A Review of the Image Dissector Meteorological Cameras and a View of Their Future

1969 (6th) Vol. 1 Space, Technology, and The Space Congress® Proceedings Society

Apr 1st, 8:00 AM

Edward W. Koeing ITT AOD

Gilbert A. Branchflower NASA, GSFC

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Scholarly Commons Citation Koeing, Edward W. and Branchflower, Gilbert A., "A Review of the Image Dissector Meteorological Cameras and a View of Their Future" (1969). The Space Congress® Proceedings. 3. https://commons.erau.edu/space-congress-proceedings/proceedings-1969-6th-v1/session-16/3

This Event is brought to you for free and open access by the Conferences at Scholarly Commons. It has been accepted for inclusion in The Space Congress® Proceedings by an authorized administrator of Scholarly Commons. For more information, please contact [email protected]. A REVIEW OF THE IMAGE DISSECTOR METEOROLOGICAL CAMERAS AND A VIEW OF THEIR FUTURE

Branchflower Edward W. Koenig Gilbert A. Division NASA Goddard Space Flight Center ITT Aerospace/Optical Maryland Fort Wayne, Indiana Greenbelt,

SUMMARY inches diameter, the Fourth Space Conference, a paper was and the large tube, 2 l/^ During and ERTS programs. presented entitled "The Image Dissector Camera, used in the ATS-F A new Approach to Spacecraft Sensors". This paper. Two daylight The ATS-III and Nimbus-B cameras are shown in is a continuation of that of were discussed in the Figure 3, emphasizing the compact nature cloud cover cameras camera is only They were the Applications such a system, since the Nimbus earlier paper. 12 watts input for Technology Satellite III Image Dissector Camera 12 pounds and required but the Nimbus Image Dissector all tube, video, scan and signal processing (ATS III IDC) and scanning permits System (NIMBUS IDCS). Since the ATS III requirements. Electronic Camera of an imaging system with was initially activated in orbit on November adaptive operation IDC image quality without mechani r 7, 1967, it has sent back to earth more than full control of pictures with near full earth cal shuttering or iris control mechanisms. 1300 cloud cover been demonstrated per picture. The first Nimbus Reliability of such systems has disk coverage of l6 months orbital IDCS flew aboard the illfated Nimbus B which by the ATS-III operation had to be destroyed immediately following activity. lift-off, but launch of the backup booster ATS-III IDC camera aboard Nimbus B-2 is scheduled within a few weeks. This camera was flown aboard ATS-III not so presently being funded much as a scientific experiment as a technolo Development studies are of Space Flight Center on two gical experiment. The ultimate intent, by NASA Goddard sensors, is dissector camera applications. The course, as with all remote earth other image community with addi first is a 5000 TV line camera that is scheduled to supply the scientific The major objective tional information about the earth and its to be flown aboard ATS-F. this system is to supply environment, but the prime objective of of this high resolution capabilities, of the full earth disk from first camera was to demonstrate the cloud photographs limitations, of motion studies can be made. The and possibly discover unknown which cloud nucleus of cloud study involves a three aperture image the image dissector as the second review of the ATS-III IDCS dissector which is being developed as the sensor cover cameras. A camera for earth resources requirements is given in Table I. Performance for e. multi-spectral Sensi The resolution capability of of the camera has been extremely good. applications. by more than 5$ since this system is 2600 TV lines. tivity has not degraded initial turn-on, and resolution is also un changed. The satellite was launched November 5, November 7* REVIEW OF 3MAGE DISSECTORS 1967, and the camera turned on Camera operation and system tests were performed from Cameras are based on a regularly. The camera was used extensively The Image Dissector support of tube that is related to multi March 10 through April lU, 1968, in simple camera ESSA. One of the phototubes, with the added capability tornado watch activities for plier hurricane Abby was obtained of high resolution electronic scanning. A first pictures of of this tube is from the IDC. The camera was also used for diagram of the components of the Apollo 1, showing the photocathode, weather observations in support given in Figure Starting in mid- components, defining aperture, and 7 and Apollo 8 missions. scanning cloud cover pictures from the electron multiplier section. The electron October 1968, deflecting the IDC have been sent in near real time (within scanning is accomplished by if field of electrons from 25 minutes of receipt from the satellite continuously emitted facility the defining aperture. desired) to ESSA's Suitland, Maryland the photocathode past and telephone size in relation to photo- through the use of a WEFAC scanner Choice of aperture show IDC pictures determines the sensor resolution. lines. Figures k through 8 cathode size and from various in the system is a function of the number obtained at various times Noise (ATS-III has ranged from electrons passing through the aperture in satellite locations of to 95° W longitude). a sampling time interval so is also a function ^6° W longitude of the resolution. All of the cameras des to use the opti The prime ground station for the IDC is located cribed here have been designed Wideband and scan methods to attain at NASA's Goddard Space Flight Center. mum size tube elements received at the ratios of 30 to Ho db, with video from the satellite is signal-to-noise station and sent in no sensor related noise in the dark Rosman, North Carolina CDA essentially to GSFC where the data Two tubes are shown in Figure 2, real time via microwave image areas. and recorded on tape tube, one inch diameter, having is displayed on hard copy the smaller processing. been used in the ATS-III and Nimbus B cameras, for later off-line

