JPS591989B2 - multispectral scanner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multispectral scanner for simultaneously obtaining images of one field of view in two different radiation wavelength regions.

For example, in academic research on geology, water or oil resources, or pollution, both visual and infrared images of one target field of view may be required, and for this reason, resource exploration satellites are equipped with multispectral scanners. ing.

Conventional multispectral scanners separate scanning output light containing visible and infrared components from a scanning mirror into visible and infrared regions using dichroic mirrors, and separate these output lights into infrared and visible regions, respectively. The signal was converted into a corresponding electrical signal by a detector, each amplified by a separate amplifier, and a display device such as a cathode ray tube provided a visible and infrared image of the field of view at the same time. . Therefore, two devices are required from the detector to the amplifier, one for visible light and one for infrared light, and when transmitting both video signals obtained in this way, the highest frequency of both video signals is set to FMA.
If x, a transmission band of 2 fmax is required, which has the drawback of increasing the size, weight, and power consumption of the device. An object of the present invention is to provide a multispectral scanner that is small, lightweight, and consumes little power.

The features of the present invention for achieving the above object include an optical scanning device that optically scans an object back and forth and obtains optical scanning signals during both the forward scanning period and the backward scanning period; a photodetector that converts into an electrical signal; and a filter in a first wavelength range that is disposed between the optical path of the optical scanning device and the detector and is used during either the forward scanning period or the backward scanning period. and an optical filter device into which a second wavelength range filter is inserted during the other period of the forward scanning period. The present invention will be explained in detail below with reference to the illustrated embodiments.

FIG. 1 shows a multispectral scanner 10 according to the present invention.
This multispectral scanner J-10 is mounted on an artificial satellite and optically scans the ground to obtain a scanning signal in the visible range and a scanning signal in the infrared range. The information is processed and transmitted to the ground by a transmitting device (not shown).

The multi-vector scanner 10 includes an optical scanning device 20 that scans the ground reciprocatingly with an instantaneous field of view and obtains optical output during both the forward scanning period and the backward scanning period. It mainly consists of a scanning mirror 22 that reciprocates in the A direction and optically scans the ground, reflecting mirrors 23 and 24 and relay lenses 25 and 26 that form this visual field image on a detector. The reciprocating movement of the scanning mirror 22 is provided by a torquer 27 consisting of a torque motor attached to the rotating shaft 21, and the torquer 27 is a torquer drive circuit controlled by a scanning width switching signal S1 from the ground. 2
8 to scan a predetermined width.
To ensure this reciprocating motion, an encoder 29 is provided to detect the reciprocating motion of the torquer 27 and convert it into an electrical signal.This output electrical signal S2 is input to the torquer drive circuit 28 to can perform the desired reciprocating motion. The satellite mounted on the scanner tower is flying in a direction perpendicular to the reciprocating direction of the scanning mirror 22 by an attitude control device (not shown), that is, in a direction perpendicular to the plane of the paper in FIG. By the 22 reciprocating scans, the visual field is subjected to so-called line scanning. FIG. 2 shows a state in which the field of view 1 is scanned by the scanning mirror 22.
In the figure, the scanner is scanning back and forth in the direction of arrow A, and since this scanner is flying in the direction of arrow B by the satellite, the field of view is A, b, c, etc. by forward scanning. is optically scanned, and by backward scanning a/, b', c'...
The field of view is optically scanned as shown in FIG.

Therefore, as shown in FIG. 4, each optical scanning line A, a', B,
An optical scanning signal St corresponding to bl, is obtained, and A, b, c
, and the optical scanning signal obtained during the forward scanning period of , Al,b/c
The optical scanning signals obtained during the backward scanning periods of ', . In FIG. 1, reference numeral 30 indicates a relay lens switching motor, which can change the resolution by appropriately switching the relay lenses 25 and 26 in response to a resolution switching signal S3 from the ground.

The scanner 10 further includes an optical filter device 50 for filtering the optical scanning signal between the optical scanning device 20 and the detector 40. Infrared filters 51 and 52 that pass only the outer range components, and visible range filter 5 that passes only other wavelength range components, such as visible light components, in the incident light.
A disc-shaped optical filter wheel 55 provided with 3 and 54.
(See Figures 1 and 5).

