JP3087731B2 - Imaging device with variable imaging light quantity - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus mounted on an artificial satellite or the like for imaging the surface of a celestial body or the like including the earth. The present invention relates to an imaging device for imaging a partial ground surface pixel.

[0002]

2. Description of the Related Art In general, an image pickup device mounted on an artificial satellite or the like and for picking up an image of the surface of a celestial body or the like has a linear shape such as a one-dimensional CCD for the purpose of miniaturization, weight reduction, and high accuracy of pixel-to-pixel arrangement. Many adopt a method of performing electronic scanning using a multi-element sensor. The one-dimensional CCD includes a photoelectric conversion unit, a charge transfer register, and the like. The photoelectric conversion unit is a silicon photodiode, and a one-dimensional CCD having a structure in which 5000 or more silicon photodiodes are connected is also common.

FIG. 6 shows a conceptual diagram of imaging by a conventional imaging device. 2 is an optical system, 11 is an artificial satellite, 12 is an instantaneous field of view,
Reference numeral 12a denotes a bisecting instantaneous visual field obtained by bisecting the instantaneous visual field 12 in the scanning direction, and 13 denotes a ground surface pixel. Here, it is appropriate to consider one ground pixel from immediately below the scanning start point to immediately below the scanning end point, and L [m] in the two instantaneous visual fields 12 and the two equally-divided instantaneous visual fields 12a. × L [m] of the ground surface pixels 13. In an imaging apparatus for imaging the earth's surface, an instantaneous visual field 12 divides a square ground surface pixel 13 of L [m] × L [m] into N parts in a scanning direction which is a traveling direction of the artificial satellite 11 (N is a positive integer). ) One-dimensional C in a horizontally long shape
In the case of using a CD, a conventional imaging device captures incident light and captures an image at a time T [sec] from the start to the end of one scanning cycle as shown in FIG. Here, the scanning cycle T [sec] is the length L [m] of one side of the ground pixel 13
Is the time required to scan at the ground surface velocity V [m / sec] of the instantaneous visual field 12, and T [sec] = L [m] / V [m
/ Sec].

[0004]

In the design of an image pickup apparatus mounted on an artificial satellite for picking up an image of the earth's surface, the aperture of the optical system is generally fixed for miniaturization, weight reduction and high reliability. . For this reason, the F / No. Of the optical system needs to be determined by performing a trade-off so that the input / output of the one-dimensional CCD does not saturate when the incident light amount is large, while the S / N is secured even when the incident light amount is small. According to the present invention, the problem of reducing this trade-off can be solved.

Further, in imaging using a one-dimensional CCD, it is necessary to perform scanning by moving the one-dimensional CCD and the surface of the object to be imaged relatively. Therefore, an MTF (Modula) in the scanning direction is required.
Tion Transfer Function)
Since it deteriorates compared to the direction perpendicular to the scanning direction, it is a problem to improve it. According to the present invention, these problems can be solved even when the amount of incident light from the imaging target is sufficiently large.

[0006]

In order to solve the above-mentioned problem, according to the first aspect of the present invention, the instantaneous field of view of the one-dimensional photodetector element array is such that the ground surface pixels are N (N is positive) in the traveling direction of the satellite. In the case of the divided horizontally long form, the scanning cycle in which the traveling direction is the scanning direction is set to N , the same as the division number of the ground pixel.
Divided, it controls the operation timing of the one-dimensional light detector element array to image partial the ground pixels in each N divided intervals, the amount of incident light from the surface pixels is large situ
In this case, make the scanning time shorter than the scanning time.
MTF (Modulation Transf)
that to improve the deterioration of er Function).

[0007]

[0008] The invention of claim 2 is the scanning start signal and the imaging data read clock and timing control circuit supplies a control signal, the one-dimensional photodetector to receive said scan start signal and the imaging data read clock An element array, the one-dimensional photodetector element array, and the ground image
An optical system provided between the element takes the imaging data transmitted in accordance with the imaging data read clock, and a sample-and-hold circuit for receiving the control signal, the imaging data from receiving the sample and hold circuit the control signal An A / D converter for capturing and A / D converting;
The control signal is received, and N is divided within the scanning cycle, and N is obtained by partially capturing the ground pixels in each of the N divided sections.
And a formatter for adding the A / D-converted image data to a format for transmission to the ground.

