JPS649797B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an imaging and data transmission system for observing high-resolution images of the earth's surface from a satellite.

The amount of image data transmitted from satellites to the ground is increasing as the demand for high-resolution observations increases.

In particular, when collecting data from all over the earth using an orbiting satellite, there are severe constraints such as the storage capacity of the memory function of the data recorder etc. installed on the satellite, and the power and bandwidth of the transmission line to the ground. It is necessary to limit the amount of imaging data as much as possible. Conventionally, in such cases, methods have been taken to shorten the imaging time or increase the number of ground receiving stations.

FIG. 1 shows a system diagram of a conventional general imaging method from a satellite and a transmission method to the ground. In FIG. 1, an artificial satellite 1 moves at a speed v relative to the earth's surface. Optical system 2 for forming images of the ground surface
is usually composed of a lens or a reflecting mirror. This optical system 2 produces an image 3 of the earth's surface on an imaging plane 4
The image is formed on the imaging light-receiving element 5 placed at . A photoelectric conversion element such as a CCD (charge-coupled device) is used as the light-receiving element, and the image signal on the ground surface is converted into an electrical signal and supplied to the signal processing section 6, where it is conveniently transmitted to the ground. It is converted into a digital signal, etc.

Here, if the receiving station 10 on the ground is visible from the artificial satellite 1, this digital signal is directly modulated and
It is also possible to supply the signal to the transmitter 7 and send it out from the antenna 8, but in the case of an orbiting satellite, the time during which it can communicate with a specific receiving station is short. For this reason, there is a method of recording the digital signal in a recording unit 9 having a memory function such as a data recorder, and reading out the recorded image data and transmitting it to the ground after communication with the receiving station 10 on the ground becomes possible. has been taken.

As the demand for high-resolution observation advances, the imaging data rate becomes a high-speed signal of tens to hundreds of Mb/s. For this reason, with the conventional method shown in FIG. 1, it is difficult to record imaged data within the satellite for a long time, and also to transmit the recorded data to the ground in a short time. As a result, a practical method is to shorten the time required to import data into the recording unit 9 each time, set the recording/reading speed ratio to about 1:1, and transmit image data to the ground in small increments. However, there is a problem in that it takes a considerable amount of time to collect data on the entire earth's surface. One way to shorten this data collection period is to install a large number of ground receiving stations and shorten the cycle from recording to reading. There are problems such as the need for means for collecting high-speed image data.

The object of the present invention is to eliminate these drawbacks and provide an image data transmission system that uses a small number of ground stations to acquire and transmit effective high-resolution observation data of the earth's surface in a short period of time.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 2 shows a system diagram of the imaging device section of the image data transmission system according to the present invention. In the figure, 4 and 5
1 is an image forming surface and an imaging light-receiving element similar to that in FIG. Reference numeral 11 denotes a predictive imaging light receiving element arranged to capture an image W (m) ahead of the imaging target with respect to the traveling direction of the satellite 1 shown in FIG.
Its function as a light receiving element is similar to that of the light receiving element 5. There are various types of light receiving elements, but
Here, we will explain an example in which output data is output as serial data for each scanning line, such as a one-dimensional CCD (charge-coupled device).

Generally, optical observation information from artificial satellites includes cloud data in addition to information from land and sea areas. The output signal level when clouds are imaged is usually much higher than the reflected light from the ground surface, and the signal level from the ocean area is the lowest level.

The present invention utilizes the differences in these output signals to predict in advance whether the target to be imaged contains a lot of land area information or whether the area is mostly covered by clouds. Detected by 11,
The purpose is to control the output data rate, the recording speed of the recording unit, etc. On the short wavelength side of the visible range, scattered light from the atmosphere is added to the reflected light from the ground surface,
Although the level difference in the ocean area becomes smaller, the above-mentioned level difference between the three can be obtained by using a band on the slightly longer wavelength side as the observation wavelength band of the predictive imaging light receiving element 11.

The output signal of the light receiving element 11 is generally an analog signal whose amplitude is proportional to the input light.
In such cases, one pulse output is output for each pixel in the form of pulse amplitude modulation (PAM), as shown in FIG. By sampling even when the output waveform is a continuous analog waveform, the third
The waveform shown in the figure can be obtained. In FIG. 3, the horizontal axis shows time, and the vertical axis shows the output level of the light receiving element. In the figure, information near level H corresponds to clouds, information near level M corresponds to land area, and information near level L corresponds to sea area. Therefore, as shown in the figure, the thresholds T ₁ and T ₂ are set to values near the middle between levels L and M, and near the middle between levels M and H, and the thresholds for T ₁ and T ₂ are By generating a value level from the threshold generation circuit 12 shown in FIG. 2 and supplying it to the level discrimination circuit 13,
Keep the signal level of the light receiving element output below T ₁ , T ₁ ~ _{T 2} ,
It can be divided into three areas: T ₂ and above. If the number of pulses divided into these three regions is counted for a certain period of time (for example, one scanning line period), it can be determined from the counting results of each region which region the imaged object of the light receiving element 11 mainly contains information. It is possible to determine whether As a result, the actual imaging light receiving element 5
The outline of the object to be imaged can be sensed approximately τ=W/v seconds before the object is imaged.

