Light and small wide coastal zone detection system

Abstract

The invention discloses a light and small wide coastal zone detection system. A main body bracket is mounted on a satellite cabin; the outer light shield and the ray machine assembly are respectively and fixedly arranged on the main body bracket; the outer light shield is located at the front end of the swing mirror assembly. The outer light shield is of a cylindrical structure, and the connecting line of the center points of the two end faces of the outer light shield and the mirror face center point of the swing mirror assembly are collinear. The oscillating mirror assembly is located at a light inlet in the front end of the light machine assembly, can rotate around a rotating shaft and is used for transmitting imaging light to the light machine assembly; the focal plane assembly is used for receiving the imaging light transmitted by the light machine assembly. According to the system, the visual range is expanded through the oscillating mirror assembly, and rapid positioning and fine investigation of a hot spot area are achieved.

Description

Technical Field

[0001] The present invention relates to the acquisition of remote sensing image data of land-sea interaction areas, monitoring of offshore, islands and coastal zones, scientific development and utilization of coastal zone resources, and effective monitoring and early warning of marine environmental disasters, and belongs to the field of aerospace remote sensing camera technology. Background Art

[0002] "Progress in China's Marine Satellite Remote Sensing Technology" in Volume 41, Issue 10, published in October 2019 of the journal "Acta Oceanologica Sinica" and "Current Status and Trends of Ocean Color Satellite Development" in Volume 30, Issue 6, published in December 2021 of the journal "Spacecraft Engineering" describe the development history of China's marine satellite remote sensing technology. Although China's marine satellite development started late, after decades of development, China's marine satellites and marine remote sensing applications have achieved remarkable results and played a significant role in China's marine information service guarantee.

[0003] At present, the coverage width of high-resolution imaging systems at home and abroad is generally 20 to 30 km. In the local target area, if you want to use a narrow-band system to complete a larger range of imaging, you need to use a multi-track stitching method. Taking a 30km width and an orbital period of 90 minutes as an example, to observe the imaging within a 90km target range, about 3 tracks are needed to stitch it together. Ocean wide-band imaging currently relies on the geometric stitching of two cameras on the same satellite platform to achieve wide-band detection. The coastal imager uses dual-camera stitching imaging to obtain wide-band images. At present, the detection spectrum of the coastal imager payload on domestic in-orbit ocean satellites is mostly 4 multi-spectral bands. Therefore, there is room for improvement in the detection spectrum and detection width of the coastal imager.

[0004] Traditional multiple spectral imaging (taking nine spectral bands as an example) is a scheme such as Fig.13 As shown in the figure, a dual-detector side-by-side design is adopted. Due to the structural limitation of the focal plane circuit, the maximum difference in the observation angle of the same object in different spectral bands is 3.58°. Fig.14 As shown in the figure, with the split-field-of-view design, the maximum difference in the observation angles of different spectral bands for the same object is 3.49°. The spatial position difference and imaging time interval difference of multi-spectral bands for coastal monitoring imaging are relatively large, and the registration accuracy of the nine-spectral band coastal target observation is greatly reduced. At the same time, this detector parallel or split-field-of-view design method results in a large optical lens area, which cannot meet the requirements of compact and miniaturized coastal detection system design.

[0005] In order to meet the growing demand for high spatial and high temporal resolution remote sensing image data of coastal zones in the civil field, and at the same time meet the demand for rapid response capabilities to specific targets and hot spots, this invention is an urgent technical requirement for the development of optical remote sensor systems for application in large-scale ocean fields. Summary of the invention

[0006] The technical problem solved by the present invention is: to overcome the deficiencies of the above-mentioned prior art and to provide a wide-width coastal zone detection system that can realize lightweight, large-width, multi-spectral high-resolution coastal zone observation and imaging, thereby improving the efficiency of obtaining information within the global land-sea boundary and having important application value.

[0007] The technical solution of the present invention is:

[0008] A light and small wide-area coastal zone detection system, comprising: a main body bracket, an external light shield, a swing mirror assembly, an optical-mechanical assembly and a focal plane assembly;

[0009] The main frame is installed on the satellite cabin; the outer sunshade and the optical-mechanical assembly are fixedly installed on the main frame respectively;

[0010] The outer light shield is located at the front end of the swing mirror assembly; the outer light shield is a cylindrical structure, and the line connecting the center points of the two end faces of the outer light shield is collinear with the center point of the mirror surface of the swing mirror assembly;

[0011] The swing mirror assembly is located at the light entrance of the front end of the optical-mechanical assembly. The swing mirror assembly can rotate around the rotation axis. The swing mirror assembly is used to transmit imaging light to the optical-mechanical assembly.

[0012] The focal plane component is used to receive the imaging light transmitted by the optical-mechanical component.

[0013] Preferably, the outer sunshade is made of Kevlar fiber composite material, the inner wall of the outer sunshade is pasted with a hexagonal honeycomb structure, and the honeycomb structure is sprayed with stray light-eliminating black paint.

[0014] Preferably, the swing mirror assembly comprises: a plane reflector, a swing mirror rotation execution module, a telemetry module and a swing mirror support structure;

[0015] The plane reflector is used to reflect the incident imaging light to the optical-mechanical component; the plane reflector is installed at the light entrance of the front end of the optical-mechanical component through a swing mirror support structure;

[0016] The oscillating mirror rotation execution module and the telemetry module work together to realize the closed-loop control of the plane reflector rotating around the X-axis of the satellite body coordinate system; wherein, the satellite body coordinate system takes the satellite center of mass as the coordinate origin O, the positive direction of the Z-axis points from the coordinate origin O to the center of the earth, the X-axis is perpendicular to the Z-axis on the orbital plane, the positive direction of the X-axis points to the direction of the satellite's forward movement, and the Y-axis is perpendicular to the X-axis and the Z-axis to form a right-handed rectangular coordinate system.

[0017] Preferably, when the plane reflector is at the initial position, the line connecting the center point of the plane reflector and the sub-satellite point is a line segment H, and the angle between the normal line of the plane reflector and the line segment H is 45°.

[0018] Preferably, the optical-mechanical assembly comprises: a detector light shield, a primary mirror, a secondary mirror, a tertiary mirror, a secondary mirror aperture sheet and a flat glass mirror;

[0019] The primary mirror, the secondary mirror and the tertiary mirror are arranged in sequence; the light reflected by the swing mirror assembly passes through the primary mirror, the secondary mirror and the tertiary mirror in sequence and then is incident on the flat glass mirror;

[0020] A flat glass mirror is used to transmit light to the focal plane assembly;

[0021] The secondary mirror aperture plate is located between the secondary mirror and the third mirror, and the secondary mirror aperture plate is parallel to the optical axis of the secondary mirror; the secondary mirror aperture plate is used to prevent stray light from reaching the third mirror from both sides of the secondary mirror;

[0022] The detector light shield is fixed on the main body bracket, and the detector light shield is located at the light entrance of the focal plane component.

[0023] Preferably, the secondary mirror aperture piece is an aluminum alloy thin plate structure, and the surface of the secondary mirror aperture piece is sprayed with a special stray light eliminating black paint.

[0024] Preferably, the detector light shield is a cylindrical structure, and a plurality of detector aperture pieces are installed inside the cylindrical structure, and the plurality of detector aperture pieces are arrayed along the axial direction of the cylindrical structure.

[0025] Preferably, the number of detector aperture plates is not less than 5, and the axial distance between two adjacent detector aperture plates is not greater than 3 cm.

[0026] Preferably, the detector light shield is made of aluminum alloy, and the surface of the detector aperture piece is blackened.