Furthermore, the invention of claim 3, run査start signal
Voyeur image data read clock and control supply to filter <br/> timing control circuit control signal, and the one-dimensional photodetector element array to receive said scan start signal and the imaging data read clock, the one-dimensional Photodetector element array and the ground surface
An optical science system provided between the pixel, the imaging data read clock captures an imaging data that is sent according to receiving said control signal, is divided into N by the scanning cycle partial each N divided section A sample-and-hold circuit for adding the N A / D-converted image data obtained by imaging the ground pixels, receiving the control signal, taking in the image data from the sample-and-hold circuit, and performing A / D conversion
It comprises an A / D converter for conversion, and a formatter for receiving the control signal and editing the imaging data into a format for transmission to the ground.

Further, in the invention according to claim 4 , the one-dimensional photodetector element array is a one-dimensional CCD.

[0011]

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to an improvement in an imaging apparatus provided with a one-dimensional photodetector element array mounted on an artificial satellite or the like. Although the surface of the earth will be described, it is needless to say that the invention can be applied to the surface of other celestial bodies such as the planet and the moon.

In the present invention, one scanning period is divided into N (N is a positive integer), and the time for taking in the incident light and taking an image in each divided section is controlled by a command from the ground. Thus, the amount of incident light received by the one-dimensional photodetector element array can be varied.

As a result, the dynamic range of the amount of incident light from the surface of the object to be imaged becomes large, and in the conventional image pickup apparatus in which the image pickup time is equal to the scanning period, the MT in the scanning direction is
F (Modulation Transfer Fun
ction) is degraded compared to the MTF in the direction perpendicular to the scanning direction. However, in the imaging apparatus of the present invention, when the amount of incident light on the imaging target is large, the imaging time is made shorter than the scanning cycle to reduce the MTF. Deterioration can be improved.

An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a conceptual diagram showing an image pickup according to the present invention. Here, N = 3, and the scanning cycle is divided into three.
2 is an optical system, 11 is an artificial satellite, 12 is an instantaneous field of view, and 13 is a ground pixel. Here, L in three instantaneous visual fields 12
It constitutes [m] × L [m] ground pixels 13. In an imaging apparatus for imaging the earth's surface, the instantaneous field of view 12 on the earth's surface reduces the square ground surface pixel 13 of L [m] × L [m] to one third in the scanning direction which is the traveling direction of the artificial satellite 11. When a one-dimensional photodetector element array such as a horizontally-divided one-dimensional CCD 1 is used, incident light is emitted for a time T [sec] from the start to the end of one scanning cycle as in a conventional imaging device. Is not taken and imaging is performed, but imaging is performed during the time of Q [sec], which is the imaging section, and imaging is not performed at other times. Here, the scanning cycle T [sec]
Represents the length L [m] of one side of the ground pixel 13 in the instantaneous visual field 12
T [sec] = L [m] / V [m / sec], which is the time required for scanning at the ground speed V [m / sec].

FIG. 2 is a block diagram showing an embodiment of the present invention. One-dimensional CC as one-dimensional photodetector element array
D1 is used. The light receiving element is a large number of one-dimensional CCDs 1 arranged one-dimensionally.
1 is a direction orthogonal to the traveling direction. An optical system 2 for forming an image of the imaging target surface 10 on the one-dimensional CCD 1 is arranged between the one-dimensional CCD 1 and the imaging target surface 10.
The optical system 2 has a fixed visual field, condenses the incident light 9 in the visual field on the one-dimensional CCD 1, and forms a light image on the one-dimensional CCD 1. The one-dimensional CCD 1 receives scanning start signals 4 a and 4 b from the timing control circuit 3 and an imaging data read clock 5.
Configuration.

