Space-time remote sensing instrument imaging time acquisition and corresponding method

Abstract

The present application relates to a kind of aerospace remote sensing instrument imaging time acquisition and corresponding method, in the method, probe head software sends time request pulse to main control software at exposure starting moment, main control software records the system time code of receiving time request pulse moment, the time is called time code, main control software adopts first-in first-out principle, saves the time code of last n times, and the group of time code is sent to probe head software through the command frame of next cycle, probe head software will last n times of time code, imaging command, parameter, remote sensing data together with package, download.This imaging time acquisition and corresponding method produces time error, which is determined by the accuracy parameter of crystal oscillator, and the software does not produce error, so under the condition that the accuracy parameter of crystal oscillator is better than the requirement of time error, the method can obtain imaging time with high precision and assist data corresponding in later period.

Description

Technical Field

[0001] This invention relates to the field of software time synchronization methods, and in particular to a method for acquiring and corresponding the imaging time of aerospace remote sensing instruments. Background Technology

[0002] In the aerospace field, remote sensing instruments must record the start time of each image exposure when performing missions to detect atmospheric targets, for data inversion. Typically, this time is achieved through the coordinated action of two or more software configuration items; therefore, this time is called the synchronization time. Remote sensing instruments often require minimal synchronization time errors; for example, the on-orbit synchronization time error for atmospheric remote sensing instruments is ±100 μs. Currently, no publicly available solution combining general hardware design principles and software synchronization methods has been found to meet these accuracy requirements.

[0003] The following example, using two software configuration items to implement atmospheric sounding by a spaceborne remote sensing instrument, illustrates the general principles of time synchronization methods and hardware design to meet time synchronization error requirements. The software system consists of main control software and probe head software. The main control software maintains the timecode; its error, known as the system timecode error, is determined by the accuracy parameter of the main control software's crystal oscillator. Taking a value of 50 ppm as an example, this error is ±50 μs. The probe head software performs self-timekeeping by acquiring the main control software's system timecode to maintain the timecode (this timecode is called the self-timekeeping timecode). If the exposure time is recorded using the probe head software's self-timekeeping timecode, the exposure time error is the probe head software's self-timekeeping timecode error. This error includes both the main control software's system timecode error and the probe head software's self-timekeeping timecode error, resulting in an error superposition phenomenon. This makes it difficult to control the exposure time error, and the software system implementation is complex. Summary of the Invention

[0004] To address the problems of existing methods for acquiring and corresponding imaging time in aerospace remote sensing instruments, such as the accumulation of errors, difficulty in controlling exposure time errors, complex software system implementation, and inability to meet the requirements of remote sensing data inversion, this invention provides a method for acquiring and corresponding imaging time in aerospace remote sensing instruments. The time synchronization error generated by this method is determined by the crystal oscillator accuracy parameter, and the software does not generate errors, reducing the complexity of the software system. At the same time, it has the advantages of simple, reliable, high-precision, real-time performance, and no bus transmission error.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0006] A method for acquiring and corresponding the imaging time of a space-based remote sensing instrument includes the following steps:

[0007] Step 1: The main control software receives the imaging command, parameters, timing pulse, and UTC time sent by the satellite computer, and maintains the system time code based on the timing pulse and UTC time. When the imaging conditions are met, the main control software sends the imaging command and parameters to the probe head software through the command frame.

[0008] Step 2: After receiving the imaging command and parameters, the detection head software controls the detector to expose. At the same time, at the start of the detector exposure, the detection head software sends a timing request pulse to the main control software. The falling edge of the timing request pulse is valid, the low level lasts for 1ms, and the timing request pulse period is consistent with the imaging frame period.

[0009] Step 3: When the main control software detects the falling edge of the time synchronization request pulse, it records the system time code at this moment, which is called the time synchronization time code. The main control software adopts the first-in-first-out principle and opens a FIFO with a depth of n to save the most recent n time synchronization time codes. The main control software then sends this set of time synchronization time codes to the probe head software through the command frame of the next cycle.

[0010] Step 4: When remote sensing data is being downloaded, the detection head software packages and downloads the most recent n time synchronization timestamps, imaging commands, parameters, and remote sensing data together.

[0011] The present invention has the following beneficial effects:

[0012] This invention proposes a method for acquiring and corresponding imaging time of aerospace remote sensing instruments. When the detector begins imaging exposure, the head software sends a timing request pulse signal to the main control software. When the timing request pulse changes from high to low, the main control software records the current system timecode (called the timing timecode) and sends it to the head software in the next command frame. When remote sensing data is available for download, the head software packages and downloads the timing timecode, imaging command, parameters, and remote sensing data together for data inversion and post-processing. This method eliminates the error caused by the head software maintaining the timecode; the timing timecode error originates only from the main control software's system timecode error, which is the crystal oscillator accuracy parameter (±50μs). Therefore, this invention reduces the time error between imaging time acquisition and correspondence (timing time) to the main control software's crystal oscillator accuracy parameter. With a crystal oscillator accuracy parameter better than ±100μs, this method can meet the requirements for remote sensing data inversion. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the information flow of the imaging time acquisition and corresponding method of aerospace remote sensing instrument according to one embodiment of the present invention;

[0014] Figure 2 This is a schematic diagram of the time synchronization request pulse waveform in this invention. Detailed Implementation

[0015] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and preferred embodiments.