[0027] Preferably, the focal plane assembly comprises: a first focal plane assembly and a second focal plane assembly;

[0028] The first focal plane component and the second focal plane component are respectively used to receive light transmitted from the optical-mechanical component; the detection spectrum of the first focal plane component and the second focal plane component is different;

[0029] Detector light shields are respectively provided at the light entrances of the first focal plane assembly and the second focal plane assembly;

[0030] The detection spectrum of the first focal plane assembly specifically includes: A1 spectrum, A2 spectrum, A3 spectrum and A4 spectrum;

[0031] The detection spectrum of the second focal plane assembly specifically includes: B1 spectrum, B2 spectrum, B3 spectrum, B4 spectrum and B5 spectrum;

[0032] The ranges of the A1 band, B1 band, A2 band, B2 band, A3 band, B3 band, A4 band, B4 band and B5 band are as follows:

[0033] The A1 band has a wavelength range of 400-450nm, and the main observation objects are the depth of sea ice, coasts and islands and reefs; the B1 band has a wavelength range of 450-520nm, and the main observation objects are pollution monitoring near the coastline and mudflats; the A2 band has a wavelength range of 520-585nm, and the main observation objects are suspended sediment on the coast and islands and reefs; the B2 band has a wavelength range of 585-630nm, and the main observation objects are special vegetation on the coast and islands and reefs; the A3 band has a wavelength range of 630-700nm, and the main observation objects are It mainly observes the chlorophyll concentration of water bodies near coasts and islands and reefs; the B3 spectral band has a wavelength range of 700-770nm, and the observation object is mainly the vegetation health index of coasts and islands and reefs; the A4 spectral band has a wavelength range of 770-860nm, and the observation object is mainly the water body identification of coasts and islands and reefs; the B4 spectral band has a wavelength range of 860-1040nm, and the observation object is mainly the seaweed vegetation of coasts and islands and reefs; the B5 spectral band has a wavelength range of 450-800nm, and the observation object is mainly the port construction and near-shore projects of coasts and islands and reefs.

[0034] The beneficial effects of the present invention compared with the prior art are:

[0035] 1) The present invention adopts the technical means of "swing mirror assembly + optical-mechanical assembly" to realize the front-end large-range pointing structure imaging system with a large side-swing field of view, which produces the effect of expanding the coverage range at the front end of the optical system and expanding the channel at the back end, bringing the technical effect of minimizing the scale of the coastal zone detection system and making the functional modules independent and expandable. It effectively reduces the number and size of high-precision aspheric reflectors and greatly reduces the cost of optical processing and assembly. The main optical system is relatively independent of the functional modules at the front and back ends, which is convenient for the expansion and optimization of imaging functions.

[0036] 2) The present invention adopts field of view multiplexing imaging technology with controllable transmission and reflectance ratios to produce a lightweight and miniaturized multi-spectral staggered layout detection effect. It achieves the shortest time difference for multiple spectral observations of the same ground object, while minimizing the field of view angle. The effect of this technical means is to effectively eliminate the spectral registration error introduced by the time interval of the satellite platform stability. At the same time, it meets the compact and miniaturized design requirements of optical components.

[0037] 3) The “external + internal” nested two-stage stray light elimination scheme can effectively suppress the propagation path of stray light and significantly reduce the influence of stray light in the field of view of the coastal zone detection system, so as to improve the imaging quality of the coastal zone detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the structure of the coastal zone detection system of the present invention;

[0039] Figure 2 This is a schematic diagram of the optoelectronic flow of the coastal zone detection system of the present invention;

[0040] Figure 3 It is a schematic diagram of the composition and three-dimensional structure of the swing mirror assembly of the present invention;

[0041] Figure 4 This is a schematic diagram of the angle closed-loop control program of the oscillating mirror assembly of the present invention;

[0042] Figure 5 It is a schematic diagram of the half-step angle criterion method of the swing mirror assembly of the present invention;

[0043] Figure 6 This is a working schematic diagram of the controllable transflective flat glass mirror of the present invention;

[0044] Figure 7 Schematic diagram of the positions of the three-mirror off-axis module and the flat glass mirror of the optical-mechanical assembly of the present invention

[0045] Figure 8 It is a schematic diagram of the spatial alignment and registration of the optical paths of the two focal plane spectrum segments of the present invention;

[0046] Fig. 9 This is a schematic diagram of the field of view splicing enlargement of the present invention;

[0047] Fig.10 This is a schematic diagram of an outer light shield with a honeycomb structure attached to the inner wall of the present invention;

[0048] Fig.11 Schematic diagram of stray light elimination by the secondary mirror aperture plate of the present invention;

[0049] Fig.12 This is a schematic diagram of the detector light shield eliminating stray light of the present invention;

[0050] Fig.13 Schematic diagram of the field of view designed for dual detectors side by side;

[0051] Fig.14 This is a schematic diagram of the design of different field of view angles. DETAILED DESCRIPTION

[0052] Coastal zone detection has the imaging characteristics of bright background and weak target. The traditional stray light suppression method of the external light shield with a light blocking ring can no longer meet the requirements of stray light suppression for coastal zone detection. The present invention adopts a "external + internal" nested two-stage stray light elimination method to effectively suppress stray light inside and outside the field of view, thereby enhancing the stray light suppression effect. At the same time, the size of the external light shield is reduced to meet the requirements of miniaturized design for coastal zone detection.

[0053] A light and small wide coastal zone detection system, such as Figure 1 As shown, it includes: an external light shield, a swing mirror assembly, a main body bracket, an optical-mechanical assembly and a focal plane assembly;

[0054] The outer sunshade is made of low-density and high-strength Kevlar fiber composite material. The inner wall of the outer sunshade is pasted with a hexagonal paper honeycomb structure, and the honeycomb structure is sprayed with black paint to increase the absorption rate of the inner surface and minimize the scattering of the inner wall of the outer sunshade. The honeycomb thickness is uniform, ensuring that the imaging light can completely pass through the outer sunshade and maintain a 3mm pass margin with the outer edge of the structure.

[0055] As the first-level stray light elimination component, the external light shield is located at the front end of the coastal zone detection system (i.e. the front end of the swing mirror component) and is the first component through which the imaging light passes in the coastal zone detection system. The external light shield is fixedly mounted on the main bracket, which is mounted on the satellite cabin. Fig.10 As shown, the outer light shield is a "flat trumpet-shaped" cylindrical structure, located at the front end of the swing mirror assembly, with one end close to the swing mirror assembly being the trumpet-shaped narrow end, and the other side being the trumpet-shaped wide end. The mounting surface of the outer light shield is the trumpet-shaped narrow end. Along the direction of the light, the opening centers of the two end surfaces of the outer light shield are both collinear with the center of the mirror surface of the swing mirror assembly.

[0056] The swing mirror assembly is located at the light entrance of the front end of the optical-mechanical assembly, and the swing mirror assembly can rotate around the rotation axis to transmit the imaging light to the optical-mechanical assembly.

[0057] The swing mirror assembly is the secondary front end of the coastal zone detection system. The swing mirror assembly includes: a plane reflector, a swing mirror rotation execution module, a telemetry module and a swing mirror support structure.

[0058] Swing Mirror The rotation execution module is used to drive the plane reflector to rotate precisely around the X-axis (i.e., the rotation axis) of the satellite's coordinate system. Through a large range of conversions in the pointing area, an ultra-large coverage range of 1,200 kilometers of detection capability is achieved. Through high-precision control of the rotation angle of the swing mirror assembly, rapid positioning and detailed investigation of hot coastal areas are achieved. The satellite's coordinate system uses the satellite's center of mass as the coordinate origin O, the positive direction of the Z axis points from the coordinate origin O to the center of the earth, the X axis is perpendicular to the Z axis on the orbital plane, the positive direction of the X axis points to the direction of the satellite's forward movement, and the Y axis is perpendicular to the X axis and the Z axis to form a right-handed rectangular coordinate system.

[0059] The plane reflector in the swing mirror assembly is used to reflect the imaging light to the optomechanical assembly. Under the joint action of the driving source (swing mirror rotation execution module) and the position feedback (telemetry module), the plane reflector realizes the closed-loop control of the swing mirror assembly according to the coastal zone pointing control instructions issued by the satellite service subsystem.

