CN108401105B - Method for adjusting dynamic transfer function of space remote sensing TDICCD camera - Google Patents

Abstract

The method and the space camera for improving the dynamic transfer of a space remote sensing TDICCD camera provided by the present invention combine the TDICCD charge burst transfer sequence with the continuous transfer sequence to form a new charge transfer sequence and retain the dynamic range of the TDICCD charge burst transfer sequence At the same time, the characteristics of continuous charge transfer are used to maximize the charge transfer transfer function and improve the imaging quality of remote sensing cameras.

Description

A Method of Adjusting Dynamic Transfer Function of Space Remote Sensing TDICCD Camera

technical field

The invention relates to the field of space optics, in particular to a method for improving the dynamic transfer function of a space remote sensing TDICCD camera and a space camera.

Background technique

The modulation transfer function (MTF) of a camera is a description of the contrast drop of the light signal after passing through the camera, which can objectively evaluate the imaging quality of the camera. For the Time Delay Integration CCD remote sensing camera, the dynamic transfer function can more truly reflect its imaging quality.

TDICCD is an area-array CCD that works in line array mode. It images in motion, exposes the same object multiple times through multiple series, and increases the integration time to increase the light energy. Since the TDICCD is imaging in motion, in order to ensure the imaging quality, it is required that the satellite push-broom speed and the CCD charge transfer speed must match; Therefore, when designing a TDICCD camera, the push-broom speed and charge transfer speed of the camera should be strictly controlled to match the two. But even so, the resolution of the TDICCD in the push-broom direction is still lower than that in the vertical push-broom direction. The current TDICCD remote sensing camera, in addition to ignoring factors such as motion mismatch and satellite vibration, has only a vertical orbit along the orbit. 0.64 times the direction letter. This is caused by the charge transfer process of TDICCD. The reason is that the charge transfer process of TDICCD is discrete, while the camera push-broom process is uniform and continuous. This image shift is called charge transfer image shift and cannot be eliminated. How to effectively improve the dynamic transfer function of the push-broom remote sensing camera along the track direction is a key technology to improve the imaging quality of the remote sensing camera.

There are two types of TDICCD charge transfer modes: continuous transfer and burst transfer. Burst transfer means that the transfer time of the charge is very short relative to the line integration period, and the image shift of the charge transfer is approximately the size of a pixel. The continuous transfer refers to the uniform and continuous distribution of the charge transfer in a line integration period. When using continuous multi-phase transfer, the charge is transferred evenly from one stage to the next stage in multiple times (the number of times is related to the number of phases), which can reduce the image shift of the charge transfer and improve the modulation transfer function of the charge transfer image shift. However, in the current high-resolution remote sensing cameras, burst-type charge transfer is used. The reason is that if the continuous charge transfer is used, when the charge is transferred from the electrode to the horizontal transfer register, compared with the burst charge transfer method, the number of full wells of the CCD will be reduced, thereby reducing the dynamic range of the camera.

Referring to accompanying drawing 1, the traditional TDICCD electric charge vertical transfer is the burst clock charge transfer, from top to bottom are respectively vertical transfer clock CI1, vertical transfer clock CI2, vertical transfer clock CI3, vertical transfer clock CI4 and transfer clock TCK, in a During the line transfer period, the charge transfer is completed in a very short time. In this way, the charge transfer image shift is approximately the size of the pixel. At this time, the charge transfer image shift modulation transfer function at the Nyquist frequency is

MTF _{image shift (discrete clock)} =sinc(a·f)=0.6366

Among them, a represents the pixel size, f represents the spatial frequency, and f=1/2a at the Nyquist frequency. Referring to Figure 2, the sequence of continuous charge transfer is in one row transfer period, and the charge transfer is evenly completed in 8 times. At this time, the image shift of the charge transfer is one-eighth the size of the pixel, and the modulation transfer function of the charge transfer image shift is:

MTF _{image shift (discrete clock)} =sinc(a/8·f)=0.9936

It can be seen that at this time, the modulation transfer function caused by the image shift of the charge transfer is close to 1 and can be ignored. However, as can be seen from the figure, before the last vertical transfer clock CI4 is transferred to TCK, only CI4 is at a high level, that is, the charge can only be stored in the potential well under CI4 at this time, and the dynamic range is reduced to a burst 1/2 of the clock shift mode, which is intolerable for space remote sensing cameras.

SUMMARY OF THE INVENTION

The embodiments of the present invention provide a method and a space camera for improving the dynamic transfer of a space remote sensing TDICCD camera. The TDICCD charge burst transfer sequence and the continuous transfer sequence are combined to form a new charge transfer sequence, and the TDICCD charge burst is reserved. The advantage of high dynamic range of transfer timing, and at the same time, the continuous transfer of charges is used to maximize the transfer function of charge transfer.

