Lucky imaging technology is a post-processing technique for eliminating the influence of atmospheric turbulence in astronomical images to obtain high-resolution images. Reconstruction usually realized by using a desktop computer system. However, this post-processing method based on CPU can’t meet the real-time requirements of some astronomical observers. Based on a prototype of a FPGA-based lucky imaging system developed with our laboratory, a technical solution of lucky imaging technology based on Gigabit Ethernet is presented in this paper. The original short exposure images can input into the FPGA-based lucky imaging system via a Gigabit Ethernet interface. Some functional modules related to data transmission through Gigabit Ethernet are designed, and the lucky imaging processing and VGA display modules in the prototype system are transplanted. After all these works, a new lucky imaging processing system which is based on Gigabit Ethernet, has been built. This paper will firstly introduce the design methods and the implementation techniques of the Ethernet receiving module, FIFO module, DDR3 module, and the transplantation methods for the s election module, registration module, superposition module, and display module. The observed short exposure images are sent to the FPGA system by an image workstation via Gigabit Ethernet. The software in the workstation is developed in C#. The programming method is also introduced in this paper. Experiments show that compared with the old prototype system, the total time for processing 1,000 short exposure images is reduced from 42 seconds to about 10 seconds, and the real-time performance of the new system is improved.
In order to improve the real-time and portability of the moving target detection and tracking (MTDT) system, a compact FPGA-based MTDT system is built in this paper by using the parallel computing and flexible programming of Field Programmable Gate Array (FPGA). In order to realize the detection and tracking of moving targets on resource -constrained FPGA, some MTDT algorithms is analyzed firstly, and appropriate modifications were made without changing the basic principles to make it adapt to the limited logical resources of the Xilinx Spartan -6 series of FPGA chip selected in this design. Then the FPGA system is composed of four units: the image acquisition unit, the image storage unit, the image pre-and post- processing unit and the image display unit. Two image difference methods, an inter-frame and a background difference method, are implemented in the system. Finally, the moving target can be directly indicated on a video graphics array (VGA) displayer in the image display unit. The test results show that the system can detect and track a single target in real time in various resolutions at various frame rates, i.e. VGA @30fps and 15fps, 720p @15fps.
KEYWORDS: Cameras, Electron multiplying charge coupled devices, Computer programming, Clocks, Field programmable gate arrays, Image transmission, Control systems design, Manufacturing, Software, Software development
This paper presents an appropriate solution for self-developed EMCCD cameras based on Camera Link. A new interface
circuit used to connect an embedded processor Nios II to the serial communication port of Camera Link in the camera is
designed, and a simplified structure diagram is shown. To implement functions of the circuit, in the hardware design, it is
necessary to add a universal serial communication component to the Nios II when building the processor and its
peripheral components in the Altera SOPC development environment. In the software design, we use C language to write
a UART interrupt response routine for instructions and data receiving and transmitting, and a camera control program in
the slave computer (Nios II), employ a Sapera LT development library and VC++ to write a serial communication
routine, a camera control and image acquisition program in the host computer. The developed camera can be controlled
by the host PC, the camera status can return to the PC, and a huge amount of image data can be uploaded at a high speed
through a Camera Link cable. A flow chart of the serial communication and camera control program in Nios II is given,
and two operating interfaces in the PC are shown. Some design and application skills are described in detail. The test
results indicate that the interface circuit and the control programs that we have developed are feasible and reliable.
EMCCDs have been used in the astronomical observations in many ways. Recently we develop a camera using an
EMCCD TX285. The CCD chip is cooled to −100°C in an LN2 dewar. The camera controller consists of a driving board,
a control board and a temperature control board. Power supplies and driving clocks of the CCD are provided by the
driving board, the timing generator is located in the control board. The timing generator and an embedded Nios II CPU
are implemented in an FPGA. Moreover the ADC and the data transfer circuit are also in the control board, and
controlled by the FPGA. The data transfer between the image workstation and the camera is done through a Camera Link
frame grabber. The software of image acquisition is built using VC++ and Sapera LT. This paper describes the camera
structure, the main components and circuit design for video signal processing channel, clock driver, FPGA and Camera
Link interfaces, temperature metering and control system. Some testing results are presented.