16-23 To date no efforts have been made to digitize for the ATS-III camera (averaged over the first the data for later expansion and video enhance year). ment. The Spin Scan Camera on ATS-III already had that capability and it was felt that the The Nimbus camera was initially to be a true additional cost required to gain that redundant line scan system, similar to the HRIR, but capability was not worthwhile. ESSA scientists due to the need for wide angle coverage and at Suitland have, though, made cloud motion the desire to retain APT rates, a complimentary movies of the IDC pictures and have stated that scan was conceived. The camera will supply full the photographs are stable enough on a picture- east-west or horizontal scan and complement to-picture basis to allow meaningful cloud mo spacecraft motion to provide the south-to-north tion studies to be made from them. or vertical coverage. By using this method, each picture will image 1600 n mile on a side Since the IDC was described in detail in the with a 1 to 1 aspect ratio, while picture over Fourth Congress paper, and also in the papers lap will be approximately 50$. Ground resolu mentioned in the bibliography, no detailed tion at the subsatellite point will be 1.78 n circuit description will be given here. A simp mile. lified block diagram is shown as Figure 9. Inputs from the spacecraft are power, command, NEW PROGRAMS and clock. The camera contains the image dis sector, a sun sensor for spin rate, and the The completion and operation of the two basic electronics required to synchronize camera ti Image Dissector cameras in the ATS-III and ming and operation with spacecraft spin and to Nimbus B spacecraft indicate the performance retain proper phasing for earth viewing once and quality of these unique sensors for cloud initial phasing has been commanded from the cover imaging. ground. The camera generates one line of video each time the spacecraft rotates. A full The major factors contributing to the usefulness picture contains 1328 lines. North-to-south of this camera approach are: coverage is ih.J degrees which cuts off the polar regions, but full earth coverage is pro Reliability vided in the west-to-east or line scan direc*- Wide dynamic range tion. Resolution is limiting at 1600 TV lines Optimized resolving capability across the earth. Photometrically useful output Long term stability The camera composite output contains frame sync, Adaptability to spacecraft conditions line sync, sun pulse, and video amplitude modu lated onto a subcarrier whose frequency varies Each of these characteristics may be extended in proportion to the spacecraft spin speed. to increased capability for future camera The IDC is, therefore, unique from the Spin systems. The availability of a fully control Scan Cameras not only in that it is an elec led electronic scanning sensor has led to tronic scan device versus a mechanical scanner, consideration of two advanced camera systems; but in that the IDC output contains all of the one, for ATS-F, using a significantly increased frame and line sync information required to resolution for high quality images from syn display the video with a minimum amount of chronous orbit, and another using the flexibility special ground support equipment. of tube design to provide a multi-spectral image from a low orbiting satellite. Both applications NIMBUS IDCS use the full set of characteristics given above, but the approach for each camera is so different The Nimbus IDCS has an output format identical as to be worth consideration. to that of the Nimbus and ESSA APT cameras. It is an eight hundred TV line system with a HIGH RESOLUTION CAMERA line rate of k hz and a video bandwidth of 1800 Hz. The video from the camera will be A contract was received by ITT Fort Wayne in transmitted to earth in real time AM/FM with October 1968 to determine a realistic upper an AM subcarrier of 2^00 Hz and simultaneously limit of resolution for an Image Dissector recorded on spacecraft recorders. The recorder Camera. Based on the results of the previous playback is speeded up 32 to 1 to yield play camera programs and tube developments now in back at AVCS rates over the Nimbus Ground progress, it was estimated that a camera having Stations. Camera resolution is 25$ at 800TV 5000 television lines limiting resolution could lines and the output video has a highlight be developed. This camera would necessarily signal-to-noise of 38 db (p-p/rms). require a larger tube and commensurate improve ments in the electronic systems, but is within Average image dissector photocathode loading for the achievable state of the art. Results of both the ATS and Nimbus Cameras is the same, the study and experimental work on improved but the Nimbus application should be a more sensor tubes indicate that this goal may be severe test of sensor sensitivity with loading met. The resulting camera is expected to have because the camera will be operating hQ% of the the general characteristics given in Table 2. time (daylight portion of every orbit) as opposed The approach was based on the requirements for to an operating time of roughly 5$ of the time an earth imaging sensor for the ATS-F satellite

