RU2498365C1 - Scanning device for remote image capturing - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: scanning device includes at least one optical-mechanical system, each comprising: a flat scanning mirror with a reflecting coating, which moves according to a given program through a drive; N information optical units of the optical spectrum range, where N is an integer greater than or equal to 1; radiometric calibration units for information optical units of the middle and far infrared spectrum ranges; an optical calibration unit which forms an image in the middle or far infrared spectrum range; black body imitators based on phase transition of pure metals and eutectic alloys; radiometric calibration units for information optical units of the visible and near infrared spectrum ranges, each having a lens, a filter and a stabilised radiation source.

EFFECT: high radiometric accuracy of remote earth probing equipment.

2 cl, 3 dwg

Description

The invention relates to the field of optical instrumentation and is intended to obtain spectrozonal images of the Earth’s surface and cloud cover from spacecraft for solving hydrometeorological and natural resource problems, as well as for monitoring thermal anomalies of a natural and technogenic nature.

The prior art many scanning devices (see, for example, US patents for inventions US 4097115, US 6005682, US 7285779 and patents of the Russian Federation for inventions RU 2313111, RU 2319187, RU 2324151).

Closest to the claimed invention is a multi-zone scanning device for remote imaging in a wide viewing angle (see patent of the Russian Federation for invention RU 2306583, publ. September 20, 2007).

The device includes two identical optical-mechanical systems, each of which contains a flat scanning mirror with a double-sided reflective coating, performing continuous circular rotation by means of a drive, and N information optical blocks, where N is an integer of at least 1, the optical axes of which are parallel, each of which includes serially mounted and optically coupled swivel mirrors, a filter that forms the spectral transmission range, a lens and a radiation detector, single-element or multi-element tny. The device also includes N calibration units, where N is an integer of at least 1, each of which is optically connected through a scanning mirror to one of the information optical units. Calibration blocks for information optical blocks of the visible and near infrared ranges of the spectrum contain a lens, a filter, a stabilized radiation source, and calibration blocks in the middle and far infrared ranges of the spectrum are two completely black body simulators, the first and second having different temperatures, the value and stabilization of which is achieved using an adjustable heating element. The radiation receivers in the middle and far infrared ranges of the first and second optical-mechanical systems are cooled using a common radiation cooling system, and the simulators of the black bodies of both optical-mechanical systems that form the minimum temperature through the heat pipe are structurally connected to the radiation screen oriented in the same direction as the radiation cooling system of radiation receivers.

A disadvantage of the technical solutions known from the prior art, which provide shooting in the infrared range of the spectrum, and in which the on-board calibration is carried out using absolutely black body simulators, forcibly heated or cooled, is a temporary change in the output signal of the information channels during operation. It's connected:

- with a change in the sensitivity of the optical path of the equipment both in the process of putting the spacecraft into orbit, and under the influence of various factors in the process of space flight;

- with a temporary change in the emissivity of airborne radiation sources.

Practice shows that the change in the sensitivity of Earth remote sensing (ERS) equipment during operation, according to various estimates, is from 4 to 25%, for example, the time drift recorded in the thermal channels of the AVHRR radiometer is ~ 0.5 ⁰ K / year, while current requirements for the stability of radiometric signals over time require changes of not more than 0.2 ⁰ K per decade, that is, with existing control methods, the required radiometric accuracy is not ensured and is actually an order of magnitude or more lower necessary accuracy, which leads to distortion of the received data.

The technical result of the claimed invention is to increase the radiometric accuracy of the Earth remote sensing equipment by additionally introducing blackbody simulators based on the phase transition into the equipment, since the phase transition temperature of the substance is constant and not subject to temporary changes, provided the pressure of the environment and the composition of the working fluid are constant.

