Compact optoelectronic scanning device for aerial photography in the visibleand IR regions

N. I. Pavlov and G. I. Yasinski 

Scientific Research Institute for Comprehensive Testing of Optoelectronic Devices and Systems, Sosnovy Bor,Leningrad Region~Submitted October 2, 2002!Opticheski� Zhurnal70, 11–14~April 2003!

This paper presents the results of the development of a multispectral optoelectronic scanningdevice. The basic version of the device has the following characteristics: the working spectralregion is 0.4–12.5mm, including the 0.4–0.9 and 8.0–12.5-mm regions, the visual field is120°, the instantaneous viewing angle is 0.5 mrad, and the detectable temperature difference froma distance of 200 m is 0.1 K. The mass of the optomechanical unit of the device is 6 kg,and the overall dimensions are 253B20 cm. An application of the device for terrestrialmeasurements is considered. ©2003 Optical Society of America

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The main development trend in airborne optoelectrosystems for remote probing and monitoring of the eartsurface is the creation of complexes that provide digitalages in several spectral ranges simultaneously, as well adevelopment of methods for combined analysis of the resing images.1,2

The spectral attributes that characterize the section ofvisible radiation spectrum within 0.4–0.9mm are widelyused to distinguish terrestrial objects of observation fromsurrounding background and to identify them. The recordof IR images in the 2.5–12.5-mm region in the daytime al-lows remote detection of thermal radiation sources anddetermination of the shape of objects hidden by shadosmoke, and clouds, the detection of disturbed and laterstored sections of soil, the recognition of underground comunications and cavities, the detection of objects buriedthe ground, etc.3

The studies that have been carried out show that mspectral systems that simultaneously form digital images

230 J. Opt. Technol. 70 (4), April 2003 1070-9762/2003/0402

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the visible and IR regions make it possible to use new infmational attributes of objects that express a correlationreflected solar and intrinsic IR radiations under conditionsnatural heat exchange.4,5 Theoretical and preliminary experimental results of the studies show that it is promising tothe correlation attributes to distinguish and classify techgenic and natural objects, including by constructing corretion images or maps.6,7

To illustrate the possibilities of the new attributes, Figshows pictures of a segment of the underlying surface invisible and IR ranges, along with a correlation image–msynthesized from these pictures.

These pictures were obtained from the Vesuvius-ECborne multispectral optoelectronic system, in which sevedigital images are simultaneously formed in the 0.412.5-mm spectral range, combined by the point-to-poprinciple.8

This article presents the results of the developmentthe basic version of a compact dual-spectral scanning de

ce.

FIG. 1. Segments of images of the underlying surfa~a! in visible light, ~b! in IR, ~c! correlation image–map.

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that provides digital images in the visible and IR rangesdescription is given of the structure of an application pgram for combined processing of visible and IR images, wconstruction of a synthesized correlation map.

Experience in creating the Vesuvius-EC optoelectrosystem, intended for the solution of a wide range of geolocal problems and ecological monitoring of the eartsurface,8 as well as the use of modern optical and electrocomponents, made it possible to develop a compact anof this device and to significantly reduce the mass and oall dimensions while retaining comparable technical charteristics~see Table I!.

Significant improvements became possible by usingIR photodetector device integrated with a microcryogegaseous-nitrogen cooling system, by fabricating the optelements from aluminum alloys with diamond turning, aalso by introducing computer technologies to control theeration of the device and the recording process and tocess the image data.

The resulting compact scanning device structurally csists of three units: an optomechanical unit, an electrounit, and a hardware–software package.

The functional layout of the device is shown in Fig.where1 is the optomechanical unit, which includes a twsided scanning mirror~1-1!, an electric drive~1-2!, a scan-rate sensor~1-3!, a line-start sensor~1-4!, a parabolic mirror~1-5!, a CCD lens objective~1-6!, an IR photodetector~1-7!,a micro-Stirling cooling system~1-8!, and a linear CCD ar-ray ~1-9!; 2 is the electronic matching device~the controller!,containing a multiple switch~2-1!, an analog-to-digital con-verter ~2-2!, a USB controller~2-3!; and3 is the hardware–software package.

