Remote Sensing

Remote sensing is obtaining information about objects without entering into physical contact with them. However, this definition is too broad.

Therefore, we introduce some restrictions that allow us to specify the features of the concept of “remote sensing”, and in particular, the concept of atmosphere remote sensing, which is important for ensuring aviation safety. First, it is believed that information is obtained using technical means.

Secondly, we are talking about objects located at significant distances from technical means, which fundamentally distinguishes remote sensing from other scientific and technical areas, such as non-destructive testing of materials and products, medical diagnostics, etc. We add that remote sensing uses indirect methods measurements.

Remote sensing includes studies of the atmosphere and the earth’s surface, and subsurface remote sensing methods have recently developed. The use of methods and means of remote non-contact information about the state and parameters of the troposphere contributes to aviation safety.

The main advantages of remote sensing are the high speed of obtaining data on large volumes of the atmosphere (or large areas of the earth’s surface), as well as the ability to obtain information about objects that are practically inaccessible to research in other ways. With traditional meteorological measurements in the upper atmospherecarried out using balloons, sophisticated remote sensing methods are widely and systematically applied.

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, ground and airborne radar systems, saved thousands of human lives by preventing natural disasters and avoiding dangerous meteorological phenomena. Therefore, research. experimental, design and operational activities in the field of remote sensing (which is intensively developed in the leading countries of the world) is fully justified.

Objects and applications of remote sensing

The main objects of remote sensing are:

  • weather and climate (precipitation, clouds, wind, turbulence, radiation);
  • environmental elements (aerosols, gases, atmospheric electricity, transport, i.e., redistribution of a substance in the atmosphere);
  • oceans and seas (sea waves, currents, amount of water, ice);
  • Earth’s surface (vegetation, geological studies, resource studies, altitude metrics).

Information obtained by means of remote sensing is necessary for many branches of science, technology and economics. The number of potential consumers of this information is constantly growing.

In order to ensure the safety of remote sensing operations, they use the following:

  • meteorology, climatology and atmospheric physics (operational data for weather forecasting, determining the profile of temperature, pressure and water vapor content in the atmosphere, measuring wind speed, etc.);
  • satellite navigation, communications, in radar observations and radio navigation (these areas require data on the propagation conditions of radio waves, which are quickly obtained by means of remote sensing);
  • aviation, for example, forecasting weather conditions at airports and airways, prompt detection of dangerous meteorological phenomena, such as hail, thunder, turbulence, wind shear, microexplosion and icing.

In addition, there are important areas in which aircraft are used as carriers of remote sensing:

  • hydrology, including assessment and management of water resources, forecasting snowmelt, flood warnings;
  • agricultural areas (forecast and weather control, control of the type, distribution and condition of the vegetation cover, mapping of soil types, determination of moisture, prevention of hail damage, crop forecast);
  • ecology (control of pollution of the atmosphere and the earth’s surface);
  • oceanography (for example, measuring the temperature of the sea surface, studying ocean currents and spectra of sea waves);
  • glaciology (for example, mapping the distribution and movement of ice sheets and sea ice, determining the possibility of maritime navigation in ice conditions);
  • geology, geomorphology and geodesy (for example, identification of the type of rocks, localization of geological defects and anomalies, measurement
    Earth parameters and observation of tectonic movement);
  • topography and cartography (in particular, obtaining accurate data on elevation and linking them to a given coordinate system, producing maps and making changes to them);
  • control of natural disasters (including flood control, warning of sand and dust storms, avalanches, landslides, determination of avalanche routes, etc.);
  • planning in other technical applications (for example, inventory of land use and change control, land valuation, monitoring of traffic);
  • military applications (control of the movement of equipment and military units, terrain assessment).

Remote sensing systems and methods

The classification of remote sensing systems is based on the differences between active and passive systems customary for radar experts. Active systems irradiate the test medium with electromagnetic radiation (EMR), which provides the remote sensing system, i.e., in this case, the remote sensing tool generates electromagnetic energy and radiates it in the direction of the object under study. Passive systems perceive EMR from the studied object in a natural way. This can be either the intrinsic EMR occurring in the sensing object itself, for example, thermal radiation, or the scattered EMR of some natural external source, for example, solar radiation. The advantages and disadvantages of each of the two indicated types of remote sensing systems (active and passive) are determined by a number of factors. For example, a passive system is practically not applicable in those cases when there is no sufficiently intense intrinsic radiation of the studied objects in a given wavelength range. On the other hand, an active system becomes technically unfeasible if the radiated power necessary to obtain a sufficient reflected signal is too large.

In some cases, 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 evaluate the target’s movement relative to the sensor (receiver) or changing the polarization of the reflected signal relative to the probing signal. Like any information-measuring systems that use EMR, remote sensing systems differ in the frequency ranges of electromagnetic waves, for example, ultraviolet, visible light, infrared, millimeter, centimeter, decimeter.

Let us consider the remote sensing of the atmosphere, in particular, of the troposphere – part of the Earth’s atmosphere that is directly adjacent to the Earth’s surface. The troposphere extends to heights of 10-15 km, and in tropical latitudes – up to 18 km. According to the Remote Sensing Journal, the use of remote sensing for the purpose of meteorological safety assurance requires attention to systems that regard the atmosphere as a three-dimensional, spatially distributed object, and allow obtaining atmospheric profiles in different sensing directions.

Sensing objects, or targets, can be fluctuations that naturally occur in the atmosphere, as well as fixed objects at a certain distance from the remote sensing means. It is important to understand the essence of the different types of interaction between the EMP and the atmosphere. Different types of such interaction are a convenient way to classify remote sensing methods. They are based on the attenuation, scattering and emission of electromagnetic waves by sensing objects. Schemes of the main processes of interaction of electromagnetic waves with atmospheric inhomogeneities as some remote sensing problems.

In the first case, radiation from a given known source (transmitter) is fed to the input of the receiver after it has passed through the object under study. The magnitude of the attenuation of radiation on the propagation path from the transmitter to the receiver is estimated, and it is assumed that the magnitude of the loss of electromagnetic energy when passing through an object is associated with the properties of this object. The cause of the loss may be absorption or a combination of absorption and scattering, which underlies obtaining information about the object. Many remote sensing methods are essentially based on this approach.

In the second case, when the source itself is a radiation source, the problem usually arises of measuring infrared and / or microwave emission, which is used to obtain information about the thermal structure of the atmosphere and its other properties. In addition, this approach is typical for the study of a lightning discharge based on its own radio emission and for the detection of thunderstorms over long distances.

The third case is the use of scattering of electromagnetic waves by atmospheric formation to obtain information about it. Various scattering methods are based on the scattering property. One of them is characterized by the fact that the medium under study is illuminated by some source of incoherent radiation, for example, sunlight or infrared radiation that comes from the Earth’s surface, and the remote sensing means sensor 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 considered corresponds to the active sensing system, the second to the passive one, and the third is implemented both in the passive and active versions.

An active remote sensing system can be monostatic when the transmitter and receiver of the remote sensing means are placed at one position, bistatic, or even multistatic, when the system consists of one or more transmitters and several receivers located in different positions.

The classification will not be sufficiently complete if you do not specify the main technical means of remote sensing: radars, radiometers, leaders and other devices or systems used as sensors of remote sensing.

Studying the atmosphere with the help of remote sensing involves the use of instruments installed on artificial Earth satellites and orbital stations, airplanes, rockets, balloons, as well as means placed on the ground. Most often, carriers of remote sensing are satellites, aircraft and ground-based platforms.