16-24 satellite is primarily requirement in this case would, therefore, shown in Figure 10. This 5000 over experiment but has room avail suggest a stability of one element in for communications motion of the sat a visible spectrum camera and an infra a twelve hour period. The able for this constant, nor red camera. The availability of a stabilized ellite itself will not be at synchronous altitude will the combined effects of power source and earth-oriented satellite that unit to be optimized for a electronic component drift. We anticipate allows the camera maintained over picture taking interval, resolution, the one element stability may be trade-off of giving accurate to noise ratio, resulting in the a one picture frame interval, and signal to each image. The characteristics given below. geometrical relationships electronic systems will have a goal of one eight hour period. Since the completion of the Nimbus and ATS-III element stability over an the capability of the Matching techniques similar to those used on development programs, have have improved dramatically. In Spin Scan and IDC images in the past will sensor tubes photographic the photocathode, originally an Sll to be applied to obtain successive particular, for cloud motion with an average sensitivity of 30 microamperes image registration suitable per lumen, was considered to have a lifetime of studies. with a loading factor (average contin one year Dissector Camera is uous current emitted) of 3 microamperes per The versatility of the Image We have now established expected to be used for an added purpose in this square centimeter. to ground dis techniques of forming multi-alkali photocathodes application as a means to adapt typical resolving with low resistivity that provide sensitivities play equipment having more per lumen and will capacity. This will be achieved by controlling of more than 150 microamperes less year with 10 microamperes per the electronic scan of the camera to cover operate for a the scan centimeter. At the same time, these than the complete earth disc. Since square in nature, it is surfaces have greatly improved red response, system is completely digital haze filtering for higher con possible to command the camera to start scanning allowing better and scan a earth scenes. Other improvements in at pre -selected points in the image trast in a shorter quality of construction and better electron raster of 100 elements on a side structure add to the space worthy time interval than the nine minutes used for multiplier arriving at nature of the sensor system. The size of tube full earth scanning. These images, program is shown in Figure 2. the 20 seconds per frame, would show typical to be used in this and in the use of the information from cloud cover over half of the US in one image Activities meteorological the High Resolution Camera have grown also. be immediately available for For the past experiment Mr. Branchflower of analysis. Flight Center acted as the NASA Goddard Space for a investigator. In the present program, The combining of optics and electronics technical be installed in Mr. Branchflower and Mr. Werner of NASA will self contained camera that may Co-Investigators, but Mr. the ATS-F spacecraft results in a package that remain Technology require a F. Hubert, Chief, Synoptic Meteorology will weigh forty pounds or less and Lester less. Although Branch, NESC, will be Principal Scientific power input of twenty watts or for the program. Data from the the camera uses a 2 "L/'k inch diameter tube Investigator the present will be used for cloud motion studies and compared to the one inch tubes of camera size is still only other experiments under their control. cameras, the total package half of a cubic foot in volume. The absence of requirements, characteristics of motorized scanning or iris control and the Of the various the concern are resolving power and stability. absence of mechanical shutters maintains most It is anticipated Resolution of 5000 elements in 1.5 inches stability of the spacecraft. per inch. The test that the camera will meet or exceed the goals requires 3300 elements suitable in Figure 11 demonstrate the achieve given and provide high quality images patterns a continuing ment of 3200 television lines per inch at for cloud cover analysis and greater than 10$ modulation at the center of the meteorological program. tube and approximately 2600 lines per inch at MULTI-SPECTRAL CAMERAS the position corresponding to the edge of the earth image. It is anticipated that these Perhaps one of the more interesting applications figures will be maintained or improved upon of the Image Dissector camera is its potential during the development of an operational system. use as an Earth Resources sensor. Calling on the adaptive nature of the basic tube concept, Perhaps just as important to the meteorologist it is possible to generate continuous output is the stability of the image as it is trans signals corresponding to three colors of the lated from an optical input into the transmitted scene. This is possible using a single sensor signal and finally received and used as the tube with the approach shown in Figure 12. ground station. In order to make use of the one From the earth stabilized ERS satellite the mile resolution of a cloud element, and to make Multi-Spectral Camera scans the scene in a line possible cloud motion studies, it is desirable to scan, generating a continuous strip image of the maintain geometric positions to this accuracy earth over which the satellite passes. over a significant time period. The maximum Color information is generated from the image as