The parabolic mirror is made in the form of an off-ax

TABLE I. Comparative characteristics of the compact scanning devicethe Vesuvius-EC optoelectronic system.

Characteristics, measurement unitsCompact

scanning device Vesuvius-EC

Working spectral region,mm 0.4–12.5 0.4–12.5Number of working ranges 2 4Scan angle, deg 120 84Instantaneous viewing angle, mrad 0.5 1.0Radiometric indices:

digital resolution,bit/element 12 8measurement error:absolute/relative, % – 5.0/1.0

Spectral resolution, nm – 30.0–500.0Observable temperature difference, K 0.10 0.05Interface USB 1.1 ParallelInformation data:

digital map, image format GIS, bmp bmpdata carrier, type HDD, CD HDD

Application software 1 1

Size of optomechanical unit, cm 253B20 51347352Mass of optomechanical unit, kg 6.0 65.0Power requirement for the dc circuit 30.0 700.0

~voltage 27 V!, W

Note: USB is a universal serial bus, GIS is a geographical informatsystem, HDD is a computer hard disk, and CD is a laser disk.

231 J. Opt. Technol. 70 (4), April 2003

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paraboloid with focal length 100 mm and diameter 100 mThe two-sided scanning mirror, controlled by the electdrive, provides a visual field of up to 120°.

The IR photodetector includes a CdHgTe photoresisin the form of eight photosensitive elements, located in olinear array and integrated with a miniature Stirling-tygas–cryogenic cooling system, as well as a unit for contling the cooling system and an electronic preamplifier uwith voltage stabilizers.

The main technical characteristics of the photodetecdevice for the IR range are as follows: The spectral sensity range is 8.0–12.5mm, the size of the photosensitive element is 50.0350.0mm, the specific detectivity is 431010 cm•Hz1/2/W, the working cooling temperature of thphotosensitive elements is 77 K, and the mass of the deis 1 kg.

A PD3798 CCD was chosen as a photodetector for0.4–0.8-mm range. The other main characteristics of tPD3798 CCD are as follows: The number of elements inlinear array is 5348, the element size is 737 mm, the maxi-mum polling frequency is 5 MHz, and the device hCMOS-compatible output.

The controller is based on an LM9831 microcircuwhich converts analog video signals to digital data and traports these data in real time to the software–hardware page. The data-transfer rate is as much as 12 Mbit/sec.controller uses the promising USB 2.0 and IEEE 1394 daexchange protocols, which provide an exchange rate of u400 Mbit/sec.

The hardware–software package is based on the Disery KT6 computer, PIII-1000, and theETNA-3 applicationsoftware.8 A block diagram of the hardware–software pacage appears in Fig. 3. The computer has 128 MB of on-memory and a 20-GB hard disk. There are two USBinput ports, providing a data transfer rate of up to 12 Mb

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FIG. 2. Functional layout of compact dual-spectral scanner.

231N. I. Pavlov and G. I. Yasinski 

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sec, and an IEEE 1394 input port, with a data transfer ratup to 400 Mbit/sec. The active LCD monitor has a resolutof up to 10243768 pixels with 32-bit color. The mass of thcomputer is 3.3 kg.

The basic application software, with the general naETNA-3, includes the main programBUF3 to control the scan-ner, the picture-taking regimes, and the processing, recing, and real-time display of the resulting images; progrTOFILE for creating an archive of files; programVIEWFILE toview the contents of the archive; and standard program pageIMAGE for topical processing of multispectral images.

At the same time the images are being recorded, recare made of the service information~date, time, order number of the picture, etc.!, the flight data~height, speed, roll,pitch, yaw, etc.! and geographical data~latitude and longi-tude! when they are obtained from the navigational equment of the airplane and the GPS. Digital images invisible and IR ranges can be formed as a topographicalreferenced to the geographical coordinates, and this enscomplete geographical referencing of all the image eleme~pixels!.

The fact that the scanning device is equipped withsingle-coordinate rotatable platform based on a rotating fosided mirror prism makes it possible to reference it to a fixpoint on the earth. The platform provides framewise scning in a 90° angle; i.e., when it is used, the device formultispectral images in a visual field of 90°3120°. Theframewise scanning rate can be varied from 5 to 60 frasec. The use of a single-coordinate platform broadensfunctional possibilities of the scanning device in terms ofuse in terrestrial experiments, including the formation odatabase on the baseline situation and the study of the inmation content of the correlation attributes of objects invisible and IR regions of the spectrum.

