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New progress of airborne scanners at sitp from 1986 to 1990

Xue Yongqu, Shen Mingming, Yang Cunwu,
Wang jainyu, Guo Yiping
Shanghai Institute of Technical Physics, Academia Sinica,
Shanghai 200083, China


Abstract
This paper describes some new airborne scanner systems manufactured at SITP in the recent five years. The spectral resolution of the sensors has become higher. The installation of bands is more complete and has formed series. The onboard electronics has made progress on multiple, high speed, large content, automatic operation and flexible function. The ground preprocess facility provides fast reproduction, information transfer, process service, and standard products the Computer Compatible Tape (CCT). The whole system lays stress on total effect, generalization and standardization. And standardization. A fair technical system with complete units from getting data to standard products in multispectral remote sensing has been formed. Some typical applications are also introduced here.

Introduction
Since 60's, the SITP has obtained a big achievement in scanning image based on the infrared detect technology. Some infrared image systems were successfully made. Because of the research ability in optical remote sensing, the SITP has been taking part in some important plan on scientific and technology. The airborne spectral scanner DGS completed in 1986 was the representative work in that period. Since 1986 the study of airborne optical remote sensing instruments has developed in quality and range. this paper introduces the development of airborne scanners at the institute during recent five years and some application examples.

Sensors
There are two developing directions for the sensor.
One is in the technology itself. The spectral bands should be more complete. The spectral resolution and space resolution should be higher. The instrument will be developed towards resolution and space resolution should be higher. The instrument will be developed towards image spectrometer. The AMS has 16 bands in VIS/NIR and 3 bands corresponding to the 5th, 6th, 7th, CH of TM. The thermo-infrared multispectral scanner TIMS with 7 bands in the range of 8.2-12.2 micron was also manufactured. Through pre-research a test model of image spectrometer 64 CH VIS/NIR SCANNER is being built which is convenient for practical application for its large total FOV.

The second direction is in the specialization of instruments. we had finished the UV/IR 2 CH ACANNER for sea pollution monitoring and the VIS/NIR 3CH SCANNER for forest fire detecting.

Tab. 1 shows the specifications of these scanners and a comparison with the scanner DGS.

Scanners Completed in 1986-1990
Table. 1
Sensor DGS Multi-spetral
scanner		 19CH AMS 7CH TIMS 64CH Prototype
Scanner		 UV/IR 2CH Scanner VIS/NIR/TIR
3CH Scanner
Application Multipurpose
Remote Sensing		 Multipurpose
Remote Sensing		 Multipurpose
Remote Sensing		 Multipurpose
Remote Sensing		 Pollusion Monitoring
on sea		 Forest Fire
Detecting
Tot. View of Field 100 degree 90 degree 90 degree 90 degree 100 degree 100 degree
Ins. View
of Field		 3 mrad 3 mrad 3 mrad 1.5 mrad 3 mrad 3 mrad
Scan Rate
(C/S)		 25-100 20-50 10-30 10-20 100 100
Optical Area 52cm2 52cm2 200cm2 200cm2 64cm2 52cm2
Focal Length 666m2 666m2,217m2 180m2 180m2 800m2 666, 217m2
Scan Mirror 4 Sided Mirror 4 Sided Mirror 45 Degree Mirro 45 Degree Mirror 45 Degree Mirror 4 Sided Mirror
Working Bands(um) 0.40-0.43
0.43-0.48
0.48-0.54
0.53-0.62
0.60-0.70
0.68- 0.90
3.0-5.0
or TM 1,2,3,4,5,7
ALL 8CH		 16 Bands in
0.46-1.1
1.55-1.75
2.08-2.35
8.0-12.5
ALL 19CH		 8.2-8.6
8.6-9.0
9.0-9.4
9.4-9.8
9.8-10.6
10.6-11.4
11.4-12.2
ALL 64CH 		32 Bands in
0.465-1.1
16 Bands in
1.40-1.82
16 Bands ln
1.98-2.40
ALL 64CH		 0.28-0.38
8.0-12.5		 0.4-0.8
3-5
8-12.5
Detector & Working
Temperature		 PMT Insb(77k) Si Line Array
HgCdTe(77k)		 Si Line Array
HgCdTe(77k) Line array		 Si & HgCdTe(77k)
Line Array		 PMT HgCdTe(77k) Si HgCdTe(77k)
Record & Display Multi-Channel
Analog Tape,
CRT Display,
Film Reproducing		 Analog Tape,
Laser-desk,
Multi-colour Real
Time Display		 Same as Left Same as Left Analog TApe,
Multi-colour Real
Time Display,
Film Reproducing		 Multicolour
Real Time
Display Transmission
in TV Format
Flying Paramenter No Display & Record Display & Record Display & Record Display Display
On-board
Pre-processing		 No Programmable
in Bands		 Programmable
in Bands		 Programable in Bands & Space No No
Completed Data 1986 1990 1990   1987 1987