16-25 is lost if the images it is focused on the photocathode of the two The value of the equipment Since the sensor converts all are not consistent from image to image. The inch sensor tube. this stability input into an electron image, it is able Image Dissector Camera can provide light and a single optic to view a continuously changing scene without since it uses a single lens, exposed only during the short time system with no intermediate color separation smear, being stability of in which an element of the scene is filters, wedges, or mirrors. The interval bands as three adjacent sampled by the electron aperture. Separation the color separation is performed by the three strips mounted directly on the tube faceplate of output signals by thermal or apertures that replace the single eliminates disturbance caused sampling The absence of mechanical aperture of the high resolution camera. Each structural changes. electron multiplier, shutters is made possible by the instantaneous aperture has its own only its signal from the others. action of the phot©emitting surface. The completely separating of the scene in the apertures is critical since it is smear is that caused by movement Spacing of which one element is separation distance that determines the the 2 microseconds during the motion is less than one registration of the three looks. We predict an being sampled. This inches between foot, so it is negligible. In the same sensor, effective spacing of only 0.015 tube, of 20 scan lines. To using the wide dynamic range of the sensor apertures, the equivalent accurate an individual color identity, it is possible to maintain extremely give each aperture varying the amplifier scanning methods are set such that photometric information by the tube and the need for a motor driven one aperture scans the area slightly ahead of gain, eliminating vertical, one scans vertical, and one slightly iris. the off-axis angles being only 2.5 behind, tube output the image data will be minutes of arc. From the simultaneously amplified and provided as to the transmitter. Simple filters on the faceplate of the camera parallel outputs Color techniques will insure accurate time tube provide the separate inputs to the three multiplex .015 inches wide referencing of the data such that display apertures. Strip filters only time can be light activating systems receiving the data in real may be used to restrict the the precise time regions sampled by the recording the color image at the photocathode for the the scene. Since possible only in a line scan that the camera, is viewing apertures. This is for recording or trans since the image is being broken into the vodeo bandwidth system, is only 150,000 Hz per channel, the strips along which the detection process takes mission total signal can be carried over a 1MHz or less place. transmission bandwidth without channel inter ference. In the normal Image Dissector process, the electrons from all parts of the photocathode Camera show that plane Studies of the Multi-Spectral are accelerated to the aperture can be provided in a Since the three apertures are these characteristics simultaneously. that is compact and reliable. The to receive the electrons from the three camera spaced reliability of the approach has been generally respective bands, the electron beam is de in which filter bands demonstrated by the flight of ATS-III flected along the direction of the very well for its respective a similar camera has operated so that each aperture reads only the ERS camera will have scan is required over 15 months. Since color signal. No orthogonal sensor tube, no mechanical of the spacecraft moves the only a single since the flight and relatively simple electronics, across the bands in turn. activators images we can anticipate nearly the same lifetime the it is performance. In mechanical structure, Although the process appears complex, version of the promotes a high camera will be an enlarged really simple and particularly shown earlier, having dimensions between the look angles of Nimbus B Camera degree of stability of approximately five by eight by thirteen inches. the various apertures. All information lens, this will is con Since the camera uses a single generated by the sampling apertures provide maximum set of be as large as practical to trolled by a single lens and a single as large as ten inches The position of sensitivity. A lens deflection and focus coils. may be used. Total weight of the cam remains fixed in the field of diameter the three apertures sensor and electronics is only thirty constant corrections can be era view, such that pounds, while the lens itself may exceed this to make element by element registration. applied weight. By keeping the aperture separation small, mis attitude motion registration due to spacecraft CONCLUSIONS can generally be ignored. Comparing this color of a three tube registration stability to that made at the Fourth Space Con normal color television, The predictions system, such as used in of the technical feasibility and poten as the resolution gress becomes most important future use of the Image Dissector Camera figures used for this program. tial increases to the appear to be coming true. Results from the Resolution of color images having over 2500 in the life by first program have been dramatic elements per line could be severely degraded the ATS-III IDCS and its and require time in orbit of loss of registration stability output of useful meteorological pictures. demands on ground station steady nearly impossible Global coverage of cloud pictures are now equipment for compensation, if possible at all.