[0060] like Figure 3 As shown, through the separate swing mirror support structures on both sides, the swing mirror rotation execution module and the telemetry module of the swing mirror assembly are coaxially installed on both ends of the plane reflector rotation axis, and together with the plane reflector form a combination of the swing mirror assembly.

[0061] The plane reflector of the swing mirror assembly is fixedly installed at the light entrance in front of the optical-mechanical assembly through the swing mirror support structure. The plane reflector can rotate around the rotation axis relative to the swing mirror support structure. The axis of the rotation axis coincides with the X-axis of the satellite body coordinate system. The initial position of the plane reflector is at a 45° angle to the ground (subsatellite point) (i.e., the initial position: the line connecting the center point of the plane reflector and the subsatellite point is line segment H, and the angle between the normal line of the plane reflector and line segment H is 45°). Structural mounting interfaces are designed on both sides of the plane reflector, and the rotating shafts on both sides are respectively installed by nested bonding, with a coaxiality better than 0.005mm. The swing mirror rotation execution module adopts the design scheme of "stepping motor rotation + harmonic gear reducer transmission", which can drive the plane reflector of the swing mirror assembly to rotate around the X-axis of the satellite, thereby reflecting the light of the pointing area of ​​the target detection ground to the optical-mechanical assembly. The swing mirror rotation execution module receives the coastal zone pointing control instruction forwarded by the swing mirror angle control module in the controller assembly, and drives the plane reflector to rotate.

[0062] The telemetry module adopts the design of "Hall effect digital switch circuit + absolute photoelectric encoder" to realize real-time monitoring of the rotation angle of the plane reflector. The absolute photoelectric encoder realizes high-precision measurement of the rotation direction and angle. The Hall effect digital switch circuit is installed at the extreme positions of the rotation ends of the plane reflector of the swing mirror assembly, and real-time feedback is given to whether the plane reflector is rotated to the extreme position to ensure the safety of the rotation of the plane reflector. The telemetry module collects the real-time rotation angle of the plane reflector and feeds it back to the swing mirror angle control module in the controller assembly.

[0063] The plane reflector is made of silicon carbide material, and the size of the plane reflector should be sufficient to ensure that all imaging light is incident in all swing positions. The position of the swing mirror assembly is as close to the optomechanical assembly as possible, and on the basis of the maximum active envelope, a 5mm safety distance is reserved from other optical elements and structural parts of the optomechanical assembly.

[0064] The optical and mechanical components are designed as long focal length, large aperture and unobstructed three-mirror off-axis type. The optical and mechanical components include: detector light shield, primary mirror, secondary mirror, third mirror, secondary mirror aperture and flat glass mirror.

[0065] like Figure 7 As shown, the primary mirror, secondary mirror, third mirror and flat glass mirror are arranged in sequence according to the propagation order of light and are fixed on the main support. The primary mirror, secondary mirror and third mirror are reflectors, which receive the light reflected by the swing mirror assembly and converge the light. The flat glass mirror is located after the third mirror and transmits the light to the first focal plane assembly and the second focal plane assembly at different positions in the focal plane assembly.

[0066] The "secondary mirror aperture plate + detector light shield and inner surface stray light elimination measures" of the optomechanical assembly serves as a second-level stray light elimination solution. First, the present invention first designs a secondary mirror aperture plate of the optomechanical assembly. The secondary mirror aperture plate is used to block the light from directly reaching the third mirror without passing through the secondary mirror, that is, to prevent the stray light path that has a greater impact on the imaging quality of the focusing surface from passing through the two sides of the secondary mirror to reach the third mirror. In order to suppress the stray light of this path, secondary mirror aperture plates are added to the structures on both sides of the secondary mirror. In the embodiment of the present invention, the secondary mirror aperture plate is a 3mm thick aluminum alloy rectangular thin plate, sprayed with special stray light eliminating black paint. The secondary mirror aperture plate is located between the secondary mirror and the third mirror, and the distance between the surface of the secondary mirror aperture plate and the incident light of the secondary mirror and the incident light of the third mirror is not less than 3mm, and the secondary mirror aperture plate is parallel to the optical axis of the secondary mirror.

[0067] Secondly, detector hoods are designed at the light entrances of the first focal plane assembly and the second focal plane assembly, respectively, and the detector hoods are fixed on the main support. The detector hood is a cylindrical structure, and a plurality of detector aperture pieces are installed inside the cylindrical structure, and the plurality of detector aperture pieces are arrayed along the axial direction of the cylindrical structure. There are no less than 5 detector aperture pieces, and the axial distance between two adjacent detector aperture pieces is no more than 3 cm, and the surface of the detector aperture piece is blackened.

[0068] The detector light shield is located inside the optomechanical assembly and is the last component that the imaging light passes through before reaching the detector.

[0069] In the embodiment of the present invention, the detector light shield is made of lightweight aluminum alloy material and is designed as a thin-walled structure (thickness is 1mm). The inner side is a light aluminum alloy extinction ring (i.e., detector aperture piece) (thickness is 2mm) with equal spacing (9mm). The opening size of the extinction ring ensures that the imaging light passes completely and maintains a margin of 1.5mm distance from the extinction ring structure. The outer surface of the detector light shield is oxidized with metal black, and the inner extinction ring (i.e., detector aperture piece) is sprayed with special stray light black paint.

[0070] Third, improve the roughness of the main support structure surface to increase the stray light absorption rate. The surface of the structural frame around the secondary mirror, the main structural surface between the primary mirror and the third mirror, the surface of the plane reflector fixing frame, the surface of the flat glass mirror fixing frame structure and the inner wall of the detector light shield are all surfaces that generate scattered light. The above surfaces are treated to eliminate stray light. The surface absorption rate of the structure surface is improved and the light scattering direction is changed by spraying special stray light eliminating black paint and using matte threads.

[0071] The present invention adopts an "external + internal" nested two-stage stray light elimination design: combining the combined effect of the first-stage stray light elimination scheme (external light shield) and the second-stage stray light elimination scheme ("secondary mirror aperture piece + detector light shield and main bracket surface stray light elimination measures" of the optical-mechanical assembly), the propagation path of stray light is effectively suppressed without blocking the various imaging light paths.

[0072] The focal plane assembly includes: a first focal plane assembly and a second focal plane assembly; the first focal plane assembly and the second focal plane assembly are used to receive light transmitted from the optical machine assembly. The first focal plane assembly and the second focal plane assembly differ only in the difference in the detection spectrum, and both the first focal plane assembly and the second focal plane assembly include: a focal plane detector unit, a focal plane timing control unit, a focal plane data processing unit and a focal plane power supply unit.

