Synthetic aperture radar reflector

Abstract

To provide a reflector for a synthetic aperture radar which can be easily assembled at an installation site and is compatible with both southbound and northbound orbits of an artificial satellite. [Solution] A reflector 1 that retroreflects radio waves emitted from a synthetic aperture radar 21, and comprises four supports 11 made of single tubes SP and a plurality of reflective grating bodies 12 in which a plurality of single tubes SP are fixed in a crisscross lattice pattern with fasteners 13, and the reflective grating bodies 12 are fixed in multiple rows above and below the four supports 11.

Description

[Technical Field]

[0001] The present invention relates to a reflector suitable for use at a displacement measurement point of a synthetic aperture radar. [Background technology]

[0002] Synthetic aperture radar (hereinafter also referred to as SAR) observes the Earth's surface irregularities and other features by emitting radio waves toward the Earth's surface from satellites orbiting the Earth and receiving the reflected scattered waves. Interferometric SAR time series analysis is also known, in which the same area is observed at two or more different times and the differences between the observations are analyzed to understand changes in the Earth's surface over time. In this type of interferometric SAR time series analysis, reflectors that stably reflect radio waves are installed at appropriate locations within the observation area to understand trends in surface objects that stably and strongly reflect microwaves between observation data acquired at multiple times. The present applicants previously proposed a SAR reflector that can be easily transported even when the reflector is installed in a difficult-to-access location such as a forest (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7367947 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above-mentioned conventional technology uses a unit reflector with three sides of a triangular pyramid as reflecting surfaces for radio waves, so it is necessary to weld steel plates into the triangular pyramid in advance. Furthermore, while typical SAR satellites can observe from polar orbits (southbound and northbound) or inclined orbits, interferometric SAR time series analysis uses data observed from the same orbit. Since the above-mentioned conventional technology is designed to support only one of these orbits, it is necessary to install reflectors compatible with each orbit.

[0005] The problem to be solved by the present invention is to provide a reflector for SAR that can be easily assembled on site and is compatible with both southbound and northbound satellite orbits. [Means for solving the problem]

[0006] The present invention solves the above problem by providing a reflector that retroreflects radio waves emitted from an SAR, comprising four support pillars made of single tubes and a plurality of reflective lattice bodies in which a plurality of single tubes are fixed in a crisscross pattern using fasteners that fix the single tubes at right angles, such as orthogonal clamps, and by fixing the reflectors in multiple rows above and below the four support pillars. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a SAR reflector that can be easily assembled on site and is compatible with both southbound and northbound satellite orbits. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a perspective view showing a reflector according to an embodiment of the present invention. [Figure 2] FIG. 1 is a plan view showing a reflector according to an embodiment of the present invention. [Figure 3] 1 is a side view showing a reflector according to an embodiment of the present invention. [Figure 4] FIG. 1 is a perspective view showing a fastener for a reflector according to an embodiment of the present invention. [Figure 5] 1 is a diagram illustrating the reflection and scattering of radio waves emitted from a SAR to a single tube. FIG. [Figure 6] This diagram shows the southbound and northbound orbits of the Advanced Land Observing Satellite Daichi-2 (ALOS-2). [Figure 7] This is a diagram of the reflector installed to match the northbound orbit of the Advanced Land Observing Satellite Daichi-2 (ALOS-2). [Figure 8]This is a diagram of the reflector installed to match the southbound orbit of the Advanced Land Observing Satellite Daichi-2 (ALOS-2). [Figure 9] This diagram shows the reflectors installed for both the southbound and northbound orbits of the Advanced Land Observing Satellite Daichi-2 (ALOS-2). DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a perspective view showing one embodiment of a reflector according to the present invention, Fig. 2 is a plan view, Fig. 3 is a side view, and Fig. 4 is a perspective view showing a fastener 13. Note that the fastener 13 is not shown in Figs. 1 to 3.

[0010] The reflector 1 of this embodiment is a reflector that retroreflects radio waves emitted from a synthetic aperture radar (SAR). The SAR is mounted on an artificial satellite orbiting the Earth, mounted on an aircraft, or fixed to an appropriate location on the Earth. In the embodiment described below, an example is shown in which the reflector 1 according to the present invention is applied to an artificial satellite-mounted SAR 21 mounted on an artificial satellite 2 such as the Advanced Land Observing Satellite "DAICHI-2 (ALOS-2)" operated and managed by JAXA (Japan Aerospace Exploration Agency).

[0011] However, the reflector 1 of the present invention is not limited to the SAR mounted on Daichi 2, but can also be applied to SARs mounted on other artificial satellites. Furthermore, the reflector 1 of the present invention is not limited to the SAR mounted on an artificial satellite, but can also be applied to SARs mounted on aircraft or other flying objects, or SARs fixed at appropriate locations on the Earth.