In FIG. 2, a counting circuit 14 counts the number of pulses divided into each area by the above-mentioned discrimination circuit 13 for a certain period (for example, one scanning line period).
The mode setting circuit 15 sets the imaging mode by comparing the output of the counting circuit 14 with each built-in reference count value and determining the magnitude of the count value as described later. The timing signal generation circuit 16 is a circuit that generates a timing signal necessary for the imaging light receiving element 5 to process data from a clock signal by frequency downshifting and logical operation. A partial output selection is performed to generate a timing signal that matches a predetermined data rate. The encoding circuit 17 includes a sampling circuit, a hold circuit, an A/D converter, etc., and changes the sampling frequency for the output of the imaging light receiving element 5, following the output of the timing signal generation circuit 16, and performs encoding processing. Change the output data rate. FIG. 4 shows an example of the output waveform of the sampling circuit. Figure 4a shows the output waveform when the speed is normal, and Figure 4b shows the output waveform when the sampling frequency is halved.

Referring again to FIG. 2, circuit 18 generates a rate code for identifying the rate of data being transmitted after demodulation on the ground. According to the output of the mode setting circuit 15, one of several speed codes is selected by the circuit 18 and inserted into the output data of the code circuit 17 at a data rate determined by the output of the timing signal generation circuit 16. The multiplexing circuit 19 performs time division multiplexing of these data. The multiplexed data is recorded in a recording section 9, which is constituted by a magnetic tape, magnetic memory, semiconductor memory, etc., and whose recording and reading speeds can be electrically controlled. When performing speed switching, mode setting circuit 1
The clock frequency of the recording section 9 is switched by the timing signal generating circuit 16 set in response to the output of the timing signal 5, and the recording speed is switched.

An example of a specific mode setting method is shown below. First, as a simple method example, a method of setting only from counting results within one scanning line period will be shown.

Let n _H be the counting result of level T ₂ or higher within one scanning line period, and n _M be the counting result of the area between levels T ₁ and T ₂ . First, if n _M is larger than a certain set reference number n ₁ within one scanning line period, it is determined that there is a lot of information on the land area that is the main target, and the encoding circuit 17 and the recording 9. Operate section 9 at normal speed. Then n _M is less than n ₁ and n _H
If the number _n2 does not reach a certain standard, it is determined that there is a lot of information about the sea area, and the sampling frequency of the encoding circuit 17 and the recording speed of the recording unit 9 are reduced by, for example, 1/2.
Reduce to ~1/4. Furthermore, if n _M < n ₁ and n _H n ₂ , most of the area is covered with clouds,
The above sampling frequency and recording speed are lowered to, for example, 1/10 to 1/100. Alternatively, in such a situation, it is also possible to set the recording speed to 0 and stop recording data.

The values of n ₁ and n ₂ are set based on system design, but for example, n ₁ should be set to 5% and n ₂ to 90% of all signal output circuits n within one scanning line period. I can do it. The values of n ₁ and n ₂ and the degree of speed reduction can be changed step by step and set to appropriate values using command signals from the ground.

The above method of setting the data rate from the counting results within one scanning line period is a method suitable when the response time of speed switching of the recording section 9 is fast. In this case, the recording section and the timing signal generation circuit,
Assuming that the response time of the encoding circuit is very small, the predictive imaging light-receiving element is configured to image the object at an earlier time by approximately one scanning line period, for example, as shown in FIG.
The predictive imaging light receiving element may be placed close to the imaging light receiving element 5 as shown in FIG. Furthermore, even if the response time for switching the speed of the recording section 9 or the like is long, this system can prevent the loss of effective information by the following method. In this case, the predictive imaging light receiving element 11 is arranged at a distance w from the imaging light receiving element 5 as shown in FIG. 5b. As a result, the imaging light-receiving element 5 images the same location r (sec) after the predictive imaging light-receiving element 11 takes an image, as shown in the following equation.

τ=W/v =H/·w/v Here, H: height of the satellite from the ground surface,: focal length of the imaging optical system.

