection with satellite datauses short or medium infrared images. However, byoptimizing the threshold level, we can detect a wildfire fromthe thermal infrared image alone.
In order to check wildfire detectability, we used theModerate-resolution Imaging Spectroradiometer (MODIS)
Thermal Anomalies/Fire products (MOD14v4). The
MOD14 algorithm detects fire locations using 4μm and11μm brightness temperatures with a spatial resolution of1km.
This simulation demonstrated that the detectability of forest
fires or tundra fires using thermal infrared images with aspatial resolution of 180m is comparable to the detectability
using the MOD14 algorithm. However, a higher spatial
resolution is required to detect peat fires because peat fires
burn at a lower temperature than other wildfires.
Although further improvements of the detection algorithm
are needed, especially for peat fires, we find that 200m
spatial resolution is adequate for wildfire detection. The
detectability of wildfires should depend on the burning
area. In addition, “false” wildfires may be detected incities due to various heat sources like heat power plants.
We therefore plan to apply this algorithm to various otherdatasets and check the detectability.

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

6. OTHER POSSIBLE APPLICATIONS
The other CIRC mission is to demonstrate the possibilityof microbolometers as a thermal infrared imager for otherobservation targets like volcanoes or heat island
phenomena in a city.
Figure 5 presents an image of Mt. Merapi volcano,Indonesia, acquired by ASTER on June 6, 2006. We cansee fumes and volcanic ash at the crater and its
surrounding area from the VNIR image. Figure 6 shows
TIR images around the crater with different spatialresolutions. The two streaks are relics of a pyroclastic
flow. We can see these features from the images of 90m
and 180m spatial resolution. However, it is difficult toresolve from 270m or 360m spatial resolution.
As with wildfire detection, the visibility of these features
depends on the scale of the observation target. We willcontinue this kind of work to investigate the feasibility.

5.2 Dynamic range
The sensor dynamic range is also important for detecting
wildfires. If the burning temperature is too high, thesensor output may saturate.
Figure 4 depicts a histogram of the radiation temperatureof a wildfire acquired by ASTER/TIR in the 11μm band.
The radiation temperature of 370K is the saturation levelof the ASTER/TIR. This implies that the dynamic range
needed for CIRC is 400K.

3

Fig. 5. ASTER/VNIR image of Mt. Merapi Volcano, Indonesia,acquired by ASTER on June 6, 2006.

Fig. 6. ASTER/TIR images of the crater of Mt. Merapi. The
spatial resolutions of images are 90m, 180m, 270m, and 360m
from left to right.

7. SUMMARY
The compact infrared camera (CIRC) aboard the Small
Demonstration Satellite (SDS) is a thermal infrared
imager using a microbolometer. The main CIRC mission
is technology demonstration of wildfire detection using amicrobolometer.
We set the baseline specification to meet requirements forwildfire detection and other applications. The feasibility
study indicates that the CIRC baseline specification isadequate for these purposes. We will start to develop
CIRC this year based on the specifications.

Fig. 3. ASTER/TIR images of peat fire in Indonesia on October
12, 2006. The spatial resolutions are 90m (top), 180m (middle),and 270m (bottom). Red filled squares and yellow open squares
are the same as in Fig. 1.

Fig. 4. Histogram of the radiation temperature of a
wildfire acquired by ASTER/TIR in the 11μm band.

4REFERENCES
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