Data picked up by a photoelectric conversion unit (not shown) in the one-dimensional CCD 1 is transferred to a charge transfer register (not shown) in the one-dimensional CCD 1 every time the scanning start signals 4a and 4b are received. The data transferred to the charge transfer register is output to the sample and hold circuit 6 as image data 1a according to the image data read clock 5. The sample hold circuit 6 outputs the imaging data 6a according to the control signal 3a from the timing control circuit 3. A
The / D converter 7 controls the control signal 3 from the timing control circuit 3
b, A / D conversion is performed on the imaging data 6a to output imaging data 7a. A format for transmitting to the ground after the three A / D-converted imaging data 7a obtained by dividing the image into three within one scanning period and being added in the formatter 8 by the control signal 3c from the timing control circuit 3 And is output as the imaging data 8a.

FIG. 3 is an explanatory diagram of the operation in the embodiment of the present invention where N = 3, and FIG. 4 is a scanning start signal. A scanning start signal 4 shown in FIG.
a and 4b are supplied. That is, the scanning cycle T [se
c], the scan start signal 4a is supplied every one-third, and after Q [sec], another scan start signal 4a is supplied.
b is supplied. The imaging is performed in the time of Q [sec] of the imaging sections -1 to 3 divided into one third, and the data of the time of (T / 3)-Q [sec] in the discarding section is discarded. Control signal 3 from timing control circuit 3 to sample and hold circuit 6, A / D converter 7, and formatter 8
a, 3b, and 3c are turned off in the discarded section, and data in the discarded section is not transmitted to the ground. As shown in FIG. 3, the maximum imaging time at each point of the imaging target when performing such imaging is Q as shown in FIG.
[Sec] trapezoidal shape.

FIG. 5 shows the imaging time at each point of the imaging object where N = 3. The imaging time 14 is the imaging time at each point of the imaging target when the image is captured by the conventional imaging device.
Indicates the imaging time at each point of the imaging target when the image is captured by the imaging device according to the present invention. The imaging time 16 is an imaging time of each point of the imaging target in a direction perpendicular to the scanning direction, and is always a constant time R in the conventional imaging apparatus and the imaging apparatus of the present invention. Here, R is 0 ≦ R ≦ Q [sec].

Next, the incident light amount will be described. When the incident light amount received from the imaging target is E [W / m ² ], 1
The amount of incident light received in the scanning cycle is (1/3) × E × L × L × T in the conventional imaging apparatus based on the imaging time shown in FIG.
[J], and E × L × L × Q in the imaging apparatus of the present invention.
[J]. As described above, the amount of incident light is Q / (T / 3) times larger in the imaging device of the present invention than in the conventional imaging device. That is, the amount of incident light can be reduced at an arbitrary rate by controlling the time Q [sec] of the imaging sections -1 to 3 by a command from the ground. From this, when the minimum value of the amount of incident light from the imaging target required for the imaging apparatus is given, the time of the imaging section may be selected as Q = T / 3 [sec] and the F number of the optical system may be determined. become. When the incident light amount is equal to or more than the minimum value, the imaging sections -1 to -3 are set according to the incident light amount.
T / sec when the one-dimensional CCD 1 does not saturate
It may be set to a value of 3 [sec] or less.

Further, as shown in FIG. 5, the image pickup section of the present invention is compared with the conventional image pickup apparatus in the image pickup sections -1 to -3.
As the time Q [sec] is shortened, the spread in the scanning direction decreases, and the length L of one side of the ground surface pixel 13 is reduced.
Approach [m]. Therefore, when the amount of incident light from the imaging target surface 10 is large, by shortening Q [sec], the one-dimensional C
In the case of CD1, the MTF in the scanning direction can approach 0.637, which is the MTF in the direction perpendicular to the scanning direction determined by the opening width.

In the embodiment, three pieces of image data obtained by dividing the image into three parts in one scanning cycle are A / D converted and then added. However, a sample hold for processing analog data before A / D conversion is performed. The same effect as in the embodiment can be obtained even if the addition is performed by the circuit 6 or the like. In the embodiment, N = 3
However, if N is a positive integer, such as when N = 2 or N = 4, the same effects as in the embodiment can be obtained.