The invention provides a method for improving the dynamic transfer function of a space remote sensing TDICCD camera, the method comprising:

Adjust the charge transfer timing and complete the charge transfer according to a predetermined number of times within each row transfer cycle;

obtaining the pixel size and spatial frequency of the camera;

The charge transfer image shift modulation transfer function is rescaled according to the pixel size and spatial frequency.

Optionally, the adjusting the charge transfer sequence to complete the charge transfer according to a predetermined number of times in each row transfer period, including:

Adjust continuous charge transfer timing and burst charge transfer timing;

In the continuous charge transfer state, the charge transfer is completed eight times in one row transfer period.

Optionally, the readjustment of the charge transfer image shift modulation transfer function according to the pixel size and the spatial frequency includes:

In one line transfer period, the charge transfer is completed in 8 times, and the charge transfer image shift is approximately three-eighth the size of the pixel. At the Nyquist frequency, the charge transfer image shift modulation transfer function MTF is:

MTF _{image shift (discrete clock)} =sinc(3a/8·f);

Among them, a represents the pixel size, f represents the spatial frequency, and f=1/2a at the Nyquist frequency.

Optionally, the charge transfer image shift modulation transfer function MTF at the Nyquist frequency is 0.9432.

Optionally, the method further includes:

The charge transfer sequence is performed using a four-phase transfer clock that satisfies: at any instant, at least one phase clock is in a high-level state, and at least one phase clock is in a low-level state.

Optionally, the method further includes:

The timing pulses of the camera are counted by the counter and generated by multiple sets of fixed decoders. When each line ends, a set of variable-value decoding circuits are used to generate clearing pulses to clear the counter. Restart the timing for the next row.

Optionally, the timing pulse is generated by a TDICCD timing circuit, the TDICCD timing circuit includes a clock generating circuit, a counter circuit, and a decoding circuit, the clock generating circuit includes a crystal oscillator circuit and a frequency dividing circuit, and the two crystal oscillators share one. The group inverters switch the frequency of the main clock through the control signal sent by the main control microcomputer;

The counter circuit is composed of three four-bit synchronous counters to form a 12-bit synchronous counter, generates 12-bit counting pulses, and is combined with a comparator to generate a clock signal;

The decoding circuit is composed of a plurality of comparators, flip-flops and logic gate circuits. A group of 12-bit comparators, a 2-bit counter and a period determined by the main control microcomputer are used. When the two values are equal, it means the end of a line period. , the comparator output signal clears the counter to start the next line cycle.

The present invention also provides a space camera, which applies the above-mentioned method for improving the dynamic transfer function of a space remote sensing TDICCD camera.

Optionally, the space camera adopts a TDICCD space remote sensing camera.

As can be seen from the above technical solutions, the embodiments of the present invention have the following advantages:

The method and the space camera for improving the dynamic transfer of a space remote sensing TDICCD camera provided by the invention combine the TDICCD charge burst transfer sequence and the continuous transfer sequence to form a new charge transfer sequence, and retain the dynamic range of the TDICCD charge burst transfer sequence At the same time, the characteristics of continuous charge transfer are used to maximize the charge transfer transfer function and improve the imaging quality of remote sensing cameras.

Description of drawings

Fig. 1 is a sequence diagram of sudden change charge transfer in the prior art;

Fig. 2 is a sequence diagram of continuous charge transfer in the prior art;

3 is a schematic diagram of equipment construction during testing of the method for improving the dynamic transmission of a space remote sensing TDICCD camera provided in the embodiment of the present invention;

Fig. 4 is the time sequence diagram of the method for improving the dynamic transfer function of the space remote sensing TDICCD camera provided in the embodiment of the present invention;

Fig. 5 is the MTF test diagram under the conventional charge transfer sequence in the prior art;

FIG. 6 is an MTF test chart under the charge transfer sequence of the method for improving the dynamic transfer function of a space remote sensing TDICCD camera provided in an embodiment of the present invention.

Among them: 1, vertical transfer clock CI1, 2, vertical transfer clock CI2, 3, vertical transfer clock CI3, 4, vertical transfer clock CI4, 5, transfer clock TCK, 6, target roller, 7, collimator, 8, remote sensing TDICCD camera, 9. Air flotation platform.

Detailed ways

In order to make those skilled in the art better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only Embodiments are part of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The terms "first", "second", "third", "fourth", etc. (if present) in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It is to be understood that data so used may be interchanged under appropriate circumstances so that the embodiments described herein can be practiced in sequences other than those illustrated or described herein. Furthermore, the terms "comprising" and "having" and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those expressly listed Rather, those steps or units may include other steps or units not expressly listed or inherent to these processes, methods, products or devices.

The modulation transfer function is also called the spatial contrast transfer function and the spatial frequency contrast sensitivity function. As a function of spatial frequency, it reflects the ability of an optical system to transmit sinusoidal modulations of various frequencies.