The technical result is achieved in that the scanning device for remote image acquisition includes:

at least one optical-mechanical system, each of which contains:

- a flat scanning mirror with a reflective coating, making a movement according to a given program using a drive;

- N information optical blocks of the optical range of the spectrum, where N is an integer ≥1;

in addition, each information optical unit includes a series-mounted and optically coupled rotary flat mirror, a filter that forms the spectral bandwidth of the channel, a lens and a single or multi-element radiation receiver;

- radiometric calibration blocks for information optical blocks of the middle and far infrared spectral ranges, each of which contains absolutely black body simulators having different temperatures: less than 300 K and more than 300 K, the value and stabilization of which is achieved using an adjustable heating element;

- radiometric calibration blocks are optically connected to information optical blocks through a flat scanning mirror and rotary flat mirrors included in information optical blocks;

- absolutely black body simulators based on the phase transition of pure metals and eutectic alloys to control absolutely black body simulators having different temperatures: less than 300 K and more than 300 K, and optically coupled to them through a flat scanning mirror with a reflective coating, moving at a given program using the drive;

- at least one comparing optical unit, optically coupled to all simulators through a flat scanning mirror with a reflective coating, moving in accordance with a given program using a drive, and including a lens and a radiation receiver;

- radiation receivers of information optical blocks of the middle and far infrared spectral ranges are cooled using a cooling system.

In a preferred embodiment, the scanning device further includes radiometric calibration units for information optical units of the visible and near infrared spectral ranges, each of which contains a rotary flat mirror, a lens, a filter and a stabilized radiation source.

Black body simulators based on the phase transition of pure metals and eutectic alloys are used in terrestrial thermometry and radiometry and have unique reproducibility of radiometric characteristics due to the fundamental property of constant phase transition temperature. In the device, absolutely black body simulators based on a phase transition are used as highly stable radiation sources that allow one to evaluate the change in the characteristics of the working absolutely black body simulators (basic) having different temperatures: less than 300 K and more than 300 K, and adjust the output data of infrared information channels. The inclusion of simulators of a completely black body based on a phase transition is carried out in special sessions with the required frequency.

The features and essence of the claimed invention are explained in the following detailed description, illustrated by the drawings, which show the following.

Figure 1 - diagram of a scanning device for remote imaging in 4 spectral infrared channels, where:

1 - flat scanning mirror with a reflective coating;

2 - drive flat scanning mirrors;

3 _{(1 ... 4)} - a rotary mirror for each information optical unit;

4 _{(1 ... 4)} - a filter for each information optical unit, forming the spectral bandwidth of the channel;

5 _{(1 ... 4)} - lens for each information optical unit;

6 _{(1 ... 4)} - radiation receiver for each information optical unit;

7 _{(1 ... 4)} - cooling system for each information optical unit;

8 - a simulator of a completely black body with a temperature of more than 300 K;

9 _{(1 ... 2)} - a simulator of a completely black body with a temperature of less than 300 K;

10 _{(1 ... 2)} - a black body simulator based on the phase transition of pure metals and eutectic alloys;

11 _{(1 ... 2)} - a comparing optical unit including a lens and a radiation receiver;

Figure 2 - the General principle of operation of the scanning device for remote image acquisition on the example of one channel, where:

1 - flat scanning mirror with a reflective coating;

3 - a rotary mirror of the information optical unit;

4 - filter information optical unit, forming the spectral bandwidth of the channel;

5 - lens information optical unit;

6 - single or multiple detector radiation information optical unit;

8 - a simulator of a completely black body with a temperature of more than 300 K;

9 - a simulator of a completely black body with a temperature of less than 300 K;

10 - a simulator of a completely black body based on a phase transition of pure metals and eutectic alloys;

11 is a comparing optical unit including a lens and a radiation receiver.

Figure 3 presents a sample of a simulator of a completely black body (IAHT) at a gallium melting phase transition including: a resistance thermometer, a Ga cell, an aperture diaphragm, a heat exchanger, a radiating cavity, and a housing.

The principle of operation of the claimed scanning device for remote image acquisition is as follows.

In accordance with the scheme shown in figure 1, the device is mounted on the platform of the spacecraft and contains a flat two-sided scanning optical mirror (1), making a circular motion using the drive (2), four information optical units, a radiometric on-board calibration system, including hot ( more than 300 K) an absolutely black body simulator (8) and two cold (less than 300 K) absolutely black body simulators (9), two reference absolutely black body simulators based on a phase transition (10) and comparing ptichesky unit (11). Cold imitators (9) and optical information blocks (3-7) are located on both sides of a flat two-sided scanning mirror (1).