[0073] Focal plane detector unit: The focal plane detector unit with filters of different spectral bands receives the optical signal transmitted by the optical-mechanical system, performs photoelectric conversion, and obtains the analog electrical signal of the corresponding spectral band information;

[0074] Focal plane timing control unit: provides the timing drive control signal required by the focal plane detector unit;

[0075] Focal plane data processing unit: performs analog-to-digital (AD) conversion on the analog electrical signals of the corresponding spectrum band, formats the image data and outputs it to the satellite data transmission subsystem;

[0076] Focal plane power supply unit: used to provide the working power required by the focal plane detector unit, the focal plane timing control unit, and the focal plane data processing unit;

[0077] The first focal plane assembly and the second focal plane assembly are combined into a pair, such as Figure 8As shown, a detection with the same wide field of view is formed. In general, the use of nine-spectral band detection in the application field of coastal zone detection has met the use requirements (the present invention can be expanded to more spectral bands to achieve more precise coastal zone target detection. In one embodiment of the present invention, a nine-spectral band design scheme is used as an example). The first focal plane component is a focal plane of four spectral bands (A1, A2, A3, A4), and the second focal plane component is a focal plane of five spectral bands (B1, B2, B3, B4, B5). After combination, the spectral band distribution is as follows: A1 spectral band, B1 spectral band, A2 spectral band, B2 spectral band, A3 spectral band, B3 spectral band, A4 spectral band, B4 spectral band, B5 spectral band. Among them, the intervals between the four spectral bands A1, A2, A3, and A4 are fixed intervals d (2mm), and the intervals between the five spectral bands B1, B2, B3, B4, and B5 are fixed intervals d (2mm). After the light is split in the same field of view by the flat glass assembly, the spectral segments of each pair of focal plane combinations are aligned, that is, the A1 spectral segment is aligned with the B1 spectral segment, the A2 spectral segment is aligned with the B2 spectral segment, the A3 spectral segment is aligned with the B3 spectral segment, and the A4 spectral segment is aligned with the B4 spectral segment, thus forming nine spectral segments for detection in the same wide field of view. The nine spectral bands are as follows: the A1 spectral band has a wavelength range of 400-450nm, and the observation objects are mainly the depth of sea ice, coasts and islands and reefs; the B1 spectral band has a wavelength range of 450-520nm, and the observation objects are mainly pollution monitoring near the coastline and mudflats; the A2 spectral band has a wavelength range of 520-585nm, and the observation objects are mainly suspended sediment on the coast and islands and reefs; the B2 spectral band has a wavelength range of 585-630nm, and the observation objects are mainly special vegetation on the coast and islands and reefs (mainly sea scutellaria, reeds, Spartina alterniflora, etc.); the A3 spectral band has a wavelength range of 630-700nm, and the observation objects are mainly chlorophyll concentrations in water bodies near coasts and islands and reefs; the B3 spectral band has a wavelength range of 700-770nm, and the observation objects are mainly vegetation health indexes on coasts and islands and reefs (vegetation health index, i.e. vegetation health index, The A4 band has a wavelength range of 770 to 860 nm, and the main observation objects are the identification of water bodies on the coast and islands and reefs (mainly the precise determination of the boundaries of water bodies such as coastlines and nearshore lakes and estuaries); the B4 band has a wavelength range of 860 to 1040 nm, and the main observation objects are seaweed and other vegetation on the coast and islands and reefs; the B5 band has a full-color wavelength range of 450 to 800 nm, and the main observation objects are port construction and nearshore projects on the coast and islands and reefs.

[0078] Among them, stitching multiple pairs of focal planes (i.e. overlapping a certain number of pixels, such as 100 pixels) can achieve detection of a larger width at the same time. For example, stitching three fields of view can achieve detection of 180 kilometers at the same time. Fig. 9 shown.

[0079] The focal plane assembly of the present invention places the digital conversion of analog image signals in the focal plane circuit, and the timing drive, signal processing and data transmission functions are completely integrated in the focal plane assembly, thus becoming the most integrated TDICCD focal plane circuit. The analog signal generated by the focal plane detector unit is immediately converted into a digital signal, which is then transmitted to the focal plane data processing unit for image data processing and then sent to the data transmission system. This avoids interference with the analog signal and enhances the anti-interference capability of the system.

[0080] The controller components include: a command and telemetry unit, a CPU control unit, a power module unit, and a swing mirror angle control module.

[0081] Command and telemetry unit: used to receive the coastal zone pointing control command and focal plane imaging parameter control command of the satellite, and send them to the swing mirror angle control module and focal plane component after parsing according to the coastal zone detection system bus protocol. At the same time, it receives and monitors the telemetry of the coastal zone detection system (including power supply analog telemetry, digital telemetry on the bus, etc., and the real-time rotation angle received by the swing mirror angle control module), and uploads them to the satellite service subsystem;

[0082] The CPU control unit is the core control program running location of the controller component, including: command and dispatch instructions and telemetry unit and swing mirror angle control module;

[0083] Power module unit: used to provide working power for the command and telemetry unit, CPU control unit, and swing mirror angle control module;

[0084] Swing mirror angle control module: includes: a swing mirror angle telemetry unit, a swing mirror motor drive unit and a swing mirror angle calculation and instruction unit.

[0085] The swing mirror angle telemetry unit is used to monitor the swing mirror angle telemetry information.

[0086] The oscillating mirror motor drive unit is used to provide a four-phase eight-beat drive signal for the motor drive.

[0087] The swing mirror angle calculation and command unit is responsible for receiving the direction and angle of the swing mirror component control command, and outputting the correct swing mirror motor drive signal to the swing mirror component. At the same time, it determines whether the angle position of the swing mirror matches the setting requirements. According to the judgment result, the step length of the swing mirror motor is corrected in a closed loop to meet the requirements of swing mirror control accuracy.

[0088] The optical system of the present invention expands the coverage range at the front end and expands the channel at the back end. The three-mirror off-axis optical design is adopted, and the light and small design of the wide-band coastal zone detection system is realized through the folded optical path and small relative aperture technology. The imaging system of the front-mounted large-range pointing structure, that is, the design scheme of the rotatable swing mirror assembly in front of the imaging lens, realizes the ultra-large coverage range of 1,200 kilometers with light and small optical and mechanical components, realizes the function of directional and precise control of the detection field of view, and meets the needs of both wide-band detection and refined detection.

[0089] The light and small wide-width coastal zone detection system of the present invention can be applied to the coastal zone detection method. By adopting the "successive approximation + half-step angle interpretation method", the drive control of the swing mirror assembly with a minimum rotation resolution of 1 / 2 can be realized. In order to overcome the influence of the inertia of the mechanism, the motor is driven by a variable frequency method, and the delay is designed and the angle telemetry is interpreted redundantly multiple times, so as to realize the high-precision swing mirror angle directional control. The detection method is specifically as follows:

[0090] Step 1: According to the ground injection instruction received by the satellite service subsystem, the angle and direction of rotation of the swing mirror assembly are obtained by parsing and processing;

[0091] Step 2: According to the angle that the oscillating mirror assembly needs to rotate (coastal zone pointing control instruction), the number of driving times N of the oscillating mirror rotation is obtained according to the single oscillating mirror adjustment angle d°; the value range of the single oscillating angle step is not greater than 2°. In the embodiment of the present invention, the single oscillating mirror adjustment angle d is 0.9±0.009°.

[0092] Step 3: The swing mirror angle calculation and instruction unit calculates the current single motor driving step number, issues a driving instruction to the swing mirror motor driving unit, and outputs a driving pulse signal of the swing mirror motor;

[0093] Step 4: The swing mirror angle telemetry unit periodically obtains the absolute angle information of the swing mirror rotation position from the absolute photoelectric encoder of the swing mirror assembly in milliseconds, and sends it to the swing mirror angle calculation and command unit. After each single drive is executed, the swing mirror angle calculation and command unit delays for 2 seconds and reads the absolute angle information of the swing mirror position 5 times (with an interval of 300ms). Among the 5 telemetry values, remove the maximum value and the minimum value, and take the average value of the remaining 3 values ​​as the absolute angle value corresponding to this drive. The value is interpreted according to the 1 / 2 minimum step angle threshold (0.00225° in the embodiment of the present invention), and it is decided whether to send a correction drive pulse signal based on the interpretation result. The specific judgment method is: if the difference between the absolute angle value of the swing mirror position and the theoretically calculated angle value is less than 0.00225°, then proceed to drive the next angle d°; otherwise, first send out a correction drive pulse signal, and reversely execute 1 minimum step angle (the minimum step angle in the embodiment of the present invention is 0.0045°) as a correction drive pulse signal, and then proceed to step five to continue driving the next angle d°.

[0094] Step 5: Repeat steps 3 to 4 until N drives are completed to achieve the angle adjustment of the swing mirror.