The valley filters 51 to 54 are provided at equal intervals of 900 from the center 0, and as shown in FIG.
The filter wheel 55 is rotatably provided so that each filter can be sequentially inserted into the optical path between the optical scanning device 20 and the detector 40. The filter wheel 55 is driven by a motor, and a filter wheel motor 57 driven by a drive circuit 56 inserts one of the infrared filters into the optical path during the forward scanning period of the optical scanning signal.
During the backward scanning period of the optical scanning signal, one of the visible range filters is intermittently rotated in synchronization with the reciprocating movement of the scanning mirror so that it is inserted into the optical path. This synchronization is performed by the synchronization signal generator 5.
This is done by means of a synchronization signal generated by an electrical signal S2' corresponding to the reciprocating movement of the scanning mirror from an encoder 29 inputted to 8. Therefore, as shown in FIG. 6, the detector 40 receives near-infrared light S, l, sr2, ... and visible light SVl, S, which are optical signals S5 separated for each scanning period.
V2, . . . are input alternately. Detector 40
The sensor is composed of detection elements such as silicon photo diodes that are sensitive in the visible and near-infrared regions, and in the illustrated embodiment, it is constructed as a multi-element detector with six detection elements arranged vertically. Thus, six electrical signals are simultaneously taken out to channels CH to CH2. In this way, the 6 channels of parallel video signals are processed by the preamplifier 4.
1. It is amplified to a predetermined level by the post amplifier 42, DC-regenerated by the clamp and blanking device 43, and a synchronization signal from the synchronization signal generator 58 is added.Furthermore, it is amplified by the main amplifier 44 and sent to a processor (not shown). and sent to the ground by a transmitting device.
In FIG. 1, reference numeral 59 indicates a filter identification signal generator for indicating whether an infrared filter or a visible filter is inserted in the optical path, and the identification signal S4 from this generator is synchronized. The signal is sent to the processor via the signal generator 58 and added to the video signal of each scanning period. Therefore, at the receiving station, it is possible to identify whether the image signal is in one of the two wavelength regions, in this embodiment, the infrared region or the visible region. In addition, in this embodiment, the optical scanning device 20 has a calibration light source 31 so that the level of the video signal received on the receiving side can be calibrated, and the known energy emitted from the light source 31 is By entering the light into the detector 40 and appropriately inserting it between the scanning signals, an image corresponding to the energy level can be obtained. You can know the size of the signal. Further, a detector 4 is installed between each filter of the filter wheel 55 shown in FIG.
Since the level between each scanning signal is set to zero by blocking the incident light to zero, the magnitude of the video signal corresponding to the zero energy level can be determined from the magnitude of the video signal at this time. Therefore, since the video signal level for the two known energy radiations can be known in the video signal, the absolute value of the level of each part of the video signal can be known on the receiving side. In the above embodiment, six channels of parallel video signals are obtained in one optical scan, but the present invention can of course be applied regardless of the number of channels.

According to the present invention, as described above, the optical scanning device extracts the optical scanning signals for both forward scanning and backward scanning, and by applying an optical filter, the infrared scanning signals and the visible scanning signals are separated. Since the images are taken out alternately and converted into electrical signals using a single detector, only one video signal device is required compared to conventional equipment, making it possible to keep the size and weight small. S/N is only about 1/2
If the S/N ratio is large, and the same S/N ratio is acceptable, the transmission power can be reduced by that amount, so power consumption can be kept low from this aspect as well, so satellites with strict size, weight, and power consumption requirements can be It is possible to provide a multi-vector scanner which is particularly suitable as a device for

[Brief explanation of the drawing]

Fig. 1 is a series diagram of an embodiment of the present invention, Fig. 2 is a diagram for explaining the method of scanning the field of view of the device shown in Fig. 1, and Fig. 3 is a drive voltage waveform diagram of the torquer drive circuit 1. , FIG. 4 is a waveform diagram of the optical scanning signal St, FIG. 5 is a front view of the filter wheel,
Figure 6 shows the separated optical scanning signal Ss input manually to the detector.
FIG.

Claims (1)

[Claims] 1. An optical scanning device that optically reciprocates the observation target, a detector that converts the light emitted from the optical scanning device into an electrical signal, and an optical scanning device that is arranged between the optical path of the optical scanning device and the detector. A filter for a first wavelength region is inserted during either a scanning period or a backward scanning period, and a filter for a second wavelength region different from the first wavelength region is inserted during the other scanning period. A multispectral scanner characterized in that it is equipped with an optical filter system.