[0012] 1 to 3, the reflector 1 of this embodiment includes four support posts 11 each made of single tubes SP, and a reflective grating 12 formed by fixing eight single tubes SP in a grid pattern with fasteners 13, with the reflective grating 12 fixed in two rows, one above the other, to the four support posts 11. However, the number of single tubes SP constituting one reflective grating 12 is not particularly limited, and may be more than eight. The single tubes SP of this embodiment are not particularly limited, but may be, for example, single tubes made of galvanized steel with an outer diameter φ of 48.4 mm and a thickness t of 2.4 mm.

[0013] As shown in FIG. 2 , one reflective grating 12 is constructed by assembling four single-tube SPs constituting a vertical row 121 and four single-tube SPs constituting a horizontal row 122, with the four single-tube SPs constituting the vertical row 121 positioned on top, and fastening two single-tube SPs at each intersection using fasteners 13 as shown in FIG. 4 . Since one reflective grating 12 has 16 intersections, eight single-tube SPs are fastened using 16 fasteners 13. The reflective grating 12 assembled in this manner is formed into a square with a side length a of 1 m, as shown in the plan view of FIG. 2 , although not particularly limited thereto. In other words, one reflective grating 12 is assembled using eight single-tube SPs each 1 m long. Note that the length a of the single-tube SPs constituting the reflective grating 12 is not limited to 1 m and is preferably set appropriately depending on the wavelength of the radio waves radiated from the SAR 21. Furthermore, the reflective grating 12 is not limited to a square shape and may be rectangular.

[0014] The support pillars 11 in this embodiment are made of single tube SPs of the same specifications as the single tube SPs constituting the reflective grating 12. It is desirable to set the dimensions of the support pillars 11 shown in Fig. 3, such as the overall length h, the length h1 from the bottom end of the support pillar 11 to the lower reflective grating 12, and the length h2 from the top end of the support pillar 11 to the upper reflective grating 12, appropriately according to the wavelength of the radio waves radiated from the SAR 21.

[0015] When installing the reflector 1 on flat ground, the supports 11 of this embodiment are assembled and fixed to four supports 11 of the same length h so that the reflective grid 12 is horizontal. In contrast, when installing the reflector 1 on sloping ground, the length h of the support 11 on the lower side of the sloping ground is adjusted (made longer) so that the reflective grid 12 is horizontal and the length h of the support 11 on the upper side of the sloping ground is an appropriate length. Note that a base for fixing the support 11 to the installation location may be provided at the lower end of the support 11.

[0016] The fastener 13 of this embodiment has a pair of clamps 131, 131, and the bases of these pair of clamps 131, 131 are fixed to each other. Each clamp 131 is openable and has an inner diameter corresponding to the outer diameter of the single pipe SP. When the clamps 131 are open, they clamp the single pipe SP and the bolts and nuts are tightened to fix the two single pipes SP at a right angle to each other.

[0017] In the reflector 1 of this embodiment, the reflective grating 12 serves as a reflecting surface for the radio waves radiated from the SAR 21, and the reflective grating 12 is composed of a single tube SP. FIG. 5 is a diagram illustrating the reflection and scattering of the radio waves radiated from the SAR 21 relative to the single tube SP. When radio waves such as microwaves are radiated onto a cylindrical object such as a single tube SP, the radio waves radiated from the front of the cylindrical surface of the single tube SP are backscattered as shown in FIG. 5(B) and reflected back to the satellite 2. In contrast, radio waves radiated from an oblique angle to the cylindrical surface of the single tube SP are forward scattered as shown in FIG. 5(C) and do not return to the satellite 2.

[0018] Since microwaves and other radio waves emitted from SAR 21 of satellite 2 are emitted while being scanned, in the case of a single-tube SP installed horizontally, as shown by dotted line D in Figure 5(A), the radio waves are backscattered in the area where they are irradiated from the front (the area of ​​dotted line D) and reflected back to satellite 2, but are forward scattered in other areas and do not return to satellite 2.

[0019] Figure 6 shows the southbound orbit ST and northbound orbit NT of the Advanced Land Observing Satellite Daichi-2 (ALOS-2), which is operated and managed by JAXA. Daichi-2 is an artificial satellite 2 that orbits the Earth at an altitude of approximately 630 km and an orbital inclination of 97.9° relative to the equator, and observations are usually made with the satellite line of sight X pointing diagonally downward to the right relative to the direction of satellite 2's movement. As shown in Figure 6, there is a southbound orbit ST that observes Japan from the east, and a northbound orbit NT that observes Japan from the west.