[0095] The present invention realizes wide-band, high-resolution, precise pointing and positioning and multi-spectral fusion with a light and small coastal zone detection system, and realizes high-precision mobile detailed investigation and detection of hot spots within the track width coverage range.

[0096] Example

[0097] like Figure 1 As shown, the light and small-sized wide-area coastal zone detection system of the present invention comprises: a swing mirror assembly, a main body bracket, an optical-mechanical assembly, a focal plane assembly and a controller assembly. Figure 2 As shown, the components of the four major components of the system and the schematic diagram of the coastal detection light path, as well as the control signal, telemetry signal, and image signal flow chart of the coastal detection system.

[0098] Swing mirror components such as Figure 3As shown, it includes: a plane reflector, a swing mirror rotation execution module and a telemetry module (Hall effect digital switch circuit + absolute photoelectric encoder) and a swing mirror support structure. The swing mirror assembly adopts a front-end design, and the swing mirror is driven by a motor variable frequency to rotate accurately. Wide-range imaging is achieved through a large-range pointing rotation. Combined with the rear-end optical-mechanical assembly, a light and small optical-mechanical system is used to achieve an ultra-large coverage range of 1,200 kilometers, and rapid positioning and detailed investigation of hot coastal areas can be achieved through the rotation of the swing mirror assembly. The swing mirror assembly is used to reflect the light of the push-scan imaging area to the optical-mechanical assembly. Through the support structure on both sides, the telemetry module and the swing mirror rotation execution module are coaxially installed at both ends of the plane reflector rotation bearing, and together with the plane reflector, form a combination of the swing mirror assembly. Under the joint action of position feedback (telemetry module) and drive source (swing mirror rotation execution module), the plane reflector realizes closed-loop control driven rotation according to the coastal pointing control instruction of the entire satellite.

[0099] The front end of the system adopts a large-range pointing mechanism to expand the visual range through the swing mirror assembly. The high-precision swing mirror angle closed-loop control of the swing mirror assembly completes the accurate on-orbit line of sight positioning function of the system, realizing rapid positioning and detailed investigation of hot spots. The optical system of the optomechanical assembly adopts a small field of view design, and combines the folded optical path and small relative aperture technology to reduce the aperture and envelope of the optical system, so as to realize the light and miniaturization of the optomechanical assembly. The optomechanical assembly is used to receive the light signal reflected by the swing mirror assembly, converge the light signal using a three-reflection off-axis optical assembly, and adopt the field of view multiplexing imaging technology with controllable transmission and reflectance ratio. After the same field of view is split through the flat glass assembly, it is transmitted to the first focal plane assembly and the second focal plane assembly of different filter spectrum bands after position registration. The system adopts an "external + internal" nested two-stage stray light suppression design scheme, which can achieve a stray light suppression technical index better than 2% under the premise of ultra-large coverage field of view, so as to improve the design requirements of high signal-to-noise ratio of the coastal zone detection system. The TDICCD focal plane circuit of the present invention has completely integrated the timing drive, signal processing and data transmission functions into the focal plane circuit, converting the analog signal output by the detector into a digital signal and sending it to the data transmission system after image data processing. This avoids interference to the analog signal, enhances the anti-interference ability of the system, and greatly simplifies the scale of the focal plane circuit. This realizes product miniaturization, and greatly reduces power consumption and volume.

[0100] (1) Imaging system of the front-end large-range pointing structure

[0101] The imaging system of the front-mounted, wide-range pointing structure with a large side-swing field of view is realized by using "high-precision swing mirror rotation + imaging lens". The swing mirror is located at the front end of the main optical system. The light emitted by the ground scene enters the main optical system through the reflection of the swing mirror and is imaged through the TDICCD push-scanning of the focal plane. The focal plane solution of multi-channel same-field spectroscopic imaging is adopted to ensure the camera's registration accuracy.

[0102] The optical system of the optomechanical assembly is a long focal length, large aperture and unobstructed three-mirror off-axis optical system, including: detector light shield, three-mirror off-axis module (primary mirror, secondary mirror, third mirror), flat glass mirror. The swing mirror is a plane reflector, the primary mirror and the third mirror are four-fold concave aspheric surfaces, and the secondary mirror is a quadratic hyperboloid. The aperture diaphragm position of the optical system aperture diaphragm is optimized to coincide with the position of the secondary mirror, so that the entire optical system forms a quasi-symmetrical structure with respect to the aperture diaphragm, thereby achieving the goal of eliminating system distortion.

[0103] Since a large-range pointing mechanism is used at the front end to expand the visible range, the optical system proposes a small field of view design, and combines the folded optical path and small relative aperture technology to reduce the aperture and envelope of the optical system, thereby achieving lightweight and miniaturization of the optical-mechanical components.

[0104] The swing mirror assembly adopts a front-end design. The swing mirror angle control module drives the swing mirror to rotate precisely. Through a large range of pointing rotation, directional target imaging in a wide range is achieved. Combined with the rear-end optical-mechanical assembly, a lightweight optical-mechanical system is used to achieve an ultra-large coverage range of 1,200 kilometers. The rotation of the swing mirror assembly enables rapid positioning and detailed investigation of hot coastal areas. The design uses highly lightweight mirror materials, high-precision telemetry units, and highly integrated drive devices to achieve high precision and high lightness of the assembly. The swing mirror assembly is used to reflect the light in the push-scan imaging area to the optical-mechanical assembly.

[0105] Through the support structure on both sides, the swing mirror drive module and the telemetry module are coaxially integrated and installed at both ends of the rotating shaft of the plane reflector, and together with the plane reflector, they form a combination of the swing mirror assembly. The rotating shaft of the swing mirror assembly is installed in a "fixed + floating" manner. The fixed end is installed back-to-back with paired angular contact ball bearings, and the outer ring is axially limited by the outer ring end cover of the bearing. A deep groove ball bearing is used as a support at the floating end to solve the axial expansion and contraction problem caused by temperature changes. The outer ring of the bearing is matched with the bearing base, and there is no axial constraint, so it can float along the axial direction. To prevent loosening, the inner ring of the bearing limits the axial position of the bearing through the bearing end cover.

[0106] Under the joint action of the driving source and position feedback, the plane mirror of the swing mirror assembly realizes the driving rotation of closed-loop control according to the swing mirror control instructions of the whole satellite. The swing mirror assembly adopts the design scheme of "stepping motor rotation + harmonic gear reducer transmission" to realize the driving rotation of the swing mirror. The swing mirror assembly adopts the design scheme of "Hall effect digital switch circuit + absolute photoelectric encoder" to realize position feedback. The 24-bit absolute photoelectric encoder realizes high-precision measurement of rotation direction and angle. The Hall effect digital switch circuit is installed at the extreme positions of the rotation, and real-time feedback is given whether there is a situation of rotation to the extreme position, ensuring the safety of the rotation of the plane mirror.

[0107] The positional relationship constraints between the swing mirror assembly and the optomechanical assembly are as follows: The plane reflector of the swing mirror assembly is fixedly installed at the light entrance in front of the optomechanical assembly through the swing mirror support structure, and can rotate around the satellite's X-axis to achieve a certain angle of swing with the satellite's flight +X direction as the rotation axis. The initial position of the plane reflector is at a 45° angle to the ground (subsatellite point). The position of the swing mirror assembly is as close to the optomechanical assembly as possible, and on the basis of the maximum active envelope, a 5mm safety clearance is reserved from other optical elements and structural parts of the optomechanical assembly.

[0108] The "swing mirror assembly + optomechanical assembly" approach is characterized by modularity, which facilitates the combination of functional performance. The coverage can be expanded at the front end of the optical system and the channel can be expanded at the back end. Its advantage is that it can minimize the scale of the optical system of the coastal zone detection system, thereby reducing the number and size of high-precision aspheric reflectors, and greatly reducing the cost of optical processing and assembly. The functional modules of the swing mirror assembly and the optomechanical assembly are relatively independent, which facilitates the rapid expansion and optimization of imaging functions.

