JPH04311171A - Radiometer - Google Patents

Abstract

PURPOSE:To remove a fringe pattern generated on an image due to the output level difference of respective systems in a radiometer for multiplexing outputs from image pickup elements in plural systems and obtaining a multiplexed image. CONSTITUTION:This radiometer is provided with a CCD sensor 2 including odd picture elements 3 and even picture elements 4 to be the image pickup elements in plural systems, average computing circuits 11, 12 to be average level calculating part for calculating the average levels of respective outputs from these plural systems, an average level comparing operation circuit 13 to be an error calculating part for calculating the error of respective average levels, amplifier circuits 7, 8 to be feedback control parts for feeding back and canceling the error, and a multiplexing circuit 9 for multiplexing and sending an error-canceled output.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiometer, and more particularly to a radiometer mounted on an artificial satellite or the like to image the surface of a celestial body.

0002

[Prior Art] In general, radiometers mounted on artificial satellites to image the surfaces of celestial bodies, etc., adopt a method of electronic scanning using a line-shaped multi-pixel CCD sensor in order to meet the demand for higher precision. There are more and more things to do.

[0003] A CCD sensor is composed of a photoelectric conversion section, a charge transfer section, and an output section, but when the number of pixels in a CCD sensor becomes several thousand or more, the loss in the charge transfer section increases, so a linear photoelectric conversion section is used. A method is adopted in which charge transfer sections are arranged on both sides of the pixel, and signals of odd-numbered pixels and signals of even-numbered pixels are transferred separately to reduce losses during transfer.

[0004] When such a system is adopted, two systems of image signal output are generated from one image sensor, but conventional radiometers do not have a function to automatically adjust the level between each system, and the This was handled by controlling temperature and other measures based on pre-operation test data.

Now, let us consider a case where the above-described conventional radiometer is mounted on, for example, an artificial satellite to image the earth's surface. In such a radiometer, a linear multi-pixel CC
Continuous images of the Earth's surface are often obtained by using D sensors to electronically scan a specific width in a direction perpendicular to the direction of travel of the satellite, and repeating this scanning as the satellite travels. . As mentioned above, a line-shaped multi-pixel CCD sensor usually has two systems of image signal output, one for each even-numbered pixel and the other for an odd-numbered pixel, in order to suppress loss in the charge transfer section.

By the way, an offset voltage, which is a dark current component, is added to the image signal output from the CCD sensor in addition to the signal voltage proportional to the magnitude of the optical input. This offset voltage differs between systems depending on the characteristics of the charge transfer section and the output section, and further varies depending on the temperature and the like. Furthermore, the proportionality coefficient of the signal voltage component that is proportional to the magnitude of optical input similarly differs between systems and varies depending on temperature and the like.

[0007] Therefore, when having separate charge transfer sections for even and odd systems and obtaining two systems of output, even and odd
This results in a shift in the odd-numbered output levels, and for example, when a uniform area such as the sea surface is imaged, there is a drawback that a striped pattern parallel to the satellite traveling direction appears in the image.

Furthermore, the above-mentioned output level deviation is caused by A/
A possible countermeasure is to use an electronic computer to correct the data after D-conversion, but it is theoretically impossible to correct deviations below the minimum quantization unit. Another option is to increase the number of quantization bits, but this increase would lead to an increase in the data rate, which is difficult, especially in the case of satellite-mounted radiometers, because there are strict limits on the data rate from the satellite to the ground station. However, there is a drawback in that there is a limit to the improvement in correction accuracy due to this method.

[0009]

OBJECTS OF THE INVENTION An object of the present invention is to provide a radiometer having a function of automatically correcting minute level deviations that cannot be corrected with conventional radiometers.

0010

[Structure of the Invention] A radiometer according to the present invention includes a plurality of systems of image pickup devices, an average level calculation section that calculates the average level of the output of each of the image pickup devices of the plurality of systems, and an error in the calculated average levels. The present invention is characterized by having an error calculation section that calculates the error, a feedback control section that feeds back and cancels this error, and a multiplexing section that multiplexes and sends out the output with this error canceled.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of a radiometer according to the present invention. The operation of the radiometer according to the embodiment of the present invention shown in the figure includes an observation mode and an automatic level adjustment mode using a reference light source. The automatic level adjustment mode is started in response to input of a command.

In order to solve the above-mentioned drawbacks, the radiometer of this embodiment takes the following measures in the automatic level adjustment mode. That is, a reference light source is provided, image signal outputs of two or more systems obtained by imaging the reference light source with an image sensor are supplied to a circuit that subtracts the offset voltage of each system, and the outputs are input to a circuit that calculates an average for each system. do. Furthermore, the output of the average calculation circuit is input to a comparison calculation circuit, and is fed back to adjust the gain of the amplifier circuit so that the average level of the signals of each system is equal.