These relationships are shown in FIG. According to the above formula, the distance W is set so that τ is larger than the switching time determined by the recording unit or the like.

With this arrangement, when switching from low-speed mode to high-speed mode (faster mode than the current mode), the switching operation starts immediately after n _M ≧ n, n _H < n ₂ is detected, as in the previous example. Then, the switching operation can be completed within τ (sec). Next, when switching from high speed mode to low speed mode (slower mode than the current mode), after detecting n _M < n, n _H n ₂ , switch to low speed mode only after this counting result has been received m or more times in a row. mode setting circuit 1
5. The value of m may be set to m≧τ/τ _H (τ _H is one scanning line counting time) so that switching is not performed within τ (sec).

As described above, important other table information is recorded at high speed, and other information is recorded at low speed.
Since the recording speed of the recording unit matches the data rate, the recorded information density is constant. Thereby, in the case of reading, by operating the recording section at a constant speed, it is possible to transmit data from the modulation transmitting section 7 and the antenna section 8 to the ground station at a constant data rate.

FIG. 7 shows an example of the configuration of a receiving station when image data is transmitted using the transmission method according to the present invention.
The received image data is sent to the receiving/demodulating device 100.
After demodulation, the speed code identification circuit 20 identifies the speed code inserted by the speed code generation circuit 18 of the transmitter. This speed code identification circuit 2
By outputting 0, the speed of the image processing/recording circuit 21 is switched, and the speed is restored to the original signal speed. Note that since the image signal in the slow speed portion has a reduced amount of information, it is possible to use a correspondingly simple image processing/recording device.

As is clear from the above description, the present invention can be applied to the following applications.

At the time of speed switching, it is possible not only to switch the sampling frequency of the encoding circuit 17, but also to switch the input gain, the number of quantization levels, or switch to nonlinear quantization. In addition, the values of thresholds T ₁ and T ₂ can be controlled by command signals from the ground, or since the orbit conditions of the satellite are known, the program control function can be controlled by a threshold generation circuit. 1
It is also possible to have 2.

In order to simplify the explanation, a case has been described in which there is only one imaging light receiving element 5, but this is usually constituted by a plurality of light receiving elements and observes a plurality of wavelength bands. Therefore, when changing the speed, it is also possible to switch the wavelengths and bandwidths of these observation wavelength bands using an optical filter or the like and take an image.

Also, as is clear from the above explanation, this method
It can be applied not only to satellites but also to aircraft.

As described above, according to the present invention, it is possible to effectively increase the amount of information recorded with a simple configuration without adding a large-capacity high-speed memory circuit or the like.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing a conventional image data transmission method, Fig. 2 is a block diagram showing an imaging device section of the image data transmission method according to the present invention, and Fig. 3 is an output level characteristic of the light receiving element in Fig. 2. FIG. 4 is a diagram showing an example of the output waveform of the sampling circuit in FIG. 2, FIG. 5 is a diagram showing an example of the arrangement of the light receiving element in FIG. FIG. 7 is a block diagram showing the configuration of the receiving station side of the image data transmission system according to the present invention. In the figure, 1...satellite, 2...optical system, 3...
...image of the ground surface, 4...imaging surface, 5...light receiving element, 6
...Signal processing section, 7...Modulation/transmission section, 8...Antenna, 9...Recording section, 10...Receiving station, 11...
...Prediction light receiving element, 12...Threshold generation circuit,
13... Level discrimination circuit, 14... Counting circuit, 1
5...Mode setting circuit, 16...Timing signal generation circuit, 17...Encoding circuit, 18...Speed code generation circuit, 19...Multiple circuit, 20...Speed code identification circuit, 21...Image processing/ Recording circuit, 10
0...Reception/demodulation device.

Claims (1)

[Scope of Claims] 1. An image data transmission method in which image data of the object is obtained and transmitted by scanning a first imaging light-receiving element that moves relative to the object to be imaged, a data processing and recording unit that processes and records image data from a first imaging light-receiving element; and a second imaging light-receiving unit that images the object at a predetermined time earlier than the first imaging light-receiving element. An image data transmission method comprising: a control section that changes the processing and recording speed of the data processing and recording section in accordance with the output level of the second imaging light receiving element. 2. The control unit includes a level discrimination circuit that divides the output of the second imaging light receiving element into a plurality of level ranges, and a signal appearance frequency for each division of the level range at least of the first imaging light receiving element. a counting circuit that counts for one scanning line period or more; a determination circuit that compares the counted value of the counting circuit with a reference value to determine whether it is large or small;
2. The image data transmission system according to claim 1, further comprising a timing signal generation circuit that generates a control signal for changing the processing and recording speed of the data processing and recording section based on the output of the determination circuit.