A new astrometric telescope, Multi-Function Astronomical Transit, has been built in Yunnan Astronomical Observatory.
Its main imaging device is a digital CCD camera without refrigeration because the telescope is only used to observe stars
brighter than 7.5mag. As an astrometric telescope like the Lower Latitude Meridian Circle, some special errors from the
horizon and the altitude axis of the telescope must be measured. Thus two analog CCD cameras are used. The digital
camera is connected to a digital frame grabber via a Camera Link cable and a custom-made cable, while the two analog
cameras are connected to an analog frame grabber by two custom-made cables. The two frame grabbers are separately
mounted in two image workstations and operate in external trigger mode. Two trigger signals are generated by the
telescope control system, one for the digital camera, another for the two analog cameras. The software of image
acquisition is programmed using VC++ and Sapera LT. This paper presents an imaging system solution for the new
transit, programming methods and the test observation results.
With the advance of the PFPA technology, the design methodology of digital systems is changing. In recent years we
develop a method to implement the CCD timing generator based on FPGA and VHDL. This paper presents the principles
and implementation skills of the method. Taking a developed camera as an example, we introduce the structure, input
and output clocks/signals of a timing generator implemented in the camera. The generator is composed of a top module
and a bottom module. The bottom one is made up of 4 sub-modules which correspond to 4 different operation modes.
The modules are implemented by 5 VHDL programs. Frame charts of the architecture of these programs are shown in
the paper. We also describe implementation steps of the timing generator in Quartus II, and the interconnections between
the generator and a Nios soft core processor which is the controller of this generator. Some test results are presented in
the end.
In the optical position observations to the near earth objects, the differential measurement methods are commonly used to
improve positional accuracy, in which the object positions are calibrated by the star positions. However, due to the
characteristics of motion of the observed object and the restrictions on current CCD imaging technology, single
measurement accuracy of these methods for the object is not high. This is because there is relative motion between the
calibration stars and the observed object in the field of view of the telescope. This paper analyzes characteristics of
relative movement of the space objects on the Geosynchronous Earth Orbit and the stars in the field of view of an
equatorial telescope, and CCD imaging effects for these objects and stars, then present a new CCD imaging technique for
moving objects and stationary objects. One half of the CCD photosensitive area is used to acquire images of the moving
objects in the field of view in drift scan mode, the other half to take simultaneously images of the stationary objects in
the field of view in stare mode. Discussions about possibilities for developing this camera and its applications are
presented. A prototype camera controller has been developed in our laboratory. The paper also describes the structure of
the camera controller, the implementation method and skills, and some experimental results.
The FPGA with Avalon Bus architecture and Nios soft-core processor developed by Altera Corporation is an advanced embedded solution for control and interface systems. A CCD data acquisition system with an Ethernet terminal port based on the TCP/IP protocol is implemented in NAOC, which is composed of a piece of interface board with an Altera's FPGA, 32MB SDRAM and some other accessory devices integrated on it, and two packages of control software used in the Nios II embedded processor and the remote host PC respectively. The system is used to replace a 7200 series image acquisition card which is inserted in a control and data acquisition PC, and to download commands to an existing CCD camera and collect image data from the camera to the PC. The embedded chip in the system is a Cyclone FPGA with a configurable Nios II soft-core processor. Hardware structure of the system, configuration for the embedded soft-core processor, and peripherals of the processor in the PFGA are described. The C program run in the Nios II embedded system is built in the Nios II IDE kits and the C++ program used in the PC is developed in the Microsoft's Visual C++ environment. Some key techniques in design and implementation of the C and VC++ programs are presented, including the downloading of the camera commands, initialization of the camera, DMA control, TCP/IP communication and UDP data uploading.