[0016] In one embodiment, this embodiment provides a method for acquiring and corresponding the imaging time of a space-based remote sensing instrument, which specifically includes the following steps:

[0017] Step 1: The main control software receives imaging commands, parameters, UTC time (period of 1 second), and timing pulses (period of 1 second, falling edge valid, low level duration of 1ms) sent by the satellite computer via RS422 communication. It then maintains the system timecode based on the timing pulses and UTC time. Communication between the main control software and the probe head software is via RS422. The main control software sends command frames to the probe head software at fixed intervals. When imaging conditions are met, the main control software sends imaging commands and parameters to the probe head software via command frames. The information flow direction and content are as follows: Figure 1 As shown.

[0018] The main control software is responsible for maintaining the system timecode, imaging commands, and parameter control functions, through... Figure 1 It is known that the main control software synchronizes with the satellite computer once per second. The time maintenance error of the main control software is the timekeeping error within 1 second. This error is determined by the accuracy parameter of the crystal oscillator of the main control software. Taking this parameter as 50ppm as an example, this part of the error is ±50μs.

[0019] Step Two: After receiving the imaging command and parameters, the detection head software controls the detector exposure. Simultaneously, at the start of detector exposure, the detection head software sends a timing request pulse to the main control software. The falling edge of the timing request pulse sent by the detection head software is valid, the low level duration is 1ms, and the timing request pulse period is consistent with the imaging frame period. The timing request pulse waveform is as follows: Figure 2 As shown, in Figure 2 In the process, the timing request pulses sent by the probe head software are P1, P2, ..., P... N , where N is the number of imaging frames, and the time between the falling edges of two adjacent time request pulses is the image frame period.

[0020] Step two will produce signal delay errors, such as Figure 2 The t1 time in the figure is the time from when the detection head software code sets the level low to when the hardware timing pulse pin changes to the level low. This time is on the order of nanoseconds, and the specific value is determined by the hardware. Compared with the time maintenance error of the main control software, this error is negligible.

[0021] Step 3: When the main control software detects the falling edge of the time synchronization request pulse, it records the system time code at this moment (format: 4 bytes of second value, 2 bytes of millisecond value, 2 bytes of microsecond value). This time is called the time synchronization time code. The main control software adopts the first-in-first-out principle and opens a FIFO with a depth of n (for example, a FIFO depth of 3, i.e., n=3, or other depths designed according to requirements) to save the most recent n (for example, the most recent 3) time synchronization codes. The most recent n time synchronization codes form a set of time codes. The main control software sends this set of time codes to the probe head software through the command frame of the next cycle.

[0022] Step three will generate a timing pulse sampling delay error, such as Figure 2 The t2 time in the figure is the time from when the probe head software sets the hardware timing pulse pin to a low level to when the main control software samples and recognizes it. This time is determined by the crystal oscillator frequency. Taking a main control crystal oscillator clock of 30MHz as an example, this time is about 0.07μs.

[0023] Step 4: When remote sensing data is being transmitted down, the head software packages the most recent n time synchronization timestamps, imaging commands, parameters, and remote sensing data together, and transmits them to a large-capacity storage device via LVDS communication for data inversion and post-processing. This completes the acquisition of the imaging time of the space-based remote sensing instrument and the correspondence between the image and the time code.

[0024] This embodiment provides a method for acquiring and corresponding the imaging time of a space-based remote sensing instrument. It proposes general principles for hardware design and a software time synchronization method under the condition that the system's time synchronization error is determined. In this method, the time synchronization error mainly includes three parts: the time maintenance error of the main control software, the signal delay error, and the timing request pulse sampling delay error. The signal delay error and the timing request pulse sampling delay error are negligible; therefore, the time synchronization timecode error only originates from the timecode error of the main control software system. This timecode error is determined by the crystal oscillator accuracy parameter, and the software itself does not generate error. When the crystal oscillator accuracy parameter is better than the time synchronization error requirement, the method of this embodiment can acquire the imaging time with high precision and perform subsequent auxiliary data correspondence, thereby ensuring that the system's time synchronization error meets the requirements for remote sensing data inversion. Simultaneously, the software system timecode is maintained by the main control software, and the probe head software does not perform timecode maintenance, reducing the functional complexity of the software system. It also has advantages such as simplicity, reliability, high accuracy, good real-time performance, and no bus transmission error.

[0025] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0026] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for acquiring and corresponding imaging time of a space-based remote sensing instrument, characterized in that, Includes the following steps: Step 1: The main control software receives the imaging command, parameters, timing pulse, and UTC time sent by the satellite computer, and maintains the system time code based on the timing pulse and UTC time. When the imaging conditions are met, the main control software sends the imaging command and parameters to the probe head software through the command frame. Step 2: After receiving the imaging command and parameters, the detection head software controls the detector to expose. At the same time, at the start of the detector exposure, the detection head software sends a timing request pulse to the main control software. The falling edge of the timing request pulse is valid, the low level lasts for 1ms, and the timing request pulse period is consistent with the imaging frame period. Step 3: When the main control software detects the falling edge of the time synchronization request pulse, it records the system time code at this moment, which is called the time synchronization time code. The main control software adopts the first-in-first-out principle and opens a FIFO with a depth of n to save the most recent n time synchronization time codes. The main control software then sends this set of time synchronization time codes to the probe head software through the command frame of the next cycle. Step 4: When remote sensing data is being downloaded, the detection head software packages and downloads the most recent n time synchronization timestamps, imaging commands, parameters, and remote sensing data together.

2. The method for acquiring and corresponding imaging time of a space-based remote sensing instrument according to claim 1, characterized in that, The system timecode is formatted as follows: 4 bytes for seconds, 2 bytes for milliseconds, and 2 bytes for microseconds.

3. The method for acquiring and corresponding imaging time of a space-based remote sensing instrument according to claim 1, characterized in that, The FIFO depth is 3.

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