remote sensing

The advantages of remote sensing

Remote sensing is called to obtain information about objects without entering them in physical contact. However, this definition is too broad.

Therefore, we introduce some limitations to specify the features of the concept of "remote sensing", and in particular, important to ensure the safety of aviation concepts of remote sensing of the atmosphere. First, assume that the information is obtained by technical means.

Secondly, we are talking about objects that are at considerable distances from the hardware that distinguishes ERA from other scientific and technical areas, such as non-destructive testing of materials and products, medical diagnostics, and so on. N. Add that DZ uses indirect methods measurement.

Remote sensing involves the study of the atmosphere and Earth's surface, has recently developed methods and subsurface DMZ. Application of methods and tools for remote non-contact information on the status and parameters of the troposphere contributes to aviation safety.

The main advantages of the DMZ - a high speed data acquisition of large volumes of air (or on large areas of the earth's surface), as well as the possibility of obtaining information about objects, virtually inaccessible to study other ways. With traditional meteorological measurements in the upper atmosphere, performed with the help of balloons, widely and systematically used sophisticated methods DZ.

Remote sensing is quite expensive, especially space. Despite this, a comparative analysis of the costs and the results obtained proves the high economic efficiency of sounding. In addition, the use of sounding data, in particular meteorological satellites, terrestrial and airborne radar, has saved thousands of lives by preventing natural disasters and avoiding hazardous meteorological events. Therefore, research. Experimental, design and operational activities in the field of remote sensing, which is being intensively developed in the leading countries of the world, is fully justified.

Properties and applications of remote sensing

The main objects of the DMZ are:

• weather and climate (rainfall, clouds, wind, turbulence, radiation);

• Environmental elements (aerosols, gases, electricity, air, transport, ie redistribution in the atmosphere of a particular substance..);

• oceans and seas (ocean waves, currents, water, ice);

• the earth's surface (vegetation, geological studies, study resources, height-meters).

Information obtained by means of RS, is required for many branches of science, technology and economics. The number of potential users of this information is constantly growing.

In order to ensure the safety of flights CLE used:

• meteorology, climatology and atmospheric physics (operational data for weather forecasting, determining the temperature profile, pressure and water vapor content in the atmosphere, measuring the wind speed, etc...);

• satellite navigation, telephone, in radar observation and navigation (these fields require data on propagation conditions, which quickly obtained by means of RS);

• aviation, for example, weather conditions forecast for airports and airways, rapid detection of hazardous weather events such as hail, storm, turbulence, wind shear, icing and micro-explosion.

In addition, these are important areas in which aircraft are used as carriers funds DZ:

• hydrology, including the assessment and management of water resources, forecasting snow melt, flood warning;

• agricultural area (weather forecasting and management, control type, distribution and state of vegetation, mapping of soil types, moisture determination, hail warning crop forecast);

• the environment (control of air pollution and surface);

• oceanography (eg, measurement of sea surface temperature, ocean currents and the study of the spectra of sea waves);

• Glaciology (eg, mapping the spread and movement of ice sheets and sea ice, determine the possibility of Maritime Navigation in ice conditions);

• geology, geomorphology, geodesy (eg, identification of the type of rocks, geological localization of defects and anomalies, measurement

• parameters of the Earth's tectonic movements and surveillance);

• topography (eg, to obtain accurate data on the height and bind them to the system of coordinates, the production of maps and changes to them);

• Control of natural disasters (including volume control floods, prevent sand and dust storms, avalanches, landslides, avalanches definition of routes, etc...);

• planning for other technical applications (eg, land use inventory and monitoring of changes, evaluation of land resources, monitor the traffic);

• military applications (movement control technology and military units, assessment areas).

Systems and remote sensing techniques

Classification of DZ systems is based on the differences between active and passive systems customary for radar specialists. Active systems irradiate the medium under investigation with electromagnetic radiation (EMR), which is provided by the DZ system, ie, in this case the DZ means generates electromagnetic energy and emits it in the direction of the object under study. Passive systems perceive EMR from the object under investigation in a natural way. It can be, like own EMR, arising in the object of sounding, for example, thermal radiation, and EMR scattered by any natural external source, for example, solar radiation. The advantages and disadvantages of each of the two types of DZ systems (active and passive) are determined by a number of factors. For example, the passive system is practically inapplicable in those cases when there is no sufficiently intense intrinsic radiation of the objects under study in a given wavelength range. On the other hand, the active system becomes technically impracticable if the radiated power necessary to obtain a sufficient reflected signal turns out to be too large.

In some cases, in order to obtain the necessary information, it is desirable to know the exact parameters of the emitted signal in order to provide some special analysis capabilities, for example, measuring the Doppler frequency shift of the reflected signal to estimate the target's motion relative to the sensor (receiver) or to change the polarization of the reflected signal relative to the probe signal. Like any information and measurement systems that use EMR, DZ systems differ in the frequency ranges of electromagnetic oscillations, for example, ultraviolet, visible light, infrared, millimeter, centimeter, decimetric.

Consider RS ​​atmosphere, in particular the troposphere - the part of the atmosphere, which is directly adjacent to the surface. The troposphere extends up to heights 10-15 km, and in the tropics - to 18 km. Using the RS for the purpose of meteorological safety requires attention to systems that consider the atmosphere as a three-dimensional, spatial distribution of the object, and lead to the profiles of the atmosphere in different directions sensing.