[0109] (2) High-precision closed-loop control of the swing mirror angle

[0110] In order to precisely control the positioning accuracy of the swing mirror mechanism and reduce the accumulated gap error of the driving mechanism, the present invention designs a closed-loop control with step-by-step real-time adjustment. By real-time acquisition of high-precision angle telemetry values, the successive approximation + half-step angle criterion method is used to complete the closed-loop control of the precise positioning of the swing mirror mechanism. The block diagram of the closed-loop control principle of the swing mirror is shown in the figure. Figure 4 As shown, the half-step angle criterion method is as follows Figure 5 shown.

[0111] Step 1: The swing mirror angle control module receives the coastal zone pointing control information +D° or -D° issued by the satellite service subsystem. The pointing value has positive and negative values. The positive value indicates the right direction of the sub-satellite point 0° in the satellite flight direction, and the negative value indicates the left direction of the sub-satellite point 0° in the satellite flight direction. The swing mirror angle control module compares the currently collected real-time angle telemetry information with the received coastal zone pointing control information +D° or -D°, and obtains the swing mirror angle information △+D° or △-D° that needs to be adjusted. △+D° is used as an example below;

[0112] Step 2: The swing mirror angle control module divides the swing mirror control angle information △+D° into N equal parts. The value of N is determined according to the size of the single swing mirror adjustment angle d°, Δ(+D°)=N×(+d°). Since the error caused by a single swing mirror angle adjustment is controllable, this can ensure that the number of closed-loop steps for each step adjustment is basically consistent, reducing the cumulative error.

[0113] Step 3: The oscillating mirror angle control module converts the current single oscillating mirror angle d° into the corresponding oscillating mirror motor drive steps. The calculation method is: the current single drive step number is equal to the current oscillating mirror angle d° divided by the minimum step angle 0.0045°.

[0114] Step 4: The swing mirror motor drive unit drives the swing mirror rotation execution module to adjust the angle of the swing mirror assembly according to the current single drive step number. The swing mirror assembly telemetry module regularly monitors the absolute information of the swing mirror angle and sends a digital signal to the swing mirror angle control module. In order to prevent the motor from losing steps during operation, the swing mirror angle calculation and instruction unit of the swing mirror angle control module delays for 2 seconds after each single drive. After the mechanism is stable, the absolute angle information of the swing mirror position is read 5 times (200ms interval). Among the 5 telemetry values, remove the maximum value and the minimum value (remove the interference value or abnormal value), and take the average of the remaining 3 values ​​as the absolute angle information value after this drive. The value is interpreted according to the 1 / 2 minimum step angle threshold, and whether to issue a correction drive pulse signal is determined based on the interpretation result.

[0115] Step 5: Repeat steps 3 to 4 until the angle of the oscillating mirror assembly is adjusted to △ + D°, completing the oscillating mirror angle control.

[0116] The above steps realize the closed-loop control of the angle adjustment process of the oscillating mirror mechanism assembly, which has the following main features:

[0117] ① Successive approximation, the cumulative error is controllable. According to the input swing mirror angle control command, the swing mirror control is divided into N equal parts, and the number of steps taken by each equal part is the same. The error caused by a single swing mirror angle adjustment is controllable, which can ensure that the closed-loop steps of each step adjustment are basically consistent, reducing the cumulative error.

[0118] ② It can achieve precision control of 1 / 2 minimum resolution, and the angle comparison adopts the half-step angle judgment method. The minimum step angle of the swing mirror mechanism is 0.0045°. When real-time angle judgment is performed, the half-step angle judgment method is adopted in which the difference between the real-time angle and the theoretical required value of the control angle is less than 0.00225°. In this way, the actual position distance from the theoretical control angle position accuracy can reach half of the swing mirror angle control resolution.

[0119] ③ The design is safe. The drive motor of the swing mirror mechanism is designed to have sufficient torque margin to reliably drive the swing mirror to rotate in a certain direction. Hall sensors are set at the extreme positions on both sides of the swing mirror as soft limits, and limit blocks are set as hard limits. At the same time, limit instructions are set in the control unit. The triple safety protection setting ensures that the swing mirror mechanism is safe and reliable.

[0120] ④ In order to overcome the influence of mechanism inertia, a variable frequency method is used to drive the motor, and an acceleration and deceleration method is adopted when the swing mirror starts and stops. That is, the frequency of the driving motor adopts a low frequency method to increase the starting torque when the swing mirror just starts, and a fixed intermediate frequency is used to drive the swing mirror in the middle rotation process. When the swing mirror is about to stop rotating, a high frequency method is used to reduce the motor torque, so that the swing mirror mechanism stops as soon as possible and reduces the influence of the mechanism's inertia.

[0121] ⑤ In order to eliminate the vibration of the swing mirror and prevent the motor operation control from long-term closed-loop oscillation, in addition to the holding torque of the harmonic reducer of the swing mirror mechanism, after the swing mirror motor drive stops, the motor is still in a single-phase or two-phase energized holding state, which further enhances the locking torque and prevents the swing mirror mechanism from vibrating.

[0122] ⑥ The design is reliable. If a single instruction is executed for a period of time exceeding the maximum range of the swing mirror, the swing mirror status telemetry will be abnormal and the swing mirror movement will be stopped immediately. During the closed-loop control of the swing mirror, if the encoder angle information is out of limit, the swing mirror mechanism will stop moving. If the Hall sensor telemetry of the extreme position is received during the operation of the swing mirror, the swing mirror mechanism will stop moving and return the angle out-of-limit telemetry.

[0123] The above-mentioned oscillating mirror angle control system is designed with a high-precision measurement unit, and a 24-bit absolute photoelectric encoder is used to achieve high-precision angle measurement. The absolute photoelectric code disk encoding adopts a matrix code design, and the outermost circle is engraved with 8192 lines, which are electronically subdivided into 2048 parts to achieve the required 24-bit (0.077″) resolution. The code disk has a total of 15 code tracks, and the outermost code track is a precision code. The structure of the diameter-arranged reading head and the differential amplifier circuit amplify the signal, which can eliminate the influence of the even harmonic component and the common-mode DC level component in the signal, improve the quality of the orthogonal signal, thereby reducing the signal distortion caused by mechanical adjustment deviation and shaft system shaking, and improving the measurement accuracy of the system.

[0124] The photoelectric encoder uses RS422 level differential signals to output data to the controller in serial form. It uses a high-bit first and low-bit later serial transmission method to send:

[0125] 1) The C_Y signal is the sampling signal of the driver's encoder disk. It is sent by the drive controller and received by the photoelectric encoder disk conversion circuit. When the rising edge is detected, the conversion is started immediately.

[0126] 2) YW_CLK: When no data transmission occurs in the idle phase, the shift pulse signal maintains a high level. The encoder is triggered to load and transmit data at the falling edge of the first pulse, and then the photoelectric encoder sends data at the rising edge of each clock pulse. At each falling edge of the pulse, the level on the data line is stable, and the shift pulse signal is a square wave with a period of not less than 1μs and a duty cycle of 50%.

[0127] 3) Photoelectric encoder data serial output signal D_TXD: 24-bit natural binary code data converted by the encoder, indicating the current drive mechanism angle data.

[0128] The swing mirror angle control module accumulates and verifies the code disk data and removes abnormal data. The code disk data that exceeds the angle range is marked as abnormal, and the received normal 24-bit code disk data is locked in the data cache register to participate in the closed-loop control of the swing mirror angle control module.