  1. 19CH Scanner - AMS

    The scanner equally divides the spectrum of 0.46 - 1.1 micron into 16 bands. If necessary such bands can be grouped to form some channels of TM, MSS or HRV. Because of the complete bands visible to infrared to scanner is convenient to resources investigation. The optics is shown in Fig. 1. A Kennedy structure, which has high scan efficiency, is used for ground scanning. A two-mirros telescope converges the energy. The optical path is improved: the two split light beam do not meet each other at the symmetry line of the primary mirror , but are separated at a certain distqance, so the effective optical area is increased. For the second mirror, the front surface is coated with a long wave pass film and the rear surface having a curvature is coated with an antireflection film. The infrared focus is formed through the second mirror. The energy left, which is reflected by the second mirror, passes the filters to get all the bands. The radiation in 0.46-1.1 micro enters the spectrometer, is collimated by a parabolic mirro, and falls on the plane plaze grating with a blaze wavelength of 0,7 micro. The detector array is located on the focus position of the converging lens.


  2. 7CH Scanner -- TIMS

    Having 7CH in thermo-infrared and detecting the spectral feature of rock and mineral, the scanner is useful for geology remote sensing. It uses a slant 45-degree rotative morror for scanning. The main optical unit consists of a primary morror and a collimating mirror. Both of them have a parabolic surface with a common focus at the field stop. Such arrangement is beneficial to block design and assembly of the dispersive unit, and meets the requirement of onboard space. An infrared blaze grating with blaze wavelength of 9.0 micron is used as the disperse element. The converge unit is a specially designed Ge-lens having a FOV of 4.91 degree and F/No of 0.78. The optical diagram and the sizes of the detector array are shown in fig. 2.


  3. VIS/NIR 64CH Scanner Test Model

    This pre-research test model for image spectrometer co-uses the main optical unit of TIMS. A. Long wave pass filter separates VIS from NIR. In spectrometer I, with operation band of 0.46-1.1 micron, a concave holographic grating performs dispersing and converging. there is a special filter on the surface of the 32-element Si detector array to remove the high-order spectra. In spectrometer II, designed in 1.46-2.4 micro, the dispersive element is a plane blaze grating having blaze wavelength of 1.6 micron. The grating sways back and forth between two positions synchronously with scan line and stays at each position for a scan line. So the 16 detector elements can cover 32 bands. The rotative angle of the grating is 3.55 degree. The location precision is better than plus and minus 1.5 minute. The rotative rate is not higher than 10 c/s. The system diagram is shown in Fig.3.


    All the above-mentioned sensors employ optico-mechanical object space scanning to eliminate the defect of smaller swath in broom brush scanning. It is good for practical air borne remote sensing work. They also have to optical angle encoder to perform a sample in equal angle which is necessary for data processing.
Progress of onboard electronic system and data pre-processor
Practicality, convenience, completion and flexibility are the main features of the electronic system. It has ability to receive, process, monitor and record the remote sensing information, and it can administer and control the sensor.

Fig. 4 is a diagram of the onboard electronic system. After a series of analog processing, the original signal, which is received by the sensor, is changed into digital signal by an A/D converter. Then it is formalized as format of band interleaved by one pixel by formatter and added some auxiliary parameters which include status of airplane and sensor, time data etc.. Lastly it is sent out by a high-speed data port. A real-time monitor can display multicolour multiband remote sensing image during collecting information. The pre-processor has the functions of spectral and spatial programs, which can increase the signal to noise ratio and decrease the data rate. There are two methods of data recording:
  1. Multi-channel analog tape recorder can simultaneously record multi-channel analog signal, which is output from the data adopter or data pre-processor.

  2. 12' large content (2G) Laser Disk can directly record digital signals, which have been formalized or processed.

All operations on the instruments are programmable. Operator can input the command on fore-panel of instruments or from main controller.

Data Adopter: It is compatible for four-sided scan mirror or 45-degree scan mirror, and for 1.5 mrad or 3 mrad instantaneous field of view. The numbers of channel can be selected as 2, 4, 8, 16 or 32. Twin data adopters will be synchronously used if 64 channels are needed. The parameters of programmable filter are automatically set based on the working status of the scanner. In the programmable amplifier, eight gain of are available which can be automatically set depending on the scale of input signal, or fixed by main controller.

Formatter: The format of output data is band interleaved by one pixel (BIPI). Synchronous signals of line and word are also sent out.

Real-time Monitor; The resolution power of the monitor is 5128512 pixles. The function of monitor is as follows:
  1. Monichrome display or multicolor display of monochannel image density splitting.

  2. pseudocolour compound image display of -2 or 3 channels.

  3. Synchronous monochrome display of 1,2,4,,8,16 or 32 strip image

  4. Synchronous display of auxiliary p[parameters when image is displayed

  5. Calculating the histogram of image.
Ground data pre-processing system
The main tasks of ground data pre-processing system are management and classification for original multi-band image data of air-borne scanners. It produces computer compatible tape (CCT), as well as other pre-processing which includes image partition, bands registration, radiometric correction, and geometric correction. The system also has ability to do some special research. CCT Appliance: This is main input equipment in the system. It can change multi-band analog tape or high-density digital tape (HDDT) into CCT. The format of CCT in a line is BIPI. In order to increase the efficiency of the system. CCT is produced without the main computer.