Dynamic range is a performance parameter that describes the ratio of the minimum light energy to the maximum light energy that a CCD can detect, and is an important indicator in remote sensing cameras.

The invention provides a method for improving the dynamic transfer function of a space remote sensing TDICCD camera, the method comprising:

The charge transfer sequence is adjusted and the charge transfer is completed according to a predetermined number of times in each row transfer period, and the predetermined number of times is completed by 8 times in one row transfer period.

Acquire the pixel size and spatial frequency of the camera, where f=1/2a at the Nyquist frequency, where a represents the pixel size, and f represents the spatial frequency;

The charge transfer image shift modulation transfer function is re-adjusted according to the pixel size and spatial frequency. In one line transfer period, the charge transfer is completed in 8 times. In this way, the charge transfer image shift depends on the image shift within the time T ₈ , which is approximately three-eighths of the pixel size. At this time, the charge transfer image shift modulation transfer function at the Nyquist frequency is:

MTF _{image shift (discrete clock)} =sinc(3a/8·f)

The method for improving the dynamic transfer of a space remote sensing TDICCD camera provided by the invention combines the TDICCD charge burst transfer sequence and the continuous transfer sequence to form a new charge transfer sequence, and retains the advantage of the high dynamic range of the TDICCD charge burst transfer sequence. At the same time, the characteristics of continuous charge transfer are used to maximize the charge transfer transfer function and improve the imaging quality of remote sensing cameras.

Optionally, the adjusting the charge transfer sequence to complete the charge transfer according to a predetermined number of times in each row transfer period, including:

Adjust continuous charge transfer timing and burst charge transfer timing;

In the continuous charge transfer state, the charge transfer is completed eight times in one row transfer period.

Optionally, the readjustment of the charge transfer image shift modulation transfer function according to the pixel size and the spatial frequency includes:

In one line transfer period, the charge transfer is completed in 8 times, and the charge transfer image shift is approximately three-eighth the size of the pixel. At the Nyquist frequency, the charge transfer image shift modulation transfer function MTF is:

MTF _{image shift (discrete clock)} =sinc(3a/8·f);

Among them, a represents the pixel size, f represents the spatial frequency, and f=1/2a at the Nyquist frequency.

Optionally, the MTF of the charge transfer image shift modulation transfer function at the Nyquist frequency is 0.9432, which can improve the orbital charge transfer function of the space remote sensing camera from 0.6366 to 0.9432 while ensuring the dynamic transfer function of the remote sensing TDICCD camera.

Optionally, the method further includes:

A four-phase transfer clock is used for the charge transfer sequence. The four-phase transfer clock satisfies: at any instant, at least one phase clock is in a high-level state, and at least one phase clock is in a low-level state. In order to ensure the transfer efficiency of charges, It must be ensured that the high-level states of adjacent phases overlap at least 1μS, and the longer the overlap time, the better, as is the adjacent low-level states, and the highest clock frequency is 200kHZ.

The TCK clock is called the transfer clock, when TCK and CR1 are high, the charge is transferred from the last row of the photosensitive area to the CRI phase of the output register. The high level time of TCK cannot coincide with the high level time of CRI twice. The CI1 clock signal can be turned low after TCK and CR1 are high level for at least 100ns. The falling edge of TCK appears at least 100ns before the falling edge of CR1, and the falling edge of CI1 After at least 19s, it was found through experiments that the exact matching of TCK, CR1, and CI1 is the key to ensure the correct output of pixel charge packets.

Optionally, the method further includes:

The timing pulses of the camera are counted by the counter and generated by multiple sets of fixed decoders. When each line ends, a set of variable-value decoding circuits are used to generate clearing pulses to clear the counter. Restart the timing for the next row.

Optionally, the timing pulse is generated by a TDICCD timing circuit, the TDICCD timing circuit includes a clock generating circuit, a counter circuit, and a decoding circuit, the clock generating circuit includes a crystal oscillator circuit and a frequency dividing circuit, and the two crystal oscillators share one. The group inverters switch the frequency of the main clock through the control signal sent by the main control microcomputer;

The counter circuit is composed of three four-bit synchronous counters to form a 12-bit synchronous counter, generates 12-bit counting pulses, and is combined with a comparator to generate a clock signal;

The decoding circuit is composed of a plurality of comparators, flip-flops and logic gate circuits. A group of 12-bit comparators, a 2-bit counter and a period determined by the main control microcomputer are used. When the two values are equal, it means the end of a line period. , the comparator output signal clears the counter to start the next line cycle.

