DE2633760A1 - LINE SCANNING SYSTEM FOR TERRAIN SCANNING IN AIRCRAFT - Google Patents

Description

- . JOL! 1871

HAWKER SIDDELEY DYNAMICS LIMITED Hd. 26? 98

Manor Road,

Hatfield, Hertfordshire, England.

Line scanning system for area scanning in aircraft

The invention relates to optical scanning and film recording systems in general and to the use of particular detector aperture shapes to improve their spatial dimensions Sampling (sampling) rates and in addition to improving the subjective quality of the film recording in particular.

Aircraft infrared line scanners for scanning and manufacturing A record of the terrain under the aircraft usually uses discrete detectors and probes the field of the object in one direction while moving towards the aircraft generating the scan in the other direction (vertical) support. Such systems suffer from problems of the room sampling rate.

It is common practice with line scanners to use square detectors. The sensor system is in one Airplane and scans the object field in the direction perpendicular to the flight path of the airplane (transverse to the track scan). The aircraft movement creates the other scan or raster component on its path (along the track scan). the Object field sampling rate of the detector in the cross track scanning direction is continuous, while it is not continuous in the longitudinal track direction. Furthermore, the longitudinal lane rate variable when the ratio of aircraft speed to height changes (V / H).

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In systems with square detectors, it is common to determine the ratio of the limiting speed to the height (VH / H) to take into account, like the one where each subsequent transverse track strip is edge-to-edge with the previous one Strip collides. How limited the V / H ratio is, the sampling rate is reduced to one per dissolving element in the "longitudinal track section (here, a dissolving element defined as the respective field of view, which results from the size of the respective detector element).

Sampling theory dictates that a minimum of two samples per pixel be used to faithfully reproduce the original Waveform is necessary. In terms of spatial Samplings also require the sampling interval is spatially separated by half of a pixel. The result of this critical meeting Criterion would have to halve the V / H capability of the system.

In the case of a film recording system that matches the detector, i.e., using a square light source scanning aperture to draw the lines on the film record, becomes the Raster effect at the V / H border (after the collision of the Scan lines) obviously. If the V / H ratio decreases, either the following line overlaps the previous one, which results in a further raster effect because of the film density built up on the overlap portion, or the longitudinal track width of the line is also reduced in order to compensate so that the primary screen effect is evident remain.

The above explanations about the sampling rates for the detector also apply to the recording scanning aperture.

S09886 / 109Ö

The object of the invention is:

a) to improve the longitudinal track detector sampling rate and

b) the recording raster effect and the sampling rate improve without either the spatial. Resolution or " Detrimentally influencing the V / H limitation of the system.

According to the invention, a line scanning system for use in aircraft for terrain scanning is provided, wherein the detector arrangement of the scanning system arranged in a distributed manner Contains detector elements which lie in rows at right angles to the scanning direction and are offset from one another so that the elements of a subsequent row are opposite columns in a preceding row. The plant is now through characterized in that the individual detector element areas are rhombus-shaped, the rhombuses having diagonals which run parallel to the scanning direction and the distribution and the dimensions of the elements are so perpendicular to the scanning direction that they are significant during scanning Sampling bulge flaps result.

In infrared line scanners, for a given infrared optical aperture, the thermal sensitivity is directly proportional to the square root of the detector area. The detector surface is kept constant for a given optical opening and a given thermal system sensitivity. In a preferred embodiment, the diamonds are actually set at 45 '
bid is unchanged.

actually have squares rotated by 45 ° and the detector

An embodiment of the invention is described with the help of the drawings. In these is:

/ 1 09Q

Figure 1 shows three possible detector shapes

Figure 2 shows the relative corresponding curves for the detector shapes according to Figure 1;

Figures 3a and 3b show the effect of changing V / H for diamond-shaped detectors, and

FIG. 4 compares an arrangement of diamond detectors with the same number of square detectors of the same size.

In Figure 1 three opening shapes are considered - square, Rhome, and circular. A dimensional Fourier transform e tion can be written as follows: For the square opening:

= _sin _sin (cod)

where d is the length of the opening sides and whether the reduced spatial frequency is 2TTf (where f is the spatial frequency);

For the circular opening:

where J ^ is the Bessel function of the first kind. For the diamond opening:

21 - cos (u> 'd)

where d is the half-diagonal in the scanning direction and c is the Half diagonal is perpendicular to the scanning direction.