In FIG. 1, 1 is a reference light source, and light from this reference light source 1 is incident on a multi-pixel one-dimensional CCD sensor 2. The CCD sensor 2 has odd-numbered pixels 3 and even-numbered pixels 4, and each image output signal is supplied to a corresponding offset voltage removal circuit 5 or 6, respectively.

Generally, a CCD sensor has a part called optical black that outputs an offset voltage, and the offset voltage is removed by subtracting this from the image output signal. The image signal after the offset voltage has been removed is supplied to amplifier circuits 7 and 8.

Here, the gains of the amplifier circuits 7 and 8 are variable. The outputs of amplifier circuits 7 and 8 are
The odd numbered pixel system and the even numbered pixel system are further branched into two lines,
One set of them is added to multiplex circuit 9. Here, the outputs of multiple pixels are sequentially multiplexed into serially arranged signals. Thereafter, the signal is supplied to the A/D conversion circuit 10 and converted into a digital signal.

Among the outputs of the amplifier circuits 7 and 8, the other set is supplied to the corresponding average calculation circuit 11 or 12, respectively. Here, an average calculation of the outputs excluding the offset voltage is performed for each of the odd-numbered pixels and the even-numbered pixels.

Both outputs of the average calculation circuits 11 and 12 enter an average level comparison calculation circuit 13. This arithmetic circuit 13 compares the outputs of the average arithmetic circuits 11 and 12 to determine the magnitude, and feeds back gain control signals 14 and 15 to control the gains of the amplifier circuits 7 and 8 so that they are equal to each other. .

When the outputs of the average calculation circuits 11 and 12 become equal, the calculation circuit 13 issues a command to escape from the automatic level adjustment mode and return to the observation mode.

FIG. 2(a) is a plot of the image signal output of the multi-pixel one-dimensional CCD sensor 2, with pixels on the horizontal axis. In the figure, the output voltage from the odd-numbered pixel 3 is shown as V1o, of which V1oo is the offset voltage. This value is supplied from the optical black output of the CCD sensor 2, as described above. Similarly, the output voltage V1e and the offset voltage V1eo from the even-numbered pixel 4 are
It is shown in

FIG. 2(b) shows the offset voltage removal circuit 5.
, 6 is a plot of the image signal output after processing. In other words, the odd numbered pixel side is V2o, and the even numbered pixel side is V2o.
2e. Furthermore, these image signal outputs V2
After passing through the corresponding amplifier circuits 7 and 8, the signals o and V2e are averaged by the corresponding averaging circuits 11 and 12, respectively. The result is the output Vom of the system on the odd-numbered pixel 3 side.
and the output Vem of the system on the even-numbered pixel 4 side generally have different values.

FIG. 2(c) shows the result of matching this mismatch by changing the gains of the amplifier circuits 7 and 8.
It is. That is, the results of matching the output Vom and the output Vem are the output V3o and the output V3e, which are input to the multiplex circuit 9.

As described above, the present invention automatically and completely corrects the level difference by feeding back the average level error between two or more image signal output systems from one or more image pickup devices. It can be made to disappear.

[0023] As a result, for example, a multi-pixel one-dimensional CCD
In a radiometer that uses a sensor to take images, when the output of odd-numbered pixels and the output of even-numbered pixels are output from two separate systems, even a slight level difference is conventionally recognized as a striped pattern on the image. However, by canceling out the level differences and multiplexing them, this can be completely removed within the radiometer.

[0024]

[Effects of the Invention] As explained above, the present invention calculates the average level of each of multiple systems of image sensors, and returns and cancels these errors, thereby correcting minute level deviations and improving image quality. This has the effect of removing the striped pattern on the top.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a radiometer according to an embodiment of the present invention.

FIG. 2 is a waveform diagram of each part in FIG. 1;

[Explanation of symbols]

2 CCD sensor 5, 6 Offset voltage removal circuit 7, 8 Amplifier circuit 9 Multiplex circuit 11, 12 Average calculation circuit 13 Average level comparison calculation circuit 14, 15 Gain control signal

Claims (1)

[Claims] 1. A plurality of systems of image pickup devices, an average level calculation section that calculates an average level of the output of each of the plurality of systems of image pickup devices, and an error calculation section that calculates an error in these calculated average levels. , a feedback control unit that feeds back and cancels this error, and a multiplexing unit that multiplexes and sends out the output from which this error has been canceled.