Referring to Figures 4 and 6, the continuous and sudden change of charge transfer sequence is used to test the dynamic transfer function of the engineering camera. The test system includes a target drum 6, a collimator 7, a remote sensing TDICCD camera 8 and an air float. Platform 9, adjust the position of the collimator 7 so that the uniform light source illuminates the target of the target drum 6 to form a target image. According to the optical principle, the collimator will place the target image at infinity, and the remote sensing TDICCD camera will detect the target at infinity. Image imaging, the imaging results refer to Figure 6.

The present invention also provides a space camera, which applies the above-mentioned method for improving the dynamic transfer function of a space remote sensing TDICCD camera.

Optionally, the space camera adopts a TDICCD space remote sensing camera, which is not limited.

The space camera provided by the invention combines the TDICCD charge burst transfer sequence and the continuous transfer sequence to form a new charge transfer sequence, which retains the advantage of the high dynamic range of the TDICCD charge burst transfer sequence. Features Maximize the charge transfer function and improve the imaging quality of remote sensing cameras.

Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the system, device and unit described above may refer to the corresponding process in the foregoing method embodiments, which will not be repeated here.

In the several embodiments provided in this application, it should be understood that the disclosed system, apparatus and method may be implemented in other manners. For example, the apparatus embodiments described above are only illustrative. For example, the division of the units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components may be combined or Can be integrated into another system, or some features can be ignored, or not implemented. On the other hand, the shown or discussed mutual coupling or direct coupling or communication connection may be through some interfaces, indirect coupling or communication connection of devices or units, and may be in electrical, mechanical or other forms.

The units described as separate components may or may not be physically separated, and components displayed as units may or may not be physical units, that is, may be located in one place, or may be distributed to multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution in this embodiment.

In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically alone, or two or more units may be integrated into one unit. The above-mentioned integrated units may be implemented in the form of hardware, or may be implemented in the form of software functional units.

Those of ordinary skill in the art can understand that all or part of the steps in the various methods of the above embodiments can be completed by instructing relevant hardware through a program, and the program can be stored in a computer-readable storage medium, and the storage medium can include: Read Only Memory (ROM, Read Only Memory), Random Access Memory (RAM, Random Access Memory), magnetic disk or optical disk, etc.

A method for improving the dynamic transmission of a space remote sensing TDICCD camera and a space camera provided by the present invention have been described above in detail. For those skilled in the art, according to the idea of the embodiment of the present invention, in terms of specific implementation and application scope There will be changes. To sum up, the contents of this specification should not be construed as limiting the present invention.

Claims (4)

1. the method for adjusting the dynamic transfer function of space remote sensing TDICCD camera, is characterized in that, described method comprises: Adjust the charge transfer timing and complete the charge transfer according to a predetermined number of times within each row transfer cycle; obtaining the pixel size and spatial frequency of the camera; Readjust the charge transfer image shift modulation transfer function according to the pixel size and spatial frequency; The adjusting the charge transfer sequence to complete the charge transfer according to a predetermined number of times in each row transfer period, including: Adjust continuous charge transfer timing and burst charge transfer timing; In the state of continuous charge transfer, the charge transfer is completed eight times in one row transfer period; The readjustment of the charge transfer image shift modulation transfer function according to the pixel size and spatial frequency includes: In one line transfer period, the charge transfer is completed in 8 times, and the charge transfer image shift value is three-eighth pixel size. At the Nyquist frequency, the charge transfer image shift modulation transfer function MTF is: MTF _{image shift (discrete clock)} =sinc(3a/8·f); Among them, a represents the pixel size, f represents the spatial frequency, and f=1/2a at the Nyquist frequency; The method also includes: The charge transfer sequence is performed using a four-phase transfer clock that satisfies: at any instant, at least one phase clock is in a high-level state, and at least one phase clock is in a low-level state. 2 . The method according to claim 1 , wherein the charge transfer image shift modulation transfer function MTF is 0.9432 at the Nyquist frequency. 3 . 3. The method according to claim 1, wherein the method further comprises: The timing pulses of the camera are counted by the counter and generated by multiple sets of fixed decoders. When each line ends, a set of variable-value decoding circuits are used to generate clearing pulses to clear the counter. Restart the timing for the next row. 4. The method according to claim 3, wherein the timing pulse is generated by a TDICCD timing circuit, the TDICCD timing circuit comprises a clock generating circuit, a counter circuit, a decoding circuit, and the clock generating circuit comprises a crystal oscillation Circuit and frequency division circuit, two crystal oscillators share a set of inverters, and the main clock frequency is switched by the control signal sent by the main control microcomputer; The counter circuit is composed of three four-bit synchronous counters to form a 12-bit synchronous counter, generates 12-bit counting pulses, and is combined with a comparator to generate a clock signal; The decoding circuit is composed of a plurality of comparators, flip-flops and logic gate circuits. A group of 12-bit comparators is used to compare the cycle determined by the 2-bit counter and the main control microcomputer. When the two values are equal, it means that one line cycle is over. , the comparator output signal clears the counter to start the next line cycle.

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