Corresponding to about half a revolution per opening width Frequency, the relative response of the square opening is about 31 smaller than that of the circular system, which is about 3% smaller than that of the diamond opening. The high frequency response for the circular opening is better than the edge that of the square opening (zero occurs first at a frequency 15% higher than that of the square opening), while the high Frequency response of the diamond opening is a further improvement over that of the square opening (first zero occurs at um 401 higher frequency than that of the square opening),

It can therefore be seen that the advantages of the individual sampling opening shapes only exist in terms of addressing to occur at spatial frequencies much higher than half a circulation per opening width is what it takes in a system makes it difficult to relatively perform the scoring in terms of resolution limit alone.

The response of the three forms of opening to high frequency targets is very different because of the response characteristic following the first zero (Figure 2). This can be called a "resonance" phenomenon be considered. The first "resonance" for a square opening occurs at around 1.5 revolutions per opening, the next at 2.5 revolutions etc. Both the square and the circular opening have a significant one at the first resonance Response (more than 10%) and the square opening at around 10% At the fourth "resonance", this effect leads to a "false resolution" and can act as a source of ambient noise can be viewed in the annex.

The response of the diamond opening is at the first "resonance" less than 10%.

β09βδβ / 1090

In terms of the "edge" response of the various detector shapes on a stretched track target, the diamond-shaped opening has a more rapid rise in space at the edge than the square and circular openings (because of the high frequency response of this opening).

For a given detector area and a ratio of speed to altitude, the diamond and the circular Opening advantages over the square opening in terms the number of longitudinal track samples per pixel. FIG. 3a therefore shows rhombic openings with 50% overlap. Sampling theory suggests that an absolute minimum of 2.0 samples per pixel be used to faithfully reproduce the original image are necessary. This condition can be approximated with approximately 40% overlapping diamond openings (Figure 4).

When using a film recording device such as a light emitting device Diodes as the line-writing element for the detector arrangement apply with regard to the frequency response and the sampling rate similar arguments. If the diamond-shaped openings overlap by 401, the subjective quality of the film recording by simply allowing it the photo diode scan lines to the upper lobe on the recording film improved. The result is a smooth one Recording characteristics with a very low "raster effect". As the scan lines increasingly overlap (Figure 3b), like the film speed to correct the scale of recording is decreased as V / H decreases, the resulting halftone effect becomes high in frequency and comparative be small in amplitude. The mean brightness of the light emitting diode can change to the mean one Video level and no information is lost.

FIG. 4 shows that with an arrangement of square detectors in which the following detectors in the next row are offset to cover the column, there is no overlapping there and each pixel is checked only once. Only by realigning the detectors by 45, their number, shape and size remaining the same, so that they are now rhombuses with diagonals parallel to the scanning direction, an overlap occurs, so that each pixel is checked 1.4 times.
The invention thus enables:

1) Increasing the longitudinal track sampling rate while maintaining resolution, sensitivity and scan line density will;

2) Improvement in the writing and recording grid system to reduce the visual raster effect in the displayed recording without the detrimental influence of the Spatial resolution of the system to minimum values;

3) Arrange the detector scan and the display scan Soxvohl to keep the Ras te rs amp lings rate as big as possible as well as to make the visual raster effect as small as possible.

The invention also includes a detector arrangement in which the detectors are mounted so that the V / H ratio can be set to a special flight pattern or a broadcast or the detector arrangement optionally can be simulated to follow these requirements.

6Ö $ 886 / 1ÖÖÖ.

Claims (1)

26337Bfl 11 JiL; ^lSfB P. A T E .N T A N -. S PR O C H. E Line scanning system for use in an aircraft for scanning terrain, the detector arrangement of the scanning system contains distributed detector elements in rows, which run at right angles to the scanning direction and against each other are offset so that the elements of a subsequent row are opposite columns in a preceding row, characterized in that the individual detector element regions are rhombus-shaped, the rhombuses facing the scanning direction have parallel diagonals and the distribution and dimensioning of the elements at right angles to the scanning direction are such that they are a considerable during scanning Result in sampling overlap, 2, system according to claim 1, characterized in that the sampling overlap is practically 40%. 3. Plant according to claims 1 and 2, characterized in that that the diamonds are squares rotated so that each has a diagonal that is parallel to the scanning direction. 4, system according to the preceding claims, characterized in that that a recording grid system writing openings which are similar to the detector elements of the scanning system, 5. Plant according to the preceding claims, characterized in that that the detector elements adjustable] attached and the detector arrangement is selectively connected can be,- ;. Meissner aaiL .S098ä6 / iÖ§Q ORiGSNAL INSPECTED e e r s e i t e