The radiation receivers (6) of each information optical unit form an image in the corresponding infrared range of the spectrum. The radiation receivers (6) of the information optical blocks of the middle and far infrared spectral ranges are cooled using a cooling system (7). In the process, at the output of the optical-mechanical system, video signals are formed that allow obtaining images in the spectral ranges, for example, 3.5–4.1 μm and 8.1–9.1 μm. The rotation of the flat scanning mirror (1) of the optical-mechanical system is ensured by an independent rotation drive (2) according to a given program, and the axis of rotation of the flat scanning mirror (1) coincides with the direction of motion of the spacecraft. The rotation of the line of sight with the help of a flat scanning mirror (1) and the movement of the spacecraft itself allows continuous line-of-sight shooting at large viewing angles (up to 100 °) and provide a viewing range of up to 2400 km. The use of a two-sided flat scanning mirror (1) allows to reduce the rotation speed of the drive (2) by half and to place all the modules in the most optimal way. The optimality of the layout is also ensured by the introduction of rotary flat mirrors (3) into the information optical units of the device. The scanning device for remote image acquisition also contains a radiometric calibration system, which is carried out directly during operation. The radiometric calibration system consists of emitter blocks - absolutely black body simulators (9) and (8) having different temperatures: less than 300 K and more than 300 K, respectively. Comparative optical unit (11) provides a comparison of the temperature of all simulators of an absolutely black body (8), (9) and (10). Radiometric calibration of information optical blocks is carried out thanks to a heated (hot) simulator of an absolutely black body (8) (position of a flat scanning mirror 1 (1) in Fig. 2) and a passive (cold) simulator of an absolutely black body (9) (position of a flat scanning mirror 1 (V) in FIG. 2). The comparing optical unit (11) sequentially compares the radiometric temperature of a passive (cold) absolutely black body simulator (9), an absolutely black body simulator based on a phase transition (10), which includes a medium maintained in a state of transitional aggregate state, due to which the temperature is maintained with high accuracy, and the heated (hot) simulator of an absolutely black body (8) (mirror positions 1 (II), 1 (III), 1 (IV), respectively, in Fig. 2), based on which mathematically sky correction of radiation characteristics of the equipment. On-board simulators (cold and hot) of an absolutely black body (8) and (9) form a stable reference radiation flux, the use of which allows one to correct the nonuniform sensitivity of individual elements and the transmission coefficient of the electronic path in the equipment, which is characteristic of radiation receivers. An onboard black body simulator based on a phase transition (10) allows one to measure changes during operation of the initial properties of the optical system and to control the radiometric temperature of hot and cold simulators (8) and (9) with high accuracy.

The radiation flux from the studied surface enters the flat scanning mirror (1) with a reflective coating, rotating with a rotation motor - drive (2), around an axis coinciding with the direction of motion of the carrier (SC). Then, the radiation is directed by a flat scanning mirror to the information optical blocks that form the image. Rotary flat mirrors (3) of information optical units are introduced to reduce the dimensions of the device. The use of a two-sided flat scanning mirror (1) with a reflective coating in the device increases the scanning efficiency and reduces the rotation speed of the drive (2) by half.

The device allows to obtain radiometric accuracy in the ranges of 10.5-11.5 and 11.5-12.5 μm not more than 0.1-0.2 K, and in the range 3.5-4.1 μm - 0.5 K. For radiometric calibration, calibration units are included in the device, each of which contains a black body simulator forming the reference radiation, the temperature of the blocks of which differs by at least 30 ° C and stabilizes with an accuracy of 0.1 ° C. Each radiometric calibration unit is optically coupled through a flat scanning mirror to a single or multi-element radiation detector of only one information channel.