An original program was developed for the combin

FIG. 3. Block diagram of hardware–software package.

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processing of IR and visible images, involving the constrution of a synthesized image in the form of a map of estimaof the correlation~linear regression! coefficients. The pro-gram was written in Visual C11, using the MFC~MicrosoftFoundation Class! library of base classes.

The input data for the program are a pair of images ofobject or scene in* .bmp format, which are obtained in the Iand visible sections of the spectrum, reduced to the sascale, and brought into coincidence with each other. Eacthe input images is regarded as a gray-scale~uncolored! im-age, in which eight bits per point are used to render the glevel. From the images in the visible and IR regions, a thimage is created by means of a sliding window of a givsize, showing a map of estimates of the correlation~linearregression! coefficients. The output data for the program aimage–maps of the estimates of the correlation coefficieor linear regression coefficients, having the format of* .bmp file, in which eight bits per point are used to rendthe level of the correlation characteristic. The working widow of the program is divided into four parts: the upper lfor the image of the visible channel, the upper right for timage of the IR channel, and the lower left for the correlatiimage–map. The lower right window serves to specify talgorithm for processing and referencing the size of theages. Two parameters are used to specify the algorithm:type of coefficient~correlation coefficient and two linear regression coefficients! and the radius of the averaging apeture. An illustration of an image–map of linear regressicoefficients, obtained by the combined processing of a pof images of the visible and IR ranges, is shown in Fig. 1

A compact optoelectronic scanning device has thus bdeveloped and fabricated that is capable of simultaneoforming several digital images in the 0.4–12.5-mm spectralrange.

The main purpose of the device is digital remote imaing of terrestrial objects and of the underlying surface at atime of day.

A version of the use of the device in terrestrial condtions is envisaged that assumes that it is fixed on a sincoordinate rotating platform. An application program hbeen developed for combined processing of visible andimages with the construction and visualization of a corretion map.

The authors express appreciation to P. A. Medennikfor help in creating the application program for combinprocessing of visible and IR images.

1G. R. Dyer, ‘‘Airborne reconnaissance into the 21st Century,’’ Proc. SP3431, 26 ~1998!.

2L. I. Chapurski�, A. V. Markov, V. F. Mochalovet al., ‘‘Problems in theinformation support of spaceborne, ecology-oriented optical observasystems,’’ Opt. Zh.67, No. 7, 111 ~2000! @J. Opt. Technol.67, 696~2000!#.

3R. D. Mukhamedyarov, ‘‘Aerospace monitoring of the technical statusunderground and above-ground engineering structures,’’ Opt. Zh.69, No.4, 11 ~2002! @J. Opt. Technol.69, 228 ~2002!#.

4E. Agassi and N. Ben-Yosef, ‘‘Relation between thermal infrared avisible/near infrared images of ground terrain,’’ Opt. Eng.36, 862~1997!.

5N. I. Pavlov, Yu. A. Shuba, and V. A. Shevoldin, ‘‘Interconnection of th

232N. I. Pavlov and G. I. Yasinski 

e

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radiance of objects in the IR and visible regions during natural heatchange,’’ Opt. Zh.65, No. 3, 35~1998! @J. Opt. Technol.65, 204 ~1998!#.

6N. I. Pavlov, V. A. Shevoldin, Yu. A. Shubaet al. ‘‘Combined analysis ofimages of scenes in the thermal and visible regions, using physical mels,’’ Opt. Zh.65, No. 12, 113~1998! @J. Opt. Technol.65, 1045~1998!#.

233 J. Opt. Technol. 70 (4), April 2003

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7N. I. Pavlov, ‘‘Nature of image correlation in visible and IR thermranges,’’ Optics Comm.161, 193 ~1999!.

8B. V. Shilin and G. I. Yasinsky, ‘‘Russian multispectral-hyperspectral aborne scanner for geological and environmental investigation—‘VesuvEC,’ ’’ Geol. Remote Sensing1, 337 ~1996!.

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