[0129] The system's high-precision line of sight positioning function is achieved through the closed-loop precision control of the oscillating mirror and high-precision angle measurement, enabling rapid positioning and detailed investigation of hot spots. Closed-loop precision control uses the successive approximation + half-step angle criterion method: Figure 4 As shown in the figure, the successive approximation method is to divide the large-angle swing mirror adjustment control into N equal parts, and after each equal-division angle is adjusted, the real-time angle measurement data is compared. Figure 5 As shown, after the swing mirror angle control module receives the return 0 degree instruction, the swing mirror plans the number of steps required from the starting point to the destination (0 degree), rotates around the axis O, pauses at point C, and then reads the telemetry angle information in real time. When the distance from 0 degree is greater than 0.00225°, it drives a minimum resolution step angle of 0.0045°, so that the final angle position is less than 0.00225° from 0 degree.

[0130] (3) The field-of-view multiplexing imaging technology with controllable transmission and reflectance ratio is used to realize the design of compact, lightweight and miniaturized multi-spectral interleaved layout detection.

[0131] The present invention designs a field of view multiplexing imaging technology with controllable transmission and reflectance ratios to achieve a compact and lightweight multi-spectral detection design. A multi-spectral registration design scheme is adopted to split the light into two focal plane components using a flat glass mirror with a reflectivity and a transmission rate of 50% to achieve the design of the minimum spacing of nine spectral bands for coastal zone detection. Coastlines and islands and reefs generally use nine spectral bands for detection. The present invention can also be expanded to achieve the registration of more spectral bands. The embodiment of the present invention only uses a nine-spectral band design as an example. The first eight spectral bands are applied to monitoring objects in different spectral band ranges. The ninth spectral band is used to monitor ports, islands and near-shore construction projects.

[0132] On the one hand, it can realize that each two spectral bands can observe a ground object at the same time, and the time difference between the observation of the same ground object between these two spectral band pairs and the next two spectral band pairs can be minimized. On the other hand, it can realize the minimum field of view and meet the requirements of compact and miniaturized design of optical components. Figure 6As shown in the figure, the flat glass mirror is a thin flat element made of fused quartz glass. Due to the optical transmission and reflection layout, the spectral bands corresponding to the focal planes of the four spectral bands and the five spectral bands can be arranged in an interlaced manner, which greatly shortens the spectral band spatial position difference and imaging time interval difference of the adjacent spectral bands for coastal monitoring imaging, and greatly improves the registration accuracy of the nine-spectral band coastal zone target observation. At the same time, through the surface coating method of the flat glass mirror, the requirement of equal transmission energy / reflection energy is met, that is, the requirement of balanced energy of the focal plane imaging light of the four spectral bands and the five spectral bands is met. The energy optimization matching of each spectral band can be achieved, so that the nine spectral bands can meet the requirements of signal-to-noise ratio and dynamic range.

[0133] Coastal zone detectors are mainly used for remote sensing monitoring of sea-land interaction areas. They have high requirements for signal-to-noise ratio and dynamic range, and require multiple detection spectrum bands, taking into account the monitoring of targets such as land, water, sea ice, and vegetation. Therefore, high requirements are placed on the attitude control of the entire satellite and on the registration between multi-spectral spectrum bands. Traditional spectroscopic schemes cannot meet the requirements for coastal zone detection target image registration due to their large longitudinal field of view. The present invention adopts a transmission and reflection controllable same-field-of-view spectroscopic imaging method, which enables a pair of focal planes with minimum spatial difference to achieve imaging of the same coastal zone target with minimum time difference. Figure 8 As shown, because the two focal plane spectral bands adopt the alignment and registration design in the optical path space, the A1 and B1 spectral bands can be imaged simultaneously, the A2 and B2 spectral bands can be imaged simultaneously, the A3 and B3 spectral bands can be imaged simultaneously, and the A4 and B4 spectral bands can be imaged simultaneously. The minimum design interval of each spectral band of the detector is d, so the shortest interval of imaging time between adjacent spectral bands (when using the maximum number of series) is equal to the pixel integration time of the distance d. With this design, the maximum imaging interval time of the nine spectral bands of the conventional sub-field of view can be shortened by about half. Compared with the conventional multi-spectral band imaging or multi-spectral band detector side-by-side imaging through sub-field of view imaging, the present invention can significantly reduce the imaging time interval of the same detection target of the two focal planes, and eliminate the spectral registration error introduced by the time interval of the satellite platform stability. Coastal zone detection takes into account land, water, and sea ice, and the registration requirements between multi-spectral spectral bands are high. The traditional design scheme cannot meet the requirements of ground registration due to the large longitudinal field of view.

[0134] Among them, stitching multiple pairs of focal planes (i.e. overlapping a certain number of pixels, such as 100 pixels) can achieve detection of a larger width at the same time. For example, stitching three fields of view can achieve detection of 180 kilometers at the same time. Fig. 9 shown.

[0135] (4) “External + Internal” nested two-stage stray light suppression

[0136] Coastal zone detection has the imaging characteristics of bright background and weak target. Stray light suppression is a key link. The following designs are used to enhance the stray light suppression effect:

[0137] First, the propagation direction of stray light is suppressed, and an “external + internal” nested two-stage stray light elimination solution is designed.

[0138] According to the imaging characteristics of the front-mounted wide-range pointing structure imaging system of the present invention, the external light shield is designed as a flat trumpet shape as the first-level stray light elimination solution, such as Fig.10 As shown, the outer light shield is installed at the front end of the optical machine assembly and is the first component through which the imaging light passes in the coastal zone detection system. The outer light shield is a "trumpet-shaped" cylindrical structure, which is narrower at one end close to the optical system and wider at the other side. The mounting surface of the outer light shield is parallel to the meridian plane of the optical system, and the center line along the flight direction coincides with the projection of the rotating axis of the swing mirror on the optical meridian plane. The outer wall of the outer light shield adopts a low-density and high-strength composite material. As shown in the figure, the inner wall of the outer light shield of the present invention is pasted with a hexagonal honeycomb structure to increase the absorption rate of the inner surface and minimize the scattering of the inner wall of the outer light shield. The thickness of the honeycomb is uniform, so that the imaging light can pass completely and maintain a margin of 3mm. The honeycomb structure is sprayed with stray light-eliminating black paint. When the light enters the honeycomb structure, it can be scattered multiple times to reduce the energy of the light. The honeycomb, as a light trap, can effectively reduce the surface scattering of the outer light shield over a large area.

[0139] The coastal zone detector is limited in size due to the requirement of lightweight design, and it is impossible to increase the size of the external light shield indefinitely to suppress stray light. Therefore, in addition to designing the first-stage optical-mechanical component external stray light elimination scheme of the "trumpet-shaped + honeycomb structure" external light shield, the present invention also adopts the stray light suppression design inside the optical-mechanical component combining "secondary mirror aperture piece + detector light shield + inner surface stray light elimination".

[0140] First, if Fig.11 As shown, the present invention first designs a secondary mirror aperture. The stray light path that has a greater impact on the imaging quality of the focus plane passes through both sides of the secondary mirror to reach the third mirror. In order to suppress the stray light of this path, a secondary mirror aperture is added to the structure on both sides of the secondary mirror.

[0141] Secondly, detector shields are designed at the light entrances of the first focal plane assembly (four spectral bands) and the second focal plane assembly (five spectral bands), such as Fig.12 As shown. The detector light shield is installed inside the optical-mechanical assembly. It belongs to the last end of the coastal zone detection optical system and is the last component before the imaging light reaches the detector. It includes a five-band inner light shield and a four-band inner light shield. The mounting surfaces are parallel to the corresponding focal planes and are fastened to the structural frame by screws. The detector light shield is a cylindrical structure made of lightweight metal material and a thin-walled structure. The inside is an extinction ring of lightweight metal material with equal spacing. The opening size of the extinction ring ensures that the imaging light passes completely and maintains a 1.5mm margin. The outer surface of the detector light shield is made of metal black oxidation, and the internal extinction ring is sprayed with special stray light black paint.