To generate a digital signal, each radiation receiver is supplemented with an electric video signal generating and processing unit, which includes a power supply unit, an analog-to-digital converter, a synchronization unit, two random access memory devices, a unit for calculating correction factors and offsets, and a signal correction unit.

Airborne emitters (AISI) at the phase transitions of materials are used to control changes in the properties of the optical system and the properties of cold and hot simulators.

Calibration of the information signal is carried out according to the following formula:

Where

i, j are the numbers of elements in the row and frame, respectively;

U _o - calibrated signal at the output of the processing unit of the optical signals;

U _{i, j} is the signal from the radiation receivers after the analog amplifier and ADC;

- усредненное значения сигнала, формируемого от АЧТ с температурой менее 300 К;

- the average value of the signal generated from the blackbody with a temperature of less than 300 K;

- усредненное значения сигнала, формируемого от АЧТ с температурой более 300 К;

- the average value of the signal generated from the blackbody with a temperature of more than 300 K;

C _mountains - the number of quantization levels corresponding to the signal level from the blackbody with a temperature of more than 300 K (set at -90% of the signal maximum, for example, for 10-bit quantization of C _mountains ≈900), the value is taken during ground calibration;

C _chole — the number of quantization levels corresponding to the signal level from the blackbody with a temperature of less than 300 K (set at <10% of the signal maximum, for example, for 10-bit quantization C _chill ≈30), the value is taken during ground calibration;

и

изменяются в результате деградации элементов оптической системы и электронного тракта из-за воздействия космического излучения.During operation, the values

and

change as a result of the degradation of the elements of the optical system and the electronic path due to the effects of cosmic radiation.

и

уточняются в процессе эксплуатации:Using a reference blackbody simulator based on a phase transition of a value

and

are specified during operation:

Where:

U _(Thol) and U _(Tgor) - updated values of signals from the blackbody with a temperature of less than 300 K and the blackbody with a temperature of more than 300 K, respectively;

With _ET - the number of quantization levels corresponding to the level of the signal from the reference simulator is selected during ground calibration of the device;

U ' _(Thor) , U' _(TET) and U ' _(Thol) are the initial values of the signals from the blackbody with a temperature of more than 300 K, blackbody with a temperature of less than 300 K and the reference blackbody based on the phase transition, respectively, formed by the comparator (item 11 1), the values are selected during ground calibration, the accuracy of these values is confirmed through the use of high-precision reference radiation sources;

U ” _(Tgor) , U” _(TET) and U ” _(Thol) are the values of signals from the blackbody with a temperature of more than 300 K. The blackbody with a temperature of less than 300 K and the reference blackbody based on the phase transition, respectively, formed by the comparator (pos. 11, figure 1) during operation of the equipment.

With the described scheme, it will be possible to avoid distortion of radiometric information both due to changes in the properties of the optical system, electronic path, and blackbody with temperatures above 300 K and less than 300 K, as well as changes in the properties of the comparator system.

The results of the registration of changes in climate variables can be used to judge global climate changes. Table 1 selectively leads — some of the long-term stability requirements formulated by NOAA, NIST, NPOESS-IPO, and NASA. The requirements, expressed in% and K, relate respectively to the spectral region of reflected solar radiation (0.3-2.5 microns) and infrared (3-14 microns). As follows from the table, the required values lie in the range of (0.1-1)% / decade and (0.01-0.2) K / decade. That is, when developing on-board stability control devices in modern remote sensing equipment, you need to focus on the highest values: 0.1% / decade and 0.01 K / decade.

Table 1 Requirements for the long-term stability of remote sensing equipment when monitoring global climate change Parameter Required radiometric stability (per decade) Cloud cover height 0.2 K The height of the upper cloud cover 0.2 K Overcast Pressure 0.2 K Temperature at the top of the cloud 0.2 K Optical Cloud Thickness one% Thermal radiation in narrow spectral zones 0.04 K Atmospheric temperature profile 0.04 K Atmospheric humidity profile 0.03 K Ozone profile 0.1% Albedo surface one% Normalized Differential Vegetation Index 0.8% Ocean surface temperature 0.01 K

Long-term practice of remote sensing equipment operation shows that the change in the sensitivity of remote sensing equipment according to various estimates is 4-25%, for example, the temporary drift recorded in the heat channels AVHRR -0.5 K / year. This leads to the need to control the characteristics of the equipment throughout the entire period of active existence, which allows you to adjust the received data.