Charge transfer efficiency (CTE) is a very important characteristic parameter for the CCD in the scientific imaging applications, especially in the imaging systems used to observe very faint objects such as night astronomical cameras. Several popular CTE measurement techniques are introduced briefly in this paper, deficiencies in the techniques are pointed out, and then some improvements are made. The modified algorithm for CTE measurement is based on the x-ray transfer and the MATLAB. When the algorithm begins, an appropriate initial charge transfer line from the x-ray single-pixel-events plot and its interzone for computation are determined by the user-PC interaction, and then a linear fit is performed in the interzone so as to get a more accurate transfer line. Thus a new interzone is obtained and a next linear fit can be done. In this way, a more accurate value of CTE can be obtained. Usually the algorithm stops after 5 to 10 iteration steps. Moreover the accuracy of the algorithm is discussed. Finally, the algorithm is used to estimate the horizontal CTE for 2 KAF-4301E CCDs tested at low temperatures. The results indicate that, when the CCD operating temperature is reduced below its absolute minimum rating, although the dark current performance improves obviously, the CTE performance degrades rapidly. An analysis and discussion for the results at the depth of theory is presented.
Since several hundreds of CCD images are obtained with the CCD camera in the Lower Latitude Meridian Circle (LLMC) every observational night, it is essential to adopt an automatic processing method to find the initial position of each object in these images, to center the object detected and to calculate its magnitude. In this paper several existing automatic search algorithms searching for objects in astronomical CCD images are reviewed. Our automatic searching algorithm is described, which include 5 steps: background calculating, filtering, object detecting and identifying, and defect eliminating. Then several existing two-dimensional centering algorithms are also reviewed, and our modified two-dimensional moment algorithm and an empirical formula for the centering threshold are presented. An algorithm for determining the magnitudes of objects is also presented in the paper. All these algorithms are programmed with VC++ programming language. In the last our method is tested with CCD images from the 1m RCC telescope in Yunnan Observatory, and some primary results are also given.
Star image tracking in the LLMC is composed of two direction movements, that is, a horizontal tracking of the CCD chip (camera) and a vertical tracking of the telescope tube in the zenith distance. Based on an idea that the two tracking control systems should be incorporate. A new hardware structure of tracking control system in the LLMC is presented in this paper. The system can simultaneously output two gates of motor driving pulses, one for the CCD tracking in horizontal direction and another for the tube tracking in vertical direction or for the slow motion placement of the tube in vertical direction. Experiments indicate that the driving pulses output from the new system can be controlled more easily than those from old systems in software mode and its frequency can be higher. The programming methods for the ASM control program in the micro-controller system and for the C++ control program in the host PC are described. Some primary results and experiences from the experiments are also presented in the last.
KEYWORDS: Signal processing, Collimators, Microscopes, Electronic filtering, Filtering (signal processing), Telescopes, Signal to noise ratio, Observatories, Reticles, Algorithm development
The functions and characteristics of the 1st to 9th Reticon signals used to measure positions of reticle/slit images in the LLMC are described in this paper. According to their characteristics, we present a new method to process these Reticon signals, which consists of a filtering algorithm and a centering algorithm. The filtering algorithm is developed to process the 5th to 9th Reticon signals, because in these signals there are obvious disturbance components caused by the background light in the microscopes. An auto-estimating technique is developed to estimate and eliminate the disturbance signal of the background light by a piecewise-linear fitting. The centering algorithm is used to determine the positions of all the reticle/slit images in 3 steps. The first is to search all the wave crests and troughs of a Reticon signal, the next is to determine a threshold for each wave and then to center the wave by a modified moment method so as to get the position of the reticle/slit image, and the last step is to average all the position data of the waves in a Reticon signal to get an integrate position data of a group of reticles/slits in the corresponding reading microscope. The technique of implementation of the method in C++ programming language is also described in the paper.