[0024]

As described above, according to the present invention,
The amount of incident light is Q / (T / 3) times that of the conventional imaging device.
That is, by controlling the time Q [sec] of the imaging section by a command from the ground, the amount of incident light can be reduced at an arbitrary rate. From this, when the minimum value of the amount of incident light from the imaging target surface required for the imaging apparatus is given, the time of the imaging section is selected as Q = T / 3 [sec], and the F of the optical system is selected.
You only need to decide on the number. When the light amount is equal to or more than the minimum light amount, the time Q [sec] of the imaging section may be set to a value equal to or less than T / 3 [sec] at which the detector is not saturated according to the incident light amount. Further, in the imaging apparatus of the present invention, as compared with the conventional imaging apparatus, as the time Q [sec] of the imaging section is shortened, the spread in the scanning direction is reduced, and the length L [m] of one side of the ground pixel is reduced. Get closer. For this reason, when the amount of incident light from the surface of the imaging target is large, if Q [sec] is shortened, the MT in the direction perpendicular to the scanning direction determined by the opening width of the one-dimensional CCD can be obtained.
The MTF in the scanning direction can be made closer to 0.637 which is F.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating imaging according to the present invention.

FIG. 2 is a block diagram showing an embodiment of the present invention.

FIG. 3 is an explanatory diagram of an operation in the embodiment of the present invention.

FIG. 4 is a scanning start signal according to the embodiment of the present invention.

FIG. 5 shows an imaging time at each point to be scanned in the embodiment of the present invention.

FIG. 6 is a conceptual diagram showing conventional imaging.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 One-dimensional CCD 1a Image data 2 Optical system 3 Timing control circuit 3a Control signal 3b Control signal 3c Control signal 4a Scan start signal 4b Scan start signal 5 Image data read clock 6 Sample hold circuit 6a Image data 7 A / D converter 7a Imaging data 8 formatter 8a imaging data 9 incident light 10 imaging target surface 11 artificial satellite 12 instantaneous visual field 12a bisecting instantaneous visual field 13 ground pixel 14 imaging time 15 imaging time 16 imaging time

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-53-51921 (JP, A) JP-A-63-98286 (JP, A) JP-A-3-34787 (JP, A) JP-A-4- 14968 (JP, A) JP-A-4-122178 (JP, A) JP-A-4-130877 (JP, A) JP-A-6-86182 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) H04N 5/30-5/335

Claims (4)

(57) [Claims] When the instantaneous field of view of a one-dimensional photodetector element array is a horizontally long shape obtained by dividing ground pixels into N (N is a positive integer) in the traveling direction of an artificial satellite, scanning is performed with the traveling direction as a scanning direction. The cycle is divided into N as in the number of divisions of the ground surface pixels, and the operation timing of the one-dimensional photodetector element array is controlled so as to partially image the ground surface pixels in each of the N divided sections, and from the ground surface pixels, Imaging when the incident light amount is large
The scanning time to be shorter than the scanning time,
TF (Modulation Transfer Fun
(Ction), wherein the imaging light quantity is variable. Wherein a timing control circuit for supplying a scanning start signal and the image data read clock control signal, and the one-dimensional photodetector element array to receive said scan start signal and the imaging data read clock, the one-dimensional An optical system provided between a photodetector element array and the ground pixel, a sample and hold circuit that captures image data transmitted in accordance with the image data read clock, receives the control signal, and receives the control signal, The image data from the hold circuit is taken in and A
An A / D converter for performing the A / D conversion, and the N A / D converters that receive the control signal and divide the N in the scanning cycle and image the ground pixels partially in each of the N divided sections. 2. The imaging apparatus according to claim 1 , further comprising a formatter that adds the imaging data and edits the format for transmission to the ground. 3. A run査start signal and an imaging data read clock and control and filter timing control circuit to supply control signals, the one-dimensional photodetector element array to receive said scan start signal and the imaging data read clock When a light science system provided between the surface pixel and the one-dimensional photodetector element array are sent in accordance with the imaging data read clock
That shooting takes in image data, receiving the control signal, adding the N divided N number of A / D conversion is the imaging data is obtained by capturing the partial the ground pixels in each N divided intervals in the scanning period An A / D converter that receives the control signal, takes in the imaging data from the sample / hold circuit, and A / D converts the data.
2. The imaging apparatus according to claim 1 , further comprising a formatter that receives the control signal and edits the imaging data into a format for transmitting the imaging data to the ground. 4. The imaging apparatus as claimed in claim 1, 3 Symbol placement variable imaging light amount of which is characterized in that the one-dimensional photodetector element array is one-dimensional CCD.