boeing staring sensor

1024x1024 Tactical IR HgCdTe Staring Sensor SystemStephen R. Barrios, Arsen Bogosyan, Gilbert Y. Chan, Michael B. Gubala, Herbert Huey,

Raymond Kwok, Raymond G. Lawrence, Mark Muzilla, John W. Yang

The Boeing CompanyElectronic Systems & Missile Defense Division

3370 Miraloma AveAnaheim, CA 92803

ABSTRACT

Boeing has demonstrated Mid-Wave Infrared (MWIR) imaging performance of a large format tacticalsensor based on a 1024x1024 focal plane array (EPA). The ultra-high density infrared (IR) sensor systemconsists of a 10.47 mm aperture optics, a 10242 Mercury Cadmium Telluride (HgCdTe) EPA, a Sterlingcycle integrated cooler dewar assembly (IDA), and a pre-processor with advanced algorithms for datacorrection and image enhancement. In this paper, we will present measured performance parameters of thestaring sensor system including minimum resolvable temperature (MRT), noise equivalent temperaturedifference (NEDT), and noise equivalent irradiance (NET). Key features and attributes of the integratedhardware will also be described. A similar instrument to enhance situational awareness is under evaluationas part of a panoramic camera system to demonstrate feasibility of sensor-guided landing in adverseenvironments for heavy transports such as the Boeing C17 aircraft. Considerations are underway to utilizethe camera as part of the Joint Strike Fighter (JSF) sensor suite. We will introduce other systemapplications for which the large format imagery can be strategically employed and discuss its operationaladvantages.

Keywords: High Resolution Camera, 10242, HgCdTe, Focal Plane Array, 2 Color FPA, Boeing

1. INTRODUCTION

Two dimensional, staring, infrared sensors are becoming an important element in advanced battlefieldengagement to maintain our military superiority as demonstrated in Desert Storm and Bosnia. Withadvancing next generation weapons systems such as Joint Strike Fighter, Tactical High Energy LaserWeapon, and Multi-mission sensor systems, improved sensor resolution and wide area surveillance forenhanced engagement range coverage are essential for the responsiveness, accuracy, and lethality of theseadvanced weapon systems.

To support the competing requirements of high resolution and wide field-of-view coverage while providingincreased sensitivity and reliability, very large area focal plane arrays are necessary. Boeing, through itshistorical association with Rockwell Science Center since the early 1980s, has been producing highperformance two-dimensional staring focal plane arrays for military and commercial applications. As acontinual advancement of EPA technology, Boeing has demonstrated the feasibility of an ultra-high density10242 portable tactical camera using MWIR HgCdTe EPA. The performance of this camera will besummarized within the contents of this paper.

With the maturity of this technological advancement, Boeing has been expanding its research effort intoultra-high density two-color FPAs through its IR&D effort and government funded developments.

Infrared Technology and Applications XXVI, Bjrn F. Andresen, Gabor F. Fulop, Marija Strojnik, Editors,Proceedings of SPIE Vol. 4130 (2000) 2000 SPIE. 0277-786X/00/$15.00640

Downloaded From: http://proceedings.spiedigitallibrary.org/ on 04/24/2015 Terms of Use: http://spiedl.org/terms

2. SENSOR DESCRIPTION

The Boeing ultra-high density camera, shown in Figure 2-1, is a modular design that consists of four majorsubassemblies: 1) A 10242 IDA, 2) Lens Assembly, 3) FLIR Imaging Electronics, and 4) HousingAssembly. The optics consists of a 3 1 .42mm, F/3.O, 33 x 33 wide-angle lens with matching cold shield inthe IDA. The 10242 EPA is read out in four quadrants. The FLIR Imaging Electronics consists of a powersupply, a video display controller, a EPA timing controller, four digitizer-NUC modules, and a fourquadrant stitching module. The EPA runs at a 30 Hz frame rate, and the four quadrants operatesimultaneously. The data from the four quadrants are combined by the stitching electronics, and then fed tothe video display. The display conforms to the EIA-343A 1023 lines composite video format, with 946lines displayed tO preserve the aspect ratio. The display electronics also adjusts the brightness and contrastto compress the 1?-bit data into 8-bits for the video DAC. Figure 2-2 , illustrates the top level functionalblock diagram of the camera. Table 2-1 summarizes the key parameters of the camera system.