However, with existing control methods, the required radiometric accuracy is not ensured and is actually an order of magnitude or more lower than the required accuracy, which leads to a distortion of the data obtained. It's connected:

- with a change in the sensitivity of the optical path of the equipment both in the process of putting the spacecraft into orbit, and under the influence of various factors in the process of space flight,

-with a temporary change in the emissivity of airborne radiation sources.

Controlling the stability of the equipment at a given level over the earth’s test plots gives an even greater error due to the problems of such accurate accounting of atmospheric parameters and the emissivity of test objects.

Thus, stricter requirements for the information received on the one hand and an increase in the period of active use of remote sensing equipment (up to 7-10 years) on the other hand require the search for new solutions to control radiometric parameters.

Phase transition-based IATI data are used in terrestrial thermometry and radiometry and have reproducibility of radiometric characteristics that have no tendency to change with time due to the fundamental property of constant phase transition temperature.

Some materials whose phase transition can be used as reference calibration points and transition temperatures are presented in Table 2.

table 2 Substances suitable for use as reference points based on the melting / solidification phase transition. Material (metal or eutectic alloy) Phase transition temperature, K Ga 302.91 Ga-cd 302.55 Ga-al 300.08 Ga-zn 298.35 Ga-sn 293.63 Ga-in 288.80 Ga-in-sn 283.96

The approximate dimensions of the AECI based on the phase transition depending on the diameter of the radiating surface are presented in table 3.

Table 3 The basic dimensions of the AHI based on a phase transition. Diameter of the radiating surface, mm The length of the cavity with the material undergoing a phase transition, mm 5 40 10 80 fifteen 120 twenty 155

The use of blackbody simulators based on phase transitions as part of radiometric equipment for remote sensing of the Earth will make it possible to qualitatively increase the accuracy of radiometry data and the service life of the equipment due to increased temperature stability over time of on-board reference radiation sources.

Ground tests of a sample of absolutely blackbody simulators at phase transitions showed an order of magnitude higher stability of the generated radiation, which significantly exceeds the required [1].

The invention improves the radiometric accuracy of the scanning equipment and can be implemented in devices that provide hydrometeorological and environmental information, as well as monitoring thermal anomalies of a natural and technogenic nature.

Literature

Claims (2)

1. Scanning device for remote image acquisition includes:
at least one optical-mechanical system, each of which contains:
- a flat scanning mirror with a reflective coating, making a movement according to a given program using a drive;
- N information optical blocks of the optical range of the spectrum, where N is an integer ≥1;
- in this case, each information optical unit includes a series-mounted and optically coupled rotary flat mirror, a filter that forms the spectral bandwidth of the channel, a lens and a single or multi-element radiation receiver;
- radiometric calibration blocks for information optical blocks of the middle and far infrared ranges of the spectrum, each of which contains absolutely black body simulators having different temperatures: less than 300 K and more than 300 K, the value and stabilization of which is achieved using an adjustable heating element;
- radiometric calibration blocks are optically connected by information optical blocks through a flat scanning mirror and rotary flat mirrors of information optical blocks;
- a comparing optical unit forming an image in the middle or far infrared range of the spectrum, including a lens and a radiation receiver, sequentially optically connected to all simulators through a flat scanning mirror;
- black body simulators based on the phase transition of pure metals and eutectic alloys for monitoring black body simulators having different temperatures: less than 300 K and more than 300 K, and optically coupled through a flat scanning mirror with a reflective coating, moving at a given program using the drive;
- radiation receivers of information optical blocks of the middle and far infrared spectral ranges are cooled using a cooling system. 2. The scanning device according to claim 1, further includes radiometric calibration blocks for information optical blocks of the visible and near infrared spectral ranges, each of which contains a lens, a filter, and a stabilized radiation source.

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