CN103353922B - A kind of OTF observes scan method - Google Patents

Abstract

The invention relates to an OTF observation scanning method, which divides a scanning area into several lines, scans a plurality of spaced lines each time, performs multiple interlaced scanning, and completes scanning of the entire scanning area. Using the interlaced scanning method, in the case of the same parameters such as antenna scanning speed, sampling interval, and observation reference point time interval, one scan can quickly cover an area, reducing the influence of factors such as telescope system performance and weather changes on the distribution of the entire area; When the results of interlaced scanning are re-grid, the reference points used by adjacent rows of data in a grid area are observed at different times, the reference points of different rows are independent, and the reference points of different rows The sum of the integration time is the effective integration time of the reference point, so the integration time for the reference point can be 1/k of the progressive scanning, k is the number of scans of a scanning area.

Description

A method of OTF observation and scanning

technical field

The invention relates to the field of radio astronomical telescopes, in particular to an OTF observation and scanning method.

Background technique

OTF (On The Fly) is an observation method for radio telescopes. The antenna scans the specified area at a constant rate without tracking a single grid point. Multiple source points can share reference points and blackbody calibration, saving time; Since the entire area is quickly scanned, changes in system performance and weather over time will have less impact on observations.

In order to avoid the loss of information due to insufficient sampling, there are some restrictions on OTF scanning parameters, such as the distance between two adjacent scanning lines cannot be greater than the "Nyquist interval"; the sampling interval, that is, the single integration time, should be greater than the receiver backend The minimum time required to obtain a set of valid data; the distance scanned by the antenna within the sampling interval must be close to the line spacing.

In the process of OTF observation, very dense spatial sampling is carried out. These sampling points are not necessarily equally spaced, and further regrid processing (regrid) is required to obtain grid point data in the usual form.

The traditional scanning method is to divide a scanning area into several lines, and start scanning line by line from one direction (as shown in Figure 1). Scanning speed means shortening the integration time of each point; shortening the integration time of each point means that the integration time of each grid point is short after the data regrid of a single scan, and the noise is large, requiring multiple scans; shortening the scan of each row Time means that the antenna turns around frequently, which is not conducive to improving observation efficiency; if the scanning speed is slow, it will take a long time to complete a scan, which is not conducive to reducing the impact of telescope system performance and weather changes on observation.

In addition, the integration time of the reference point is limited, too long will waste time and reduce the observation efficiency, too short will increase the noise; how long to observe the reference point is also affected by factors such as receiver stability, pitch angle change, etc. Constraints, if the interval is too long, the baseline of the spectral line will be uneven, and if it is too short, it will waste time; when regrid, the value of a certain grid point is the data of sampling points within a certain range near this point, according to the distance between the sampling point and the grid point Use a certain function for weighting, usually using a gaussian function; the effective integration time of these weighted points to the reference point is equal to the effective integration time of the source. If the points in this range share a reference point, then the effective integration of the reference point is the integration time of a single reference point, and the integration time of a single reference point must be equal to the effective integration time of the source.

How to quickly cover the entire area without increasing the scanning speed, and reduce the influence of system performance and weather changes on the distribution of the entire area; how to reduce the impact on the reference point without increasing the noise level The integration time and improving the observation efficiency have become technical problems that need to be solved.

Contents of the invention

The purpose of the present invention is to overcome the defects of the prior art, provide an OTF observation and scanning method that can quickly cover the entire area, and has a short integration time for the reference point, and improves the observation efficiency.

The technical solution for realizing the purpose of the present invention is: an OTF observation scanning method, which divides a scanning area into several lines, scans a plurality of spaced lines each time, performs multiple interlaced scanning, and completes the scanning of the entire scanning area.