16-26 readily available to potential users. An increased resolving capability and multi- spectral output are possible with the use of improved sensor tubes and equipment technology. The ability to apply such information has grown also during this period, allowing such experiments to become increasingly significant. The combined effort of NASA, ESSA, and in dustry to capitalize on improved sensor tech nology will aid major areas of environmental research and application. ACKNOWLEDGEMEINT

The effort reported was performed under direction of Systems Branch, NASA Goddard Space Flight Center on contracts NAS5-9619, WAS5-9671, NAS5-11617, and NAS5-ll6l8. Reports available on these programs include:

Branchflower, G. A., and Koenig, E. W., The Image Dissector Camera, A New Apporach to Spacecraft Sensors, Proceedings of Fourth Space Congress, April 3-6, 1967.

Branchflower, G. A., Foote, R. H., and Figgins, D. A., The Applications Technology Satellite Image Dissector Camera Experiment, NASA TN D-4186.

Branchflower, G. A., Image Dissector Camera Experiment, Applications Technology Satellite Technical Data Report, Section 8.5, (WASA/GSFC).

16-27

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16-30 Figure ^ IDG Picture Taken On the Day of Initial Activation, 7 Kover^ber 1967, Spacecraft at ^7° W Longitude.

16-31

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16-37 Figure 11

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