[0142] Third, improve the surface roughness of the structure and increase the absorption rate of stray light. The surface of the structural frame around the secondary mirror, the main structural surface between the primary mirror and the third mirror, the surface of the plane reflector fixing frame, the surface of the flat glass mirror fixing frame structure, and the inner wall of the detector front light shield are all surfaces that generate scattered light. The above surfaces are treated to eliminate stray light, and the surface absorption rate of the structure surface is improved and the light scattering direction is changed by spraying stray light eliminating black paint and matte threads.

[0143] In summary, the above "external + internal" nested two-stage stray light elimination scheme can effectively suppress the propagation path of stray light without blocking the imaging light paths, significantly reducing the influence of stray light in the field of view of the coastal zone detection system, so as to improve the imaging quality of the coastal zone detector. Under the premise of ultra-large coverage field of view, it can achieve a stray light suppression technical index better than 2%.

[0144] (5) AD conversion front-end highly integrated focal plane circuit

[0145] The traditional design scheme is: four-spectral-band focal plane TDICCD circuit + four-spectral-band focal plane timing circuit + five-spectral-band focal plane TDICCD circuit + five-spectral-band focal plane timing circuit + cable long-distance transmission of analog signal + signal processing unit (integral control circuit + data processing circuit). The two focal plane circuits output the collected TDICCD analog signals to the signal processing unit for analog-to-digital (AD) conversion and image data processing.

[0146] In order to realize the miniaturization and integration of the focal plane circuit, the TDICCD focal plane circuit of the present invention has completely integrated the timing drive, signal processing and data transmission functions into the focal plane circuit, realizing the miniaturization of the product, and greatly reducing the power consumption and volume. The present invention immediately converts the analog signal output by the detector into a digital signal and processes the image data before sending it to the data transmission system. This avoids the interference of the analog signal, enhances the anti-interference ability of the system, and greatly simplifies the scale of the focal plane circuit.

[0147] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solution of the present invention by using the above disclosed methods and technical contents without departing from the spirit and scope of the present invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall belong to the protection scope of the technical solution of the present invention. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments can be combined with each other.

[0148] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A light and small wide coastal zone detection system, characterized in that: include: Main frame, external light shield, swing mirror assembly, optical-mechanical assembly and focal plane assembly; The main frame is installed on the satellite cabin; the outer sunshade and the optical-mechanical assembly are fixedly installed on the main frame respectively; The outer light shield is located at the front end of the swing mirror assembly; the outer light shield is a cylindrical structure, and the line connecting the center points of the two end faces of the outer light shield is collinear with the center point of the mirror surface of the swing mirror assembly; The swing mirror assembly is located at the light entrance of the front end of the optical-mechanical assembly. The swing mirror assembly can rotate around the rotation axis. The swing mirror assembly is used to transmit imaging light to the optical-mechanical assembly. The focal plane component is used to receive the imaging light transmitted by the optical-mechanical component.

2. A light and small wide coastal zone detection system according to claim 1, characterized in that: The outer sunshade is made of Kevlar fiber composite material, the inner wall of which is pasted with a hexagonal honeycomb structure, and the honeycomb structure is sprayed with stray light-eliminating black paint.

3. A light and small wide coastal zone detection system according to claim 2, characterized in that: The swing mirror assembly includes: a plane reflector, a swing mirror rotation execution module, a telemetry module and a swing mirror support structure; The plane reflector is used to reflect the incident imaging light to the optical-mechanical component; the plane reflector is installed at the light entrance of the front end of the optical-mechanical component through a swing mirror support structure; The oscillating mirror rotation execution module and the telemetry module work together to realize the closed-loop control of the plane reflector rotating around the X-axis of the satellite body coordinate system; wherein, the satellite body coordinate system takes the satellite center of mass as the coordinate origin O, the positive direction of the Z-axis points from the coordinate origin O to the center of the earth, the X-axis is perpendicular to the Z-axis on the orbital plane, the positive direction of the X-axis points to the direction of the satellite's forward movement, and the Y-axis is perpendicular to the X-axis and the Z-axis to form a right-handed rectangular coordinate system.

4. A light and small wide coastal zone detection system according to claim 3, characterized in that: When the plane reflector is at the initial position, the line connecting the center point of the plane reflector and the sub-satellite point is a line segment H, and the angle between the normal line of the plane reflector and the line segment H is 45°.

5. A light and small wide coastal zone detection system according to any one of claims 1 to 4, characterized in that: The optical and mechanical components include: detector light shield, primary mirror, secondary mirror, tertiary mirror, secondary mirror aperture piece and flat glass mirror; The primary mirror, the secondary mirror and the tertiary mirror are arranged in sequence; the light reflected by the swing mirror assembly passes through the primary mirror, the secondary mirror and the tertiary mirror in sequence and then is incident on the flat glass mirror; A flat glass mirror is used to transmit light to the focal plane assembly; The secondary mirror aperture plate is located between the secondary mirror and the third mirror, and the secondary mirror aperture plate is parallel to the optical axis of the secondary mirror; the secondary mirror aperture plate is used to prevent stray light from reaching the third mirror from both sides of the secondary mirror; The detector light shield is fixed on the main body bracket, and the detector light shield is located at the light entrance of the focal plane component.

6. A light and small wide coastal zone detection system according to claim 5, characterized in that: The secondary mirror aperture is made of aluminum alloy thin plate structure, and the surface of the secondary mirror aperture is sprayed with special stray light eliminating black paint.

7. A light and small wide coastal zone detection system according to claim 5, characterized in that: The detector light shield is a cylindrical structure, and a plurality of detector aperture pieces are installed inside the cylindrical structure, and the plurality of detector aperture pieces are arrayed along the axial direction of the cylindrical structure.

8. A light and small wide coastal zone detection system according to claim 7, characterized in that: The number of detector aperture pieces shall not be less than 5, and the axial distance between two adjacent detector aperture pieces shall not exceed 3 cm.

9. A light and small wide coastal zone detection system according to claim 7, characterized in that: The detector light shield is made of aluminum alloy, and the surface of the detector aperture is blackened.

10. A light and small wide coastal zone detection system according to claim 9, characterized in that: The focal plane assembly comprises: a first focal plane assembly and a second focal plane assembly; The first focal plane component and the second focal plane component are respectively used to receive light transmitted from the optical-mechanical component; the detection spectrum of the first focal plane component and the second focal plane component is different; Detector light shields are respectively provided at the light entrances of the first focal plane assembly and the second focal plane assembly; The detection spectrum of the first focal plane assembly specifically includes: A1 spectrum, A2 spectrum, A3 spectrum and A4 spectrum; The detection spectrum of the second focal plane assembly specifically includes: B1 spectrum, B2 spectrum, B3 spectrum, B4 spectrum and B5 spectrum; The ranges of the A1 band, B1 band, A2 band, B2 band, A3 band, B3 band, A4 band, B4 band and B5 band are as follows: The A1 spectral band has a wavelength range of 400-450nm, and the observation objects are the water depth of sea ice, coasts and islands and reefs; the B1 spectral band has a wavelength range of 450-520nm, and the observation objects are pollution monitoring near the coastline and mudflats; The A2 spectral band has a wavelength range of 520-585nm, and the observation object is the suspended sediment on the coast and islands and reefs; the B2 spectral band has a wavelength range of 585-630nm, and the observation object is the special vegetation on the coast and islands and reefs; the A3 spectral band has a wavelength range of 630-700nm, and the observation object is the chlorophyll concentration of the water body near the coast and islands and reefs; the B3 spectral band has a wavelength range of 700-770nm, and the observation object is the vegetation health index of the coast and islands and reefs; the A4 spectral band has a wavelength range of 770-860nm, and the observation object is the water body identification of the coast and islands and reefs; the B4 spectral band has a wavelength range of 860-1040nm, and the observation object is the seaweed vegetation on the coast and islands and reefs; the B5 spectral band has a wavelength range of 450-800nm, and the observation object is the port construction and near-shore engineering on the coast and islands and reefs.

Images