[0020] FIG. 7 is a diagram showing the reflector 1 of this embodiment installed to match the northbound orbit NT of Daichi-2, FIG. 8 is a diagram showing the reflector 1 of this embodiment installed to match the southbound orbit ST of Daichi-2, and FIG. 9 is a diagram showing the reflector 1 of this embodiment installed to match both the northbound orbit NT and the southbound orbit ST of Daichi-2.

[0021] As explained in Fig. 5, when a cylindrical single tube SP is used as the reflecting surface of the reflector 1, the reflection intensity increases if the reflector 1 is installed so that the direction of travel of the satellite 2 is parallel to the axial direction of the single tube SP. Therefore, to prepare for radio waves from the SAR 21 when flying on a northbound orbit NT, it is preferable to install the reflector 1 so that either one of the vertical columns 121 or horizontal columns 122 of the reflective grid 12 of the reflector 1 is parallel to the northbound orbit NT, as shown in Fig. 7. Furthermore, to prepare for radio waves from the SAR 21 when flying on a southbound orbit ST, it is preferable to install the reflector 1 so that either one of the vertical columns 121 or horizontal columns 122 of the reflective grid 12 of the reflector 1 is parallel to the southbound orbit ST, as shown in Fig. 8.

[0022] However, as shown in Figures 7 and 8, if the reflector 1 of this embodiment is installed in the optimal orientation for each of the northbound orbit NT and the southbound orbit ST, two reflectors 1 are required for one installation location, which not only increases costs but also may cause problems with installation space. Therefore, in addition to or instead of the installation example shown in Figures 7 and 8, the reflector 1 of this embodiment may be installed so that one side of either the vertical column 121 or the horizontal column 122 of the reflective grid 12 of the reflector 1 is parallel to the equator, as shown in Figure 9. However, if installed in this manner, the single tube SP of either the vertical column 121 or the horizontal column 122 of the reflective grid 12 will not be parallel to either the northbound orbit NT or the southbound orbit ST, which may reduce the reflection intensity.

[0023] However, since the installation orientation of the reflector 1 of this embodiment is such that it has an angle of only 7.9° with respect to both the northbound orbit NT and the southbound orbit ST, the reflection intensity decreases, but the decrease is small. In addition, since the reflector 1 of this embodiment has two tiers of reflective grids 12, one above the other, the radio waves irradiated onto the lower tier of reflective grid 12 that are irradiated onto the front of the single tube SP return to the satellite 2, and further, some of the radio waves irradiated onto a location other than the front of the single tube SP and scattered may be scattered by the upper tier of single tube SP and return to the satellite 2. As a result, the decrease in reflection intensity can be compensated for.

[0024] As described above, the SAR reflector 1 of this embodiment is a reflector 1 that retroreflects radio waves irradiated from the SAR 21, and comprises four pillars 11 made of single tubes SP, and a plurality of reflective lattice bodies 12 in which a plurality of single tubes SP are fixed in a crisscross pattern with fasteners 13. The reflective lattice bodies 12 are fixed in multiple layers above and below the four pillars 11, so that by transporting the plurality of single tubes SP, the plurality of fasteners 13, and tools to the installation location, the reflector 1 can be assembled and installed at the installation location in a short time with simple work.

[0025] Furthermore, in the SAR reflector 1 of this embodiment, the reflective grid body 12 has four single tubes SP fixed vertically and horizontally in a crisscross pattern, which minimizes the number of single tubes SP required, improving the ease of transportation to the installation site and assembly at the installation site, as well as ensuring the reflection strength of radio waves.

[0026] Furthermore, in the SAR reflector 1 of this embodiment, the reflective grid 12 is fixed to the four pillars in two tiers, one above the other, so that the number of single tubes SP is minimized, which improves the ease of transporting the reflector to the installation site and assembling it at the installation site, and also ensures the reflection strength of radio waves. [Explanation of symbols]

[0027] 1...Reflector SP...Single pipe 11...Strut 12...Reflection grid body 121...Vertical 122...row 13...Fastener 131...Clamp section 2…Artificial satellite 21...Synthetic Aperture Radar (SAR)

Claims

1. A reflector that retroreflects radio waves irradiated from a synthetic aperture radar, Four pillars made of single pipes, a plurality of reflective grid bodies in which a plurality of single pipes are fixed in a grid pattern by fasteners; The reflecting grating is a reflector for an SAR, and is fixed to the four supports in multiple stages, one above the other.

2. 2. The reflector for SAR according to claim 1, wherein the reflecting grating body has four single tubes fixed vertically and horizontally in a grid pattern.

3. 3. The reflector for SAR according to claim 2, wherein the reflective gratings are fixed to the four support columns in two stages, one above the other.

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