ra : . 4 r%rJ{& t__*_a ::a -:xUt arj4.fl: ;t "::t:tl

Figure 2-2. 10242 Camera Functional Block Diagram

Figure 2-1. 10242 HgCdTe Camera

Proc. SPIE Vol. 4130 641


Table 2-1. 10242 Camera Parameter Summary

PERFORMANCEPARAMETERS

SPECIFICATIONS

Focal Plan Array MWIR HgCdTe (MCT)Number Of Detector(elevation_x_azimuth)

1024 x1024

Detector Pitch (jim) 18Fill Factor >90%Spectral Band (jim) MWIR (3.8 4.8)Type of Cooling 1 watt Linear Split Sterling Closed Cycled CoolerCool Down Time minutes)

SiTF

0.1A

A

. 0.05 ACl)

.3 A

.- 0> A

-u.05 A

0.1 - i I I I I-3 -2 -1 0 1 2 3

A I (K)

Figure 3-1 Measured (A) SiTF of the Large Format Sensor

3.2 Noise Equivalent IrradianceNoise equivalent flux irradiance (NET) was measured with the sensor viewing a 100 microradian pointsource at background temperatures ranging from 300K to 450K. Figure 3-2, shQws the measured NETsuperimposed on the theoretical curve. The NET agreement at 300K is excellent, measuring 1 .0 x 1013Watts/cm2. Measured NET values above 300K are higher than the theoretical prediction. This may becaused by excess electronics noise in the demonstration camera and the test equipment. It is expected thatfuture NET measurements will show improvement in this area when the electronics noise is reduced.

Noise Equivalent Irradiance

1.OOE-11

E 1.OOE-12

1.00E-1

1.OOE-14300 350 400 450

Background Temperature (K)

Figure 3-2 Experimental (A) and Analytical (--)Results of NEI



3.3 Noise Equivalent Differential TemperatureFigure 3-3, is a plot of NEDT against integration time, with the background temperature held at 295K. Thetheoretical curve is shown together with measured data for comparison. The nominal NETD at 5.82 msecis 0.048K. The measured NEDT at integration times between 4 and 6 msec match the theoretical curvewhile at longer integration times the measured data is slightly better than our models predicted. Shortintegration times below 4 msec produce higher NETDs than theoretical primarily due to dominance ofelectronics noise.

Noise Equivalent Differential Temperature0

I' _

OO.15A

. 0.1G)

_____________

-

0.05

G)A A

I..... 0 1 r I I0 2 4 6 8 10 12 14 16 18 20

Integration Time (msec)

Figure 3-3. Experimental (z) and Analytical (--) Results on NEDT

3.4 Minimum Resolvable Temperature and Range PerformanceFigure 3-4, is a plot of measured MRT, based on three observers, using standard target patterns of variousspatial frequencies. The test results are consistant with the predicted curve. The predicted MRT is O.4Cat the sensor Nyquist frequency of 0.87 cycle/mrad.

Apparent Minimum Resolvable Temperature

1 0 - - .

h! :;0.001

0 0.2 0.4 0.6 0.8 1

Spatial Frequency (cycle/rn rad)

Figure 3-4. Measured (z\) and Analytical (--) Results on MR

Proc. SPIE Vol. 4130644


3.5 High Resolution ImageAs examples of the resolution capability of the large format sensor two still-frame images of highresolution scenes are shown in Figure 3-5. Sensitivity is excellent as can be seen in the image of thelaboratory personnel. Details such as vest pockets are clearly visible in the image. The wide FOVcoverage and resolution is evident in the second image. The image was taken from the second floor withthe sensor pointing about 600 downward at the two trucks yet much of the neighboring building andparking lot are also in the 33.6 x 33.6 image. A dark area between the Humvee and the building isevidence that the Humvee was parked at that spot earlier. The yellow striped lines and "No Parking" signsat the front of the vehicles are also evident in the image. The unexpected dark spot in the Humvee hoodarea is actually the radiator circulating water over the top of the engine.