Sensing objects, or targets, may be fluctuations that occur naturally in the atmosphere, and the objects are fixed at a certain distance from the DZ means. It is important to understand the different types of interactions between the EMR and the atmosphere. Different types of such interaction - is a convenient way to classify RS methods. They are based on the attenuation, scattering and radiation of electromagnetic waves sensing objects. Scheme of the basic processes of interaction of electromagnetic waves with atmospheric irregularities in relation to the tasks of the DMZ.

In the first case from a predetermined known radiation source (transmitter) to the input of the receiver after it has passed through the object under study. Radiation attenuation value estimated in the propagation path from the transmitter to the receiver, it is assumed that the amount of electromagnetic energy loss through the object properties associated with this object. The cause of the loss can be absorption or a combination of absorption and scattering, which is the basis of information about the object. Many DZ methods essentially based on this approach.

In the second case, when the source is itself a source of radiation, usually there is a problem of measurement of infrared and / or microwave emission that is used to obtain information on the thermal structure of the atmosphere and its other properties. In addition, this approach is characteristic of the study of the lightning discharge on the basis of his own radio emission and the detection of thunderstorms over large distances.

The third case consists in using the scattering of electromagnetic oscillations by atmospheric formation to obtain information about it. Different scattering methods are based on the scattering property. One of them is characterized by the fact that the investigated medium is illuminated by some source of incoherent radiation, for example, by sunlight or infrared radiation, which emanates from the Earth's surface, and the sensor of the DZ facility receives radiation scattered by the object. Another is that the object is irradiated with a special artificial (coherent or incoherent) source, for example, a laser or a source with a wavelength from decimeters to millimeters (as in the case of a radar). This radiation is scattered by the object, detected by the receiver and used to extract information about the scattering object.

Note that the first of the cases correspond to the active sensing system, the second - the passive, and the third is implemented as a passive and active versions.

The active RS system can be mono-static when the transmitter and receiver means are placed on one DZ position bistatic or even multi-static, the system consists of one or several transmitters and several receivers located in different positions.

The classification will not be enough to complete if you do not specify the basic hardware DMZ: radars, radiometers, and other leaders of the device or system used as RS sensors.

The study of the atmosphere with the help of RS includes the use of devices installed on the artificial earth satellites and space stations, airplanes, rockets, balloons, as well as by funds placed on the ground. The most common means of DZ carriers include satellites, aircraft and ground-based platforms.

Inverse problems

The tasks of the DZ are inverse problems, that is, those in whose solution one has to go from the result to the cause. These include all the tasks of processing and interpreting observational data. The theory of inverse problems is an independent mathematical discipline, and the DZ of the atmosphere is only one of the scientific and technical directions for which the theory of inverse problems is important. In the applied aspect, it is necessary to understand well how EMP interacts with the investigated atmospheric objects, forming signals that are used to obtain information about the atmosphere. In the ideal case, there is a one-to-one correspondence between the measured signal parameter and the estimated characteristic of the atmosphere. But in real situations, problems characteristic of inverse problems always arise.

Consider a simple example that relates to the passive sounding of the atmosphere. Suppose that the absorbing gas in the atmosphere is characterized by its own radiation, depending on the temperature of the gas. This radiation is perceived by the sensor located on the satellite. Suppose also that there is a relationship Between the wavelength of the radiation and the temperature, and the temperature depends on the height of the atmosphere layer. Then the knowledge of the relationship between the intensity of radiation, the wavelength of the radiation and the temperature of the gas gives a method of estimating the temperature of the atmospheric gas as a function of the wavelength and, consequently, of the height. In fact, the situation is much more complicated than the described ideal case. Radiation at a given wavelength does not originate from a single layer at the appropriate altitude, but is distributed throughout the atmosphere, so there is no one-to-one correspondence between wavelength and height, as was assumed for the ideal case, which causes a smearing of this connection. This example is typical for many inverse problems, where the boundaries of integration depend on the features of a particular problem. This equation is known as the Fredholm integral equation of the first kind. It is characterized by the fact that the boundaries of the integral are fixed, appearing only in the integrand. The function is called the kernel or function of the equation kernel.

Various problems DZ reduced to an equation or a similar equation. To solve these problems it is necessary to perform the inverse transformation to the results of measurements of g. get distribution. Such inverse problems called incorrect or ill-posed problems. Their decision is associated with overcoming the following three challenges. In principle, a decision may be ill-posed mathematically non-existent, ambiguous or unstable. The lack of solutions

From the perspective of the DMZ, dangerous meteorological phenomena (OMYA) can be considered as the spatial distribution of objects, which occupy some space in the zone or in the cloud cloudless atmosphere (clear skies). Physical signs of external manifestations OMYA usually describes the parameters characterizing the intensity of OMYA and which in principle can be measured, for example, the parameters of wind speed, the electric and magnetic fields, the intensity of the rainfall. Physical parameters OMYA considered.

Areas of the atmosphere in which the parameters characterizing the intensity of OMYA exceed a certain predetermined level, called zones OMYA. The discovery process OMYA and the allocation to certain areas of their spatial coordinates at a given time on the basis of the DMZ is called localization zones OMYA.

Thus, the localization process by means of microwave zone DZ atmosphere OMYA detect and determine their location in a predetermined coordinate system. In some cases, we can estimate the degree of intensity of OMYA.

Localization of hazardous fly zones airborne radar facilities - a rapid detection and location using meteo-navigation radar (MNRLS) bor and other devices that can be paired with MNRLS.