Multi-band Image Monitor: It is used to examine original image and CCT image or to monitor the image quality in producing CCT.

Apart from CCT, The film of reproduction from analog tape, photography of CRT and monochrome hard copy of CRT are also available.

Applications
The sensors presented above have had successful application in environment investigation, pollution surveillance, fire detection of forest and other fields.
  1. Hydrology

    Shanxi province used AMS multiband imagery to research the hydrological problems of the Shenmu Coalfields, The hydrological surface features, such as springs, surface water and damp soil, could be evdently located in the thermal infrared images and their parameters, including the area, shape and length, could been indentified. It was proved that the total number of springs in the whole area was 311, twice about that shown in the old topographic map. According to the spring tone, the stripe density and the analysis of main flow, the classification of spring flux has been made. In addition, 7 strata have been classfied.

  2. Archaeology

    By interpreting the multiband image with the aid of other ways, the blindness which exits generally in archaeological work due to the lack of prediction could been prevented. Through examination of he thermo-image of the lack of prediction could been prevented. Through examination of the thermo-image of the QinShihuagn mousoleum in Qin Shihuang, Lintong County; Shanxi Piovince, 2 thermal abnormal layers which surround the sealed soil of the tomb and have regular shape can be found evidently. They are considered to be the ruins of the inner and outer city walls of the tomb. There is a thermal abnormal strip inclined above the spot between the Qin Mausoleum and the Exhibition of Warrior Figures of Qin Dynasty, it is vgelieved that it was the remmed dike to prevent the tomb from floods. The material proved to be valuable.

  3. Geology and Mineral Exploration

    The remote sensing applied in geology is based on the spectral features of rock and mineral. It is possible for the airborne scanners covering he spectrum from VIS to TIR to acquire the spectral characteristics and to determine the altered bands that most likely contain mineral deposits. In fact, the scanners have been applied in Guilin, Chende and Xinjiang Province many times to explore the gold, multimetal, coal and petroleum resources. A large amount of data have been obtained, which are very useful to rock classification , getting information of altered band and determination of the mineralized region or the exploration target area.

  4. Polluting Mointoring

    It is reported that remote sensing of pollution monitoring with AMS in the Yangzi river mouth has been completed successfully. The results show that 0.53-0.62um, 0.60-0.70um and 8-12.5um are the optimum bands for pollution monitoring. The pollution distribution map, pollution isogram and typical thermal and oil pollution maps in Shanghai west region, south region and Wusong estuary have been made. Based on these maps, the pollution grade, and diffusion area and diffusion path at the 3 drainages for two temporal, high and low water means, have also been evaluated.

    The UV/IR scanner developed in 1987 has been the major device in the ocean surveillance system and taken an important part in oil pollution detecting since it served the national ocean law enforcement flight. fig. 5 is a photography obtained by the UV/IR scanner for oil pollution monitoring.


  5. Oceanography

    To guarantee the shipping and petroleum exploring on sea, it is absolutely significant to know the rule about sea ice, its formation, distribution and movement. In 1986 and 1987 AMS acquired large scale and continual multi spectral images of sea ice int he Bo Hai Sea for the research of ice conditions and provided important materials for the organizations of sea engineering.

  6. Forest Fire Detection

    The VIS/NIR/TIR scanner, with a real-time transmission device and the Cessna Citation aircraft form an fores fir detecting and transferring system. In an emulating experiment, it could detect 1 square meter of fire at the altitude of ten thousand meters and transfer the images to the ground commander center. Fig. 6 shows a pseudocolour compound image for forest fire detection.

Conclusion
With the development of Remote sensing, sensor technology will proceed continually. Of all the airborne optical sensors, scanner is the major set to get information because it obtains the image having a large amount of information contents directly. Otherwise the scanners have formed a series with complete bands and high resolution. The development is towards image spectrometer. Having integrated units, the scanner system possesses a total capacity from getting information to providing standard products. Airborn scanner system will certainly be applied successfully in an increasing number of fields.

References
  1. Guo Yiping, of the 6th National Conference on Remote Sensing (1989), P22.

  2. Shen Mingming et al., Proc. of the 6th National Conference on Remote Sensing (1989) , p20.

  3. Wang Jianyu et al., Proc. of the 6th National Conference on Remote Sensing (1989), p13

  4. Guo Yiping, Proc. of the 6th National Conference on Remote Sensing (1989), p110.

  5. Wang Jianyu et al., Proc. of the 6th National Conference on Remote Sensing (1989) p 97.

  6. Ye Anqi, Proc. of the 6th National Conference on Remote Sensing ( 1989) p107.

  7. Tong Qingxi and Xue Yongqi, Proc. of the 5th national Conference on Remote Sensing. (1988), p12

  8. Shen Mingming and Sun Jixu, Proc. of the 5th National Conference on Remote Sensing (1988), p 12

  9. Shen Mingming, Mao Peifen and Xue Yongqi, Proc. of the 8th Asian Conference on remote Sensing (1987), E-8-1.