4. SYSTEM APPLICATIONS

There are numerous applications for an ultra high resolution infrared camera in commercial, scientific, andmilitary fields. In the field of thermography the user can apply the higher resolution and sensitivity todistinguish subtle variations in surface temperatures. Hyperspectral imagers and spectrometers can takeadvantage of the large number of rows available for registering distinct spectral lines. Infrared astronomy,earth mapping, surveillance, and Infrared Search and Track (IRST) systems can all benefit from the higherresolution and wide field coverage. With the increase in image resolution, finer details of the scenes andobjects of interest can be analyzed and used to identify specific characteristics unattainable with lowerresolution cameras without increasing the optical focal length of the camera. The 1024 x 1024 camera alsoallows the user to cover wider fields of view while maintaining high spatial frequency response.

4.1 Implications to System DesignAn advantage of using the 1024 x 1024 camera in applications where size or weight are critical designparameters, is that it allows the system designers to reduce the sensor size by reducing the optics focallength while maintaining comparable spatial resolution to cameras with smaller arrays. For example, if wecompare the Boeing 640 x 480 focal plane (with a pixel pitch of 27um x 27um) to the Boeing 1024 x 1024focal plane (with a pixel pitch of l8um x l8um), we see that it is possible to reduce the 1024 camera focal

Figure 3-5. 1024x1024-Element Still-Frame Images



length by 33% and be able to achieve the same spatial r,esolution. Depending on the optical design this canbe a significant improvement in size and weight as well as costs of the system.

Field coverage is an important system design factor. In this aspect, the 10242 array can attain an increase ininstantaneous coverage area of 52% compared to a 640 x 480 camera using the same focal length opticalsystems. With a step stare system, this will allow the user to reduce the coverage time, on the average overa large area, by a factor of 52% or to increase sensitivity by dwelling at each step within the field by thesame factor. If the system is background limited and the target is unresolved, this can translate into anincrease in sensitivity of 85%, accounting for both detector area differences and integration timedifferences in maintaining the same coverage time.

4.2 Relative System Performance ImprovementFor target detection, recognition, surveillance, as well as search and rescue missions there is a distinctimprovement in range performance of the large format sensor over lower resolution cameras if the systemis limited by the resolution of the focal plane. Again, comparing the 1024 x 1024 camera against the 640 x480 camera, using the same optical design and matching the field of view in the display, it is possible toshow that detection, recognition, and identification ranges for an imaging system can be increased by 75%with 90% probability. From the end user standpoint this significantly increases the system utility.

Figure 4-1, is a plot of detection ranges for the 1024x1024 array and other standard HgCdTe EPA types.Detection ranges are normalized to the maximum value achieved by the 1024x1024 array. The FOV, F-number, and target signature are held fixed to allow direct comparison of range capability. The advantageof the large format array in comparison with other standard devices is apparent. At Pd=S, the 1024x 1024sensor has a range advantage of 1.4x, 1.6x, and 3.8x, respectively, compared to the 640x480 starer, the480x4 LWIR Gen-2 scanner, and the 256x256 starer.

Figure 4-1. Range Comparison Between the 1024x1024 Array and Other HgCdTe ArrayTypes

1.2

Detection Performance Comparison

1C)C)

0.6

E 0.40z 0.2

00 0.2 0.4

Detection Probability (P d)0.6 0.8 1

Proc. SPIE Vol. 4130646


5. SUMMARY

Boeing has developed and successfully demonstrated an ultra high resolution 1024 x 1024 HgCdTe EPAcamera system. Preliminary performance measurements compare very well with theoretical predictions.

With this ultra high resolution camera the system designer has more freedom in addressing the criticaldesign factors of a system when compared to existing smaller format cameras. Size, weight, andperformance are key parameters that the designer and end user can directly benefit from by integrating thissystem into their designs.

Future developments for the 1024 x 1024 camera will incorporate the next generation 2- color HgCdTefocal plane arrays with micro lenses, which are being developed jointly between Boeing and RockwellScience Center, tith the added advantage of improved array yields as well as increased focal plane fillfactor.



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