Described OTF observation scanning method specifically comprises the following steps:

S1. Calculate the total number of lines scanned in an area: n = scan range ÷ scan line spacing

S2. Set the number of scans k, calculate the number of lines x for each scan: x=n/k, and round up the calculation result to an integer;

S3. According to the set reference point observation time interval and the time used for scanning one line, after calculating how many lines to scan, the reference point needs to be observed once;

S4. Calculate the scan times m of the i-th row, i=1, 2...n, m=i/x, and round up the calculation result to an integer;

S5. Calculate the number of rows y actually scanned when scanning the i-th row:

y=(i-1-x*(m-1))*k+m;

S6. If the number of lines y actually scanned reaches the number of interval lines required to observe the reference point, then observe the reference point;

S7. Continue scanning from the yth row;

S8. Steps S4-S7 are repeatedly executed until the set scanning times k is reached, and the process ends.

The beneficial effects of the present invention are as follows: 1. By adopting the interlaced scanning method, under the condition that the parameters such as antenna scanning speed, sampling interval, and observation reference point time interval are the same, one scan can quickly cover an area, and the data of a position after regrid processing The spectral line is the average of multiple results, and each time is separated by a long time. The points in a gridded range are distributed in different time periods, so it can reduce the influence of factors such as telescope system performance and weather changes on the distribution of the entire area; ②Interlacing When the scanning results are regrid, the reference points used by adjacent rows of data in a gridded area are observed at different times, the reference points of different rows are independent, and the integration of the reference points of different rows The sum of time is the effective integration time of the reference point, so the integration time of the reference point can be 1/k of the progressive scanning, k is the number of scans of a scanning area.

Description of drawings

Fig. 1 is a schematic diagram of progressive scanning in the prior art of the present invention;

Fig. 2 is the interlaced scanning schematic diagram of embodiment 1 of the present invention;

Fig. 3 is a flowchart of the present invention.

detailed description

As shown in Figure 2, an OTF observation interlaced scanning method divides n lines of a scanning area into 3 scans, the first scan is 1, 4, 7... lines, and the second scan is 2, 5, 8... Line, the third scan 3, 6, 9... lines.

As shown in Figure 3, the OTF observation interlaced scanning method specifically includes the following steps:

S1. Calculate the total number of lines scanned in an area: n = scan range ÷ scan line spacing

S2. Set the number of scans k, calculate the number of lines x for each scan: x=n/k, and round up the calculation result to an integer;

S3. According to the set reference point observation time interval and the time used for scanning one line, after calculating how many lines to scan, the reference point needs to be observed once;

S4. Calculate the scan times m of the i-th row, i=1, 2...n, m=i/x, and round up the calculation result to an integer;

S5. Calculate the number of rows y actually scanned when scanning the i-th row:

y=(i-1-x*(m-1))*k+m;

S6. If the number of lines y actually scanned reaches the number of interval lines required to observe the reference point, then observe the reference point;

S7. Continue scanning from the yth row;

S8. Steps S4-S7 are repeatedly executed until the set scanning times k is reached, and the process ends.

The number of scans k is generally divided into 2-4 times based on the overall consideration of factors such as the total time used to scan an area, receiver stability, and post-data processing requirements.

Claims (2)

1. On The Fly observes a scan method, and a scanning area is divided into several rows, scans multiple row separately every time, carries out interlacing scan repeatedly, complete the scanning of whole scanning area；

It is characterized in that, the method specifically includes the following step:

S1. calculate and scan a total line number in region: n=sweep limits ÷ scanning line spacing

S2. setting scanning times k, calculate each number of scanning lines x:x=n/k, result of calculation rounds up number；

S3. according to the time used by the reference point observation interval set and scanning a line, after calculating scanning how many row, a reference point need to be observed；

S4. calculating scanning the pass m, i=1,2 of the i-th row ... n, m=i/x, result of calculation rounds up number；

When S5. calculating scanning the i-th row, line number y of actual scanning:

y=(i-1-x*(m-1))*k+m；

If S6. line number y of actual scanning reaches the interval line number of the need observation reference point that S3 calculates, then observe reference point；

S7. start to continue to scan on from y row；

S8. repeated execution of steps S4-S7, to reaching to set scanning times k, end.

On The Fly the most according to claim 1 observes scan method, it is characterized in that, the value of described scanning times k is 2-4.