JPS58213269A - Synthetic aperture radar - Google Patents

Abstract

PURPOSE:To obtain exactly a data at an SAR of a position visible from a ground station, and to process a signal of the SAR with high flexibility, by selecting optionally the number of quantizing bits if necessary, when digitizing the analog signal of the synthetic aperture radar (SAR). CONSTITUTION:When digitizing an SAR analog signal 1, the number of bits is set by a control device 4 controlled by an external control signal 10 in accordance with a demand, so that when picture information of a wide range is necessary but a picture having a high quality is not always necessary, the number of quantizing bits is made small, and when a picture having a high quality is necessary even in case of a picture of a narrow range, the number of quantizing bit is made large. Also, the device 4 stores track information and time information of a satellite, can control recording start, end time, reproducing start and end time of a recording and reproducing device, stores an SAR data of a place which cannot be seen from a ground receiving station, and can send out the SAR data when it reaches a position which can be seen from the ground receiving station.

Description

[Detailed description of the invention] The present invention relates to a synthetic aperture radar device.

Synthetic Aperture Radar
E-Radar (hereinafter referred to as SAR) is a type of side-looking radar that is mounted on platforms such as aircraft, satellites, etc., and is a device that takes photographs of the earth's surface using radio waves.

Generally, the distance resolution of a radar improves as the effective pulse width of a transmission pulse becomes narrower, and the azimuth resolution improves as the antenna beam width becomes narrower. Therefore, in order to obtain high resolution, a high power transmitter with a narrow pulse width and a large diameter antenna are reliable. The element array antenna is synthesized. As the platform moves, the antenna emits waves at regular intervals and receives reflected waves from the target. Amplitude information and phase information are recorded as the received signal at each time point. The received signal is affected by Doppler shift due to the velocity vector of the platform and the velocity vector of the target, and the Doppler frequency changes with time. In SAR, processing is performed through a filter having a frequency vs. time delay characteristic opposite to this Doppler frequency, that is, the sum t2. By performing #fI processing, high azimuth resolution equivalent to that of a large diameter antenna is obtained.

On the other hand, pulse compression technology is used to improve distance resolution. Pulse compression technology increases the average power by lengthening the transmission pulse width instead of increasing the transmission peak power, and at the same time widens the occupied bandwidth by applying appropriate modulation within this long pulse time. This is a method to obtain resolution equivalent to short pulse width. Chirp modulation, in which the frequency changes linearly with time, is often used for modulation. In pulse compression processing, all spectra in a signal are integrated at one point by passing the signal through a filter whose frequency vs. time delay and low characteristics are reversed, and a sharp pulse is output.

Conventionally, when digitizing an analog signal output from a BAR receiver, quantization using a specific quantization bit slope has been considered.

However, when SAR is mounted on a satellite, the time during which the satellite is visible from one ground receiving station (at that ground receiving station,
Since the time during which SAR signals can be received is limited, the 8AR data collected behind the ground receiving station is temporarily stored in the data recording and reproducing system inside the satellite, and then the satellite receives the ground receiving station. When you come to a position where you can see through the data, it is necessary to send out data from the data recording/reproducing thread. However, when a BAR signal within a certain frequency band is digitized with a large number of quantization bits, the amount of data increases.
In general, a data recording/reproducing thread with a small storage capacity that can be mounted on an artificial satellite can only record information about a small imaging target surface. -Also, when quantizing with a small number of quantization bits to reduce the amount of data, the quantization error increases,
There is a drawback that image quality deteriorates, and there is no device with a control function to solve the conflicting problem between data amount and image quality.
There was also no device that stored AR data and automatically transmitted the data when the satellite came to a position visible to a ground receiving station.

Therefore, the present invention solves the above-mentioned conflicting problem between data amount and image quality by quantizing a SAR analog signal with an arbitrary number of quantization bits and automatically recording and reproducing the quantized signal. The purpose of the present invention is to provide a device that can perform rational control over the data and automatically control the recording and playback times.

That is, an object of the present invention is to configure a SAR signal processing device with extremely high flexibility regarding BAR image quality and data amount.

The main part of the device according to the present invention is composed of a quantization device, a control device, and a recording/reproducing device, and the quantization device receives an analog signal output from a BAR receiver and is specified by a program stored in a satellite onboard computer. Quantization can be performed with any number of quantization bits. The recording and reproducing device also records and reproduces the BAR digital signal output from the quantizer jθ. The control device can appropriately control the number of quantization bits of the quantization device using the external control signal under the program control, and can also automatically control the recording time and playback time of the recording and playback device. , allowing for reasonable control of the data and both questions.

Next, embodiments of the present invention will be described with reference to the drawings.

The SAR analog signal 1 output from the SAR receiver is
SAR signal processing device 9 ambiguous device WV! , 2. The quantizer i#2 digitizes the EIAR analog i#1 with an arbitrary number of quantization bits according to the quantizer control signal 3 that enters the quantizer 2 from the controller \t4, and records it as a SAR digital signal 5. Output to the playback device 6. At that time, if a wide range of image information is required but the image does not need to be very high quality, the number of quantization bits may be reduced, or if a narrow range of image information is required but a high quality image is required. The control device 4, which is regulated by the external control signal 10, sets an arbitrary number of quantization bits according to demand, such as increasing the number of quantization bits. This external control signal IO is sent out according to a program stored in a computer installed in the satellite, and sets the optimum number of digitized bits in accordance with ever-changing conditions (required conditions as described above).

In addition, the control device 4 automatically controls the recording start time, recording end time, playback start time, and playback end time of the recording and reproducing device by storing orbit information and time information of the artificial satellite. Can be done. As a result, SAR data in locations that cannot be seen by the C1 ground receiving station is also stored in this recording and reproducing device, and when the satellite comes to a position where it can be seen by the ground receiving station, BAR data can be sent out from the recording and reproducing device. .

As explained above, when digitizing SAR analog signals, the present invention can arbitrarily select the number of quantization bits as necessary and automatically record and reproduce SAR data, thereby reducing the amount of SAR data and the image quality. The effect of this is that it enables rational control between the two locations, enables extremely flexible BAR signal processing equipment, and also allows SAR data at locations that cannot be seen at the soil receiving station to be obtained with certainty. is obtained.

[Brief explanation of the drawing]

The figure is a block diagram of an embodiment of the invention. 1... SAR analog signal, 2... Aggregation device, 3
...Quantizer control signal, 4...Control device, 5...
・SAR digital fI No. 6...recording/reproducing device a1
7... Recording/reproducing device control signal, 8... SAR data, 9... SAR signal processing device, 10... External control signal. Patent applicant Space Exploration Agency

Claims (1)

[Claims] In a synthetic aperture radar device mounted on a flying object such as an artificial satellite, a quantization means for quantizing a synthetic aperture radar analog signal output from a receiver at a predetermined quantization rate, and a signal obtained by this quantization means are used. a recording and reproducing device for recording and reproducing the digitized signal; and a recording and reproducing device for recording and reproducing the digitized signal; A synthetic aperture radar device comprising a control device that controls recording time and playback time of a recording and playback device.