Two data acquisition systems of the Lower Latitude Meridian Circle (LLMC) are described in this paper, of which one is based on a video CCD and the other is based ona scientific CCD. To determine the position of a celestial body absolutely and precisely, the LLMC is equipped with several precision measurement devices such as one precision clock, nine Reticon linear photodiode arrays, one video CCD, one scientific CCD, one rotary inductive synchronizer, and one grating linear displacement transducer. To control these devices properly and collect data from these devices orderly during observations, two data acquisition and control systems are developed. The one based on a video CCD is used to test the instrumental precision of the LLMC. The other based on a scientific CCD is used for normal observations, and is composed of three subsystems. We will illustrate the functions of the measurement devices in the two systems, discuss the methods of data acquisition, and present our thoughts about software programming in the paper.
KEYWORDS: Control systems, Microcontrollers, Process control, C++, Switches, Control systems design, Sensors, Adaptive optics, Stepper motor drivers, Observatories
A new control system of the azimuth transmission mechanism used in the Lower Latitude Meridian Circle (LLMC) is described in this paper. Because the original azimuth transmission mechanism causes too much vibration during the transposition of the horizontal axis of the instrument, we decided to modify the original system by two ways. One is to modify the lift mechanism and the azimuth transmission mechanism. The other is to replace the original stepper motors with a new type of stepper motor. According to the requirement of the new motor and its sine subdivided microstep driver, the original control system has been modified. The new system has an expansion output board and a new control program compared with the original one. The hardware architecture of the new system is described. The program in the single chip microcontroller is written in ASM, which is composed of 10 subroutines. The program in a host PC is written in C++. The methods using in controlling motors and skills in designing these programs are discussed. Two sketch flow charts of the control program are presented in the paper. Modification of the lift mechanism is also introduced. All this works make the vibration very slight.
KEYWORDS: Control systems, Microcontrollers, Process control, C++, Charge-coupled devices, CCD cameras, Signal processing, Lead, Computer programming, Control systems design
A control system of the vertical angle transmission used in the Lower Latitude Meridian Circle (LLMC) is described in this paper. The transmission system can change the zenith distance of the tube quickly and precisely. It works in three modes: fast motion, slow motion and lock mode. The fast motion mode and the slow motion mode are that the tube of the instrument is driven by a fast motion stepper motor and a slow motion one separately. The lock mode is running for lock mechanism that is driven by a lock stepper motor. These three motors are controlled together by a single chip microcontroller, which is controlled in turn by a host personal computer. The slow motion mechanism and its rotational step angle are fully discussed because the mechanism is not used before. Then the hardware structure of this control system based on a microcontroller is described. Control process of the system is introduced during a normal observation, which is divided into eleven steps. All the steps are programmed in our control software in C++ and/or in ASM. The C++ control program is set up in the host PC, while the ASM control program is in the microcontroller system. Structures and functions of these r\programs are presented. Some details and skills for programming are discussed in the paper too.
According to the requirement of the Lower Latitude Meridian Circle (LLMC) that the instrument can still determine absolutely the position of a celestial body after a scientific CCD is attached to it, a new control plan is presented in this paper. The plan includes two parts. One is that the CCD camera is driven to track the stellar image in the horizontal direction when observed in the meridian direction. The other is that the CCD camera still moves in the horizontal, while the tube of the instrument moves in the vertical direction when observed in the prime vertical direction. In order to accomplish the plan we have developed a control system that includes three main parts: a personal computer (PC), a single chip microcontroller system for CCD driving scan and a vertical angle control system. The first to parts are described in the paper. The PC sends all kinds of instructions and data to the microcontroller via an output interface board. The control software in the PC is written in C++, and the one in the microcontroller is written in ASM. Two simplified program flow charts are presented. We also discuss the CCD tracking error caused by the control system, and propose a corresponding way to solve the problem.
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